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Stem and root anatomy and functions. vegetative propagation

Stem and Root Anatomy and Functions. Vegetative Propagation What are root's functions?
The three universal functions of all roots are anchorage, absorption and translocation of water with
dissolved mineral nutrients. In many perennial and biennial species, roots are also sites for food
storage. These food reserves keep the plant alive through the non-growing season, and are used to
resume growth in spring or after cutting or grazing. Some species that store food in their roots are
yams, alfalfa and red clover. Food storage organs of some vegetables (carrots, beets, and radishes) are
actually a combination of root and stem tissues.
Types of root systems
There are two major types of root systems: fibrous and taproot (left). Grasses have fibrousroot system. Their roots are adventitious, arising from the lowest nodes of the stems.
Species with a fibrous system are more shallowly rooted than plants with a persistenttaproot. Most dicots have a taproot system. The taproot originates from the primary root (radicle) of the seed. The taproot may have many branches originating from it. Roots of legumesmay also have root nodules, which are sites for .
Zones of the root
A root can be divided into the mature zone, zone of maturation, zone of cell elongation,
and the zone of cell division (the apical meristem) protected by the root cap (right).
All of the root cells originate from the divisions of the cells of the apical meristem. These
cells are small, thin-walled, and contain large nuclei. Root meristem is protected by a
root cap. The root cap is a dynamic, multifunctioning organ. For many years it was
believed that the root cap functioned solely to protect the apical meristem of the root.
Recently, it was shown that the cells of root cap percieve both light and gravity. Root
caps of both dicots and monocots produce large numbers of metabolically active root
"border" cells, which are programmed to separate from the root into the surrounding soil.
In soil, border cells play important roles in protecting the roots from the soil-borne
diseases (Hawes et al, 1998).
What are the root tissues?
The primary root tissues are the epidermis, the outermost layer of cells covering the root surface, the
cortex that surrounds the stele, and the vascular tissue or stele, which occupies a central position.
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Stem and Root Anatomy and Functions. Vegetative Propagation The root epidermis (1 on the cross-sections below) is usually a single cell layer that
protects the root. The cells of epidermis can elongate to produce root hairs. These root
hairs have larger surface area and are more efficient in absorbing water. Root hairs are
also the sites of
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Why are legumes important?
Each year legume-Rhizobium symbiosis generates more useful nitrogen for plants than all the nitrogen
fertilizers produced industrially -- and the symbiosis provides just the right amounts of nitrogen at the
right time at virtually no cost to the farmer. This symbiotic nitrogen fixation is very beneficial for two
reasons:
it supplies the legume with nitrogen, it can significantly decrease spending on N-containing fertilizers for the subsequent crops.
Symbiosis is defined as a mutually beneficial relationship between two organisms.
In case of legume Rhizobium symbiosis, a legume provides the bacteria withenergy-rich carbohydrates and some other compounds, while host legume with nitrogen in the form of ammonia. Unlike any plant, rhizobia (andsome other microorganisms) can fix inert N2 gas from the atmosphere and supply it tothe plant as NH4+ which can be utilized by the plant. Compare images on the left: asoybean plant inoculated with Bradyrhizobium japonicum (left), and a plant that Adding nitrogen fertilizer, on the other hand, suppresses N2 fixing symbiosis because the plantsencounter enough nitrogen in the soil and don't need to expand energy to form the nodules and "feed"rhizobia inside the nodules. Let's briefly review the sequence of events leading to establishing a successful symbiosis.
Rhizobial inoculum is usually added at planting as seed coating. Commercial
formulations of inoculum, like the one we will use in today's lab, contain live bacteria.
On the right is a scanning electron microscope image of the free-living cells of
Bradyrhizobium japonicum which can form symbiosis with soybeans. You'll notice that
the bacterial cells have flagella, thread-like organs that allow bacteria to swim andmove in soils toward the host plants.
Roots of legumes produce flavonoids, - chemicals that attract rhizobia.
Different legumes produce different flavonoids to attract differentrhizobia.
On the left is a scanning electron microscop image of root hairs on
soybean roots. Root hairs are extentsions of the root epidermal cells, they
are the sites of rhizobial attachment and infection. When a plant senses Nod-factors (chemicals produced by rhizobia), a root hair curls (right).
Rhizobium then invades the root cells.
http://www.hcs.ohio-state.edu/hcs200/LegRhiz.html (1 of 9) [10/08/2001 09:57:23 a.m.] into Nitrogen-fixing "bacteroids". On the left is microscopic picture of dissected
nodules on the root of a cow pea. The effectiveness of a given nodule may be checked
by cutting it open: an effective nodule should be pink (or purple) in color, while
immature or ineffective ones are either green or white inside.
Rhizobia inside the nodules, differentiated into "bacteroids", fix inert atmospheric N2
for the plants, and supply it in the water-soluble form for the plants.
). One should remember, though, that only certain species of Rhizobia can formeffective symbiotic nodules with specific legumes. In other words, Rhizobia used to inoculate peas willnot be effective in inoculating soybeans or alfalfa.
What is the Nitrogen Cycle?
The Nitrogen Cycle is a microorganism-aided recycling of different forms of nitrogen in nature. Let'sbriefly review these biochemical conversions.
Nitrogen gas (N2) is the most abundant gas in the atmosphere. However, it is inert and cannot bereadily used by plants or animals. Symbiotic and non-symbiotic N2 and convert it into NH4+, a form that can be easily absorbed by plants. Nitrogen can also be fixed
by industrial N2-fixation which requires high temperatures and catalysts.
This "fixed" nitrogen, now in the soluble form, when applied to soil can be either absorbed by plants,
lost with rainfall (leaching) or converted back to gaseous oxides of nitrogen or to N2 (denitrification).
Ammonia (NH4+) and nitrate (NO3-) are the nitrogen forms that can be readily taken up by plants and
used to build plants' own biological molecules (DNA, proteins, chlorophyll, vitamins, etc.). Animals
and humans can thereby utilize plants as sources of nitrogen-containing protein and vitamins.
As the plants and other soil inhabitants die, soil microbes break down decomposing organic matter
and convert the nitrogen from the biological molecules into ammonia and nitrates. Some denitrifying
microbes can sequentially convert various forms of reduced nitrogen back to gaseous forms, and
nitrogen is therefore lost into the atmosphere.
The sequence of events briefly discussed is usually called Nitrogen cycle. This is the way Nitrogen
(and many other nutrients) cycles in nature.
Your group will have a choice of doing either Experiment A or Experiemnt B. Read below forinstructions.
Experimental Design for Experiment A.
(Legume-Rhizobium Symbiosis)
http://www.hcs.ohio-state.edu/hcs200/LegRhiz.html (2 of 9) [10/08/2001 09:57:23 a.m.] Under the greenhouse conditions, Rhizobia can supply plants with sufficient available Nitrogen, andthis will result in higher yield of green mass and higher chlorophyll content as compared withuninoculated plants.
variables in this experiment are yield (fresh weight, and number of seeds), and
inoculation (infection) of
the plants with Bradyrhizobium japonicum.
We will use several in this experiment:1) No nitrogen fertilizer, no inoculum. This treatment should have no effect on yield.
2) The application of urea CO(NH2)2 fertilizer (1/8 of a teaspoon per pot every other week) shouldcause plants to yield more green mass and have higher chlorophyll content as compared to "No urea, Noinoculum" control.
To randomize the treatments, place your pots in random order on the bench of the greenhouse(nevertheless, keep +INOCULUM treatments away from the other treatments to avoid contaminationwith Bradyrhizobium japonicum). Treatments set up by other teams will serve as replications. At theend of the experiment, we will compare the data obtained by different teams.
Protocol A. (Legume-Rhizobium Symbiosis)
1. Label each pot with the treatment, date, and your team number. Fill the pots with soil.
2. Apply 1/8 teaspoon of a fertilizer () to all pots.
3. Place five seeds of each species on the soil surface in the appropriate pots.
4. Moisten (do not saturate) the soil. Cover the seeds with soil except for +INOCULUM treatment.
) to +UREA treatments.
6. Designate one person to inoculate +INOCULUM treatments.
Inoculator: Bring your +INOCULUM pots to the inoculation area. Take a pinch of dry inoculumand sprinkle a little onto each seed. Then cover the seeds with soil. Wash your hands with soapimmediately.
Inoculum is safe to work with, but you MUST NOT allow it contaminate all of your treatments. Inoculate your "+Inoculum" treatments last. Inoculate in the designated area only.
7. Place +INOCULUM pots on a separate bench in the greenhouse.
Observations and Data Collection
Measure heights and chlorophyll contents of each of your treatments according to the class calendar.
http://www.hcs.ohio-state.edu/hcs200/LegRhiz.html (3 of 9) [10/08/2001 09:57:23 a.m.] Once you have collected the data, you will need to calculate variance and standard deviation. Everyteam member should record all data.
1. When the seedlings appear, thin the plants to two per pot. Keep the largest healthiest looking plants.
2. Add 1/8 teaspoon of urea to the +UREA treatments every other week.
use only marked meter sticks to measure heights of the +INOCULUM treatments to avoid contamination of the "No inoculum" treatments with Bradyrhizobium japonicum. Contamination ofother treatments with inoculum will make the collected data useless! 3. To measure height of soybeans, measure the distance from the soil surface to the apical meristem (thetopmost bud) of the plant.
4. Measure the chlorophyll content of the first true leaf and the newest fully developed leaf of all yourplants with the Minolta SPAD meter. In soybeans, the unifoliate leaf (not the cotyledon) is the first trueleaf.
At harvest (at the end of the quarter):
1. Carefully uproot the plants from their pots. Shake the roots. Rinse the soil from the roots. Briefly letthe excess water dry off the plants by placing them for a moment on a dry paper towel.
2. Measure: the fresh mass of the plants, number of branches per plant, the number of pods per plant.
3. Calculate average fresh weight of above ground parts of the plants from each treatment, . Complete the Data Sheets.
Experimental Design for Experiment B (Fertilizer Trial)
Under greenhouse conditions, vermicompost can supply adequate nutrition to plants and will result in asimilar yield of green mass and chlorophyll content as compared to those plants receiving traditionalgarden fertilizer (12-12-12).
Your group can decide which plant you prefer to use. You will be using seedlings of either sorghum, orsunflower.
variables in this experiment are yield (fresh weight, height) and chlorophyll or (12-12-12)-traditional garden fertilizer) 1. + vermicompost (15% of total volume)-treatment D http://www.hcs.ohio-state.edu/hcs200/LegRhiz.html (4 of 9) [10/08/2001 09:57:23 a.m.] 2. + traditional fertilizer (12-12-12)-treatment E 3. control- no fertilizer- treatment F . There will be three replications of each treatment for a total of nine pots Protocol B. (Fertilizer Trials)
1. Label each pot with the treatment, replication, date, and your team number. There will be a total ofnine pots for each group (i.e. D1, D2, D3; E1, E2, E3; and F1, F2, F3.) 2. For the pots labeled D1, D2, and D3, mix in 15% vermicompost with the soil provided. Your groupwill need to figure out the volume of the pots first before adding the appropriate amount ofvermicompost. Use your hands to mix thoroughly 3. Fill the remaining pots (treatments E and F) with the soil provided. Do not add vermicompost to thesetreatments.
4. Moisten each pot with water, do not saturate the soil.
5. Transplant one seedlings of the plant that your group chose to work with into each pot of alltreatments. Be GENTLE and careful not do break the root system while transplanting.
6. Add the traditional garden fertilizer to those pots labeled E (ask your instructor about the correctapplication rate).
7. Do not add anything to those pots labeled F.
8. Place in random order on the bench of greenhouse.
9. Fertilize your E treatments every week until the end of the quarter Observations and Data Collection
Measure heights and chlorophyll contents of each of your treatments according to the class calendar.
Once you have collected the data, you will need to calculate . Every team member should record all data.
To measure height of sunflower, measure the distance from the soil surface to the apical meristem (the topmost bud) of the plant. To measure height of sorghum, measure the distance from the soilsurface to the end of the longest leaf blade.
Measure the chlorophyll content of the first true leaf and the newest fully developed leaf of all your plants with the Minolta SPAD meter. In soybeans, the unifoliate leaf (not the cotyledon) isthe first true leaf.
http://www.hcs.ohio-state.edu/hcs200/LegRhiz.html (5 of 9) [10/08/2001 09:57:23 a.m.] At harvest (at the end of the quarter):
1. Carefully uproot the plants from their pots. Shake the roots. Rinse the soil from the roots. Briefly letthe excess water dry off the plants by placing them for a moment on a dry paper towel.
2. Measure: the fresh mass of the plants, number of branches/nodes per plant, 3. Calculate average fresh weight of above ground parts of the plants from each treatment, Complete the Data Sheets.
Guidelines for writing the Lab Report
For Experiment A. (Legume-Rhizobium)
Your groups may chose to write either a report on Nutrient Deficiencies or on Legume-Rhizobiumsymbiosis. This is a group report, contributions of every team member will be evaluated by peers. Thereport should be typed, double-spaced and should contain the following sections: Introduction This section is usually 2-3 paragraphs long. It introduces the topic and provides
background information on why the study was undertaken. Make sure you include objectives and
hypotheses. Clearly define what symbiosis is and discuss the importance of legume-Rhizobium
symbiosis in nature and agriculture (15 points).
Materials and Methods Briefly (in one paragraph) summarize the protocol you followed. What tools
did you use for measurements? Explain, why Bradyrhizobium japonicum, and not another Rhizobium
species was used in this experiment (5 points).
Results and Discussion This section is the "heart" of any report. It should be the longest part (2-3 pages
+ figures) of your report. Present data from the experiment in tables or graphs to support your
conclusions. Title your figures. Titles are usually put at the top of tables and the bottom of figures in
written documents. Refrain from using the laboratory data sheets to present data in your report (these
data sheets are only guides for collecting information and lack the appropriate organization for a report).
These questions will guide you in writing this section of the lab report.
1. Did you see any nodulation on the "NO INOCULUM" treatments? If yes, what happened? What didthey look like?(5 points) 2. Which treatment(s) developed plants with the highest chlorophyll content, the most branches andpods, and highest mass? How variable were the results between replications What can you concludefrom these observations?(15 points) 3. Using the data you collected, discuss chlorophyll content in old and younger leaves of the treatments: Is there a difference in chlorophyll content between older and younger leaves? What can you conclude from this finding? (10 points) Is there a difference in chlorophyll content between the treatment and the controls? What can you http://www.hcs.ohio-state.edu/hcs200/LegRhiz.html (6 of 9) [10/08/2001 09:57:23 a.m.] attribute it to? (10 points) Did you expect inoculation with Rhizobium to have an effect on the chlorophyll content? Explain 4. Do you think that chlorophyll content provide an accurate estimate of Nitrogen-status of the plant? (5points).
5. Were there any confounding variables that might have interfered with the experiment? Would you setup the experiment differently? (5 points).
6. Attach Xerox copies of the completed data tables (10 points).
8.Include clearly labeled Figures and Tables (10 points) Literature Cited Include the list of the reference materials that you used to prepare your report. Cite onlythe materials that you have actually read (5 points) On a separate sheet of paper, evaluate contribution of each team member (including yourself-evaluation) to this project. Evaluate contributions as percentages, rather then letter grades, i.e. ifeach member contributed equally, than each one gets 25%. Sign your name on the evaluation sheet.
Turn in the evaluation individually. These evaluations will be confidential and will not be returned.
For Experiment B. (Fertilizer Trials)
This is a group report, contributions of every team member will be evaluated by the peers. The reportshould be typed, double-spaced and should contain the following sections: Use the following guidlines: Introduction This section is usually 2-3 paragraphs long. It introduces the topic and provides
background information on why the study was undertaken. Make sure you include objectives and
hypotheses. Describe what is meant by inorganic and organic fertilizers. What is vermicompost and
how is it produced? Briefly describe findings of other studies which have incorporated the use of
vermicompost (15 points).
Materials and Methods Briefly (in one paragraph) summarize the protocol you followed. What tools
did you use for measurements? How did you fertilize your treatments? What was the experimental
design?(5 points).
Results and Discussion This section is the "heart" of any report. It should be the longest part (2-3 pages
+ figures) of your report. Present data from the experiment in tables or graphs to support your
conclusions. Title your figures. Titles are usually put at the top of tables and the bottom of figures in
written documents. Refrain from using the laboratory data sheets to present data in your report (these
data sheets are only guides for collecting information and lack the appropriate organization for a report).
These questions will guide you in writing this section of the lab report: 1. Which plants overall responded better to treatments? Which treatments developed plants with thehighest cholorophyll content? (10 points) 2. Is there a difference in growth responses between treatments/controls? How can you account forthese diferences?(10 points) http://www.hcs.ohio-state.edu/hcs200/LegRhiz.html (7 of 9) [10/08/2001 09:57:23 a.m.] 3. Are there signs of deficiecies in any of the treatments. If so, can you narrow them down to specificnutrient deficiencies? Describe the symptoms. (10 points) 4. Do you think that chlorophyll content provides an accurate estimate of Nitrogen-status of the plant?(5 points).
5. How variable were your results betwen treatments? Were there any confounding variables that mighthave interfered with the experiment? Would you set up the experiment differently?(10 points) 6. In conclusion, which fertilizer out of the two would you recomend for other growers and why? Doyou think the application rate of either the vermicompost or traditional fertilizer was effective or shoulda different recomendation be made? (10 points) 6. Attach Xerox copies of the completed data tables (10 points) 7.Include clearly labeled Figures and Tables (10 points) Literature Cited Include the list of the reference materials that you used to prepare your report. Cite onlythe materials that you have actually read (5 points) On a separate sheet of paper, evaluate contribution of each team member (including yourself-evaluation) to this project. Evaluate contributions as percentages, rather then letter grades, i.e. ifeach member contributed equally, than each one gets 25%. Sign your name on the evaluation sheet.
Turn in the evaluation individually. These evaluations will be confidential and will not be returned.
Guidelines for group Oral Presentations
presentations will be given on the last day of lab
Each group will be expected to make an oral presentation to their lab section that lasts no longer than15-20 minutes including questions and discussion. During this presentation, the group should present anintroduction including objectives and hypothesis, materials and methods, results, and discussion. Visualaids should be used. Data should be presented in a visual form and be explained thoroughly. Thediscussion should include interpretations of data. If results did not comply with the original hypothesis,other possible explanations need to be addressed. Your grade is not contingent on whether your resultscomplied with the hypothesis, but rather on the reasoning and explanations your group is able give tosupport or reject the hypothesis. All members of each group are encouraged to participate in the oralpresentation, but the main presentation can be made by one or two persons as long as each hascontributed equally. Contributions of every team member will be evaluated by the peers and will beincorporated into the final grade.
All materials on this website are for personal use only. Pictures, text or files cannot be legallyreproduced or duplicated in any form. For commercial or instructional use of this website or materialsfrom it, please contact Dr. P. McMahon or Max Teplitski.
http://www.hcs.ohio-state.edu/hcs200/LegRhiz.html (8 of 9) [10/08/2001 09:57:23 a.m.] Copyright by M.Teplitski and P.McMahon, 1999 For more information, email us at , . http://www.hcs.ohio-state.edu/hcs200/LegRhiz.html (9 of 9) [10/08/2001 09:57:23 a.m.] Nutrient Deficiency Symptoms Law of Minimum
An important concept to remember is that one has to "feed" plants before the plants can
provide us with food. As you have learned in the previous exercises, plant "food"
consists of carbon dioxide and water (sources of C, H, O), and 16 elements (N, P, K, S,
Mg, Ca, Fe, Mn, B, Cu, Zn, Mo, Na, Ni, Si and Cl). The 16 elements should be present in
a water-soluble form so that a plant can take them up. The16 nutrients are divided into
primary nutrients (N, P, K), secondary nutrients (S, Ca, and Mg) and micronutrients (Fe,
Mn, B, Zn, Cu, Mo, Na, Ni, Si and Cl).
Even if only one nutrient is missing from the soil (or hydroponic) solution the plant willnot develop and produce normally. This notion was postulated by his Law of the Minimum. The Law of Minimum maintains that yield is proportional to the amount of the most limiting growth resource. As you recall, such growth resourcesare nutrients, light, temperature, water and space.
The corn plant on the left is nitrogen-deficient. It developed deficiency symptoms which
include stunted growth, chlorosis (yellowing), and necrosis (death).
Nitrogen is part of a chlorophyll molecule (right, below). As you recall, chlorophyll is
the green pigment that plays an important part in photosynthesis. If nitrogen is limiting,
chlorophyll molecules cannot be synthesized. The plant loses its green color, and can't
photosynthesize As a result, the N-deficient plant does not produce required
carbohydrates. Older leaves develop deficiency symptoms earlier, because N istranslocated inside the plant from the older leaves to the younger ones. Below are several examples of nutrient deficiencies. Some of these minerals are
involved in the formation of biologically active molecules, such as pigments
(nucleic acids (DNA and RNA), energy molecules
(ATP, NADPH) and enzymes. All of these molecules have different important
functions within a plant cell. Nucleic acids, for example, carry an organism's genetic
information, ATP provides energy for the reactions within a cell, while enzymes catalyze the reactions.
Let's briefly talk about enzymes. An enzyme is a protein (sometimes RNA) that functions as a
biological catalyst.
aminoacids. Aminoacids are assembled together by ribosomes. When this amino acid chain isreleased from a ribosome, interactions between aminoacids cause unique folding of the protein. http://www.hcs.ohio-state.edu/hcs200/Defrme.html (1 of 6) [10/08/2001 09:57:46 a.m.] Nutrient Deficiency Symptoms This uniquely folded protein, sometimes associated with co-enzymes and metals, functions as abiological catalyst.
Enzymes are very selective in the substrates they act upon and in the kinds of the reactions they catalyze. Rubisco, an enzyme involved in photosynthesis, catalyzes the conversion ofribulose1,5-biphosphate to two molecules of 3-phosphoglycerate. Considering how many biological reactions take place inside an organism (bacteria, plant or human),
you can only imagine how many different enzymes are present! The product of one enzymatic reaction
is usually a substrate for another enzyme. This sequence of enzymic reactions in an organism is known
as metabolism. If an enzyme (or any other important biological molecule) is not produced inside the
cell due to a mineral deficiency, then the biological reactions catalyzed by this enzyme do not take
place, the organism's metabolism is severely impaired, and deficiency symptoms develop.
Nitrogen (N) deficiency
N-deficiency is the most common nutrient deficiency. N is
a part of a chlorophyll molecule, aminoacids, and many other important bioldogical molecules. Older leaves corn (top);
of nitrogen- deficient plants are yellow from the tipoutside, plant is light green. Stalks of the N-deficient plants short and slender. Leaves drop.
Excess N may cause K deficiencies. Potato, carrot, beet healthy leaf
grown with excessive N, show prolific shoot growth with small underground organs. Excess N leads to splitting of tomato fruits as they ripen.
Phosporus (P) deficiency
Second to N, P is often the limiting element in soils. Older leaves of and healthy
P-deficient plants are purple or dark green. Stalks short and thin. New growth is weak and stunted. Poor flowering and fruiting. Phosphorus isimportant in nucleic acids, and in energy molecules (ATP, NADP).
Potassium (K) deficiency
Potassium is imporntant in many essential for photosynthesis. Like N and P,
potassium is freely translocated inside the plant, so
the deficiency symptoms first occur on the older
leaves. Lack of potassium causes leaf margin
chlorosis, followed by necrosis from outside to the
midvein. K-deficient grasses are more prone to root
infections, and are easily bent to the ground
(lodged) by rain or wind. Researchers from U. of corn (above), K-deficient
Georgia suggest that K-deficient cotton plants are more susceptible to fungal infections. They suggestsplit K applications (half at planting, half as http://www.hcs.ohio-state.edu/hcs200/Defrme.html (2 of 6) [10/08/2001 09:57:46 a.m.] Nutrient Deficiency Symptoms side-dressing), and use foliar fertilization if thedeficiency occurs.
Calcium (Ca) deficiency
Calcium is often limited in acidic soils that recieve abundant rainfall.
When calcium is deficient, terminal bud dies, young leaves are hooked,
because Ca++ is not easily translocated inside the plant. Dying back
Ca-deficient occurs at tips and margins, foliage may become distorted. Stalk dies off at
tomato
the terminal bud. Root systems may be damaged by the root tip death.
Calcium is bound to enzymes, it also participates in cell wall formation.
Calcium is required for cell division and is required for normal membrane Excess Ca may cause boron or magnesium deficiencies.
Sulfur (S) deficiency
S-deficient
Because enough sulfate is present in most soils, corn (right)
sulfur deficiency is fairly uncommon. S is noteasily translolcated inside the plant, so sulfur-deficient plants develop interveinalchlorosis on younger leaves first. Necrotic spots are usually not present.
cotton plant
and healthy
Sulfur is essential for protein structure, it also occurs in vitamins.
Magnesium (Mg) deficiency
Mg is a part of the chlorophyll molecule, it is also important foractivating some enzymes. Plants lacking magnesium have leaves with interveinal chlorosis. Leaves may redden, develop dead (necrotic) spots; tips and margins sometimes cup upward. Stalks are usually slender.
Magnesium deficiency is rarely a problem in most soils. Excessivemagnesium, on the other hand, can induce potassium deficiency due tointerference with K uptake and utilization.
http://www.hcs.ohio-state.edu/hcs200/Defrme.html (3 of 6) [10/08/2001 09:57:46 a.m.] Nutrient Deficiency Symptoms Iron (Fe) deficiency
Iron often becomes poorly soluble and therefore limited in soils withneutral or basic pH. Fe-deficient plants develop interveinal chlorosis occuring first on younger leaves. In severe cases, younger leaves become white with necrotic lesions.
peanut plant
Iron is important because it is a part of some enzymes. Its ability toundergo oxidations and reductions (Fe2+ <->Fe3+) is essential for electron transport in many biochemical reactions inside the plant.
Deficiencies making front pages.
Here is how a recent journal PLANT PHYSIOLOGY desecribed its recentcover(right): the interveinal chlorotic sunflower leaves shown in the photograph sufferfrom Fe chlorosis. Fe chlorosis occurs mainly on calcareous soils with nitrate as theexclusive N form, and leaves are frequently chlorotic in spite of abundant Feconcentrations. Kosegarten et al. (pp. 1069-1079) have shown that pH of theintercellular space ("apoplast") regulates Fe3+ reduction and thus Fe2+ transportacross the cell membrane. Microscope imaging combined with the fluorescence ratiotechnique revealed high apoplastic pH at cellular sites in the interveinal area of youngleaves due to nitrate nutrition (see inset of the interveinal area). In the interveinal area, Fe3+ reduction was depressed at sites of high apoplastic pH, thus inducing leafyellowing. In contrast, apoplastic pH in the xylem vessels (see related inset) was loweven with nitrate nutrition, and, due to high rates of Fe3+ reduction at low apoplasticpH, the tissue around the leaf xylem remained green.
Deficiency symptoms could be sometimes confused with herbicide injuries. Refer to the following webpages for an illustrated list of some herbicide injuries on common crops: For more information on plant mineral nutrition and role of various nutrients, visit: Why do deficiency symptoms differ?
The deficiency symptoms for any nutrient depend on two factors:
the role of the element in the plant; whether or not the element is translocated from older leaves to younger ones.
Ability of a nutrient to be translocated depends upon its mobility in the phloem. The mobility isdetermined by solubility of the chemical form of the element. Symptoms vary somewhat betweenspecies, and according to the severity of the problem, the growth stage, and complexities resulting from http://www.hcs.ohio-state.edu/hcs200/Defrme.html (4 of 6) [10/08/2001 09:57:46 a.m.] Nutrient Deficiency Symptoms deficiencies of two or more elements.
Hydroponic production
The first hydroponic systems were developed in France and England during the 17th century.
Hydroponics is the technology of growing plants in a nutrient solution with or without the use of an
artificial medium (vermiculite, sand, gravel, etc.) to provide mechanical support. Hydroponic systems
are classified as liquid or aggregate, respectively. The vast majority of hydroponic systems are
enclosed in greenhouses to provide temperature monitoring, reduce evaporation, and to protect the
systems from unfavorable weather conditions.
Several hydroponic techniques have been developed in the recent years:
Nutrient Film Technique
. A thin film of nutrient solution is driven by gravity through plastic-lined channels. The roots grow inside the channels and form a tangled mat.
s. Usually used to germinate seeds in beds floating on top of a nutrient solution. Lettuce is grown in this manner in 2.5 cm-thick plastic floats for 4-6 weeks.
. Plants are grown in holes of expanded polystyrene panels. Plant roots are suspended in midair beneath the panel and enclosed in a spraying box. Aeroponics is valuable for the rootingof stem cuttings and in the production of leafy vegetables. Space is used more efficiently in thissystem.
Aggregate hydroponics systems
. A solid, inert medium provides support for the plants. As in liquid systems, the nutrient solution is delivered directly to the plant roots.
About the experimental setup
In this exercise we will use an aggregate/wick hydroponics system. Solid medium (vermiculite) will
provide support for the growing plants, nutrient solution will be driven into the medium by the capillary
action. You will replace the mineral solution every week to compensate for the removal of the nutrients
by the plants and pH changes resulting from this removal.
.
The medium contains phosphates, which act as a buffer to prevent rapid pH changes in the solution.
Chelating agents are added to the solution to prevent ions (mostly divalent metals) from precipitating.
Click here to learn more about You may choose from -N, -P, -K, -Ca, -S and control solutions. You may also decide to work with tallfescue, lettuce, cucumber or a corn plant.
1. Decide which crop and which deficiency your group would like to work with in this exercise.
2. Dilute the stock solution 5 times (i.e. 1 part of the stock per 4 parts of distilled water).
http://www.hcs.ohio-state.edu/hcs200/Defrme.html (5 of 6) [10/08/2001 09:57:46 a.m.] Nutrient Deficiency Symptoms 3. Add the prepared mineral solution to the white bucket so that there is approximately 9 cm (3.5inches) of liquid in the white bucket.
4. Place 2 sheets of cheesecloth inside the green pot. Pull the cheesecloth through the orifices in thegreen pot, so that when the green pot is inserted into the white bucket, cheesecloth is immersed into themineral solution.
5. Fill the green pot with vermiculite. Wet vermiculite with the appropriate mineral solution.
6. Plant the seedling into vermiculite.
7. Place the green pot inside the white bucket with the mineral solution.
8. Clearly label the pot with your group number, date and treatment. Move the hydroponic assemblyinto the designated part of the greenhouse.
All materials on this website are for personal use only. Pictures, text or files cannot be legallyreproduced or duplicated in any form. For commercial or instructional use of this website or materialsfrom it, please contact Dr. P. McMahon or Max Teplitski.
Copyright by M.Teplitski and P.McMahon, 1999 http://www.hcs.ohio-state.edu/hcs200/Defrme.html (6 of 6) [10/08/2001 09:57:46 a.m.] Discussion questions
Preparing for the class, let's all think about the social aspects of plant biotechnology. Here are some
questions that have been igniting political debates recently:
1. Who owns the genes? Represenatives of Western companies travel to the developing countries to
collect seeds of the local crop varieties. Commercial breeders work with these varieties and eventually
protect them by their patents. Who do you think owns the rights to the crop varieties based on local
"landraces".
2. Should you keep the "designer" genes from the wild relatives? Cultivated grasses easily and
freely outbreed with their wild weedy relatives. Some breeders try to introduce herbicide-resistance
genes into turf grasses using techniques described in this lab. What effects, do you think, introduction of
herbicide-resistance genes into turf grasses will have on control of grass weeds?
3. As you'll learn in a couple of minutes, Russian botanist Nickolai Vavilov developed one of the first
theories of crop origin. In the beginning of the 20th century, his studies of genetics and crop evolution
clashed with the government's ideology. He was arrested and later died in Stalin's concentration camps.
In your opinion, can government, society or interest groups impose their ideals on scientists? Can
you think of other examples when different groups try to dictate their values to the scientists?
Frankenstein Foods or Crops for the Future?
Genetic engineering more and more often becomes a front-page news in popularmagazines. Crop breeders come up with new more productive crops that arestress-tolerant, disease-resistant, have higher qulatity yields and other superiortraits. Corn and cotton plants were engineeried to carry genes of a bacteriumBacillus thuringiensis allowing the plants to fight off insects. RoundUp Readysoybeans are not destroyed by the herbicide which allows less expensive weedcontrol. High-starch potatoes have higher starch content in their tubers andtherefore are more nutritious. FlavrSavr tomatoes stay firm as they are stored andtransported. Tobacco plants can synthesize vaccines and biodegradable plastics.
Cotton, with genes from indigo plant, produce blue cotton fibers for natural,environment friendly denim. A variety of "decaf" coffee has been developed to produce naturally caffeine-free product.
, genetically engineered to synthesize βmagazine (left).
Click on the image (left) to read the article in TIME.
According to a recent article in "Trends in Plant Science", scientists at Monsanto inserted a gene forb-carotene production in canola plants. Oil from this new canola variety contains b-carotene, whichhuman body converts into vitamin A. One teaspoon of the oil could provide the daily recommendedintake for an adult. In the same journal, they report that a Spanish scientist, Jesus Fernandez, has http://www.hcs.ohio-state.edu/hcs200/Breefrme.html (1 of 8) [10/08/2001 09:58:34 a.m.] developed a variety of artichoke that grows 12 feet (3 meters) high. Artichokes grow well in theinfertile dry soils. The biomass of genetically modified artichoke is harvested and used for fuel. Afactory was built to use up to 105, 000 tons of artichokes to produce 91.2 GW of electricity.
Crops: where did they come from?
Crop domestication, a process of selection and adaptation of a wild species to cultivatedlentil, forage grasses, oil palm,sugar beet, and strawberry were domesticated relatively recently (1750 c.e.-present).
Planting, growing and harvesting the crops led to selection of types suitable to cultivation.
Selection of plants with desirable traits was - for centuries - the only form of cropbreeding.
According to the Russian scientist Nickolai Vavilov, there were 12 centers of crop
domestication around the world. Vavilov's theory has been modified since. Visit this nifty
revisions of the Vavilov's theory. What are the origins of the 10 crops we have mentionedduring this quarter? For additional information about the crops, click on the highlighted text above.
to learn more about Crop Genetic Diversity. You will also find out why the British are teadrinkers and why Boston basketball team is called Celtics.
To learn more about life of N.Vavilov, click on his photograph (above right) Brief history of crop breeding
Crop breeding changed significantly since the discovery of inheritance and development of genetics.
Gregor Mendel (left), in the 1850s made the first
observations that plant traits are inherited. Mendel noticed
that when green and yellow peas were crossed, all
progeny seeds were yellow. When plants of this first
hybrid generation (F1) were allowed to self-pollinate, the
progeny (F2) segregated with one green seed per three
yellow (right).
Mendel experimented further, and cross-pollinated plantswith green wrinkled and yellow smooth seeds (at the time, Gregor Mendel the talented scientist did not know that texture and color
of pea seeds are inherited independentenly from each
other). In the first hybrid generation, F1, all seeds
http://www.hcs.ohio-state.edu/hcs200/Breefrme.html (2 of 8) [10/08/2001 09:58:34 a.m.] appeared yellow smooth (diagram below).When allowed to self-pollinate, F1 plants produced segregating F2
progeny, with one green wrinkled seed, three yellow
smooth seeds, three yellow wrinkled and nine yellow
smooth seeds per each 16.
Based on the appearance of the seeds from F1 generation, onecan conclude that the allele coding for yellow seed color isdominant over the allele coding for the green seed color; andsmooth or round allele is dominant over the allele coding forwrinkled seed coat. In F2 generation, therefore some of the seedsthat appear yellow and smooth still carry alleles coding for greenwrinkled seeds.
Note that in the F2 generation there are green smooth and yellowwrinkled seeds, a combination of traits that is different from both parents. These new traits arose due to an independentassortment of the alleles in meiosis. "Mendelian inheritance"assumes that genes are inherited independently from each other.
In many cases, however, genes located close to each other on the chromosome are
inherited together, and the simple segregation discussed above does not take
place. Genes located on the same chromosome can be inherited separately due to
an event known at "crossing-over". Crossing-over can occur during the first
meiotic division. Crossing-over is the exchange of some of the corresponding
parts of homologous chromosomes. Crossing-over leads to recombination of the
traits.
Barbara McClintock was one of the first people to study chromosome
crossing-over in maize, she was awarded Nobel Prize for her studies and thediscovery of the mobile elements in maize chromosomes.
to read an essay by D. Ardell on the fascinating life of B. McClintock Brief review of genetic principles
http://www.hcs.ohio-state.edu/hcs200/Breefrme.html (3 of 8) [10/08/2001 09:58:34 a.m.] Diversity among individuals is the raw material of genetics. Variation among cropplants is observed by breeders and farmers and allows them to select for theindividuals with desired traits. Genetics studies the mechanisms by which traits arepassed from one organism to another and how they are expressed. Here is a briefoverview of some genetic principles.
Each cell of an organism contains at least one set of basic genetic information. This
set is called a genome. In a diploid organism, there is one set of chromosomes
derived from one parent and one chromosome set derived from the other parent
(that explains yellow wrinkled and green smooth seeds in Mendel's experiments).
A chromosome is one long double-stranded molecule of DNA. The double helical
structure of DNA was discovered by a British and an American scientists,
J.Watson and F.Crick (left). For them, a clue about the structure of DNA came
from X-ray photographs of DNA taken by Rosalind Franklin. Watson and Crick
were awarded Nobel Prize for their discovery.
Genes are the regions of a DNA molecule. A gene specifies the structure of a
single protein. Each protein () catalyzes a biochemical reaction within an
organism that leads to formation of other biological molecules.
for an essay about life and Nobel Prize-winning discoveries of F.Crickand J.Watson.
Another genetic discovery: decoding of human genome is probably the mostexciting scientific breakthrough of this year! What does it mean to the cropscientists? Genome of Arabidopsis thaliana, a weedy plant from the MustardFamily, is already sequenced. Genetic sequences of rice and Medicago truncatula(a relative of alfalfa) are on their way.
Click on the image to the right to read the article in TIME magazine onsequencing of human genome.
Click on the highlightedquestion to read a great compilation of pro and con arguments (including the storyon "crossing" tomato with cod)! Plant transformation
So, how did they genetically engineer rice to synthesize β-carotene? Plant transformation (or genetic engineering) is the transfer of specific foreign DNA into a plantspecies. Transformation involves several steps: http://www.hcs.ohio-state.edu/hcs200/Breefrme.html (4 of 8) [10/08/2001 09:58:34 a.m.] isolation of a useful gene; transfer of the gene into a plant cell; integration of the gene into the plant genome; regeneration of fertile plants through tissue culture; transmission of the transgenic (transformed) from generation to generation through cross pollination, as you will perform in today's lab.
" example (left).
Scientist isolated a useful gene for β-caroteneproduction from daffodil, and excised that gene(piece of DNA). The gene was then "glued" into acarriers (small loops of DNA called plasmids).
Such plasmids are then introduced into plant cells, anew transgenic organism is then re-generated froma single cell.
There are several ways to introduce foreign DNA into a plant. In this Exercise, we will use the PIG,Particle Inflow Gun improved by the OSU scientists (Dr. J.Finer and colleagues). The gun is used tobombard (literally!) plant tissue with tungsten particles coated with DNA. DNA-coated particles areaccelerated inside a chamber under pressurized helium and partial vacuum. DNA is later integratedinto transformed cells' genome and transgenic plants are regenerated.
Review of flower anatomy and pollination
Flowers are highly specialized reproductive organs, adapted for the entire
range of reproductive functions: advertising, pollination, fertilization, seed
development, and dispersal of seeds. Flowers can be male, female or both.
By far the most common arrangement is having both male and female parts
within each flower, otherwise known as perfect flower. Imperfect flowers
have either male or female parts. Monoecious plants have male and female
parts on the same plant (e.g., corn, cucurbits, birch, walnut). Dioecious
plants have male and female flowers on separate plants (hemp, American
holly, hazel nut). Complete flowers have all four parts (sepals, petals,
stamen and pistil), while incomplete flowers are missing one or more of
these parts.
No two species of plants have identical floral anatomy, but the followingdiagrams illustrate "typical" flowers with both male and female parts.
http://www.hcs.ohio-state.edu/hcs200/Breefrme.html (5 of 8) [10/08/2001 09:58:34 a.m.] Apple (above) has a perfect flower. Green sepals (6) protect the bud before the
flower opens. Petals (1) which people see as white, are highly visible to the
insect pollinators. Male parts of the flower are called stamens, and consist of a
filament (5) and anther (4). Pollen is produced in its anthers (4). When pollen
grains mature, they land on the stigma (2), which is a receptacle for the style (a
long tube that empties into the ovary (7)). The pollen grain then forms a pollen
tube that grows down the style (3) and reaches the ovary (7), where it releases
the male gamete. The gamete proceeds down the tube to fertilize an ovule in the
ovary. The fertilized ovule develops into a seed and the ovary typically develops
into the fruit.
Sepals and petals in flowers of tulip (right), and its monocot relatives (lilies,
daffodils, onions, etc) evolved into one organ, sometimes referred to as "tepal"
(8, right). Flower parts of tulip are labeled similarly to the flower parts of apple.
Grasses are also monocots. You'll notice that flowers of grasses are less
showy (eg. fescue flower, left). Grasses typically produce significant
amounts of pollen in their anthers (4). Carried by wind, pollen lands on
sticky feather-like stigma receptacles (2). Sepals and petals of grasses have
evolved into three layers of protective bracts -glume, palea, and lemma (9).
1. Study flower anatomy. Identify flower parts.
2. Cross-polinate tomato flowers according to the protocol below.
Tomato (Lycopersicon esculentum Mill.) is a highly self-pollinating species. Itsflower is perfect, having male (anthers) and female parts. Four to eight flowers areborne on a compound inflorescence (right). A single tomato plant may produce up to20 successive inflorescences during its life cycle.
The cultivated tomato forms a tight protective anther cone that surrounds the stigma.
Style elongation occurs within the anther cone and usually coincides with pollenrelease. Outdoors, wind aids in release of pollen with subsequent fertilization, butunder greenhouse conditions, manual vibration of open flowers enhances effectivepollination and fruit set.
http://www.hcs.ohio-state.edu/hcs200/Breefrme.html (6 of 8) [10/08/2001 09:58:34 a.m.] 1. Select plump buds which are not yet open. The sepals can be separated but the petalsare still closed. The outside of the petals should appear creamy white in color.
2. With clean fine-pointed tweezers, peel open the sepals and petals. The anther coneshould be very pale yellowish-green and the petals should be pale yellowish-white. Ifthe anther cone is yellow or the petals are yellow the flower is too old. With tweezers,remove all sepals. Take them off all the way down to the base of the bud.
3. Carefully remove all flower petals.
4. Completely remove anther cone by puncturing the base of the cone with tweezers,gently lifting upwards and away. This exposes the style and stigma of the flower.
Emasculation for the purpose of cross pollination must be done approximately one dayprior to anthesis (flower opening) to avoid accidental self-pollination. At this time, thesepals begin to change from light yellow-white to a dark-yellow. The stigma is fullyreceptive which allows for pollination immediately after emasculation. However,stigmas do remain receptive to pollen up to seven days. Under greenhouse conditions,hand-pollinated stigmas require no protection to prevent uncontrolled crossing, aswould be the case under field conditions.
5. With your pollen source in hand, insert the stigma of the emasculate flowers into thepollen, making sure the stigma receives ample pollen.
Gently snip off any immature flower buds located on the inflorescence.
Under greenhouse conditions, hand-pollinated stigmas require no protection. In 4-5days, if the fertilization was successful, the ovary will begin to show signs of swellingand enlargement as fruit development advances. Temperatures can influence the rate ofripening with optimal temperature for fruit maturation and color development between20oC and 24oC.
http://www.hcs.ohio-state.edu/hcs200/Breefrme.html (7 of 8) [10/08/2001 09:58:34 a.m.] Techniques of plant transformation
As you recall from our previous discussion of plant transformation, it is a rather time-consumingprocess. We will not have time to carry a transformation experiment all the way through. We will,however, learn some techniques of plant transformation.
1. Suppose we want to introduce a gene for RoundUp resistance into soybeans.
2. A gene for the herbicide resistance has already been isolated from another organism. Thisherbicide-resistance gene has been excised with special enzymes, working as biological "scissors".
Another set of enzymes, working as biological "glue", inserted the gene of interest into the carrierplasmids. Your TA has coated gold particles with these prepared plasmids.
3. Your TA will demonstrate how to "shoot" these DNA-coated particles into plant tissue. Now it's yourturn to play with the PIG.
4. Place bombarded tissue onto a regeneration tissue culture medium.
It will take time to grow a plant from this tissue. When the tissue gives rise to a plant, it is time to testthe plants for herbicide resistance.
5. Your instructor will spray seedlings of resistant and susceptible soybean seedlings with RoundUp.
Materials on this website are for personal use only. Text or files cannot be legally reproduced orduplicated in any form. For commercial or instructional use of this website or materials from it, pleasecontact Dr. P. McMahon or Max Teplitski.
Copyright by M.Teplitski and P.McMahon, 1999 For more information, email us at , . http://www.hcs.ohio-state.edu/hcs200/Breefrme.html (8 of 8) [10/08/2001 09:58:34 a.m.] Untitled Document A Grain of Hope--and
Fear: Ingo Potrykus
Grains Of Hope
had a simple idea:create genetically Genetically engineered crops could
modified rice to feed revolutionize farming. Protesters fear they
the starving poor and could also destroy the ecosystem. You
give it away. Now, amid fresh protestsagainst BY J. MADELEINE NASH/ZURICH "Frankenfoods," hisgolden grain is caughtin an increasinglypolarized public debate Taking It to MainStreet How to Make Golden Rice for full diagram At first, the grains of rice that Ingo Potrykus siftedthrough his fingers did not seem at all special, but that was because they were still encased in their dark, crinkly husks. Once those drab coverings were stripped away and the interiors polished to a glossysheen, Potrykus and his colleagues would behold the seeds' golden secret. At their core, these grains were not pearly white, as ordinary rice is, but a very pale Are you concerned yellow--courtesy of beta-carotene, the nutrient that serves as a building block for vitamin A.
genetically alteredfruits, vegetables and Potrykus was elated. For more than a decade he had dreamed of creating such a rice: a golden rice thatwould improve the lives of millions of the poorest people in the world. He'd visualized peasant farmers wading into paddies to set out the tender seedlingsand winnowing the grain at harvest time in Coverage of the new handwoven baskets. He'd pictured small children consuming the golden gruel their mothers would profoundly change our make, knowing that it would sharpen their eyesight and strengthen their resistance to infectious And he saw his rice as the first modest start of a new green revolution, in which ancient food crops would Find out if frankenfood acquire all manner of useful properties: bananas that will feed the world wouldn't rot on the way to market; corn that could supply its own fertilizer; wheat that could thrive indrought-ridden soil.
But imagining a golden rice, Potrykus soon found, was one thing and bringing one into existence quite another. Year after year, he and his colleagues ran http://www.hcs.ohio-state.edu/hcs200/rice.html (1 of 3) [10/08/2001 09:58:41 a.m.] Untitled Document into one unexpected obstacle after another, beginning with the finicky growing habits of the rice they Genetically Modified transplanted to a greenhouse near the foothills of the Swiss Alps. When success finally came, in the spring of 1999, Potrykus was 65 and about to retire as a full professor at the Swiss Federal Institute of Technologyin Zurich. At that point, he tackled an even more So far, mostly just Having created golden rice, Potrykus wanted to Europeans. But thanks make sure it reached those for whom it was intended: to a little uncertainty malnourished children of the developing world. And and a lot of agitprop, that, he knew, was not likely to be easy. Why? Because in addition to a full complement of genes NOVEMBER 29, 1999 from Oryza sativa--the Latin name for the mostcommonly consumed species of rice--the golden grains also contained snippets of DNA borrowed from bacteria and daffodils. It was what some would call Frankenfood, a product of genetic engineering. As planting 20 million such, it was entangled in a web of hopes and fears acres of bioengineered and political baggage, not to mention a fistful of corn. Will it poison the ironclad patents.
monarchs? MAY 31, 1999 For about a year now--ever since Potrykus and his chief collaborator, Peter Beyer of the University ofFreiburg in Germany, announced their achievement --their golden grain has illuminated an increasingly polarized public debate. At issue is the question of what genetically engineered crops represent. Are A case study of golden they, as their proponents argue, a technological leap forward that will bestow incalculable benefits on the Department of Natural world and its people? Or do they represent a perilous step down a slippery slope that will lead to ecological Environment (NRE) of and agricultural ruin? Is genetic engineering just a Victoria, Australia more efficient way to do the business of conventional crossbreeding? Or does the ability to mix the genes of any species--even plants and animals--give man presentation about more power than he should have? genetically modifiedfoods, including real The debate erupted the moment genetically video on how to extract engineered crops made their commercial debut in the DNA from an onion mid-1990s, and it has escalated ever since. First to launch major protests against biotechnology wereEuropean environmentalists and consumer-advocacy groups. They were soon followed by their U.S.
Introduction to issues counterparts, who made a big splash at last fall's and controversies World Trade Organization meeting in Seattle and last surrounding genetically week launched an offensive designed to target one modified food by the company after another (see accompanying story).
Over the coming months, charges that transgenic crops pose grave dangers will be raised in petitions, editorials, mass mailings and protest marches. As a result, golden rice, despite its humanitarian intent, will probably be subjected to the same kind of hostile scrutiny that has already led to curbs on the Contains information commercialization of these crops in Britain, Germany, on biotechnology and Switzerland and Brazil.
http://www.hcs.ohio-state.edu/hcs200/rice.html (2 of 3) [10/08/2001 09:58:41 a.m.] Untitled Document The hostility is understandable. Most of the genetically engineered crops introduced so far represent minor variations on the same two themes: resistance to insect pests and to herbicides used tocontrol the growth of weeds. And they are oftenmarketed by large, multinational corporations thatproduce and sell the very agricultural chemicalsfarmers are spraying on their fields. So while manyfarmers have embraced such crops as Monsanto'sRoundup Ready soybeans, with their geneticallyengineered resistance to Monsanto's Roundup-brandherbicide, that let them spray weed killer withoutharming crops, consumers have come to regard suchthings with mounting suspicion. Why resort to astrange new technology that might harm thebiosphere, they ask, when the benefits of doing soseem small? Indeed, the benefits have seemed small--until goldenrice came along to suggest otherwise. Golden rice isclearly not the moral equivalent of Roundup Readybeans. Quite the contrary, it is an example--the firstcompelling example--of a genetically engineered cropthat may benefit not just the farmers who grow it butalso the consumers who eat it. In this case, theconsumers include at least a million children who dieevery year because they are weakened by vitamin-Adeficiency and an additional 350,000 who go blind.
IMAGE CREDITS TIME DIAGRAM BY JOE LERTOLASOURCE: DR. PERET BEYER, CENTER FOR APPLIEDBIOSCIENCES, UNIVERSITY OF FREIBURG http://www.hcs.ohio-state.edu/hcs200/rice.html (3 of 3) [10/08/2001 09:58:41 a.m.] Untitled Document Nikolai I. Vavilov (1887-1943)
----------------------------------------------------------------------------
From : http://www.dainet.de/genres/vir/ (Russian Institute of Plant
Industry )
Nikolai I. Vavilov was born into the family of a merchant in Moscow onNovember 25, 1887. In 1911, having graduated from the Agricultural Institute,Vavilov continued to work at the Department of Agriculture Proper headed byProf. Pryanishnikov. In 1911-1912 Vavilov did practical work at the Bureau forApplied Botany and at the Bureau of Mycology and Phytopathology of theAgricultural Scientific Committee. In 1913-1914, Vavilov traveled to Europewhere he studied plant immunity, mostly with Prof. W. Bateson, a co-founderof the science of genetics.
In autumn 1917 the Head of the Bureau for Applied Botany Robert. E. Regel(1867-1920) supported the nomination of N.I.Vavilov, a young professor fromthe Saratov Higher Agricultural Courses, as Deputy Head of the Bureau. AsRegel wrote in his reference letter, "In the person of Vavilov we will employ .
a talented young scientist who would become the pride of nationalscience". Regel's prediction turned out to be true. Since then, all Vavilov's lifeand creative work have been inseparable from the world's largest crop researchinstitute, into which he transformed the Bureau in the1920-30's.
Vavilov continued his investigations in Saratov where he has awarded the titleof Professor of the Saratov University in 1918. During the Civil War, from1918 to 1920, Saratov became the scientific stronghold for the Department ofApplied Botany (Bureau till 1917). In 1920 Vavilov was elected head of theDepartment, and soon moved to Petrograd (St.Petersburg now) together withhis students and associates.
In 1924, the Department was transformed into the Institute of Applied Botanyand new Crops (VIR since 1930), and occupied the position of the centralnationwide institution responsible for collecting the world plant diversity andstudying it for the purposes of plant breeding.
Vavilov is recognized as the foremost plant geographer of contemporary times.
To explore the major agricultural centers in this country and abroad, Vavilovorganized and took part in over 100 collecting missions. His major foreignexpeditions included those to Iran (1916), the United States, Central and SouthAmerica (1921, 1930, 1932), the Mediterranean and Ethiopia (1926-1927). Forhis expedition to Afghanistan in 1924 Vavilov was awarded theN.M.Przhevalskii Gold Medal of the Russian Geographic Society. From 1931to 1940 Vavilov was its president.
These missions and the determined search for plants were based on the http://www.hcs.ohio-state.edu/hcs200/vavilov.html (1 of 4) [10/08/2001 09:58:52 a.m.] Untitled Document Vavilov's concepts in the sphere of evolutionary genetics, i.e. the Law ofHomologous Series in Variation (1920) and the theory of the Centers of Originof Cultivated Plants (1926).
N.I.Vavilov was a prominent organizer of science. In the period from 1922 to1929 he headed the Institute of Experimental Agronomy (the former ASC)which developed in 1930 into the V.I.Lenin All-Union Academy ofAgriculture; from 1930 to 1935 Vavilov was its first president. From 1930 to1940 he was director of the Institute of Genetics. Vavilov organized andparticipated in significant home and international scientific meetings andcongresses on botany, genetics and plant breeding, agricultural economy, andthe history of science. All around the world N.I.Vavilov has gained respect andrenown; he was elected member of many academies of sciences and variousforeign scientific societies.
Vavilov, the symbol of glory of the national science, is at the same time thesymbol of its tragedy. As early as in the beginning of the 1930's his scientificprograms were being deprived of governmental support. In the stiflingatmosphere of a totalitarian state, the institute headed by Vavilov turned into aresistance point to the pseudo-scientific concepts of Trofim D.Lysenco. As aresult of this controversy, Vavilov was arrested in August 1940, and his closestassociates were also sacked and imprisoned.
Vavilov's life ceased in the city where his star had once risen. He died in theSaratov prison of dystrophia on 26 January 1943 and was buried in a commonprison grave.
Nevertheless, the memory of Vavilov has been preserved by his followers.
During that tragic period they kept on gathering Vavilov's manuscripts,documents and pictures. Since mid-50's, after the official rehabilitation ofVavilov, hundreds of books and articles devoted to his life and scientificaccomplishments have been published. Memorial displays have been opened in Major N.I.Vavilov's Expeditions
----------------------------------------------------------------------------1916 Expedition to Iran (Hamadan and Khorasan) and Pamir (Shungan, RushanandKhorog).
1921 Acquaintance trip to Canada (Ontario) and USA (New York,Pennsylvania,Maryland, Virginia, North and South Carolina, Kentucky, Indiana, Illinois,Iowa, Wisconsin, Minnesota, North and South Dakota, Wyoming, Colorado,Arizona,California, Oregon, Maine).
1924 Expedition to Afghanistan (Herat, Afghan Turkestan, Gaimag, Bamian,Hindu Kush,Badakhshan, Kafiristan, Jalalabad, Kabul, Herat, Kandahar, Baquia, Helmand, http://www.hcs.ohio-state.edu/hcs200/vavilov.html (2 of 4) [10/08/2001 09:58:52 a.m.] Untitled Document Farakh, Sehistan), accompanied by D.D. Bukinich and V.N. Lebedev.
1925 Expedition to Khoresm (Khiva, Novyi Urgench, Gurlen, Tashauz).
1926-1927 Expedition to Mediterranean countries (France, Syria, Palestine,Transjordan,Algeria, Morocco, Tunisia, Greece, Sicily, Sardinia, Cyprus and Crete, Italy,Spain, Portugal, and Egypt, where Gudzoni was explored by Vavilov's request)and to Abyssinia (Djibouti, Addis Ababa, banks of Nile, Tsana Lake), Eritrea(Massaua) and Yemen (Hodeida, Jidda, Hedjas).
1927 Exploration of mountainous regions in Wuertemberg (Bavaria, Germany).
1929 Expedition to China (Xinjiang - Kashgar, Uch-Turfan, Aksu, Kucha,Urumchi,Kulja, Yarkand, Hotan) together with M.G. Popov, then alone to Chine(Taiwan),Japan (Honshu, Kyushu and Hokkaido) and Korea.
1930 Expedition to USA (Florida, Louisiana, Arizona, Texas, California),Mexico,Guatemala and Honduras.
1932-1933 Trip to Canada (Ontario, Manitoba, Saskatchewan, Alberta, BritishColumbia),USA (Washington, Colorado, Montana, Kansas, Idaho, Louisiana, Arkansas,Arizona, California, Nebraska, Nevada, New Mexico, North and SouthDakotas,Oklahoma, Oregon, Texas, Utah); Expedition to Cuba, Mexico (Yucatan), Ecuador (Cordilleras), Peru (LakeTiticaca, Puno Mt., Cordilleras), Bolivia (Cordilleras), Chile (Panama River).
Brazil (Rio de Janeiro, Amazon), Argentina, Uruguay, Trinidad and Porto Rico.
1921-1940 Systematic explorations of the European part of Russia and thewhole regions ofthe Caucasus and the Middle Asia.
---------------------------------------------------------------------------- Major Collecting Missions Accomplished by N.I.Vavilov's Associates 1922-1923 Expedition of V.E.Pisarev and V.P.Kuzmin to Mongolia.
1923 Expedition of E.I.Barulina to Crimea (Ukraine).
1924 Expedition of E.I.Sinskaya to Altai.
1925-1926 Expedition of S.M.Bukasov and Yu.N.Voronov to Mexico,Guatemala and Colombia.
1925-1926 Expedition of E.N.Stoletova to Armenia.
1925-1927 Expedition of P.M.Zhukovsky to Turkey.
1926 Expedition of N.N.Kuleshov and V.V.Pashkevich to Azerbaijan.
1926 Expedition of K.A.Flyaksberger to Azerbaijan and Russia (Daghestan).
1926 Expedition of N.N.Kuleshov and V.K.Kobelev to Uzbekistan.
1926 Expedition of K.A.Flyaksberger to Far East of Russia.
http://www.hcs.ohio-state.edu/hcs200/vavilov.html (3 of 4) [10/08/2001 09:58:52 a.m.] Untitled Document 1926-1928 Expedition of V.V.Markovich to Palestine, Pakistan, India, Java andCeylon.
1926-1928 Expedition of S.V.Yuzepchuk to Peru, Bolivia and Chile.
1927 Expedition N.N.Kuleshov to Turkmenia.
1927 Expedition K.G.Kreier to Central and Western part of Siberia.
1928-1929 Expedition of E.N.Sinskaya to Japan.
1928-1932 Expedition of G.K.Kreier to Georgia and Azerbaijan.
1930 Expedition of E.A.Stoletova to Georgia (USSR).
1930 Expedition of G.K.Kreier to Kirgizia and Uzbekistan.
1933 Expedition of E.I.Barulina to Georgia (USSR).
http://www.hcs.ohio-state.edu/hcs200/vavilov.html (4 of 4) [10/08/2001 09:58:52 a.m.] Untitled Document Barbara McClintock (1902 - 1992)
Essay by David Ardell Until recently, scientific research was considered beyond most women's abilities,despite notable historical exceptions - such as that of the great 19th centuryco-discoverer of radioactivity, Marie Curie. If a woman displayed natural talent inscience and mathematics, the option to pursue her talents as a scientist was likely tobe closed off in favor of more traditional roles: mother, wife, and homemaker. Sadly,this was true in America even as late as the 1950s. That is what makes BarbaraMcClintock and her lifelong achievements in genetics all the more notable.
McClintock launched her scientific career at Cornell in1919 and, in the face of socialadversity and tremendous intellectual challenges, established herself among the greatgeneticists of this century.
At the time McClintock started her career, scientists were just becoming aware of theconnection between heredity and events they could actually observe in cells underthe microscope. McClintockpioneered the field of maize cytogenetics, or the cellular analysis of geneticphenomena in corn, which for the first time provided a visual connection betweencertain inheritable traits and their physical basisin the chromosome.
McClintock rose to many challenges throughout her career - not only scientific butpersonal - from other scientists who felt intimidated or threatened by what one of hercolleagues described as her"independence, originality, and extraordinary accomplishment." In the most notablecase, Lowell Randolph, her advisor and colleague, became extremely irritated withMcClintock's success in solving a problem he had spent his entire life working on.
McClintock became the dominant member of his research team, and Randolph foundthis intolerable. McClintock soon departed, going on to greater things.
For her ground-breaking work in the genetics of corn, Barbara McClintock earned aplace among the leaders in genetics. She was elected to the prestigious NationalAcademy of Sciences in 1944.
Despite this, she still met with social adversity in her department at the University ofMissouri and finally left there, too. She kept her next appointment at the CarnegieInstitute at Cold Spring Harbor forthe rest of her life.
In 1983, Barbara McClintock was awarded a Nobel Prize in Genetics. To this day,her work is highly esteemed, still relevant despite the fact that much of it wascompleted over half a century ago, before theadvent of the molecular era.
http://www.hcs.ohio-state.edu/hcs200/McCl.html (1 of 2) [10/08/2001 09:59:10 a.m.] Untitled Document http://www.hcs.ohio-state.edu/hcs200/McCl.html (2 of 2) [10/08/2001 09:59:10 a.m.] The Genetics Revolution Press releases and news from the company on its A quarterly online Italian institute promoting biotechnology world-wide A genetically engineered tomato on the vine The Killer Tomatoes
Somewhere, someone is crossing a fish with a tomato.
Researchers are inserting an antifreeze gene from the winter flounder to produce a cold-resistant love apple, one that American consumers seem indifferent to but has Europeans taking to the streets to keep off their shelves. These are the front lines of the genetics revolution, the practical applications of the truly amazing discoveries of the past two decades. Here are miracles and wonders that could help feed an ever-more crowded world: extra-starch The latest discoveries and potatoes, coffee beans grown decaf right on the vine, low-sugar strawberries. Wonder Bread-quality wheat courtesy a plant with extra gluten built right in. Super high-protein grains that could be a boon to the developing world. And cotton and potatoes with herbicide-producing Dolly was just the first.
genes that could eliminate the need for toxic sprays. How long until humans Here are dragons: Activists worry that plants with an innate herbicide might breed a new generation of resistant "super Plant & Animal
insects." Or that man-made seeds might cross-pollinate with other plant species, with unknown and potentially Why the farm will never be devastating results. Already, early studies show Monsanto's Designer babies, maybe.
Then there's the matter of intellectual property. To protect But also designer its billion-dollar investment, Monsanto hopes to introduce an http://www.hcs.ohio-state.edu/hcs200/plgenti.html (1 of 2) [10/08/2001 09:59:16 a.m.] The Genetics Revolution treatments for your specific elegantly malevolent technology, called "Terminator," that is a set of genetic instructions that render a seed sterile after just one planting -- thus enforcing the company's copyright. What to do with our From a biotech standpoint, this is a marvel, what one newfound knowledge scientist has called "the most intricate application of genetic engineering to date." From a human standpoint, it's a potential time bomb. The UN has already expressed concern The worth of the gene that Terminator seeds could force farmers into total dependence on seed companies. Others are worried about possible cross-pollination that could render other plants From discovery of the sterile. Meanwhile, the U.S. Army War College is reportedly double helix to deciphering intrigued about the possibilities of technologies that could the human genome tell plants to commit suicide on demand. Which means the only certain thing is that there's a crop dustup in our from TIME
Genetically modified food has met fierce opposition among well-fed Europeans, but it's the poor and the hungry who What Happens To These Ordinary Salmon If The Genetically Modified Lunkers Ever Get Loose? So far, mostly just Europeans. But thanks to a little uncertainty and a lot of agitprop, that's changing NOVEMBER 29, 1999 U.S. farmers are planting 20 million acres of bioengineered corn. Will it poison the monarchs? Terminator genes could mean big biotech bucks--but big trouble too, as a grass-roots protest breaks out on the Net JANUARY 19, 1999 Fears of "Frankenstein" food run deep, especially in Europe PHOTO: GERRY GROPP/SIPA Copyright 1999 Time Inc. New Media. All Rights Reserved.
http://www.hcs.ohio-state.edu/hcs200/plgenti.html (2 of 2) [10/08/2001 09:59:16 a.m.] Untitled Document MAPPING THE GENOME The Race Is Over
The great genome quest is officially a tie,
thanks to a round of pizza diplomacy. Yet
lead researcher Craig Venter still draws
few cheers from his colleagues
BY FREDERIC GOLDEN AND MICHAEL D. LEMONICK
One day last April, Aristides (Ari) Patrinos, a scientistat the Department of Energy who directs thatagency's share of the Human Genome Project, got acall from Francis Collins, director of the NationalInstitutes of Health's National Human GenomeResearch Institute and the project's unofficial head.
"Let's try it," said Collins--and at those words Patrinosknew that a longstanding scientific feud finally had achance of being resolved. For months, Collins hadbeen under pressure to hammer out his differenceswith J. Craig Venter, the prickly CEO of CeleraGenomics, which was running its own independentgenome-sequencing project--differences over whoshould get the credit for this scientific milestone; overwhose genome sequence was more complete, moreaccurate, more useful; over the free exchange ofwhat may be mankind's most important data versusthe exploitation of what may also be its mostvaluable.
The bickering had become downright nasty at times,upstaging the enormous importance of the projectand threatening to slow the pace of scientificdiscovery. Therefore Patrinos had been lobbying hiscolleague to make love, not war, despite Venter'suncanny ability to get under the skin of Collins andother leaders of the U.S.-British genome project. Sohad Collins' counterparts at other NIH institutes. Andso, most important, had President Clinton, who atone point scribbled a note to science adviser NealLane with the terse instruction: "Fix it.make theseguys work together." Venter was clearly ready. His tactless rhetoric had http://www.hcs.ohio-state.edu/hcs200/timege.html (1 of 3) [10/08/2001 09:59:27 a.m.] Untitled Document lost him respect among his colleagues, and herecognized that more controversy could overshadowa historic moment in biomedicine. Beyond that, he'dtaken a beating in the marketplace. After a jointdeclaration by Clinton and British Prime MinisterTony Blair in March that all genomic informationshould be free, the value of Celera stock plummetedfrom $189 a share to $149.25.
So on May 7, over pizza and beer at Patrinos'Rockville, Md., town house, the two wary antagonistssat down in a deliberately casual setting to work outtheir differences. In an exclusive conversation withCollins, Venter and TIME correspondent DickThompson last Thursday night, Patrinos recalled, "Idon't think I've ever seen them as tense as they werethat day." Yet despite mistrust on both sides, Collinsand Venter met a second time and a third. And finally they came, if not to a meeting of theminds, at least to a workable understanding--and aframework for this week's joint announcement. Aftermore than a decade of dreaming, planning and heroicnumber crunching, both groups have decipheredessentially all the 3.1 billion biochemical "letters" ofhuman DNA, the coded instructions for building andoperating a fully functional human.
It's impossible to overstate the significance of thisachievement. Armed with the genetic code, scientistscan now start teasing out the secrets of human healthand disease at the molecular level--secrets that willlead at the very least to a revolution in diagnosingand treating everything from Alzheimer's to heartdisease to cancer, and more. In a matter of decades,the world of medicine will be utterly transformed, andhistory books will mark this week as the ceremonialstart of the genomic era.
But while the announcement has been exquisitelychoreographed to make the two scientists look likeequals, it's clear to insiders that Venter's project is alot further along. HGP scientists may have decoded97% of the genome's letters--the remaining 3% aregenerally considered unsequenceable andirrelevant--but they know the order of only 53% ofthem. It's as if they've got the pages in the so-calledbook of life in the proper order but with the letters oneach page scrambled. "It's going to take us a coupleof years to put this together," Collins told TIME.
Celera, by contrast, has not only the pages but allthe words and letters as well--though neither side canyet say what most of these words and letters mean.
And while the HGP boasts that it has done itssequence nearly seven times over to guaranteeaccuracy, Celera has gone over its own almost five http://www.hcs.ohio-state.edu/hcs200/timege.html (2 of 3) [10/08/2001 09:59:27 a.m.] Untitled Document times. Moreover, the company came up with a newtechnique that made its sequencing rate, already thefastest around, even faster. In addition, Venter claimsthat by the end of the year, he'll have sequenced thegenome of the mouse--whose 2.3 billion letterscontain enough similarities to ours to make it vitallyimportant to scientists tracking down human genefunction.
Given this remarkable record, why are so few ofVenter's fellow scientists trumpeting his success? Ortalking him up for a Nobel Prize? Why, in fact, is thischerubic-looking, blue-eyed ex-surfer hated by somany colleagues, who have called him everythingfrom a greedy megalomaniac to a Hitler? Forgetabout easy explanations, such as his outsize ego(yes, one of the samples he is analyzing is rumoredto contain his own DNA) or his penchant for doingscience by press release (yes, he keeps his dooropen to reporters) or his tendency to do not sciencebut, as pioneer DNA mapper James Watson sneered,tedious assembly-line labor on machines that "couldbe run by monkeys" (yes, most of Celera's analysiswas done by robot gene sequencers and high-speed http://www.hcs.ohio-state.edu/hcs200/timege.html (3 of 3) [10/08/2001 09:59:27 a.m.] Biochemistry: Proteins Plant Biochemistry: Proteins
Proteins are long chains of amino acids linked together by peptide bonds.
All enzymes are proteins, not all proteins are enzymes.
Some are parts of membranes (channels and gates).
Some are structural and/or storage units.
There are 20 common amino acids.
All amino acids have a carboxyl (COOH) end and an amino (NH2) end. This is the first time we have
seen where N is a major component of a structure.
The peptide bonds form a backbone with the unique portion of the amino acid attached to the backbone.
These amino acids are arranged in very specific order for each different protein. There can be 100,000'sper molecule. They are what gives a protein it's specific role as an enzyme.
The aminoacid sequence causes the protein to coil up in a very specific, convoluted (folded) form. Theform is what determines if it is active or inactive many times.
Only a slight conformational change is enough to activate or deactivate a protein.
Adding or taking away even a single CH3 (methyl) from the entire molecule is enough to put it into ortake it out of action.
Other things can activate or deactivate.
(enzymes that phosphorylate and de-phosphorylate a molecule using ATP as the P donor) need Mg+ to work. Without Mg+ the Calvin and TCA cycles shut down. Not good.
Remember, all enzymes are proteins and an enzyme is needed for every single step of every
single biochemical pathway - including protein synthesis.
But not all enzymes are present in every cell all the time. They are synthesized as needed. Every
cell has a complete set of genes. Proteins are synthesized when a gene is 'turned on'.
Some proteins are soluble in H2O, some are not. The soluble ones can be transported to other
cells in the plant.
Remember, N is a mobile element, this is partly why.
Two amino acids, methionine and cysteine also contain sulfur.
Peanuts contain all the amino acids essential for human nutrition.
The problem with peanuts is they also contain high amounts of lipids so they are high calorie.
Some proteins help to make cellulose more rigid in the cell walls. These proteins are not mobile.
Some proteins are a storage compound in legume seeds such as soybean, chickpeas (garbanzos),
http://www.hcs.ohio-state.edu/hcs200/prtns.html (1 of 2) [10/08/2001 10:00:51 a.m.] Biochemistry: Proteins and lentils. These seeds are an important nutrient source for people in developing areas where thetraditional primary diet is based on high carbohydrate seeds such as rice and corn.
http://www.hcs.ohio-state.edu/hcs200/prtns.html (2 of 2) [10/08/2001 10:00:51 a.m.] Index Page of HCS200 Class Schedule
Lectures
Plant morphology and anatomy
Environmental factors affecting crop
growth and ,
Environmental factors cont'd.
Plant physiology and
Crop growth and development
Crop breeding (genetics, reproduction and
Cropping systems, Agroecology
http://www.hcs.ohio-state.edu/hcs200/Index.html (1 of 2) [10/08/2001 10:00:59 a.m.] Index Page of HCS200 All materials on this website are for personal educational use only. We ask you not to reproduce anyfiles, texts or figures without our permission. We are gratefull to Dr. M.Knee, Dr. X.Wei, AmericanSociety of Plant Pathology, PLANT PHYSIOLOGY journal, TIME magazine, Liebig Museum, NobelPrize Archives, and Vavilov Research Institute for allowing us to use their copyright images. We thankDr. D. Bauer, N. Cavender, G. Glaunsinger, T. Mangen, H. Brown, and J. Schmoll for contributing theirideas and suggestions. We are indebted to our students and colleagues for their constructive criticismand help in designing the website.
Development of this website was supported, in part, by the Faculty Innovator Grant (2000) to Dr.
P.McMahon.
Copyright by M.Teplitski and P.McMahon, 2000 http://www.hcs.ohio-state.edu/hcs200/Index.html (2 of 2) [10/08/2001 10:00:59 a.m.] HCS 200 - Winter Quarter 2001 Syllabus for CROP SCIENCE
Horticulture and Crop Science 200
Winter 2001
Instructor: Dr. Joe Scheerens
Columbus Office: 232 Kottman Hall
Wooster Office: 213 Williams Hall
Columbus Phone (work): 614-247-6859
Wooster Phone (work): 5-3826 from Campus
Wooster Phone (work): 330-263-3826
Wooster Phone (home): 330-264-4930
Wooster Fax: 330-263-3887
Ms. Nicole Cavender Ms. Gitta Glaunsinger Kottman Greenhouse Supervisor:
Phone: 614-292-3866 Course Description: Study of environmental, genetic and cultural factors which influence plant productivity
Final Examination: Monday, March 12, 2001, 9:30 -11:18 AM.
Required Text; Plant Science Barden, Halfacre and Parish McGraw Hill, Publ.
http://www.hcs.ohio-state.edu/hcs200/syllabus.htm (1 of 5) [10/08/2001 10:01:02 a.m.] HCS 200 - Winter Quarter 2001 Lab Manual; http://hcs.ohio-state.edu/hcs200 Lab Worksheets; Available at Cop-EZ Supplementary; Placed on reserve in Agric. Library Purpose: This class give students interested in the production of plants and crops for food, fiber, ornamental,
and recreational use the basic understanding of how environmental, cultural and genetic factors influence crop
productivity. Students are introduced to contemporary issues surrounding plant agriculture and to the current
concepts and techniques for improving crop productivity. Students are encouraged through interactive
discussions and hands-on projects to develop skills needed to make informed decisions about the growing,
production, and utilization of plants and crops. In addition, students develop an appreciation for the
contribution that cultivated plants make to the environment and humanity.
Goals: Class goals for Winter 2001 will be determined by the class.
Lecture Schedule and Content: The majority of lecture topics that will be covered in H&CS 200 are listed
below. However, several class periods (exact number to be determined collectively by students) will be
devoted to exploring student-relevant topics or issues. Students will be involved in the development and
perhaps, the presentation of these issues.
and the consequences of an agrarian society - Crop growth and development (continued) http://www.hcs.ohio-state.edu/hcs200/syllabus.htm (2 of 5) [10/08/2001 10:01:02 a.m.] HCS 200 - Winter Quarter 2001 Topic 4. Environmental factors (light, heat, soil/media, water, nutrients, atmospheric gasses) affecting cropgrowth and development through modification of crop physiology and biochemistry Topic 5. Crop products and their relationship to our daily lives Topic 6. Cropping systems at all levels of technology Topics 7-? Additional topics to be determined by class Lab Schedule and Content: See lab manual and accompanying materials
Discussion Section Schedule and Content: A portion of each discussion period will be devoted to
clarification of lecture material if necessary or for pre-examination reviews . However, most of the discussion
classes will be devoted to exploring individual crops (history, production, use, etc.) of importance to the world
or of particular interest to students. Assignments in discussion sections will accomplished individually or in
teams. For the most part, activities in discussion sections will be student-directed and interactive. This is your
chance to be creative, productive and to have some fun at the same time.
Evaluation Methods: The relative importance of class activities and how and in some instances, by whom
they are graded was determined by the class. The results are as follows
http://www.hcs.ohio-state.edu/hcs200/syllabus.htm (3 of 5) [10/08/2001 10:01:02 a.m.] HCS 200 - Winter Quarter 2001 Percent of Grade
Two Midterms + Final* Discussion Projects *Each test will be worth 25% of the class grade - the lowest score on the three tests will be dropped.
Grading Scale: A = 94-100 points C = 73-76 points
A- = 90-93 points C- = 70-72 points B+ = 87-89 points D+ = 67-69 points B = 83-86 points D = 60-66 points B- = 80-82 points E < 60 points C+ = 77-79 points Midterm Examinations: Midterms will be given during lecture periods and will be announced at least 5 days
before being given. There will be ample opportunity for review prior to each examination. Examinations may
contain objectively graded questions (e.g., matching or one word answer), but most assuredly will contain short
essay questions. Students will always have a choice as to which short essays they write (i.e., students do not
answer all questions that are posed, only those for which they have the most complete understanding of the
subject).
Final Examination: A final examination will be given on the date/time listed previously. The structure (style)
of the final exam will be similar to that used for midterms.
Second Chance Examinations: Students will have the opportunity to turn into the instructor (within an
agreed-upon time frame) revised answers to any questions for which they lost points. The final score for each
question that has an improved answer will be the average of the old and new score for that question. Students
will not be penalized if they change an answer incorrectly. For the second chance exam, students can use any
source or reference (except the instructor, teaching assistants, guest lecturers or classmates) to determine the
appropriate answer. Second chance examinations for the final exam will be offered only if time permits.
Make-up Examinations: A full credit, written make-up midterm exam with a second chance will be given to
students who notify the instructor or TA's ahead of time of their absence from the exam. There must be a
verifiable, reasonable excuse (e.g., field trip, illness, transportation problems, family emergencies, etc). An
unacceptable excuse would be any excuse that indicates a lack of responsibility on the part of the student. A
student who has missed a midterm exam without an excuse has the option of taking a full-length, written exam
http://www.hcs.ohio-state.edu/hcs200/syllabus.htm (4 of 5) [10/08/2001 10:01:02 a.m.] HCS 200 - Winter Quarter 2001 worth 75% of the original points with no second chance exam option. Failure to attend the final exam will beadjudicated on a case by case basis.
Attendance: Students are encouraged to attend class regularly. Material presented in lectures may or may not
be found in the text book. Detailed lecture notes will be posted upon the completion of each topic at the web
site indicated above. However, these notes are made available to students so as to provide best possible
opportunity for students to listen and think as lectures are being delivered. They are not be designed to act as
comprehensive web-based learning materials on their own. Because much of discussion and lab activities are
team-based and interactive, failure to attend either will result in the inconvenience of others and the loss of
experiences important to the educational process.
Class Participation: Although the instructor and TA's assume responsibility for most of the instruction in this
course, each student brings to class, relevant personal experience that will relate to the subject matter. Students
are asked to share this experience with their classmates, if they feel comfortable doing so. Students who enroll
in this course come from a diversity of backgrounds and personal skills. The sharing of knowledge or insight
with others is encouraged as a means to enrich the experience for all.
Effort: It is understood that individuals within the class will have other commitments (educational and
personal) that he/she must fulfill. Moreover, because students in this course are diverse, it is unlikely that all
will be able to devote equal amounts of time or effort to performing assignments in this class. However, the
instructor and TA's ask that students work as diligently as possible to complete the activities in this course to
the best of their abilities. A portion of the lab and discussion section grades will result from an assessment of
effort. If students are experiencing difficulty (i.e, a crisis has arisen) please let the instructor or TA's know as
soon as possible.
Code of Conduct: In H&CS 200, courtesy and respect for others will be given by all participants, including
the instructor, teaching assistants and guests, in the class at all times. An environment that fosters free,
non-confrontational expression of ideas will be maintained. When working on teams, each team member will
assume full responsibility for their role as a member of that team. Academic misconduct or suspected academic
misconduct will be handled according to policies of the Code of Student Conduct in the Student Handbook or
Faculty Rule 3335-5-487.
http://www.hcs.ohio-state.edu/hcs200/syllabus.htm (5 of 5) [10/08/2001 10:01:02 a.m.] Horticulture and Crop Science 200
Winter Quarter 2001 Lecture Topic #1: Crop origins, crop development and the effect of crops and crop science on human
life
Brownowski, J. 1973. The harvest of the seasons. In: The ascent of man. Little, Brown Inc., Boston, MA.
Chandler, R.F. 1992. The role of the international agricultural research centers in increasing the worldfood supply. Food Tech. 46(7):86.
Council for Agricultural Science and Technology. 1985. Plant germplasm preservation and utilization in U.S. agriculture.
Goldblith, S.A. 1992. The legacy of Columbus, with particular reference to foods. Food Tech46(10):62-85.
Hanson, H., N.E. Borlaug and R.G. Anderson. 1982. Wheat in the third world. Westview press, Boulder, CO.
Harlan, J.R. 1992. Crops and man (2nd ed.) Amer. Soc. Agron., Madison, WI.
Hartmann, H.T., A.M. Kofranek, V.E. Rubatzky and W.J. Flocker. 1988. Plant Science (2nd ed.).
Prentice-Hall, Englewood Cliffs, NJ.
http://www.hcs.ohio-state.edu/hcs200/topics/topic1.htm (1 of 17) [10/08/2001 10:01:07 a.m.] Hawkes, J.G. 1990. The potato: evolution biodiversity and genetic resources. Belhaven Press.
International Potato Center. 1984. Potatoes for the developing world. International Potato Center, Lima,Peru.
Metcalf, D.S., and D.M. Elkins. 1980. Crop production principles and practices (4th ed.) MacMillanPublishing Co., New York, NY.
National Academy of Sciences. 1972. Genetic vulnerability of major crops. NAS, Washington, D.C.
Niderhauser, J.S. 1992. The role of the potato in the conquest of hunger and new strategies forinternational cooperation. Food Tech. 46(7):91-95.
Zohary, D., J.R. Harlan and A. Vardi. 1969. The wild diploid progenitors of wheat and their breedingvalue. Euphytica 18:58-65.
"Man during his history in all parts of the world has used for food more than 3000 species of plants. Ofthese, only some 150 parts have ever been extensively cultivated and only about dozen are importantfrom the standpoint of the energy which they contribute." (Paul S. Mangelsdorf) http://www.hcs.ohio-state.edu/hcs200/topics/topic1.htm (2 of 17) [10/08/2001 10:01:07 a.m.] 1. Definitions for "agriculture" and "crop" The field of agriculture is diverse and not easily defined. A crop could be defined as a cultivated plantthat yields an economically-valuable product (other definitions are valid). Crops are genetically distinctfrom their wild relatives.
2. The change in human society from that of "hunter-gatherer" to "agriculturist" is recent and irreversible.
The neolithic revolution (the dawn of agriculture) began about 10,000 years ago, corresponding with theend of the last ice age. There is evidence to suggest that plant agriculture was "invented" in various areasof the world independently. The changes to both man, animals and plants resulting from this inventionwere gradual and promoted a mutual dependency between man and agriculture.
Agriculture is a recent invention. About 90% of the humans who have ever lived made their living ashunters-gatherers, 6% were agriculturists and only 4% were urban dwellers.
3. What happened? A. Ecological prospective-biological vs. agricultural fitness- general characteristics of potentialdomesticates.
A natural ecosystem includes the interrelated factors of: climate, soils, man, and other animals, andplants.
http://www.hcs.ohio-state.edu/hcs200/topics/topic1.htm (3 of 17) [10/08/2001 10:01:07 a.m.] Natural ecosystems contain a diverse number of species.
The diversity of niches and organisms to fill them makes the system relatively stable and resistant There is no net yield. All the energy arriving to the system via the sun is utilized by members of the ecosystem.
Successful plants in the first ecosystem are those which are biologically fit (i.e. produce the greatest number of offspring).
Plants in the community are subject to natural selection.
An agricultural ecosystem includes the interrelated factors of: climate, soils, man as the manipulator,crop plants, and domestic animals.
Agricultural ecosystems contain a select number of species (few).
The number of niches in very finite so the system is not very stable (i.e. vulnerable to change).
There is no net yield (i.e. something to store or sell). The ecosystem outperforms the needs of its Successful plants in the second ecosystem are those which are Plants in the community are subject to natural selection and to the active or passive selection pressures for agricultural fitness by man.
The transition from biological fitness to agricultural fitness involves genetic changes in the
organism.
The characteristics of potential domesticates are that: -they produce a useful product -they are adapted to grow in disturbed soils (agricultural fields) -they exhibit high levels of genetic diversity Weedy species often exhibit these traits.
B. Genetic changes mechanisms for change http://www.hcs.ohio-state.edu/hcs200/topics/topic1.htm (4 of 17) [10/08/2001 10:01:07 a.m.] Morphological and physical changes in species undergoing domestication include: gigantism of horticultural/agronomic yield components (e.g. the development of corn ear from a small terminal inflorescence bearing a few kernels).
loss of speed dispersal mechanisms (e.g. passive selection for non-shattering wheat rachis) loss of delayed seed germination (e.g. hard seed coat in wild beans absent from domesticates) loss of bitter or toxic substances (e.g. deleterious fats- canola: cyanogenic glycosides- canola and cassava: antagonists to digestion- lima and other legume crops; bitter steroids- squashes andmelons; alkaloids-potato) changes in photoperiodic responses (e.g. development of day neutrality in cotton) changes in floral structures or pollination schemes (e.g. multiple petals- rose: increased self-pollination - chili) changes in flowering cycle (e.g. biennial bearing and development of tap root-carrot) synchronous tillering (e.g. rice amenable to single harvests) diversity of form (e.g. the multiple forms of Brassica oleracae - cabbage, cauliflower, broccoli, kohlrabi, kale, Brussels sprouts, etc) mechanisms to protect against predators (e.g. pendant rather than upright fruit in chili protecting from predatory birds; the corn husk) Genetic mechanisms effecting (causing) these changes include: mutation- Mutations are sudden heritable changes in a gene. In wild populations, the natural mutation rate is about 10-6 (a low frequency) and unless they offer a strong reproductiveadvantage over the original gene, these mutant alleles remain at low frequency in the population.
However, under selection for agricultural fitness by and for man, the new trait may become fixed rapidly(e.g. non-shattering rachis in wheat). Therefore, emerging crops and their wild and weedy relatives beganto diverge (separate).
human migration-As man moved into new areas, his crops went with him. Planting a crop in a new area has several consequences including the passive or active selection pressure to adapt to a newenvironment (e.g. short day cottons into northern areas with long summer days) and new contactswith compatible weedy species.
introgression- Introgression is the transfer of small amounts of genetic information from one http://www.hcs.ohio-state.edu/hcs200/topics/topic1.htm (5 of 17) [10/08/2001 10:01:07 a.m.] species to another. The initial step in this process is a chance interspecific hybridization betweenan emerging crop (e.g., AA) and its relative (BB). Although the resulting hybrid (AB) is mostlysterile (i.e., chromosomes from the crop fail to pair with those of the related species so the meioticprocess in the hybrid is hampered), sometimes a few viable gametes will be formed. With repeatedbackcrossing to the crop, the fully-fertile crop type can be recovered. However, a small number ofuseful genes from the related species will now be incorporated (AA B). "It is the genetic support oftheir companion weed races" (Jack Harlan).
Stephens demonstrated the effects of introgression using two species of cotton -- upland cotton(Gossypium hirsutum) and sea island cotton (G. barbadense). Sea island cotton, a short day plant (SDP)that initiates flower buds as the days grow shorter, was crossed to an SDP segregate of upland cotton,normally day-neutral (DN).
Gossypium hirsutum X Gossypium barbadense F1 Hybrid (genes are ½ Gh and ½ Gb) The F1 hybrid was backcrossed to Gossypium barbadense for 11 generations. With each successivegeneration, the percentage of Gh genes decreased and the percentage of Gb increased. After 11backcrosses, there were few Gh genes left, but enough to demonstrate a high level of variability inflowering times among BC11 progeny.
Weeks to flower among individuals in two Gossypium barbadense populations.
G. barbadense introgressed with G. hirsutum genes G. barbadense (control) Polyploidization- Polyploidization is also initiated by the chance hybridization between an emerging crop (AA) and its relative (BB). However, an additional event also occurred- a chancedoubling of chromosomes in the hybrid resulting in an AABB individual with twice as many genesas either parent. Polyploidization may increase hybrid vigor through complementary gene action, adosage effect or due to greater tolerance for mutant alleles). Polyploidization, in some instances,conferred new traits to crops also.
http://www.hcs.ohio-state.edu/hcs200/topics/topic1.htm (6 of 17) [10/08/2001 10:01:07 a.m.] All of these genetic mechanisms played major roles in the development of modern wheat.
wild einkorn- (AA, brittle rachis) to cultivated einkorn (AA, durable rachis)- a major step in this process involved the incorporation of the mutation for non-shattering.
migration of einkorn from cultivation in the Zagaros Mtn. Foothills to the Fertile Crescent. Growth of a crop innew environment (i.e., new selection pressures).
cultivated einkorn (AA) crossed with wild emmer (BB, wild relative with brittle rachis). Chance doubling of chromosomes in the hybrid to form tetraploid cultivated emmer (AABB). Emmer wasadapted to a much broader range of soil types and environments than was einkorn. Emmer becamea crop of commerce and traded throughout the region. Emmer is the forerunner to the moderndurum or pasta wheats.
cultivated emmer brought to Iran (another migration) where chance crossing and polyploidization with a third species (DD) resulted in formation of the hexaploid bread wheats (AABBDD). Theaddition of the gene D genome did two important things-first, the seed storage proteins of emmerwere highly modified. New wheat seed storage proteins were high in gluten, a protein complexwith highly elastic properties which are responsible trapping yeast-derived CO2 in bread doughcausing it to rise. Second, the adaption range of wheat was greatly increased again allowing for itscultivation in colder and drier climates. Eventually wheat culture was spread worldwide.
in addition, there is ample evidence that wheat gathered genetic material from many other species as it evolved through the process of introgression, bringing disease resistance and additional usefultraits.
Why did human kind domesticate plants and animals? What conditions might have promoted the originof agriculture? -Greek and Roman mythology suggest that agriculture was a gift from the gods to save the human racefrom savagery.
-Judeo-Christians believe that man was forced to till the soil as punishment for sins committed in theGarden of Eden.
http://www.hcs.ohio-state.edu/hcs200/topics/topic1.htm (7 of 17) [10/08/2001 10:01:07 a.m.] -Modern scholars (within the last 100 yrs or so) have put forth many theories concerning whyhunter-gatherer societies began to domesticate the plants and animals they used. Theories that supposedthat agriculture was "invented" out of desperation by starving people have been more or less dismissed asinaccurate. There is ample evidence to evidence to suggest that hunter-gatherers had a relatively stableeconomy and ecosystem, had a fair amount of leisure time (i.e., they supposedly worked about 15 hrs perweek) and enjoyed a well-developed society as evidenced by the art they left behind. The exact reasonsand methods of domestication are lost in antiquity. Moreover, as domestication occurred in manydifferent places throughout the world about the end of last ice age, these methods and reasons may havevaried from group to group. However, Carl Sauer (one of the domestication gurus) suggested someconditions which were necessary for the domestication of plants to occur.
the domesticating society must already have a flourishing economic base- starving people are not innovative and they can't afford to experiment.
the domesticating society must be oriented to food gathering as a way of existence (most likely this was accomplished by females whereas males hunted) the domesticating society must be partially sedentary the domesticating society must live in areas (such as woodlands) where the soil is tillable using the society must be relatively safe from natural disasters which would discourage settlement. The overall climatic situation was improving greatly at this time.
there must be a wide diversity of plants and animals to exploit. This condition is certainly true with modern-day hunter-gatherers. African h-gs have been found to collect 60 species (ssp) of grains,50 ssp of legumes, 90 species of root and tuber-bearing plants, 60 ssp of oil seeds, 500 species offruits and nuts , and 600 ssp of vegetables and spices. Their North American Indian counterpartshave been shown to collect over 1000 species of plants from 400 genera and 120 families ofplants.
In 1926, N.I. Vavilov published a teatise stating that diversity in plant species is not evenly distributed.
Crops were likely to have been developed in these Centers. See lecture outline for a map of the Centersof Diversity (Fig. 4.1).
C. What happened to human society as a result of adopting an agricultural way of life? Essentially, like the Greeks and the Romans believed, we domesticated ourselves as well.
1. Increased carrying capacity of the land http://www.hcs.ohio-state.edu/hcs200/topics/topic1.htm (8 of 17) [10/08/2001 10:01:07 a.m.] Carrying capacity for human habitation under several cultural systems Land capacity (people/mile2) Higher hunters and fishers Simple cultivators Pastoralists and nomads (possessing domesticated animals) Advanced cultivators 2. Formation of sedentary societies 3. Development of technology (e.g., serrated scythe, plough, wheel) 4. Development of crafts-job diversity 5. Development of new products 6. Emergence of the concept of property and ownership 7. Development of complex distribution system for goods and services 8. Formation of trade centers and trade routes 9. Development of a legal code-especially laws controlling water rights 10. Advent of architecture for storage and protection of property The net results of the domestication process were That plants and animals that were domesticated underwent significant and irreversible genetic change(i.e. from biological or natural fitness to agricultural fitness) which makes them solely dependent uponus for survival. And, conversely, that humankind underwent significant and irreversible cultural changes (i.e., from http://www.hcs.ohio-state.edu/hcs200/topics/topic1.htm (9 of 17) [10/08/2001 10:01:07 a.m.] hunter-gatherer to urbanized (civilized) society) which makes them solely dependent upon domesticatedplants and animals (i.e., agriculture) for survival. 6. Plant improvement and consequences A. Formation of land races Prior to modern breeding efforts crop varieties were land races. These land races were formed primarilyby the practice of saving seed for planting from year to year by farmers.
Land races of self-pollinating crops (individuals breed true) were mixtures of pure lines. Land races ofcross-pollinated crops (individuals do not breed true) were composed of heterogeneous populations witheach plant possessing a unique genotype.
Land races had the following characteristics: they were endemic to a specific area or region they were extremely well-adapted to the area because.
they were composed of a mixture of plant genotypes DIVERSITY=STABILITY (remember our models of agricultural vs. natural ecosystems?)
The use of land races is relatively "safe" (for an ecological ecosystem) because the variability within thevariety buffers against biotic and abiotic stresses/hazzards thus, avoiding potential disasters. Land racesaren't particularly high yielding by today's standards, but when crop failure means starvation, a yieldevery year is preferable to high yield one year and none the next B. Modern plant breeding and genetic vulnerability http://www.hcs.ohio-state.edu/hcs200/topics/topic1.htm (10 of 17) [10/08/2001 10:01:07 a.m.] The scientific age for plant breeding starts in the late 1800's. For most crops, this process resulted in thegradual and systematic decrease in variablity (and genetic diversity). Many successful land races wereabandoned/lost.
For self-pollinated crops-methods included pure line selection and pedigree breeding (developing newpure lines by inbreeding after crossing).
For cross-pollinated crops the method of choice was mass selection-formation of very successfulopen-pollinated varieties such as Krugs Yellow Dent-improvement by mass selection is a slow processwith potentially diminished returns per cycle of selection.
To continue, the discussion will focus on corn (Zea mays), a cross-pollinated crop. However, before itdoes, a few definitions must be given: inbreeding depression - the loss of general adaptation and reproductive capacity associated with the accumulation of homozygosity. Plants are weak, highly subject to environmental stress, and
are poor seed producers. Cross-pollinated crops suffer inbreeding depression, self-pollinated
crops do not!!!!
heterosis - the increased general adaptation and reproductive capacity associated with the accumulation of heterozygous loci following the cross of two unrelated inbreds (i.e., the oppositeof inbreeding depression).
combining ability - a relative measure of heterotic response through the combination of any two There are two theories why heterosis occurs: The dominance theory suggests that a hybrid resulting from a cross between unrelated inbreds displays heterosis because it possesses at least one dominant allele at a maximum number of loci.
The overdominance theory states that a hybrid resulting from a cross between unrelated inbreds displays heterosis because it is heterozygous at a maximum number of loci. This explanation http://www.hcs.ohio-state.edu/hcs200/topics/topic1.htm (11 of 17) [10/08/2001 10:01:07 a.m.] presumes that heterozygosity is superior to either homozygous condition.
Most cross-pollinated crops suffer inbreeding depression. Understand the consequences of inbreeding(self pollinating) a cross-pollinated species by considering the fate of heterozygosity at a single locus.
Notice that ½ of the heterozygosity in the population is lost with each successive generation of selfpollination.
Decrease in heterozygosity at a single locus as affected by inbreeding.
Generation Frequency of The progeny of inbreds, i.e., F1, hybrids, usually display a great deal of heterosis, especially when theyare relatively unrelated. In other words, unrelated inbreds exhibit good combining ability because theiroffspring possess a high level of dominant alleles or heterozygous loci (depending on what theory yousupport.
http://www.hcs.ohio-state.edu/hcs200/topics/topic1.htm (12 of 17) [10/08/2001 10:01:07 a.m.] Even though the phenomenon of heterosis was known, it was not exploited in corn or othercross-pollinated crops because F1 seed (the seed for sale) would have been produced on a very weak,low-yielding inbred plants.
Until.D.F. Jones 1917 created the double cross below Inbred A x Inbred B = Hybrid C Inbred D x Inbred E = Hybrid F Inbred C x Inbred F = Hybrid G Seed of the Hybrid G born on Hybrid C (maternal parent) ears was what was sold to the farmer. Seed onyield on Hybrid C plant exhibited heterosis.
Immediate increases in yield of over 25% were realized through the use of these double-cross hybrids!!Later, as inbreds improved, F1 hybrids were produced directly which maximizes heterotic response.
The consequences of the use of F1 hybrids include: yield and acreage increased (see original handout) dependence on high yield dependence on uniformity- increased mechanization, consumer demand for uniform product. Note that the hybrid progeny of two inbreds are all genetically identical.
the loss of diversity
. Land races and open-pollinated varieties which held considerable genetic diversity were being abandoned. Within each field genetic diversity was essentially non-existent aseach plant is genetically identical.
http://www.hcs.ohio-state.edu/hcs200/topics/topic1.htm (13 of 17) [10/08/2001 10:01:07 a.m.] Scientists began to worry about the loss of diversity as early as the 1930's. Then in the 1960's the FAObegan cataloging variability in major crops, but no collections were made.
The triggering event in 1970 was an outbreak of Southern Corn Leaf Blight in the US caused by thefungus Helmenthosporium maydis. About 15% crop losses, primarily in southern states. Because of themethod in which hybrid corn was produced, almost all corn in US was uniformly susceptible. This couldhave been a disaster.
The epidemic and near disaster sparked a flurry of scientific and political interest to collect and preserveplant germplasm, especially close crop relatives. In the 1980's combating the genetic vulnerability ofcrops became a national priority.
C. Loss of diversity in natural communities The loss of natural habitats for plants (and animals) due to human development is a process that has beenoccurring throughout our history as cultivators. Ohio, after all, was not originally covered withmonocultures of corn (Zea mays) and soybeans (Glycine max), but rather with hardwood and white pineforests. Clearing land for agricultural production and other uses, even if buffer zones of diversity are leftin tact, has major consequences on gene pools.
In our lifetimes, perhaps the most notable examples of wholesale habitat destruction is occurring inAfrica and South America. Deforestation is occurring in rainforests and in other areas as well at analarming rate. These events certainly have caused the loss of important germplasm and may be effectingour global weather patterns (i.e., global warming through the greenhouse effect). It is beyond the scopeof this course to delve into this controversial subject deeply, but for those who are interested, I urge youto explore the topic on your own.
See Fig. 1.1 and Table 1.2 in your lecture outline.
D. Efforts to preserve germplasm http://www.hcs.ohio-state.edu/hcs200/topics/topic1.htm (14 of 17) [10/08/2001 10:01:07 a.m.] "To feel a world population growing by up to 160 people per minute, with >90% of them in developingcountries, will require an astonishing increase in food production.Access to a range of genetic diversityis critical to the success of breeding programs. The global effort to assemble, document and utilize theseresources is enormous, and the genetic diversity in the collections is critical to the world's fight againsthunger." (Hoisington et al., 1999).
Potentially useful genetic resources for combating genetic vulnerability include: •current varieties •obsolete commercial varieties •breeding lines •induced or natural mutations in breeding lines •old land races •primitive forms of the crop •related weed races •related wild races Collections for individual crops should focus upon material in their Center of crop origin/diversity(especially for disease resistance genes).
In-situ vs. ex-situ collections and their maintenance.
"The conservation of germplasm can be managed according to two models: in situ, in its place of origin,or ex situ, outside its place of origin, as in zoos, botanical gardens, and germplasm banks. In situconservation, clearly the more complex of the two attempts to protect species under the naturalconditions in which than are normally found, be they pristine or anthropogenic habitats. In contrast withex situ conservation, which saves germplasm under artificial conditions, in situ conservation seeks tomaintain the genetic diversity of the species under the conditions in which it evolved so as to allow theprocess of adaption to continue". (B.F. Benz).
National/international efforts to combat the problem include: National germplasm preservation system-visit this web site to learn more- http://www.hcs.ohio-state.edu/hcs200/topics/topic1.htm (15 of 17) [10/08/2001 10:01:07 a.m.] CGIAR -visit this web site to learn more- FAO Seed and Plant Genocide Resources Service -AGPS - visit these web sites to learn more- 7. Summary of crop domestication effects •There was a gradual change in way of life from hunter-gatherer societies to agrarian societies.
•Cultivation brought about new selection pressures (active or passive) on emerging crops.
•Emerging crops underwent significant genetic changes to become "agriculturally" fit. In the beginning, genetic variability increased as crop-weed complexes interacted.
•Domestication was irreversible.
•Domestication occurred most often in Centers of Diversity.
•Domesticators had broad-spectrum economy. They were not starving.
•Origin of agriculture caused an irreversible cultural revolution in human society. Sedentary life greatly increased the carrying capacity of the earth and the complexity of civilization.
•Agriculture as it evolves continues to both solve problems and, at the same time, create others such as the example given above with F1 hybrid corn.
8. Crop Science- its role and challenges in 2000 and beyond? •Solving problems •Reducing chemical inputs •Reducing risks for and instances of environmental degradation •Devloping new commodities-value added •Maintaining profitability in a global economy •Feeding an ever-increasing world population http://www.hcs.ohio-state.edu/hcs200/topics/topic1.htm (16 of 17) [10/08/2001 10:01:07 a.m.] http://www.hcs.ohio-state.edu/hcs200/topics/topic1.htm (17 of 17) [10/08/2001 10:01:07 a.m.] Horticulture and Crop Science 200
Winter Quarter 2001 Lecture Topic #2: Crop classification Hartmann, H.T., A.M. Kofranek, V.E. Rubatzky and W.J. Flocker. 1988. Plant science growth,development and utilization of cultivated plants. Prentice Hall,Inc., Englewood Cliffs, NJ.
Botanical classification by binomial nomenclature There are over 500K species of plants - classification and naming system is important to be able tocommunicate about plants and to show relationship between them.
Classification of plants was first attempted by Theophrastus, the "father of botany", in the 3rd CenturyBC. He based his classification schemes primarily on plant form, growth habit and differences in flowerstructures.
Today, we actually use many different classification systems in everyday communication (see below),but perhaps botanical classification (the binomial nomenclature) system used by scientists is the most "information-rich" and least ambiguous of these naming systems.
This system was developed by Carlus Linnaeus in the 18th Century AD. His was also based primarialy onflower morphology. Living organisms were divided into groupings (taxa) at many different levels ofcomplexity. The first division, " Kingdom" is the most general (refer to Table 3-1 from Hartmann et al inhandout); with each subdivision thereafter, the descriptions of members in the taxa are more specific andthe number of members within the taxa decreases until at the species level, an individual plant withunique characteristics is identified. Today this system also considers other factors (e.g., genetic evidence)to distinguish one species from another. Note: the classic definition of species presumes that members ofthe species can freely interbreed and that member of different species can not, but in the case of plants,this is not clearcut.
In terms of crops - Members of the Plant Kingdom are thought to have some common characteristics: they are stationary, http://www.hcs.ohio-state.edu/hcs200/topics/topic2.htm (1 of 5) [10/08/2001 10:01:10 a.m.] contain chlorophyll and photosynthesize, they have cells with rigid walls made of cellulose,and continueto grow throughout their life cycle. However, there are organisms that are considered plants which do notconform to one or more of these characteristics.
I can't think of any crops that are not considered to be in the Plant Kingdom. Although we do useproducts derived from bacteria (genetically engineered or otherwise), we commonly don't think ofproduction of this type as "cropping". Almost all of the crops that we study will be in the Division ofSpermatophyta - seed - bearing. Mushrooms(edible) and ferns(ornamental) are two exceptions.
Moreover, most crops that are grown are in the Class Angiospermae - plants that produce seeds insideovaries. A notable exception to this statement, of course, is the production of conifers ( Members of theGymnospermae - plants that bear naked seeds) as ornamental or industrial(forest) crops. Order, Family,Genus and Species will vary from crop to crop.
Genus and species names are either underlined of italicized to indicate that they are in Latin. The formeris capitalized while the latter is not e.g.,Agrostis stolonifera - creeping bent grass. Note that the speciesname is often descriptive - ie.,stolonifera referring to the fact that the plant produces lateral above groundstems called stolons.
Question: Can you identify some of the important families which contain crop plants? What are someexamples of crops (genus and species) that belong in these families? Do they have some characteristics incommon? cultivar - a name derived from the term "cultivated variety". Cultivars describe a subject of plants within
a species which demonstrate some recognizable uniformity in traits. This uniformity results primarily
from mans efforts through breeding and selection, even though the genetic path by which uniformity is
achieved and maintained varies depending on whether the plant is cross pollinated, self pollinated or
asexually reproduced (discussed in detail in a later lecture). Cultivar identities are extremely
important to producers because indicate what to expect in term of performance in the field(growth rate,
flowering time , potential yield, etc.), resistance to diseases and other pests, and crop quality factors, etc.
Confusion about what cultivar is being planted may lead to cropping disasters - consider your chagrin
when you discover that your field of peppers is yielding chilies instead of bell peppers - the crop you
were contracted to grow. This mix - up actually happened and, of course, resulted in some serious
litigation.
Cultivar designations are made in one of two ways: E.g.,Jubilee sweet corn should be designated as Zeamays ' Jubilee'. Note that the cultivar name is always capitalized and never italicized or underlined.
- botanical variety - Botanical varieties also describe subspecies with specific traits. The difference is thatbotanical varieties are wild segregates. For instance in Aesculus parviflora,(a type of Buckeye tree) thereis a botanical variety called serotina, which blooms several weeks later that its partent species. It isdesignated as Aesculus parviflora var. serotina. http://www.hcs.ohio-state.edu/hcs200/topics/topic2.htm (2 of 5) [10/08/2001 10:01:10 a.m.] - group - Group is another subspecies classification. In a species with great diversity of form, the groupdesignation literally "groups" cultivars with characteristics. E.g.,Brassica oleraceae Italica = broccoli,Gemmifera = Brussels sprouts, Capitata = cabbage, Botrytis = cauliflower, Gonglylodes = kohlrabi,Acephala = kale and collards. Roses would be another example of a species with groups.
-hybrid (interspecific) - Interspecific hybrids are example of how the "species" designation can getsomewhat "muddy" when considering plants. Case in point, Fragaria chiloensis ( the beach strawberry)was isolated from Fragaria virginiana ( the Virginia strawberry )in the wild, separated by 1500 miles ofprairie, mountains and deserts between the Mississippi River and the Pacific Coast. However, whenbrought in close proximity to each other in the 18th century botanic gardens of Europe, these two "species" hybridized readily to form Fragaria X ananassa the cultivated strawberry of commerce. Thelatter is a "species" formed by a planned interspecific hybridization, therefore to designate it as such ,there is an X between its genus and species names.
-the problem with common names Consider a home owner entering a nursery and asking to jasmine (see list on handout). If you were anemployee of this nursery, would you know what to get him/her? You might be in trouble even if theyasked specifically for "star jasmine" because several species are commonly referred to by that name. Inthis case a single common name is used to designate several species. Can you think of a similar example? The other possibility is that a single species is known by several common names. Often these names arespecific to regions. My ex-father-in-law, a native Ohioan, called bell peppers "mangos" his entire life asdid many others in SW Ohio. The first time he referred to this, I presumed he meant the fleshy tropicalfruit that I know by that name. This problem is not confined to reference to horticultural crops - If yourefer to alfalfa in many other countries of the world, they won't know what you are talking about - theycall that crop "Lucerne". In many regions of Africa, ground nuts are an extremely important food cropproviding protein and energy. One of our ex-Presidents was a ground nut producer at one point in his life,but he called them peanuts. Some of his fellow Southerners might also refer to this food as "gooberpeas".
A complex example of this problem involves the term "corn". In this country, corn means the grain fromZea mays. The same grain in England is called maize, and if you say corn, they think you are referring towheat or barely.
Classification by production - There are obviously many different ways to classify crop plants in additionto their botanical classification using binomial nomenclature. For instance, plants could be grouped astemperate or tropical, annual, biennial or perennial, etc. Some useful classifications for out purposes arediscussed below: One very useful scheme is to consider our overall use of the plant/or in other words, how much of the http://www.hcs.ohio-state.edu/hcs200/topics/topic2.htm (3 of 5) [10/08/2001 10:01:10 a.m.] plant do we produce. To develop such a scheme, one might consider data on either land area devoted toproducing each crop or to their overall yield (tonnage produced). Table 1.1 on your handout classifiescrops as either edible or industrial, then within each of these groups separates species by their overallyields. Notice that of the five crops the world relies upon for food, four of them are grain crops (sort of--- look at the footnotes in the Table --- one might argue over their definition of "food crop").
Classification by nutritive value = One might also consider classifying crops by the nutritive value theydeliver. Certainly, in the grand scheme, hunger in the world is a matter of protein-calories malnutrition(See Table 1.2 on your handout). Note that there are some crops in this Table that are a fair source ofboth. However, other crops are also important for nutritive reasons, especially those which providevitamins, minerals, dietary fiber, and other compounds that promote human health. Crops that producesecondary plant products that improve or maintain health (i.e., anticancer compounds, compounds thateffect mood or performance) have been recently referred to as nutraceuticals. Documentation concerningthe effectiveness of these secondary products varies tremendously from crop to crop. However, ingeneral, these crops enjoy limited production and high profit margins (e.g.,ginseng).
4.Classification by crop use - perhaps the most useful (Class - derived list) Pulses- (beans) common bean, soybean,cowpeas,chickpeas,fava beans,peas Oil crops- canola,safflower,peanuts,olives,coconut, sunflower,flax Forages - clovers,alfalfa, timothy,birdsfoot trefoil Sugar crops-cane,sugar beet, corn(various corn syrups) Herbs, spices and stimulants - tobacco,cinnamon, sage Vegetables- cabbage, zucchini, peppers, tomato, pumpkin, watermelon Fruits- strawberry, blueberry, peach http://www.hcs.ohio-state.edu/hcs200/topics/topic2.htm (4 of 5) [10/08/2001 10:01:10 a.m.] Ornamental crops - red maple, dogwood, parsley, gourds, cabbage, pumpkins Turf- tall fescue, Kentucky bluegrass, Zoyzia, Bermuda, bentgrass Industrial crops- soybeans, pulpwood, rubber, southern yellow pine Note that many crops can be fit in multiple categories.
http://www.hcs.ohio-state.edu/hcs200/topics/topic2.htm (5 of 5) [10/08/2001 10:01:10 a.m.] Horticulture and Crop Science 200
Winter Quarter 2001 Lecture Topic #3: Crop Plant Morphology
Campbell, N.A. 1996. Biology. Benjamin Cummings Publ. Co., Menlo Park, CA = Chapter 34.
Copeland, L.O. and M.B. McDonald. 1985. Principles of Seed Science and Technology. Burgess, Publ.
Co., Minneapolis, MN.
Hartmann, H.T., A.M. Kofranek, V.E. Rubatzky and W.J. Flocker. 1988. Plant science - growth,development and utilization of cultivated plants. Prentice Hall, Inc., Englewood Cliffs, NJ = Chapter 2.
Pollock, B.M. and V.K. Toole. After-ripening, rest period and dormancy. In. Seeds - 1961Yearbook ofAgriculture. U.S. Govt. Printing Off., Washington, DC.
Raven, P.H., R.F. Evert and S.E. Eichhorn. 1999. Biology of plants. W.H. Freeman and Co., New York,NY = Chapters 23-27.
Toole, E.H. and V.K. Toole. 1961. Until time and place are suitable. In. Seeds - 1961Yearbook ofAgriculture, U.S. Govt. Printing Off., Washington, DC.
".plants and their features can be identified and appreciated from their external structure, but theirinternal structure and function are often overlooked. The beauty of an orchid blossom is greatly admired,but just as impressive are the parts of a cell as recorded with a scanning electron microscope".
Hartmann et al., 1988.
Crop Life Cycles (in brief) A crop's life cycle is determined by the seasonal pattern it exhibits between seed germination and the http://www.hcs.ohio-state.edu/hcs200/topics/topic3.htm (1 of 11) [10/08/2001 10:01:19 a.m.] development of mature seed for the next generation. As you may guess, crops vary tremendously in thisrespect and the definition of "crop" life cycle is confounded significantly when one considers crops thatare typically asexually reproduced (e.g., chrysanthemum). However, even in the latter case, we can stillconsider the "seed to seed" model with respect to traditional crop breeding.
Most agronomic crops and quite a few horticultural crops are considered to be annuals. That is, they
complete the crop life cycle in a single season [i.e., it germinates, grows, flowers, fruits, matures seed
then senesces (dies)]. Almost all of them are herbaceous (non-woody). The annual life cycle begins with
the germination of the seed and emergence of the new plant (see diagram in handout) which is usually a
relatively rapid process. The rate of seed germination is species specific and can be highly influenced by
a number of environmental factors (see detailed discussion below). During germination and for the first
few days after emergence, the new plant is nourished by stored reserves present in the cotyledons or
endosperm of the seed. As these reserves are depleted, newly developed leaves begin the photsynthetic
process and newly developed roots begin to supply water and nutrients to the growing plant body. For a
period of time, the plants develop vegetatively (i.e., their "growing tips" and "buds" produce only new
leaves, stems or roots. The length of the vegetative phase of the annual life cycle varies per crop and may
be as short as a few weeks (e.g., certain members of the Brassicaceae or cabbage family) or may last up
to nearly a year (e.g., banana). However, at some point, one or more vegetative shoot growing tips or
buds undergoes a transformation (floral initiation) which re-programs it to produce flowers and fruit. To
ensure that flowering occurs at the most opportune period for plant survival and/or agronomic fitness,
floral initiation is often triggered by an environmental trigger, such as the day length (see discussion
below). Floral development progresses over time and when its development is visually obvious, it can be
said to have emerged. The floral development process continues for a period of time before the flower is
ready to open. During this period, pollen and egg cells are typically developing and are usually fully
formed (or nearly so) at the time of flower opening (anthesis). Flowers vary tremendously with respect to
the exact timing of pollen shed or stigma receptivity; in some species floral structure, pollen shed and
stigma receptivity favor self-pollination of the flower (e.g., pea) whereas with others, these phenomenon
are arranged to promote cross-pollination (e.g., corn). Pollen tube growth through the style is usually a
rapid process requiring from 1-3 days to complete. The period following fertilization is marked by
development of both fruit and seed structures in a set pattern which varies with species (see discussion
below). During this period, much of the energy produced by the plant and the mineral nutrients it
acquires from the soil/media are devoted to the fruit and seed maturation process. Therefore, fruit and
seed development accounts for much of the addition of dry weight to the plant during this period. Some
annuals have distinct vegetative and flowering phases (e.g., cereal grains) and are said to be determinant,
whereas others are indeterminant and continue to grow vegetatively while flowers are periodically
produced (e.g., some types of beans and tomatoes).
Biennial plants require two seasons to complete their life cycle (e.g., carrots and onions), although in
some cases we crop them for only one season because the yield component of interest is not the seed.
Biennials are typically plants with a rosette form (i.e., vegetative shoots are extremely short and leaves
appear to be in a whorl pattern). Floral initiation occurs during the first season of growth but is arrested
early in its development, resuming only after receiving an appropriate environmental signal. In temperate
crops, this signal is a period of chilling requiring temperatures from 1-7° C (34-45° F). The process of
chilling is called vernalization. Once vernalized, floral development advances with the formation of a
http://www.hcs.ohio-state.edu/hcs200/topics/topic3.htm (2 of 11) [10/08/2001 10:01:19 a.m.] blooming stalk (typically attaining heights much in excess of the leaf canopy) and a "seed head" orflower. After seed is matured, the plant usually dies. In the case of carrots and onions, the root or bulbthat we eat serves as a storage of food reserves that are almost entirely consumed by the plant in order toflower and mature seed.
Herbaceous perennials (e.g., tulips, chrysanthemums, etc.) annually produce aerial vegetation and
flowers from perennial plant parts [crowns (stem bases), rhizomes (underground stems) or bulbs]. The
patterns of above-ground growth, flowering, seed maturation and senescence vary dependent upon
species.
Woody perennials produce top growth over a period of years, adding new stems, leaves, flowers and
fruit every year while typically increasing the girth (thickness) of stems and roots produced in earlier
seasons. Growth therefore is cumulative. Annual growth often occurs in flushes followed by sessation
and the "setting" of a terminal bud. Many hardwoods (e.g., oaks) have only one growth flush, others
(e.g., some pines) exhibit recurrent growth flushes throughout a season, whereas others exhibit sustained
growth throughout the season. Optimum conditions must be maintained during the production of woody
perennials, because growth flushes can terminate prematurely if stressed by unfavorable environmental
conditions.
1. Seed Germination "One for the buzzard, One for the crow, One to rot, and One to grow!" (Fay Yauger) "In many ways, the seed is a microcosm of life itself. The seed is a neatly wrapped package containing aliving organism capable of exhibiting almost all of the processes found in the mature plant." (Copelandand McDonald, 1985).
"A seed is essentially a young plant whose life activities are at a minimum" (Toole and Toole, 1961).
"The [biological] function of a seed is to carry its embryonic plant through the hazzards of time andspace to a time and place where the new plant can grow, flower, and in its turn, produce seeds" (Pollockand Toole, 1961) Crop life cycles often begin with the germination of seeds. Each seed contains the following: a) anembryonic plant that has a radicle (embryonic root) and a plumule (embryonic shoot); one or twocotyledons that are used as a food source by the embryonic plant until it is able to photosynthesize on itsown; (NOTE: in moncots, this function is also performed by the endosperm, a storage tissue for starchand other compounds) and c) a method of protecting the embryonic plant (seed coat or fruit structures).
Shown in your original handout are the first phases of the lives of the quintessential monocot (corn) and http://www.hcs.ohio-state.edu/hcs200/topics/topic3.htm (3 of 11) [10/08/2001 10:01:19 a.m.] the quintessential dicot (bean). Notice some of the similarities and the differences in their overallstructure.
As in all other phases of a crop plant's life, environmental conditions have a profound effect on plantperformance. The exact conditions necessary for optimum seed germination are specific to each cropspecies. However, in general seeds often germinate best when the following requirements are met: Adequate soil or media mosture content. Seeds will not germinate in dry soil or media. Likewise they will not germinate under waterlogged conditions. Certain types of rice and aquatic speciesrepresent notable exceptions to the latter for they will not germinate unless they are under water.
Proper temperature (15-26°C or 59-79°F common) Adequate soil or media aeration Soil or media free of diseases and other pests Soil or media with low salt concentrations In addition, some seeds require light where others require darkness to germinate.
A seed is said to be quiescent (resting) if it fails to germinate unless the above mentioned conditions are
met. The quiescent seed is physically and physiologically ready to germinate, but awaits the proper
conditions before doing so.
A seed is said to be dormant if it fails to germinate even though the above mentioned conditions are
met. Dormant seeds are not yet physically or physiologically ready to germinate no matter what
environmental conditions are present. There are several common forms (types) of seed dormancy; a few
are listed below:
Hard seed coat (a physical dormancy) - the seed coats of some species (most notable examples are in the Fabaceae, the bean family) are either highly lignified or covered with waxy or oilysubstances (cutin and/or suberin) so as to be impervious to water and or gasses. Germination canonly occur after the seed coat has been ruptured or breached. In nature, the disruption can resultfrom conditions brought about by heavy rains (abrasion), fire, or consumption by birds or otheranimals (acid digestion).
Embryo dormancy (a physiological dormancy). In many temperate zone species, seeds physically mature on the plant, but are physiologically unable to germinate until exposed to cold temperaturesover a prolonged period of time. There is evidence to suggest that during the cold period, levels ofa growth-inhibiting hormone (abscisic acid) decrease while levels of growth promoting hormones(gibberellins and cytokinins) increase. Similarly, in some species (e.g., Cucurbitaceae, the squashfamily) allowing physically mature seeds to "after-ripen" in detached fruit will increase theirgerminability.
Rudimentary embryos (a physical and perhaps physiological dormancy). Some species (e.g., holly, http://www.hcs.ohio-state.edu/hcs200/topics/topic3.htm (4 of 11) [10/08/2001 10:01:19 a.m.] magnolia) shed their fruit before fully maturing the seed. The seed continue to develop in oroutside the fruit until competent to germinate.
Chemical inhibition (physiological dormancy). Chemical inhibitors to germination (e.g., caffeic acid, coumarin) can be present in the embryo itself, in the seed coat or in the fruit tissuesurrounding the seed. These compounds must be metabolically inactivated, leached, degraded orremoved in some other way before germination can occur. For instance, the gelatinous materialsurrounding a tomato seed contains an inhibitor which prevents the seed from germinating insidethe fruit. This inhibitor must be removed prior to germination.
Under natural conditions, dormancy is an important phase of a seed's life as it often ensures that the seeddoes not germinate inside the fruit (vivipary) or does not germinate when environmental conditions areunfavorable. Delayed and staggered germination is a undoubtedly a selective advantage in a naturalecosystem, but it is not a trait commonly associated with agricultural fitness. See discussion of thedifference between natural and agricultural fitness in Topic 1 notes.
As agriculturists, we often "process" seed in order to overcome dormancy using a variety of techniques.
Hard seededness is often alleviated through various scarification (scratching) methods using abrasives
and mechanical devises to move seed across abrasive surfaces. Hot water treatments are also sometimes
used as are acid scarification treatments using concentrated sulfuric or hydrochloric acids (these are
somewhat dangerous). The exact timing and conditions of these treatments necessary for optimum
success vary tremendously with species (of course).
Embryo dormancy can be overcome by stratification, a process which can be done outside under
"natural" conditions, but is more commonly practiced under controlled conditions. The critical factors in
the stratification process include:
chilling temperatures - (1-7°C or 34-45°F). The physiological processes necessary to alter hormone levels progress under these conditions. If the temperature is below freezing or abovecritical temperatures, the processes are delayed or halted Moisture - Seeds are usually soaked prior to stratification and then placed in moist sand or paper to keep them moist (but not immersed) throughout the stratification procedure.
Oxygen - Oxygen is necessary for continued respiration which keeps the seed viable and physiologically active. Therefore, stratification procedures should not be conducted in air-tightcontainers or under water-saturated conditions.
Time - The period of time necessary to complete the stratification process varies tremendously with species and must be determined experimentally. However, 30-90 days is a typical time frame.
http://www.hcs.ohio-state.edu/hcs200/topics/topic3.htm (5 of 11) [10/08/2001 10:01:19 a.m.] Chemical inhibition may be overcome in a variety of ways depending on the inhibitor and on whether ornot the inhibitor is internal or external to the seed. When extracted from the fruit, the gelatinous matrixsurrounding tomato seeds must be "fermented" (removed) in order to remove it and the inhibitor itcontains. In other species, inhibitors may be overcome by leaching (continued washing).
Seed viability vs. maturity A seed which has reached physiological maturity when it has reached maximum dry wt (typically5-20%). Other conditions which act as indicators of maturity include the sessation of nutrient importationand the formation of abcission layer at hilum (area where seed is connected to ovary tissue by a "stalk"called the funniculus).
Most seeds viable before they are mature. For example, weed seeds (colonizing species) especially adeptat producing new plants even when seeds are not fully ripened on the plant or under environmentalsituations that are not suitable for the germination of seed from truly wild (feral) or cultivated crops.
For the seedsman, it is important to determine when maximum seed maturity is reached so that the seedthey sell will be highly vigorous.
The physiological steps in the seed germination process.
The imbibition of H 2O. Water is taken up by the seed throughout the germination process in three distinct phases (see diagram in handout). The first "log" phase of imbibition is passive (i.e., it doesnot require the espenditure of the seed's energy) and relatively rapid. The rate of water uptake isdetermined by the difference between: - The matric and osmotic potentials (pulling forces) in the soil/media as determined by the type of mediaand the level of dissolved salts that it contains and.
- the osmotic potential (pulling force) and turgor pressure (pushing force) of the seed's cells.
In order for seeds to imbibe water, their osmotic potentials must be greater (more negative) that the soilforces combined (i.e., the seed wins the tug-of-war for the water in the environment). If water in the soilremains adequate, the seed will continue to imbibe water until cells are fully hydrated. At that pointturgor pressure will be great enough to prevent further movement of water into the cells (i.e., thebeginning of the lag phase shown in the handout diagram).
The rate of uptake in this phase is influenced by the composition of the seed (protein-rich seed usuallyimbibes water faster than starchy seeds), and seed coat permeability http://www.hcs.ohio-state.edu/hcs200/topics/topic3.htm (6 of 11) [10/08/2001 10:01:20 a.m.] An environmental trigger? As stated above, some seeds require light in order to germinate. The compound in plants that senses light and the duration of light and dark periods is calledphytochrome. Phytochrome, in its active form, promotes membrane permeability, and stimulatesenzymatic and metabolic activity (see below). Phytochrome-mediated triggers often act in concertwith or can be complicated by temperature factors. For more on phytochrome, see discussion on itseffects upon the flower initiation process (daylength sensitivity).
Enzymatic and metabolic activity. As the first log phase of imbibition ends, a "lag" phase begins, characterized by a greatly diminished rate of water uptake (see diagram in hand out). This periodcorresponds with an acceleration of metabolic and enzymatic processes within the seed as itprepares for growth. In this period, membrane-bound enzyme systems are activated and activetransport (ATP-requiring) transport of ions and solutes across membranes is promoted. Geneexpression occurs. Enzymes are also synthesized -- especially hydrolytic enzymes that control theglycolytic process (metabolism of sugars for the production of energy). Hormonal contents ofseeds may also be altered so as to favor growth promoting substances over inhibitors.
Some aspects of cereal crop (e.g., corn, barley) seed germination illustrates how some of these processesare coordinated within the germinating seed. In cereals, the first step in the process of enzymaticstimulation is based upon the synthesis of gibberellic acid (GA3) in the scutellum (cotyledon) and itssubsequent transportation to the protein-rich cells of the aleurone layer cells (i.e., the outer layer of theendosperm or storage tissue). The GA3 acts as a messenger to the aleurone cells, "informing" them thatthe conditions are now adequate for germination to occur. Peleg and coworkers demonstrated thenecessity of the GA3 as a messenger in barley seeds (see figure in handout). If the embryo of barley isremoved (i.e., including the scutellum), hydrolysis of starch in the endosperm does not occur. However,if it is exogenously-treated with GA3, the breakdown of carbohydrate progresses rapidly. Thus, theidentity of GA3 as the messenger is confirmed. Exogenous application of GA3 breaks dormancy and/orstimulates germination in many species (both monocot and dicot) and many species have been shown toproduce GA3 during the lag phase of the germination process. In other species, including most dicots, thestimulation of metabolic processes by hormones is much more complex and is based upon a balance ofpromoting and inhibiting substances.
Initiation of growth. The cell division and elongation necessary to form the new plant begins during the lag phase as metabolic and enzymatic activity progress. During this process, storagetissues decrease in dry weight while tissues in the embryo increase in dry weight.
Protrusion of the radicle. In most instances, the protrusion of the radicle is the first physical sign of germination and is an indication of the seed's viability. However, at this stage, many "slings andarrows of outrageous fortune" (sorry Will) may still prevent the ultimate establishment of the newplant. The protrusion of the radicle also signals the beginning of the second log phase of wateruptake. Rapid growth of both the root and shoot systems depends upon the rate of cell division andcell elongation which, in turn, requires optimum cell turgor pressure (pushing forces on cell wallsand membranes caused by water uptake).
http://www.hcs.ohio-state.edu/hcs200/topics/topic3.htm (7 of 11) [10/08/2001 10:01:20 a.m.] Emergence and seedling establishment. Emergence is the process wherein the shoot of the new plant breaks through the soil/media surface and becomes aerial. The factors which promote orinhibit this process (e.g., whether or not the soil surface is crusted) are numerous and primarilysoil/media dependent. There are several classic categories of emergence based primarily upon therelative position (above or below ground) of the cotyledons and other seed tissues. See any plantscience text book, if you are interested in learning about these - we won't consider them furtherhere).
As the embryonic plant begins to grow, it undergoes a planned (genetically programmed) sequence oftissue development which it continues throughout its life. Although there are obviously some majoranatomical and physiological differences among higher plants, there is also substantial commonality inthe types of tissues that are present.
All higher plants have meristems. Meristematic regions are composed of undifferntiated,parenchymatous cells which, when active (not dormant) are rapidly undergoing cell elongation and celldivision. Meristematic tissues give rise to permanent tissues (containing mature, often specialized cells)which comprise the bulk of the plant body. Meristems can be found in various places on the plant.
One might argue that the most obvious and logical place for a meristem to be is at the growing point
(tips) of shoots and roots. It is so, and these meristems are referred to as apical meristems. Apical
meristems of above-ground shoots give rise to cells that will eventually become the shoot epidermis,
cortex, primary xylem and phloem and central pith. Some shoot apical meristems remain vegetative
throughout their life while others undergo a transition to a flowering meristem in response to internal
dictates and/or environmental cues. Some shoot apical meristems experience several seasons of growth
punctuated by periods of dormancy. Apical meristems are also the source of axillary buds which, when
allowed to develop, form new shoots (branches), inflorescences or both. Axillary bud growth is often
suppressed by plant hormones produced by the apical meristem resulting in the phenomenon of apical
dominance. Root tips also have apical meristems that give rise to the various tissue systems of the root,
the stele, the root vascular system, the pericycle, the endodermis, the cortex and the epidermis.
Shoot apical meristems also give rise eventually to other meristematic regions such as subapical
(axillary) and lateral shoot meristems. Sub apical meristems are located just "underneath" the apical
meristem. Some plants grow vegetatively following a "rosette" growth habit where internodes are very
short and leaf petioles are in a compact bunch close to the crown of the plant. If such plants also have a
terminal flowering habit, like carrots, for instance, one might expect the flower to also be very close to
the ground. However, in these instances, after the terminal meristem has already transitioned to a
flowering meristem, the subapical meristem produces the cells necessary for the development of an
inflorescence or bloom stalk.
http://www.hcs.ohio-state.edu/hcs200/topics/topic3.htm (8 of 11) [10/08/2001 10:01:20 a.m.] Lateral meristems refer to cell layers in stems that give rise to new xylem and phloem members (the
vascular cambium) or to new bark (the cork cambium). The vascular cambium in woody plants is
cylindrical and the development of new xylem elements inward results in increased girth and the
development of annual growth rings due to differential rates and cell sizes of xylem production
throughout the season. Phloem gets produced outward from the cambium but as the season progresses,
older phloem members get crushed and obliterated. Herbaceous stems have vascular cambiums as well,
but these meristems are arranged with vascular tissue in "bundles" (i.e., not in a continuous cylinder).
Intercalary meristems are meristems that have been separated from the shoot terminal meristem by
intervening mature tissue. One good example of an intercalary meristem is that which is associated with
the lower regions of a grass leaf sheath. Grass blades grow from this meristem rather than from a
terminal meristem. I.e., they elongate from the base of the blade, not the tip of it.
4. Primary and secondary development of stems Stems and branches are the scaffolds which support leaves, flowers, fruit and other above-ground plantorgans. A typical shoot (Figures 2-6, 26-3 and 26-7) has the following tissue groups: epidermis, cortex,primary xylem and phloem and central pith. It is punctuated in its growth by the development of nodes.
Nodes typically contain a leaf supported by a petiole and an axillary bud which possesses a dormant,flowering or vegetative meristem of its own. A repeating stem unit containing a leaf, node, internode andaxillary bud is called a phytomere. Each node (leaf axil) must be supplied with a vascular trace. In stemsthat are young, the vascular system is arranged in bundles which are located just interior to the cortex.
The arrangement of these vascular bundles is well ordered but complex. Three typical arrangements areshown in Figure 26-7. Many dicot stems (e.g., basswood) have vascular bundles that more or less form aring around the pith (Fig. 26-7 a), whereas others (e.g., elderberry) have more descrete vascular bundlesthat have wide interfascicular regions (spaces) between them (Fig. 26-7 b). Monocots (e.g., corn) andsome herbaceous dicots have vascular bundles scattered throughout the central cylinder.
Secondary growth occurs primarily in woody perennials. It can be defined as an increase in girth(thickness) of stems or roots in regions where individual cells are no longer dividing or elongating. In thecase of stems, this growth is characterized by presence and activity the vascular cambium, a lateralmeristem. The progression of from primary growth to secondary growth in elderberry is illustrated inFig. 27-6. Note that in secondary growth, the interfascicular regions disappear and the vascular cambiumforms a complete cylinder around the xylem and pith. The vascular cambium continues to produce xylemand phloem tissues and also a system of vascular (fluid conducting) rays which connect (radially) thevarious layers of xylem and phloem produced in successive growth phases. The vascular cambiumincreases in girth by anticlinal (lateral) cell division.
What we commonly refer to as wood is secondary xylem. Secondary xylem that is still functional iscalled sapwood whereas that which no longer conducts is called heartwood. The transition from sapwoodto heartwood often involves the loss of food reserves and the infiltration of oils gums and resins andtannins which give woods their characteristic color and odor. In a given season, new xylem members that http://www.hcs.ohio-state.edu/hcs200/topics/topic3.htm (9 of 11) [10/08/2001 10:01:20 a.m.] formed early are wider, thinner-walled and less densely packed than those which are formed in lateseason. This pattern coupled with periodic yearly activity of the cambium results in "annual growthrings" which give wood its characteristic grain and arguably, its beauty.
Any tissue located to the "outside" of the vascular cambium is considered bark. Bark includes operationaland defunct phloem, periderm if present and epidermal-derived tissues. As girth increases, older phloemmembers are crushed and there is a tremendous stress on outer layers of bark resulting in itscharacteristic irregular surface. This material eventually sloughs off as new phloem are formed insubsequent seasons. Common products that we obtain from secondary phloem growth include barkmulches, maple syrup (tapped from active phloem members nearest the cambium - for an instructionalwebsite visit http://www.mi-maplesyrup.com/howto.html), and cork.
5. Primary and secondary development of roots Root systems have five functions: to anchor the plant, to absorb water and nutrients, to conduct water andnutrients to aerial portions of the plant, to synthesize plant hormones (primarily cytokinins) and to act asa storage organ for carbohydrates. Like the shoot or stem, primary root growth is a function of the rootapical meristem and, in turn, tissues derived from this meristem develop into primary meristems, primarytissues and eventually, secondary growth. In some species, a quiescent center with reduced cell divisionforms within the meristematic region which may play a role in the organized development of root tissues.
The apical meristem is protected by a rootcap; root cap cells are scraped off as the root penetrates thesoil/media and mucigel, a "slimy" substance associated with the cap helps to lubricate the entire process.
The region of [cell] elongation, typically only a few mm in length, constitutes an area of the new rootwhere pith, vascular, cortical and epidermal tissues are beginning to mature. Water and nutrient uptake,however, occur most readily in the region of maturation characterized by the development of root hairs(see below). Tissue systems within this region are as follows: vascular cylinder - composed of differentiating xylem and phloem and associated parenchyma pericycle - a root tissue system meristematic region that gives rise to new vascular tissue, new endodermal tissues and adventitiously to branch roots.
endodermis - the boundary layer between the vascular cylinder and thr root cortex. This tissue system includes a specialized layer of cells which are surrounded by a suberized (oily) substance
called the casparian strip. The casparian strip serves a very important function - it prevents the
free movement of solutes (nutrients) from the soil solution (water + dissoved nutrients) to the
vascular cylinder. Therefore, in order to enter the vascular cylinder, solutes must first enter a living
cell which is bounded by a cell membrane. The cell membrane is selective allowing only certain
solutes to enter. It also prevents solutes that have entered from effluxing (escaping) back out into
the soil solution due to osmotic potential.
cortex - The cortical tissue system is composed of apoplastic (non-living intercelluar spaces) and
symplastic (living cortical cell) regions. Movement of the soil solution is virtually unrestricted in
http://www.hcs.ohio-state.edu/hcs200/topics/topic3.htm (10 of 11) [10/08/2001 10:01:20 a.m.] this region. Cortical cells are interconnected by plasmodesmata and are a primary sites of nutrientassimilation. Assimilation by cortical cells is affected by the environmental parameters oftemperature (assimilation generally increases up to 40 C, then declines) , soil aeration, light(shading of leaves affects CHO movement to roots restricting their energy levels), pH (because itaffects membrane Ca content), and the relative conc. of ions in the soil solution.
epidermis - the primary functions of the epidermis are that of uptake and to protect cortical cells from the soil environment. Root hairs develop from tricoblasts (specialized epidermal cells) in the
region of elongation. Root hairs are short-lived and are continually renewed. The function of root
hairs is to increase surface area of the root which increases contact with the soil solution. It was
estimated that a 4 month old rye plant root system contained 14 billion root hairs constituting 400
m2 of surface area and that if placed end to end, would stretch 10 thousand kilometers. Root hairs
are especially important for the acquisition of phosphorus.
Some species (a few of them are crops) do not develop root hairs. Often, these plants have co-evolvedwith species of mycorrhizal fungi capable of forming a symbiotic relationship wherein fungal hyphaefunction similarly to root hairs.
Secondary growth in roots is similar in its characteristics to those exhibited by stems. Although roots thathave undergone secondary growth are not actively absorbing water and nutrients, they are involved withaeration and gas exchange through lenticels (pores).
http://www.hcs.ohio-state.edu/hcs200/topics/topic3.htm (11 of 11) [10/08/2001 10:01:20 a.m.] HCS 200 Winter Quarter 2001 Horticulture and Crop Science 200
Winter Quarter 2001 Lecture Topic #3a: Crop Plant Morphology (continued)
Bernier, G., J.M. Kinet and R.M. Sachs. 1981. The physiology of flowering. Vols. 1-2. CRC Press, BocaRaton, FL.
Buban, T. and M. Faust. 1982. Flower bud induction in apple trees. Hort Rev. 4:174-203.
Campbell, N.A. 1996. Biology. Benjamin Cummings Publ. Co., Menlo Park, CA = Chapter 34.
Hartmann, H.T., A.M. Kofranek, V.E. Rubatzky and W.J. Flocker. 1988. Plant science - growth, developmentand utilization of cultivated plants. Prentice Hall, Inc., Englewood Cliffs, NJ = Chapter 2.
Pratt, C. 1988. Apple flower and fruit: morphology and anatomy. Hort Rev 10:273-308.
Raven, P.H., R.F. Evert and S.E. Eichhorn. 1999. Biology of plants. W.H. Freeman and Co., New York, NY =Chapters 23-27.
Salisbury, F.B. and C.W. Ross. 1992. Plant physiology. 4th ed., Wadsworth Publ. Co., Belmont, CA.
Westwood, M.N. 1978. Temperate zone pomology. H.W. Freeman and Co., San Francisco, CA "It has been said that an oak is an acorn's way of making more acorns. Indeed, in a Darwinian view of life, thefitness of an organism is measured only by its ability to replace itself with healthy fertile offspring . Thesetwo developments, pollen and seeds, are among the most important adaptations of plants to life on land."Campbell "Due to its tremendous agricultural and economic importance, reproduction has perhaps been one of the moststudied processes in plant development." Scheerens (PhD Dissertation, 1985) http://www.hcs.ohio-state.edu/hcs200/hcs200top3a.htm (1 of 17) [10/08/2001 10:01:32 a.m.] HCS 200 Winter Quarter 2001 Outline: (Continued) Previously we discussed
1. Crop Life Cycles 2. Seed Germination 4. Primary and Secondary Development of Stems 5. Primary and Secondary Developmetn of Roots See Topic 3 Handout and Lecture Notes to review these concepts.
Leaf structures vary considerably with respect to size and shape. For instance, some species have simple leavesconsisting of a single leaf blade or lamina (e.g. oak, corn) whereas others develop compound leaves that arecomprised of several "leaflets" (e.g., tomato, rhododendron). Further, compound leaves are either palmatelycompound where all leaflets are joined at a central point or pinnately compound where leaflets are attached to arachis in some organized fashion (usually two by two). Leaf size also varies greatly among species; considerthe size difference between a Blue Spruce "needle" and a banana leaf. Please review Lab 1 for some details.
Moreover, structural and morphological variations in leaves often can be understood in relation to differencesin environmental adaptation among species. For example, leaves on desert species are often small or in otherways highly modified to protect against water loss. Cacti are, of course, an extreme example of modificationfor environmental stress as leaves have been "replaced" by a photosynthesizing plant body.
Despite their differences, leaves typically share some general morphological features and functions (Figs 2-33and 2-34).
- Upper and lower surfaces of the leaf blade are formed by a single layer of parenchymatous cells which comprise the epidermis. The epidermis provides strength and some rigidity to the blade.
Often, epidermal cells are covered by a cuticle (waxy material) which further protects the leaf from
damage and water loss. The leaf epidermis also contains a group of specialized cells called Guard cells
which flank (surround) the stomates (pores) through which water vapor and atmospheric gasses enter
and exit the leaf. Because guard cell shape fluctuates over time in rapid response to environmental ques,
guard cells can act as gate keepers, allowing gaseous interchange between the interior of the leaf and the
surrounding atmosphere only when it is to the plant's advantage (see discussion below). Stomate size,
shape (Figs. 3.18 and 3.19), density, order (random or ordered in rows) and position varies substantially
among crop plants. Stomates are often more prevalent on the lower surface of the leaf, but this is by no
means, universal. The stomates of aquatic plants (e.g., water lily), for obvious reasons, are primarily
found in the upper epidermis. In some species, epidermal cells also give rise to trichomes or hairs
(collectively called pubescence) that perform a number of important functions (see below).
http://www.hcs.ohio-state.edu/hcs200/hcs200top3a.htm (2 of 17) [10/08/2001 10:01:32 a.m.] HCS 200 Winter Quarter 2001 Spongy mesophyll and palisade layer - The spongy mesophyll and palisade layers of the leaf are composed of parenchymatous cells, both of which are present in many dicot leaves. As they contain
chloroplasts, the double-membraned organelles that house pigments and enzymes responsible for
photosynthetic processes, they are the "work horse" cells of the leaf. The cells in the spongy mesophyll
are loosely and irregularly arranged resulting in relatively large intercellular spaces. Especially evident
in some species are the large intercellular chambers that are associated with stomatal openings.
Intercellular spaces enhance the process of gas exchange (primarily CO2, O2 and H2O) with the
atmosphere. In contrast, palisade layer cells are more highly organized and contain minimal
intercellular spaces. However, because they have expanded surface areas that are 2 to 4 times as
extensive as those of the spongy mesophyll, they carry on the bulk of photosynthesis in most dicot
leaves. In some leaves, the palisade layer is more than one cell thick.
Vascular bundles - Vascular bundles distributed throughout the leaf contain both primary xylem
(usually oriented toward the upper surface of the leaf) and primary phloem (usually oriented toward the
lower surface of the leaf) elements. Larger vascular bundles are often called veins. Visually, venation
appears to be netted (dicots) or parallel (monocots) in organization, but in every arrangement, vascular
systems are continuous and connect to the stem through the midrib. The midrib of the leaf acts as the
principal vascular conduit of the leaf and because it contains some secondary growth (lignification) the
midrib adds rigidity to the leaf (i.e., it acts as a "main support beam").
Note 1: lignin is a polyphenolic material that is deposited in secondary cell walls. It is extremely resistant todegradation and is responsible for the durable characteristics of wood. If you witness the leaf decompositionprocess you will note that the midribs remain long after the rest of the leaf blade has disintegrated.
Note 2: The midribs of simple leaves are continuous with the petiole or "leaf stem" which attaches to the stem
at the nodes. In compound leaves, each leaflet possesses a midrib which is attached to the petiole by a
petiolule, in pinnately compound leaves the leaflets are attached through the petiolule to a continuation of the
petiole called the rachis (See lab #1). Sorry -- natural variation sometimes makes naming structures somewhat
complicated.
A bundle sheath, a tightly organized group of parenchymatous cells surrounds each vascular bundle. This
tissue acts to prevent direct access of atmospheric gasses to the vascular system of the plant and insures that all
compounds entering the vascular system from the "outside" must pass through cellular membranes which
discriminate against potentially harmful substances. In most plants, these cells do not contribute much to the
photosynthetic capacity of the plant as they contain relatively few chlroplasts. However, there is an important
group of plants, C4 plants, in which the bundle sheath cells are extremely important for the photosynthetic
process (see below).
Guard cell function - As stated above, act as gate keepers, allowing gaseous interchange between the interior of the leaf and the surrounding atmosphere only when it is to the plant's advantage (i.e., when
photosynthesis is likely to take place). Guard cells open and close stomates by virtue of their ability to
rapidly change shape in response to turgor pressure (the pushing force that the cytoplasm and cell
membrane exerts on the cell wall). At a given moment, the turgor pressure results from the relative
concentration of solutes (dissolved materials) in the cell and the effect they have on the importation of
water into the cell. Teliologically, nature tends to want to increase the distance between molecules of
dissolved solids so that their concentration (weight/volume) is at a minimum (one of the laws of
http://www.hcs.ohio-state.edu/hcs200/hcs200top3a.htm (3 of 17) [10/08/2001 10:01:32 a.m.] HCS 200 Winter Quarter 2001 thermodynamics). In aqueous systems such as the cell cytoplasm, nature does this by adding water.
Remember, the plant cell membrane is permeable to water molecules; therefore, if the concentration of
solutes on the inside of the cell is greater than on the outside of the cell, water will move into the cell to
reduce solute concentration by a process called osmosis (see any biology text for a review of this
phenomenon). As the quantity of water inside the cell increases, the turgor pressure increases exerting
more force on the cell wall. Turgor pressure is maximized, of course, when the tensile strength (pulling
forces) in the cell wall will not allow it to be stretched further. Otherwise the cell would burst. Guard
cells that are fully turgid are open; those that are flaccid (the opposite of turgid) are closed (see a and b in
handout)
Guard cell turgor pressure is affected by several main controlling elements: light, CO2 concentration,temperature and water concentration of the leaf (Fig. 4-11). In most plants, stomates are closed at night (seeexceptions below). When light strikes a leaf surface, photosynthesis commences causing the production ofATP (energy), decreases in CO2 levels, and increases in the concentration of sugar and other solutes such asthe malate -2 ion.
Note: malic acid is a commom organic acid containing 4 carbon atoms; its anion is called malate. Because itis associated with the Calvin (tricarboxyllic acid) cycle of respiration, it is ubiquitous and essential to allhigher forms of life.) Then, the guard cell membranes open channels that permit the influx of K+1, and Cl-1 through active transport
(energy requiring) mechanisms from the surrounding cell wall and intercellular spaces. The influx of these
materials along with sugar and other cellular components increases the solute concentration and osmotic
potential of the guard cell. Water then enters the cell by osmosis and the turgor pressure increases, "inflating"
the guard cells and opening the stomates.
This whole process can be reversed by increases in ABA (which stands for abscisic acid, a plant hormone that
usually inhibits metabolic processes) concentrations. When water availability is limited (a function of soil
moisture levels, temperature and relative humidity), ABA concentrations in the leaf are increased by synthesis
in mesophyll cells or importation from the plant roots. Elevated ABA causes the efflux of solutes and water out
of the guard cell, thus, closing the stomates to protect against wilting or in extreme cases, leaf death.
Trichome function - Trichomes or hairs (collectively called pubescence)are specialized epidermal cells
that perform a number of important functions. Because they increase the surface area of the epidermis,
they aid the leaf in dissipating heat and retarding water loss. Some trichomes secrete oily resins which
also help maintain leaf water balance. Trichomes may also protect the plant by discouraging insect
predation or ovipositioning (egg laying) by a phenomenon known as antixenosis (xenos is Greek for
stranger or guest; antixenosis literally means repelling guests). In simple terms, the antixenotic response
occurs because insects simply do not prefer "hairy" leaf surfaces as they have to expend more energy to
eat or lay eggs there than on glabrous (non-hairy) leaf surfaces. Trichome (pubescence) density, color
and position varies, of course, with species and in the case of ornamental crops (e.g., african violets,
lambs ear) can be one of their most attractive features.
http://www.hcs.ohio-state.edu/hcs200/hcs200top3a.htm (4 of 17) [10/08/2001 10:01:32 a.m.] HCS 200 Winter Quarter 2001 3 VS. C4 Leaf anatomy and function - Most crop plants capture CO2 by incorporating it into a 5-carbon sugar phosphate (ribulose 1,5-bisphosphate) to form a transient 6-carbon compound that almost
immediately disintegrates to for 2 molecules of a 3-carbon compound (3-phosphoglycerate). The enzyme
that catalyzes this reaction is "nicknamed" rubisco (i.e., ribulose 1,5-bisphosphate
carboxylase/oxygenase).
C5 + CO2 C6 C3 + C3 catalyzed by rubisco Thus these plants are called C3 plants.
The fate of the two C3 molecules is as follows: Five of the six carbon atoms are used to regenerate the initial C5compound while the other carbon atom is used in the synthesis of a glucose (simple sugar) molecule.
C3 + C3 C5 + C used for glucose synthesis This complex and cyclic process is called the Calvin Cycle (after the person who figured it out experimentally).
Obviously, since glucose contains six carbon atoms, the cycle must turn six times in order to fix the carbonfrom six CO2 molecules to one molecule of glucose. As we will discuss in detail in Topic 4, this process takesenergy and requires the addition of electrons (i.e., it is accomplished via chemical reduction).
Although most of our crop plants are C3 plants, a number of notable exceptions have an additional scheme totrap CO2. In these species CO2 can be added to a 3-carbon compound (PEP or phosphoenolpyruvate) to form a4-carbon structure (oxaloacetate). The enzyme that catalyzes this reaction is called PEP carboxylase.
C3 + CO2 C4 catalyzed by PEP carboxylase Thus, these plants are called C4 plants
The fate of the 4-carbon product is as follows: Three of the four carbon atoms are used to regenerate the initialC3 compound while the other carbon atom is passed to the Calvin cycle to be used for glucose synthesis in aprocess identical to that in C3 plants.
C4 C3 + CO2 passed to Calvin Cycle where it is used for glucose synthesis This complex and cyclic process is called the Hatch-Slack Cycle (again after the researchers who figured it outexperimentally). Again this process requires energy and electrons.
http://www.hcs.ohio-state.edu/hcs200/hcs200top3a.htm (5 of 17) [10/08/2001 10:01:32 a.m.] HCS 200 Winter Quarter 2001 Although this additional system in C4 plants seems to add unnecessary metabolic complexity to the capture ofCO2, it has some real physiological advantages do to the nature of the two enzymes involved.
PEP carboxylase has a greater affinity for CO2 than rubisco does so photosynthesis rates are high in C4 plantseven when CO2 concentrations are limiting.
The operation of the Hatch-Slack pathway in C4 plants feeds carbon (CO2) directly to the Calvin Cycle keeping
it functioning at more optimum rates. If CO2 levels are low and oxygen levels are high, rubisco (Calvin Cycle
enzyme) adds oxygen to the C5 starting sugar which is the beginning of another cyclic phenomenon called
photorepiration. We will not discuss photorespiration in detail in this course except to say that it is a rather
futile cycle which uses oxygen and releases CO2 and seems to waste energy and accomplish nothing (i.e., its
positive attributes, if any, are not well understood). In C3 plants, photorespiration rates may be relatively high
under certain conditions so that as much as 50% of the carbon fixed by photosynthesis is reoxidized and
released as CO2. In C4 plants, rates of photorespiration are much lower because rubisco has a constant supply
of CO2.
C3 and C4 plants differ with respect to how photosynthetic rates are affected by light intensity. C4 plantscontinue to respond to higher light levels long after C3 plants have reached their maximum photosynthetic rates(see Topic 4 notes).
C4 plants exhibit greater water use efficiency than C3 plants (see below).
C4 metabolism has been observed in 19 plant families and may be active in thousands of plant species. C4metabolism is perhaps most common in the Poaceae (grass family) which includes notable examples of cropssuch as corn (maize), sorghum, sugarcane, millet and bermudagrass and of weeds such as crabgrass andbermudagrass.
The leaves of C4 plants function a little differently than do those of C3 plants. Most notably, CO2 is originally
captured by the Hatch Slack pathway in the mesophyll cells and then is transferred to the Calvin Cycle which
operates primarily in the bundle sheath cells. The bundle sheath layer is more highly organized in C4 plants
(see Fig 26-26) and resembles a "wreath". Kranz is German for wreath and this arrangement in C4 plant leaves
is called Kranz anatomy. In C3 plants, the bundle sheath cells contain few chloroplasts and contribute little to
photosynthetic output. In C4 plants, the reverse is true, bundle sheath cells contain well developed chlorplasts
that are highly active (Calvin Cycle).
Crassulacean Acid Metabolism or CAM is a notable variation of C4 metabolism was
first witnessed in stonecrop an ornamental succulent in the Crassulaceae family. Thereafter, it was foundto be prevalent in a number of xerophytic (desert-dwelling) species, especially succulents and cacti. Inthese species, stomates are opened at night when temperatures are relatively cool. At night, CO2 is fixedvia the Hatch Slack Cycle and stored as 4-carbon compounds in mesophyll cell vacuoles. During theday, in the presence of light, these stored compounds are remobilized and further metabolized to sugar http://www.hcs.ohio-state.edu/hcs200/hcs200top3a.htm (6 of 17) [10/08/2001 10:01:32 a.m.] HCS 200 Winter Quarter 2001 via the Calvin Cycle. Since the carbon supplied to the Calvin Cycle was previously fixed, stomates mayremain closed during the day, which drastically improves water use efficiency.
Water Use/CO2 Fixed (g/g) Information from Raven et al., 1999 CAM metabolism is perhaps more widely spread than C4 metabolism since it is present in 23 families. Thepineapple is probably the quintessential example of CAM crop plant; prickly pears (a minor crop grown forfruit or pads "leaves") also exhibit CAM metabolism. CAM metabolism is also active in many ornamentalspecies including wax plant, snake plant (mother-in-law tongues), bromiliads, cacti and euphorbs The diversity among species with respect to flower structure is as vast as the diversity among leaf types or anyother plant organ. As stated in Topic 2, differences in floral structure is one of the primary keys we use toclassify plants and to determine phylogenetic (evolutionary) relationships among species. As with other organs,floral structure influences function and as such may influence how a crop is cultured. Last, but not least, floraldiversity among species provides us with a stunning array of ever-changing beauty (sorry - had to wax poetic).
Flowers are attached to an inflorescences or flower stalk by means of a pedicel, which in turn is attached to thestem. As with leaves, the vascular system of a flower is continuous with that of the stem. Inflorescences can besimple (bearing a single flower) or extremely complex (see Lab 1 for some details).
An Apple Flower - An apple flower (Fig. 2-39) is a good "typical" flower as it is simple and complete (contains all possible flower parts). All flowering meristems are the result of transitions in previously
vegetative meristems. Thus, in some ways, flowers can be considered as modified leaves and stems.
Typically, flower parts are arranged in whorls. The outermost whorl contains the sepals (collectively the
calyx). Sepals are usually green in color but may also pigmented in a manner similar to that of the petals.
In many species, the sepals surround and protect the other floral parts during flower bud development,
but "peel back" or separate as the flower reaches anthesis (e.g., the transition from rose bud to open rose
flower). In others, portions of the calyx remain joined even after the flower opens (e.g., petunia,
carnation). The next outermost whorl is composed of the flower petals (collectively the corrolla).
Flower petal color extremely diverse among and within species and is mediated by at least three different
pigment classes (chlorophylls, carotenoids and anthocyanins). In many wind-pollinated grasses, flowers
are green in color and not usually conspicuous whereas in crops that require pollination by insects or
animals, flowers are often colored and showy (e.g., hummingbirds are attracted to red). In addition to
color, flower fragrance resulting from essential oils in the petals also attract certain pollinators; some of
http://www.hcs.ohio-state.edu/hcs200/hcs200top3a.htm (7 of 17) [10/08/2001 10:01:32 a.m.] HCS 200 Winter Quarter 2001 these fragrances are extremely strong (e.g., lilac, orange, viburnum); some are somewhat ethereal orsubtle (e.g., apple). Some fragrances are pleasing to humans whereas others are decidedly not (i.e., someinsects are attracted to smells reminiscent to us of rotten meat -- yuk!) Note: nectars from nectaries or nectriferous glands also attract insects, bats and birds, as well as pigments in
other flower parts. For instance, the yellow carotenoid pigments in most anthers reflects ultraviolet light which
can be seen easily by bees.
In most simple flowers the petal number and sepal number are the same, but this is not always the case. The
inner most two whorls of the flower contain the sexual organs. The male sexual organ, the is called the stamen
(collectively the androecium). Stamens each have two parts, an anther, which is the site of male
gametogenesis, and a filament or stalk upon which the anther rests. The innermost whorl of the flower contains
the female sex organ, the pistil (collectively the gynoecium). Each pistil is composed of three parts, the stigma,
the style and the ovary. The stigma is composed of a relatively shallow tissue group and is the site of
pollination and pollen germination (i.e., its where the pollen grain lands and begins to grow). The style is a
columnar shape tissue group through which the germinated pollen grows, moving its male gametes toward the
female gamete located within an ovule of the ovary. The ovary is the site of female gametogenesis and
contains one or more ovules; each ovule contains an embryo sac (see below) containing the female gamete, the
egg. In some fruit, ovaries can be subdivided into chambers called carpels, each of which may be serviced by
its own stigma and style. In an apple flower, there are typically five stigmas and five styles. The apple ovary is
divided into five carpels, each with two ovules that when pollinated, for two seeds. In many fruits (ripened
ovaries), the ovary wall develops into the pericarp, which is sometimes edible (e.g., pea pods, outer surfaces
of the tomato fruit, the flesh of a peach) and sometimes not (the peel of an orange, the shell of a nut, and the
outer pit of a peach) The fleshy portion of the apple which we consume is actually derived from the
hypanthium, an accessory structure that surrounds the ovary, whereas the pericarp is located in the portion we
commonly call the core.
Flower structure often reflects a species' preferred pollination scheme. Flower structures which are open at the
time of pollination (chasmogamous; e.g., apple) invite cross pollination. Outcrossing species often bear flowers
that are wind pollinated. Cross-pollination can also be promoted if the pollen of an individual flower is shed
before the stigmatic surface is receptive (protandry) or if the reverse is true (protogeny). Species that are
monoecious, bearing unisexual flowers on the same plant (e.g., corn, pecan) dioecious species that bear male
and female flowers on different plants (e.g., hemp, fig, date) are outcrossing species. Species that produce
sticky pollen that adheres to the body of insect pollinators are also often cross pollinated. Outcrossing species
often develop showy fragrant and nectar-producing flowers in order to attract the appropriate pollinators.
In contrast, self pollinating species often produce flowers which are not conspicuous (e.g., wheat). Flowerswhich are closed (cleistogamous; e.g., pea) when pollen is shed are obligatorily self pollinated. Flowers whichare pendulous (hang down) with stigmatic surfaces below the anthers (e.g., tomato, some peppers) are oftenself pollinated, with gravity being the pollinating force.
Self or cross incompatibility are additional mechanisms that promote outcrossing or self-pollination,
respectively. Examples of species that employ incompatibility mechanisms can be found in almost every plant
family.
http://www.hcs.ohio-state.edu/hcs200/hcs200top3a.htm (8 of 17) [10/08/2001 10:01:32 a.m.] HCS 200 Winter Quarter 2001 Incompatibility refers to a chemically-based recognition system wherein proteins excreted by the pollen graininteract with specialized receptor proteins in the cell walls of the stigma. Both stigma and pollen proteins arecoded for at a single locus - the S locus. The S locus of most species has many potential alleles. That is, mostspecies have the potential of producing a whole series of different S proteins; each stigma (2n) has the potentialto produce two protein types and each pollen grain (n) will produce only one type depending upon what allelesare present within each genotype. The case of self incompatibility is illustrated below: In this situation, because the genotype of the stigma is S1S2, it will recognize any pollen grains that are eitherS1 or S2 as being produced by itself. The recognition event will trigger the production of ribonucleases(enzymes) in stigma cell which are released at the S1 or S2 pollen grain, destroying its RNA and effectivelyneutralizing it. If a pollen grain from a different plant lands on the stigmatic surface, chances are its genotypeholds a different allele at the S locus (e.g., S3). If so, the stigmatic recognition system will not detect it and itmay germinate and grow unheeded, eventually effecting fertilization.
Note: In class, we discussed the topic of self and cross incompatibility under the section on fertilization andembryo growth. I have moved it here, as this is where I had originally intended to present this material Types of flowers - We have actually been discussing types of flowers since the beginning of this section, but there are two additional sets of terms that you may encounter at some point in your career. They are: Complete flowers vs. incomplete flowers. This pair of terms refers to whether or not all of the whorls of a
flower are present. A complete flower contains sepals, petals, an androecium and a gynoecium. An incomplete
flower lacks one or more of these whorls.
Perfect flowers vs. imperfect flowers. This pair of terms refers to whether or not both sexual whorls of a
flower are present. Perfect flowers contain both an androecium and a gynoecium. Imperfect flowers are
unisexual; when they contain only an androecium they are called staminate and when they contain only a
gynoecium they are called pistillate.
Flower bud initiation as controlled by daylength and other factors. Flower bud initiation is the point in time when a vegetative meristem is transformed irreversibly to a flower meristem. For each species, thetiming of flower bud initiation is obviously quite important for the successful maturation of the fruitunder optimum environmental conditions and for survival of the seed. Flower bud initiation is definitelyunder genetic control and as all other phenomenon we have studied, the exact timing variestremendously from species to species.
As well as being genetically controlled, flower bud initiation is often triggered in response to someenvironmental que. One of the most studied of these ques is that of daylength. Some examples of daylength http://www.hcs.ohio-state.edu/hcs200/hcs200top3a.htm (9 of 17) [10/08/2001 10:01:32 a.m.] HCS 200 Winter Quarter 2001 control of flower initiation are listed below.
LDP - long day plants, species in which flowering is triggered by long days (e.g. chrysanthemum) SDP - short day plants, species in which flowering is triggered by short days (e.g. hibiscus) IDP - intermediate day plants, species which flower at median daylengths (e.g. coleus) DNP- day neutral plants, species in which flowering is unaffected by daylength.(e.g. cucumber) In daylength sensitive plants, the length of darkness is actually the important factor! The controlling or
triggering mechanism is mediated by phytochrome, a ubiquitous plant pigment that controls a number of other
functions as well as flower initiation (e.g., the germination of some seeds, tuberization in potatoes, leaf
coloration in the fall, the onset of dormancy in temperate perennials just to name a few). A symplistic
explanation of how phytochrome controls plant function is illustrated in Figures 29-16 (legend in bottom right
corner) and 29-17 in your Topic 3a handout. Phytochrome exists in two forms, one which is sensitive to red
light (Pr) at 660 nanometers and one which is sensitive to far-red light (Pfr) at 730 nanometers.
Note: a nanometer equals 10-9 meters; a wavelength of 660 nm is 0.000000660 meters long. In darkness, most of pigment will be in the Pr form. When light containing wavelengths of 660 nm strikes Pr, itis almost instantaneously converted to the Pfr form. When light containing wavelengths of 730 nm strikes Pfr itis reconverted back to the Pr form.
Note: For those of you who are biochemically inclined the actual chemical change that occurs in the molecule
when it is converted involves a shift in the double bond preceeding the 4th (right most) heterocyclic ring in Fig.
29-17 from the trans to the cis isomer. This, of course drastically changes the conformational shape of the
pigment and thus its function. For those of you who are not biochemically inclined, just remember that the
pigment's shape changes.
In sunlight, which contains both red and far-red light, an equilibrium between the forms will be established. In
the absence of light (i.e., darkness, night), pigment in the Pfr form will slowly be reconverted to Pr even though
no far-red light is present. This slow change is called dark reversion and it is the mechanism by which a plant
can measure daylength or nightlength. The longer the night, the greater the extent of dark reversion.
For most functions, the Pfr form of phytochrome is the one that elicits a biological response. LDPs requirephytochrome to be in the Pfr form for an extended period in order to initiate flowers. However, the converse istrue for SDPs, which rely on the absence of Pfr for an extended period before flowers are initiated (i.e., lots ofdark reversion during long nights).
Experimental evidence proved that the phytochrome-mediated floral response is dependent upon the darkreversion process. For instance, when SDPs were grown under inductive conditions (i.e., long nights), they http://www.hcs.ohio-state.edu/hcs200/hcs200top3a.htm (10 of 17) [10/08/2001 10:01:32 a.m.] HCS 200 Winter Quarter 2001 flowered as expected. But when the long nights were interrupted by a very brief burst of light (termed a night
break), flowering was inhibited. Presumably the night break phenomenon resulted from the instantaneous
conversion of Pr to Pfr during the light burst.
Flowering in response to daylength is obligatory in some species (i.e., they will not flower unless a criticaldaylength is supplied) where as in others it is quantitative (i.e, flowering occurs more readily and abundantlywhen the critical daylength is supplied, but some flowering may occur at other times as well).
The phytochrome-mediated response can be highly specific and highly sensitive. For example, rice is a SDP
that can be planted at various times throughout the year in the tropics. Before it will flower, two criterion must
be met. First, the plant must be physiologically "ripe to flower" which basically means that undergoes a basic
vegetative phase before it is ready to receive a floral stimulus. Second, the daylength must be less than some
minimum threshold (exact photoperiod is variety-dependent) before flowering will commence. If rice is planted
from Aug - Dec, there is sufficient time to meet the requirement for the basic vegetative phase while the
photoperiod is inductive (i.e., less than about 11.5 h Sept-April). Therefore, after the requirement for the basic
vegetative phase has been met, flower induction will occur. However, if the crop is planted in January, the
photoperiod will be too long by the time the basic vegetative phase is completed. Therefore, the plant will
remain vegetative (flowering will be inhibited) until the following Sept. when the next inductive photoperiod
occurs. Rice varieties can be extremely sensitive to the critical photoperiod. For the cultivar Siam 29 the
critical photoperiod is just under 12 h. When this cultivar was planted in Malacca Malaysia in Sept, the crop
cycle (planting to harvest) was 161 days; when it was planted in January, the crop cycle was 329 days. Since
Malacca is only 2 north of the equator, daylengths on June 21 and Dec 21 (the solstices) differ by only 14
minutes!
The expression of photoperiodicity can be highly influenced and in some cases overridden by temperatureeffects. Most commercial strawberry cultivars are SDP that initiate floral buds in the fall. In temperate regionslike Ohio, these initiated buds remain dormant until the following spring, then flower. Flowering is relativelysynchronous, and in Ohio that means that only one inflorescence/year (one flowering cycle/year) is producedfrom each plant. The fruit is ripe by June - hence the name Junebearing strawberries.
However, the flowering response to daylength can be overridden in strawberries if temperatures are cool(especially night temps). California production illustrates how daylength and temperature interact to controlflowering in strawberries. In California, there are two coastal regions of production, one centered near Venturajust north of Los Angeles, and the other located in Salinas, somewhat south of San Francisco.
Production of strawberries in Ventura occurs from Feb - June (i.e., floral induction occurs from Jan - May).
During this period, photoperiods are short enough and temperatures are cool enough that multiple cycles ofinduction occur. That is, the strawberry plant undergoes several flowering cycles per year instead of just onelike they do in Ohio. As summer advances, both the LD photoperiod and the higher night temperatures shutdown floral induction so production ceases.
Production in Salinas occurs from late March - November. Early in the season, both SD photperiod and lowtemperatures promote floral induction. However, unlike production in Southern California, plantings in Salinascontinue to flower throughout the summer when photoperiods are too long to promote flowering. Why doesthis occur? It occurs because the ocean moderates summer temperatures so that nights stay cool, and it is the http://www.hcs.ohio-state.edu/hcs200/hcs200top3a.htm (11 of 17) [10/08/2001 10:01:32 a.m.] HCS 200 Winter Quarter 2001 cool nights which override the the effects of an unfavorable photoperiod. Again several cycles of induction andfruiting occur.
The net result of these two interactive factors allows California growers to typically harvest around 30tons/acre/year of fruit whereas the rest of us do well to harvest around 5 tons/acre/year.
As stated above, phytochrome-mediated control of flowering is obviously an adaptive advantage in naturalcommunities which forces synchronous flowering at a time when the probability of fruit set, development andmaturation will be maximized.
Plants within species display phytochrome-mediated responses in relation to their specific area of adaptation.
For example, soybeans (a SDP) also respond to daylength in accordance with their region of development.
Some soybean varieties are so sensitive, that they flower at the correct time for maximum yield only whencropped within a N-S band 40 miles N or S (i.e., 80 miles thick) from where they were developed. As with rice,soybeans must undergo an obigatory vegetative phase before they will recognise the photoperiodic floweringstimulus. However, if they have met this requirement, they will be induced to flower at some point aftermid-July as daylengths are getting shorter.
When Lincoln' soybeans (adapted to Urbana, IL) were planted in mid-May at various locations from north tosouth, the following harvest dates were observed.
Locations from N-S Harvest date Madison Wisconsin Oct 2 Dwight, Illinois Sept 27 Urbana, Illinois Sept 17 Eldorado, Illinois Sept 8 Sikeston, Missouri Aug 30 Stoneville, Mississippi Aug 12 Obviously, as one goes south, the critical photoperiod is reached at an earlier date, so the crop matures earlier.
In northern locations, the obigatory vegetative phase is met long before the inductive photoperiod so that plantswaiting to be induced go through an additional vegetative phase. During this extra phase the plants are storingcarbohydrates and mineral nutrients which will be used later during fruit (sink) development. That is, this extravegetative phase maximizes yield.
However, northern-adapted soybeans are planted by southern farmers as a double-crop with winter wheat.
Although the yields are diminished, these farmers can make money by harvesting two crops off the same fieldwithin a year. The nitrogen-fixing capacity of soybeans is also a plus in this cropping system.
Flower bud development (FBD) http://www.hcs.ohio-state.edu/hcs200/hcs200top3a.htm (12 of 17) [10/08/2001 10:01:32 a.m.] HCS 200 Winter Quarter 2001 Flower bud differentiation can be rapid, but it can also be a protracted process requiring several months tocomplete. In addition, in temperate zone plants that initiate fall flowers, the process can be interrupted bywinter and completed in the following spring. In any event, the differentiation pattern is sequential - fromoutside to inside - with calyx and petal whorl primordia being developed prior to stamens and pistils. Once allstructures are finally formed and fully developed, the reproductive cells are formed through the process ofmeiosis. The entire process of FBD ends at anthesis. The following time line describes this sequence for appleflowers.
Flower bud initiation June 15-30 Calyx primordia formed early July Petal primordia formed early to mid July Anther primordia formed mid to late July Pistil primordia apparent mid August Ovarian cavity formed late September Meiosis in megaspore mother cells late September? Rest subject to chilling requirement November - March Meosis in pollen mother cells March Ovule and pollen differentiation April Note that flower bud initiation for the next season is occurring simultaneously with fruit set of this year's crop.
Both floral initiation and fruit set depend upon critical levels of available energy (carbohydrates) and hormonal
balance. Overall plant vigor is extremely important. If the plant is weak or has set too many fruit,
carbohydrates available for floral initiation will be limiting and fewer flower buds will be formed for next year.
If the reduction in flower initiation is severe enough, the tree enters an "alternate bearing" cropping cycle in
which commercial crops are produced every other year. Alternate bearing is difficult to correct culturally once
it is initiated and it has disastrous economic consequences for the orchardist.
The length of the rest period is controlled by the plant's chilling requirement. The chilling requirement is
defined as "the cumulative number of hours below 7 C (45 F) needed to satisfy the rest requirement and
break dormancy in vegetative and floral buds." In some species, the chilling requirement for vegetative
buds is less than that for floral buds. In other species such as apple, the converse is true. Note that the
temperature range that satisfies chilling requirement is identical to that which satisfies vernalization and
stratification requirements. Chilling requirements are a selective advantage and confer adaptation to specific
growing regions. Many perennial crops fail in temperate growing regions not because they cannot withstand
midwinter cold, but because their low chilling requirement allows them to break dormancy during the first
warm spell of spring. Peaches and some other stone fruits are not well adapted to Ohio because they flower too
early; their flowers are damaged by late spring frosts. Conversely, oaks and maples never leaf out until May,
regardless of warm April temperatures.
http://www.hcs.ohio-state.edu/hcs200/hcs200top3a.htm (13 of 17) [10/08/2001 10:01:33 a.m.] HCS 200 Winter Quarter 2001 The formation of the male gametophyte (pollen grain) occurs in the anther. A typical anther consists of four
sporangia or pollen sacs. These sacs contain sporogenous cells or microsporocytes which will undergo
meiosis to form pollen grains during anther development and nutritive cells, collectively called the tapetum.
During the process of meiosis, each microsporocyte produces four microspores, each containing ½ of the
number of chromosomes present in the mother plant
Note: If you are fuzzy about the process of meiosis, I urge you to review it in any biology text. It is an extremelyimportant concept to understand. Once meiosis is complete, each of the microspores undergoes mitosis to form two cells within each pollen
grain: a generative cell and the tube cell. The tube cell nucleus is responsible for controlling cellular activities
as the pollen germinates on the stigmatic surface and grows through the style toward the embryo sac. The
generative nucleus will mitotically divide a second time to form two sperm nuclei. In some species this is
completed prior to pollination whereas in others it occurs after pollen germination on the stigmatic surface.
Pollen grains are enclosed within very resistant outer and inner walls. The inner wall (the intine) is composed
of pectin and cellulose as are many primary cell walls, whereas the outer wall (the exine) contains a very
resilient material comprised of carotenoid polymers called sporopollenin. The outer walls of the pollen grain
are "sculpted" differently in each species in such a way that they can serve as a "fingerprint". Not only are these
patterns aesthetically pleasing and interesting scientifically, they also serve as a means to archaeologically
verify plant use by indigenous people and infer evolutionary relationships among plant species in the fossil
record. Pollen grains vary in size from 20 microns to 250 microns.
Note: a micron or µ is equal to 10-6 meters. The formation of the female gametophyte occurs within the ovule. Each ovule contains a megasporocyte
which undergoes meiosis to form four cells which contain ½ the chromosome number of the mother plant. One
of these cells (usually the one distal to the micropyle or ovule pore) survives while the other three disintegrate.
The process from megasporocyte to surviving megaspore is termed megasporogenesis. Megagametogenesis
begins with the mitotic of the megaspore (three divisions in all) and the formation of eight genetically identical
nuclei. These nuclei are specifically arranged within the embryo sac so as to perform specific functions.
Membranes form around these nuclei to form 7 cells within the embryo sac. The three cells distal to the
micropyle are called the antipodals (function obscure) and the three cells near the micropyle form the egg
apparatus consisting of one egg and two synergids. Synergids are important in guiding the sperm nuclei to the
embryo sac. The egg, upon fertilization will become the embryo. The remaining two nuclei are positioned near
the center of the embryo sac. These nuclei will also be fertilized by one of the sperm nuclei to form the
endosperm.
The process of megasporogenesis and megagametogenesis shown here is typical but there are many variationsof these schemes among plant species.
http://www.hcs.ohio-state.edu/hcs200/hcs200top3a.htm (14 of 17) [10/08/2001 10:01:33 a.m.] HCS 200 Winter Quarter 2001 Fertilization and Embryo Growth Pollination is perhaps the first step in the process of fertilization. When an anther and the pollen grains it
contains are mature, the anther wall dehisces (ruptures), releasing pollen into the environment. Pollen can be
transferred from the surface of a dehisced anther to the stigmatic surface of the same or different flowers by
wind, gravity, insects, or a variety of animals (birds, bats, etc.) including humans. The stigmatic surface in
many species is "sticky" because it is coated with a sugar-containing solution secreted by glandular cells within
the stigma. Climatic factors which either influence the activity of pollinators (e.g., bees don't fly when its cold
or rainy) or the status of the stigmatic surface (e.g., extreme wind, rain, heat, etc.) can affect the transfer of
pollen and its adherence to the stigma.
If the pollen is compatible with the stigma upon which it has landed, it will "germinate". A pollen tube then
begins to grow through the stigma and into stylar tissue, a process which is controlled by the tube nucleus. In
some species, the pollen tube grows through a channel within the stylar tissue whereas in others it penetrates
through the style's intercellular spaces (i.e., cell walls and middle lamella). In the latter case, tube growth is
directed to the embryo sac via specialized cells which form tissue transmitting strands. The two sperm nuclei
traverse the style through the pollen tube. In some species, the mitotic division of the generative cell forming
two identical sperm cells occurs in the style whereas in others, it precedes pollination. As the pollen tube nears
the embryo sac, one or both synergids located near the micropyle begin to disintegrate. Disintegration of
synergid cellular membranes release Ca+2 into surrounding tissue which acts as an attractant to the growing tip
of the pollen tube. As the tube enters the embryo sac through the micropyle, it releases the two sperm nuclei.
One of the sperm nuclei fertilizes the egg cell to become the zygote, whereas the other fuses with the two polar
to form the endosperm nucleus through a process called double fertilization.
Typically, the processes of pollination and double fertilization take about 24-48 hours.
Once double fertilization is complete, embryogenesis and seed development commences.
In many species, endosperm development precedes embryo development. In the early stages, the endospermsof monocots and dicots develop similarly. First, the endosperm nucleus undergoes an extensive series ofmitotic divisions, resulting in a multinucleate "super cell". At this point the endosperm is without internalstructure. However, eventually, each nucleus in the super cell is surrounded by a cell membrane and wall andthe endosperm starts to develop into a recognizable tissue group. A some point endosperm developmentpatterns in monocots and dicots diverge. In monocots, the endosperm continues to enlarge and in the maturemonocot seed, it is the principle storage organ for starch and other potential nutrients that will be needed forseed germination. The cotyledon in monocots aids in regulating seed metabolic processes and acts as a conduitof energy from the endosperm to the developing new plant. On the other hand, in dicot species, the endospermis utilized during the development of the cotyledons so that in the mature dicot seed, little if any endospermtissue is left.
The zygote undergoes its first mitotic cycle, forming two distinct cells: the basal cell and the terminal cell. The
basal cell further divides transversely creating a stalk-like structure called a suspensor. The suspensor
suspends and anchors the developing embryonic plant in the ovule and connects it to the ovule integuments
(rudimentary wall-like structures) through an attachment of the basal cell. At the same time that the suspensor
is forming, the terminal cell undergoes several cycles of cell division in order to form a spherical mass that will
http://www.hcs.ohio-state.edu/hcs200/hcs200top3a.htm (15 of 17) [10/08/2001 10:01:33 a.m.] HCS 200 Winter Quarter 2001 eventually differentiate into primary meristematic regions or tissues (i.e., protoderm, ground meristem andprocambium). Notice that similar tissue groups are also formed from apical meristems of the root and shoot. Asthe embryo develops root and shoot axes are formed, each with their apical meristems. Cotyledon tissue gainsprominence and in the case of dicot seeds, the cotyledons will form the bulk of the seed dry weight. The ovuleinteguments develop into the seed coat.
Fruit set and fruit development A fruit is a ripened ovary or group of ovaries. The characteristics and morphology of fruits of course varies inaccordance with the flower and inflorescence structures which precede them. You will discuss this variation inan upcoming lab, so I won't belabor the point in this lecture.
The early life of a fruit (i.e., shortly after ovule fertilization) is somewhat precarious. There are many physical
and physiological changes that must take place. If internal or external conditions are not adequate, the newly
formed fruit will abscise (drop off). Of course, sacrificing newly formed fruit in order to preserve maternal
plant health may be of selective advantage to perennial plants as there will be additional chances to produce
offspring in subsequent seasons. However, for annual plants, fruit drop is somewhat of a disaster biologically.
Fruit set occurs when this early critical period has passed; fruit which have set enjoy a good chance that they
will reach maturity.
Several factors affect fruit set including: Successful embryo development - competent embryos which develop normally produce hormonal signals(usually mediated by auxin or gibberellins) to ovary tissue, stimulating it to grow and enlarge. In some crops,horticultural treatments using natural and synthetic growth hormones have been developed to enhance fruit setor to limit fruit set.
Fruit set and subsequent development of seedless fruit (e.g., bananas, seedless grapes) results from the action of
the same hormones, but, in this case, they (the hormones) are produced in sufficient quantities by fruit tissues
themselves. The process of setting fruit without seed development is called parthenocarpy.
Carbohydrate reserves - See discussion above about alternate bearing Competition - Many crops will drop fruit if fruit set is extremely high primarily due to competition fornutrients and energy.
Other stress factors (e.g., heat, drought, low light intensity, cold weather etc.) can also result in fruit drop.
Fruit growth is characterized by abundant gas exchange and rapid and extensive increases in H2O and overalldry weight. It is also controlled by hormonal balances. Early growth of all fruits results from cell division andelongation enhanced by the presence of auxin and giberellins. The relative level of these compounds determinethe fruit's ultimate shape. Therefore, horticultural practices, such as treating 'Thompson Seedless' grapes withgiberellin to elongate the berries and the rachis (fruit stem), have been developed and routinely practiced.
http://www.hcs.ohio-state.edu/hcs200/hcs200top3a.htm (16 of 17) [10/08/2001 10:01:33 a.m.] HCS 200 Winter Quarter 2001 Fruits can be classified into two groups, depending primarily on hormonal changes (primarily ethylene, a
gasseous hormone) that occur as the fruit ripens. Climacteric fruits exhibit rapid rises in respiration and in
ethylene generation which signals the onset of the ripening process (i.e., softening, changes in color, sugar
content, etc.), whereas non-climacteric fruits seem to ripen without fluctuations in ethylene evolution. In
crops with fleshy fruits, whether or not a fruit is climacteric affects when it is harvested, and how it is stored
and how long its shelf life might be. Biotechnologically enhanced tomatoes (a climacteric fruit) have been
produced through the incorporation of an Arabidopsis gene coding for defective counterparts to enzymes that
responsible for ethylene production. The lack of ethylene production in these recombinants greatly increases
the shelf life of this product over that of common fresh market tomatoes. Conversely, fruits that are climacteric
can be ripened artificially by treating them with ethylene gas or products that evolve ethylene (e.g., banana,
tomato, etc.) Fruits such as apple are stored in chambers designed to limit respiration and ethylene evolution
(i.e., in controlled atmospheric storage chambers), which greatly prolongs their storage life.
As you might expect, environmental factors can affect fruit growth rate and there is considerable variation inthe time necessary for fruits to ripen (i.e., the obligatory time necessary to progress from pollination to fruitmaturation (harvest or abscission). However, there are really only two fruit growth patterns: sigmoid growthcurves and double sigmoid growth curves (Fig 9-2). In the double sigmoid pattern, fruit growth is retarded for aperiod during mid-season to allow rapid growth and development of seeds. In fruits that follow a sigmoidpattern (e.g., pecan), seed maturation often occurs in the latter stages of fruit development, or about the timewhen fruit development slows (see Table 1 and its associated graph).
http://www.hcs.ohio-state.edu/hcs200/hcs200top3a.htm (17 of 17) [10/08/2001 10:01:33 a.m.] Horticulture and Crop Science 200
Winter Quarter 2001 Lecture Topic #4A: Radiant Energy and Its Effect on Crop Growth - Part 1- Light.
Text = Chapters 7 and 8 Hartmann, H.T., A.M. Kofranek, V.E. Rubatzky and W.J. Flocker. 1988. Plant science, growth, developmentand utilization of cultivated plants. Prentice Hall, Inc., Englewood Cliffs, NJ. = Chapter 10 Janick, J., R.W. Schery, F.W. Woods and V.W. Ruttan. 1981. Plant science, an introduction to world crops.
H.W. Freeman and Co., San Fransico, CA. = Chapters 10 and 11.
Raven, P.H., R.F. Evert and S. E. Eichhorn. 1999. Biology of plants (6th Ed.). W.H. Freeman and Co., NewYork, NY = Chapter 29.
". Although a small amount of the energy to power civilization comes from the interior of the earth and more iscontributed by atomic fission, our most abundant source of energy is the sun". " The total incoming solarenergy reaching the outer edge of the earth's atmosphere averages 1.94 cal/cm-2/min-1, a value known as thesolar constant. We can put this in perspective by noting that in 1 0 days, the energy arriving at the periphery ofthe earth's atmosphere is equal to the total known fossil fuel reserves." from Text.
"It has been estimated that about 1.4 x 1014 kg of carbon from carbon dioxide in the air is converted tocarbohydrates each year by the green plants that live on the land and in the oceans, seas and lakes. A number ofthis magnitude is beyond our comprehension. To put it another way, assume that the 1.4 X 1014 kg of carbon is http://www.hcs.ohio-state.edu/hcs200/light.htm (1 of 14) [10/08/2001 10:01:43 a.m.] converted entirely to an equivalent amount of coal, which would be 1.4 X 1011 MT. Assume further that astandard-size railroad car holds 45.5 MT; then the carbon fixed annually by plants would yield enough coal tofill 97 cars every second of every hour of every day all year long." from Hartmann et al.
What is radiant energy.
Radiant energy - radiant energy is that which is derived from the sun. It has a unique feature in that it behaves
as both a particle (photon - a descrete unit of radiation) and a wave. We typically measure the amount of
radiation striking or reaching a given area in photons but we measure the strength (energy level) of those
photons in terms of wavelengths. Short wavelengths are very powerful while longer wavelengths are less so. In
other words 100 photons of radiation at a 800 nm wavelength has only half the energy of 100 photons of
radiation at a 400 nm wave length. The entire range of wavelengths reaching the earth's outer atmosphere is
called the electromagnetic spectrum (see diagram in handout). Notice that visible light (wavelengths from about
400 - 700 nm) comprises only a small portion of this spectrum. Radiation at the highest energy level exhibits
extremely short wavelengths. The highly energetic radiation of X-rays and rays can cause serious damage to
biological systems because when they hit organic constituents in cells, "knock" electrons out of their orbits, thus
creating ions -- hence their alternate names,
cosmic or ionizing radiation. Although less dangerous, ultraviolet light is also somewhat ionizing and is thechief culprit causing sunburn in humans and other animals. Prolonged exposure to high levels of ultravioletlight is also linked to various types of skin cancer. Radiation at wavelengths longer than 700 are more or lessundetectable by the human eye, and those that are longer than 760 nm but less than about 10,000 nm areresponsible for what we commonly refer to as "heat". Electromagnetic radiation of extremely long wavelengths(>100,000,000 nm) comprise radio waves. Wavelengths between heat waves an radio waves are considered tobe microwaves (useful for cooking and communication).
•radiation = the movement of energy without physical connection (e.g., light through space) •conduction = the movement of energy through one body to another (e.g., heat from electric stove element to kettle bottom, light through a fiber-optic cable) •convection = the movement of energy by (air) currents (e.g., heat from gas furnace flame to upstairs bedroom via forced air ) •insolation = solar radiation striking the earth's surface •diffuse radiation = radiation that has been scattered or reflected by clouds or atmospheric particles. The amount of diffuse radiation is dependent on cloudiness, latitude, season, time of day and elevation http://www.hcs.ohio-state.edu/hcs200/light.htm (2 of 14) [10/08/2001 10:01:43 a.m.] •radiant flux density = number of photons/cm2 •foot candle (lumen) = quantity (intensity) of light which falls on a 1 ft2 surface area generated from a candle that is 1 foot away.
•lux = lumens/m2 1 lumen = 10.76 lux •Einstein = energy in one mole of photons.
•microEinstein = energy in 1 µmole of photons.
At noon on a summer's day, insolation is roughly equal to about 108 K lux, 10,000 ft. candles or 1800microEinsteins.
What happens to the radiant energy arriving at the earth? About 20% of the light arriving at the earth's outer atmosphere penetrates directly to the earth's surface, about25% of it is scattered in the atmosphere and reaches earth as diffuse radiation, about 20% of it is absorbed byatmospheric particles and about 35% of it is deflected back out into space without ever entering the atmosphere.
Other than the fact that we receive enough radiation to make life as we know it possible, there are are severalimportant consequences to this scheme that bear some discussion First, light scattering in the atmosphere is a function of particulate matter such as dust, smoke and waterdroplets. These large particles scatter all visible wavelengths of light in equal proportion so that on a cloudy orhazy day, the sky appears to be white and on a smoggy or dusty day it appears to be brown, the color of thepolutants. However, smaller particles such as atmospheric gases scatter shorter visible wavelengths whileallowing longer ones to pass through without incident. That's why on a clear and dry day the sky appears to beblue.
Radiant energy that is absorbed by the atmosphere before it reaches earth's surface is comprised mainly ofwavelengths that are shorter than those in the visible spectrum. Ozone and oxygen are primarily responsible forabsorbing much of the ultraviolet rays which might otherwise have drastic consequences (mutations, cancer,etc.) on terrestrial life forms. The depletion of the ozone layer by chlorofluorocarbons (freon), methyl bromide(a fumigant) and other such compounds became a matter of concern to scientists and then to enviromentalistsand now to the public at large. There is still great controversy as to how large of a problem we have created forourselves and whether or not the steps we have taken to correct it will be effective.
http://www.hcs.ohio-state.edu/hcs200/light.htm (3 of 14) [10/08/2001 10:01:43 a.m.] Of the direct and/or diffuse radiant energy that reaches the earth, about half is in the visible range. This fact has
undoubtedly affected the evolution of both plants and animals. Those animals that had "sight" (i.e., keenly
sensed radiant enery in the 400-700 nm range), or those plants who were strong photosynthesizers had a
selective advantage over those that didn't. The relatively unrestricted penetration of visible light is called the
window effect. (Note: glass is impervious to ultraviolet light --- that's why you will never tan while working in
a greenhouse.
Once reaching the earth, only about 2-3% of solar radiation is utilized directly by plants in the process of
photosynthesis. Much of the light striking the earth's surface is radiated back into the atmosphere as heat (longer
infrared wavelengths). This longer wavelength radiation has far less of a chance of passing out of the
atmosphere than light has of entering it. Atmopheric gases such as CO2 from combustion of carbon-based fuels
such as wood, coal and gasoline impede the escape of heat further. The lack of energy balance (i.e., more light
energy enters than heat energy escapes) results in the "greenhouse effect" which is now a common concern
among scientists, politicians, enviromentalists and the public at large. The increased retention of heat in the
atmosphere due to man's activities within the 20th Century may be radically warming our atmosphere (i.e.,
global warming), again with some potentially nasty side effects such as the melting of the polar ice caps,
massive flooding, increased frequency and intensity of violent storms, catastrophic climatic changes, just to
name a few. As with the depletion of the ozone issue, the extent of global warming and its consequences are
still a matter of controversy that fosters continued debate worldwide.
Of the 2-3% of radiant energy utilized by plants for the photosynthetic process, much of it absorbed byplankton, algae, etc. in aquatic communities (Table 11-1). Cultivated land accounts for only about 5% of netproduction and only about 0.4% of world biomass accumulaion yearly.
Some climatic and geographic factors that affect the path of radiant energy in the atmosphere (besides thosementioned above) include lattitude, season, time of day (all which affect the angle of incidence (obliqueness)with respect to the earth's surface and thus, the amount of atmosphere traveled through prior to terrestrialcontact. Elevation affects the intensity of sunlight (greater at higher elevations) and the ability to lose heat (alsogreater at higher elevations). Therefore, although higher elevations receive more of the sun's radiation, theyloose heat easily and are often cold.
4. Plant growth and development as affected by light A. Photosynthesis The primary light harvesting molecules (pigments) of plants are of course, chlorophyll a and chlorophyll b. Ifyou are interested in the exact chemical structure of these molecules, you will easily be able to find them inmany of the plant science texts. However, for our discussion, remember that they each are composed of a http://www.hcs.ohio-state.edu/hcs200/light.htm (4 of 14) [10/08/2001 10:01:43 a.m.] tetrapyrrole or porphyrin ring ( a complex ring structure containing four N atoms exposed to the ring's center. AMg+2 ion is coordinately held by these four N atoms comprising the "business end" of this pigment. Electronswithin the ring can be excited (i.e., bumped to a higher orbit) after intercepting a photon of light. When theyreturn to ground state, three possible events may occur: the energy can be converted to a combination of heat and fluorescence (light of longer wavelengths) the energy, but not the excited electrons can be passed directly to another chlorophyll molecule, exciting its electrons, in turn while its own return to ground state. This is called resonance energy transfer.
the energy and excited electrons can be passed on to enzymes responsible for ATP and NADH synthesis characteristic of the light reactions of photosynthesis. This leaves an "electron hole" in the chlorophyllmolecule that must be filled with the addition of electrons through oxidation of a suitable substrate (seediscussion below for clarification).
Note: Various carotenoids serve as additional or "accessory" pigments involved in the light harvesting
process. Radiant energy captured by these pigments must be transferred to chlorophyll prior to its use in the
photosynthetic process
Chlorophylls absorb light only in two regions of the visible spectrum (Figure 7-8) in the blue-violet range (i.e.,
420-460 nm) and in the red range (630-660 nm). THESE WAVELENGTHS COMPRISE THE
PHOTOSYNTHETICALLY ACTIVE RADIATION or PAR. Notice that chlorophyll absorbs very little
light of wavelengths from 500 to 540 nm (i.e., the green region), but reflect it instead. This is why we "see"
plants as being green. It's also interesting to note that carotenoid (accessory) pigments, do absorb some light in
the green region. Although light harvesting by carotenoids may offer a selective advantage, the primary
function of carotenoids is as antioxidants protecting the chlorophyll molecule from light induced oxidative
degradation.
The effect of PAR can be demonstrated by examining the rate of photosynthesis and the rate of growth (height)of plants grown at a series of monochromatic wavelengths (Figs. 7-6 and 7-7). In these examples, bean plantsphotosynthesized most actively and grew tallest when grown using light of red and blue wavelengths.
Photosynthesis Basics The basic reaction of photosynthesis is 6 CO2 + 12 H2O C6H12O6 + 6 H2O + 6O2.
The carbon in CO2 is "fixed" within the glucose molecule via a series of enzymatic reactions within thechloroplast known as the Calvin cycle. As we studied earlier, CO2 is first combined with a C5 compound called http://www.hcs.ohio-state.edu/hcs200/light.htm (5 of 14) [10/08/2001 10:01:43 a.m.] ribulose bis phosphate to form an unstable C6 intermediate (catalyzed by the enzyme rubisco). The C6intermediate is almost immediately cleaved to for two C3 compounds. Several reactions later, one carbon atomis used in the formation of glucose while the other five are rearranged to reform ribulose bis phosphate,completing the cycle. Therefore it takes six turns of the cycle and six CO2 molecules to form one molecule ofglucose.
In order for the Calvin Cycle to work, the carbon atoms of CO2 (oxidation state +4) must be reduced (have
electrons added to them) in order to be transformed into the carbon atoms of glucose (oxidation state average of
0). To reduce molecules in a biological system almost always requires two things --- Energy in the form of
ATP and a source of electrons carried by NADPH. To build a glucose molecule via the Calvin Cycle, it
requires the energy stored in 18 ATP molecules and 24 electrons delivered by 12 NADPH molecules.
Ultimately light energy (24 photons) will be used to garner both of these required "building" materials via the
energy transduction or light reactions of photosynthesis catalyzed by membrane bound enzymes within the
chloroplast. The source of the needed electrons is water. In the light reactions, 12 H2O molecules are broken
down to their constituents 6O2 and 24H+. Notice in this reaction that each oxygen atom went from an oxidation
state of -2 in water to an oxidation state of 0 in O2. Hence the oxygen of water was oxidized (electrons were
taken away).
Diagrams 7-13 and 7-14 illustrate how all of this works. The process starts with the harvesting of light energyby Photosystem II. Photon energy may be captured by any chlorophyll molecule. Electrons within the porphyrinring are first excited and then return to their ground state passing the captured energy to another chlorophyllmolecule in the process (see above). Eventually, the energy is transferred to a chlorophyll a molecule in aspecialized reaction center. This also results in the excitation of the electrons in the chlorphyll molecule of thereaction center. However instead of returning to ground state. The energy along with the excited electrons arepassed to an electron acceptor which is part of an electron transport chain of pigment molecules. The excitedelectrons with the energy they hold are passed down this chain from pigment to pigment in a series of energyfavorable reactions forming an ATP molecule in the process. Finally the electrons and the residual energy theyhold are passed to a chlorophyll a molecule at a reaction center of Photosystem I. Again an excitation eventoccurs and the excited electrons are passed along to another electron acceptor in yet another membrane boundelectron transport chain. The net product of energy and electron movement down this chain is the formation ofan NADPH molecule.
This process leaves the entire system two electrons short (i.e., the reaction center chlorphyll a molecule inPhotosystem II is missing two of its electrons. They are replaced by the cleavage of water and the oxidation ofthe oxygen molecules within as described above.
One additional option worth mentioning here is that ATP may also be formed in an alternate Photosystem Ischeme by a process called photophosphorylation.
http://www.hcs.ohio-state.edu/hcs200/light.htm (6 of 14) [10/08/2001 10:01:43 a.m.] The Effect of Light Intensity on Photosynthetic Rate The effect of light intensity on net photosynthesis is depicted in Figure 7-8. The light compensation point is theamount of light necessary to stimulate a level of photosynthesis in plants that is equal to their level ofrespiration. A typical light compensation point might be reached at about 2% full sunlight or about 40microEinsteins. Notice that net photosynthesis is zero at that point. The Light saturation point occurs at the lightintensity level which saturates the photosynthetic mechanisms. I.e., for a given set of conditions (CO2,temperature, water availability etc.), the photosynthetic process is operating at a maximum rate - light intensityis no longer the limiting factor Values for light compensation and light saturation points vary tremendously among plant species, but is mainlydependent on dark reaction mechanisms (i.e., C3 , C4 , and CAM metabolism). A typical C3 plant will reach itslight saturation point at around 800 microEinsteins (less than ½ of full sunlight on a cloudless day). A typicalC4 plant exhibits a much higher light saturation point than the typical C3 plant -- as much as 2X higher. Thus,C4 plants have a definite advantage in environments that are usually cloudless because they can more efficientlyuse the solar radiation provided to them.
Factors which affect light intensity (the number of photons) reaching leaf surfaces, affect photosynthetic ratesincluding: season of the year the level of atmospheric pollution atmospheric moisture Additional factors which may affect photosynthetic rates include nutritional status genetics (species and cultivar differences) Ecosystems often exhibit characteristic photosynthetic maxima in relation to some of the factors listed above.
See Table 12-3.
http://www.hcs.ohio-state.edu/hcs200/light.htm (7 of 14) [10/08/2001 10:01:43 a.m.] Light saturation points also vary among shade tolerant (100 microEinsteins) and shade intolerant species(500-800 microEinsteins) (Figure 12-4). Berry and his coworkers conducted an interesting experiment whereinthey collected three plants from their native habitat: Tiderstromia oblongata, a C4 plant from Death Valley,Atriplex hastata, a C3 plant native to the Pacific Coast, and Alocasia macrorrhiza, a rainforest floor speciesnative to Queensland. (Note: The arrows on each data line indicate the typical light levels of the species' nativehabitat). They then subjected these plants to various levels of light intensity and measured photosyntheticoutput.
Alocassia behaved like a typical shade tolerant plant because: It outperformed all others at very low light intensities, It exhibited a very low light compensation point, and It became saturated at very low light intensities so that increased PAR had no effect on photosynthetic The morphological and physiological adaptations shade tolerant plants have undergone to survive on the forestfloor typically render these plants in capable of taking advantage of full sunlight. They survive, but growslowly.
Tidestromia behaved like a typical C4 plant because: It outperformed all others at very high light intensities It exhibited a light compensation point similar to sun tolerant C 3 and C4 plants, and It did not reach a light saturation point at full sunlight or beyond These species are best capable of taking advantage of their typically sunny environments. Growth rates areusually very rapid.
Atriplex behaved like a typical C3 plant because: It's performance at very high and very low light intensities was intermediate between sun-loving C shade tolerant plants It exhibited a light compensation point similar to sun tolerant C 3 and C4 plants, and http://www.hcs.ohio-state.edu/hcs200/light.htm (8 of 14) [10/08/2001 10:01:43 a.m.] It reached it's light saturation point at light intensities much less than full sunlight (typically one-fourth to one-half full sunlight).
These plants typically do not capitalize on all of the available sun light they receive. Their typical growth ratesare much faster than shade-tolerant species, but not nearly so rapid as C4 plants. Remember, however, there isgreat diversity among C3 plants with respect to light saturation. Peanut and sunflower are examples of C3 plantswhose light saturation points are near full sunlight.
Can sun-loving and shade-loving plants be "re-conditioned" to survive in the alternate environment? Those of you who will go on to take H&CS 310 will likely have a whole section on acclimatization of indoorfoliage plants to low levels of light. Sun-grown plants vary tremendously with respect to their tolerance of beingplaced in the shade (genetic limits) and of course, leaf morphology and physiology at maturation is influencedby the light levels present during leaf development (see below). However, some degree of acclimatization ispossible.
Representative plants of two clones of Solidago virgaurea were collected, one from a sunny location and theother from a shaded area of the forest floor. Representatives from the sunny location and representatives fromthe shady location were cultured under both high and low light intensities and later measured for their responseto various irradiance levels (Figure 12-6 a,b).
Representatives from the sun clone exhibited the typical C3 pattern when grown at high light intensities (theirnatural condition). When grown at low light intensities the representatives of the sun-adapted clone tended tobehave somewhat as a shade tolerant species in that both their light saturation and their light compensationpoints were reduced by exposure to low light culture. Thus, they had become somewhat adapted to the low lightenvironment. However, light saturation points and photosynthetic maximums of the sun-adapted clone growingin the shade (Fig. 12-6 a) were lower than for shade-adapted clone growing in the shade (Fig. 12-6 b). In otherwords, although some acclimatization had taken place in the sun-clone during its growth at low light, changes inits physiological status did not render it as efficient at low light intensities as was its shade-adapted counterpartwhich was both physiologically and genetically suited to perform well in this environment.
Representatives from the shade clone exhibited a typical pattern for shade tolerant species when grown at lowlight intensities. However, unlike their sun-clone counterparts, they were entirely unable to capitalize on theadditional radiant energy when cultured at high light intensities. Successful acclimatization of a shade plant tofull sun is much less common than the reverse.
B. Photoperiodism http://www.hcs.ohio-state.edu/hcs200/light.htm (9 of 14) [10/08/2001 10:01:43 a.m.] Photoperiodism, or crop development as a function of daylength (night length) is mediated by the pigmentphytochrome (see previous lectures for details). Processes we have studied (or will study) which arephotoperiodic include floral initiation, dormancy, cold hardiness, potato tuberization and membranepermeability.
Phototropism, or the orientation of plants toward light, can be transient or permanent.
Examples of transient orientation (alternate names: solar tracking, heliotropism) include: sunflower heads that
change orientation throughout the day to follow the sun; leaves that change orientation throughout the day so
that their upper surface is always perpendicular to the sun angle; and leaves that orient themselves to avoid
direct sunlight during periods of drought.
Transient orientation results from osmotic changes in specialized cells near the base of the moving leaf or
flower called pulvini. Because cell osmotic potentials (i.e., resulting from the relative concentration of solutes
in and outside the cell) can be regulated by hormones and other membrane or cellular components (enzymes,
etc.), changes in cell turgor and thus changes in orientation of the structure in question can be relatively rapid.
The permanent orientation of plants to light (e.g., shaded plants that "reach" for sunlight) occurs via a differentmechanism. Well over 100 years ago, Darwin noticed that if oat seedlings were grown with a light source at oneside rather than overhead, the coleoptile of the seedling would bend in the direction of the light (Figure 35-2).
He also discovered that this would not happen if the seedlings apical meristem was damaged or removed. Heand his son conducted a series of experiments to demonstrate the necessity of an operating meristem forphototropic response using decapitation and various types of transparent and opaque caps. They concluded thatthe meristem controlled the process, but the actual bending occurred somewhere below the meristem. They alsoconcluded that the meristem must be sending some sort of signal to the cells below directing them to grow at adifferential rate in order to bend the coleoptile. A little later, Boysen-Jensen confirmed that a signal was indeedbeing translocated from the meristem to the rest of the coleoptile using permeable and non-permeable blocks.
Later F.W. Went experimented with this phenomenon further and in the process discovered the plant hormone,auxin (indoleaceticacid) (Figure 35-3).
Auxin is a growth promoting substance (usually) which is integral to cell elongation. It is produced inmeristems, such as the apical meristem of an oat seedling. Auxin normally is translocated downward evenlythroughout the coleoptile cylinder so that expanding cells are exposed to similar levels of this promotingsubstance. However, auxin is easily degraded by light. If one side of the cylinder is illuminated and the othershaded, auxin levels will be greater on the shaded side and thus cell elongation will be greater. THIS is the basis http://www.hcs.ohio-state.edu/hcs200/light.htm (10 of 14) [10/08/2001 10:01:43 a.m.] for permanent phototropism.
D. Photomorphogenesis Hypocotyl elongation Hypocotyl elongation in several species is controlled by phytochrome in the Pr form. Therefore, longer nights,or treatment with far-red light simulates their growth whereas long days and night breaks would inhibit it.
Seed germination of some species (e.g., lettuce) is controlled by phytochrome in the Pfr form. Therefore,continuous light or treatment with red light simulates germination.
Relative to their position in the canopy, leaves on a given plant may either develop in full sunlight or in variouslevels of shade. The light intensity available to a leaf as it develops often affects its morphology and its functionwhen fully developed.
Shade leaves are usually larger than, but thinner than sun leaves. Shade leaves typically exhibit: a poorly developed palisade layer, large intercellular spaces and loose organization of the spongy mesophyll very thin (if any) cuticle layers Shade leaves often have higher chlorophyll contents (by weight) than sun leaves but less rubisco and otherphotosynthetic enzymes (both light and dark reaction enzymes). In other words, these leaves have investedmore effort in producing pigments for harvesting light than for fixing carbon. This makes some intuitive sensein that the limiting factor for photosynthesis in these leaves will be light availability. These leaves are set up tobe able to fix some carbon under low light intensities with minimum expenditures of energy to maintain the http://www.hcs.ohio-state.edu/hcs200/light.htm (11 of 14) [10/08/2001 10:01:43 a.m.] Calvin cycle and electron transport systems at levels appropriate for the amount of sunlight likely to bereceived. In other words, why develop a massive CO2 fixing capability if it is unlikely ever to operate at fullcapacity due to limited light.
Sun leaves typically exhibit: a well developed palisade layer which may be more than one cell thick, tight organization among cells of the palisade and/or spongy mesophyll relatively small intercellular spaces within the spongy mesophyll very thick cuticle layers Since sunlight is not a limiting factor in their development, these leaves are seemingly set up to maximizecarbon fixation rates.
Leaves developed in partial shade have characteristics between these two extremes All of this notwithstanding, shade and sun leaves on a given plant may show a five fold difference inphotosynthetic capacity.
5. Methods to control light Field orientation Plant row east-west to minimize shading within the row.
In field, landscape and greenhouse situations, the amount of carbon fixed per unit land area will be proportionalto the amount of the land area covered by leaves. For this reason greenhouse and container-grown materials aredensely planted as seedlings and then repotted several times as their size increases during their production. Thispractice not only maximizes photosynthetic capacity/unit area, but also minimizes costs and maximizes profit.
Under field and landscape conditions the amount of area covered by leaves is dependent on plant spacing. The http://www.hcs.ohio-state.edu/hcs200/light.htm (12 of 14) [10/08/2001 10:01:43 a.m.] literature is replete with studies concerning the effects of plant spacing on yield and or product quality, so noexample will be given here. If you want specific information about a species, it is probably available throughmany sources. For each species and in some cases cultivars, there is an optimum spacing.
The optimum spacing for a variety does not necessarily optimize the photosynthetic capacity of individual
plants. Rather, it is the spacing at which the photosynthetic capacity of individuals is balanced against
other limiting factors and production is maximized over the entire area.
If plants are grown at closer than optimum spacings, interplant competition for water, nutrients and sunlight willhave a deterimental effect. Often this is a factor of within row spacing. In apples, a 2m X 10 m spacing willhave a greater detrimental effect than a 4m X 5m spacing, even though these schemes both result in a plantdensity of 500 trees/HA. If plants are grown at wider than optimum spacings, individual photosynthetic ratesmay increase, but at the expense of overall production. In general, it is the balance of limiting effects that is ofimportance.
In general, plant spacing in field and landscape production is fixed at the time of planting. Therefore, untilmaximum canopy area is achieved, sunlight energy is being wasted. However, under certain conditions, (eg.
high value crops) it may be advantageous to overplant the area originally, with the intent of removing"temporary plants" as permanent plants become mature.
Leaf area index and leaf orientation Leaf surface area is both a vertical and horizontal phenomenon. Leaf area index (leaf surface area (oneside)/unit land area is affected by both. The vertical aspects of LAI affect the photosynthetic capacity throughthe effects of shading.
In general, about 70 percent of the light which strikes the leaf surface is absorbed. Therefore PAR rapidlydecreases as light penetrates the leaf canopy. Shading can have a dramatic effect on ps rates of lower leaves. Ingeneral LAIs between 4-8 are optimal for most crop species. If the canopy is too dense (i.e., the LAI is too high)there will be many leaves which do not photosynthesize enough to counteract their respiratory activities. Underthese cases overall yield will be reduced. Notice also that the optimum LAI is somewhat dependent on theaverage light intensity (see above right). For a given species, the optimum LAI will be less under environmentalconditions where cloudy weather is the rule.
Leaf orientation also effects the optimum LAI. The shading effects of upper leaves is far greater in crops withplanophile leaves than in those with erectophile leaves. This phenomenon is most evident in C4 plants becausetheir light saturation point is high.
http://www.hcs.ohio-state.edu/hcs200/light.htm (13 of 14) [10/08/2001 10:01:43 a.m.] Supplemental lighting - see additional handout distributed in class.
http://www.hcs.ohio-state.edu/hcs200/light.htm (14 of 14) [10/08/2001 10:01:43 a.m.] Horticulture and Crop Science 200
Winter Quarter 2001 Lecture Topic #4A: Radiant Energy and Its Effect on Crop Growth - Part 2- Heat.
Text = Chapters 7 and 8 Hartmann, H.T., A.M. Kofranek, V.E. Rubatzky and W.J. Flocker. 1988. Plant science, growth, developmentand utilization of cultivated plants. Prentice Hall, Inc., Englewood Cliffs, NJ. = Chapter 10 Janick, J., R.W. Schery, F.W. Woods and V.W. Ruttan. 1981. Plant science, an introduction to world crops.
H.W. Freeman and Co., San Fransico, CA. = Chapters 10 and 11.
Raven, P.H., R.F. Evert and S. E. Eichhorn. 1999. Biology of plants (6th Ed.). W.H. Freeman and Co., NewYork, NY = Chapter 29 "All matter is composed of atoms that are in a state of vibration that depends on their relative heat. Thetemperature of a substance is a measure of the relative speed with which its atoms are vibrating. If they arevibrating fast, the temperature is high. Theoretically, at absolute zero (0°K, -273°C), all vibration ceases andatoms at that temperature are absolutely still" Janick et al., 1981.
"The ability of plant life to adapt to changing temperatures within the life range . is remarkable. The criticalrange varies widely from species to species. Banana, sweet potato, cucurbits and many tropical plants may beseriously injured by exposure, however brief, to temperatures below 4°C. A properly acclimated apple tree onthe other hand, seldom suffers injury at -35°C" - Text http://www.hcs.ohio-state.edu/hcs200/heat.htm (1 of 8) [10/08/2001 10:01:49 a.m.] Heat vs. temperature; temperature measurement heat is a radiant energy form. It will move by conduction or convection from a warm body to a cold body temperature is a qualitative measure of heat intensity but does not measure energy quantity directly (Note: seeheat of fusion or heat of vaporization below, where energy is added or given off during a phase change, buttemperature stays the same.) Temperature can be measured using various instruments. Some of the common instruments include: •thermometers - thermometers are based on the fact that materials (most notably liquids and gases) expand when they are heated and contract when they are cooled. Common thermometers are constructedwith a reservoir filled with either mercury or alcohol which is attached to a calibrated capillary column.
As the temperature increases, the liquid in the reservoir expands and fills the capillary proportionally.
•thermocouples - thermocouples are based on the fact that the electrical conductivity of metals is influenced by temperature. They are composed of two wires of different metals (usually iron andconstantan) that are fused (arc welded) at their tip. As the temperature changes, the difference in relativeconductivity of the two metals change. Conductivity differences are then measured electronically.
•thermisters - thermisters are also based on the fact that the electrical conductivity of a metal is influenced by temperature. However, most thermisters are constructed of a single alloy which is extremely sensitiveto changes in temperature. Changes in the electrical conductivity in proportion to temperature fluctuationare measured electronically. The advantage of thermisters is that they can be constructed to be very small,so they are great for measuring temperatures of very small or delicate items (e.g., the temperature of abee, or the temperature of a seedling root).
•infrared radiometers - infrared radiometers measure directly, the amount of infrared radiation being given off by a body (i.e., the heat escaping from the body). They are very useful for estimating thetemperatures of large bodies (e.g., the temperature of a corn field).
•specific heat - the amount of energy required to change 1 g of a given substance by 1°C.
http://www.hcs.ohio-state.edu/hcs200/heat.htm (2 of 8) [10/08/2001 10:01:49 a.m.] See specific heats of various substances in Table 8-1. Notice that the specific heat of water is 1.00 and that it isrelatively high in comparison to other materials. Another way of putting this is that water is slow to heat up andslow to cool down.
•heat of fusion - the amount of energy required to change 1 g of solid to 1 g of liquid at the melting point •heat of vaporization - the amount of energy required to change 1 g of a liquid to 1 g of vapor at the See heats of fusion and vaporization of various substances in Table 8-2. Notice again that the heat of fusion andthe heat of vaporization of water are relatively high.
Figure 8-1 illustrates nicely the concepts of specific heat, heat of fusion and heat of vaporization. Starting at a
temperature of -100°C, energy is applied to a 1 kg block of ice over time at a constant rate (i.e., 100 Kcals/min).
As the specific heat of ice is 0.50 cal./g/°C (equivalent to Kcal./Kg/°C), it takes just ½ minute to raise the
temperature of the block of ice from -100°C to 0°C. As additional energy is applied, the block of ice begins to
melt. Since the heat of fusion of water is 80 cal/g (equivalent to 80 Kcals/Kg) it takes 0.8 minutes for the
melting process to be completed. Since the energy being added during this time went into the melting
process, temperature didn't change!!! Once the melting process was complete, the liquid water began to
increase in temperature in response to the added energy in proportion to the specific heat of water, 1 cal./g/°C
(equivalent to 1 Kcal/Kg/°C.) Therefore, in one minute, the temperature of the water went from 0°C to 100°C).
Then it was time for another phase change. The transition from liquid to steam took 5.4 minutes to complete as
the heat of vaporization of water is 540 cal/g (equivalent to 540 Kcal/Kg). Thereafter the temperature of the
steam rose in proportion to the energy supplied and its specific heat.
•calorie - a calorie is the amount of energy needed to raise the temperature of 1 g of water by 1° C.
Note: dietary calories (those we count as we eat a hot fudge brownie with ice cream, whipped cream andchopped nuts on top) are actually kilocalories (Kcals) = 1000 calories.
•BTU - British Thermal Units (residential and commercial building industry measures heat using these units -- the output of your furnace will be expressed in BTUs). One BTU is the amount of energy neededto raise 1 lb. of water by 1°F. 1 BTU = 253 cals.
Factors influencing temperature •Latitude and season Table 8-3 summarized latitude's effect on temperature for the Northern Hemisphere. No surprises here --however, please note that the temperature difference at the two solstices is almost nothing at the equator, but http://www.hcs.ohio-state.edu/hcs200/heat.htm (3 of 8) [10/08/2001 10:01:49 a.m.] gets larger as one moves toward the north pole. For those who don't believe this, I suggest moving from CentralOhio to Central Michigan --- not a great distance north but the winters are much more brutal.
Differences in temperature with respect to latitude actually result from latitude's effect on sun angle and daylength. Sun angle affects the relative intensity of radiation reaching the surface and it is 5.8 X greater at theequator than at the north pole. Likewise, day length flucutations are extreme at the poles and almostnon-existent at the equator.
The effect of latitude on biological communities is illustrated in the diagram to the right.
A general rule of thumb is that for every 100 m rise in elevation temperature decreases 0.6° C. Consider twocities that more or less are at the same latitude. Belan Brazil (19 m in elevation) has a mean temperature of28°C whereas Quito Ecuador (3000 m in elevation) has a mean temperature of 13°C. The effects of elevationand latitude mimic each other (Figure10-2). Latitude and elevation may act in concert. A typical snow line intropical regions is 4500 m where as in temperate regions they are only 3000 m.
•Aspect or slope exposure If you ever take a trip through mountains the effect of exposure (whether or not the slope faces N, E, S or W) ontemperature will be made obvious by the differences in vegetation. In the west, it is not uncommon at all to seedesert scrub on the south-facing slope while the adjacent north-facing slope supports juniper or pine. Crops alsoare affected by slope exposure. In general southern or western-exposed sites are warmer than eastern ornorthern-exposed sites.
A substantial portion of the radiant energy that reaches earth's surface is converted to heat. Diurnal fluctuationin temperature is obviously a function of the varying amounts of incoming insolation at different times of theday, including the night when insolation is absent (See Figure 8-6). However, diurnal fluctuations intemperature typically lag behind the curve of radiant energy gain and loss throughout the day. Just after sunrise,the ambient temperature and the relative energy (light and heat) gained from the sun are at a minimum. As theangle of the sun becomes more direct as the day advances to noon, incoming energy increases. Surfaces (such asleaves) exposed to sunlight absorb heat and become hotter than the surrounding air. Eventually they begin toradiate that heat into the surrounding air. However, as it takes some time for this to occur so that the maximumtemperature occurs in mid afternoon, several hours after the insolation peak at noon. After that point, thesurrounding air also begins to cool, but is far more buffered than surfaces. After dark, surfaces are actuallycooler that ambient air temperature. The same sort of phenomenon controls the relationship between daylength http://www.hcs.ohio-state.edu/hcs200/heat.htm (4 of 8) [10/08/2001 10:01:49 a.m.] and seasonal temperatures (i.e., summer and winter start on their respective solstices because the earthtemperature fluctuation lags behind changes in the duration or intensity of insolation.
Normally, the atmosphere on a cool night is layered such that the warmest air is nearest the earth's suface(Figure 11-13 A). However, if the nights are long, skies are clear, the air is dry and there is no wind, cold air can"drain" down-slope, setting up an inversion layer where the temperature gradient is reversed from normal. Thisphenomenon is extremely important to understand for both frost avoidance (i.e., plant orchards on the sides ofhills) and frost control (i.e., using the inversion layer air to alleviate freezing conditions via wind machines).
•Large bodies of water Large bodies of water have a moderating effect on temperature and adjacent land masses often enjoy a milderclimate than they otherwise might have. Figure 8-8 compares the seasonal fluctuation of monthly means in twocities - St. Louis and San Francisco. Both cities are approximately situated at the same latitude and both have ayearly mean temperature of 13°C. However, as San Francisco is a coastal city, their winters are warmer andtheir summers are cooler than those of St. Louis. St. Louis temps range from -1°C to 26°C whereas SanFrancisco's only ranged from 8°C to18 °C.
This phenomenon results from the fact that water heats up and cools down much slower than does air. The samesituation is responsible for "lake effect" snow as cold air crosses a "still warm" Lake Erie, picking up moistureas it goes and then dropping it as it crosses land. The lake effect is also why it is possible to grow Europeanwine grapes all around Lake Erie and why there is an extensive fruit growing region in Michigan near theeastern shore of Lake Michigan.
Plant growth and development as affected by temperature •Cardinal temperatures - One system of modeling crop growth involves the determination of cardinal temperatures. If one measures
growth rate as a function of increasing heat, the first cardinal temperature one would reach is that of the
cardinal minimum, or the lowest temperature at which growth will occur. Presumably increasing heat would
accelerate growth in some sort of predictable way. Growth is accelerated primarily because the added heat
increases enzymatic activity. The Q10 is a relative measure of enzymatic activity.
Q10 = the increase or decrease in the rate of enzymatic activity in response to raising the temperature 10 °C.
http://www.hcs.ohio-state.edu/hcs200/heat.htm (5 of 8) [10/08/2001 10:01:49 a.m.] When temperatures are moderate Q10s are typically about 2 but as temperatures reach extremes these values are
much less. Presumably one could increase temperature and experience increased growth rate up to the point
when any additional increases in temperature would result in decreases in both Q10s and growth rate. This
temperature would constitute the cardinal optimum. Finally, if one continued to increase heat past the cardinal
optimum, Q10s and growth rates would continue to drop until the plant ceased to grow thus reaching its
cardinal maximum temperature.
Cardinal temperatures will be specific to cultivar, to stage of development being monitored , to plant organ ofinterest, and growing systems or conditions.
•Degree days (growing degree days, heat units) The calculation of degree days is yet another way to model crop growth and to predict maturity dates In simple terms, a degree day is calculated as follows: GDD = mean daily temperature - a crop-specific constant The crop-specific constant is a base temperature for each crop which is experimentally determined.
Degree days are monitored daily and accumulated over time, presumably giving an estimate of how manyadditional degree days will be needed to reach maturity. If the mean daily temperature is below the crop specificconstant, the GDD count for that day is defined as "0". In this modeling process, it is presumed that therelationship between growth and heat is linear, even though that probably is not true.
Corn has a crop-specific constant of 50°F. If the mean daily temperature on a given day was 80°F then the corncrop would have received 30 degree days for that day. If the crop needed 2400 degree days to maturity, then onewould need 80 days worth of 30 degree days in order to harvest.
•Onset of dormancy http://www.hcs.ohio-state.edu/hcs200/heat.htm (6 of 8) [10/08/2001 10:01:49 a.m.] Temperate woody perennials often require a brief period(s) of cold weather in conjuction with receiving criticaldaylengths in order to "harden off" or to prepare for dormancy. Several light freezes prior to entering dormancyactually increases winter hardiness.
•Cold requirements (i.e., vernalization, stratification, chilling requirement - see previous notes and In latitudes from 20° to 40° N, midseason radiation = 400-500 cal/cm2 Since less than 5% of that insolation is used for photosynthesis, the rest is essentially converted to heat.
Remember that only 1 cal of heat is necessary to raise 1 g of water by 1°C. Since a 1 cm3 leaf volume containsless than 1 g of water, heat build up is possible. In mild cases, heat stress can cause midday wilt. It can alsocause dehydration, denaturation of enzymes and metabolic imbalances in photosynthesis, respiration andphotorespiration.
Chilling injury - read second quotation on front page Freezing injury - results from the formation of ice crystals (water expands when it freezes).
Intracellular events cause cell rupture and death; intercellular ice crystals cause tissue damage (tearing etc.)which may disrupt the vascular system of flowers or new leaves during spring frosts.
No time to discuss it, but read about ice nucleation sometime - its kind of a neat phenomenon.
•Frost tolerance There are two types of frost tolerance to consider - tolerance to severe midwinter cold and tolerance oravoidance to spring frosts. Species and cultivars differ with respect to both types of tolerance. Of the two, http://www.hcs.ohio-state.edu/hcs200/heat.htm (7 of 8) [10/08/2001 10:01:49 a.m.] spring frosts have probably caused more economic losses over time than winter kills have (my opinion).
Read more if you have time.
http://www.hcs.ohio-state.edu/hcs200/heat.htm (8 of 8) [10/08/2001 10:01:49 a.m.] Horticulture and Crop Science 200
Winter Quarter 2001 Lecture Topic 4B: Soil and Water and Their Effect on Crop Growth
Text = Chapters 7 and 8 Hartmann, H.T., A.M. Kofranek, V.E. Rubatzky and W.J. Flocker. 1988. Plant science - growth,development and utilization of cultivated plants. Prentice Hall, Inc., Englewood Cliffs, NJ. = Chapter 10.
Janick, J., R.W. Schery, F.W. Woods and V.W. Ruttan. 1981. Plant science, an introduction to worldcrops. H.W. Freeman Col., San Francisco. = Chapters 10 and 11.
Raven, P.H., R.F. Evert, and S. E. Eichhorn. 1999. Biology of plants (6th Ed.). W.H. Freeman and Co.,New York = Chapter 29.
"To many people, soil is merely dirt. From a plant's perspective, howver, soil is crucial for survivalbecause it provides support, water and a variety of elements essential for growth". (Raven et al., 1999) "The importance of water for crop production cannot be overemphasized. Within a given temperaturezone, the availability of water is the most important factor in determining which plants can grow andwhat their level of productivity will be". Text.
http://www.hcs.ohio-state.edu/hcs200/water.htm (1 of 6) [10/08/2001 10:01:51 a.m.] 1. What is soil and how is it formed? "Soil is the unconsolidated, weathered, biochemically-modified portion of the earth's surface which iscomposed of organic matter, minerals, air, water and organisms".
"Soil is the portion of the earth's crust that has formed through physical, chemical and biotic forces, inwhich the roots of plants grow".
Parent rocks (igneous, sedimentary or metamorphic) are weathered to form soil parent material which isthen further decomposed until it differentiates into distinct layers or horizons - see below.
The factors involved in soil genesis include climatic weathering agents (i.e., temperature extremes, watermovement, ice, wind, and other physical forces), chemical weathering processes (i.e., hydrolysis,hydration, carbonation, oxidation etc. - see lecture handout for details), and biologic factors (plants,insects, worms, bacteria) Soil profiles are composed of horizons •The O horizon, the top most layer is typically less than 1" thick. It is composed primarily of organic matter that is just beginning to decompose. - a litter layer or peat layer.
•The A horizon is top soil (0-25" in depth) containing highly decomposed organic matter and highly weathered mineral elements. Top soil in Ohio typically contains 2-5% organic matter mostof which is humus. Humus is highly decayed, colloidal organic matter that is chemically stable.
Humus improves soil structure.
•The B horizon is subsoil (25-36" in depth) containing less organic matter, but still showing significant weathering of mineral elements.
http://www.hcs.ohio-state.edu/hcs200/water.htm (2 of 6) [10/08/2001 10:01:51 a.m.] •The C horizon is substratum (greater than 36" in depth) which may or may not include some parent material (rocks). The C horizon has no clay or organic material.
•Parent Rock lies below the substratum.
Soil texture refers to the size of mineral particles in the soil.
•Gravel is > 2.0 mm = particles are visible to the eye •Sand is 0.05 to 2.0 mm = particles are visible to the eye •Silt is 0.002 to 0.05 = particles are visible with light microscopes •Clay is <0.002 mm = particles are visible by electron microscopy The texture triangle is a generally accepted scheme for classifying soils with respect to their relativeconcentrations of sand, silt and clay. For most crops, loam soils (those which contain approximately 20%clay, 40% sand and 40% silt) are considered optimal.
Soil texture influences many of the soil properties that are important to crop growth. Study Table 8-2,which is self-explanatory.
Soil structure refers to how the soil particles are aggregated into secondary units. These patterns ofaggregation also affect soil performance.
For our purposes here, the effect of both soil texture and structure on pore space is of most importance asit affects both water and air movement through the soil. Pore spaces typically comprise 40-60% of thesoil volume and are either filled with water, air or a mixture of both. In general, light sandy soils,although the have large pore spaces, the have less overall pore space than heavier soils with greater claycontent. Therefore, the water holding capacity of clay soils is greater than that of sandy soils. Conversely,the speed at which water percolates through sandy soils is greater than that of clay (See Figures 8-19 and8-20).
http://www.hcs.ohio-state.edu/hcs200/water.htm (3 of 6) [10/08/2001 10:01:51 a.m.] Poor soil management often results in soil compaction which severely decreases pore space, limits theamount of gas exchange and also impedes water movement through soils. In some instances, it physicallyinhibits plant growth.
Conversely, in many horticultural situations, soil and additives such as peat, perlite, vermiculite, etc. aremixed together for use as growing medium (potting soil). Aside from their effects on nutrition, theseadditives also greatly affect soil porosity (Table 6-1). Soilless mixes (primarily peat mixtures) are alsovery popular as growing media.
Soil water - soil water potential As we begin to discuss water movement in the plant, we need to mention that it is primarily caused bytensile (pulling or sucking) forces rather than compression (pushing or squishing) forces. By definition,tensile forces are expressed as negative numbers. Remember that lower numbers (those that are morenegative) indicate greater forces. A number of units are used to report these forces 1 bar is roughly equal to 1 atmosphere of pressure (actually, 0.987 atmospheres) 1 Mpa (a megapascal) = 10 bars = 9.87 atmospheres.
At this point in the lecture refer to the handout supplement entiled "A Short Discourse on Plant-WaterRelations". Additional diagrams 8-26, 8-25, and 30-7 simply augment the information provided in thehandout supplement.
Functions of water in plants (quoted from text) •It is a necessary constituent of all living plant cells and tissues.
•It serves as a biochemical medium and solvent as nutrients from the soil and some organic compounds move in solution from their site of uptake, production or storage, to sites of utilization.
•It is a chemical reactant or product in many metabolic processes, including photosynthesis, although relatively little water is actually consumed or produced in metabolism.
•Without cell turgor resulting from water movement into cells, young cells would not expand.
•Functioning of stomata and normal plant turgidity depend directly upon adequate amounts of http://www.hcs.ohio-state.edu/hcs200/water.htm (4 of 6) [10/08/2001 10:01:51 a.m.] •It is a coolant and temperature buffer (remember, water has a relatively high specific heat. The same phenomenon is responsible for the fact that sandy soils - with less pore space and moistureholding capacity - warm up faster in the spring and are ready to plant early).
The transpiration stream Review all pertinent material in the supplementary handout first.
When water is not limiting, the transpiration stream is controlled by the vapor pressure deficit (i.e., the
potential for water to vaporize into the atmosphere) at the leaf surface. Notice in the diagram below, that
the water potential of the atmosphere at 22°C and 50% relative humidity is around -100 MPa. Therefore,
it exerts a far greater pull on water than any other component of the continuum. The vapor pressure
deficit is -96 to -99 MPa. in this case
There is only one factor in the transpiration story that we have not mentioned yet. That is the
phenomenon of positive root pressure, a pushing force fueled by osmotic potential. When nutrients are
actively loaded into the xylem in the root, it creates a localized concentration of solutes greater than that
in the cortex or in the rest of the xylem system. Since the xylem sap in the roots have a greater
concentration of solutes than the rest of the system, there is an osmotic potential for these materials to
move out of the root zone to the aerial regions of the plant. This force is not nearly so large as that of the
typical vapor pressure deficit, but it is large enough in some species to cause xylem sap to exude from the
cut surface of a decapitated plant.
Transpiration rates are affected by irradiance, temperature, wind speed, soil moisture, relative humidityand other plant factors.
Water use efficiency Each crop and perhaps each cultivar has specific water requirements (Table 31-1). However, the amount
of water used is not necessarily useful information unless it is related to growth rate or yield. For
instance, a field of prickly pear cacti (Opuntia spp.) may use very little water over a season, but it also
adds biomass rather slowly when compared to corn, for instance. Transpiration ratio (one measure of
water use efficiency) expresses water use in terms of dry matter yield (Table 9-2). Notice that corn,
which was designated as a high water user in Table 31-1 has a relatively efficient transpiration ratio (i.e.,
it develops a fair amount of dry matter for the water it consumes.
http://www.hcs.ohio-state.edu/hcs200/water.htm (5 of 6) [10/08/2001 10:01:51 a.m.] No matter what the WUE a specific crop has, it can be grown most efficiently if all other factors ofproduction are in balance so that dry matter can be accumulated at optimum rates.
Agronomic/horticultural methods to conserve water.
The availability of water for plant use is obviously not evenly distributed in all agricultural areas. In areaswhere moisture is limiting, the following methods of conservation are often practiced.
•Use of arid-adapted (drought tolerant) crops - sorghum •Fallowing - cropping a field every other year allowing moisture to accumulate in off years.
CAREFUL- the dust bowl !!!!!!!! •No-till systems - crop residue reduces run off, evaporation and increases water infiltration •Mulches - can moderate soil temperature, control weeds, lower disease pressure, keep crops cleaner AND conserve water ---- but, they can be expensive. Organic vs. synthetic mulches.
•Use of any cropping system that reduces run-off and controls erosion (e.g., terracing). This promotes percolation of water into the soil http://www.hcs.ohio-state.edu/hcs200/water.htm (6 of 6) [10/08/2001 10:01:51 a.m.] Horticulture and Crop Science 200
Winter Quarter 2001 Lecture Topic 4C: Nutrients and Their Effect on Crop Growth
Text = Chapters 10 and 11 Hartmann, H.T., A.M. Kofranek, V.E. Rubatzky and W.J. Flocker. 1988. Plant science, growth,development and utilization of cultivated plants. Prentice Hall, Inc., Englewood Cliffs, NJ. = Chapter 9 Raven, P.H., R.F. Evert and S. E. Eichhorn. 1999. Biology of plants (6th Ed.). W.H. Freeman and Co.,New York, NY = Chapter 30.
Tisdale, S.L., W.L. Nelson, J.D. Beaton, and J.L. Havlin. 1993. Soil fertility and fertilizers (5th Ed.).
MacMillan Publ. Co., New, York, NY. = Chapters 1-6.
"Plant nutrition involves the uptake from the environment of all the raw materials required for essentialbiological and chemical processes, the distribution of these materials within the plant, and theirutilization in metabolism and growth." Raven et al., 1999.
http://www.hcs.ohio-state.edu/hcs200/nutrients1.htm (1 of 13) [10/08/2001 10:01:57 a.m.] Essential elements Soil fertility has been studied for at least 5000 years - a rich history of discovery •Greeks knew the value of adding materials such as animal waste (manure), green manure (crop residues) and certain inorganic salts such as saltpeter or nitre (KNO3) marl (dolomitic limestone)wood ash and other substances to soils in order to improve their fertility. They were also awarethat crop husbandry using such practices as tillage and crop rotation also improve plant growth.
Many of these practices were described fully by Theophrastus, a historian and philosopher.
The experimental approach to plant nutrition began during the Rennaisance. Philosophers of the timewere interested in identifying the "essence" of vegetation, of which they considered water, soil, saltpeterand air, likely candidates.
•Around 1600, Jan Baptiste Von Helmont conducted an experiment as follows: He planted a 5 lb.
willow sapling in 200 lbs of oven-dried soil held in a big tub. He then covered the tub so thatnothing could be added or taken away from the soil. He watered it solely with rainwater for aperiod of 5 years. At the end of this period, he disassembled his apparatus and reweighed the soiland tree. The tree now weighed 167 lbs and the soil weighed about 199 lbs and 14 oz (i.e., it hadlost only about 2 oz. in 5 years). From these results, he concluded water to be the principle ofvegetation. Of course he was not familiar with the importance of CO2 fixation by photosynthesisas it had yet to be discovered for about 200 years.
•Around 1760, Francis Home experimented with several different salts and discovered that all had an effect on crop growth.
•By 1840, oxygen, carbon dioxide had been discovered and the process of photosynthesis was understood at a rudimentary level. About that time, Justis Von Liebig published a treatise on crophusbandry in which he maintained the following; nitrogen could be garnered for the plant from soilor air, and that minerals were absorbed by roots from the soil solution. He further stated his law ofthe minimum-- ". By the deficiency or absence of one necessary constituent, all the others being present, the soil isrendered barren for all those crops to the life of which that one constituent is indispensable" In other words, crop growth requires several nutrients to be present at optimum levels to achieveoptimum growth and crop growth under limiting conditions will only proceed to the extent that the leastavailable element will allow.
http://www.hcs.ohio-state.edu/hcs200/nutrients1.htm (2 of 13) [10/08/2001 10:01:57 a.m.] •In 1939, Arnon and Stout published a paper in which they describe the concept of essential plant elements. For an element to be essential it must fit these three criteria: a) a given plant must not be able to complete its life cycle without it.
b) the function of the element must not be replaceable by another element.
c) the function of the element must be directly involved in plant structure (e.g., cell membranes) ormetabolism (e.g., an enzyme component or it must be required for a distinct metabolic step such as anenzyme reaction).
Some definitions and concepts •nutrition = supply and absorption of chemical compounds (ions) needed for growth and •nutrients = chemical compounds (ions) needed •metabolism = mechanism by which nutrients are converted to cellular material (energy and •nutrition and metabolism are related Table 30-1 lists seventeen essential elements in the relative order of their occurrence in plants. Thoseelements that are required in lesser amounts are called micronutrients whereas those required in greateramounts are called macronutrients. Notice that some essential elements are taken up by plants as cations,others as anions, others as both cations and anions (e.g., nitrogen) and still others as neutral molecules.
Note that elements not in this list may be essential for certain species (e.g. rice requires silicon for propergrowth and legumes require cobalt for symbiotic nitrogen fixation.
Table 30-2 lists some of the functions of essential elements as well as their deficiency symptoms.
http://www.hcs.ohio-state.edu/hcs200/nutrients1.htm (3 of 13) [10/08/2001 10:01:57 a.m.] Elements can be classified by function as follows; •elements involved primarily in structure or in major constituents = C, H, O, N, S, Ca •elements involved with energy transfer = P •elements involved in oxidation/reduction reactions = Fe, Cu, Zn, Mo •elements with diverse functions (e.g., K as an osmoregulator or Mn as an enzyme cofactor) Hidden hunger and the proactive approach to fertility management.
Figure 11-7 charts the relative growth and production of a crop as a function of nutrient availability. In
theory, an individual diagram such as this generic one might be created for each essential element using
data derived through experimentation with a given crop. When the concentration (availability) of an
essential element is low or very low, it is said to be in its deficiency range. Deficiencies will lead to poor
or sub-optimal performance and visible symptoms such as the interveinal chlorosis of leaves typical of
Fe deficiency and others. When the nutrient is readily available (i.e., not limiting) to the plant, it is said to
be in its optimum range. The range of concentrations than can be considered optimum varies
tremendously among species and among elements. For instance, nitrogen can be available over a wide
range of concentrations and still be considered optimal, but certainly some species are "happy" over a
wide range of N concentrations while others are more sensitive to variability in N concentration.
Likewise, N typically has a prolonged optimum range whereas certain micronutrients such as copper,
have a very narrow optimum range (i.e., just a few parts per million) between deficiency and toxicity
(i.e., decreased plant function or even plant death at high concentrations). Some elements may not result
in toxic reactions even when their concentrations are very high. However, however these high levels may
not result in better plant performance (i.e., plant growth has been "maxed out" by another limiting factor
such as water availability or photosynthetic capacity). When elements are available at levels above where
they result in increased plant performance, they are said to be in their luxury consumption range.
In terms of managing fertility, it might be important to know whether or not a nutrient was available in
its luxury consumption range so that the expenditure of additional funds and effort to apply fertilizer
containing the element might be avoided. However, a more critical situation for fertility management is
that of hidden hunger (i.e., the nutrient is available at near optimum range, but it is still deficient).
Hidden hunger results in decreased growth and performance but usually does not result in visual
symptoms. Yields will be perhaps adequate, but not optimum under these conditions.
In order to combat hidden hunger, it is necessary to take a proactive approach to fertility management.
http://www.hcs.ohio-state.edu/hcs200/nutrients1.htm (4 of 13) [10/08/2001 10:01:57 a.m.] Because visual symptoms are absent or hard to recognize, the only way to detect nutrient concentrationsin the hidden hunger range is to submit periodic samples of the soil and of the crop foliage for nutrientanalysis by a competent public or private laboratory. Soil tests are usually conducted prior to planting acrop and periodically thereafter. Tissue samples should be tested periodically as well, becauseavailability in the soil or medium does not insure that the plant will be able to assimilate it. For instancethe soil could contain adequate levels of Fe, but if the pH is near neutrality, plants may not be able totake it up. Recommendations for soil and tissue testing are crop specific. Consult State CooperativeExtension information or information from individual labs about the correct timing and protocols forthese tests. Most crops won't require more than one soil and one tissue test per year for adequate fertilitymanagement. However, some high value crops and greenhouse grown crops are monitored much moreclosely (perhaps even continuously with the aid of computer-controlled nutrient delivery systems).
The soil as the source for mineral elements Mineral elements ultimately available for plant growth are found in two soil components •The soil solution = dissolved (ionized) salts in matric water. The soil solution may also contain water soluble organic substances from biological sources (e.g., sugars from a near by root).
•Soil colloids = amorphous solids which are dispersed in the soil solution. The two types of colloids that are important to plant nutrition are clay and highly decomposed organic matter
particles called humus. For a visual image of what colloid suspensions (dispersions) are like,
consider catsup -- catsup has particulate tomato matter that is dispersed or suspended within a
liquid medium. Repelling forces keep particulate material from "settling out" (see discussion
below) without the addition of force such as centrifugation.
Properties of soil colloids •They are small - usually about 2 microns in diameter •Like other small spherical objects, they exhibit a high surface to volume ratio •They have a net charge (dependent on the colloid type, but mostly negatively charged) Negative charges on clay colloids result from isomorphous substitution of elements within the claycrystalline lattice (e.g., Al+3 ions are replaced by Mg+2 ions) or from fracturing of clay colloids resultingin localized cation deficiencies within the crystalline lattice. Note: some clays that are highly weathered(oxidized) actually exhibit a positive charge. The negative charge on organic matter particles results fromionization of organic acid groups associated with humic acids http://www.hcs.ohio-state.edu/hcs200/nutrients1.htm (5 of 13) [10/08/2001 10:01:57 a.m.] •They are dispersable in aqueous media. In order to maintain a colloidal dispersion, it is necessary for colloids to repel one another. Otherwise they would coalecse into larger units and fall out ofthe suspension. As most soil colloids are negatively charged, they naturally repel each other. Thepolar nature of water molecules helps keep them apart as well. The partially positive end of eachsurrounding water molecule associate loosely with the colloid (i.e., they are drawn electrically bythe negative charge) whereas the partially negative oxygen end of the water molecule extends outinto solution. Thus the oxygen atoms of water surround the colloids with an additional negativecharge.
Cation Exchange Capacity (CEC)
Clay and organic colloids act as a "bank account" for cationic nutrients. Just as water molecules can beloosely associated with negatively charged soil colloids, it is electrically favorable for cationic nutrientsto be loosely held as well (Figure 2.2). However, these cations are not irreversibly bound and free ions inthe soil solution can be "exchanged" for those that are bound. Consider the two K+ ions in the diagram.
As these cations in free solution move toward the colloidal surface, the colloid's pull on them increases(Figure 2.1) and when they are sufficiently close, it is possible for them to "dislodge" a Ca++ ion whichhad associated with the colloid previously. Following this exchange, the K+ ions are now loosely boundand the Ca ++ ion is now in free solution.
"Cation exchange is important because the exchangeable ions (those held on the exchange complex)
are (1) available to plants, supplementing the small quantity in solution, and are (2) retained in soils and
not lost with leaching water."
Rules governing the cation exchange process •the outgoing charge must match the incoming charge (e.g., it takes two K+ ions to dislodge one •cations of higher charge are more tighly held and are harder to replace •among cations of the same charge, those with smaller hydrated sizes are held more tightly (see •even though the hydrated size of H+ is large, it is generally tightly held.
Cation Exchange Capacity (CEC) = the number of moles of exchangeable charge held by a Kg of soil.
http://www.hcs.ohio-state.edu/hcs200/nutrients1.htm (6 of 13) [10/08/2001 10:01:57 a.m.] Note this is measured as charges not as atoms.
If a Kg of soil had a CEC = 1, it could potentially hold a mole (6.02 X 1023) of potassium ions as theyeach would only require one of the colloid's charges. As the gram molecular weight of K is 39, it meansthat this Kg of soil could retain 39 grams of K.
However, this same Kg of soil could only hold ½ mole of Ca ++ ions because each ion would take up twonegative charge sites on the colloid. Thus, since the gram molecular weight of Ca is 40, it means that thisKg of soil could retain 20 g of Ca.
Lastly, for the same reasons, only 27 g of Al+3 could be held on this Kg. of soil even though aluminumweighs 81 g/mole.
Other factors that affect soil fertility pH = log 1/[H+]. The pH scale is based upon the fact that pure H2O at 25°C dissociates into OH-1(hydroxyl ion) and H3O+ (hydronium ion) at an equilibrium frequency of 10-7. Since pure water isassumed to be neither acidic or basic, plugging this into the equation defines pH 7 as being neutral.
Effect of pH on cation exchange site occupancy pH primarily affects soil fertility by affecting the ease at which cations can be released from cationexchange sites on colloids, and thus, their relative concentration in the soil solution (see figures 1-3 onthe following page of your handout).
Since the beginning of the 20th Century, soil scientists have been studying the effect of pH on theavailability of nutrients in various mineral soils (soils that typically contain 2% or less decomposed http://www.hcs.ohio-state.edu/hcs200/nutrients1.htm (7 of 13) [10/08/2001 10:01:57 a.m.] organic matter). Although nutrient behavior is somewhat different in each soil type, the body of work
taken as a whole has resulted in the classic diagram shown in Fig. 1 (bottom right). Notice that as the soil
becomes more acid, the availability of N, P, K, S, Ca, Mg, and Mo drops off. Conversely, in basic soils,
N, P, Fe, Mn, B, Cu and Zn are less available. Therefore, the best "window of nutrient availability" in
these soils is at pH 6.5-6.8.
Similarly, pH effects on nutrient availability in organic field soils (muck soils containing @ 30% organic
matter) have been studied. The average findings of these studies resulted in the diagram depicted in Fig.
2 (top right) In general the pattern is similar to that for mineral soils. However, differences do occur
because the functioning of cation exchange in organic matter is different than in silicate clays. The
relative mix of cations occupying the cation exchange sites of clays is affected by the number of
hydrogen ions in solution, but the the CEC (number of cation exchange sites) will not change.
Conversely in organic soils, as the negative charge of organic material is dependent upon the ionization
of organic acid moieties, both the relative mix and the CEC will be altered by pH. As pH gets lower (i.e.,
hydrogen ion concentration gets higher), these organic acid moieties will not be ionized and will
therefore cease to be a cation exchange site until the acidity of the soil is neutralized. Therefore, the best
"window of availability" for this soil type is from pH 5.5-5.8.
At some point during your careers, you will likely use soil-less mixes (Pro Mix, Metro Mix and others)for greenhouse culture. As the name implies, these products do not contain soil; rather, they areessentially products made of nutrient fortified peat moss supplemented with horticultural texurizingagents such as vermiculite, perlite, sand and composted bark. Aside from the slight nutrient-holdingcapacity of vermiculite, the peat moss and composted barks in these mixes serve as the primary CE sites.
For reasons stated above, the window of availability for peat-based soil-less mixes is very different fromthat of mineral field soils John Peterson, an ex-OSU professor of floriculture, designed a study to determine the best window ofavailability in Metro Mix. He adjusted the pH of this material pots to range from pH 4.3 to 7.8 usingFeSO4 or Ca(OH)2, added fertilizers, then after an incubation period, he examined the leachates frompots at various pHs to determine the availiability of nutrients. The results of his study were summarizedin Fig 3; details can be obtained by reading the article passed out in class. Data on Mg and Mn wereparticularly interesting.
http://www.hcs.ohio-state.edu/hcs200/nutrients1.htm (8 of 13) [10/08/2001 10:01:57 a.m.] Essentially, he found the best window of availability to be from pH 5.2-5.5.
Effect of pH on base saturation The base saturation of a given soil is a relative measure of its fertility which is determined primarily byclay type and amount and by soil pH. The term base saturation is defined as the % of CE sites held byCa, Mg and K. When the pH of the soil is decreased through the continual supplementation of crops withammoniacal fertilizers, acid rain (if it exists) or other means, the increased level of H+ ions causeexchange events to occur where H is adsorbed onto the CE site while a basic cation is released into thesoil solution. Once in the soil solution, these basic cations, if not immediately taken up by plants, aresubject to leaching.
Other effect of pH on soil fertility.
pH also effects the rate of irreversible binding to clays and the rate of release of toxic ions (e.g., Al-3 atlow pHs -- see table on left margin of lecture handout). pH also affects the activity of soilmicroorganisms (see supplemental handout on nitrogen fertility) REMEMBER, the optimum pH for growth and performance is crop-specific (Figure 16-2 located onpage of your class handout which follows pH availability diagrams) •Fertilizer regimes and leaching When a fertilizer such as NH4NO3 is added to the soil and subsequently enters the soil solution (afterdissolution), the soil solution concentration of NH + 4 will rise and by their shear abundance, will begin to replace ions currently held at cation exchange sites. One ion likely to be displaced by this process is K+.
If the soil were overfertilized with the nitrogen fertilizer, much of the potassium would enter the soilsolution and be subject (at risk) for leaching (percolating down through the soil beyond the reach of plant http://www.hcs.ohio-state.edu/hcs200/nutrients1.htm (9 of 13) [10/08/2001 10:01:57 a.m.] The area just surrounding the root is called the root rhizosphere. In this area, soil bacteria, beneficial
fungi, roots and other organisms secrete compounds (e.g. phytic acid) which affect (either positively or
negatively) the plant's ability to absorb nutrients. Our time will not permit much exploration of this
fascinating subject.
Movement of nutrients from the soil solution to the root zone by contact exchange, mass flow, and diffusion (see supplementary handout).
Ion absorption by the root.
Root structure and development were thoroughly handled in Section 3, so only a brief "refresher"treatment of the subject will be offered here. Remember that the developing root has an apical meristemthat is protected by a root cap. The apical meristem gives rise to developing tissue groups whicheventually differentiate and begin to function in the process of nutrient uptake. As you might expect,most nutrient uptake is accomplished by young roots rather than those with secondary growth. However,nutrient uptake does not typically begin in root tissues until the vascular system is completelydifferentiated (Figures 4-2 and 4-3). Wiebe did an experiment where he fed radioactive 32P to variousregions of young developing barley roots. He noticed that radioactive material would accumulate evenright near the meristematic region, but it would not translocate out of the area until xylem and phloemmember were completely differentiated.
As we discussed earlier as well, the soil solution more or less has free access to the apoplastic regions ofthe root cortex (i.e. apoplastic regions = cell walls and intercellular spaces; the apoplast stops at the cellmembrane). Following the fate of an individual nutrient molecule (e.g., K+) which has entered theapoplast, one might see -- a) the K+ remains in the apoplastic region of the root cortex and perhapsbecomes loosely associated with (attracted to) a negatively charged cell wall component; b) the K+eventually migrates out of the apoplast and back into the soil solution at large; c) the K+ is taken upthrough a root hair, epidermal or cortical cell and is moved through plasmodesmata (intercellularconnections) toward the vascular system at the center of the root --- in order to do this, it must passthrough an endodermal cell prior to its entry into the vascular system (i.e., remember the function of theCasparian strip); and d) it might get taken up directly into a endodermal cell.
THE TAKE HOME MESSAGE is that in order for nutrients to be absorbed into the plant, they must http://www.hcs.ohio-state.edu/hcs200/nutrients1.htm (10 of 13) [10/08/2001 10:01:57 a.m.] cross the semi-permeable membrane of a living cell. This will have its consequences - see below Active and passive assimilation of nutrients.
The fact that nutrients must pass through at least one living endodermis cell prior to xylem loading offersthe possibility of both active and passive uptake (i.e., active uptake can only occur in living cells.
Hoagland (a very famous plant nutritionist) demonstrated active movement of nutrients accross cell
membranes using two different species of algae: Nitella, a fresh water alga and Valonia, a salt water alga
(Table 2.1). Notice that in both algae the concentration of K+ is far greater in the cell sap than it is in the
surrounding water indicating movement against a concentration gradient (a dead give-away for active
transport). Notice also that Valonia appears to be actively excluding Na+ from its cell sap, as the
concentration in sea water is 5X the concentration inside the cell. If only passive systems were at work,
these concentrations would be nearly equal. From this table we can infer that for at least some nutrients,
uptake is selective and that it occurs against a concentration gradient.
In another experiment depicting active transport of K+, plants were placed in a nutrient solutions that
were optimal for uptake or were sub-optimal due to lack of aeration, low temperatures or denatured
(non-functional) enzymes (i.e., metabolism in general and specifically ATP metabolism was restricted.
Under optimal conditions, there was an immediate rise in the K+ concentration representing free
movement into the apoplastic regions of the epidermis and cortex of the root. Thereafter, uptake occurred
at a constant rate (i.e., enzymes responsible for active uptake were working at capacity). At the time
indicated by the arrow, the plant was removed from nutrient solution and placed in distilled water.
Thereafter, there was an immediate loss of K+ as that which was still in the apoplastic regions diffused
out into the distilled water medium. Under sub-optimal conditions, movement into the apoplast was again
evident. However, there was no uptake of K+ into the plant and when it was returned to the distilled
water, the efflux (outflow) of nutrient from the apoplast to the surrounding medium was equal to that
which had entered the apoplast at the beginning of the experiment. In another trial, these authors also
showed that Ca++ was a necessary component of this system. From these trials we can determine that
active uptake is irreversible and that it requires energy, enzymatic activity and functional
membranes in order for it to occur.
Actually both active and passive uptake of nutrients occurs in plants. The conditions necessary forpassive uptake or diffusion of cations are actually set up through active processes (see below). In general,passive uptake of cations will occur under two conditions: a) there is a favorable chemical gradient whereconcentrations of cations are greater outside the cell than inside the cell, or b) there is a favorableelectrical gradient, i.e., a negative charge on the inside of the cell, which causes movement of positive http://www.hcs.ohio-state.edu/hcs200/nutrients1.htm (11 of 13) [10/08/2001 10:01:57 a.m.] charges from outside to inside the cell. In actuality, condition "a" is often not met -- the concentration ofcations inside the cell is almost always greater inside the cell than it is on the outside of the cell. In thiscase, if cations are going to continue to move into the cell, the cell's electrical gradient (negative charge)must be great enough to offset the unfavorable chemical gradient.
How does the cell maintain its negative charge? -- through the active excretion of H+ ions via a "protonpump". Proton pumps utilize the enzyme ATPase in order to cleave the terminal high energy phosphatebond of ATP to form ADP and both H+ and OH-1 ions. The H+ ions are secreted during the the formationof ADP whereas the OH-1 ions are secreted using a separate carrier protein that imports divalent anionssuch as SO -2 4 . Therefore the net result of each ATP expenditure is the increase of one negative charge on the inside of the cell. The inside of cortical cells usually maintain a negative charge of -70 to -150millivolts, which is enough to insure the passive uptake of cations.
Movement of ions in the xylem and the phloem.
•Ion transport in the xylem is primarily a function of mass flow. That is ions are more or less carried along with the movement of water during the process of transpiration (see water notes).
Therefore, nutrients in the xylem move primarily from the root to the leaves at a rate that isdetermined by the "tug of war" between the water potential of the soil and the vapor pressuredeficit at the leaf surface. Additional factors that effect ion movement in the xylem include:possible transient association of cations with organic acid ions which are structurally part of thecell wall; the size and the age of the plant (primary vs. secondary growth); and the time of day.
•Ion transport in the phloem is bidirectional from a source to a sink and its rate is determined primarily by sink strength. The phloem is rich in most nutrients except perhaps, calcium (Table
3.8). Inputs into this phloem ion pool come from two primary sources - roots and senescent leaves
- although some materials flow directly from the xylem to the phloem through parenchymatous
vascular rays in some species. Recipients of material from the phloem ion pool (sinks) include
shoot apices, developing leaves and developing fruit. Cations often move in the phloem as salts of
organic acids such as malate (Figure 3.10)
•Although the phloem sap is rich in many nutrients, nutrients are differentially mobile (i.e., it is easier to move some than others). Table 3.9 separates highly mobile nutrients such as K+ fromthose that are intermediately moveable such as Zn++, and from those that are immobile such asCa++. In particular, the immobility of calcium in the phloem causes severe calcium deficiencyproblems in fruit and other sinks under stress conditions (i.e., too cold, too hot, too dry, etc.).
Moreover, movement of calcium into sinks from the xylem is hampered by the unidirectionalmovement from roots to leaves (i.e., fruit don't transpire as much as leaves do). Perhaps the mostfamous of these nutritional deficiency diseases is tomato blossom end rot - similar diseases occurin many fruits and vegetable crops, but unfortunately, they all have different names.
http://www.hcs.ohio-state.edu/hcs200/nutrients1.htm (12 of 13) [10/08/2001 10:01:57 a.m.] •Not only are elements differentially moveable in the phloem, they are also differentially added to the phloem ion pool by senescent leaves. Some nutrients are remobilized easily in senescent leaveswhereas others that have become parts of cell structures or are covalently bonded in organicmolecules such as enzymes, are not readily remobilizable. Notice that remobilization of calcium, amajor constituent of cell walls and cell membranes, is almost nil.
•Differential mobility and moreover, differential remobilization have important consequences concerning nutrient deficiency diagnosis from visual symptoms (Table 6-5). Nutrients that are highmobile and remobilizable will become deficient in old leaves first as they sacrifice their nutrientcontent to supply developing sinks. Nutrients that are not mobile or remobilizable can not supplydeveloping sinks. Therefore in these cases, nutrient deficiencies will show first in developingleaves.
http://www.hcs.ohio-state.edu/hcs200/nutrients1.htm (13 of 13) [10/08/2001 10:01:57 a.m.] Horticulture and Crop Science 200
Winter Quarter 2001 Lecture Topic 4C (Continued: Nutrients and Their Effect on Crop Growth
Text = Chapters 10 and 11 Finck, A. 1982. Fertilizers and fertilization. Verlag Chemie., Deerfield Beach, FL.
Follet, R.H., L.S. Murphy and R.L. Donahue. 1981. Fertilizers and soil amendments. Prentice-Hall, Inc.,Englewood Cliffs, NJ.
Jones, U.S. 1982. Fertilizers and soil fertility. Reston Publ. Co., Reston, VA.
Marschner, H. 1986. Mineral nutrition of higher plants. Academic Press, NY.
Mengel, K., and E.A. Kirkby. 1987. Principles of plant nutrition. Int'l. Potash Inst., Berne, Switzerland.
Plaster, E.J. 1985. Soil science and management. Delmar Publ. Inc., Albany, NY.
Tisdale. S.L., and W.L. Nelson. 1975. Soil fertility and fertilizers. MacMillan Publ. Co., New York, NY.
http://www.hcs.ohio-state.edu/hcs200/nutrients2.htm (1 of 11) [10/08/2001 10:02:01 a.m.] *Handouts Have Individual Reference Lists "When the soil elements essential for efficient plant nutrition and economic production are low inavailability, or are not in balance, chemical fertilizers and soil amendments are required. The efficientuse of fertilizers and lime supplements the nutrient-supplying capacity of the soil minerals and soilorganic matter and decreases specific toxicities to achieve optimum agronomic and economic plantnutrition and production (Follet et al., 1981) Nutrient Cycles and Their Relevance to Plant Nutrition - Please refer to handout on nitrogen cycle as an example.
As you study the nitrogen cycle in the handout, pay attention to the factors that affect nitrogenavailability to plants. Understand how NH + 4 is converted to NO3 in the soil.
Fertilizer programs A. Program objectives http://www.hcs.ohio-state.edu/hcs200/nutrients2.htm (2 of 11) [10/08/2001 10:02:01 a.m.] Supply necessary nutrients Nutrient requirments are crop-specific and in some cases, cultivar specific. Know whether thecrop/variety is a heavy user of nutrients.
Available nutrient levels are dependent on soil interactions. For instance, for nutrients subject to leachingsuch as nitrogen, experts may recommend much higher levels of supplemental N fertilizers for cropsgrown in sandy soils than for crops grown in heavier soils.
Nutrient recommendations such as those found in Extension bulletins are general. Each cropping system
is unique. The only way to ensure that your crop is adequately nurished, is to adopt a PROACTIVE
APPROACH to nutritional management. Follow guidelines for periodic soil and tissue testing, then
provide supplements as suggested in test reports.
Balance nutrient supply and the cropping cycle Crops do not use inputs at a constant rate throughout the season. (I.e., some developmental activitiesrequire more input than others).
For example, if one were to optimize the available N for wheat throughout its cropping cycle, one wouldadd total N for the season at the following times: - 20% N applied at planting to stimulate early growth and tillering. Overall growth is important topromote flowering and eventual high grain yield. Likewise, yield is directly related to the number of seedheads (more tillers = more seed heads).
- 60% N applied during the period of stem elongation. This application adds to the development andweight of the shoot. Stem diameter and strength positively related to its resistance to lodging (fallingdown under the weight of the seed head). In addition, N during stem elongation increases storedcarbohydrates for use later by the developing inflorescence. (I.e., N at this time increases the # ofseeds/head and the wt./seed).
http://www.hcs.ohio-state.edu/hcs200/nutrients2.htm (3 of 11) [10/08/2001 10:02:01 a.m.] - 20% N applied at flagleaf stage (just prior to flowering). This application stimulates grain filling(wt./seed) and may increase overall protein content within the seed.
B. Types of fertilizers and their methods of application See self-explanatory diagram from p. 2 of notes.
Fertilizer formulations often express the level of N, P, and K as a series of numbers - for example, 5-10-5. The first number, 5-10-5 is straight forward - it indicates that this fertilizer is 5% nitrogen by
weight. The second two designations, however, are not so easy to interpret directly. The 5-10-5 refers
to the percentage of phosphorus as expressed as phosphorus pentoxide (P2O5, the anhydrous form of
phosphoric acid) and the 5-10-5 refers to the percentage of potassium as expressed by potash (K2O, the
simplest oxide of potassium).
From a molecular weight standpoint: N = 14; O = 16; P = 31; K = 39 The phosphorus in P2O5 weighs 62 Therefore the percentage of phosphorus in P2O5 = 62/142 = 0.436 K2O weighs 39 + 39 + 16 = 94 The potassium in K2O weighs 78 Therefore the percentage of potassium in K2O = 78/94 = 0.830 http://www.hcs.ohio-state.edu/hcs200/nutrients2.htm (4 of 11) [10/08/2001 10:02:01 a.m.] Conversion formulas are as follows - % P2O5 (on bag) X 0.436 = % P % K2O (on bag) X 0.83 = % K High pressure liquids (Gasses) Materials such as anhydrous ammonia (a commonly used N fertilizer) are in a liquid state whenpressurized in a delivery tank, but vaporize (i.e., change to the gas state) when released into the soil.
NH3 is toxic to plants (especially to seeds) so these materials are typically applied prior to Because it is somewhat dangerous (i.e., its toxic to us too, its basicity causes irritation to eyes, lungsetc.), it is sometimes applied by a custom applicator. However, many Ohio farmers have the equipmentand expertise to do it themselves. You must be licensed or certified to do this.
The equipment used consists of a nurse tank, an applicator or injector which releases the liquid below thesoil surface, a means of filling the applicator from the nurse tank and a vehicle to pull the apparatus.
NH3 is applied by injecting it directly into the soil. Once in the soil, it rapidly undergoes this reaction NH3 + H2O ------- NH4OH (ammonium hydroxide) Therefore the pH of the soil rises drammatically to @ pH 9. Later by the action of nitrifying bacteria http://www.hcs.ohio-state.edu/hcs200/nutrients2.htm (5 of 11) [10/08/2001 10:02:01 a.m.] 3 is formed and the pH returns to near its pre-treated level.
The major advantage of this method of application is that the N can be very evenly distributed if appliedcorrectly.
The major disadvantage is that the material is subject to volatilization (i.e., escape into the atmosphere).
Volatilization is mimimized by good application technique and proper soil conditions (good tilth, noclods and a soil water potential near field capacity).
Spray applications Spray applications of liquid formulations are typically applied with "boom-type" sprayers. Liquidfertilizers are dissolved or dispersed in water and held in a pressurized tank equipped with an agitator.
The material is delivered to the soil surface from the tank through a nozzle.
Application efficiency is affected by the following: nozzle type, nozzle number, nozzle height, tractorspeed and speed consistency (pressure changes can occur when speed fluctuates), wind, soil/fieldconditions ("lumpiness") and accuracy of swath markings Spray applications of liquid formulations have the advantage over dry fertilizers in that they can be more
evenly applied to the soil. Applications may also be made in conjuction with other materials, but
CHECK TO MAKE SURE THAT THE MATERIALS COMBINED IN THE SAME TANK ARE
COMPATABLE!!!!!!!!!
The disadvantage of spray applications is that the water in which they are dissolved drastically increasesthe weight of material applied and thus transportation costs.
Fertigation (i.e., applying fertilizer through an irrigation system) can be accomplished using a number of http://www.hcs.ohio-state.edu/hcs200/nutrients2.htm (6 of 11) [10/08/2001 10:02:01 a.m.] delivery systems, but under field conditions, most typically using overhead irrigation or trickle irrigation.
In the plains states, approximately 60-70% of the overhead sprinkler systems supply N and othernutrients to growning crops.
Fertigation through trickle systems may even be more common.
The use of fertigation in greenhouse crops is also extremely common. Greenhouse fertigation systemsuse fertilizer injectors and are often automatic and under computer control.
The major advantage of a fertigation system is that the producer can provide nutrients at optimum levelsat all times. In other words, by applying nutrients repeatedly in small doses, allows the producer to"micro-manage" nutrients delivered to the plant and to increase or decrease dosages rather rapidly inresponse to environment or crop cycle. For instance strawberry growers in California and Florida applyN through the trickle system during vegetative periods and when berries are forming, but incrementallyreduce N levels as the berries ripen to prevent oversoftening. Because only small amounts of fertilizersare applied with each application, chance for fertilizer burn, nutrient costs, and leaching are allminimized. Fertigation systems can be used in hydroponic culture or with inert media (like rockwool)which eliminates soil or media variability.
The major disadvantages of a fertigation system is that they are expensive (high capital outlay forinjectors, filters, etc. and potentially increased maintenance costs). If water is not pure enough (e.g., pondwater used) or if the wrong fertilizers are combined, precipitates can form, clogging lines and sprinklerheads/emmitters. Clogs can also be caused by soil particles, slimes or bacteria. In the case of tricklefertigation, salts can build up in the wetting zone causing localized changes in pH and soil osmoticpotential. Perhaps most importantly, because nutrient levels are maintained at optimum levels throughfrequent application of fertilizers, fertilizer reserves are low or non-existent, which, in turn, makesmanagement of the system critical and management mistakes very costly.
Applying fertilizers to above ground portions of plants is an old technique. In 1789, Forsythe in Englandrubbed a mixture of manure, wood ashes, lime and urine onto the bark of young trees and noted that it http://www.hcs.ohio-state.edu/hcs200/nutrients2.htm (7 of 11) [10/08/2001 10:02:01 a.m.] stimulated their growth. Later, Griss (1844) published a report describing the benefits of foliarapplication of Fe sprays to relieve Fe chlorosis in tree species.
The advantages of foliar feeding include the following: Material can be applied locally to the organ inneed and conversely the fertilizer will only affect the plant in a localized area. There are no soilinteractions which may bind added nutrients making them unavailable. Plant response to foliar feeding israpid.
The disadvantages of foliar feeding are as follows: Only small quantities are absorbed through the leafcuticle. Therefore, the positive effects of the applied materials are short-lived. Frequent application canincrease overall costs of operation.
Foliar feeding is typically used only for high value crops. Specific uses include: Supplying micronutrients (B, Cu, Fe, Mn, Zn) to orchard crops Supplying micronutrients when soil interaction is a problem (e.g., micronutrient availability at high pH Supplying nutrients at critical times (e.g., spraying CaCl2 on apples just after petal fall to control corkspot (a fruit development disorder) or on ripening fruit to prevent bitter pit (a storage disorder).
Applying urea to a broad range of crops -- urea applied to the surface of the leaf is converted NH3 andCO2 by the enzyme urease NH3 is taken up in gas form and then immediately detoxified in the leaf Foliar feeding efficacy is dependent upon Uniform deposition on leaves. Surfactants or wetting agents are often used to improve dispersion of theaqueous mixture on the leaf cuticle (which repels water naturally).
Deposition on the underside of the leaf. Spraying the undersides of leaves with foliar-applied nutrientsallows for greater penetration and uptake as cuticle layers are not as thick and stomates are moreprevalent (usually) http://www.hcs.ohio-state.edu/hcs200/nutrients2.htm (8 of 11) [10/08/2001 10:02:01 a.m.] Leaf age - young leaves absorb more (as much as 2X) nutrients than older ones.
Environmental factors --- High light levels increase cuticle thickness and cut down on absorption.
Temperature and humidity should be moderate -- apply during the morning hours.
Species difference -- banana, coffee, apple and pear can be foliar fed. Stone fruits do not respond well Variety difference -- there is a five fold difference among apple cultivars in the efficacy of Ca treatmentsfor bitter pit.
Solid fertilizers Methods of application Broadcasting - the spreading of fertilizer evenly over the soil surface. Commonly a broadcast
application is followed by incorporation through disking or similar tillage treatments. This is perhaps the
most common fertilizer application technique. It is accomplished using commonly available equipment
and can be accomplished using various levels of technology (i.e., consider a homeowner spreading
fertilizer by hand). The techinque is also applicable for liquids and dispersibles. For annually seeded
crops, fertilizer is often broadcast prior to planting. When fertilizer is applied after the crop has emerged,
the process is called topdressing. Broadcast methods are also used with perennial crops.
The major advantages of the broadcast method are as follows: Application can be made rapidly.
Broadcasting is less labor and technology intensive than some other methods, Different fertilizers can beblended and then applied without precipitation concerns of liquid applications.
The major disadvantages of the broadcast method are as follows: The efficacy of treatment is dependenton the uniform application of material. Fertilizers must be dissolved in the soil solution before they areavailability for plants. If incorporation is not even, fertilizer burn may result.
http://www.hcs.ohio-state.edu/hcs200/nutrients2.htm (9 of 11) [10/08/2001 10:02:01 a.m.] Banding - Banding fertilizer is the localized placement of fertilizer beside or near plant roots. In annual
crops banding applications are often implemented as beds are seeded. Banding is commonly used to
apply P and sometimes K and micronutrients. Phosphorus moves very little in the soil so placement of P
applications in the vicinity of the root zone assures that it will be "mined" by the developing plant roots.
If fertilizer is banded after the crop is emerged, the process is called side dressing; if the fertilizer is
placed directly in the seed bed, the process is called pop-up. Pop up treatments typically contain N, P
and K nutrients at low application rates. Because of the danger of salt injury, only low salt index
fertilizers and no NH3 generating fertilizers are used.
The advantages of banding include the following: localized placement of fertilizer prevents losses due toleaching or fixation onto clay surfaces (irreversible binding). Less fertilizer is used. Fewer weedproblems develop as fertilizer is not generally spread throughout the field.
The disadvantage of banding is that concentrated applications can cause fertilizer burn.
Banding is used effectively in cold soils, wet soils, soils of low or high pH, soils that are low in soil Pand soils with high concentrations of Al or Fe Types of dry fertilizers Pulverized fertilizers - made from crushing fertilizers into a powder (i.e., powdered rocks); They aredusty and tend to absorb moisture which results in caking (e.g., rock phosphate) Granules - treated to obtain large evenly sized grains which resist moisture absorption. Granules usuallyspread easily but still contain fines which results in dust (e.g., ammonium sulfate) Prills - smooth, rounded, uniform and relatively dust free pellets. Prills are coated with diatomaceousearth (a silicate compound made from diatoms or plankton) to prevent caking and to facilitate pouring,flowing and spreading. (e.g., urea) Fritts - shattered glass containing approximately 3-6% fused mineral nutrients (Cu and other traceelements). A type of slow release fertilizer.
http://www.hcs.ohio-state.edu/hcs200/nutrients2.htm (10 of 11) [10/08/2001 10:02:01 a.m.] Chelated fertilizers - chelated fertilizers are composed of multivalent cations that are stabilized in the soilsolution through association with organic molecules (ligands). Chelate is derived from the greek wordchela which means claw. Chelation helps to offset the effects of media pH on nutrient binding and allowsnutrients to remain soluble when, if unprotected, they would adhere to soil colloids very tightly.
Iron and zinc are two micronutrients that are relatively unavailable at neutral pHs that are oftenformuated as chelated fertilizers. Their association with EDTA (ethylene diamine tetraacetic acid) andEDDHA (ethylene diaminedi-o-hydroxyphenylacetic acid), respective are shown in the lecture outlinealong with information about Fe availability in soils and characteristics of additional chelating agents.
Plants produce and exude their own chelating agents such as citrate and alpha keto gluconate which helpcycle nutrients from soil colloids.
Slow release fertilizers. Fertilizers formulated to release nutrients slowly and evenly over time (i.e., theyhave lasting residual effects). Because they release nutrients slowly, they have a low burn potential.
Typically they are very expensive.
There are several types of slow release fertilizers: 1) fertilizers that are released through biologicaldegradation of their coatings (e.g., UF) 2) fertilizers that are released as their coatings weather (e.g.,IBDU and sulfur-coated urea) 3) fertilizers that are covered with a semi-permeable or impermeableplastic coating (e.g., osmocote) 4) organic fertilizers.
http://www.hcs.ohio-state.edu/hcs200/nutrients2.htm (11 of 11) [10/08/2001 10:02:01 a.m.] Horticulture and Crop Science 200
Winter Quarter 2001
Additional Material 1: Plant cells, cellular components and selected tissues
We will not discuss the following information in class, but you should be familiar with it! Most of thismaterial you should have covered in high school or university biology classes. You can finddiagrams/illustrations of the plant cell, cell types, etc. in just about any botany, biology or plant sciencetexts. I will be glad to discuss it individually with you if you need help.
The plant cell
The cell is the basic unit of living matter; the plant cell is the basic structural and functional
(physiological) unit of the organism. All plant cells are similar in the early stages of their development,
but as they mature, they can become highly specialized -- leading to the tremendous diversity we see
(and perhaps take for granted) in the plant kingdom. Individual plants then are composed of highly
differentiated cells, each adding to the structure and function of their organ or tissue group. The study of
how these cells are differentiated and then organized in tissue groups or organs is called the study of
anatomy.
A typical vascular plant contains hundreds of billions of cells. A typical apple leaf alone is composed of
50 M cells. Plant cells also vary tremendously in size and shape (e.g., comparison of meristematic
parenchyma cells with xylem vessels or tracheids). Plant cells are differentiated from animal cells
because they have cell walls.
General features of eukaryotic cells
The eukaryotic cells of higher plants have defined nuclei. Eukaryotic cells are compartmentalized;individual compartments are called organelles (e.g., mitochondria, chloroplast, vacuoles) and theseentities are bound by membranes. The membranes typically exhibit biochemical functionality (i.e., theycontain membrane-bound enzymes which perform critical metabolic reactions).
Cell components (refer to any diagram of the plant cell in any text)
cell wall - cell walls provide protection, support and shape for each cell. Primary cell walls are composed
primarily of cellulose, an indigestible polymer of glucose (as opposed to starch, which is a digestible
polymer of glucose), hemicelluloses, polymers of xylose and other sugars) and pectins (polygalacturonic
acid). Primary cell walls are formed during the early stages of a cell's growth and therefore, must be
expandable (i.e., must be able to incorporate newly synthesized cell wall constituents during cell
http://www.hcs.ohio-state.edu/hcs200/notes/notes1.htm (1 of 5) [10/08/2001 10:02:04 a.m.] expansion). Secondary cell walls are synthesized inside the primary cell walls only after growth ceases;
they are not elastic so they add overall strength and protection to the cell . Secondary cell walls also
contain cellulose and other complex sugar-derived molecules, but in addition, they contain polyphenolic
materials called lignins. Lignins are incredibly durable compounds; they render the cell wall rigid.
protoplast - the protoplast is the "living" portion of the cell - it includes the plasma membrane, thecytoplasm and all organelles, etc. found inside the cell.
plasmalemma (cell membrane) - cell membranes are semipermeable guardians of what enters or leaves
the cell. They are composed primarily of phospholipids, and proteins in a somewhat complex structural
arrangement. See Raven et al., or any other text for a discussion of the Danielli-Davidson model of the
cell membrane and how it functions. Its fascinating!!
cytoplasm - Cytoplasm is the medium in which all cell solutes (e.g., sugars and proteins) are dissolvedand all cell particles (organelles, membranes etc.) are suspended. It is primarily composed of water, butbecause of all the material dissolved in it, it has a viscosity similar to raw egg (i.e., sort of slimy). Thecytoplasm is the site of many important metabolic reactions supporting cell/plant life. Organellemovement (which can be seen by microscopy) with this body is called cytoplasmic streaming.
vacuole - Vacuoles can be considered to be the cell's storage cupboard or perhaps its garbage dump, as itcontains primarily materials that are no longer needed, or in some cases, are detrimental to cell function.
The solution in the vacuole is often referred to as cell sap. Vacuoles, through their regulation of specificions, also regulate the pH of the cytoplasm (a very important function). The vacuoles of newly-formedcells are rather small and as the cell ages, these bodies coalesce to eventually form one body that fills up80-90% of a mature cell's volume. The membrane surrounding the vacuole is called the tonoplast.
nucleus- If vacuoles are the garbage dump, then the nucleus could be considered as the cell's brain. It is astructure which is bounded by a double membrane called the nuclear envelope. The liquid (gel-like)medium in the nucleus, called the nucleoplasm, is composed of chromatin (DNA, RNA and proteins).
Obviously, chromatin contains the genetic code which directs all cell activity. During replication, DNAis transcribed and the message is "copied" per se in the form of messenger RNA. More info below and inlater lectures.
nucleolus- The nucleus also houses one or more nucleoli, spherical bodies also composed of DNA, RNAand proteins, which are the sites of ribosome subunit synthesis.
endoplasmic reticulum- a long membranous network extending throughout much of the cytoplasm. TheER is a direct extension of the nuclear envelope and, therefore, is also a double membrane. It is veryimportant as a "highway" (sort of) for the transport of materials around the cell. It is extremely importantas the site of translation, or the reading of the genetic code (as messenger RNA) to form specific proteins(enzymes). Enzymes serve as templates enabling the cell to synthesize or degrade all biochemical entitiesas needed for cell growth and function. When ER is functioning as a site for enzyme synthesis, it is http://www.hcs.ohio-state.edu/hcs200/notes/notes1.htm (2 of 5) [10/08/2001 10:02:04 a.m.] associated with spherical particles called ribosomes (mostly ribosomal RNA and protein). Because theseparticles can be seen by microscope, ER associated with ribosomes is termed "rough ER" and ER withoutribosomes is "smooth ER".
ribosomes- Ribosomes are particles responsible for the reading of messenger RNA and for the translationof this message into functional enzymes. In other words, they're sort of like "work benches" where aminoacids (the building blocks of enzymes) are assembled into chains as dictated by the blueprints providedby messenger RNA. The amino acid pattern in the chain ultimately determines its three dimensionalstructure which allows the enzyme to function.
plastids - Plant cells may contain a number of double membrane-bound organelles called plastids. Theyvary in size, shape, structure and function. The typical plastids are chloroplasts (responsible for theprocess of photosynthesis), chromoplasts (storage of pigments) and leucoplasts (storage of starch) chloroplast- (refer to diagram 3.1 at bottom of Page 2 of the original handout). The chloroplast is the siteof photosynthesis. It can be estimated that in a single leaf cell could contain from 20 - 100 chloroplastsand that a cubic mm of leaf palisade could have 500K chloroplasts. Chloroplasts contain chlorophyll, thegreen pigment responsible for light energy harvest, but also contain carotenoid pigments as well. It is thelatter pigments that give leaves their typical fall color. Stroma, the liquid matrix of the chloroplast,contains the enzymes necessary for fixing CO2 , eventually forming glucose. Within the stroma, is anelaborate system of membranes, collectively called lamellae. These lamellae contain bound enzymesresponsible for many of the biochemical reactions of photosynthesis. Concentrated bundles or stacks oflamellae are called grana. Grana lamellae specifically hold the membrane-bound enzymes responsible forthe capture of light energy.
mitochondrion- Mitochondria are also composed of a semigel stroma rich in enzymes. They also containmembrane invaginations called cristae, which serve to drastically increase overall surface area in theorganelle. Mitochondria are the site of respiration, the chemical process which breaks down sugar andother fuels to form ATP and NADH. ATP is a molecule which stores and eventually transfers chemicalbonding energy during enzymatic reactions whereas NADH has a similar function, but involvingreducing equivalents (electrons).
NOTE: Most likely because they both evolved long ago from bacteria, chloroplasts and mitochondriaboth contain some DNA of their own. This DNA is not involved in the process of meiosis and istherefore only inherited maternally.
golgi apparatus (dictyosomes) - a network of highly polarized membranes which are involved insecretion (to vacuoles or outside of the cell). They also function in providing materials for both cell walland cell membrane synthesis.
Types of cells
http://www.hcs.ohio-state.edu/hcs200/notes/notes1.htm (3 of 5) [10/08/2001 10:02:04 a.m.] parenchyma - Parenchyma cells are thin-walled cells. Primary cell walls are the most prominent in thesecells, but occasionally, secondary cell walls are formed. They are usually polyhedral (many-sided) inshape and have large central vacuoles. They are found in abundance in younger tissues such asdeveloping leaves or fruit; their thin-walled nature allows for rapid enlargement. However, they are alsocommonly found throughout the plant in pith, vascular, cortical and epidermal tissue systems. They arehighly metabolic, performing a variety of functions throughout the plant, including photosynthesis.
collenchyma - Collenchyma cells are specialized parenchyma cells that function as support during theprimary growth phase of plants. For instance, the "strings" found in celery stalks are composed ofcollenchyma cells. These cells are typically "living" when they function in the plant.
sclerenchyma - Sclerenchyma cells are highly specialized cells which function primarily withoutprotoplasts (i.e., after they are dead) as cells which provide support, protection or a means to conductwater and nutrients . They have thick, heavily lignified secondary cell walls. Two subtypes ofsclerenchyma are fibers and sclerids. Fiber cells are highly elongated cells with tapering ends, usuallythey are arranged within the plant body in an overlapping manner which allows a plant to hold a stemerect or to manage a heavy seed-head. Sclerids are more polyhedral in shape and are usually used forprotection. Seed coats, nut shells, pits, etc., contain sclerids. The stone cells found in pears (the cells inthe fruit which give it a slightly gritty texture) are also sclerids.
Xylem and Phloem (see any plant science text for illustrations)
Xylem tissue is a complex tissue that essentially has the job of conducting water and dissolved mineralsto all regions of the plant. A typical xylem tissue has four types of cells: tracheids, vessel elements, fibersand parenchyma.
Tracheids and vessel elements are sclerenchymatic cells function only after the protoplast is dead. Theyare similar in function as they are the cells that conduct water & nutrients. Tracheids are long andtapered; water is conducted from one tracheid to another by passing through "pit pairs" or matching holesin adjacent cell walls. Vessel elements are similar except that they are somewhat shorter and they arearranged end to end in one long continuous column. As these cells die, their end walls disintegrate,leaving little to impede the flow of liquid through the vessel. Xylem fibers are very thick walledsclerenchymatic cells that function as support. They are perhaps, most like tracheids. They also lack afunctioning protoplast at maturity but have much fewer "pit pairs". Parenchyma cells in xylem are eitherarranged in vertical files or scattered. They are of course, living, and act as food storage sites and lateraltransport between xylem and phloem.
Phloem tissue is also complex; its primary function is to transport food (sugars) and other metabolitesthroughout the plant-- essentially moving it from leaves to other organs (stems, roots, fruit, etc.). Phloemhas essentially four types of cells: sieve cells, companion cells, fibers and parenchyma.
http://www.hcs.ohio-state.edu/hcs200/notes/notes1.htm (4 of 5) [10/08/2001 10:02:04 a.m.] Sieve cells are elongated thin-walled, large-vacuoled, parenchymatous cells with protoplasts that arepressed against the inner surface of the cell wall. Although they are living at maturity, the protoplastscontain no nuclei. In dicots, the sieve cells are positioned vertically to form sieve tubes; each sieve cell ina sieve tube is considered to be a sieve element or a sieve tube member. At each end of a sieve element isa porous sieve plate. During the working life of a sieve tube, these plates allow for the mixing ofcytoplasm from one sieve member to another, greatly facilitating the transport of materials throughoutthe plant. As this tube ages and eventually ceases to function, these sieve plates often get "plugged up"by deposits of callose, a carbohydrate polymer. Companion cells, found primarily in angiosperms, areliving and do contain nuclei. Their function is to regulate the metabolism of the enucleated sieve cells.
Fiber and parenchyma cells in phloem have the same function that they do in xylem.
http://www.hcs.ohio-state.edu/hcs200/notes/notes1.htm (5 of 5) [10/08/2001 10:02:04 a.m.] Untitled Document I. History of Agriculture
A. Agriculture developed through the domestication of : B. 10,000 years ago (Near East) C. plentiful wild fruits and nuts precluded domestication of these crops until later 8,000; 9,000 years ago in W. Hemisphere (Mexico and Peru) Squash, chili peppers, maize, and avocado Later beans, cotton, fruits II. Agriculture and Social Change
A. End of Nomadic Lifestyle In the book "Crops and Man" Jack Harlan describes the era before Agriculture as the "Golden Age". Hestudied existing hunting and gathering communities (Australia, southern Africa). Women and childrendid the gathering. Men past puberty did the hunting. Hunting is a high-risk, low return activity.
Gathering is a low-risk, high-return activity. Hunting was more for sport than necessity. The meatacquired through hunting was not necessary for nutrition but it did make the diet more interesting.
Everyone had more leisure time compared to the modern world. Hunters and gatherers have survived inareas where agriculture has been unable to penetrate.
B. Increase in population C. Concentration of populations in urban areas surrounded by rural areas (rural/urban interface) D. Fostered trade E. Fostered sedentary way of life F. Diets narrowed G. Led to work specialization H. Creation and accumulation of wealth I. Social distinctions increased J. Loss of appreciation for rural inhabitants K. Manufacturing launched http://www.hcs.ohio-state.edu/hcs200/notes1.html (1 of 7) [10/08/2001 10:02:08 a.m.] Untitled Document L. Back now to rethinking past 100 years.
The past 100 years have been the era of "scientific agriculture". Productivity increased dramatically,especially for major food crops like wheat, rice, and corn. Up until 1970 we relied on the use of externalinputs like inorganic fertilizers and pesticides. We are now concerned about the place and impact ofagricultural/horticultural activities on the world around us. Most of our newer research looks at methodsof maintaining productivity with reduced inputs and more accurate use of external inputs with the goalbeing more favorable effects of crop production and utilization on the environment.
Why do you think agriculture (agrarian) societies evolved from hunting gathering societies in spite ofsuch negatives as a narrower diet and less leisure time? Why do you think that agriculturists came to be looked upon as lower class citizens as agrarian societiesevolved into manufacturing societies? In other why words, why does it suck to be you and me sinceeveryone is this room has some interest in agriculture (even if it is only to pass this class to fulfill aGEC requirement)? Why do students with majors outside this college look at you funny when you haveto talk about your major/interests in classes across the river? III. What is a crop????
A. Plants grown and utilized by humans for economic gain B. Food, fiber, forage, forestry, ornamental, and recreational uses Agronomy " agros" and "nomos"; the science of crop production and soil management Horticulture ("hortus") the science of intense cultivation of plants Forestry ñ foris ñ the science of forest management and wood production IV. History of Crop Science
A. Earliest crop scientists were observers and selectors observed better growth of plants near water and waste heaps selected certain species for yield , usefulness, harvest predictability B. Followed by scientists studying ways to improve production Tillage (managing of soil in fields, landscape, athletic facilities for drainage, root and seedling growth, greenhouse; nursery soilless growing mixes) Planting (mechanization/automation; including seed drills, field transplanters for vegetable crops, greenhouse and nursery seeders and transplanters) http://www.hcs.ohio-state.edu/hcs200/notes1.html (2 of 7) [10/08/2001 10:02:08 a.m.] Untitled Document Cultivation (managing of growing crops; weed control in field crops, mowers, aerators, etc for landscapes and athletic facilities, energy intense greenhouse environmental control) Irrigation (fields (agronomic, horticulture, intensely managed forests, landscapes, athletic facilities, greenhouses, and nurseries) Harvest (combines, corn pickers, fruit and vegetable harvesting machines, mobile benches or conveyance systems in greenhouses and nurseries).
Storage (post-harvest handling); grain elevators, refrigerated storage/transport systems, fast transport systems, modified/controlled atmosphere storage, chemical preservatives Processing traditional uses of grains, legumes, fruits, vegetables and floral crops.
C. Today's scientists study integrated approaches to crop and environmental management Crop diversity - germplasm (gene) preservation, traditional breeding, biotechnology and gene Low-input/impact crop production - reducing chemical dependency [Bt crops, Round-up Ready ( crops, integrated pest/crop management (IPM/ICM) systems], more energy efficientenvironmental manipulation of greenhouses, low-till/no-till Environmental stewardship - reducing NO3- and pesticide run-off (fields, greenhouses/nurseries, athletic facilities), top-soil conservation, wildlife habitat on farms and golf courses, wetlandpreservations Value-added; ethanol, specially packaged foods, double-use floral crops, specialty wood products from formerly waste products, Flvr-Savr tomatoes, Lunaria (money plant) common gardenornamental now being cultivated and harvested for neuronic acid used in treatment of M.S. andpremature birth problems, Fiber (including wood products) Industrial; mainly replacements for petroleum products Lost medicine; ethanobotany http://www.hcs.ohio-state.edu/hcs200/notes1.html (3 of 7) [10/08/2001 10:02:08 a.m.] Untitled Document problem; large ecosystems difficult to maintain in small (often middle of crop lands) areas VI. Crops defined
A. Grains
Almost all are cereal grains in the Grass Family ( most common species grown) 1) most widely cultivated 2) primary human food grain in U.S.
3) winter vs. spring wheat a) winter wheat planted in the fall, germinates and overwinters as seedling, matures and produces seeds
in the summer, needs cold (vernalization) to become reproductive
b) spring wheat planted in spring, germinates in spring, produces seed in summer. No vernalization to
become reproductive
c) winter wheat grown where winters are mild enough to allow survival of seedlings (central U.S., westof Mississippi, (Eastern, Southeastern, and Pacific Northwest U.S bread, Spring wheat -- pastries, cookies, cakes pasta made from T. durum grown mainly in ND 1) Chief food of nearly world's population a) paddy. flooded during itís growing season
b) upland. can grow without standing water
3) 7-8% protein (amino acids - CarbonHydrogenOxygen +Nitrogen, Sulfur), 75-80% carbohydrates (CHO only) 4) Wild rice is different species (Zizania aquatica) and is native to N. America. Minnesota, S. Canadaprimary production areas.
http://www.hcs.ohio-state.edu/hcs200/notes1.html (4 of 7) [10/08/2001 10:02:08 a.m.] Untitled Document Corn (Zea mays)
1) Corn occupies acreage of wheat, worldwide production is equal to wheat 2) Leading US grain crop 3) 90% used for livestock feed b. silage
5) Human consumption: cereals, sweeteners, corn meal, starch, alcohols and spirits, popcorn, sweetcorn 6) Industrial uses: adhesives, plastics, laundry starch, gasohol, paints and millet
1) Diverse group used for cereals, syrups, forage, livestock feed, birdseed 2) Short growing season 3) Drought tolerant 4) Warm temperatures (Nebraska and Texas primarily) B. Pulse crops
1. Legumes with edible pods 2. Grown on less than 10% of non-forage cropland but extremely valuable as source of high qualityprotein and oil Soybean (Glycine max)
a. 2/3 world's production in US and Brazil b. less than 10% consumed by humans c. most processed for oil and high protein mean d. lack sulfur containing amino acids Peanuts (Arachis hypogea)
a. direct food source for oil and protein, contain all essential amino acids C. Oil, sugar, fiber, and pleasure crops
http://www.hcs.ohio-state.edu/hcs200/notes1.html (5 of 7) [10/08/2001 10:02:08 a.m.] Untitled Document 1. Oil, others
2. Sugar: sugar cane, sugarbeet, maple sap
3. FiberCannabis sativa), kenaf
4. Pleasure: tobacco , coffee, tea
D. Forages : plants that produce vegetative matter that is fed to animals either in a fresh or
preserved state
1. Grazed pasture or range 2. Harvested or gathered - preserved in dry form (15-20% H2O) preserved moist (40-55% moisture) under limited O2 (fermented)<BR> 3. World wide more land in forage than all other crop land combined 4. The value of forages is to support animals for human diet (milk and meat products) or pleasure(horses and other foraging pets).
E. Vegetables and fruits
1. Plant parts needing little or no processing to be consumed by humans (FL, CA, TX, AZ, SoutheastStates, NJ (Garden State), NY, OH, MI), , spinach), green beans, corn 2. Note: botanically speaking, a fruit is a fertilized and fully grown ovary. Tomatoes are technically afruit, as are beans, peas, etc. but we call them vegetables in everyday language (common vernacular).
F. Ornamental or recreational crops
1. Floral crops plants grown for the aesthetic appeal of their flowers and sold mainly for indoor use, e.g.
chrysanthemums, poinsettias, Easter lilies, 100's of others (FL, TX, CA, OH, MI) 2. Foliage crops plants grown for the aesthetic appeal of their leaves and sold mainly for indoor use, e.g.
pothos, ficus (same family as figs), spathyphyllum, many others (FL, TX, CA) 3. Landscape plants grown for aesthetic appeal of either flowers or foliage and intended for use asplantings outdoors in the landscape, e.g. ornamental trees and shrubs, annual bedding plants (100's ofspecies, perennial herbaceous plants 3. Turf: grasses grown and maintained for golf courses, athletic fields and landscapes.
Types of grasses used in turf applications: Bentgrass, Bermudagrass, Kentucky Bluegrass, Buffalo http://www.hcs.ohio-state.edu/hcs200/notes1.html (6 of 7) [10/08/2001 10:02:08 a.m.] Untitled Document http://www.hcs.ohio-state.edu/hcs200/notes1.html (7 of 7) [10/08/2001 10:02:08 a.m.] Introduction to Experimental Design Introduction to Experimental Design and
Data Analysis
How to study crop production
Studying improvement of crop production is not a simple task. Crops are rarely grown in isolated,
perfectly controlled environments. Rather, they are cultivated in the systems shaped by weather,
geological history of earth, human activities, and by other surrounding organisms. All these factors
affect crop development and yields. Therefore it is important to take them into consideration when
setting up the experiments and interpreting the experimental results.
The main objective of the lab portion of this course is to introduce you to the principles of
experimental design, collection of useful information (data), interpretation and analysis of experimental
data. Once you are comfortable with these techniques, you will be able to set up your own experiments
to test whether different treatments can increase crop yields.
This interactive website is designed to help you get acquainted with the experimental process.
Experiments on each website contain brief summaries of known information on the subject we are
about to investigate. Based on this information you can decide which unexplored phenomenon you and
your teammates would like to study in your experiment.
To help you prepare for more productive lab work, we have included pre-lab assignments. Please,
take your time to complete these assignments. It is always a good idea to prepare a flow chart of an
experiment that you are about to begin. In your flow chart, identify the hypothesis you want to test, the
independent and dependent variables and the control treatments.
Principles of Experimental Design
Before you start any experiment, identify the prediction (hypothesis) to be tested. Suppose, you have
decided to test whether a new fertilizer "WonderGro" really increases corn yields by 25% as the
manufacturer claims. The prediction you are about to test is:
Under field conditions, application of the WonderGro fertilizer at the rate of 500kilograms/hectare (446 lb/acre) increases grain yields of corn by 25%.
This statement anticipates the outcome a fertilizer application might have on crop yield. This statement
is called a hypothesis. A hypothesis should:
describe the conditions for conducting the experiment ( field conditions in our example); identify the dependent variable ( corn yield in our example); identify the independent variable ( fertilizer application); define what data will indicate a relationship between the variables ( predict what effect the independent variable will have on the dependent variable ( What are the variables in this experiment? The variable to be tested is the dependent variable. In
http://www.hcs.ohio-state.edu/hcs200/IntLab.html (1 of 4) [10/08/2001 10:02:13 a.m.] Introduction to Experimental Design other words, a dependent variable is the result observed in response to the independent variable. Grain
yield of corn depends on fertilizer application, therefore, in this example grain yield is a dependent
variable. Fertilizer application is an independent variable.
Are there any other variables in this experiment? Can history of the field (crop rotation, previous
herbicide application, field disease history, form of tillage, etc.) affect the dependent variable?
Unfortunately, yes. The variables that obscure the relationship between the independent and dependent
variables are known as confounding variables.
To reduce the effect of the confounding variables on the dependent variable, three important
experimental design principles are used: control, randomization and replication.
A control treatment elicits either no response or a highly predictable response, which serves as a
standard to compare with the results from other treatments in the experiment. To test the above
hypothesis one can set up the following treatments:
Control: no fertilizer applied
Treatment: Apply 500 kg/ha of the fertilizer.
Application of no fertilizer should result in a certain yield that could serve as a standard for
comparison with the yield of the Treatment. Even with the proper controls, confounding variables can
still greatly affect your experiment. Randomization and replication are the two techniques that further
minimize the obscuring effect of the confounding variables. Simply stated, randomization is using
chance to assign individual plants, seeds, etc., to the treatments, and assigning the treatments to
locations within the experimental area. Repeating the treatment at different locations or over time is
called replication. Often, 3-4 randomized replications are sufficient to generate reliable results from the
treatments. Although better in theory, ten replications may be too expensive and impractical for a
scientist to manage. An experiment that exceeds a scientist's resources (including labor, space and time)
is unlikely to succeed.
How to analyze data experimental data?
Upon completion of each experiment you will collect very valuable information. Now your goal is to
analyze this information critically, interpret, evaluate and present the data in order to decide whether the
data support or do not support the hypothesis you intended to test in the experiment.
Suppose you have completed the experiment described above. You have harvested from four
randomized plots:
Control: 40, 40, 40 and 40 bu/plot
Treatment:30, 50, 20 and 60 bu/plot
Both samples have the same mean value (40 bushels/plot), yet the yield in the Control is much less
variable than the yield from the Treatment. Listing only the average value omits an important
component of the data - the variance. The variance σ2 gives an indication of how variable your data
(note that the word "data" is plural) are from one observation to the next. You can calculate the variance
using the following formula:
where, N is the number of observations made (four in our example)
Xi is the value of the i-th observation, and
X is the mean value of all the observations made in the sample.
The standard deviation (SD) is the square root of the variance. Most
calculators and computer programs (Excel, Lotus 1,2,3) will calculate bothvariance and SD for you.
http://www.hcs.ohio-state.edu/hcs200/IntLab.html (2 of 4) [10/08/2001 10:02:13 a.m.] Introduction to Experimental Design Control: σ2 = ((40-40)2+(40-40)2+(40-40)2 +(40-40)2)/3 =0 (no variance)
SD = 0
Treatment: σ2=((30-40)2+(50-40)2+(20-40)2+(60-40)2)/3=333 (high variance)
SD = 18.25
In general, less variable data are more reliable. Higher values of SD often indicate that the effect of the
confounding variables was very significant, often even more significant than the effect of the
independent variable on the dependent variable.
What conclusions about the effect of the WonderGro application (independent variable) on the yield
(dependent variable) will you make based on the given information?
You can earn extra-points (up to 2 points per correct answer, counted toward your final lab grade) whenyou answer the following questions correctly. To receive credit, please E-mail your answers to 1. Suppose you wanted to investigate a manufacturer's claim that WonderGro performs better than acheaper leading fertilizer brand. What controls would you set up in this case? What would dependentand independent variables be in this experiment? 2. What factors might confound the results of an experiment conducted in a greenhouse? 3. Why are highly variable data less reliable? How can one decrease this variability? All materials on this website are for personal use only. Pictures, text or files cannot be legallyreproduced or duplicated in any form. For commercial or instructional use of this website or materialsfrom it, please contact Dr. P. McMahon or Max Teplitski.
Copyright by M.Teplitski and P.McMahon, 2000 For more information, email us at , . http://www.hcs.ohio-state.edu/hcs200/IntLab.html (3 of 4) [10/08/2001 10:02:13 a.m.] Introduction to Experimental Design http://www.hcs.ohio-state.edu/hcs200/IntLab.html (4 of 4) [10/08/2001 10:02:13 a.m.] It is hard to underestimate the importance of knowing how to identify plants. Each one of us can thinkof a few reasons why we need to be able to ID both crops and wild plant. It is easy to identify plantsusing special plant ID guides which require knowledge of basic identifying features of the plants. Toidentify a plant correctly, one has to describe form, shape, color, odor and arrangement of a plant'sleaves, flowers, fruits, stems and roots. Let's go over the most common nomenclature used to describeand identify plants.
What to look for to identify plants?
Leaf shape, size, color, odor, venation, pubescence -- all help to identify a plant
correctly. Most leaves consist of a blade (lamina) (1) with veins (2) in it. Leaves are
connected to the node by a short stalk, called "petiole" (3). You have noticed that the
ivy leaf (left) looks glossy because it is covered by a layer of cutin, a waxy substance
that protects leaves. Shapes of the leaf blades, presence of petioles and other features
differ between species. We will discuss these differences in a moment. Microscopicstructure and functions of leaf tissues, as well as leaf modifications will be discussed inthe upcoming labs.
Leaf shapes can greatly help in identifying plants. The two figures on the right illustrate15 most common leaf shapes: 1 - lobed leaf of , 2 - heart-shaped leaf of tallmorning glory, 3 - lanceolate leaf of lady's-thumb, 4 - linear leaf of fan-shaped leaf of Ginkgo biloba, 6 - arrowhead leaf of honeyvine milkweed, 7-spade-shaped leaf of buckwheat, 8 - star-shaped leaf of Japanese maple, 9 - pentagonalleaf of ivy, 10 - obovate leaf of crab apple, 11 - oblong leaf of sugar beet, 12 - ellipticleaf of tobacco, 13 - spoon-shaped leaf of Portulaca, 14 - ovate leaf of pigweed, 15 -rhombic leaf of lamb's- quarter. Here is an easy way to distinguish between ovate,obovate, elliptic and oblong leaf shapes: ovate leaves are slightly wider at the base (nearthe petiole), obovate leaves are somewhat wider at the top half of the leaf, elliptic leavesare the widest in the middle of the leaf, while oblong leaves are equally wide on the top,bottom and the middle of the leaf.
Leaves we have discussed above consist of only one leaf blade, - they are simple leaves.
On the right, there are three common "compound" leaves. Compound leaves consist of In pinnately compound leaves (rose, vetches and garden pea), leaflets occur along an extension of a
petiole called a rachis. If all leaflets arise from a common point (buckeye, Virginia creeper), it is a
palmate leaf. To distinguish between these two terms, it might help to remember that pinnae means
"feather" and palmae is Latin for "palm" . Trifoliate leaves (strawberry, clovers, beans) haved three
http://www.hcs.ohio-state.edu/hcs200/CrIDLab.html (1 of 5) [10/08/2001 10:02:41 a.m.] leaflets arising from a common point on a petiole.
Leaves vary in their venation, i.e. the pattern of leaf veins. Dicots usually have either
pinnate or palmate venation (left). In a pinnately veined leaf of sugar beet (1) there is
a main vein (the midrib), with secondary veins branching from it. Palmately veined leaf
has several veins which arise from the base of the blade. Corn leaf (3), like
almost all monocots, has parallel veins. Leaf of an ancient plant ginkgo (4) hasdichotomous leaf venation, with each vein branching in two smaller veins.
Pubescence (tiny hairs on different plant parts) can help to
distinguish between seedlings of alfalfa and clover, thyme and
mother-of-thyme, which otherwise are very much alike. On the left
are magnified leaves of mother-of-thyme, on the far left are
pubescent leaves of thyme.
Leaves are arranged in a specific manner on a plant. On a stem, leaves grow from nodes
(4). Nodes are spaced along stems, with internodes (5), spaces between nodes. There are
four main leaf arrangements: alternate, opposite, whorled and a rossette. Leaves of tomato
(on the right) are arranged alternately, with one leaf at each node.
In plants with oppositely-arranged laves (left), the two leaves at the
node are opposite from each other. Members of the Mint Family (sage,
basil, thyme, catnip, etc) characteristically have opposite leaves. Other
examples of oppositely arranged leaves include first, unifoliate leaves of
soybean, leaves of lilac, etc.
When there are three or more leaves arising from a node, leaves arearranged in a whorl (right).
Leaves of rosette. Rosette is a structure in which
leaves are arranged in a tight spiral on a short stem (dandelion, strawberry, etc). Members
of Mustard Family (cabbage, radish, wild mustard, etc), some members of Aster Family
(lettuce, daisies, etc), and Carrot Family (celery, anise, etc) spend part of their life cycle
as rosettes, and then "bolt" , i.e. produce long stems with flowers. Bolting is controlled by
a number of environmental conditions (daylength, temperature, light quality, etc).
Grasses have other morphological features that aide in plant identification. Below, is a diagram of agrass. http://www.hcs.ohio-state.edu/hcs200/CrIDLab.html (2 of 5) [10/08/2001 10:02:41 a.m.] Grass stems are called culms, they are usually hollow. Grass leaves (4)
are simple, linear with parallel veins. Leaves can be either folded at
growing point (D) or rolled (E). Grass leaves don't have petioles.
Lower part of a grass leaf that wraps around the culm is called a
"sheath. The place where sheath meets the blade is known as "collar".
At the collar, a grass leaf might have a ligule (1) which can be
membranous (B), or hairlike (C), in some grasses ligules are absent
(A). Some grass leaves have claw-like projections, known as auricles
(2). If auricles are present, they are either short, long, or clasping. On
the right is a micrograph of a barley collar. Barley has a membranous
ligule (1B) and clasping auricles (2).
Grasses can have three types of modified stems, shown on the grass diagram above.
tillers (5)
, secondary stems that arise from nodes at the base of the main stem, and are almost vertical in position; stolons (6)
, horizontal aboveground stems that can produce new plants from their nodes. Bermudagrass (as well as white clover and strawberries) propagate themselves with stolons; rhizomes (7
), horizontal underground stems that can produce new stems from their nodes.
Smooth bromegrass, Kentucky bluegrass and johnsongrass use rhizomes to propagate and storefood.
Grass flowers are arranged in compound inflorescences (3 on a grass diagram above). A"unit" of grass inflorescence is called a "spikelet". On the left is a spikelet of tall fescue.
Click on the image to learn more about spikelet anatomy.
Spikelets are usually arranged in spikes (wheat, rye, etc) or panicles (rice, fescue, oat,Kentucky bluegrass, etc).
Stems
Shape of a stem in cross section, color, modifications and pubescence can help in plant ID. Shape of
a stem in cross section may be round, flat, square or triangular. Most plants have round stems.
Members of the Mint family (coleus, peppermint, basil) have square stems. Sedges have distinguishing
triangular stems.
Roots
Most monocots have fibrous root system. Most dicots have a tap root system. Roots of legume may
also have root nodules, which are sites of nitrogen fixation. We will talk more about root and stem
anatomy and functions in the upcoming .
Flowers and inflorescences
http://www.hcs.ohio-state.edu/hcs200/CrIDLab.html (3 of 5) [10/08/2001 10:02:41 a.m.] As you recall from Plant Biology classes, no two plant species have identical flowers.
The number of flower parts is one of the major identifying characteristics of a plantfamily. Click here to review Sweet potato (left) and some other plants has single flower. Most plants have their smallflowers in inflorescences.Why do you think it is advantageous to a plant to have its smallflowers arranged in an inflorescence? Often it is hard to decide whether one is dealing with a single flower or aninflorescence. Roses, and peonies are single flowers. Sunflowers, daisies andchrysanthemums are actually inflorescences. The outer flowers of these inflorescencesare called "ray florets". The centers of these inflorescences are comprised of manysmall short disk flowers. Flowering structures of dogwood (right) and Poinsettia contain enlarged and brightly colored leaf structures called bracts. Actual flowers are small yellow. They are
arranged in an inflorescence surrounded by bracts.
Below are examples of some common inflorescences. spadix of
umbell of apple
head of daisy
spike of wheat
birch in a catkin
panicle of brome
The number of cotyledons in a seed will immediately steer you in a right direction when identifyingplants. As you remember, dicotyledonous plants have two cotyledons, while monocotyledonous plantshave only one. Seed size, color, shape, and presence of various decorations (hooks, wings, etc.) are alsovery helpful in plant identification. Grass fruits have many other characteristics that will help identifygrass grains.
http://www.hcs.ohio-state.edu/hcs200/CrIDLab.html (4 of 5) [10/08/2001 10:02:41 a.m.] 1. Choose 5 plants (crops or weeds) your group would like to describe.
2. Label five blank sheets of paper with the common names of the crop or weed you decided todescribe.
3. On the labeled sheet of paper, describe identifying features of the plant as thoroughly as possible. Use the following guide in your description:a) Leaves: shape, simple/compound, venation, color, odor, arrangement, pubescence, petiole (present orabsent). Describe shape of leaflets in compound leaves. In grasses describe ligules and auricles;b) Flowers: single or inflorescence, type of the inflorescence, color, odor. Count the number of flowerparts;c) Stem: shape, color, modifications (if present), pubescence; 4. Select a pot with two grass species (one of the grasses is a grain crop, the other is a weed common inthis area). Using the grass ID guide, decide which grass species are growing in the pot.
After class, turn in your work.
Materials on this website are for personal use only. Text or files cannot be legally reproduced orduplicated in any form. For commercial or instructional use of this website or materials from it, pleasecontact Dr. P. McMahon or Max Teplitski.
Copyright by M.Teplitski and P.McMahon, 1999 For additional information about the crops, click on their highlighted names http://www.hcs.ohio-state.edu/hcs200/CrIDLab.html (5 of 5) [10/08/2001 10:02:41 a.m.]

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