HORT 604
APPLIED PHYSIOLOGY OF
HORTICULTURAL CROPS
David Wm. Reed
Department of Horticultural Sciences
Colegio de Postgraduados
Campus Montecillo
Summer 2007
Table of
Contents
Topics Page
Plant Anatomy and Morphology 2
Hormones and Elicitor Molelules 15
The Genetic Basis of Life 24
Genetically Modified Organisms
(GMOs) or Transgenic Crops 30
Seed Germination, Dormancy and
Priming 33
Growth Kinetics 38
Source Sink Relations 44
Senescence and Post Harvest
Storage 50
Plant Anatomy
and Morphology
A horticulturist who does not know the basic anatomy of plants is like is like a nurse that does not know basic human anatomy. It could turn out to be down right uncomfortable where he/she sticks that thermometer! So we are going to take a tour of plant structure. A working knowledge of plant anatomy is absolutely essential in:
§ plant propagation: grafting, budding, division, cuttings, layering, tissue culture
§ pruning
§ making crosses in plant breeding
§ diagnosing plant disorders
Anatomy is very simply. Anatomists simply look at the outside and inside of plants and when they see distinctive structures they give them a name. At the whole plant level, plants are divided into four organs: The root, stem and leaf are vegetative organs, and the flower, and resultant fruit, is a reproductive organ.
Plant Organs
§ root
§ stem
§ leaf
§ flower
Each organ is composed of three tissue systems:
Tissue Systems
§ dermal tissue system
§ vascular tissue system
§ ground or fundamental tissue system
Each tissue system is composed of distinctive tissues (epidermis, periderm, xylem, phloem, cortex, pith and mesophyll), and tissues are in-turn composed of cells (parenchyma, collenchyma, sclerenchyma, and specialized cells such as trichomes, vessels, companion cells, laticifers, etc.).
Plants produce all these structures by growing from discrete clusters of dividing cells called meristems. Herbaceous tissue is growth in length from: 1) apical meristems, which occur at the end of every shoot and root, and 2) intercalary meristem at the base of grass leaves. Woody tissue is due to growth in diameter from: 1) vascular cambium, which produce secondary xylem (wood) and phloem, and 2) phellogen, which produces the periderm (bark).
Virtually all of the crops we grow in horticulture are monocots (linear leaves, ex. grasses, corn, dracaena, and palm), dicots (broad-leaved plants, ex. oak, lettuce, apple) or gymnosperms (leaves as needles and scales, ex. pine, juniper). The internal anatomy of monocots, dicots and gymnosperms are sometimes similar and sometimes different. Different types of plants are not like animals - all the tissues and organs are not always in the same location. Thus, one must know the basic anatomical similarities and differences of each, or else you are not going to know where to insert that thermometer - ouch!
Organs and Tissue Systems
Plants are composed of 3 vegetative organs and 1 reproductive organ.
Three tissue systems comprise each organ and are contiguous between each of the four organs.
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How Do Plants
Grow?
Meristems and Growth
Primary Growth - growth in length that gives rise to primary (herbaceous) tissues called the primary plant body.
2 -Types
apical meristem or apex - the growing points located at the tips of stems and roots
intercalary
meristem - the growth region
at the base of grass leaves which causes
leaves
to elongate.
Secondary Growth - growth in width or diameter which gives
rise to secondary (woody
or
corky) tissues called the secondary plant body.
lateral meristem - meristematic regions along the sides of stems and roots.
2
Types
vascular
cambium or cambium - gives rise to secondary xylem (wood) on the
inside
and phloem on the outside.
cork cambium or phellogen - gives rise to the periderm (bark).
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Stem Anatomy
Herbaceous Dicot or Gymnosperm - Primary
Growth
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(Fig. 16.1 from Esau 1960)
Stem Anatomy
Woody Dicot or Gymnosperm - Secondary
Growth
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(Plate 28 from Esau 1965)
Stem Anatomy
Herbaceous Monocot - Primary Growth
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(Plate 58 from Esau 1965, Fig. 17.8 from Esau 1960)
Root Anatomy
Herbaceous Dicot, Gymnosperm or Monocot - Primary Growth
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(Plate 84 & 86 from Esau 1965)
Root Anatomy
Woody Dicot or Gymnosperm - Secondary Growth
A woody dicot or gymnosperm root in secondary growth looks very similar to a stem in secondary growth. The tissue is more porous and less dense, and the periderm is thinner. Rings of xylem growth may not be as distinctive as occurs in stems. This is because roots of temperate plants do not posses a distinctive “rest” or “physiological dormancy” period during the winter as do buds and shoots. Root growth may occur whenever the soil moisture, fertility and temperature are favorable.
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(Fig.15.4 from Esau 1960)
Leaf Anatomy
Dicot
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(Plate 73 from Esau 1965)
Monocot
(Similar to dicot, except no palisade, mesophyll is all spongy parenchyma)
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(Fig. 19.6 from Esau 1960)
Leaf Anatomy
Gymnosperm
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(Plate 78 from Esau 1965)
SUMMARY OF ANATOMY – VEGETATIVE STRUCTURES
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MONOCOT |
DICOT |
GYMNOSPERM |
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STEM |
PRIMARY (herbaceous) GROWTH |
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SECONDARY (woody) GROWTH |
none |
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ROOT |
PRIMARY (herbaceous) GROWTH |
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SECONDARY (woody) GROWTH |
none |
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LEAF |
PRIMARY (herbaceous) GROWTH |
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SECONDARY (woody) GROWTH |
none |
none |
none |
FLOWER STRUCTURE
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FRUIT STRUCTURE
Example of a dry fruit Example
of a fleshy fruit
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SEED STRUCTURE
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Anatomical
Structure and Function
"Structure and function" is a term used when the anatomy of a plant part explains how it functions. Structure and function brings anatomy to the real world, and it is what makes anatomy exciting. We are going to take a close look at one of the most important structure function relationships in plants - translocation. The tissues responsible for long distance translocation in plants are xylem and phloem.
Xylem is composed dead, hollow cells with perforated walls. The xylem cells are called vessel elements or tracheids. . They are connected end to end and clustered side by side. They are like a cluster of leaky pipes with holes on all sides. If you took sewer drain field pipe and connected them end to end, and bundled many of them together side by side, you would have a perfect model of xylem. Xylem only flows up. All xylem is dead and the water is "passively" pulled up stems by transpiration of water from the leaves. It is like sucking water up a straw. In young tissue, these bundles of xylem cells occur inside the vascular bundles, which are the stringy tissue in herbaceous tissue (ex. veins in leaves). In woody plants, xylem is the wood. The sapwood is functional because the hollow xylem cells are open and water easily flows up the tubes. All the water flows up the sapwood. The heartwood is old clogged xylem, and does not translocate water, and thus is not functional. The heartwood is clogged with resins and tannins and this makes the heartwood both waterproof and prevents it from rotting.
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Phloem is composed of specialized cells that remain alive and "actively" translocate solutes (salts, sugars, metabolites, hormones, etc.) around plants. The phloem tissue is very concentrated in sugars, amino acids, and many nutrients. It is the phloem that sucking insect, such as aphids, puncture in order to feed on the sugar and nutrients... This is similar to a mosquito piercing your veins and arteries as a food source.
Phloem flows both up and down and all around. It is commonly stated that phloem flows down, but this is wrong. Phloem flows to where it is needed. Phloem flows from sources to sinks, which will be discussed next.
HORMONES AND ELICITOR MOLECULES
Hormone - an endogenous or naturally-occurring compound
that is produced or synthesized in one part of the plant and causes a change in
physiology, growth or development in another part of the plant; usually present
in very small quantities.
Elicitor Molecule - a compound which, when introduced in
small concentrations to a living cell system, initiates or improves the
biosynthesis of specific compounds; a
compound with hormone-like activity.
Growth Substance - all naturally-occurring or synthetically
produced compounds that affect the physiology, growth and development of
plants.
References
Plant Hormones and Elicitor Molecules
Classically, plants have been known to contain five hormones, which are auxin, cytokinin,
gibberellic acid, ethylene and abscisic acid.
Recently, other endogenous compounds have been shown to elicit
hormone-like reactions, which are brassinosteroids, jasmonic acid, salicylic
acid and polyamines. Some do not elevate
these to the status of one of the five classical hormones, so often they are
called elicitor molecules.
1) Auxin
2) Cytokinin
3) Gibberellic
Acid
4) Ethylene
5) Abscisic
Acid
6) Brassinosteroid
7) Jasmonic
Acid
8) Salicylic
Acid
9) Polyamines
AUXIN
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Naturally-Occurring |
Synthetic |
Structure |
Site of Production |
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indoleacetic acid (IAA) |
indolebutyric acid (IBA) naphthaleneacetic acid (NAA) 2,4-dichlorophenoxy-acetic acid (2,4-D) |
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shoot tips, embryos |
SYNTHESIS
tryptophan ® indoleacetic acid
TRANSPORT
· 3:1 basipetal transport
· primarily in phloem parenchyma
EFFECTS
1) Cell elongation - causes acid induced cell wall growth
2) Cell division - stimulates
3) Tropism - response of plants to environmental or physical stimuli.
a) phototropism - response to light
b) geotropism - response to gravity
c) thigmotropism - response to touch
4) Apical dominance - determined by correlative inhibition of apical bud, partly due to auxin produced
5) Sprout Inhibitors – retard basal branching.
6) Branch angle - causes wide branch angles
7) Fruit set - low concentrations stimulate
8) Fruit or flower thinning - high concentrations cause
9) Herbicides - 2,4-D at high concentrations
10) Adventitious root formation - a) stem and leaf cuttings
b) tissue culture
CYTOKININ
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Naturally-Occurring |
Synthetic |
Structure |
Site of Production |
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zeatin kinetin (not in plants) |
benzyladenine (BA) pyranylbenzyladenine (PBA) |
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root tips, embryos |
SYNTHESIS
adenine ® zeatin
TRANSPORT
· xylem transported, found in root exudates
·
primarily acropetal, but not necessarily polar
EFFECTS
1) Cell division -
stimulates cell division; named after cytokinesis
2) Nutrient mobilization - nutrients transported towards high cytokinin concentration.
3) Apical dominance - high cytokinin/low auxin may overcome apical dominance
4) Chlorophyll breakdown - decreases chlorophyll breakdown
5) Leaf Aging or abscission - may delay
6) Seed germination - may overcome dormancy or stimulate germination
7) Adventitious shoot formation - a) leaf and root cuttings
b) tissue culture
8) Root growth - may be inhibitory to root growth
GIBBERELLIC
ACID (GA)
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Naturally-Occurring |
Synthetic |
Structure |
Site of Production |
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over 50 |
none |
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shoot tips, root tips, embryos |
SYNTHESIS (see next page)
mevalonate ® farnesyl pyrophosphate ®
® geranylgeranyl pyrophosphate ® copalyl pyrophosphate® kaurene ® GA
growth retardants - chemicals that block synthesis of GA; most block the ring closure steps between geranylgeranyl pryophosphate ® copalyl pyrophosphate ® kaurene.
TRANSPORT
· no polarity
· in phloem or xylem
EFFECTS
1) Protein synthesis - triggers de novo synthesis of some proteins, ex. a-amylase.
2) Cell elongation - primary stimulus for cell elongation
3) Rosette or dwarf plants - lack of endogenous GA often contributes to decreased height.
4) Height control
· GA used to increase height
· growth retardants used to decrease height
5) Flowering
- may cause bolting in biennials
6) Fruit
size - increases size of seedless grapes
7) Bud dormancy - may overcome and substitute for cold treatment
8) Seed germination - may increase or speed up
9) Sex expression - favors staminate flower formation on monoecious plants
Biosynthetic Pathway of
Gibberellic Acid
(from

· block ring closure between geranylgeranyl pyrophosphate and copalyl pyrophosphate
· block ring closure between copalyl pyrophosphate and kaurene
ETHYLENE
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Naturally-Occurring |
Synthetic |
Structure |
Site of Production |
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ethylene |
ethephon or ethrel (release ethylene inside plant) |
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ripening fruits, aging flowers, germinating seeds, wounded tissue |
SYNTHESIS
methionine ® s-adenosylmethionine ® 1-aminocyclopropane-1-carboxylic acid ® ethylene
(SAM) (ACC)
ETHYLENE
INHIBITORS
ethylene inhibitors - chemicals that inhibit the synthesis or action of ethylene
Synthesis Inhibitors (block synthesis of
SAM ® ACC)
· AVG - aminoethoxyvinyl glycine
· MVG - methoxyvinyl glycine
· AOA - aminoacetic acid
Action Blockers (ethylene ® block action)
· STS - silver thiosulfate
· CO2 - carbon dioxide
· Ni - nickel
· Co – cobalt
· MCP – 1-mehtylcyclopropane
o it is a gas that can saturate the receptor sites, and block action for several days
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EthylBloc – commercial compound
TRANSPORT
· diffusion as a gas throughout plant (in and out)
EFFECTS
1) Auxin transport - alters basipetal transport
2) Membrane permeability - increases
3) Respiration - increases
4) Cell elongation – decreases
5) Aerenchyma formation – induces aerenchyma formation under anaerobic or hypoxic conditions (i.e. under low oxygen or flooded conditions)
6) Fruit ripening - stimulates in many fruits, ex. banana
7) Flowering - triggers flowering in some bromeliads, ex. pineapple
8) Flower fading - increases
9) Flower longevity - causes senescence (death) of cut flowers
10) Fruit color - decreases green, increases other colors
11) Seed germination - increases in some seeds
12) Leaf abscission (leaf drop) - causes in some plants
13) Leaf epinasty (curling and contortion or leaves) - causes in some plants
14) Sex expression - favors pistillate flower formation on monoecious plants
ABSCISIC
ACID (
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Naturally-Occurring |
Synthetic |
Structure |
Site of Production |
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abscisic acid |
none |
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plastids,
especially |
Historically also called:
abscisin - because early investigators found caused leaf abscission
dormin - because early investigators found caused dormancy
SYNTHESIS
mevalonate ®
farnesyl pyrophosphate ®
EFFECTS
1) Dormancy - causes bud or seed dormancy
2) Leaf abscission (leaf drop) - may cause in some plants
3) Stoma - causes stomata to close (a response to drought stress)
ELICITOR
MOLECULES
Brassinosteroid
Effects:
Jasmonic
Acid
Effects:
·
defense
mechanisms, promotes antifungal proteins
·
growth
inhibitor
·
inhibit
seed and pollen germination
·
promotes
curling of tendrils
·
induces
fruit ripening
Salicylic
Acid
Effects:
Polyamines
Effects:
(From http://generalhorticulture.tamu.edu) |
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Analogy
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DEFINITIONS Base Pairing of
Nucleic Acids between the double strands of DNA gene - a length of
DNA that codes for the production of a protein or protein subunit. |
The Central Dogma of
Molecular Biology
(From: http://www.accessexcellence.org)
Legend: 1. The DNA replicates its information in a process that involves many
enzymes: replication. 2. The DNA codes for the production of messenger RNA (mRNA) during transcription. 3. In eucaryotic cells, the mRNA is processed
(essentially by splicing) and migrates from the nucleus to the cytoplasm. 4. Messenger RNA carries coded information to ribosomes. The ribosomes
"read" this information and use it for protein synthesis. This
process is called translation. Proteins do not code for the production of protein, RNA or DNA. |
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Restriction Enzymes
Cut DNA at Specific Sequences
to Create
“Sticky Ends” (From: http://www.accessexcellence.org)
The EcoRI
restriction enzyme--the first restriction enzyme isolated from E. Coli
bacteria--is able to recognize the base sequence 5' GAATTC 3'. Restriction
enzymes cut each strand of DNA between the G and the A in this sequence. This
leaves "sticky ends" or single stranded overhangs of DNA. Each
single stranded overhang has the sequence 5" AATT 3'. These overhanging
ends will bond to a fragment of DNA which has the complementary sequence of
bases. See text of Background Paper for additional details. |
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(From: http://www.accessexcellence.org)
Process by which a plasmid is used to import recombinant DNA into a
host cell for cloning. The plasmid carrying genes for antibiotic resistance,
and a DNA strand, which contains the gene of interest, are both cut with the
same restriction
endonuclease. They have complementary "sticky ends." The opened
plasmid and the freed gene are mixed with DNA ligase, which reforms the
two pieces as recombinant DNA. This produces
recombinant Deaths recombinant DNA stew transforms a bacterial
culture, which is then exposed to antibiotics. All the cells except those
which have been encoded by the plasmid DNA recombinant are killed, leaving a
cell culture containing the desired recombinant DNA. DNA cloning allows a
copy of any specific part of a DNA (or RNA) sequence to be selected among
many others and produced in an unlimited amount. This technique is the first
stage of most of the genetic engineering experiments: production of DNA
libraries, PCR, DNA sequencing, et al.
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Using
restriction enzymes for Mapping or Finger Printing
When DNA from the same source is digested with a
particular restriction enzyme it will always give a set of the same sized
fragments. For example if lambda bacteriophage DNA is cut with EcoR1 we know
that it will give six fragments of the sizes: 21.23, 7.42, 5.8, 5.65,
4.87, 3.53 kbp. This is because, mutations apart, the phage sequence will
always be the same, and so EcoR1 cutting sites will always be present in the
same places. The fragments can be separated and their sizes determined by
agarose gel electrophoresis.
We can use the positions of restriction enzyme
sites as convenient markers along DNA sequences. The map obtained can be used
for DNA identification and to plan DNA manipulations.
Finger Printing
Gel
Showing Banding from use of Different Restriction Enzymes
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Genetically Modified Organisms (GMO) or
Transgenic Crops
(From: http://www.colostate.edu/programs/lifesciences/TransgenicCrops/index.html)
Authors: Pat Byrne, Sarah Ward, Judy Harrington, Lacy
Fuller (Web Master)
Crops
and acreage

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Transgenic crop production area by country (source: James, 2000b) |
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Country |
Area planted in 2000
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Crops grown |
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74.8 |
soybean, corn, cotton, canola |
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24.7 |
soybean, corn, cotton |
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7.4 |
soybean, corn, canola |
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1.2 |
cotton |
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0.5 |
corn, cotton |
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0.4 |
cotton |
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minor |
cotton |
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minor |
corn |
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minor |
soybean, potato |
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minor |
corn |
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minor |
corn |
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minor |
corn |
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minor |
soybean |
Widely Used
GMOs
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Worldwide
production area of transgenic crops – Traits (source: Science 286:1663, 1999). |
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Trait |
Area planted in 1999 (millions of acres) |
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Herbicide tolerance |
69.4 |
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Bt insect resistance |
22.0 |
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Bt + herbicide tolerance |
7.2 |
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Virus resistance |
0.3 |
Herbicide Tolerance Herbicide
tolerant crops resolve many of those problems because they include transgenes
providing tolerance to the herbicides Roundup® (chemical name:
glyphosate) or Liberty® (glufosinate). These herbicides are
broad-spectrum, meaning that they kill nearly all kinds of plants except
those that have the tolerance gene. Thus, a farmer can apply a single herbicide
to his fields of herbicide tolerant crops, and he can use Roundup and
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Weed-infested soybean plot (left) and Roundup Ready® soybeans after Roundup treatment. Source: Monsanto |
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Bt Insect-Resistant Crops
"Bt" is short for Bacillus thuringiensis, a soil bacterium whose spores contain a crystalline (Cry) protein. In the insect gut, the protein breaks down to release a toxin, known as a delta-endotoxin. This toxin binds to and creates pores in the intestinal lining, resulting in ion imbalance, paralysis of the digestive system, and after a few days, insect death.
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European corn borer
(left) and cotton bollworm (right) are two pests controlled by Bt corn and
cotton, respectively. |
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Bt insect-resistant crops currently on the market include
· Corn: primarily for control of European corn borer, but also corn earworm and Southwestern corn borer. Cotton: for control of tobacco budworm and cotton bollworm
· Potato: for control of Colorado potato beetle. Bt potato has been discontinued as a commercial product.
Papaya ringspot virus
Papaya is a tropical fruit rich in
Vitamins A and C, but susceptible to a number of serious pests and diseases.
The transgenic variety UH Rainbow, resistant to the papaya ringspot virus, is currently
in production in
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Papaya is an important source of vitamins in tropical areas. Source: USDA |
Risks And Concerns
(http://www.colostate.edu/programs/lifesciences/TransgenicCrops/risks.html)
The introduction of transgenic crops and foods into the existing food production system has generated a number of questions about possible negative consequences. People with concerns about this technology have reacted in many ways, from participating in letter-writing campaigns to demonstrating in the streets to vandalizing institutions where transgenic research is being conducted. What are the main concerns? What scientific support is there for these concerns?
Seed
Germination,
Dormancy and Priming
Terminology
pollination - deposition of pollen on the stigma of the
pistil.
fertilization - the union of male and female gamete
(nuclei, 1N) to produce zygote (2N).
double
fertilization - in higher plants only (angiosperms)
-
union of 1 1N male gamete with 1 1N female gamete (the egg) to
produce
a 2N zygote; and union of 1 1N male gamete with 2 1N
polar
nuclei to produce a 3N endosperm.
apomixis - development
of an embryo without fertilization; hence, it is not true sexual
propagation even
though it produces a seed.
parthenocarpy - development of fruit without seeds.
vivipary - germination of seeds inside the fruit
while still attached to the parent plant.
Seed
Dormancy Terminology
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Primary Dormancy |
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Old Term |
New Term |
Definition |
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Quiescence |
Ecodormancy |
Dormancy imposed by an external unfavorable environmental factor or external structure. Example: too dry, external hard seed coat |
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Correlative Inhibition |
Paradormancy |
Dormancy imposed by physiological factor external to the embryo. Example: inhibitors in testa or pericarp |
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Rest or Physiological Dormancy |
Endodormancy |
Dormancy imposed by a physiological factor internal to the embryo. Example: embryo rest |
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Secondary Dormancy |
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Photodormancy |
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Dormancy due to lack of light (red) in light requiring seeds. |
STAGES OF SEED GERMINATION
1st Stage
a) imbibition - initial absorption of
water to hydrate seed
b) activation of metabolism - increased
respiration and protein synthesis
2nd
Stage
a) digestion of stored food - for example,
starch to sugars in cotyledon or endosperm
b) translocation to embryo
3rd
Stage
a) cell division and continued growth and
development of seedling

SEED DORMANCY
CAUSED
BY TYPE DORMANCY HOW OVERCOME?
1) Dry
Seeds:
dehydration of seed quiescence sow in moist environment
2) Seed Coat Dormancy or Hardseededness:
hard seed coat impermeable quiescence scarification - physical or
to water and gases chemical
abrasion of seed coat.
3) Embryo Rest:
low growth promoters rest stratification - cold (35-40 oF
and/or high growth (or physiological moist storage for 4-12 weeks.
inhibitors in embryo dormancy)
4) Double Dormancy:
hard seed coat plus quiescence scarification then stratification
embryo rest and rest (or
physiological
dormancy)
5) Chemical Inhibitors:
inhibitors in pericarp (fruit correlative I) remove fleshy pericarp (fruit
wall) or testa (seed coat) inhibition wall) or testa (seed
coat).
2) leach in running water if
pericarp
or testa is dry.
6) Immature Embryo:
underdeveloped or developmental I) after ripening - store for 4-6 rudimentary embryo dormancy weeks
under ambient
conditions
2) warm stratification - warm moist storage.
3) embryo culture
7) Light
Requirement
phytochrome in Pr form secondary I) expose to any white light
dormancy 2) expose to red light
3) sow shallow or on surface
Seed Treatments to Enhance
Germination
Seed Priming
Seed
priming is a seed treatment that allows
imbibition and activation of the initial metabolic events associated with seed
germination, but prevents radicle emergence and growth. Obviously, seeds are tolerant of desiccation,
and even though during seed priming imbibition allows water uptake, the
tolerance to desiccation is not lost.
Thus, the seed can be dried again and stored. If the seeds are primed too long, desiccation
tolerance will be lost, and the seeds may loose viability upon re-drying. The secret to successful seed priming is to
stop the priming treatment at just the right time to allow re-drying.

The advantage of primed seed is that when the
primed seeds are planted their germination is faster and more uniform.

Types of
seed priming
1) Osmopriming (osmoconditioning):
This
is the most common technique used. The seeds are soaked in an osmotic solution
to allow imbibition and metabolic activation, but the osmotic conditions do not
allow expansion and growth of cells.
Osmotica used are: mannitol,
polyethyleneglycol (PEG) or salts such as KCl.
2) Hydropriming:
Imbibition is obtained by partially hydrated the seeds using a limited amount of water by exposing them to a limited amount of water, using very humid air or exposing them for a short time in warm water.
3) Matrix priming:
A solid, insoluble matrix is used to obtain a water solution with low water potential. The matrix potential keeps the water potential low. Vermiculite, diatomaceous earth or cross-linked highly water-absorbent polymers are used.
Hormone Treatments to Enhance Germination
Seeds of some species are very difficult and slow to germinate due to primary and secondary dormancy, the need for after ripening periods, immature embryos, etc. Many of the seeds respond to hormones to increase the speed of germination, uniformity of germination and/or percent germination. For example, the seeds of many tropical foliage plants are difficult to geminate, but respond to hormonal treatments. Hormones can also be added to seed priming treatments.
1) cytokinin – 100 to 200 mg/liter for a 12-24 hour soak.
2) gibberellic acid – 200 to 1,000 mg/liter fro 12-24 hour soak
GROWTH
KINETICS
Growth - an irreversible increase in size, mass or number.
Many growth phenomena in nature exhibit a logarithmic or exponential increase. The size, mass or number increases by a constant, similar to simple compound interest. The principal (current size, mass or number) times the interest rate (growth rate) yields the interest (growth increase for that day). The interest is added to the principal, to yield a new principal. The new principal times the interest rate yields and even higher interest for the next day, which again is added back to the principal. So growth occurs at a compounded rate (logarithmic or exponential growth).
Absolute Growth Rate (AGR)
If you plot growth (size, mass or number) versus time, a constantly increasing growth curve is obtained. If you calculate the slope between any two times, you get the absolute growth rate, which is the change in actual growth over time. You get a different slope, hence different AGR for each pair of times chosen to calculate the slope. (Fig. 2.23A, Wareing and Philips 1981)

Relative Growth Rate (RGR)
If you plot the logarithm of growth (size, mass or number) versus time, a linear line is obtained. If you calculate the slope of the line, you get the relative growth rate, which is the change in relative growth over time. Since the line is linear, you get the same RGR, regardless of which time interval chosen to calculate the slope. (Fig. 2.23A, Wareing and Philips 1981).

GROWTH KINETICS- con't
Sigmoidal Growth Curve
Exponential growth can never be sustained indefinitely. Eventually, substrates are depleted, the population exceeds the area available, tissues or individuals begin to die, etc., which decreases the growth rate. Growth may still increase, but at a reduced rate (ex. if crowding causes shading), it may reach a steady state (everything is in equilibrium, for example in a population), or growth may begin to decrease (ex. due to death or senescence of individuals or plant parts). If you plot long term growth versus time you get the classical sigmoidal growth curve. If you plot the logarithm of the sigmoidal growth curve, you get a linear line during the exponential phase, after which the curve decreases over time. (Fig. 2.24, Wareing and Philips 1981)
|
|
Changes In Growth Rates Over Time
If you calculate the absolute growth rate (AGR) over increments of time, then plot AGR versus the time interval, you get a bell-shaped curve, i.e. the AGR changes constantly with time. If you calculate the relative growth rate (RGR) over increments of time, then plot RGR versus the time interval, you get a straight-line region during the logarithmic phase followed by a decreasing RGR. The RGR is constant during the logarithmic phase. (Fig. 2.27, Wareing and Philips 1981).
|
|
MATHEMATICAL MODELS OF GROWTH

Linear Model – Used During Logarithmic or
Exponential Phase
ln n = ln no +
(slope) (time)
where n = number, size (height, leaf area), or mass (dry weight, fresh weight) at any time > 0.
no = number, size (height, leaf area,), or mass (dry weight, fresh weight) at time = 0.
slope = rate of growth
Or more commonly expressed as the slope
equation
y = a + bx
y = intercept + (slope) (x)
Absolute Growth Rate (AGR)
AGR = dn
dt
= n2 - n1 yields average
slope over that time interval
t2 - t1
Relative Growth Rate (RGR)
RGR = dn · 1
dt n
= ln n2
- ln n1 yields constant slope
during logarithmic phase
t2 - t1
QUANTITATIVE MEASUREMENTS OF GROWTH
Leaf
Area Ratio (LAR)
a) over
life of crop LAR = final leaf area = LA
final
plant dry weight W
b) over
any time LAR = leaf area2 - leaf
area1 = LA2
-LA1
interval plant
dry weight2 - plant dry weight1 W2 - W1
; units = cm2 g-1 or cm2/g
LAR is an indication of the efficiency of a
given leaf area to produce a given plant size.
Net
Assimilation Rate (NAR)
NAR = RGR = 1 · RGR
LAR LAR
= 1 · ln W2
- ln W1
LA2
- LA1 t2
- t1
W2
- W1
= W2 - W1 ·
ln W2 - ln W1
; units = g cm-2 day-1 or g/cm2/day
LA2
- LA1 t2
- t1
NAR measures the accumulation of plant dry weight per unit leaf area
per unit time.
It is a measure of efficiency of production.
Leaf Area
Index (LAI)
LAI = leaf
area = LA ; units
= cm2leaf cm-2soil or cm2leaf/cm2soil
soil area A
Measures the fraction of crop cover.
LAI is near 0 at planting, and is usually 2-3 at full canopy coverage
Crop Growth Rate (CGR)
CGR = NAR · LAI
; units = g cm-2soil
day-1 or g/cm2soil/day
CGR measures the efficiency of production of a
total field of plants over a given soil area.
APPLICATION OF QUANTITATIVE
MEASUREMENTS OF GROWTH
Efficiency of Different Species of
Plants
The following table gives the net assimilation rates (NAR) of various
species. The higher the NAR the more
efficient the species, which usually translates into higher growth rates. (from Table 3.10, Larcher 1980)
|
|
Net Assimilation Rate (mg dry matter per dm2 leaf area per day) |
|
|
Plant Type |
Average Over Growing Season |
During Growth Phase |
|
C4 Grasses |
>200 |
400-800 |
|
Herbaceous
C3 Plants |
50-150 50-100 |
70-200 100-600 |
|
Woody
Dicots |
10-20 10-15 3-10 5-10 |
30-50 30-100 10-50 15 |
|
|
2-4 |
10 |
Efficiency of Sun versus Shade
Plants
The following table gives the net assimilation rates (NAR), leaf area
ratio (LAR), and relative growth rate (RGR) of shade versus sun plants at both
high and low light intensities. (from
Table 3.1, Leopold and Kreidmann1975).
Note: At low light intensities,
the sun plant has 6-fold decrease in NAR and tries to compensate by increasing
its LAR (i.e. produces about 2-fold more and/or larger leaves), but the RGR
still decreases dramatically. At low
light intensities, NAR of the shade plant only decreases 3-fold, and increases
its LAR 2.4 fold, both of which help maintain a higher RGR; in other words the
shade plants have adapted themselves to the lower light intensity.
|
|
NAR |
LAR |
RGR |
||
|
% Daylight |
mg/cm2/ wk |
% |
cm2/g |
g/g wk |
% |
|
Sun Plant - Sunflower |
|||||
|
100% 24% 12% |
8.0 2.9 1.3 |
100 36 17 |
82 140 170 |
0.66 0.42 0.23 |
100 64 35 |
|
Shade Plant - Impatiens |
|||||
|
100% 24% 12% |
6.1 3.3 2.0 |
100 54 33 |
132 239 315 |
0.80 0.78 0.63 |
100 98 79 |
APPLICATION OF QUANTITATIVE
MEASUREMENTS OF GROWTH - con't
Effect of Leaf Area Index (LAI) on
Net Assimilation Rate (NAR) and Crop Growth Rate (CGR)
Note that as the LAI increases (due to greater canopy coverage of soil), the NAR (productivity of each plant) decreases (probably due to increased plant-plant shading), but the CGR (productivity of the entire crop over a given area of soil) increases. Thus, the best LAI is somewhere around 4.
(from Fig. 3.64, Larcher 1980)
|
|
Use of Quantitative Growth Measurements to Explain
Other Growth Phenomena
Increasing ambient carbon dioxide increases photosynthesis, which in turn increases growth. In tomato and bean, increasing carbon dioxide increases both total plant growth, as measured by increased RGR, and the efficiency of growth, as measured by increased NAR. This increased growth efficiency allows the plant to have a smaller shoot system (decreased LAR), which is the source, while still enhancing the size of the root system (see increased root/shoot ratio), which is a sink (from Table 3-2, Leopold and Kriedemann 1975).
|
|
Tomato |
Bean |
||
|
|
300 ppm CO2 |
1,000 ppm CO2 |
300 ppm CO2 |
1,000 ppm CO2 |
|
RGR (mg g-1 d-1) |
222 |
254 |
122 |
172 |
|
NAR (mg dm-2 d-1) |
71 |
89 |
46 |
80 |
|
LAR (dm2 g-1) |
3.0 |
2.8 |
3.2 |
2.7 |
|
root/shoot ratio |
0.19 |
0.21 |
0.18 |
0.25 |
Source Sink
Relations
PHLOEM AND XYLEM TRANSLOCATION
(Figure 3.9 and Table 3.8 from Marshner 1986, Summary from Bidwell 1974)
|
|
Fig 3 9
Long-distance transport in xylem (X) and phloem (P) in a stem with a
connected leaf, and xylem-to-phloem transfer mediated by a transfer cell (T). |
Table 3.8. Solutes in
the Phloem and Xylem Exudates of tobacco.
|
Substance |
Phloem
exudate (stem incision) pH 7-8-8-0 (/ig/ml)* |
Xylem exudate (tracheal) pH 5-6-5-9 (Mg/ml)* |
Concentration ratio phloem/ xylem |
|
Dry matter |
170-196C |
M-1-2C |
155-163C |
|
Sucrose |
155-168C |
ND |
— |
|
Reducing sugars |
Absent |
NA |
— |
|
Amino compounds |
10,808-0 |
283-0 |
38-2 |
|
Nitrate |
ND |
NA |
— |
|
Ammonium |
45-3 |
9-7 |
4-7 |
|
Potassium |
3,673-0 |
204-3 |
18-0 |
|
Phosphorus |
434-6 |
68-1 |
6-4 |
|
Chloride |
486-4 |
63-8 |
7-6 |
|
Sulfur |
138-9 |
43-3 |
3-2 |
|
Calcium |
83-3 |
189-2 |
0-44 |
|
Magnesium |
104-3 |
33-8 |
3-1 |
|
Sodium |
116-3 |
46-2 |
2-5 |
|
Iron |
9-4 |
0-60 |
15-7 |
|
Zinc |
15-9 |
1-47 |
10-8 |
|
Manganese |
0-87 |
0-23 |
3-8 |
|
Copper |
1-20 |
0-11 |
10-9 |
4ND, Not detectable; NA, data not
available., 'Milligrams per milliliter.
summary. The general
conclusions about the pathways and tissues of translocation:
1.
Salts and inorganic substances move upward in
the xylem.
2.
Salts and inorganic substances move downward
in the phloem.
3.
Organic substances move up and down in the
phloem.
4.
Organic nitrogen may move up in the xylem
(trees) or phloem (herbaceous plants).
5.
Organic compounds like sugar may be present in the xylem sap in
large concentrations during the spring when
sap rises in trees before the leaves emerge.
6.
Lateral translocation of solutes from one
tissue to another occurs, presumably by normal mechanisms of transfer
(osmosis, active transport, and so on).
7.
Exceptions to these generalizations are known
to occur.
CARBON MOBILIZATION
Redistribution Between Sources and Sinks
(Fig. 10.19 from Taiz and Zeiger 1998, Fig. 3.61 from Larcher 1980)

Figure 10.19 Autoradiographs
of a leaf of summer squash (Cucurbita pepo), showing the
transition of the leaf from sink to source status. In each case, the leaf imported 14C
from the source leaf on the plant for 2
hours. Label is visible as black accumulations.
(A) The entire leaf is a sink, importing sugar from the source leaf.
(B-D) The base is still a sink. As the tip of
the leaf loses the ability to unload and stops importing sugar, as shown
by the loss of black accumulations in B through
D, it gains the ability to load and to export sugar. (From Turgeon and
Webb 1973, courtesy of R. Turgeon.)

Fig. 3.61. Variations
in starch deposition by trees throughout the year. Maximal accumulation of starch is indicated by black,
large amounts by cross-hatching, and small amounts by stippling; in the parts left white, starch is present in traces or not at
all. Fagus sylvatica (
NUTRIENT
MOBILITY
Redistribution
Between Sources and Sinks
(Fig. 13-12 from Bidwell 1974, Table 3.9 from
Marschner 1986)

Figure 13-12 (opposite). A sequence of six
autoradiograms showing the fate of an aliquot of 35S absorbed as 35S04
during a 1-hr absorption period. The
plants, after the hour in the nutrient solution containing the tracer, were removed to a normal (nonradioactive)
solution where they remained for the
following periods: A, 0 hr; B, 6 hr; C, 1 2 hr; D, 24 hr; E, 48 hr; and F, 96 hr. Most of the 35S,
which moved directly into the mature leaves, was withdrawn within 1 2-24
hr. It moved predominantly into younger
leaves near the stem apex, where it remained. [From 0. Biddulph: Plant Physio/. 33:295 (1958).
Used with permission. Photograph
courtesy Dr. Biddulph.]
Table
3.9. Mobility of Mineral
Elements in Phloem
|
|
Intermediate |
Immobile |
|
Potassium Rubidium Sodium Magnesium Phosphorus
Sulfur Chlorine |
Iron Manganese
Zinc Copper Molybdenum |
Lithium Calcium Strontium Barium Boron |
From Bukovac and Wittwer (1957).
DIAGNOSING NUTRIENT DEFICIENCIES
Based on Nutrient Mobility
(from Vetanovetz 1996)
Mobile Nutrients – deficiencies typically appear on older growth first.
Immobile nutrients – deficiencies typically appear on newer growth and shoot tips first

MONOCARPIC SENESCENCE
Changing Sources and Sinks During
Vegetative and Reproductive Growth
(Fig. 1 from Egli and Leggert 1973, Fig. 3 from Harper 1971)

Fig. 1. Dry matter accumulation patterns
for

Fig. 3. Seasonal uptake and
accumulation of N, P, K, Ca, and Mg by soybeans at
weekly intervals1 from field hydroponic gravel culture systems.
EPISODIC GROWTH OF TEMPERATE WOODY PLANTS
Cycling Between Shoot and Root Growth and
Implications on Fertilizer Timing
(Fig. 2 on growth from Mertens and Wright 1978, Fig. 2 on uptake from Hershey and Paul 1983, Table 1 from Gilliam and Wright 1978)
|
Fig. 2. Root and shoot growth rates of 'Helleri' holly grown at 150 ppm N applied as 20N-8.7P-16.5K soluble fertilizer. |
Fig. 2. Uptake rates for K+ and Mg2+ for a single plant of Euonymus japonica (plant 5). Bars indicate periods of shoot elongation |
Table 1. Effect of the time and no. of weekly fertilizer applications during 1st growth flush on tissue N accumulation and subsequent shoot and root dry wt of 'Helleri' holly.
|
Week Fertilizer Applied |
No. Appl |
%N |
Shoot dry wt (g) |
Root dry wt (g) |
|
1 |
1 |
1.88 |
5.1 |
2.4 |
|
2 |
1 |
1.99 |
5.3 |
2.4 |
|
3 |
1 |
2.01 |
4.9 |
2.9 |
|
4 |
1 |
2.27 |
6.2 |
2.4 |
|
5 |
1 |
2.04 |
5.2 |
2.2 |
|
1-2 |
2 |
2.10 |
5.5 |
2.3 |
|
2-3 |
2 |
2.23 |
5.9 |
2.4 |
|
3-4 |
2 |
2.26 |
6.9 |
2.4 |
|
4-5 |
2 |
2.45 |
6.1 |
2.0 |
|
|
3 |
2.13 |
6.1 |
1.9 |
|
|
3 |
2.38 |
7.1 |
1.9 |
|
|
3 |
2.58 |
6.7 |
2.0 |
|
1-2-3-4 |
4 |
2.69 |
6-5 |
1.8 |
|
2-3-4-5 |
4 |
2.55 |
6.5 |
1.6 |
|
1-2-3-4-5 |
5 |
2.59 |
7.0 |
1.7 |
Senescence and
Post-Harvest Storage
MONOCARPIC SENESCENCE
Monocarpic
senescence literally means “flower once then die”. During the reproductive phase, the “sink”
demand of the developing flowers, fruit then seed can drain the vegetative
“sources” to the point that senescence occurs.

Fig. 1. Dry matter accumulation patterns
for

Fig. 3. Seasonal uptake and
accumulation of N, P, K, Ca, and Mg by soybeans at
weekly intervals1 from field hydroponic gravel culture systems.(from Harper 1971)
RESPIRATION AND SENESCENCE
All living organisms must conduct respiration in every living cell and at all times. Sometimes respiration is very fast, for example if the organ if actively growing, and sometimes it barely perceptible, for example if the organ is dormant. Respiration breaks down glucose and uses the energy that was in the carbon-carbon bond to make metabolic energy (mainly a compound called adenosine triphosphate or ATP). Carbon dioxide is given off as a by-product. If there is no oxygen around, then only partial respiration occurs in the form of anaerobic fermentation. This produces ethanol as a by-product and is the basis of wine making and all fermentation (yogurt, cheese, etc.).
One process involving respiration that is particularly important to horticulturist is ripening of fruit. In climacteric fruit, the respiration rises very rapidly during ripening, then decreases as the fruit senesces. If you prevent or decrease the rise of respiration, then you can prolong post-harvest storage life. Ethylene is what causes the increase in respiration, so decreasing ethylene is also a strategy used to increase post-harvest storage life.
What are other ways to decrease respiration and prolong the storage life of fruit and vegetable produce or cut flowers? Look at the equation for respiration. We can make the reaction go slower by either decreasing things on the left side of the arrow or increasing things on the right side of the arrow. Practically, we can decrease respiration by either increasing carbon dioxide or decreasing oxygen. You want to increase carbon dioxide to about 2-5% (up from about 350 ppm in the ambient air) and/or decrease oxygen to about 3% (down from 21% in the ambient air). You never want to decrease oxygen to near zero, because anaerobic fermentation would occur and anaerobic bacteria might start growing.
Of course the easiest way to decrease respiration is to decrease temperature. You may not have thought about it, but the refrigerator in your house is nothing more than a respiration inhibitor chamber.
All of the above is the basis of controlled-atmosphere storage.
If in addition to the above, if you store produce or flowers under a light vacuum, you will pull the ethylene out of the inside of the plant and the atmosphere around the plant. This will dramatically decrease respiration. This is called hypobaric storage.
Summary, we can decrease respiration by doing the following:
§ decrease temperature
§ decrease oxygen
§ decrease pressure, e.g. light vacuum
§ decrease ethylene
§ increase carbon dioxide
NET CHEMICAL EQUATION FOR RESPIRATION

BIOCHEMICAL REACTIONS OF RESPIRATION

Ethylene, Respiration and Senescence
Relations
1) Climacteric Fruit – a
fruit where ethylene triggers an
increase in respiration and the ripening process..
Climacteric Fruit Ripening and
Climacteric Rise

|
Climacteric Fruit |
Non-Climacteric Fruit |
|
|
apple apricot avocado banana cantaloupe fig guava ? mango |
olive pawpaw peach pear plum persimmon tomato |
bell pepper blueberry cherry grape pineapple strawberry citrus watermelon |
2) Non-Climacteric Fruit color – used to cause degreening of
citrus
3) Flower Senescence
a) Flower fading – flower fade after pollination
b) Flower longevity - causes senescence (death) of cut flowers
4) Leaf Senescence
a) Leaf epinasty (curling and contortion or leaves) - causes in some plants
b) Leaf abscission (leaf drop) - causes in some plants
Manipulating Ethylene, Respiration and
Senescence
1) Ethylene
Biosynthetic Pathway of Ethylene Synthesis
methionine ® s-adenosylmethionine ® 1-aminocyclopropane-1-carboxylic acid ® ethylene
(SAM) (ACC)
Ethylene inhibitors - chemicals that inhibit the synthesis or action of ethylene
Ethylene Synthesis Inhibitors (block
synthesis of SAM ® ACC)
· AVG - aminoethoxyvinyl glycine
· MVG - methoxyvinyl glycine
· AOA - aminoacetic acid
Ethylene Action Blockers (ethylene ® block action)
· STS - silver thiosulfate
· CO2 - carbon dioxide
· Ni - nickel
· Co – cobalt
· MCP – 1-mehtylcyclopropane
o it is a gas that can saturate the receptor sites, and block action for several days
o
EthylBloc – commercial compound
2) Temperature
3) Oxygen

4) Carbon Dioxide
Post-Harvest Storage to
Extend Shelf Life
1) Refrigeration
2) Controlled Atmosphere Storage – CA Storage
|
|
How Apples are Packaged and Stored Apples are stored
in cold storage warehouses. Inside a regular warehouse, apples can be stored
for about 5 months because it is cooled to 30-32 degrees Fahrenheit. Inside a special
controlled atmosphere warehouse, apples can be stored for almost 12 months
because the temperature, humidity, oxygen and carbon dioxide are constantly
monitored and controlled to prevent the fruit from ripening too quickly. (from Dole: www.dole5aday.com/ReferenceCenter/ |
· high CO2 - approx. 2-5%)
3) Hypobaric Storage low pressure storage, i.e. a light vacuum.
Hypobaric Storage Shipping Container
(from http://www.refrigeratedvehicles.com/)
· same as above, plus
· low pressure
o
decreases 02
o
decreases ethylene
4) Modified
Atmosphere Packaging – MAP
MAP broccoli
(from http://www.packagingdigest.com/articles/200203/32.php)
MAP uses selectively permeable bags and the fruit or vegetable’s own respiration to maintain an increased level of carbon dioxide and decreased level of oxygen, but avoiding low enough oxygen to avoid anaerobic respiration.
Fruits and vegetables continue to respire after harvest. If you seal them in a plastic bag, the produce will deplete the atmosphere in the bag of oxygen and will cause the produce to undergo anaerobic respiration. This will causes ethanol and off-flavors to form and may allow anaerobic bacteria to grow and cause spoilage.
In MAP, the produce is place in a selectively permeable bag that allows oxygen, carbon dioxide and ethylene to diffuse in and out so equilibrium is set-up between the inside of the bag to the outside of the bag. The goal is to use a bag that allows some oxygen to diffuse in to avoid anaerobic fermentation, but allow excessive carbon dioxide and ethylene to escape..
Permeability of Various Films
|
Film |
Thickness (micron) |
Permeability (l/m2/d/atm) |
|
|
O2 |
CO2 |
||
|
polyvenylchloride |
14-18 |
20 |
120 |
|
ethylenevenlyacetate |
10-25 |
32 |
134 |
|
low density
polyethylene |
25-50 |
6 |
20 |
|
p0lystyrene |
50 |
4 |
13 |
The bag must be designed for each fruit and vegetable. Produce with very high rates of respiration require a bag that allows more oxygen to diffuse in to avoid anaerobic respiration.
Respiration Rates of Vegetables
|
Class |
Respiration |
Commodities |
|
Very Low |
Below 10 |
Onion |
|
Low |
10 - 20 |
Cabbage, tomato |
|
Moderate |
20 - 40 |
Carrot, celery |
|
High |
40 - 70 |
Lettuce, radish |
|
Very High |
70 - 100 |
Spinach, bean |
|
Extremely High |
Above 100 |
Broccoli, pea |
Two Types of MAP
1) Passive MAP
The produce is put in a bag. If the permeability of the bag is properly matched with the respiration of the produce, the ideal atmosphere will evolve inside the sealed bag. Absorbers may be added to scavenge ethylene.
2) Active MAP
The produce is put in a bag, and the air in the bag is replaced with air that has the proper mixture of oxygen and carbon dioxide. Absorbers may be added to scavenge ethylene.
Maximum
Storage Time with Various Storage Methods
(from
http://atlasuhv.com/products/hypobaric_storage/hypobaric_storage.php
|
Commodity |
Maximum
Storage Time (days) |
Hypobaric Benefit Factor |
||
|
Standard
Refrigeration |
Control Atmosphere |
Hypobaric Advanced Atmosphere |
||
|
spinach |
14-Oct |
slight benefit |
50 |
5 x |
|
avocado (Lula) |
30 |
42-60 |
>102 |
3.5 x |
|
banana |
14-21 |
42-56 |
150 |
11 x |
|
cherry (sweet) |
14-21 |
28-35 |
56-70 |
4 x |
|
lime (Persian) |
14-28 |
juice loss, peel
thickens |
90+ |
6.5 x |
|
mango ( |
14-21 |
little or no benefit
|
>50 |
3.5 x |
|
papaya (Solo) |
12 |
12+ (slight benefit)
|
28 |
2.3 x |
|
pear ( |
60 |
100 |
200 |
3.3 x |
|
strawberry |
7 |
7+ (off-flavor) |
21 |
3 x |
|
asparagus |
14-21 |
slight benefit - off
odors |
28-42 |
2 x |
|
cucumber |
14-Sep |
14+ (slight benefit)
|
49 |
3.5 x |
|
green pepper |
14-21 |
no benefit |
50 |
3.5 x |
|
mushroom |
5 |
6 |
21 |
4.2 x |
|
apples (various) |
200 |
300 |
300+ |
1.5 x |
|
carnation (flower) |
21-42 |
no benefit |
140 |
6.6 x |
|
protea (flower) |
<7 |
no benefit |
30+ |
4.2 x |
|
rose (flower) |
14-Jul |
no benefit |
42 |
6 x |
The above data
from S.P. Burg in Postharvest Physiology and Hypobaric Storage of Fresh
Produce, CABI Publishing, 2004, ISBN 0 85199 801 1