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) |