Hort 201 Part 4- Hormones And Growth Substances

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hormone

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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.

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growth substance

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all naturally-occurring or synthetically produced substances that affect the physiology, growth and development of plants.

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naturally occurring example of auxin?

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indoleacetic acid (IAA)

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naturally occurring example of cytokinin

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zeatin, kinetin (not in plants)

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# of naturally occurring examples of gibberellic acid (GA)

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over 90

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naturally occurring example of ethylene

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ethylene

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naturally occurring example of abscisic acid (ABA)

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abscisic acid

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3 synthetic examples of auxin

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indolebutyric acid (IBA), naphthaleneacetic acid (NAA), 2,4-dichlorophenoxyacetic acid (2,4-D)

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2 synthetic examples of cytokinin

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benzyladenine (BA), pyranylbenzyladenine (PBA)

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synthetic example of gibberellic acid (GA)

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none

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synthetic example of ethylene

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ethephon or ethrel (both release ethylene inside plant)

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synthetic example of abscisic acid (ABA)

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none

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sites of production of auxin

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shoot tips, embryos

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sites of production of cytokinin

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root tips, embryos

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sites of production of gibberellic acid (GA)

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both shoot and root tips, embryos

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sites of production of ethylene

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ripening fruits, aging flowers, germinating seeds, wounded tissue

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sites of production of abscisic acid (ABA)

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plastids, especially chloroplast

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tropism

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response of plants to environmental or physical stimuli.

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phototropism

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response to light

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geotropism

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response to gravity

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thigmotropism

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response to touch

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6 effects/practical applications of auxin

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1) Tropism - response of plants to environmental or physical stimuli.
(phototropism, geotropism, thigmotropism)
2) Apical dominance - determined by apical bud, partly due to auxin produced
3) Fruit set - low concentrations stimulate
4) Fruit or flower thinning - high concentrations cause
5) Herbicides - 2,4-D at high concentrations
6) Adventitious ROOT formation (stem and leaf cuttings, tissue culture)

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3 effects/practical applications of cytokinin

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1) Leaf aging or abscission - may delay
2) Seed germination - may overcome dormancy or stimulate germination
3) Adventitious SHOOT formation (leaf and root cuttings, tissue culture)

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6 effects/practical applications of gibberellic acid (GA)

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1) Rosette or dwarf plants - lack of endogenous GA often causes
2) Flowering - may cause bolting in biennials
3) Fruit size - increases size of seedless grapes
4) Bud dormancy - may overcome and substitute for cold treatment
5) Seed germination - may increase or speed up
6) Sex expression - favors STAMINATE flower formation on monoecious plants

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6 effects/practical applications of ethylene

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1) Fruit ripening - stimulates in many fruits, ex. banana
2) Flowering - triggers flowering in some bromeliads, ex. pineapple.
3) Flower longevity - causes senescence (death) of cut flowers
4) Leaf abscission (leaf drop) - causes in some plants
5) Leaf epinasty (curling and contortion of leaves) - causes in some plants
6) Sex expression - favors PISTILLATE flower formation on monoecious plants

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3 effects/practical applications of abscisc acid (ABA)

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1) Dormancy - causes bud or seed dormancy
2) Leaf abscission (leaf drop) - may cause in some plants
3) Stomata - causes stomata to close (a response to drought stress)

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growth retardants

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chemicals that block gibberellic acid (GA) synthesis; are used in greenhouse and bedding plant production to produce compact plants.

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leaf abscission

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leaf drop

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leaf epinasty

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curling and contortion of leaves