Water

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Plant Growth Substances/Regulators

• a natural or synthetic organic material
• regulates plant growth in low concentrations
• is readily transported and is not a nutrient or a
  vitamin

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Plant Growth Substances/Regulators

• Plant growth substances - Hormones
• natural, internal compounds
• Plant growth regulators
• name most often used for external compounds

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Plant Growth Regulators - PGR

• each substance has several different functions
• they can interact with each other to produce
  different plant responses
• they are involved in all plant developmental
  stages

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5 main substances/hormones

• Auxins
• Gibberillins
• Cytokinins
• Ethelyne
• Abscisic Acid

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Auxins

• Natural compound IAA - indole-3-acetic acid
• breaks down in light (photooxidation)
• Produced in meristematic tissues
• buds, root shoot tips, young leaves
• seeds, embryos, developing fruits

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Auxins

• Apical dominance - growing shoot tip influence
  growth of lateral buds
• auxin transported basipetally, inhibit bud break

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Auxins

• phototropism - bending toward light
• Auxin destroyed by light
• Auxin accumulates on darkened side
• promote cell elongation

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Auxins

• root initiation
• cell division and differentiation- vascular
  tissue
• fruit set, size shape
• flower initiation sex expression

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Commercial Use

• IBA, NAA - synthetic auxins
• Root initiation - cuttings and tissue culture
• Fruit thinning - apples
• Stopdrop - inhibit abscission in apples
• sprout prevention

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Gibberillins

• Gibberillic Acid - GA3, 4, and 7
• gt80 different GAs
• produced in
• stem apex, leaf primordia, roots
• embryos, cotyledons, fruits tubers

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Gibberillins

• cell elongation
• cell division
• seed germination

• sex expression
• flowering
• fruit set, growth maturation

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Commercial Use

• GAs extracted from fungus
• beer brewing
• flowering - cyclamen
• vernalization
• fruit size - seedless grapes
• delay budbreak - peaches, grapes

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Cytokinins

• zeatin, 2iP, kinetin
• produced in roots, embryos, shoot tips

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Cytokinins

• cell division
• cell enlargement
• leaf enlargement
• inhibit stem elongation
• delay senscence

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Commercial Use

• hydrogen cyanamide - synthetic compound
• promote uniform bud break
• tissue culture

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Tissue culture

• Cytokinin interaction with Auxin determines
  tissue differentiation
• high Cytokininlow auxin shoot initiation
• low cytokinin high auxin root initiation
• moderate cytokinin moderate auxin callus -
  undifferentiated cells

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Ethylene

• C2H4 - gas at room temperature
• produced in many locations of the plant
• oxygen must be present
• also produced as a result of
• wounding
• 2,4-D applications
• high levels auxins
• fruit maturation

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Ethylene promotes

• abscission
• senescence - chlorophyll degradation
• flowering- pineapples
• fruit ripenining

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Commercial Use

• Florel - Ethephon
• degreening - bananas, lemons, tomatoes
• maintain latex flow - rubber trees
• enhance color development - cranberries
• promote abscission - fruit drop - nuts, cherries

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Abscisic Acid (ABA)

• dormin, abscisin
• produced in leaves, seeds, shoot tips, roots

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Abscisic Acid

• inhibit growth
• promotion of dormancy - seeds buds
• promote stomatal closure
• No current commercial use - expensive
• however synthetic stable compounds are currently
  being tested

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Growth Retardants

• block gibberillin synthesis
• effect transport of auxin

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Commercial Use

• several synthetic chemicals
• Bonzi - paclobutrazol
• Cycocel chlormequat chloride
• B-Nine - daminozide
• Sumagic - uniconazol
• A-Rest - ancymidol
• Application
• Spray
• Drench