Chapter 28 Regulating Growth and Development: The Plant Hormones

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Chapter 28Regulating Growth and Development
The Plant Hormones
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Outline

• Intro
• Auxins
• Cytokinins
• Ethylene
• Abscisic Acid
• Gibberellins

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Intro

• Development internal external factors
• internal hormones
• external light/temperature/daylength/gravity
• Hormones organic subst produced in small
  amounts that has role in regulation of growth,
  highly specific chemical signal
• active at site of syn. or transported
• chemical regulator (stimulate/inhibit)
• active in small quantities
• Greek work horman to set in motion
• sensitivity amount hormone required to cause
  effect

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Classes of Hormones

• 5 traditional classes
• auxin apical dominance/tropisms/cambial
  activity/rooting
• cytokinin cell division/lateral bud dormancy
• ethylene fruit ripening/leaf/flower
  senescence/abscission
• abscisic acid stomatal closure/dormancy/embryoge
  nesis
• gibberellins cell division/elongation/seed
  germination/ flowering
• Newly discovered growth regulators
• brassinolides (steroids) cell
  division/elongation
• salicylic acid defense
• jasmonates seed germination/root growth/defense
• systemin defense

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Auxins

• Jessicas Talk

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Auxins

• Early research of Darwin and son
• cover tip no bending
• auxein to increase
• Most abundant auxin is indoleacetic acid (IAA)
• Produced in leaf primordia/young lvs/seeds
• Transport is polar (unidirectional) via
  parenchyma
• basipetal (toward base) in stems/lvs
• acropetal (toward tip) in root tips

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Auxins

• Func.
• apical dominance/lateral bud inhibition
• tropic response
• vascular tissue differentiation
• stimulate cambial activity in spring
• stimulate adventitious roots on cuttings
• inhibit leaf/fruit abscission
• stimulate ethylene synthesis
• inhibit/stimulate flowering
• stimulate fruit development
• removal of auxin (from seeds) fruit wont
  develop
• argiculturally used to produce pathenocarpic
  fruit
• parthenos virgin

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Auxins

• Synthetic auxin herbicides
• 2,4-D (2,4-dichlorophenoxyacetic acid)
• Agent Orange (auxins dioxin)
• dioxin toxic/carcinogenic to animals
• diseases now on VA's Agent Orange list
• Chloracne, Hodgkin's disease
• Multiple myeloma
• Non-Hodgkin's lymphoma
• Porphyria cutanea tarda
• Respiratory cancers, soft-tissue sarcoma
• Acute and subacute peripheral neuropathy
• Prostate and adult-onset diabetes
• Chronic lymphocytic leukemia (CLL)
• http//www.chinadaily.com.cn/english/doc/2004-02/0
  5/content_303315.htm

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Cytokinins

• Cyto cell, kinesis division
• Derivative of adenine
• Produced in root tips, transported in X
• also found in seeds, fruits, lvs
• Func.
• promote cell division
• release lateral bud dormancy
• shoot formation tissue culture
• delay leaf/fruit senescence/abscission
• agriculturally used to prevent early fruit drop

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Cytokinins

• ? IAA (auxin) root formation
• ? kinetin (cytokinin) shoot formation

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Ethylene

• C2H4
• gaseous
• moves via diffusion
• Produced as response to stress/
  maturation
• Func.
• inhibit cell expansion
• promote fruit maturation/ripening
• promote leaf/flower/fruit senescence/abscission
• sex determination (femaleness) in Cucurbits
• aquatic plants
• promotes cell expansion
• lacunae (air spaces in tissue) formation

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Ethylene

• Fruit ripening
• chlorophyll degradation
• fruit softening (enzymatic digestion of
  pectin in middle
  lamella)
• starch and oil breakdown
• YUM!
• Climacteric fruits (tomato/avocado/apple/pear)
  ripen slowly
• due to ? R due to ? O2 uptake
• agriculturally used to ripen unripe fruit/fruit
  thinning/promote fruit abscission for easier
  harvesting

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Abscisic Acid

• a.k.a. ABA
• Produced in mature leaves (water stress)
• exported via P
• Response to water stress
• Func.
• no direct role in abscission
• promotes stomatal closure
• transport of photosynthates to seeds
• embryogenesis
• production of seed storage proteins
• maintains seed germination (? ABA ? seed
  dormancy)
• maintains bud dormancy

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Gibberellins

• Foolish seedling disease
• grow fast/spindly/pale/sickly/ fall over
• 84 gibberellins
• Produced in young tissues of shoots/seeds

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Gibberellins

• Func.
• cell division/elongation
• hyperelongation of shoots
• promote flowering
• break seed dormancy (substitute for light of cold
  trmts)
• endosperm breakdown in grains
• induce seed germination
• induce bolting (flowering)
• agriculturally used for uniform germination/
  germination/parthenocarpic fruits/
  loosening in
  grapes