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Plant hormones

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Plant Hormones Plant hormones Organic compounds produced in low concentrations Produced in one part of plant (i.e. source) Transported to another part of plant (i.e ... – PowerPoint PPT presentation

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Title: Plant hormones


1
Plant Hormones
  • Plant hormones
  • Organic compounds produced in low concentrations
  • Produced in one part of plant (i.e. source)
  • Transported to another part of plant (i.e. target)
  • Cause physiological or developmental responses
    (stimulatory or inhibitory)
  • Also called plant growth regulators

2
Plant Hormones
  • Major types of plant hormones
  • Auxins
  • Cytokinins
  • Gibberellins
  • Ethylene
  • Abscisic acid

3
Plant Hormones
  • Auxins
  • Types of auxins used in horticulture
  • Natural auxin is indole-3-acetic acid (IAA)
  • IAA is broken down in sunlight
  • Synthetic auxins used in horticulture
  • Indole-3-butyric acid (IBA)
  • Naphthaleneacetic acid (NAA)
  • 2, 4-dichlorophenoxyacetic acid (2, 4-D)
  • Site of auxin production in plants
  • Shoot and root tips (apical meristems)
  • Young, expanding leaves
  • Young seeds

4
Plant Hormones
  • Auxins
  • Action of auxins in plants
  • Stimulate cell elongation
  • Bend toward light because more auxin remains in
    cells on opposite side of light source
  • Etiolated plants have long internodes because
    auxin not quickly broken down
  • Promotes apical dominance
  • Pinching bud removes source of auxin and releases
    axillary buds from apical dominance
  • Promotes growth of adventitious roots
  • We used both IBA and NAA with geranium cuttings

5
Plant Hormones
  • Auxins
  • Actions of auxins in plants
  • Promotes or inhibits abscission of leaves,
    flowers and fruit
  • NAA applied shortly after bloom is used to thin
    apples
  • NAA applied during fruit development inhibits
    abscission of apples
  • Auxin concentration determines if action is
    stimulatory or inhibitory
  • Low concentration promotes adventitious root
    growth, but high concentration inhibits root
    growth of cuttings
  • 2, 4-D is used as herbicide by applying at high
    concentrations

6
Plant Hormones
  • Gibberellins
  • Types of gibberellins used in horticulture
  • Several different gibberellins (GA) produced by
    plants
  • Large, complicated molecules not synthesized
  • Commercial gibberellins produced by fungus
  • Site of gibberellin production in plants
  • Shoot and root tips (apical meristems)
  • Young, expanding leaves
  • Embryos
  • Fruits
  • Tubers

7
Plant Hormones
  • Gibberellins
  • Action of gibberellins in plants
  • Stimulate cell elongation
  • Dwarf plants treated with gibberellins produce
    normal growth
  • Applied to grapes to elongate the peduncle (stem
    of flower cluster) and pedicels (stem of single
    flower), making looser cluster
  • Promotes cell division in vascular cambium
  • Promotes seed germination
  • causes production of enzymes that break down
    starch into energy needed for growth
  • Used by beer brewers to stimulate sugar
    production in barley malt (sugar is converted
    into alcohol during fermentation)
  • Influences flower and fruit development

8
Plant Hormones
  • Cytokinins
  • Types of cytokinins used in horticulture
  • Several natural forms
  • Zeatin first cytokinin isolated
  • Synthetic cytokinins used in horticulture
  • Benzyladenine (BA)
  • Site of cytokinin production in plants
  • Embryos
  • Young leaves and fruit
  • Apical meristems of roots

9
Plant Hormones
  • Cytokinins
  • Actions of cytokinins in plants
  • Promotes cell division (cytokinesis)
  • Contributes to cell enlargement (in leaves)
  • Stimulates differentiation of cells (with auxins)
  • High cytokinin and low auxin promotes shoot
    initiation in tissue culture, whereas reverse
    combination promotes root formation
  • Moderate levels of both hormones promotes callus
    growth
  • Delays senescence in leaves (maintains and
    promotes synthesis of chlorophyll)

10
Plant Hormones
  • Ethylene
  • Gas at physiological temperatures
  • Liquid form used in horticulture (ethephon)
  • Site of ethylene production in plants
  • Throughout plants
  • Actions of ethylene in plants
  • Inhibits root and shoot elongation by blocking
    transport of auxins from apical meristems
  • Stimulates leaf curling (epinasty)

11
Plant Hormones
  • Ethylene
  • Actions of ethylene in plants
  • Induces adventitious root formation by blocking
    (and accumulating) auxin at tip of stem cutting
  • Enhances flow of latex in rubber trees
  • Enhances flowering in pineapples
  • Stimulates abscission of leaves and fruit
  • Used as a harvest aid for cherries
  • Promotes fruit ripening (apple, tomato, citrus,
    coffee)
  • Promotes senescence of flowers

12
Plant Hormones
  • Abscisic Acid (ABA)
  • Similar structure as gibberellins
  • Site of abscisic acid production in plants
  • All organs (e.g. roots, leaves, stems, fruits)
  • Actions of abscisic acid in plants
  • Counteracts effects of auxins and gibberellins
  • Maintains dormancy in seeds and buds
  • Stimulates guard cells to close stomates (to
    conserve water)
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