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Plant Growth Regulators

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Apical dominance high levels of auxin in the stem just above lateral buds ... ( the auxin which formed the blockage to keep lateral buds small is reduced so ... – PowerPoint PPT presentation

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Title: Plant Growth Regulators


1
Plant Growth Regulators
  • Chemical Messengers

2
Hormones
  • In plants, many behavioral patterns and functions
    are controlled by hormones. These are chemical
    messengers influencing many patterns of plant
    development.
  • Plant hormones a natural substance (produced by
    plant) that acts to control plant activities.
    Chemical messengers.

3
Hormones
  • Are produced in one part of a plant and then
    transported to other parts, where they initiate a
    response.
  • They are stored in regions where stimulus are and
    then released for transport through either phloem
    or mesophyll when the appropriate stimulus occurs.

4
Growth Regulators
  • Plant growth regulators include plant hormones
    (natural synthetic), but also include
    non-nutrient chemicals not found naturally in
    plants that when applied to plants, influence
    their growth and development.

5
Growth Regulators
  • 5 recognized groups of natural plant hormones and
    growth regulators.
  • 1. Auxins
  • 2. Gibberellins
  • 3. Cytokinins
  • 4. Ethylene
  • 5. Abscisic acid

6
Auxins
  • Influence plant growth found in leaves and
    stems growth regulators and hormones
  • Cell enlargement or elongation located in
    meristems and shoot tips (terminal lateral
    buds). Auxins move mainly from apex (top) down.
  • Lengthening of the internodes and influence the
    developing embryos in the seed.

7
What happens when auxin is added to a stem. The
stem will bend away from the auxin. It elongates
faster on the extra auxin side.
8
Auxins
  • Apical dominance high levels of auxin in the
    stem just above lateral buds block their growth
    (blockage of growth of lateral buds by presence
    of terminal buds). If shoot tip is removed. The
    auxin level behind the lateral buds is reduced
    and the lateral buds begin to grow. (the auxin
    which formed the blockage to keep lateral buds
    small is reduced so they can grow)

9
Auxins
  • Photo (light) and geotropism (gravity) involved
    in tropism responses positive responses
  • Flower initiation and development
  • Root initiation and development (rootone) used
    on cuttings to help stimulate root growth

10
Auxins (IAA)
  • Plant Growth Regulators - Indobutyric acid
    (IBA)(synthetic), napthaleneacetic acid
    (NAA)(synthetic), 2,4-dichlorophenoxyacetic acid
    (2-4D)(synthetic)
  • Hormone - indoleactic acid (IAA)(naturally
    occurring).

11
Auxin
12
Gibberellins (GA)
  • Gibberellic Acid
  • Have a regulatory function
  • Are produced in the shoot apex primarily in the
    leaf primordial (leaf bud) and root system
  • Stimulates stem growth dramatically

13
Gibberellins (GA)
  • Stimulates cell division, cell elongation (or
    both) and controls enzyme secretions. Ex dwarf
    cultivars can be treated with GA and grow to
    normal heights indicates dwarf species lack
    normal levels of GA

14
Gibberellins
  • Involved in overcoming dormancy in seeds and
    buds.
  • GA translocates easily in the plant (able to move
    freely) in both directions because produced in
    not only shoot apex but also in the root
    structure.

15
Gibberellins
  • Used commercially in
  • Increasing fruit size of seedless grapes
  • Stimulating seed germination seedling growth

16
Gibberellins
  • Promoting male flowers in cucumbers for seed
    production.
  • Overcoming cold requirements for some seed,
    application of GA foregoes the cold requirements
    (some seed require to be frozen or placed in the
    refrigerator for a period of time before they
    will germinate).

17
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18
Cytokinins
  • Promotes cell division
  • Found in all tissues with considerable cell
    division.
  • Ex embryos (seeds) and germinating seeds, young
    developing fruits

19
Cytokinins
  • Roots supply cytokinins upward to the shoots.
  • Interact with auxins to influence differentiation
    of tissues (may be used to stimulate bud
    formation).

20
Cytokinins
  • As roots begin to grow actively in the spring,
    they produce large amounts of cytokinins that are
    transported to the shoot, where they cause the
    dormant buds to become active and expand.

21
Cytokinins
  • Tissue cultures use cytokinins to induce shoot
    development
  • Cytokinins may slow or prevent leaf senescence
    (leaf ageing or leaf fall).

22
Cytokinin
23
Ethylene
  • Gaseous hormone
  • Produced in the actively growing meristems of the
    plant, in senescing ripening or ageing fruits, in
    senescing (ageing or dying) flowers, in
    germinating seeds and in certain plant tissues as
    a response to bending, wounding or bruising.
  • Ethylene as a gas, diffuses readily throughout
    the plant.

24
Ethylene
  • May promote leaf senescing and abscission (leaf
    fall).
  • Increases female flowers in cucumbers
    (economically - will increase fruit production).
  • Degreening of oranges, lemons and grapefruit
    ethylene gas breaks down chlorophyll and lets
    colors show through.

25
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26
Inhibitors
  • Abscisic Acid (ABA)
  • Widespread in plant body moves readily through
    plant
  • ABA appears to be synthesized (made) by the
    leaves.
  • Interacts with other hormones in the plant,
    counteracting the growth promoting the effects
    of auxins gibberellins.

27
Abscisic Acid
  • Involved with leaf and fruit abscission (fall),
    onset of dormancy in seeds and onset of dormancy
    (rest period) in perennial flowers and shrubs
  • ABA is effective in inducing closure of stomata
    in leaves, indicating a role in the stress
    physiology in plants. (ex increases in ABA
    following water, heat and high salinity stress to
    the plant)

28
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