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Plant responses to hormones

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Plant responses to hormones What the spec says . Types of plants hormone Auxins Gibberellins Cytokinins Abscisic acid Ethene Growth substances can be – PowerPoint PPT presentation

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Title: Plant responses to hormones


1
Plant responses to hormones
2
What the spec says.
3
Types of plants hormone
Cell division
Cell elongation
  • Auxins
  • Gibberellins
  • Cytokinins
  • Abscisic acid
  • Ethene

Promotors of growth
Initiation of organs
Differentiation
Inhibitors of growth / Antagonists to growth
stimulators
4
Growth substances can be
  • Synergistic enhance each others effects
  • Antagonistic counteract each other

5
Auxin
  • Indoleacetic acid
  • Causes elongation of cells
  • Increases plasticity of cells
  • Cell walls soften
  • Cell becomes less turgid and take up more water
  • Cell expands
  • Responsible for phototropism

6
Phototropism experiments
7
Other activities of auxins
  • Apical dominance apical bud inhibits lateral
    (axillary buds)
  • E.g. pruning stimulates axillary buds
  • Formation of lateral roots stimulates
    INITIATION of lateral roots and adventitious
    roots
  • E.g. napthalene acetic acid (NAA)
  • Indole butyric acid (IBA)

8
More auxin functions
  • Abscission of leaves and fruit
  • Abscission falling of fruit and leaves
  • IAA delays early stages, promotes later stages
  • Stimulates ethene production
  • Ensure fruit stays on trees until harvest

9
Even more auxin functions
  • Fruit development
  • Produced in pollen developing seed
  • Stimulates fruit development after fertilisation
  • Used in production of seedless fruits
  • Weed killers
  • 2,4-D causes abnormal growth of Dicots (e.g.
    dandelions) monocots are unaffected

10
Giberellins
  • Stem elongation in dwarf plants
  • E.g. dwarf peas
  • Bolting of long day plants when the days are
    short i.e. cause them to flower
  • Overcome lack of cold period required for
    flowering in long day plants

11
  • A wild type rice plant (left) compared to a
    semidwarf transgenic plant (right) containing 
    the gai mutant allele. 
  • The gai mutant allele confers giberellin
    insensitivity upon the transgenic plant, and
    causes its reduced stature.

12
More giberellins
  • Fruit development
  • Stimulates growth of fruit stalk
  • Delays senescence (aging)
  • Seed germination stimulates
  • Stimulate a amylase production in seeds,
    improves malt yields from barley

13
Cytokinins
  • Produced by meristemic tissue
  • Apices of roots and shoots
  • Development of roots, shoots and lateral buds
  • Cell enlargement
  • Maturation of chloroplasts
  • Dependant on auxin for function

14
  • Cytokinins are commonly used tostimulate shoot
    initiation in culture as is shown by
    shoot/bulblet formation on bulb scales of
    Bowieavolubilis. Benzyladenine was used here to
    stimulate shoot growth

15
Abscissic acid
  • Inhibit / alter growth
  • Linked to environmental stress
  • Seeds can become dormant
  • Abscission of leaves, flowers and fruits
  • Close stomata in times of water deficiency

16
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17
Ethene (ethylene)
  • Promotes ripening of fruits
  • Promotes abscission (auxin prevents it)
  • Abscission layer
  • Antagonistic to auxin
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