Growth and development in plants

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Growth and development in plants
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Response ? Stimulus

• Results in survival of species
• respond by changing their growth pattern
• Tropism growth toward or away from a
  unidirectional stimulus, toward , away -
• Phototropism - light
• Gravitropism - gravity
• Thigmotropism touch
• Reception ? transduction ? response

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Nastic movements

• Movements that do not involve growth, not
  dependent on direction of stimulus
• Seismonastic movements touching, shaking, light
  or thermal stimulation
• Mimosa plant, prayer plant
• Changes in turgor pressure, K
• Circadian rhythm biological rhythm with 24
  hours cycle
• Biological clock mechanism by which the
  biological rhythm is maintained

4
Plant Hormones

• Chemical signals produced in very low
  concentrations for communication

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Auxin

• affect many aspects of plant growth and
  development
• Indoleacetic acid(IAA) most common occurring
• Apical dominance prevents lateral buds
• Promotes root growth if applied
• Promotes growth of fruit
• Induce development of fruit without pollination
• Weed control (Agent Orange)
• Gravitropism and phototropism
• moves to shady side, 2nd messengers lead to
  production of growth factors, elongation of stem
  on shady side, bends toward light

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Gibberellins

• Growth promoting hormones
• Gibberellic acid (GA)
• Stem elongation (bush beans to pole beans)
• Used to break dormancy, bring on onset of flowers
• Induce growth of plants and increase size of
  flowers

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cytokinins

• Promote cell division, derivative of adenine
• Occur n actively dividing tiwwues of roots, seeds
  and fruits
• Used to prolong life of flower cuttings and
  vegetables in storage
• Senescence aging process, loss of leaves
• Can be prevented by applying cytokinins

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Abscisic Acid (ABA)

• Stress hormone
• initiates and maintains seed and bud dormancy
• Stimulates closure of stomata when in water
  stress
• Natural progression in Fall for plants, levels
  decrease in spring (gibberellins increase)
• Abscission dropping of leaves, fruit, flowers
  if applied externally, not naturally

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Ethylene

• Involved in abscission, stimulates enzymes which
  cause leaves, fruit or flowers drop
• Used to speed up ripening of fruit
• Applied to citrus to keep color
• Release gas at wound, speeds up ripening of fruit
  around fruit

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Photoperiodism

• Physiological response prompted by changes of
  length of day or night
• Germination breaking of bud dormancy
• Can influence flowering
• 3 groups of flowering plants
• Short day day length 14 hours or shorter
• Long day 14 hours or longer
• Day neutral - not dependent on day length
• If dark period is interrupted, flowering will not
  result, not the same result if reversed

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Phytochrome

• blue/green leaf pigment,
• has 2 forms that absorbs red light at different
  wavelengths
• Phytochrome red 660 nm
• Phytochrome far-red 730 nm
• Allows a plant to detect photoperiod changes
• Other functions of phytochrome
• Promotes seed germination
• Inhibits stem elongation