External factors and Plant growth

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Chapter 28

• External factors and Plant growth

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Nastic Movement

• Nastic Movements- plants movement that occur in
  response to a stimulus independent of position of
  stimulus ( leaves light and dark cycle)
• Phototropism- response to light- caused by
  elongation- under the influence of Auxin
• Gravitropism- response to gravity
• Thigmotropism- response to touch

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External Factors and Plant Growth

• Tropism- the growth response involving bending,
  or curving, of a plant part toward or away from
  an external stimulus determines the direction of
  movement

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Wents experiment- chemical produced by growing
tips influences direction of growth
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What role does the light play in the phototropic
response?

• Light decreases the auxin sensitivity of the
  cells on the lighted side
• Light destroys auxin
• Light drives auxin to the shaded side
• Light eliminates auxin activity
• Tropism video

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Gravitropism- starch-statolith plastids hypothesis
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Auxin and root gravitropism
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Gravitism video
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Thigmotropism is growth in response to touch

• Tendrils of bur cucumber
• Enables shoots and roots to navigate, cling and
  climb
• Thigmotropism in Opuntia acanthocarpa flowers
  video

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Thigmotorpism- tendrils of bur cucumber,
twisting Caused by different growth Rates on the
inside and Outside of tendril
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Phototropism

• Common response to light

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Diurnal movements of Wood sorrel (Oxalis)
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Diurnal movement- biological clock is the
organism keeping itself in time with some
external stimulus?
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Other types of Movement

• Thigmonastic (seismonastic) Movement are results
  of mechanical stimulation
• Most night closure (nyctinastic movement) are
  results from changes in the size of perenchyma
  cells in the jointlike thickening (pulvinus)
  structure at the base of each leaf.

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Pulvini Mimosa pudica vascular tissue
surounded By a cortex which consists largely of
thin-walled Parenchyma cells
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Mimosa pudica
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Entire leaf drops in response To movement, shock,
thermal Stimulation, touch
Results from changes in turgor Pressure in pulvini
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Touch reponse in the venus flytrap (Dionaea
muscipula)
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Thigmomorphogenesis- The inhibition of growth by
touch Arabidopsis thaliana both six weeks of age
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Solar tracking Lupine (Lupinus arizonicus)
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Sunflower solar tracking