Plant Responses (tropisms)

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Plant Responses (tropisms)

• Chapter 39

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At every stage of life plants are responding to
their environment.

• Flowers following the sunlight (phototropism)
• Curling pea tendrils (thigmotropism)
• dead heading flowering plants produces more
  flowers
• Roots grow down and shoots grow up (gravitropism)

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Reception of stimulus ?relay molecules ?response
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Plant hormones - Auxins

• Promote cell elongation (growth)
• Enhances apical dominance
• Regulates fruit development
• Functions in photo and gravitropisms

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Cytokinins

• Stimulate cell division
• Work in concert with auxins to control apical
  dominance

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Plant Hormones - ethylene

• Responsible for triple response (seedling hits a
  stone and can maneuver around it)
• Present during apoptosis
• Stimulates leaf dropping (abscission)
• Stimulates fruit ripening

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The Triple Response to Mechanical Stress

• Ethylene induces the triple response
• Which allows a growing shoot to avoid obstacles
  slows stem elongation, thickens stem, stem grows
  horizontally

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Plant Hormones - Gibberellins

• Stimulates fruit development
• Stimulate shoot (leaf and stem) growth
• Encourage germination after water is imbibed -
  dormancy is broken

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Phytochromes cytoplasmic photorecpetors
responsible for de-etiolation
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Phototropisms - plant responses to light

• Plants detect wavelengths, intensity, and
  direction of light!
• Phytochromes are the receptor proteins

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Responses to herbivores