Chapter 36

Overview of plant behavioral responses

• Behavior is a response of an organism to an internal or external stimulus
• types of plant behavior
  • movement
    • bending,twisting, or rotating
      • nutation
    • rapid movement as in sensitive plants
      • response to touch
  • growth
  • seed germination
  • seasonal production of reproductive structures
  • defensive responses to attacks
    • thorns, spines, chemicals

Responses to internal and external stimuli

Internal

• Internal biological clock
  • circadium rhythms
• chemical signals
  • transcriptions factors and other proteins or hormones
  • often interact with each other and external signals

External

• light atmospheric gases (CO2 and water vapor) temperature, touch, wind, gravity, water, rocks, and soil minerals
• Herbivors, pathogens, organic chemicals from neighboring plants, and beneficial or harmful organisms

Plant Behavior

Involves internal and external stimuli

• tropism
  • growth response that is dependent on a stimuli that occurs in a particular direction
• Reception molecules
  • located in plant cells
  • sense stimuli and cause response

Phototropism

• Growth response to light
• light causes movement of hormone auxin away from said light
• result in unequal distribution of auxin
  • causing unequal cell elongation
• positive tropism

Gravitropism

• growth response to gravity
• positive tropism
  • roots
• negative tropism
  • shoots
• columella cells in root cap/tip region sense gravity 

Thigmotropism 

• Growth response to touch
• roots
  • columella cells cause roots to grow around obstacles

Regulation of plant growth

Hormones

• chemical messengers that regulate plant growth
• most transported in phloem tissue
• all require an expenditure of energy on part of the plant (ATP) for transport
• interact with external environmental stimuli