CHAPTER 39 PLANT CONTROL SYSTEMS

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CHAPTER 39PLANT CONTROL SYSTEMS

• I. hormones - chemicals that control growth
  development by allowing communication and
  coordination between different parts of an
  organism also mediate short-term physiological
  responses to environmental stimuli response to a
  hormone depends on its relative concentration
  the target tissue
• 7 major hormones - Table 39.1 (p.754)

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II. Plant Movements

• A. tropism - growth response that results in
  curvature of a whole organ toward or away from
  stimulus
• 1. phototropism - response to light
• 2. gravitropism - response to gravity
• 3. thigmotropism - response to touch

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B. turgor movements

• 1. rapid leaf movements - In some plants,
  leaves respond to touch by a rapid loss of
  turgor pressure in certain cells which causes a
  collapse of the leaf.
• 2. sleep movements - Many legumes lower their
  leaves in the evening and raise their leaves in
  the morning.

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III. Control of Daily Seasonal Responses

• A. circadian rhythm - Plants exhibit daily
  physiological cycles that persist even in the
  absence of environmental cues.
• B. photoperiodism - physiological response to
  day length (actually responding to night
  length) through the use of phytochromes

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IV. Plant Responses to Stress

• A. water deficit - guard cells lose turgor and
  stomata close abscisic acid produced to keep
  stomata closed inhibits leaf growth wilting
  decreases water loss photosynthesis slowed
• B. oxygen deprivation - formation of air tubes
  provides O2 to submerged roots

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Responses to Stress (cont.)

• C. salt stress - production of compatible
  solutes that keep the water potential of root
  cells more negative than soil
• D. heat stress - increased transpiration (up to
  a point) synthesis of heat- shock proteins
  which protect proteins from denaturing

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Responses to Stress (cont.)

• E. cold stress - altered lipid composition of
  membranes (increased unsaturated fatty acids)
  altered composition of cytoplasm
• F. herbivores - physical defenses (thorns)
  chemical defenses (distasteful or toxic
  compounds) recruitment of predatory animal
  defenders

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V. Defense Against Pathogens

• A. first line of defense - physical barrier of
  the epidermis periderm
• B. coevolution of resistance by the plant to
  specific pathogens through gene- for-gene
  recognition
• C. cell damage due causes production of
  antimicrobial compounds and formation of
  local barricades