Ch. 39 Warm-Up

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Ch. 39 Warm-Up

• Elaborate on the methods plants use to defend
  themselves from pathogens and herbivores.
• How do plants cope with
• Flooding
• Drought
• Heat stress
• Salt stress
• If a long day plant needs at least 9 hours of
  dark, which scenario(s) will prevent flowering?
• 16 hours light, 8 dark
• 14 hours light, 10 dark
• 14 hours light, 10 dark w/ flash of light

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Ch. 39 Warm-Up

• Match the following terms with the descriptions
  below
• Auxin
• Cytokinins
• Gibberellins
• Abscisic Acid
• Ethylene
• Inhibits growth, closes stomata during H2O stress
• Fruit ripening, promotes or inhibits growth
• Affects root growth, stimulates cell division
  growth, stimulates germination
• Stimulates stem elongation, root growth, fruit
  development, photo- gravitropism
• Promotes seed bud germination, stem elongation,
  flowering development of fruit

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What you must know

• The three steps to a signal transduction pathway.
• The role of auxins in plants.
• How phototropism and photoperiodism use changes
  in the environment to modify plant growth and
  behavior.
• How plants respond to attacks by herbivores and
  pathogens.

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Chapter 39

• Plant Responses to Internal and External Signals

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Experiments with Light and the coleoptile
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Cells on darker side elongate faster than cells
on brighter sideAUXIN chemical messenger that
stimulates cell elongation
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• Important plant hormones
• Auxin stimulate cell elongation ? phototropism
  gravitropism (high concentrations herbicide)
• Cytokinins cell division (cytokinesis)
  differentiation
• Gibberellins stem elongation, leaf growth,
  germination, flowering, fruit development
• Abscisic Acid slows growth closes stomata
  during H2O stress promote dormancy
• Ethylene promote fruit ripening (positive
  feedback!) involved in apoptosis (shed leaves,
  death of annuals)

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The effects of gibberellin on stem elongation and
fruit growth
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Ethylene gas fruit ripening
Canister of ethylene gas to ripen bananas in
shipping container
Untreated tomatoes vs. Ethylene treatment
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Plant Movement

• Tropisms growth responses ? SLOW
• Phototropism light (auxin)
• Gravitropism gravity (auxin)
• Thigmotropism touch
• Turgor movement allow plant to make relatively
  rapid reversible responses
• Venus fly trap, mimosa leaves, sleep movement

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Positive gravitropism in roots the statolith
hypothesis.
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Thigmotropism rapid turgor movements by Mimosa
plant ? action potentials
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Plant Responses to Light

• Plants can detect direction, intensity,
  wavelenth of light
• Phytochromes light receptors, absorbs mostly red
  light
• Two forms Pr (red light) and Pfr (far-red light)
• Pr ? Pfr switches depending on light in greatest
  supply
• Pfr aids in detection of sunlight
• Regulate seed germination,
• shade avoidance

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Biological Clocks

• Circadian rhythm biological clocks
• Persist w/o environmental cues
• Frequency 24 hours
• Phytochrome system Biological clock plant can
  determine time of year based on amount of
  light/darkness

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Sleep movements of a bean plant. Caused by
reversible changes in turgor pressure of cells on
opposing sides of the pulvini, motor organs of
the leaf.
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Photoperiodism physiological response to the
relative length of night day (i.e. flowering)

• Short-day plants flower when nights are long
  (mums, poinsettia)
• Long-day plant flower when nights are short
  (spinach, iris, veggies)
• Day-neutral plant unaffected by photoperiod
  (tomatoes, rice, dandelions)

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How does interrupting the dark period with a
brief exposure to light affect flowering?
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Plant Response to Stress

• Causes of stress
• Drought (H2O deficit)
• Flooding (O2 deprivation)
• Salt excess
• Heat
• Cold
• Herbivores
• Pathogens

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• H2O deficit
• close stoma
• release abscisic acid to keep stoma closed
• Inhibit growth
• roll leaves ? reduce SA transpiration
• deeper roots
• Flooding (O2 deprivation)
• release ethylene ? root cell death ? air tubes
  formed to provide O2 to submerged roots

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• Salt
• cell membrane impede salt uptake
• produce solutes to ?? - retain H2O
• Heat
• evap. cooling via transpiration
• heat shock proteins prevent denaturation
• Cold
• alter lipid composition of membrane (?unsat.
  fatty acids, ?fluidity)
• increase cytoplasmic solutes
• antifreeze proteins

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• Herbivores
• physical (thorns)
• chemicals (garlic, mint)
• recruit predatory animals (parasitoid wasps)
• Pathogens
• 1st line of defense epidermis
• 2nd line pathogen recognition, host-specific