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Transcript of Plant Responses Chapter 39. Signal Transduction Plants have cellular receptors that detect important...
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Plant Responses
Chapter 39
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Signal Transduction
Plants have cellular receptors that detect important changes in their environment
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Etiolation Greening Response
Grown in Dark 1 week exposure to Light
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Signal Transduction Pathway Model signal triggers receptor receptor triggers internal cellular
messengers & then cellular response
receptor signal pathway(2° messengers)
response
What kinds of molecules are the receptors?
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Signal Transduction Pathway
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Plant Hormones
Chemical signals that coordinate different parts of an organismonly minute amounts are required produced by 1 part of bodytransported to another partbinds to specific receptortriggers response in target cells &
tissues
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Plant Hormones
auxins cytokinins gibberellins brassinosteroids abscisic acid ethylene
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The Discovery of Plant Hormones
Tropisms : Phototropism
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Signal is a a mobile chemical
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The Went Experiments
Went named the chemical “auxin”
Later purified as indolacetic acid(IAA)
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How Auxins Cause Cell Elongation
Increase in H+ activates expansins Weakened cell wall allows more water to
enter
H+ pump
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Auxins
Herbicides2-4-D Affects secondary growth Synthetic auxins
sprayed on green house plants induce fruit development
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Cytokinins
Stimulate Cytokinesis Are produced in actively growing
tissues
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Gibberellins Stimulate cell elongation and division Bolting Fruit Growth Germination Effects
stem elongation fruit growth seed germination
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Figure 39.11 The effect of gibberellin treatment on seedless grapes
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Abscisic Acid (ABA)
Slows growth Maintains seed dormancy Drought tolerance
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Ethylene A magic gas?
Response to stress Leaf abscission Fruit ripening Slowing,
thickening, curving
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Ethylene induces the triple response in pea seedlingsSlowing, thickening,curvingETHYLENE
A magic gas?
Response to stress
Leaf abscission Fruit ripening
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Abscission of a maple leaf
Apoptosis Caused by
ethylene/auxin shift
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Responses to gravity How does a sprouting shoot “know” to grow
towards the surface from underground?environmental
cues? roots = positive
gravitropism shoots = negative
gravitropism settling of statoliths
(dense starch grains) may detect gravity
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Molecular Switch Mechanism of Phytochromes
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Phytochrome photoreceptors Molecular switch reaction to red light
conversion of Pr Pfr in sunlight stimulates germination, flowering, branching…
conversion of Pfr Pr in dark inhibits response, & stimulates other responses: growth in height
Light induced
Phytochrome
ChromophorePhotorecptor
Kinase activity
Response:Vertical growth
Phytochrome
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Circadian Rhythms Internal (endogenous) 24-hour cycles
Morning glory
4 O’clock
Noon Midnight
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Figure 39.21 Sleep movements of a bean plant
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Figure 39.x1 Biological clocks
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Figure 39.22 Photoperiodic control of flowering
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Figure 39.23 Reversible effects of red and far-red light on photoperiodic response
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Is there a flowering hormone? Plant on left is
induced to flower & then grafted onto plant on rightplant on right is
triggered to flower
What can you conclude?
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Thigmomorphogenesis Change in form
resulting from mechanical perturbation
Altering gene expression by touch in Arabidopsis
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Figure 39.27 Rapid turgor movements by the sensitive plant (Mimosa pudica)
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Plant Defenses Defense against herbivores Defense against pathogens Systematic acquired resistance
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Figure 39.29 A corn leaf recruits a parasitoid wasp as a defensive response to an herbivore, an army-worm caterpillar
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Figure 39.31 Defense responses against an avirulent pathogen