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Plant Response to Signals. Ch 39. Plant Response. Stimuli & a Stationary Life animals respond to stimuli by changing behavior move toward positive stimuli move away from negative stimuli plants respond to stimuli by adjusting growth & development. Signal Transduction Pathway model. - PowerPoint PPT Presentation
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Plant Response to Signals
Ch 39
Plant Response Stimuli & a Stationary Life
animals respond to stimuli by changing behavior move toward positive stimuli move away from negative stimuli
plants respond to stimuli by adjusting growth & development
Signal Transduction Pathway model signal triggers receptor receptor triggers internal cellular
messengers & then cellular response
receptor signal pathway(2° messengers)
responseWhat kinds of molecules are the receptors?
Signal Transduction Pathway example
1. Light signal is detected by the phytochrome receptor, which then activates at least 2 signal transduction pathways2. One pathway uses cGMP as a
2nd messenger to activate a protein kinase.The other pathway involves increases in cytoplasmic Ca2+ that activates a different protein kinase.
3. Both pathways lead to expression of genes for proteins that function in greening response of plant.
Signal Transduction Pathway example
1. Light signal is detected by the phytochrome receptor, which then activates at least 2 signal transduction pathways2. One pathway uses cGMP as a
2nd messenger to activate a protein kinase.The other pathway involves increases in cytoplasmic Ca2+ that activates a different protein kinase.
3. Both pathways lead to expression of genes for proteins that function in greening response of plant.
Plants do not have brains Or nervous systems for that matter,
So how do they communicate with itself and coordinate beneficial responses?
Plant hormones Chemical signals that coordinate
different parts of an organism only tiny amounts are required produced by 1 part of body transported to another part binds to specific receptor triggers response in target cells & tissues
Plant hormones auxins cytokinins gibberellins abscisic acid ethylene
2005-2006
Hormones in review: AUXINS __ Promote cellular elongation __ by softening of cell
walls __ Involved in phototropism __ Involved in geotropism __ Involved in apical dominance
CYTOKININS __ Promotes lateral growth_ growth in size of leaf cells __ Stimulate cell division (hence name) __ Release buds from apical dominance
GIBERELLINS __ seasonal growth___ Stimulate cell elongation __ Produce bolting in biennials __ Stimulate production of starch digestion enzymes in some seeds
ABSCISIC ACID __ opposite of giberellins__causes slow down or “cut off” of growth__Promotes stomatal closure __ __ Promotes seed and bud dormancy _
ETHYLENE __ Promotes ripening of fruit
Response to light: Phototropism Growth towards light Hormone: Auxin
asymmetrical distribution of auxin, moves away from sunny side of stem (-ve phototropism, -ve gravitropism)
cells on darker side elongate faster than cells on brighter side
Apical dominance Controls cell division &
differentiation axillary buds do no grow while
apical bud exerts control
2005-2006
shootroot
Figure 39.8
Cross-linkingpolysaccharides
Cell wall–looseningenzymes
Cellulosemicrofibril
Expansin
CELL WALL
Plasma membrane
CYTOPLASM
Plasmamembrane
Cell wall
Nucleus CytoplasmVacuole
H2OH
H
H
H HH
H
H
HATP
Cell elongation in response to auxin: the acid growth hypothesis
Gibberellins Family of hormones
over 100 different gibberellins identified Effects
fruit growth seed germination plump grapes in
grocery stores have been treated with gibberellin hormones while on the vine
Abscisic acid (ABA) Effects
slows growth seed dormancy
high concentrations of Abscisic acid germination only after ABA is inactivated down or
leeched out survival value:
seed will germinate only under optimal conditions light, temperature, moisture
drought tolerance rapid stomate closing
Ethylene Ethylene is a hormone gas released by plant
cells Multiple effects
response to mechanical stress triple response
slow stem elongation thickening of stem curvature to stem growth
leaf drop (like in Fall) apoptosis
fruit ripening
Apoptosis & Leaf drop:combination of hormones
Ethylene & auxin many events in plants
involve apoptosis (pre-programmed cell death) death of annual plant after
flowering differentiation of xylem
vessels loss of cytosol
shedding of autumn leaves
What is the evolutionary advantage of loss of leaves in autumn?
Fruit ripening Adaptation
hard, tart fruit protects developing seed from herbivores
ripe, sweet, soft fruit attracts animals to disperse seed
Ethylene triggers ripening process
breakdown of cell wall softening
conversion of starch to sugar sweetening
positive feedback system ethylene triggers ripening ripening stimulates more ethylene production
Applications Truth in folk wisdom…..
one bad apple spoils the whole bunch ripening apple releases ethylene to speed ripening
of fruit nearby Ripen green bananas by bagging them with an
apple Climate control storage of apples
high CO2 storage = reduces ethylene production
2005-2006
Plant stimuli
Flowering Response Triggered by photoperiod
relative lengths of day & night night length—“critical period”— is trigger
Short-day plants Long-day plants
Plant is sensitive to red light exposure
What is the evolutionary advantage of photoperiodism?
Synchronizes plant responses to season
Circadian rhythms Internal (endogenous) 24-hour cycles
Morning glory
4 O’clock
Noon Midnight
Response 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
2005-2006
Response to touch Thigmotropism
2005-2006
Mimosa (Sensitive plant) closes leaves in response to touch
Caused by changes in osmotic pressure = rapid loss of K+ = rapid loss of H2O = loss of turgor in cells
Plant defenses Defenses against herbivores
2005-2006
Plant defenses Defenses against herbivores
Parasitoid wasp larvae emerging from a caterpillar
coevolution
Any Questions??