Transcript Plant Responses/Behavior

Plant
Responses/Behavior
Cell division, germination, cell
differentiation, flowering, fruit
ripening, root growth, branching, etc
Tropisms
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Growth response toward (+) or away from (-) a
stimulus
Phototropism
 Response to light
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Shoots (stems) +
phototropism
Roots – phototropism
Gravitropism
 Response to gravity
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Shoots (stems) –
gravitropism
Roots + gravitropism
Thigmotropism
 Response to touch
Other Responses
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Apical dominance
 Apical bud/shoot represses lateral growth
Photoperiodism
 Plants detect & respond to periods of darkness
Abscission
 Aging of leaves
Circadian rhythms
 Cycles of daily behaviors
 Controlled by endogenous clocks
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 Sleep movements
(varies)
Need specific amt of uninterrupted
Darkness, MORE than critical night length
Need specific amt of uninterrupted
darkness SHORTER than critical
night length
So what makes plants behave the way they do?
HORMONES!!!!
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Chemical signals produced in
one part of an organisms that
influence another
Triggers a response at the
cellular level, relies on specific
hormone receptor binding
Effective at extremely small
concentrations
Overall behavior/growth is a
result of a combo of all
hormones
Experimenting w/ Hormones
Conclusions:
Darwin-chemical in tip, light required
Boysen-Jenson-signal is mobile,passed
thru agar
Went Experiments:
Chemical is produced in tip,
Concentrates on dark side,
Causes elongation of cells
The answer is…..
AUXIN
Mechanism of Auxin
Stimulatory Hormones
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Auxins
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Elongation of cells in
developing shoots
Induces cell division in
vascular cambium
Promotes fruit growth
Responsible for photo &
gravi tropisms
Stimulatory cont….
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Cytokinins
 Produced in actively
dividing
tissues(germinating
seeds, fruits, roots)
 Delay senescence
 Controls
differentiation (w/
auxin)
More stimulation…
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Gibberellins
 Produced in roots,
stimulate stem &
leaf growth
 Promote fruit
development (W/
auxin)
 Stimulate
germination (if
environmental
conditions are right)
Inhibitory Hormones
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Abscisic acid
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Prepares for dormancy
by inhibiting vascular
cambium & slowing
bud growth
Keeps seeds dormant
Produced during water
stress (causes guard
cells to lose water,
closing stomata)
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Inhibitory continued…
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Ethylene
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Only gaseous hormone
Inhibits cell growth &
elongation in all plant
organs
Causes senescence
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Fruit ripening-degrades
cell walls, reduces
chlorophyll
Leaf abscissiondegrades cell wall
between stem & petiole
Even more plant behaviors
(and you thought they were boring!)
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O2 deprivation
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High salt
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Heat shock proteins bind to enzymes
& prevent denaturing
Cold
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Produce extra solutes
Heat
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Release of ethylene from roots, holes
form
Synthesize more unsaturated FAs
Herbivores
Pathogens
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Anti-microbial compounds, alarm
chemicals, PR genes