Download Environmental responses

Plant Responses to the
Environment
Stationary Life
• Animal response to stimuli
– Move toward or away
• Plant response to stimuli
– Adjust patterns of growth
– Plasticity varied forms
– Chemicals
Signal Transduction Pathways
• Reception Transduction Response
– Ex. Potato greening
– Ex. Seed germination
• Reception
– Receptor proteins undergo conformational
changes in response to stimuli
• Transduction
– Second messengers amplify signal
– Turn on kinases phosphorylate enzymes
• Response
– Stimulates RNA production
• Make new enzymes
– Activates existing enzymes
• phosphorylation
Response
Hormones
• Coordinate growth, response
• Specific receptor, specific response
• Minute quantities cause large reactions
Plant movement
• Tropism- growth toward or away from
stimuli
– Light- phototropism
– Gravity-gravitropism
– Pressure-thigmotropism
• Affect division, elongation and
differentiation of cells
phototropism
• Auxin (hormone) is distributed
asymmetrically
• One side grows more quickly
• Plant grows toward light
Response to Mechanical stress
• Triple response due to
– Slowing of stem elongation
– Thickening of stem
– Horizontal growth
• “feels” for obstacle
• Seedlings respond the same way
when ethylene is applied without an obstacle
Apoptosis-programmed cell death
• Vessel element formation
• Leaf abscission
– Nutrients are stored in stem parenchyma
– Abscission layer has weak cell walls, sensitive
to ethylene
Fruit ripening
• Ethylene triggers cell wall breakdown
• Starch converted to sugar
• Chain reaction: ethylene triggers
ripening ripening triggers more ethylene
• Fruit ripens at the same time
• Commercial use
• GMO tomatoes lack ethylene
Delayed germination
• Abscisic Acid prevents germination
• Removal/inactivation of ABA allows
germination
• Cold
• Light
• Water
Gravity
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Gravitropism
Controlled by Auxin
Statoliths=starch grains in cytoplasm
High concentration of starch attracts Auxin
High concentration of Auxin in roots slows
down cell growth root bends down
• High concentration of Auxin in stem
speeds up stem growth
Touch
• Thigmotropism-move toward solid object
• React to touch –open ion transport
chanels
• Cells deflate, leaves collapse
Defense mechanisms
• Secondary compounds
– Tannins
– Jasmonic acid= messenger
• Symbiosis
– Damaged leaves release volatile molecules
– Attract parasitic wasps
– Wasps kill caterpillars
• In a diseased state known as witches
broom branches grow and proliferate
excessively.
Suggest a hypothesis
to explain how a
pathogen might
induce this growth
pattern?
Responses to light
• Photosynthesis
• Development
– photomorphogenesis
• Timing
– germination
– Flowering
– Fruit
Light receptors
• Blue light photoreceptors
– Phototropism
– Opening stoma
– Slowing of cotyledon growth
• Phytochromes (red and far red light)
– Seed germination (break dormancy)
– Shade avoidance (primary vs. apical growth)
Red-Far Red phytochrome switch
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Protein has two shapes: Pr and Pfr
Phytochromes “see” red and far red light
Pr absorbs red light  turns into Pfr
Pfr absorbs far red turns in to Pr
Germination and shade avoidance
• Germination
– Sunlight contains red light, Pr turns into Pfr
– Pfr (exposure to sunlight )promotes
germination
• Shade avoidance
– Canopy filters out more red light, leaves far
red light
– Pfr more resources to growing taller
– Pr branching, more leaves
Circadian rhythms
• Growth chamber experiments
– Photosynthetic enzymes
– Stomata
– Leaf position
Pfr is made during
the day, reverts at night
Dawn resets biological
clock by putting more
Pfr into the system
when the sun comes
out
Photoperiodism
• Germination, budding, flowering, etc.
correspond to the season
• Seasons have different relative day/night
• Day/Night length determine timing of
events (temperature is irrelevant)
• Fall leaves
Flowering
• Short day (long night)- need longer period
of continuous darkness
• Long day (short night)- requires shorter
period of continuous darkness
• Leaves detect period of darkness, transmit
signal to flower buds,
• Red light can
interrupt night
• Far red light cancels
red light interruption
• Manipulate
plants to flower
– Chrysanthymums
long night plant,
interrupt each night
w/light, delay flowering
until mother’s day