Definitions
Etiolation
Morphological adaptations for growing in darkness. Provide an example.
What are the 3 transduction pathways?
1. Reception: Includes receptors
2. Transduction: Has second messengers
3. Response
What does auxin do?
Stimulates the activity of proton pumps in the plasma membrane which causes a low pH. Can stimulate plant growth, can determine phyllotaxy, direct pattern of leaf venation.
Cytokinins
Stimulate cytokinesis, produced in roots, embryos and fruits, control cell division and differentiation. Have no effect alone. Slow the aging of plant organs.
What is senescence?
Programmed death of cells, organs or entire plant. Caused by vessel element formation, death of an annual after flowering, leaf abscission.
De-etiolation
"Greening". Changes that follow exposure to light that lead to shoots, leaves and roots growing normally.
What is the receptor in de-etiolation?
The receptor is a cytoplasmic phytochrome that is capable of detecting light by opening Ca2+ channels, increasing Ca2+ levels in the cytosol. It also activates an enzyme that produces cGMP
What does the low pH cause?
Gibberellins
Stimulate stem and leaf growth by enhancing cell elongation and division, induce bolting (rapid growth of floral stalk), facilitate fruit growth, seed germination
What are the 2 kinds of light receptors?
1. Blue-light photoreceptors: Case light-induced opening of stomata, slow hypocotyl elongation
2. Phytochrome (absorb mostly red): De-etiolation, seed germination, shade avoidance
Tropism
Any growth response resulting in curvature of organs toward or away from a stimulus.
Bonus: What is phototropism?
What are 2 second messengers found in transduction?
1. Ca2+ ions
2. Cyclic GMP
Turgor pressure and increased cell wall plasticity
Abscisic Acid (ABA)
Slows growth, antagonizing actions of growth hormones. Effects on seed dormancy, helps with drought tolerance
In phytochrome, red light triggers the conversion of..
Pr to Pfr
(far red light does the opposite)
Apical dominance
Terminal bud's ability to suppress development of axillary buds under the control of sugar, cytokinins, auxin and strigolactone.
What type of enzymes does de-etiolation activate?
It activates enzymes that function in photosynthesis directly, supply the chemical precursors for chlorophyll production, affect level of plant hormones that regulate growth
**NOT ABOUT ACID GROWTH HYPOTHESIS**
What is florigen (FT)?
Protein signal that induces transition of apical meristem to a flowering state. Photoperiod detected by leaves --> cue buds to develop as flowers.
Ethylene
Gas produced in response to drought, flooding, mechanical pressure, injury and infection. Effects include fruit ripening, leaf abscission
Leaves in canopies absorb mostly...
Triple Response
1. Stem elongation slows
2. Stem thickens
3. Stem grows horizontally
**NOT ABOUT TRANSDUCTION***
Differentiate between short-day, long-day and day-neutral plants.
Short-day: Flower when a light period is shorter than a critical length.
Long-day: Flower when a light period is longer than a critical length.
Day-neutral: Controlled by plant maturity, not photoperiod.
**NOT ABOUT ACID GROWTH**
Gravitropism.
Response to gravity detected by statoliths.
Roots have positive gravitropism.
Shoots have negative gravitropism.
Strigolactones
stimulate seed germination, suppress adventitious root formation, establish mycorrhizal associations.
Shaded plants receive...
Far-red light. Phytochrome ratio shifts in favor of Pr, shifts resources to growing taller.. "shade avoidance"