Plant Behavior Flashcards
Tropism
plant growth that results in the curvature of whole organism towards (+) or away (-) from stimulus
Types of Tropism
phototropism, gravitropism, thigmotropism, heliotropism
Phototropism
the effect of light on direction of plant growth in which plant tip curves toward stimulus due to movement of auxins from plant tip to target stem cells in order to promote elongation
Gravitropism
The effect of gravity on the direction of
plant growth
roots exhibit positive gravitropism
shoot exhibits negative gravitropism
Thigmotropism
Straight growth until touching something stimulates a
coiling growth response
- structural support
Heliotropism
The diurnal or seasonal movements of
plants parts in the direction of the sun
Light Receptors
Two Major Classes:
- blue-light photoreceptors - phytochromes
Blue-Light Photoreceptors
- Initiate phototropism
- Control light induced opening of stomata (leaf pores that allow for gas exchange)
- Slow hypocotyl growth as seedling breaks ground in order to focus on growth of leaves and photosynthesis
- Neighbor detection/shade avoidance
Phytochromes
- Regulates seed germination
- Relays information about quality of light
- Provides biological clock
- Controls photoperiodism
Photoperiodism
- Plants use environment stimuli to detect
time of year & then provide a
physiological response - Flowering is regulated by this method
PR and PFR
Inactive PR receives red light (660nm) and converts to PFR
Active PFR absorbs far-red light (730nm) and is converted into PR light
Net gain of PR and PFR during the day and night
sunlight contains more red light than far-red light. In the day, PR is converted into PFR, so there is a net gain of PFR
In darkness, PFR gradually changes to PR because PR is more stable than PFR
Flowering and Phytochromes
In long day plants: large amounts of PFR remain after dark period to bind to receptors. This promotes the transcription of flowering genes
In short day plants: the plant remains flowering until nights become shorter than a critical period, allowing amounts of PFR to remain after the dark period. This remaining PFR binds to receptors to inhibit the transcription of flowering genes.
long day plants flower in the _________ when nights are ________ than the critical period
summer; shorter
short day plants flower in the _________ when nights are _______ than the critical period
autumn; longer
