Lecture 29 - Plant Control Systems (part 2) Flashcards
Photomorphogenesis
is the effect of light on plant growth and development
What does Photomorphogenesis allow?
Allows plants to measure day length, time of year, seasons
Action spectra
depicts the relative EFFECTIVENESS of different wavelengths of light on processes
What can Action Spectra help determine?
what photoreceptors are active in a response
What are the 2 main photoreceptors?
- Blue-light photoreceptors (450-500 nm)
* Phytochromes (red (660nm) and far-red (730nm)
Blue-light photoreceptors (450-500 nm)
Phototropism, light-induced opening of stomata, light-induced hypocotyl growth reduction after breaking ground
Phytochromes (red (660nm) and far-red (730nm)
- Red and far-red have reversible, opposite effects
* Red light = germination, far-red = inhibits germination
Red light =
germination
Far-red =
inhibits germination
What are Phytochromes essential for?
seed germination
Phytochromes
- a type of light receptor in plants that mostly absorbs red light & regulates many plant responses, such as seed germination & shade avoidance
- There are several kinds of phytochromes, even within the same plant
- The light absorbing part is photoreversible
- Higher ratio of Pfr:Pr forms initiates germination
Photoreversible
The light absorbing part (of phytochromes)
- changes in shape due to light exposure is reversible with exposure to other forms of light (ie red vs far-red)
Higher ratio of Pfr:Pr forms…
initiates germination
What do Phytochromes assess?
the quality of light
During the day, the conversion between phytochrome states (Pr and Pfr)…
reach equilibrium
What does the ratio of Pr & Pfr help?
helps the plant assess relative amounts of light wavelengths
Shade avoidance
if plant is shaded, phytochrome ratio of Pr is HIGHER
• Leaves in canopy ABSORB red light in the chlorophyll, LEAVING BEHIND far-red
• Shift allows allocation of more resources for growing taller
If ratio of Pfr is higher…
lateral branches develop rather than height
Circadian Rhythms
• Plants respond the daily changes in light, temps and relative humidity
• Some responses occur on a 24hr cycle, without a known underlying cause -> circadian rhythms
- Controlled by gene transcription
What are Circadian Rhythms controlled by?
gene transcription
Photoperiodism and response to seasons
a physiological response to photoperiod, the relative lengths of night & day
- ex: flowering response
Flowering response
- Short-day plants
- Long-day plants
- Day-neutral plants
- Interestingly, CONTROLLED BY NIGHT LENGTH, not day length
Short-day plants
shorter photoperiod induces flowering
Long-day plants
longer photoperiods induce flowering
Day-neutral plants
flower when a certain stage of maturity is reached RATHER than day length
Gravitropism
allows the plant to grow towards the light, REGARDLESS OF POSITION
Roots display…
positive gravitropism (grow down)
Shoots display…
negative gravitropism (grow against)
Positive gravitropism
grow down
Negative gravitropism
grow against
Statoliths
are starch containing plastids in plant tissues that settle due to gravity
• Roots contain these near the root cap
• Settle near basal ends of the cells, triggering redistribution of calcium and LATERAL TRANSPORT of auxin within the root
Thigmomorphogenesis
refers to changes in morphology due to physical/mechanical perturbations
• Short, stocky trees in super windy areas
- a mechanical stimuli