L2 and 3 Kerry Franklin - Light responses Flashcards
What is photomorphogenesis?
Plant development controlled by light quantity, direction, periodicity, and quality.
what is a photoperiod?
Give an example of photoperiod affecting photomorphogenesis
- the length of light (of a ‘day’)
- Chrysanthemums are short day plants - flowers in 8h days. no flowers in 16h days.
describe etiolated and de-etiolated apearence of arabidopsis seedlings
Etiolated - dark grown - Long hypocotyl, cotyledons folded up in apical hook. If cotyledons were open, would be damaged in soil.
De-etiolated - light grown - large cotyledons, short hypocotyl.
What is a monocot version of the apical hook?
coleptie
Which photoreceptors detect red/far red light?
Phytochromes
Which photoreceptors detect blue light?
Cryptochromes, phototropins
What two components are in a phytochrome molecule?
Protein - Apophytochrome
Chromophore
What is a chromophore?
A light absorbing molecule, formed by Protoporphyrin in the chloroplast.
Wha does the chromophore and the Apophytochrome together make?
holophytochrome
Which is the active and inactive phytochrom form?
Pr- inactive
Pfr - active, regulated gene expression.
Red light favours activation, and far red light favours inactivation.
Describe the flip flop germination experiment.
- Under red light, arabidopsis seedlings germinated (Pfr)
- Under red then FR light, Pfr converted into Pr so no germination
- Red, FR then Red again, germination, as the final molecule was Pfr
- Shows he last molecule present caused germination or not germination.
What phytochrome types do dicots and monocots have?
Dicots - (A,C) (E, B, D)
Monocots - (A, C) B
What are the functions of phytochromes?
Germination timing
Suppress flowering, plant energy is used for leaves and photosynthesis.
Regulate development through lifecycle
Regulate plant architecture
How can you use genetics to determine phytochrome function?
- create mutants with genes defective in phytochrome function
- Compare photoresponses with wild type, to determine what the phenotype is of the mutated gene
What does a light grown phya mutant look like?
Long hypocotyl.
Phy A supresses hypocotyl elongation in light.
Describe photoresponses in Dark, Red, FR and blue light
dark - long hypocotyl, cotyledons inside apical hook
Red - small plant, cotyledons open
FR - small, open cotyledons and yellow
Blue - Taller, small cotyledons
Why is it weird that phyA signals in far red light?
It gets inactivated in far red light, Pfr -> Pr
How does phy a manage to signal in FR light even though it gets inactivated?
- Pfr is rapidly degraded, and more Pfr = faster degradation.
- accumulates to high levels in dark grown seedlings
- FR is very inefficient at producing Pfr, so cycling between Pr and Pfr causes a signal and protects it from degradation.
Simply, what does Phy A do?
Acts as a sensitive light antenna, which rapidly degrades and triggers photomorphogenesis following soil emergence.
What do plants with less phytochromes look like?
Long and spindly, early flowering
How do plants adapt in an enclosed habitat to low light conditions?
Shade tolerance mechanisms. Adapted to endure shade, with thinner leaves, higher chlorophyll content, increase photosynthetic efficiency.
How do plants adapt in an open habitat to low light conditions?
Adapted to escape, shade avoidance techniques.
Elongate leaves and stems to overlap competitors
in sunlight are phytochromes mainly active or inactive?
Active, more Pfr, as sunlight has more red than FR light.
Why is having more Pfr in sunlight beneficial?
Keeps stems short so energy and resources are directed at leaf development, for photosynthesis.
