Light sensing and signaling in plants Flashcards
(26 cards)
3 reasons light input is needed
metabolism, predicting conditions, timekeeping
example of light-regulated processes
developmental transitions e.g. flowering
germination
phototropism
stomatal opening
leaf expansion
light sensing proteins are called
photoreceptors
how do photoreceptors generally work
light absorbtion leads to a reversible conformational change, which affects protein reactivity and generates a signal
some categories of photoreceptor
cytochromes, phytochromes, phototropins
example of a process controlled by red, blue, and both light types
red- germination
blue- stomatal opening
both- flowers
2 important variables for describing photoresponses
wavelength, or intensity as measured by irradiance and photon fluence
red light and germination
germination is triggered by red light, but reversed by far-red light- suggestive of low light quality
example of how to identify photoreceptors involved in something
look at action spectrum, and then check for overlap with the absorbtion spectrum of specific proteins
also genetic screening etc
phytochromes protein structure
dimers, both sides interacting with diff protein partners
chromophore in phytochromes
cphytochromobillin - has 2 forms, Pr (RED LIGHT) and Pfr (FAR-RED LIGHT)
gene duplication- allowed what
2 types of photochromes, with complementary function
how do plants know if other plants are blocking their light
red/far red light ratio- lack of red light suggests other plants are absorbing it, can then trigger growth upwards to outcompete
how does phytochrome signal transduction work
some phytochromes contain nuclear localisation sequences, others use shuttle proteins - either way enter the nucleus with a targeted partner
PIF
phytochrome interacting factors- TFs which help integrate light, temp, hormone signalling
3 classes of photoreceptors responding to blue light
phototropins, zeitlupe, cryptochromes
cryptochromes- how many are generally present in plants
2, overlapping function so generally need a dual mutant to see phenotypes
how are cryptochromes activated
FAD semireduction, opens the CRY state by phosphorylating, so interaction can occur with partners
ways cryptochromes can cause signal transduction
inhibit degradion proteins for regulators, stabilising the signal they produce
direct interactions- inhibition or activation
photomorphogenesis control
cryptochrome and phytochrome convergence on master regulators HY5 and PIFs, triggers photomorphogenesis via proteins like HFR1
phototropism activation
light triggers growth at sites of blue light detection, via proteins like NPH3, and asymmetric growth leads to growth in the direction of the light source
phytodynesis- what is it and how is it activated
movement of chloroplasts into or away from light
strong light triggers an avoidance signal, weak light triggers an accumulation signal- something to do with movement along actin filaments
what mediates stomatal opening
phototropins, which trigger guard cells to take up water- phototropins exclude protons
how is flowering time regulated
via f-box proteins- light signals interact with circadian clock elements and the regulator CO
