light as a developmental cue Flashcards
name the 4 things involved in light as a ligand in the signal transduction pathway
phytochrome
phototropism
photomorphogenesis
circadian rhythms
does light directly activate promoter elements?
no, instead light is perceived, then a signaling pathway is activated where TFs bind to light responsive elements
studies of seed germination led to discovery of ___
phytochrome (plant photoreceptors)
phytochrome structure consists of two ____ joined to form ____
each of these proteins has 2 domains:
identical proteins joined to form one functional dimer molecule
photoreceptor activity & kinase activity
phytochrome is a ____, it exists in two different protein form that are reversible by ___
photoreceptor
light wavelengths (interconversion triggers diff responses)
phytochrome alternates between 2 forms:
Pr absorbs red light (660 nm) and is converted to Pfr
Pfr absorbs far-red light (730 nm) and is converted to Pr
phytochrome: red light stimulates ___ and far-red light inhibits ____
seed germination
seed germination
how does light effect phytochrome?
light activation of phytochrome to the Pfr (active) form allows it to rapidly accumulate in the nucleus and activate gene expression
light signaling in the eye:
cone cells are sensitive to ___
rod cells are sensitive to ___
colors
light, not colors
photoreceptors in the retina: light induces…
dissociation of retinal from opsin
- in the dark, enzymes convert retinal back to its cis-configuration (going from bright environment to a dark one: not enough cis-retinal available, blinding effect
light signal transduction in animals involves ____, followed by ___ and ____
a light induced isoform change
G-protein signal pathway
ion channal activation
name the 4 classes of plant photoreceptors
1- phytochromes
2- cryptochrome
3- phototropins
4- UVR8
cryptochrome is ___ light
blue
phototropins are ___ light
blue
UVR8 is ___ light
UV-B
what is phototropism?
growth response to light
shoot exhibit ___ phototropism
roots exhibit ___ phototropism
positive (grows toward light)
negative (grows away from light)
tropism = any ___ response that results in the ___ of plant parts toward or away from a stimulus
what does it result from?
growth
curvature
results from differential cell growth on opposite sides of stem or root
phototropism involving auxin:
asymmetrical distribution of auxin moving down from the shoot top causes cells on the ___ side to…
darker side to elongate faster than cells on brighter side
photomorphogenesis means…
light affecting development
cyclical responses to environmental stimuli are ___
approximately ___ long
circadian rhythms
24 hrs
480 of 8,000 tested genes are under ___ control
circadian
many plants follow a circadian rhythm of ___ their leaves
raising-lowering (light regulated)
in plants - what is referred to as light quality or the ___ can determine the effect of light on the biological clock
perception of this ratio/amount is done by ___
ratio of red to far red light
phytochrome
this then provides the organisms’ biological clock with environmental cues
