Photosensing + Plant Growth Flashcards
light
key enviro signals to regulate growth and development.
= photomorphogenesis
plant photoreceptors
monitor almost all facets of light with them.
- perceive + interpret light.
- initiate signaling pathwayto regulate developmental processes.
- specific wavelength induces confomational change = initiate signal transduction
phytochromes
absorb red and far-red light
- key-regulators of photomorphogenesis
three types of photoreceptors for UV-A/blue light
cryptochromes
phototropins ( regulate phototropisms (lateral auxin redistribution), stomatal opening
zetlupe: daylegth perception and circadian rhythyms
receptors that mediate response to UVB irradiation
UVR8 - no chromophore. excite protein without it
chromoproteins
contain chromophore (light absorbing) attached to an apoprotein. - phytochrome, cryptochrome, phototropin, ZTL need one
photoresponse + spectral property of light
wavelength specificity of biological response.
germination with red light, far-red inibits it.
photoresponses + amount of light
light influence + irradiance govern photoresponse.
- some photoresponses are dose-responsive.
define fluence
total number of photons striking unit of surface area.
fr: how fast photons are arriving and how long duration of irradiation
phytochrome
primary photoreceptor, R + FR.
two states. Pr (red) and Pfr (far-red) Pr inactive & Pfr active
Phytochrome photoreversibility - diff types of light
action spectrum = absorption spectrum.
sunlight: red light over far-red
chlorophyll: under canopy = far-red, poor red ight
what is phytochromobillin
chromophore in all plant phytochromes.
- can convert between forms easily.
phytochrome gene family
multiple genes encoding.
- individual phytochromes play diff roles in regulating developmental + physiological events
few examples of what phytochrome photoreversibility mediates?
germination, leaf primordia, internode elongation, flowering, growth,
how do phytochrome responses vary?
lag time: time btw exposure + response.
escape time: time before overall sequence of reaction s become irreversible.
3 categories of phytochrome initiated responses
- Very low fluence responses
- low fluence response
- high irradiance response
what is fery low fluence response?
0.0001-1umol
sensitive: easily initiated
magnitude exhibits reciprocity: brief duration of bright light = long duration of dim ight
- non-photoreversibl
- phytA
- found in dark-grown seeds/seedlings: seed germination, gravitropic orientation, coleoptile elongation
what is low fluence response
1-1000 umol/m2
- initiated by brief pulse
- exhibits reciprocity
- R:FR reversible
- Mostly phytB
- include most phytochrome responses: seed germination, inhibit hypocotyl elongation, leaf movement
High irradiance responses
- prolonged or continuous exposure to light of relatively high irradiance
– no reciprocity. need high intensity for short time - non-photoreversible
far-red: PhytA
red + white: Phyt B
= anthocyanin synthesis, seedling de-etiolation, flowering
positively photoblastic seeds
seed germination stimulated by light
- negative photoblastic if germination inhibited by high intensity light.
germination light ratio?
high R:FR.
phytochrome regulates gene expression via
phytochrome-mediated protein degradation
phytochrome interacting factor
what is phytochrome interacting factor? what does it do?
transcription factors.
- regulate various aspects of phytochrome-mediated photomorphogenesis.
- negative regulators of photomorphogenesis in dark.
what is seedling de-etiolation
repression of skotomorphogenesis in the light via red light-induced Pfr formation promoting degradation of PIFs repressors of photomorphogenesis
