Phytochromes Flashcards
What TWO light receptors affect PHOTOMORPHOGENESIS?
Cryptochromes (Blue)
Phytochromes (Red/FRed)
Why is seed germination R/FR reversible?
Germination depends on LAST light treatment
Grow if R
How is R/FR reversibility lost?
Longer DARKNESS hours from (grow) R to (antigrow) FR leads to MORE growing
Especially from 6h (below 10%)
to 9h (around 75%) and up
(Max around 80%)
( ! ) What What does PHOTOMORPHOGENESIS include?
- Change of form
- Germination
- Stem height + thicc
- Lefa expansion
- Flowering
What effects does light have to de-etiolate seedlings?
Hypocotyl STOP elongating
LEAVES unfold, expand and green
What does a PhyA mutant look like?
Wild Type
What does a PhyB mutant look like?
Long Petioles
Small Leaves
Root Hairs
Which PHY mediate suppression elongation?
A, D + E
Which PHY regulate compact rosette phenotype?
A, B and E
Which PHY is the predominant modulator of de-etiolation?
Phy B
Are there roles for Phy A in de-etiolation?
Yes! They are normally masked by PhyB
PhyAB mutants have slightly longer Hyp than PhyB mutants
Which photoreceptors modulate light-activated CHLOROPHYLL SYNTHESIS
PhyA, PhyB, Cry1, Cry2
Act thru regulation of HEMA 1
(Gene That encodes glutamyl tRNA Reductase)
How does PhyB relate to PhyD?
PhyD has MINOR role in de-etio
Accessory roles to PhyB in HYP elongation
PhyB + D have HIGH seq similarity
(surprisingly)
PhyBD mutant HYP longer -
SYNERGISTIC EFFECT
How does PhyB relate to PhyC?
PhyC mutants have long HYP
PhyBC mutants do NOT
PhyC operates via PhyB -
Obligate Heterodimerisation of C
What is the structure of PHY (4 domains)?
~ A DIMER!! ~
GAF - binds chromophore
PAS 1 + 2 -
Bind DNA & Proteins
Nuclear Loc Signal
HKRD - His Kinase Related Domain
What is the RED peak?
665nm
What is the FAR RED peak?
725nm
How does RL activate PHY?
Light hits chromophore on GAF
Conf change
PAS domains EXPOSED
Localised (from Cytosol) to Nucleus
What is special about how PHY B, C, D + E act?
Act in Low Fluence Rate mode
> Photoreversible
> Dep. on fluence (radiant exp)
How do PHY B-E obey the Bunsen-Ruscoe law of Reciprocity?
Their response is proportional to PHOTON FLUENCE
regardless of length of irradiation time
How is PhyA unique?!
VERY light labile
More UNSTABLE
(reverts to Pr more)
∴ high levels build up in DARK
What is VLFR Response?
Very Low Fluence Rate Response
When PhyA is triggered by v. low levels of light
What is FR-HIR?
FR High Irradiance Response
PhyA can operate like this
Exposure to higher Fluence rates
