Cells and cell growthMembranes and cell walls Fertilization and
embryogenesis
Seed development and dormancy
Germination
Water transport
Water relations
Plant nutrition
Solute transport
Gene function
SkotomorphogenesisPhotomorphogenesis
Phytochrome
Three learning goals:
- what is a phytochrome
plant photoreceptor to govern light development
requirements:light sensing abilitysignal transduction
- phytochromes and their integration in developmenthow phytochrome senses light and what happens then
requirements:light sensitivity at particular wavelengths
- phytochrome interactions with downstream proteins
requirements: signal transduction apparatus that connects phytochrome activity with gene regulation
Phytochrome – plant signal transduction
Environmental signal: light
Receptor: phytochrome
Signal transduction: PIF etc.
Gene activation: PIGs
Biological response: photomorphogenesis
Germination of lettuce seeds (photoreversibility)
Reversible R/FR response system controlled by phytochrome
germination germination
synthesisgermination,flower Induction……
red light
far red light
Phytochrome: from synthesis to action
Arabidopsis: 5 phytochrome proteins (phyA - phy E),
differ in their apoproteins
Phytochrome: homodimeric chromoprotein:
apoprotein and phytochromobilin (open chained tetrapyrrol) as chromophor form holoprotein
Strasburger, 2002
R FR
PRinactive
PFRactive
PFR
active
PR
inactive
sensor signal transduction
Regulatory function
Phytochrome responses vary with amount of light
VLFR: 0.00001 µmol x m-2
LFR: 1-1000 µmol x m-2
Arabidopsis seed germination
Lettuce seed germination
Anthocyanin synthesisInhibition of hypocotyl elong.Enlargement of cotyledonsApical hook opening
HIR: >1000 µmol x m-2 x s-1
Phytochrome responses vary with amount of light
Inhibition of hypocotyl elongation
HIR: >1000 µmol x m-2 x s-1
Pr PfrRed light
Far-red light
Photoequilibrium:
660 nm 80% Pfr730 nm 2-3% Pfr
R/FRSunlight: 1.13
Dusk: 0.8/0.9
Shade of leaves:0.2
inactive ACTIVE !!!
Red light
Far-red light
PrPfr
Two holoproteins (+chromophore) form a dimer
Histidine kinase related
Chromophore binding domain
IIAIA
IIBIB
IA IIA
IIBIB