Title: Phytochromes
1Lecture 25
2Light regulates plant development
3Light regulates plant development
Skotomorphogenesis (dark form begins) plants
response to darkness etiolated growth
Photomorphogenesis (light form begins) plants
response to light
4Information-transducing photoreceptors
5The roles of light in the life of plants
6Lettuce seed germination is a typical
photoreversible response controlled by phytochrome
7Photoreversibility a distinctive feature of
phytochrome
Red light
Far-red light
8Absorption spectra of purified phytochrome
Far red
Red
9Phytochrome structure
- - soluble protein of 250 kDa
- Dimer composed of two polypeptides
- each monomer consists of two components
chromophore apoprotein - holoprotein
chromophore
I, II monomers A chromophore- binding
domain B non-chromophore domain
apoprotein
10Structure of the Pr and Pfr forms of the
chromophore (phytochromobilin)
11Phytochrome is encoded by a multigene family
Pre-dominant forms
PhyA ? responses to FR
PhyB ? responses to R or white light
Have unique roles in regulating responses to red
and far-red
12phyA mutant seedlings show reduced sensitivityto
far-red light
13phy B mutant seedlings show reduced sensitivity
to red light
Phytochrome B acts as a red light sensor
14Phytochrome deficiencies alter growth and
development in pea and tomato
15Ecological functions of phytochromes
Light-grown phyB mutants are elongated and early
flowering
Resembles phyB mutant phenotype
16Phytochrome enables plant adaptation to light
quality changes
17Shade Avoidance Response
Plants that increase stem extension in response
to shading ? shade avoidance response (sun
plants)
shade plant
sun plant
18Ecological functions of PHYA and PHYB
Effect of PHYA and PHYB on seedling development
in sunlight versus canopy shade
After Quail et al. 1995
19Reducing shade avoidance responses can improve
crop yield
20PHYA, B, C, D, E