Phytochrome
I. Overview of photomorphogenesis
- studied in flowering/seed germination
- photoreverisble phenomena
- shown that they all had same action spectra
II. Chemistry
- phytochrome
- protein
- chromophore: open chain tetrapyrrole
- dimer
- P660/P730
- red/far red absorbance
- peaks in red and blue
- studied by difference spectra
- phytochrome A in etiolated plants
- phytochrome B light grown plants
- 5 genes
- reach photoequilibrium because of overlap of spectrum
- 85% red/15% far red
- highest levels in hypocotyl region/root
III. Phytochrome responses
- angiosperms and gymnosperms
- seed germination
- hypocotyl hook opening
- internode extension
- photoperiodism
- flower induction
- anthocyanin synthesis
- bud dormancy
- sun/shade plant responses in natural settings
IV. Mode of Action
- synthesized in Pr form which is inactive
- Pfr biologically active form
- red causes change to Pfr form
- causes response
- far red burst will reverse the response
found in cytoplasm then aggregates when hit with far red light
- receptor protein
- moves to nucleus
- binds to DNA
- activate LRE
- upregulate transcription of genes
- examples
- small sub-unit of rubisco
- cab genes
- downregulate