Phytochrome: The pigment responsible for the photo induction or inhibition of flowering in short day plants and stimulation of flowering in long day plants is called Phytochrome. It is proteinaceous in nature.
Phytochrome acts as photoreceptor molecule by absorbing light and showing its effect on various developmental and morphogenetic process. Borthwick, H. A, Hendricks, S. B. And colleagues proposed the light absorbing pigment which was later called phytochrome (abbreviated as P), exists in two forms:
1) Its inactive form is phytochrome red(abbreviated as PR)
2) Active form is phytochrome far red(abbreviated as PFR)
Both forms are interconvertible
Difference between PR form and PFR form
1. It is an inactive form is phytochrome.
2. Being inactive, it does not show phytochrome mediated responses.
3. It has an absorption maximum in red region (about 680 nm)
4. It is found diffused throughout the cytosol.
5. It is converted into PFR form in presence of red light (660-665 nm)
6. When the extract is centrifuged at 20000 x g, it remains present in the supernatant.
7. It shows activity in presence of urea, metal ions Cu2+, C2+, Zn2+ etc., and N-ethyl maleimide.
8. Its original structure contains many double bonds in pyrrole rings
1. It is an active form is phytochrome.
2. Being active, it shows phytochrome mediated responses.
3. It has an absorption maximum in far red region (about 730 nm)
4. It is usually found in discrete areas of cytosol.
5. It converted into PR form in presence of far red light (730-735 nm)
6. On centrifugation PFR form settles down in the form of pillets
7. It shows comparatively more activity in presence of these chemicals
8. The PFR form shows rearrangement of double bonds in all four pyrrrole rings