Describe the concept of Phytochrome.

Explanation

Phytochrome is a bluish biliprotein pigment responsible for the perception of light in photo physiological process. Butler et al., (1959) named this pigment and it exists in two interconvertible forms: (i) red light absorbing pigment which is designated as `P_r` and (ii) far red light absorbing pigment which is designated as `P_(fr)` The `P_r` form absorbs red light in 660 nm and changes to` P_r`. The `P_r` form absorbs far red light in 730 nm and changes to `P_r` . The` P_r` form is biologically inactive and it is stable whereas `P_(fr)` form is biologically active and it is very unstable. In short day plants, `P_r` promotes flowering and Pr inhibits the flowering whereas in long day plants flowering is promoted by `P_(fr)` and inhibited by` P_r` form. `P_(fr)` is always associated with hydrophobic area of membrane systems while `P_r` is found in diffused state in the cytoplasm. The interconversion of the two forms of phytochrome is mainly involved in flower induction and also additionally plays a role in seed germination and changes in membrane conformation.