EVERYDAY SCIENCE

Detailed explanation-1: -Phytochrome is a pigment which helps in absorbing light energy. This has two forms: Pr and Pfr. It has absorbing capability within the wavelength range of 660nm to 730 nm. Phytochromes give rise to photoperiodism.

Detailed explanation-2: -Phytochrome exists in two interconvertible forms The forms are named by the color of light that they absorb maximally: Pr is a blue form that absorbs red light (660 nm) and Pfr is a blue-green form that absorbs far-red light (730 nm).

Detailed explanation-3: -Following synthesis in the cytoplasm, the phytochrome apoprotein binds chromophore and, in the absence of light, this holoprotein folds into a stable, red-light-absorbing conformation, Pr. Absorption of red light by Pr converts the protein to the far-red-absorbing conformation, Pfr.

Detailed explanation-4: -The phytochrome molecule has two different forms, Pr and Pfr, which have maximal absorption in the red and FR region of the spectrum, respectively (Figure 1). Absorption of light by one form leads to its conversion to the other.

Detailed explanation-5: -Photoreversibility occurs because phytochromes exist as two distinct but photoreversible forms in vivo: the R light-absorbing form (Pr) and the FR light-absorbing form (Pfr). The Pr form absorbs maximally at 660 nm, whereas the Pfr form absorbs maximally at 730 nm (Quail, 1997a; Figure 1).