Question

Which one of the following shows red - far-red interconversions?

• A. Carotenoids
• B. Cytochromes
• C. Chlorophyll
• D. Phytochrome

Answer 1

The correct option is D Phytochrome

The main photoreceptor for photoperiodism and many other light-initiated plant responses (such as germination and seedling establishment) is phytochrome, a family of about five blue-green pigment proteins, each of which is coded for by a different gene.

Each member of the phytochrome family exists in two forms and readily converts from one form to the other after absorption of light of specific wavelengths. One form, designated as $P_r$ (for red absorbing phytochrome), strongly absorbs light with a relatively short red wavelength (660 nm). In the process, the shape of the molecule changes to the second form of phytochrome, $P_{fr}$, so designated because it absorbs far-red light, which is light with a relatively long red wavelength (730 nm). When it absorbs far-red light, $P_{fr}$ reverts to the original form, $P_r$. $P_{fr}$ is the active form of phytochrome, triggering or inhibiting physiological responses such as flowering.