Explanation

Phytochrome is an amorphous photoreceptor protein pigment. It exists in two states, i.e., phytochrome Red $(P_{r})$ and phytochrome far-red $\left( P_{fr} \right).$ [image:15_image17.jpeg] It is considered that during the day, $P_{fr}$ from of the phytochrome is accumulated in the plant which is inhibitory to flowering in short-day plants, but is stimulatory in long day plants.