The photoreceptors in the high irradiance response of plants

Abstract

Several studies show that the high irradiance response (HIR) of plants is probably due to two photoreceptors. One of the photoreceptors is phytochrome, and the other is an unidentified pigment provisionally named heliochrome. One of the functions of heliochrome is the synthesis of phytochrome, using far‐red and blue radiations of high intensities, to replace the phytochrome destroyed by light. Another possible function could be an interaction of heliochrome with a substance produced by phytochrome. The data presented show that heliochrome is a pigment with different properties from phytochrome. It shows a far‐red/green reversibility. Heliochrome has been shown to participate with phytochrome in such HIRs as leaf movement in Albizzia and flowering in a long‐day plant. The first event initiated by phytochrome and by heliochrome could be the generation of a strong positive, electrostatic charge in the cell membrane.