BLUE LIGHT INDUCED PHOTOTRANSFORMATION OF PHYTOCHROME IN THE PRESENCE OF FLAVIN*

Abstract

Abstract— Irradiation of the Pr form of phytochrome in the presence of flavin mononucleotide (FMN) which absorbs the actinic blue light yields Pfr at a rate greater than that in the absence of FMN. The actinic blue light absorbed by FMN enhances the phototransformation of Pr via the energy transfer from the former to the latter. On the other hand, the photoreversion of Pfr was inhibited by the presence of FMN when illuminated with blue light. The lack of photo‐enhancement of the reversion of Pr, by blue light suggests that the Pfr chromophore (acceptor) transition dipole is virtually perpendicular to the FMN transition dipole, as the result of a chromophore reorientation in the Pr→Pfr phototransformation. The fact that blue light absorbed by flavin preferentially enhances the forward phototransformation of phytochrome while inhibiting the reversion may have an important implication in the high irradiance responses in plants in terms of a preferential accumulation of Pfr by blue light excitation.