Dark Transformations of Phytochrome in Vivo

Abstract

The phytochrome in dark-grown seedlings was found to be present entirely as P660 and, as such, was quite stable. After irradiation with red light, however, the P730 which was formed was not stable. the P730 was either destroyed or altered to a nonreversible form of phytochrome. The rate of loss of P730 was studied as a function of the fraction of phytochrome maintained as P730 as a photosta-tionary state. In continuous light of a quality which maintained approximately 10 per cent of the phytochrome as P730. the rate of loss was the same as in continuous red light. The rate of loss was somewhat slower when 3 per cent of the phytochrome was maintained as P730. but was still appreciable even in continuous far-red light which maintained less than 1 per cent of the phytochrome as P730.