Particle-bound phytochrome from maize and pumpkin.

Abstract

PHYTOCHROME-induced changes in membrane properties have been inferred from physiological studies for some time1–7. Hendricks and Borthwick6 have proposed that the primary action of phytochrome is indeed the induction of such membrane changes and Smith7 has proposed a mechanism for phytochrome-membrane interaction. The interest in a search for evidence of a direct association between phytochrome and cellular membranes has therefore been considerable. The polarotropic response of Dryopteris8, chloroplast movement in Mougeotia9 and the photoconversion of phytochrome in corn coleoptiles in polarized light10 have all been taken to indicate that at least some phytochrome is located and orientated in the periphery of the cytoplasm or the plasmalemma itself. An immunological approach has been attempted11 and Ptr-induced changes in black lipid membrane permeability have recently been reported12 (Pr and Ptr are the two photo-reversible forms of phytochrome). Rubinstein et al.13 reported that about 4% of the total extractable phytochrome from Avena could be pelleted at 40,000g from a 1,500g supernatant, pH 7.4. Here we report the presence of particle-bound phytochrome in extracts from maize coleoptiles and pumpkin hooks and suggest a mechanism for the interaction of the pigment with its binding site(s).