Bight irradiation induces fragmentation of the plasmodium, a novel photomorphogenesis in the true slime mold Physarum polycephalum: Action spectra and evidence for involvement of the phytochrome

A new photomorphogenesis was found in the plasmodium of the true slime mold Physarum polycephalum: the plasmodium broke temporarily into equal-sized s pherical pieces, each containing about eight nuclei, about 5 h after irradi ation with light, Action spectroscopic study showed that UVA, blue and far- red lights were effective, while red light inhibited the far-red-induced fr agmentation. Difference absorption spectra of both the Living plasmodium an d the plasmodial homogenate after alternate irradiation,vith far-red and re d light gave two extremes at 750 and 680 nm, which agreed with those for th e induction and inhibition of the fragmentation, respectively. A kinetic mo del similar to that of phytochrome action explained quantitatively the flue nce rate-response curves of the fragmentation. Our results indicate that on e of the photoreceptors for the plasmodial fragmentation is a phytochrome.