Dark Transformations of Phytochrome in vivo. II

Abstract
Dark transformations of phytochrome were measured in dark-grown maize seedling and in curds of cauliflower. The red-absorbing form of phytochrome, PR, was stable in the dark in both tissue. The far-red-absorbing form, Pfr, was not stable. In the seedling tissue PFR either lost photoreversibility or was destroyed over the course of several hours in the dark with little indication of a dark conversion of PFR to P[R]. In the cauliflower tissue PFR was converted to PR in the dark without any loss of phytochrome. The conversion of Pfr in cauliflower appeared to occur in 2 phases, the latter of which was prolonged so that some Pfr persisted for 24 hours or longer. The loss of phytochrome in seedling tissue was related to the respiration of the tissue. Inhibition of respiration by low oxygen concentration or by respiratory inhibitors such as carbon monoxide, potassium cyanide and sodium azide resulted in the inhibition of Pfr destruction. The carbon monoxide inhibition was reversed by white light. The dark conversion of PFr to PR in cauliflower tissue occurred as well in N as in air.