Light-induced Polysome Formation in Etiolated Leaves

Red light-induced, far red light-reversible increase in etiolated bean (Phaseolus vulgaris, var. Asgrow Valentine) leaf polyribosomes was shown to be sensitive to actinomycin D, cycloheximide, and rifampicin inhibition. Actinomycin prevented response to red light if administered simultaneously with a 10-minute illumination, had no immediate effect if given 2 hours after illumination, but was again rapidly inhibitory at 4 and 6 hours. The effects of actinomycin and far red light were more than additive.Cycloheximide consistently inhibited polysome formation within 1 hour at all times tested.Formation of both cytoplasmic and organelle polysomes was depressed by rifampicin, an antibiotic whose action is primarily on RNA synthesis in organelles.The results are interpreted to show that light-triggered polysome formation exhibits a changing need for RNA synthesis and an obligate dependence on protein synthesis during the 1st hours following brief illumination.