Phytochrome-controlled Leaf Unrolling and Protein Synthesis

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Abstract
In the primary leaf sections of etiolated wheat (Triticum aestivum L.) seedlings, red light-induced unrolling is accompanied by an increase in incorporation of (14)C-leucine into protein. By differential centrifugation, the unrolling response was found to be closely related to incorporation of the amino acid into the supernatant fraction (105,000g). Cycloheximide and chloramphenicol inhibit both leaf unrolling and synthesis of the supernatant protein, although chloramphenicol exerts its effect more strongly on the fraction which presumably contains the plastids. In a barley (Hordeum vulgare L.) albino mutant completely devoid of ribulose diphosphate carboxylase activity, only incorporation of (14)C-leucine into the supernatant fraction is substantially promoted by red light. This mutant exhibits the photoresponse of leaf unrolling.Both unrolling and increased incorporation of (14)C-leucine induced by red light are prevented by indoleacetic and abscisic acids. Kinetin promotes leucine incorporation into protein and can induce unrolling in complete darkness. Protein synthesis is still promoted by red light when unrolling is almost completely inhibited by an osmoticum. It is suggested that the action of red light on leaf unrolling is dependent on synthesis of a soluble protein in the tissue.