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Changes in Enzymatic Activities in Etiolated Bean Seedling Leaves After a Brief Illumination ^1,2

Biology Department, Brandeis University, Waltham, Massachusetts 02154

The phytochrome controlled increase in total protein in the primary leaf pair of etiolated bean (Phaseolus vulgaris var. Black Valentine) seedlings, which occurs during growth in the dark subsequent to a brief illumination, was investigated. Enzymes from the chloroplasts, the mitochondria, and the soluble cytoplasm all increase in total activity after the illumination.

The total protein and the ribulose carboxylase increases are not inhibited by FUdR, an inhibitor of DNA synthesis. Cycloheximide, an inhibitor of protein synthesis, applied at a time when the ribulose carboxylase activity increase has already commenced, blocks further increase. It was concluded that the total protein and the enzyme increases in the leaf are the result of increases in the per cell levels.

The initial brief illumination is saturating, but 40 minutes later the seedlings have acquired the ability to respond to a second brief illumination. The rate of increase in ribulose carboxylase activity in seedlings that have been illuminated twice is greater than the rate in seedlings that have been illuminated only once.

Far-red light prevents further increase in enzyme activity 48 hours after the initial illumination. There is a lag period interposed between the time of illumination with far-red light and the time at which the seedlings show the greatest effect of far-red light. It was concluded that the phytochrome influence on protein synthesis is not at the terminal steps.

¹ Investigation supported in part by Grant GB3415 from the National Science Foundation, and in part by Developmental Biology Training Grant T1-HD-22 of the Public Health Service.

² This work represents part of a thesis presented by B. Filner to the faculty of the Graduate School of Brandeis University in partial fulfillment of the requirements for the Ph.D. degree.