Photoregulation of nitrogen metabolism and protein accumulation in the red alga corallina elongata ellis et soland

Abstract

Red and blue light pulses of 5 min applied together with 45 (aM K N 0 3 stimulated the nitrate uptake and reduction and the assimilation of ammonium in darkness in the red alga Corallina elongata. N itrate reductase and glutamine synthetase activities were increased in darkness after the application of both red and blue light pulses. Red light produced a dram atic increase in enzyme activities after the first hour in darkness but after 4 h the effect of blue light pulses was greater. The photostim ulation of nitrogen metabolism was correlated with light-regulated accumulation of soluble proteins. Nitrogen incorporation, assimilation of am monium, accum ulation of total proteins and the increment in total intracellular nitrogen was greater in N-limited algae (C : N = 17.3) than in N-sufficient algae (C : N = 10.3) after the application of light pulses and nitrate. Because the stimulant effects of red and blue light on N-metabolism were partially reversed by far-red light, the possible involvement of the photoreversible red far-red photoreceptor, phytochrome, is proposed. In addition, the blue-light effect seems to be mediated by a specific B-light photoreceptor besides phytochrome due to the different time course of the response and the extent of the stimulation after blue compared to red light pulses. © 1993, Walter de Gruyter. All rights reserved.