Effects of light quality on Nitrate reductase and Glutamine synthetase activities in the red alga Porphyra leucosticta Thur. in Le Jol. and other macroalgae
F.L. Figueroa

The effects of different light treatments, i.e. (a) red or blue light pulses (5 or 15 min) followed by darkness (4 h), (b) pulses of red or blue light of 20 min applied at the end of the light period for 14 d (in 12h light: 12h dark regimes) and (c) 12 h red or blue light per day for 24 d, on the activities of two key enzymes of inorganic N metabolism, nitrate reductase and glutamine synthetase in the red alga Porphyra 1eucosticta were investigated. Far-red light was applied after red or blue light pulses to investigate the possible action of phytochrome. Red or blue light pulses (5 or 15 min) stimulated nitrate reductase activity and soluble protein synthesis in darkness, whereas, glutamine synthetase activity was similar to that in the dark control. Both specific nitrate reductase and specific glutamine synthetase activities were higher after blue than after red light pulses. End-of-day blue light pulses stimulated nitrate reductase activity. The inductive effect of B light was partially reversed by far-red light whereas end-of-day red light pulses decreased the activity. Nitrate reductase activity was higher when B light was applied for 12 h for 28 d than in red light. In this last treatment, i.e. 12 h for 28 d red light a transient increase was observed. Nitrate reductase activity was not correlated with photosynthetic activity in both red and blue light indicating the involvement of a non-photosynthetic photoreceptor system. Due to the reversion of far-red light and the higher effect of blue rather than red light pulses, the involvement of phytochrome and a blue light photoreceptor was suggested. The effect of light quality on N metabolism in Porphyra leucosticta was compared to that reported in other macroalgae, namely Corallina elongata and UIva rigida.

Keywords: B light photoreceptor, glutamine synthetase, light quality, nitrate reductase, Porphyra leucostica, phytochrome.
Contents of this volume Sci. Mar. 60(Suppl.1) : 163-170 Back PDF
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