Effect of nitrogen starvation on ammonium assimilation by Chlamydomonas reinhardtii |
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Authors: | Alberto Menacho José M Vega |
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Institution: | Dept. de Bioquimica Vegetal y Biologia Molecular. Facultad de Quimica, Univ. de Sevilla, Apartado 553, E-41080 Sevilla, Spain. |
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Abstract: | In nitrogen-starved Chlamydomonas reinhardtii , wild type, strain 21 gr cells, consumption of nitrate, nitrite and ammonium may occur in the dark in the absence of an added carbon source. Consumption of ammonium in the dark was about 25% higher than in the light, while consumption of nitrate or nitrite in the dark was lower than in the light. N starvation produced a linear increase with time in the intracellular level of glutamine synthetase (GS, EC 6.3.2.1) and glutamate synthase (NADH-GOGAT, EC 1.4.1.14 and ferredoxin-GOGAT, EC 1.4.7.1) activities in C. reinhardtii . The effect on GS1 (3-fold) and NADH-GOGAT (4.5-fold) was higher than that on GS2 (1.5-fold) and ferredoxin-GOGAT (1.5-fold). Experiments with methylammonium, L-methionine-D, L-sulfoximine (MSX) and azaserine suggest that: 1) Ammonium itself decreases the intracellular levels of glutamine synthetase and ferredoxin-glutamate synthase activities; and 2) a metabolite resulting from ammonium assimilation by the alga may be a negative modulator of NADH-glutamate synthase activity. |
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Keywords: | Chlamydomonas reinhardtii glutamate synthase glutamine synthetase inorganic nitrogen assimilation nitrogen starvation |
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