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| Nitrate Assimilation |
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HORT640 - Metabolic Plant Physiology
Ammonia Assimilation and Recycling
Regulation of glutamine synthetase
Algae
Chlamydomonas reinhardtii has at least 2 GS isoforms; GS1, cytosolic; and GS2, chloroplastic. Unlike higher plants, no decreased level of GS2 transcripts was
detected when cells were grown under conditions that repress photorespiration. The level of GS2 transcripts is not affected by ammonium or nitrate. However, the level of GS1 transcripts is repressed by
ammonia and induced by nitrate. Expression of both GS1 and GS2 is regulated by light (Chen and Silflow, 1996).
GS is rapidly deactivated when cells of Chlamydomonas grown on nitrate are treated with 5 mM ammonium and switched to darkness (Cullimore, 1981). Activity is partly restored in vivo by reillumination (Cullimore, 1981).
References
Chen Q, Silflow CD 1996 Isolation and characterization of glutamine synthetase genes in Chlamydomonas reinhardtii. Plant Physiol. 112: 987-996.
Cullimore JV 1981 Glutamine synthetase of Chlamydomonas: rapid reversible deactivation. Planta 152: 587-591.
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David Rhodes
Department of Horticulture & Landscape Architecture
Horticulture Building
625 Agriculture Mall Drive
Purdue University
West Lafayette, IN 47907-2010
Last Update: 01/07/08
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