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N Use By Plants
Nitrate Assimilation
Ammonia Assimilation
Glu, Gln, Asn, Gly, Ser
Asp, Ala, GABA
Val, Leu, Ileu, Thr, Lys
Pro, Arg, Orn
Non-protein AAs
Sulfate Assimilation
Cys, Met, AdoMet, ACC
His, Phe, Tyr, Tryp
Secondary Products
Onium Compounds
HORT640 - Metabolic Plant Physiology

Ammonia Assimilation and Recycling

Regulation of glutamine synthetase


  • 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).


    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: 10/01/09