EXPRESSION OF GLUTAMINE-SYNTHETASE DURING THE ANAEROBIC GERMINATION OF ORYZA-SATIVA L

Glutamine synthetase (GS; EC.6.3.1.2.) occurs as cytosolic (GS(1)) and plastidic (GS(2)) polypeptides. This paper describes the expression o f GS isoenzymes in coleoptile during the anaerobic germination of rice (Oryza sativa L.) and the influence of exogenous nitrate on this. By immunoprecipitation with anti-GS serum, two polypeptides of 41- and 44 -kDa were detected of which the former was predominant. After fraction ation by ion-exchange chromatography, the 41 and 44 kDa bands were ide ntified as GS(1) and GS(2), respectively. Northern blot analysis with specific probes showed the presence of mRNA for cytosolic GS but not f or the plastidic form. The presence of exogenous nitrate did not alter the activity and expression of GS in the coleoptile. The role of GS d uring the anaerobic germination of rice seems to induce the re-assimil ation of ammonia rather than the assimilation of nitrate.