NITRATE ASSIMILATION DURING THE ANAEROBIC GERMINATION OF RICE - EXPRESSION OF FERREDOXIN-DEPENDENT GLUTAMATE SYNTHASE

Ferredoxin-dependent glutamate synthase (Fd-GOGAT; EC 1.4.7.1) is the last enzyme involved in the pathway of nitrate assimilation in higher plants. This gaper describes the synthesis and expression of the enzym e in anaerobic coleoptiles of rice (Oryza sativa L.) and its regulatio n by exogenous nitrate. The activity of Fd-GOGAT was strongly inhibite d by cycloheximide between 4 and 9 d of anaerobic germination. The add ition of nitrate slightly increased, in the first 5 h, the specific ac tivity of Fd-GOGAT as well as the amount of a 160-kDa protein specific ally immunoprecipitated with anti-Fd-GOGAT serum. Northern blot analys is, performed with a specific riboprobe, showed the presence of mRNA o f the expected size and the inductive effect of nitrate. The role of F d-GOGAT is discussed in relation to the anaerobic assimilation of nitr ate by rice coleoptiles.