Glutamate synthase isoforms in tobacco cultured cells

Abstract

Glutamate synthase in tobacco cultured cells ( Nicotiana tabacum L. cv. Xanthi) was assayed with different electron donors upon greening of etiolated cells. Ferredoxin-dependent glutamate synthase (EC 1.4.7.1) activity increased 4-fold, whereas NADH-dependent glutamate synthase (EC 1.4.1.14) and NADPH-dependent glutamate synthase (EC 1.4.1.13) activities remained constant during greening of the cells. Ferredoxin-dependent glutamate synthase and NAD(P)H-dependent glutamate synthases were distinguished by their chromatographic behaviour on ferredoxin-Sepharose affinity column. The immunoglobulin G (IgG)-anti-ferredoxin-dependent glutamate synthase from rice green leaves cross-reacted with ferrodoxin-dependent glutamate synthase, on the other hand, NAD(P)H-dependent glutamate synthases were not immunoprecipitated with the IgG, indicating also that ferredoxin-dependent glutamate synthase and NAD(P)H-dependent glutamate synthase activities are carried out by the distinct protein molecules in tobacco cultured cells, and some physiological functions of the enzymes are discussed.