Response of Glutamine Synthetase and Glutamate Synthase Isoforms to Nitrogen Sources in Rice Cell Cultures

As a model system with no photorespiration and no long distancetransport, rice cell cultures (Oryza saliva L. cv Sasanishiki)were used to investigate the effect of nitrogen sources on thelevels of isoforms of glutamine synthetase (GS) and glutamatesynthase (GOGAT). Isoforms of GS and GOGAT were analyzed byimmunoblotting methods and their activities in early growthphase of the cells. Cytosolic type GS (41 kDa subunit) and NADH-GOGATwere the major isoforms in the rice cells grown in normal R-2medium. However, contents of plastid type GS (44 kDa subunit)and Fd-GOGAT increased in response to NO_–³ supply. NADH-GOGATactivity also increased following the supply of NO_–³.In vitro translated products from poly(A)⁺RNA prepared fromthe cells showed that the precursor of plastid type GS (49 kDa)was detected at 48 h after the inoculation. Supply of NH₊⁴ resultedin an increase in NADH-GOGAT activity but had no effect on thelevels of Fd-GOGAT, of polypeptides of the plastid type GS orof the corresponding mRNAs. (Received May 30, 1990; Accepted August 23, 1990)