Inducible Accumulation of mRNA for NADH-Dependent Glutamate Synthase in Rice Roots in Response to Ammonium Ions

Abstract

In developing young tissues of rice plants, NADHdependent glutamate synthase (NADH-GOGAT; EC 1.4.1.14) has been suggested to play an important role in the utilization of glutamine, which is transported from senescing tissues and roots (Hayakawa et al. 1994). Because NADH-GOGAT protein is located in specific cells in both the leaf blade and grain of rice (Hayakawa et al. 1994) and because its protein content and activity change dramatically during the early stage of the seed ripening (Hayakawa et al. 1993), the expression of NADH-GOGAT gene might be regulated as a cell specificand age specific manner. We recently showed that the mRNA, protein, and activity of NADH-GOGAT in roots of rice seedlings increased more than 10-fold within a day of the start of a supply of nitrogen (Yamaya et al. 1995). This increase was specific to NADH-GOGAT in the roots; little change was observed in the activity or protein content of Fd-GOGAT (EC 1.4.7.1) or GS (EC 6.3.1.2). A supply of NH^ was most effective on the apparent inducible increase in NADH-GOGAT, but adding NOJ, glutamine, or asparagine also caused rapid increases to a lesser extent in both rice roots (Yamaya et al. 1995) and rice cell cultures (Watanabe et al. 1996). In this study, we further characterized the expression of mRNA for NADH-GOGAT in rice roots in more detail, because our previous work with roots was mainly directed toward studying the response of activity and protein content for