Comparison of contents for cytosolic-glutamine synthetase and NADH-dependent glutamate synthase proteins in leaves of japonica, indica, and javanica rice plants

As reported previously with a Japonica-type rice, Sasanishki, cytosolic glutamine synthetase (GSI: HC 6.3.1.2) was detected in companion cells as well as vascular-parenchyma cells of vascular bundles of senescing blades (Sakurai et al., 1996), while NADH-dependent glutamate synthase (NADH-GOGAT; EC 1.4.1.14) in the developing young tissues was located in cell types where the solutes are transported from phloem and xylem (Hayakawa el al., 1994). These results suggest that GSI is important for the export of leaf nitrogen from senescing leaves, whereas NADH-GOGAT is involved in the synthesis of glutamate from the glutamine that is transported through the vascular system. To evaluate their functions further in the nitrogen rcmobilization and reutilization in rice, several cultivars of indica and javanica rice were tested to estimate the contents for GSI and NADH-GOGAT proteins in senescing and developing leaf blades, respectively. Chinsurah Boro I and Blue Stick, indica cultivars tested in the current study, contained more GS1 protein than Sasanishiki, a japonica, in the senescing leaf blades, when the content was compared on an unit of g fresh weight basis. On the other hand, NADH-GOGAT content in the young leaf blades of Sasanishiki was the highest.