水稻种子萌发期间谷氨酰胺合成酶和NADH-谷氨酸合酶的变化

测定了水稻种子不同萌发时期胚乳、胚芽鞘和幼根的谷氨酰胺合成酶（GS）和依赖于NADH的谷氨酸合酶（NADH－GOGAT）活性变化。胚乳和胚芽鞘的GS活性在萌发过程中升高，幼根的GS活性则有所降低。NADH－GOGAT的活性变化趋势与GS相同。Native-PAGE活性染色表明，在萌发阶段的水稻种子胚乳和幼根里，始终只观察到一种GS活性带。但是，在水稻种子萌发3d后，在胚芽鞘中除继续检测到GS1的活性外，还可以观察到GS2的活性。蛋白质印迹显示，水稻种子胚乳中的GS（GSe)和GS1和GSra一样是一种胞质型GS。实验结果提示，这些不同组织中的GS与NADH－GOGAT构成的循环途径也许是水稻种子萌发时氨同化的主要途径。

Changes in Activity of Glutamine Synthetase and NADH-glutamate Synthase During Germination of Rice Seeds

The changes in activity of glutamine synthetase and NADH-glutamate synthase in endosperms, coleoptiles, and roots were determined during the germination of rice (Oryza sativa L. cv Tai Chong Native 1) seeds. GS activity in the endosperms and coleoptiles increased during the germination(Fig.1). The increase in GS activity of the coleoptile was more remarkable than that of the endosperm. GS activity in roots was higher than that of endosperms, but the activity decreased gradually with germinating course (Fig.1). The tendency of the change in activity of NADH-GOGAT activity change was similar to that of GS in these tissues (Fig.5). Only GSe (endosperm GS) and GSra activity bands were detected by the activity staining in the endosperms and roots, respectively(Fig.2A and C). Besides GS1 activity, GS2 activity was also observed in the coleoptiles during the later phase of germination(Fig.2B). The result of Western blotting showed that GSe of the endosperms is a cytosolic enzyme as GS1 and GSra (Fig.4). The changes in GS and NADH-GOGAT activities in these tissues suggest that the cytosolic GS-NADH-GOGAT cycle may be the main pathway for ammonium assimilation.