Glutamine synthetase (GS) and glutamate synthase (GOGAT) play a central role in plant nitrogen (N) metabolism. In order to study the effect of powdery mildew (Blumeria graminis f. sp. tritici, Bgt) on N metabolism, field experiments were carried out to evaluate GS and GOGAT activity, GS expression and grain protein content (GPC) in susceptible (Xi'nong 979) and resistant (Zhengmai 103) wheat cultivars under three treatments. The three treatments were no inoculation (CK), inoculated once with Bgt (MP) and inoculated nine times with Bgt (HP). For Xi'nong 979, the activities of GS and GOGAT in grains as well as GS activity in flag leaves increased at 10–15 days after anthesis (DAA), and decreased significantly at 15 or 20–30 DAA in HP and MP. However, GS activity in grains decreased from 20 DAA, which was later than that of flag leaves (15 DAA). At the same time, GS expression in grains was up-regulated at early stage, with GS1 at 10 DAA and GS2 at 15 DAA, followed by a continuous down-regulation. This result indicated that GS and GOGAT activity as well as GS expression were inhibited by powdery mildew, indicating that N metabolism in grains was inhibited at 20–30 DAA. The current study also found out that the yield of the susceptible cultivar decreased significantly, while its GPC increased obviously in HP. It was shown that the increase of GPC was not due to the enhancement of N metabolism, but due to the passive increase caused by yield reduction.

中文翻译：

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小麦白粉病对籽粒氮代谢的影响

谷氨酰胺合成酶 (GS) 和谷氨酸合成酶 (GOGAT) 在植物氮 (N) 代谢中起核心作用。为了研究白粉病的影响（禾本科蓝花F。sp。小麦,BGT）在氮代谢方面，进行了田间试验，评估了三个处理下敏感（西农979）和抗性（正麦103）小麦品种的GS和GOGAT活性、GS表达和籽粒蛋白含量（GPC）。三个处理均为不接种（CK），接种一次BGT(MP) 并接种 9 次BGT（生命值）。对于西农979，籽粒中GS和GOGAT活性以及旗叶中GS活性在开花后10-15天（DAA）增加，而在HP和MP的15或20-30 DAA显着降低。然而，谷物中的 GS 活性从 20 DAA 开始下降，晚于旗叶（15 DAA）。同时，谷粒中 GS 表达在早期上调，GS1在 10 DAA 和GS2在 15 DAA，随后持续下调。该结果表明GS和GOGAT活性以及GS表达受到白粉病的抑制，表明谷物中的N代谢在20-30 DAA受到抑制。本研究还发现，感病品种的产量明显下降，而其GPC在HP明显增加。结果表明，GPC的增加不是由于N代谢的增强，而是由于减产引起的被动增加。