Abstract Previous studies reported the ability of l -glutamate (glutamate) to induce host resistance against Alternaria alternata, but the underlying mechanism is still scarce. Here, temporal alteration in antioxidant enzymes and glutamate consuming pathways were transcriptionally and enzymatically monitored in tomato fruits. The results showed that exogenous glutamate application enhanced the activities of antioxidant enzymes, including peroxidase, superoxide dismutase and catalase, in tomatoes upon inoculation with Alternaria alternata, while lower concentrations of H2O2 and malondialdehyde were observed. Interestingly, glutamate led to a decline in carbon:nitrogen ratio and induction of deaminating activity of glutamate dehydrogenase, resulting in replenishment of the tricarboxylic acid cycle. Concurrently, proline dehydrogenase mediated the proline catabolism was downregulated by glutamate, accompanied by the enhanced biosynthesis of proline due to increased expression of pyrroline-5-carboxylate synthase. Together our findings favored a model whereby overactivation of antioxidant enzymes and glutamate consuming pathways, deamination of glutamate and proline biosynthesis from glutamate, played a vital role in the mechanism of glutamate-induced resistance.

中文翻译：

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L-谷氨酸处理的番茄果实中谷氨酸消耗途径的过度激活导致对链格孢的抗性

摘要 以往的研究报道了l-谷氨酸(glutamate)诱导宿主对链格孢菌产生抗性的能力，但其潜在机制尚不明确。在这里，抗氧化酶和谷氨酸消耗途径的时间变化在番茄果实中进行了转录和酶促监测。结果表明，外源性谷氨酸盐的施用增强了接种链格孢的番茄中抗氧化酶的活性，包括过氧化物酶、超氧化物歧化酶和过氧化氢酶，而观察到较低浓度的 H2O2 和丙二醛。有趣的是，谷氨酸导致碳氮比下降并诱导谷氨酸脱氢酶的脱氨活性，导致三羧酸循环的补充。同时，脯氨酸脱氢酶介导的脯氨酸分解代谢被谷氨酸下调，同时由于 pyrroline-5-carboxylate 合酶的表达增加，脯氨酸的生物合成增强。总的来说，我们的研究结果支持一种模型，其中抗氧化酶和谷氨酸消耗途径的过度激活、谷氨酸脱氨和谷氨酸的脯氨酸生物合成，在谷氨酸诱导的抗性机制中起着至关重要的作用。