Nitrogen (N) deficiency is one of the critical environmental factors that induce leaf senescence, and its occurrence may cause the shorten leaf photosynthetic period and markedly lowered grain yield. However, the physiological metabolism underlying N deficiency-induced leaf senescence and its relationship with the abscisic acid (ABA) concentration and reactive oxygen species (ROS) burst in leaf tissues are not well understood. In this paper, the effect of N supply on several senescence-related physiological parameters and its relation to the temporal patterns of ABA concentration and ROS accumulation during leaf senescence were investigated using the premature senescence of flag leaf mutant rice ( psf ) and its wild type under three N treatments. The results showed that N deficiency hastened the initiation and progression of leaf senescence, and this occurrence was closely associated with the upregulated expression of 9-cis-epoxycarotenoiddioxygenase genes (NCEDs) and with the downregulated expression of two ABA 8′-hydroxylase isoform genes ( ABA8ox2 and ABA8ox3) under LN treatment. Contrarily, HN supply delayed the initiation and progression of leaf senescence, concurrently with the suppressed ABA biosynthesis and relatively lower level of ABA concentration in leaf tissues. Exogenous ABA incubation enhanced ROS generation and MDA accumulation in a dose-dependent manner, but it decreased the activities of glutamine synthetase (GS) and glutamate dehydrogenase (GDH) in detached leaf. These results suggested that the participation of ABA in the regulation of ROS generation and N assimilating/remobilizing metabolism in rice leaves was strongly responsible for induction of leaf senescence by N deficiency.

中文翻译：

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缺氮引起的水稻叶片衰老与ROS产生和ABA浓度的关系

氮(N)缺乏是诱导叶片衰老的关键环境因素之一，其发生可导致叶片光合周期缩短，粮食产量显着降低。然而，氮缺乏引起叶片衰老的生理代谢及其与叶组织中脱落酸（ABA）浓度和活性氧（ROS）爆发的关系尚不清楚。本文以旗叶突变水稻（ psf ）及其野生型的早衰为研究对象，研究了供氮对几种衰老相关生理参数的影响及其与叶片衰老过程中ABA浓度和ROS积累的时间模式的关系。在三个 N 处理下。结果表明，缺氮加速了叶片衰老的发生和发展，这种情况与 LN 处理下 9-顺式-环氧类胡萝卜素双加氧酶基因 (NCEDs) 的上调表达和两个 ABA 8'-羟化酶同种型基因（ABA8ox2 和 ABA8ox3）的下调表达密切相关。相反，HN 供应延迟了叶子衰老的开始和进展，同时抑制了 ABA 的生物合成和叶组织中相对较低的 ABA 浓度水平。外源ABA培养以剂量依赖性方式增强ROS的产生和MDA的积累，但它降低了离体叶片中谷氨酰胺合成酶（GS）和谷氨酸脱氢酶（GDH）的活性。