Nitrogen (N) deficiency is one of the factors limiting crop productivity worldwide. As major forms of N, nitrate (NO 3 − ) and ammonium (NH 4 + ) regulate plant growth as signals. Although there are abundant studies on the response of many plants to N stress, the mechanism by which wheat ( Triticum aestivum L.) roots adapt to low N, especially to low-NH 4 + stress, has not been fully elucidated. In this study, wheat seedlings were planted in 1/2-strength Hoagland’s solution containing 5 mM NO 3 − , 0.1 mM NO 3 − , or 0.1 mM NH 4 + to characterize root physiological responses to N deficit. Under low-N stress, root fresh weight, lateral root number increased compared with those under control conditions. Moreover, the concentrations of indole-3-acetic acid (IAA), cytokinins (CKs), gibberellin (GA 3 ), and jasmonic acid (JA) increased, while the salicylic acid (SA) concentration decreased under low-N stress. Assays using enzyme-linked immunosorbent assay (ELISA) and non-invasive micro-test technology (NMT) showed that H + -ATPase activity, the H + efflux, and the IAA influx increased, while N influx decreased under low-N stress. Further study revealed that low-NO 3 − stress increased nitrate reductase and glutamine synthetase activities, while low-NH 4 + stress increased the activities of glutamine synthetase and glutamate synthase. In conclusion, low-N stress altered root IAA, CKs, GA 3 , JA, and SA concentrations; increased H + -ATPase activity and H + efflux; promoted an increase in lateral root number and thus N absorption area. Besides, low-N stress increased the activities of key enzymes related to N assimilation, promoted protein biosynthesis, and ultimately enhanced root growth.

中文翻译：

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低氮胁迫刺激小麦侧根启动和氮同化：植物激素信号传导的作用

氮 (N) 缺乏是限制全球作物生产力的因素之一。作为 N 的主要形式，硝酸盐 (NO 3 - ) 和铵盐 (NH 4 + ) 作为信号调节植物生长。尽管已有大量植物对氮胁迫响应的研究，但小麦（Triticum aestivum L.）根系适应低氮特别是低NH 4 + 胁迫的机制尚未完全阐明。在本研究中，将小麦幼苗种植在含有 5 mM NO 3 - 、0.1 mM NO 3 - 或 0.1 mM NH 4 + 的 1/2 强度 Hoagland 溶液中，以表征根对 N 缺乏的生理反应。低氮胁迫下，根鲜重、侧根数较对照条件增加。此外，吲哚-3-乙酸（IAA）、细胞分裂素（CKs）、赤霉素（GA 3 ）和茉莉酸（JA）的浓度增加，而在低氮胁迫下水杨酸（SA）浓度降低。使用酶联免疫吸附测定 (ELISA) 和无创微量测试技术 (NMT) 进行的测定表明，在低氮胁迫下，H + -ATPase 活性、H + 流出和 IAA 流入增加，而 N 流入减少。进一步的研究表明，低NO 3 - 压力增加了硝酸还原酶和谷氨酰胺合成酶的活性，而低NH 4 + 压力增加了谷氨酰胺合成酶和谷氨酸合成酶的活性。总之，低氮胁迫改变了根 IAA、CKs、GA 3 、JA 和 SA 浓度；增加 H + -ATPase 活性和 H + 流出；促进了侧根数量的增加，从而增加了氮吸收面积。此外，低氮胁迫增加了与氮同化相关的关键酶的活性，促进了蛋白质的生物合成，