College of Life Sciences, Laboratory Center of Life Sciences, Nanjing Agricultural University, Nanjing 210095, China.
National Key Laboratory of Crop Genetics and Germplasm Enhancement, Jiangsu Collaborative Innovation Center for Modern Crop Production, Nanjing Agricultural University, Nanjing 210095, China.
Int J Mol Sci. 2018 Jun 29;19(7):1912. doi: 10.3390/ijms19071912.
Although melatonin (-acetyl-5-methoxytryptamine) could alleviate salinity stress in plants, the downstream signaling pathway is still not fully characterized. Here, we report that endogenous melatonin and thereafter nitric oxide (NO) accumulation was successively increased in NaCl-stressed rapeseed ( L.) seedling roots. Application of melatonin and NO-releasing compound not only counteracted NaCl-induced seedling growth inhibition, but also reestablished redox and ion homeostasis, the latter of which are confirmed by the alleviation of reactive oxygen species overproduction, the decreases in thiobarbituric acid reactive substances production, and Na⁺/K⁺ ratio. Consistently, the related antioxidant defense genes, (), and () transcripts are modulated. The involvement -nitrosylation, a redox-based posttranslational modification triggered by NO, is suggested. Further results show that in response to NaCl stress, the increased NO levels are strengthened by the addition of melatonin in seedling roots. Above responses are abolished by the removal of NO by NO scavenger. We further discover that the removal of NO does not alter endogenous melatonin content in roots supplemented with NaCl alone or together with melatonin, thus excluding the possibility of NO-triggered melatonin production. Genetic evidence reveals that, compared with wild-type Arabidopsis, the hypersensitivity to NaCl in and mutants (exhibiting null nitrate reductase activity and indirectly reduced endogenous NO level, respectively) cannot be rescued by melatonin supplementation. The reestablishment of redox homeostasis and induction of signaling are not observed. In summary, above pharmacological, molecular, and genetic data conclude that NO operates downstream of melatonin promoting salinity tolerance.
虽然褪黑素（-乙酰-5-甲氧基色胺）可以缓解植物的盐胁迫，但下游信号通路仍未完全阐明。在这里，我们报告在盐胁迫油菜（ Brassica napus L.）幼苗根中，内源性褪黑素和随后的一氧化氮（NO）积累依次增加。褪黑素和 NO 释放化合物的应用不仅抵消了 NaCl 诱导的幼苗生长抑制，而且重建了氧化还原和离子稳态，这一点通过减轻活性氧过度产生、降低丙二醛的产生和 Na⁺/K⁺ 比值得到证实。一致地，相关抗氧化防御基因（）和（）的转录本被调节。暗示了 NO 触发的氧化还原依赖的翻译后修饰——-亚硝基化的参与。进一步的结果表明，在响应 NaCl 胁迫时，在幼苗根中添加褪黑素可以增强 NO 水平的增加。上述反应在幼苗根中添加 NO 清除剂去除 NO 后被消除。我们进一步发现，单独添加 NaCl 或与褪黑素一起添加时，NO 清除不会改变根中内源性褪黑素的含量，从而排除了 NO 触发褪黑素产生的可能性。遗传证据表明，与野生型拟南芥相比，在硝酸盐还原酶活性缺失的突变体（）和内源 NO 水平间接降低的突变体（）中，NaCl 敏感性增加（），不能被褪黑素补充所挽救。氧化还原稳态的重建和信号的诱导都没有观察到。总之，上述药理学、分子和遗传学数据表明，NO 作为褪黑素促进耐盐性的下游信号发挥作用。
