Lu Xuping, Min Weifang, Shi Yafei, Tian Lei, Li Peifu, Ma Tianli, Zhang Yinxia, Luo Chengke
Agricultural College, Ningxia University, Yinchuan, China.
Front Plant Sci. 2022 Mar 9;13:849553. doi: 10.3389/fpls.2022.849553. eCollection 2022.
Saline-alkali stress seriously restricts rice growth, development, and production in northern China. The damage of alkaline stress on rice is much greater than that of salt due to ion toxicity, osmotic stress, and especially high pH. As a signal molecule, melatonin (N-acetyl-5-methoxytryptamine, MT) mediates many physiological processes in rice and participates in protecting rice from abiotic stress. The potential mechanism of exogenous melatonin-mediated alkaline stress tolerance is still largely unknown. In this study, the effects of melatonin on the morphological change, physiological property, and corresponding genes expression in rice seedlings were analyzed under alkaline stress (20 mmol L, pH 9.55). The results showed that the expression levels of MT synthesis genes (, , , , and ) were induced by both exogenous MT and alkaline stress treatment. The cell membrane was protected by MT, and the MT furtherly play role in scavenging reactive oxygen species (ROS), reducing lipoxygenase (LOX) activity, and malondialdehyde (MDA) content. The scavenging of ROS by melatonin is attributed to the coupling of the improvement of redox homeostasis and the enhancement of antioxidant enzyme activity and antioxidant content by upregulating the transcriptional levels of antioxidase genes. In the meantime, MT pretreatment promoted the accumulation of free proline, sucrose, and fructose by regulating the , , and gene expression level and increased chlorophyll content upregulating the expression of chlorophyll synthesis-related genes. Ultimately, the alleviating effect of exogenous melatonin on alkaline stress was reflected in increasing the leaf relative water content (RWC) and root-shoot ratio and reducing the leaf tip wilt index (TWI) through a series of physiological and biochemical changes. Melatonin pretreatment changed the expression level of MT synthesis genes which might contribute to MT synthesis in rice, consequently, activated the ROS scavenging system and alleviating the damage of alkaline stress on rice seedlings. Our study comprehensively understands the alleviating effect of exogenous melatonin on rice under alkaline stress.
盐碱胁迫严重制约了中国北方水稻的生长、发育和产量。由于离子毒性、渗透胁迫，尤其是高pH值，碱性胁迫对水稻的损害远大于盐胁迫。褪黑素（N-乙酰-5-甲氧基色胺，MT）作为一种信号分子，介导水稻中的许多生理过程，并参与保护水稻免受非生物胁迫。外源性褪黑素介导的耐碱性胁迫的潜在机制仍 largely 未知。在本研究中，分析了在碱性胁迫（20 mmol L，pH 9.55）下褪黑素对水稻幼苗形态变化、生理特性及相应基因表达的影响。结果表明，外源性MT和碱性胁迫处理均诱导了MT合成基因（，，，，和）的表达水平。MT保护细胞膜，MT进一步在清除活性氧（ROS）、降低脂氧合酶（LOX）活性和丙二醛（MDA）含量方面发挥作用。褪黑素对ROS的清除归因于氧化还原稳态的改善与通过上调抗氧化酶基因的转录水平增强抗氧化酶活性和抗氧化剂含量的耦合。同时，MT预处理通过调节，，和基因表达水平促进了游离脯氨酸、蔗糖和果糖的积累，并通过上调叶绿素合成相关基因的表达增加了叶绿素含量。最终，外源性褪黑素对碱性胁迫的缓解作用通过一系列生理生化变化体现在增加叶片相对含水量（RWC）和根冠比以及降低叶尖枯萎指数（TWI）上。褪黑素预处理改变了MT合成基因的表达水平，这可能有助于水稻中MT的合成，从而激活ROS清除系统并减轻碱性胁迫对水稻幼苗的损害。我们的研究全面了解了外源性褪黑素在碱性胁迫下对水稻的缓解作用。
