Exogenous Melatonin Alleviates Alkaline Stress by Removing Reactive Oxygen Species and Promoting Antioxidant Defence in Rice Seedlings

Abstract

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−1, pH 9.55). The results showed that the expression levels of MT synthesis genes (TDC2, T5H, SNAT, ASMT1, and ASMT2) 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 OsP5CS, OsSUS7, and OsSPS1 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.

Melatonin Enhances Drought Tolerance in Rice Seedlings by Modulating Antioxidant Systems, Osmoregulation, and Corresponding Gene Expression

“…This study showed that exogenous melatonin dramatically upregulated the expression levels of the ALM1 , OsPOX , OsCATC , and OsAPX2 genes, improving the activities of the antioxidant enzymes CAT, SOD, POD, and APX, respectively. Consequently, exogenous melatonin relieved drought stress in rice seedlings by primarily strengthening enzymatic antioxidant systems rather than non-enzymatic antioxidants (AsA and DHA), which was somewhat different from our earlier research on the physiological mechanisms of exogenous melatonin alleviating alkaline stress tolerance in rice [ 38 ].…”

“…A previous report showed that under salt stress, the application of 20 μM melatonin might accelerate the accumulation of osmotic compounds (such as proline and soluble sugars) in cotton seeds, improving the tolerance of seed germination to salt stress [ 41 ]. Our previous study indicated that exogenous melatonin increased the proline content while decreasing the sucrose and fructose levels in alkaline-stressed rice seedlings, which suggested that exogenous melatonin improved the alkaline tolerance by accumulating proline rather than sucrose and fructose in rice [ 38 ]. In the presented study, the application of exogenous melatonin increased the proline accumulation by activating OsP5CS gene expression and increasing the sucrose and fructose contents by upregulating the expression levels of the OsSUS7 and OsSPS1 genes in rice seedling leaves under drought stress.…”

Effects of Melatonin Priming on Suaeda corniculata Seed Germination, Antioxidant Defense, and Reserve Mobilization: Implications for Salinized Wetland Restoration

“…On the one hand, melatonin priming promoted seed germination by regulating the expression of stress tolerance, hormone synthesis, and metabolism-related genes . On the other hand, priming treatment also upregulated the antioxidant enzyme activities and accelerated the level of reserve mobilization, ultimately improving the seed germination (Arora and Bhatla, 2017;Cao et al, 2019;Lu et al, 2022). This study is the first to reveal the effect pathways of melatonin priming on the S. corniculata seed germination under salinization stress, and also proved the feasibility of melatonin priming in improving the germination of S. corniculata seeds.…”

“…Exogenous melatonin priming may have indirectly upregulated the expression of antioxidant enzyme and related genes, which then improves their efficiency as antioxidants (Arora and Bhatla, 2017;Wang et al, 2017). However, other studies have demonstrated that exogenous melatonin priming did not change the antioxidant enzymes' activity of Lolium perenne (Zhang et al, 2016;Lu et al, 2022), and we suspect that melatonin possibly uses different physiological mechanisms to strengthen the antioxidant defense. MDA is the indicator of oxidative-stress induced membrane damage under salinization stress (Ibrahim, 2016).…”

The role of melatonin in the development of postmenopausal osteoporosis

“…Melatonin is the most powerful endogenous free radical scavenger. Its main antioxidant mechanism acts through its binding to oxidative substances (Lu et al, 2022). Additionally, melatonin binds to its cellular receptor and activates the transduction signals that induce the synthesis of antioxidant enzymes, including superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase (Bantounou et al, 2022).…”