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.
Highlights
Compared to the control (Figure 1Aa), exogenous MT did not alter the phenotype of rice seedlings in the WM treatment under normal growth conditions (Figure 1Ab)
Salinity and alkaline stress led to the preferential decomposition of chlorophyll and chloroplast, resulting in leaf yellowing, premature senescence, and decreased photosynthesis (Zhu et al, 2019)
In the results of this study, the application of exogenous MT effectively alleviated the premature senescence of rice leaves under alkaline stress
Summary
Soil salinization is one of the important limiting factors affecting the sustainable development of agriculture (Shabala, 2013; Shahbaz and Ashraf, 2013). The main harmful salts in saline-alkali soil include NaCl, Na2SO4, NaHCO3, and Na2CO3 (Yang et al, 2007). The stress induced by neutral salts NaCl and Na2SO4 and alkaline salt Na2CO3 and NaHCO3 is called salt stress and alkaline stress. Mixed saline-alkaline stress is caused by both neutral and alkaline salt (Lu et al, 2021). Alkaline stress causes osmotic stress and ion toxicity in the same way as salt stress does. Alkaline stress is caused mainly due to the solidification of nutrient elements in soil at a high pH value, which seriously interferes with the absorption of mineral nutrition by plant roots, leading to nutrient imbalance in plants, disorder of metabolism, and destruction of ion balance (Guo et al, 2017; Zhang et al, 2017a)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
