Abstract

Delaying early leaf senescence is important for improving photosynthetic efficiency and crop productivity. Melatonin, a multitasking bio-stimulator, participates widely in plant development and stress responses. In recent years, the cumulative researches show that melatonin has the ability to delay senescence in plants. This review covers the most recent advances on the mechanisms of melatonin-mediated leaf senescence. Melatonin biosynthesis in senescing leaves employs an alternative pathway and is significantly regulated by light. Melatonin increases the thickness of leaf cuticle, wax accumulation and the ratio of palisade/spongy of senescing leaves to maintain intact leaf structure. Melatonin eliminates free radicals through a scavenging cascade reaction and induces antioxidants and antioxidant enzymes; and provides better protection against lipid peroxidation via arranging parallel to the bilayers at high concentration. Meanwhile, melatonin’s ability to ensure high photosynthetic efficiency is predominantly attributed to the reduction of chlorophylls and chloroplast proteins degradation, and the acceleration of chlorophyll de novo synthesis. The dual role of melatonin-regulated autophagy is beneficial for maintaining cellular homeostasis. NACs, WRKYs and DREBs play essential roles in melatonin-controlled transcriptional reprogramming of senescing leaves. Additionally, melatonin improves the activity of cytokinin and auxin; and inhibits the action of abscisic acid, ethylene and jasmonic acid to impact indirectly leaf senescence. Epigenetic modification may be part of mechanisms of melatonin-mediated alterations in gene expression. Moreover, selection of germplasms rich in melatonin and application of genetic modification in agriculture are extensively discussed. Further studies are needed to detail the mechanisms of melatonin-mediated signaling transduction in leaf senescence.

摘要

延迟早期叶片衰老对于提高光合作用效率和农作物生产力非常重要。褪黑激素是一种多任务生物刺激剂，广泛参与植物发育和胁迫响应。近年来，积累的研究表明褪黑激素具有延缓植物衰老的能力。这篇综述涵盖了褪黑素介导的叶片衰老机制的最新进展。衰老叶片中的褪黑素生物合成采用另一种途径，并且受光显着调节。褪黑素增加了叶片的表皮厚度，蜡的积累以及感性叶片的木栅/海绵状比率，以维持完整的叶片结构。褪黑素通过清除级联反应消除自由基，并诱导出抗氧化剂和抗氧化酶。并通过平行于双层以高浓度排列提供更好的脂质过氧化保护。同时，褪黑素确保高光合作用效率的能力主要归因于减少叶绿素和叶绿体蛋白质降解以及促进叶绿素从头合成。褪黑激素调节的自噬的双重作用有利于维持细胞稳态。NAC，WRKY和DREB在褪黑激素控制的衰老叶片转录重编程中起重要作用。此外，褪黑激素可改善细胞分裂素和生长素的活性。并抑制脱落酸，乙烯和茉莉酸间接影响叶片衰老的作用。表观遗传修饰可能是褪黑激素介导的基因表达改变机制的一部分。此外，富含褪黑激素的种质的选择和基因修饰在农业中的应用被广泛讨论。需要进一步的研究来详细研究褪黑素介导的叶片衰老中信号转导的机制。