Due to the insulation provided by soil, plant shoots always suffer cold stress prior to roots when ambient temperatures fall rapidly. Melatonin can enhance cold tolerance of shoots via systemic signaling from roots; however, the underlying mechanisms driving the process remain unclear. This study reports that root-pretreatment with 1.5 μM melatonin alleviated aerial cold-induced inhibition of photosystem II and oxidative stress. The fortification of the photosystem by melatonin was accompanied by increased thermal dissipation, while the melatonin-induced alleviation of oxidative stress was attributed to the improved efficiency of the ascorbate–glutathione cycle under aerial cold stress. Melatonin significantly upregulated the expressions of C-repeat binding factor 1 (CBF1), inducer of CBF expressions 1, and four cold-responsive genes after aerial cold stress. It suggests that melatonin-promoted cold tolerance might be related to the CBF-responsive pathway, which plays an important role in improving photosynthesis and redox homeostasis. Additionally, rhizospheric melatonin application increased both jasmonic acid (JA) and indoleacetic acid (IAA) levels but decreased abscisic acid (ABA) levels in leaves by regulating biosynthetic or catabolic genes under aerial cold stress. Thus, melatonin might function synergistically with JA and IAA, while antagonistically with ABA in regulating the responses of plants to cold stress. These results suggest the involvement of both CBF-responsive pathway and phytohormones in melatonin-mediated systemic tolerance against cold stress.

由于土壤提供的绝缘作用，当环境温度迅速下降时，植物新芽始终在根部之前遭受冷胁迫。褪黑素可通过根部的系统性信号传导增强芽的耐寒性。但是，驱动该过程的基本机制仍不清楚。这项研究报告说，用1.5μM褪黑素进行根部预处理可减轻空气冷诱导的对光系统II和氧化应激的抑制作用。褪黑素对光系统的强化伴随着散热的增加，而褪黑素诱导的氧化应激的缓解归因于空中冷胁迫下抗坏血酸-谷胱甘肽循环效率的提高。褪黑素显着上调了C重复结合因子1（CBF1）的表达，空气冷应激后CBF表达1的诱导因子和4个冷响应基因。这提示褪黑激素提高的耐寒性可能与CBF应答途径有关，它在改善光合作用和氧化还原稳态方面起着重要作用。此外，根际褪黑素的应用通过调节空气冷胁迫下的生物合成或分解代谢基因，增加了茉莉酸（JA）和吲哚乙酸（IAA）的水平，但降低了脱落酸（ABA）的水平。因此，褪黑激素可能与JA和IAA协同作用，而与ABA拮抗，调节植物对冷胁迫的反应。这些结果表明，CBF应答途径和植物激素都参与了褪黑激素介导的抗冷应激的系统耐受性。