Melatonin is a multifunctional signaling molecule that regulates broad aspects of responses to environmental stresses in plants. Cadmium (Cd) is a persistent soil contaminant that is toxic to all living organisms. Recent reports have uncovered the protective role of melatonin in alleviating Cd phytotoxicity, but little is known about its regulatory mechanisms in plants. In this study, we found that foliar application of melatonin (in particular 100 μmol L⁻¹) remarkably enhanced Cd tolerance of tobacco (Nicotiana tabacum L.) leaves, as evidenced by less Cd accumulation and alleviation of growth inhibition and photoinhibition, compared with nontreated Cd-stressed plants. The addition of melatonin also controlled oxidative damage of Cd on tobacco through direct scavenging and by enhancing the activities of antioxidative enzymes. Melatonin application promoted Cd sequestration in the cell wall and vacuoles based on the analysis of subcellular distribution of Cd in tobacco cells. Structural equation modeling (SEM) analysis revealed that melatonin-induced Cd tolerance in tobacco leaves was modulated by the expression of Cd-transport genes. Molecular evidence illustrated that modulation of IRT1, Nramp1, HMA2, HMA4, and HMA3 genes caused by melatonin could be responsible for weakening Cd uptake, Cd transportation to xylem, and intensifying Cd sequestration into the root vacuoles.

褪黑激素是一种多功能信号分子，可广泛调节植物对环境胁迫的反应。镉 (Cd) 是一种持久性土壤污染物，对所有生物体都有毒。最近的报告揭示了褪黑激素在减轻镉植物毒性方面的保护作用，但对其在植物中的调节机制知之甚少。在本研究中，我们发现叶面喷施褪黑素（特别是100 μmol L ^-1 ）显着增强了烟草（Nicotiana tabacum L.）叶片的镉耐受性，与相比，叶面喷施褪黑素（特别是100 μmol L -1 ）显着增强了烟草（ Nicotiana tabacum L.）叶片的镉积累，并减轻了生长抑制和光抑制。未经处理的镉胁迫植物。添加褪黑激素还可以通过直接清除和增强抗氧化酶的活性来控制镉对烟草的氧化损伤。根据对烟草细胞中镉的亚细胞分布的分析，褪黑激素的应用促进了细胞壁和液泡中镉的封存。结构方程模型 (SEM) 分析表明，烟叶中褪黑激素诱导的镉耐受性是通过镉转运基因的表达来调节的。分子证据表明，由褪黑激素引起的IRT1 、 Nramp1、HMA2 、 HMA4和HMA3基因的调节可能是削弱 Cd 吸收、Cd 向木质部运输以及加强 Cd 封存到根液泡的原因。