Melatonin is a general organizer that promotes plant development and moderates defense responses to abiotic stresses; e.g., heat, cold, and heavy metals. Cadmium (Cd) is a heavy metal that can be uptaken by cereal crops. It causes toxicity in plants and poses serious health risks due to its accumulation in the human body through the food chain. This study demonstrates that melatonin in the form of gold nanoparticles (Mel-AuNPs) can alleviate Cd toxicity to a greater extent in hydroponically grown rice plants compared to melatonin applied alone. When rice was grown in a medium supplemented with 200 μM Mel-AuNPs, the melatonin content significantly increased in the roots (18.0%) and leaves (20.3%), and the Cd level significantly decreased by 33.0% and 46.2%, respectively. Furthermore, the Mel-AuNP supplement restored chlorophyll biosynthesis and mitigated Cd-induced oxidative stresses, while the anti-oxidant enzyme activities were significantly increased. Further study showed that supplying Mel-AuNPs inhibited the Cd-induced gene expression of metal transporter-related genes (OsHMA2, OsHMA3, OsIRT1, OsIRT2, OsNramp1, OsNramp5, and OsLCT1) in rice roots. Overall, this study suggests that Mel-AuNP application could mitigate Cd toxicity in rice seedlings by enhancing melatonin absorption and suppressing Cd uptake.

中文翻译：

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使用褪黑激素合成的金纳米颗粒可抑制镉的吸收并减轻其在水稻中的毒性

褪黑素是促进植物发育并缓和对非生物胁迫的防御反应的一般组织者。例如，高温，低温和重金属。镉（Cd）是一种重金属，谷类作物可以吸收。它会在植物中引起毒性，并由于其通过食物链在人体中的积累而构成严重的健康风险。这项研究表明，与单独使用褪黑激素相比，金纳米颗粒（Mel-AuNPs）形式的褪黑激素可以在水培水稻中更大程度地减轻Cd毒性。当水稻在添加200μMMel-AuNPs的培养基中生长时，根部（18.0％）和叶片（20.3％）的褪黑激素含量显着增加，而Cd含量分别显着下降33.0％和46.2％。此外，Mel-AuNP补充剂可恢复叶绿素的生物合成并减轻Cd诱导的氧化应激，而抗氧化酶的活性则显着提高。水稻根中的OsHMA2，OsHMA3，OsIRT1，OsIRT2，OsNramp1，OsNramp5和OsLCT1）。总体而言，这项研究表明，Mel-AuNP的施用可以通过增强褪黑激素的吸收和抑制Cd的吸收来减轻水稻幼苗中Cd的毒性。