Exogenous melatonin (MT) can aid crops in mitigating drought stress, yet its impacts on cotton pollen fertility under drought remain understudied. To address this, a study on the effects of exogenous MT on cotton pollen sterility and internal physiological metabolism under drought stress was conducted. Results showed that although antioxidant enzymes catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) activities increased in drought‐stressed anthers, yet this was insufficient to balance reactive oxygen species (ROS) levels, which led to higher hydrogen peroxide (H2O2) and superoxide anion (O2−) accumulation, resulting in oxidative stress, manifested by elevated malondialdehyde (MDA) and reduced pollen viability. Remarkably, the application of MT further bolstered the activities of CAT, POD and SOD in drought‐stressed anthers, effectively mitigating the accumulation of O2− and H2O2. This enhancement facilitated the antioxidant defence system under drought conditions. Simultaneously, the activity of ascorbate peroxidase (APX) was reduced, which prevented the reduction of dehydroascorbate (DHA) to ASA, and the ascorbic acid‐glutathione (AsA‐GSH) cycle was destroyed, leading to the accumulation of GSH. Nevertheless, MT application triggered upregulation of both GhDHAR and GhMDHAR expressions, promoting AsA synthesis and regeneration, respectively, thereby elevating AsA levels. Furthermore, MT revitalised APX activity, accelerating the removal of H2O2 through AsA‐mediated reduction, ultimately restoring the balance of the AsA‐GSH cycle and enhancing the overall antioxidant capacity of drought‐stressed anthers. In summary, exogenous MT can enhance the scavenging ability of ROS in drought‐affected anthers by elevating the activities of CAT, POD and SOD and by enhancing APX activity in the AsA‐GSH cycle, thereby alleviating drought‐induced oxidative stress and improving pollen fertility under water deficit stress.

中文翻译：

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外源褪黑激素通过改善抗氧化代谢来提高干旱胁迫棉花 （Gossypium hirsutum L.） 的花粉肥力


外源褪黑激素 （MT） 可以帮助作物缓解干旱压力，但其对干旱下棉花花粉生育力的影响仍未得到充分研究。为了解决这个问题，开展了干旱胁迫下外源 MT 对棉花花粉不育性和内部生理代谢影响的研究。结果表明，尽管抗氧化酶过氧化氢酶 （CAT）、过氧化物酶 （POD） 和超氧化物歧化酶 （SOD） 活性在干旱胁迫花药中增加，但这不足以平衡活性氧 （ROS） 水平，导致过氧化氢 （H2O2） 和超氧阴离子 （O2−） 积累增加，导致氧化应激，表现为丙二醛 （MDA） 升高和花粉活力降低。值得注意的是，MT 的应用进一步增强了干旱胁迫花药中 CAT、POD 和 SOD 的活性，有效减轻了 O2− 和 H2O2 的积累。这种增强促进了干旱条件下的抗氧化防御系统。同时，抗坏血酸过氧化物酶 （APX） 的活性降低，阻止了脱氢抗坏血酸 （DHA） 还原为 ASA，抗坏血酸-谷胱甘肽 （AsA-GSH） 循环被破坏，导致 GSH 的积累。尽管如此，MT 应用触发了 GhDHAR 和 GhMDHAR 表达的上调，分别促进了 AsA 合成和再生，从而提高了 AsA 水平。此外，MT 激活了 APX 活性，通过 AsA 介导的还原加速了 H2O2 的去除，最终恢复了 AsA-GSH 循环的平衡，并增强了干旱胁迫花药的整体抗氧化能力。 综上所述，外源 MT 可以通过提高 CAT、POD 和 SOD 的活性以及增强 AsA-GSH 循环中的 APX 活性来增强 ROS 在受干旱影响的花药中的清除能力，从而减轻干旱诱导的氧化应激并提高缺水胁迫下的花粉生育能力。