Melatonin is a ubiquitous molecule having versatile physiological functions in an organism that has protective roles against biotic and abiotic stresses. Heat stress has become a serious threat to plants reported in various studies. In this study, the melatonin-induced defense mechanism of tall fescue plants under heat stress was explored in terms of physiological and biochemical responses. Heat stress (42 °C) was applied to 8-day-old tall fescue seedlings in both control-treated and 20 µM melatonin-treated plants. The results revealed that under heat stress melatonin-treated tall fescue seedlings measured the higher contents of shoot fresh weight, shoot height, chlorophyll (Chl), carotenoid, total soluble protein, and antioxidant enzyme activities (Peroxidase, POD; Catalase, CAT; Superoxide dismutase, SOD) compared to control seedlings. Oppositely, melatonin-treated tall fescue seedlings showed comparatively lower production of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) than control treatment. These results indicated that with application of exogenous melatonin, the damaging effects of heat stress on Chl a, Chl b, carotenoid, and protein synthesis machineries of tall fescue turf grass were reduced, and the activities of antioxidant enzymes, protein, and lipid molecules were enhanced that favored the lower production of H₂O₂ and MDA. Therefore, with melatonin application, antioxidant enzyme-mediated defense system of tall fescue under heat stress was positively modulated and plant’s oxidative damages were alleviated evidencing the improvement of growth and physiological activities. Thus, tall fescue treated with melatonin might exhibit heat tolerance attribute. This investigation would provide a new insight for further exploration of heat tolerant mechanisms of tall fescue treated with melatonin under heat stress.

褪黑激素是一种普遍存在的分子，在生物体中具有多种生理功能，对生物和非生物胁迫具有保护作用。在各种研究中，热应激已成为对植物的严重威胁。在这项研究中，从生理和生化反应方面探讨了褪黑激素诱导的热应激下高羊茅植物的防御机制。热应激 (42 °C) 应用于对照处理和 20 µM 褪黑激素处理植物中的 8 天龄高羊茅幼苗。结果表明，在热胁迫下褪黑激素处理的高羊茅幼苗测得的鲜重、苗高、叶绿素（Chl）、类胡萝卜素、总可溶性蛋白和抗氧化酶活性（过氧化物酶，POD；过氧化氢酶，CAT；超氧化物）的含量较高。歧化酶，SOD）与对照幼苗相比。₂ O ₂ )和丙二醛(MDA)比对照处理。这些结果表明，外源性褪黑激素的应用降低了热应激对高羊茅草坪草Chl a、Chl b、类胡萝卜素和蛋白质合成机制的破坏作用，降低了抗氧化酶、蛋白质和脂质分子的活性。有利于降低 H ₂ O ₂产量的增强和 MDA。因此，随着褪黑激素的应用，热应激下高羊茅的抗氧化酶介导防御系统得到积极调节，植物的氧化损伤得到减轻，证明其生长和生理活动得到改善。因此，用褪黑激素处理的高羊茅可能表现出耐热性。这项研究将为进一步探索褪黑激素处理的高羊茅在热应激下的耐热机制提供新的见解。