Role of Melatonin in Inducing the Physiological and Biochemical Processes Associated with Heat Stress Tolerance in Tall Fescue (Festuca arundinaceous)

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.