Melatonin and arginine combined supplementation alleviate salt stress through physiochemical adjustments and improved antioxidant enzymes activity in Capsicum annuum L.

Effects of NaCl stress, melatonin (MT), arginine (ARG), and their combined treatment on morphological, physiological, and biochemical features of Capsicum annuum L. were estimated. Antioxidants (total phenolics), total soluble protein and antioxidant enzymes were analyzed in this study. Quantum yield of photosystem II (Y[II]), inorganic ions (Na+, K+, Ca++ and Cl-) and yield characters of C. annuum were also studied in this research work. Salt stress was applied using 50 and 100 mM sodium chloride. Concentrations selected for exogenous MT and ARG treatments were 100 & mu;M and 2 mM, respectively. Results showed that NaCl salt stress significantly reduced morphological characters. Foliar application of MT, ARG and their combined treatment improved morphological characters in control as well as salt stress plants. There was negligible change in chlorophyll a and b contents of C. annuum under NaCl salt stress. Exogenous MT and ARG treatments slightly improved chlorophyll a, b contents in control and stress plants. ROS, MDA and H2O2, antioxidants (phenolics) and antioxidant enzymes were increased under salt stress. Foliar spray of MT, ARG and their combined treatment tends to decrease MDA and H2O2 but enhanced total phenolics and antioxidant enzymes under NaCl stress. Salt stress also decreased Y [II] and overall yield of C. annuum. Exogenous MT and ARG treatments not only improved photosynthetic capacity of C. annuum by improving Y[II] but also enhanced overall yield of C. annuum plants in control and stress conditions. It is concluded that exogenous MT, ARG, and their combined treatment alleviates salt stress in C. annuum through improving antioxidant enzymes activities, chlorophyll a and b contents, Y[II] and by scavenging effects of ROS. This resulted in improved plant growth and overall yield of C. annuum.