One of the important consequences of salinity stress is the overproduction of reactive oxygen species (ROS) from the pathways such as photorespiration, photosynthesis, and mitochondrial respiration. Plants have evolved an enzyme-based means involving peroxidase (POD), ascorbate peroxidase (APX), catalase (CAT), superoxide dismutase (SOD) to maintain the balance in the production and scavenging of ROS, and it is believed that the enhanced activity of these enzymes facilitates the protection of plants under stress conditions. Here, a detailed investigation of the long-term effects of increasing salinity (0, 30, 60, or 90 mM NaCl) on the activities of antioxidant enzymes of melon genotypes has been conducted to better understand and determine if any of these parameters may be useful as a selection criterion in breeding melon for tolerance to salinity. Results showed significant increases in POD, APX, CAT, and SOD activities in all genotypes following salt stress treatments relative to the controls. Antioxidant enzyme activities were different according to genotypes over all NaCl concentrations. These results suggest that melon genotypes with higher activity of antioxidant enzymes, i.e. “Galia” F1, “Ghobadlu” and “Suski-e-Sabz” can be selected and used as a parent in order to obtain the most tolerant plants against salt stress in breeding programs.
