Effect of ultraviolet radiation and abscisic acid on activity of antioxidant enzymes and physiological and morphological traits of tomato (Solanum lycopersicum L.) under different irrigation intervals

This experiment was conducted to evaluate the effect of ultraviolet radiation (UV) and abscisic acid (ABA) on the activity of antioxidant enzymes, physiological and morphological characteristics of the tomato under drought stress conditions. Experiment was conducted as a factorial based on randomized complete block design with four replications during two years. Experimental factors included radiation of ultraviolet radiation on three levels (control (non-radiation), UV-AB and UV-C), application of abscisic acid on two levels (non-application and application of abscisic acid with dose of 10 mg/L), and drought stress on two levels of without drought stress (complete irrigation during all growth period) and drought stress in vegetative stage (from 20 days after transplantation to flowering). The results showed that UV-AB radiation increased leaf relative water content and shoot dry weight while UV-C radiation reduced leaf relative water content and shoot dry weight compared to control (without ultraviolet radiation). By applying drought stress increased the activity of catalase and superoxide dismutase enzymes as well as soluble carbohydrate concentrations, while the relative water content of leaves and shoot dry weight decreased significantly. The amount of peroxidase enzyme activity, relative water content, soluble carbohydrates and shoot dry weight increased due to the application of abscisic acid. Based on the results of this study, it can be stated that drought and ultraviolet stresses had harmful effects on the tomato plants, and the interaction of these two above-mentioned environmental tensions was synergistic to induce protective mechanisms and defense systems.