THE ROLE OF ANTIOXIDATIVE ENZYMES IN TOMATO LEAVES UNDER HEAT STRESS AT TWO DEVELOPMENTAL PHASES

The role of antioxidative enzymes in response to heat stress tolerance (HST) of three tomato cultivars was investigated in this research. The leaves were obtained from tomato plants at the first bloom and yield stages and then were subjected to controlled high temperature treatments in water bath. The temperature in the water bath was increased 5 °C systematically for every half an hour from 35 to 60°C to generate a heat-stressed condition. The plants in yield stage exhibited an increase in HST when compared with the plants in first bloom stage and heat stress increased hydrogen peroxide (H2O2) level in leaves. Among the performed enzyme analysis, only catalase (CAT) involved in HST of tomato cultivars, however it may not be correlated with the degree of HST. In addition, two acidic and one basic isoperoxidases appeared in relatively heat tolerant cultivars in the yield stage, therefore isoperoxidases may be associated to HST in tomato plant.