The role of antioxidative metabolism of tomato leaves in long-term salt-stress response

The antioxidative protection system as adaptation strategy to high soil salinity in the leaves of two tomato (Lycopersicon esculentum Mill.) hybrids (Buran F1 and Berberana F1) was investigated. Changes in the activity of superoxide-dismutase (SOD, EC 1.15.1.1), peroxidase (POD, EC 1.11.1.7), ascorbate peroxidase (APX, EC 1.11.1.11), as well as total and oxidized ascorbate concentrations (AA and DHA) in the plant leaves subjected to three salinity levels (EC 3.80 dS m(-1), 6.95 dS m(-1), and 9.12 dS m(-1)) relative to non-saline control were analyzed during the fruiting phase. The obtained results clearly indicate a relation between SOD activity and AA concentration in the antioxidative protection without any peroxidase-related H2O2 detoxification. Increased SOD activity accompanied by high AA concentration was noticed at all salinity levels, but the response of hybrids was specific for the particular salt concentration. The first salinity level (EC 3.80 dS m(-1)) induced the highest level of AA in the Buran F1 (70%), while in Berberana F1 hybrid leaves the highest AA concentration (64%) was noticed at the third salinity level (9.12 dS m(-1)). All salinity levels caused a decline in POD and APX activities in both hybrids. The possibility of a predominant role of ascorbate and SOD in the antioxidative protection of mature tomato leaves under long-term salt stress is discussed.