Effects of salinity on growth, activity of antioxidant enzymes and sucrose content in tomato (Lycopersicon esculentum Mill.) at the reproductive stage

The effects of NaCl on the growth and physiology of tomato (Lycopesicon esculentum Mill.) cultivar Cln 1463 x Ace 55VF were studied. The plants were hydroponically grown in half-strength Hoagland solution for 45 days followed by treatments with 0, 25, 50 and 100 mM NaCl for 75 days. Growth parameters of 120-day-old plants were recorded. Mature leaves were harvested and analyzed for the amount of proline, protein, sucrose, activity of sucrose phosphate synthase (SPS), ascorbate peroxidase (APX), superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD). Mature fruits were analyzed for the amount of sucrose and activity of SPS. A low (25 mM NaCl) level of salinity treatment had no deleterious effects on vegetative growth parameters, but caused significant decreases in the number and average weight of mature fruits. At higher concentrations of NaCl (50 and 100 mM), both vegetative and fruit growth parameters were drastically reduced. Salinity treatments caused a reduction in protein content, accumulation of proline and enhancement of APX activity in leaves. In mature fruits and leaves, the amount of sucrose and the activity of SPS, the key enzyme in the sucrose synthesis pathway, increased with salinity treatment. Although salinity treatment caused significant reduction in fruit yield, it could improve fruit quality by increasing sucrose content.