Effect of salt stress on tomato fruit antioxidant systems depends on fruit development stage

The effects of different levels of salt stress on the oxidative parameters (H2O2 and MDA), the total pool sizes of ascorbate, the activities of antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT), as well as the activities and relative transcript levels of the enzymes of ascorbate-glutathione cycle; ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) were studied in fruits of tomato. Plants were treated by three concentrations of NaCl (50, 100 and 150 mM) and fruits at different development stages were harvested after 3 and 6 days of stress. The concentrations of ascorbate (AsA) and dehydroascorbate (DHA) generally changed with salt stress treatments. Moreover, changes in SOD and CAT activities and DHAR, MDHAR, APX and GR activities and relative transcript levels were dependent on the fruit development stage and the intensity and duration of salt stress. These results suggest that the response of antioxidant systems of tomato fruits to oxidative stress induced by salt stress treatments was different depending on the fruit development stage.