The effects of brassinosteroid on the induction of biochemical changes in Lycopersicon esculentum under drought stress

Drought stress is considered a restricting factor for plant products; therefore many compounds were applied to minimise the harmful effects of stress. One type of these compounds that have antioxidative characteristics is brassinosteroids. In this experiment, when 4 fully expanded leaves of tomato plants appeared, 24-epibrassinolide (24-EBL) was sprayed onto the leaves, at 0.01 and 1 mu M concentrations for 3 days with a 1-day interval. Three levels of drought stress (0, 3, and 5 days withholding water) were applied. Thereafter, the effects of brassinosteroids and water stress were investigated on some biochemical and antioxidative parameters of tomato plants. Lipid peroxidation, peroxide hydrogen, and proline content increased in plants subjected to drought stress. Reduction in protein content in drought conditions showed that drought stress affected protein synthesis and degradation. Decline in the activity of antioxidant enzymes (POD and APX) and increases in the SOD, GR, and CAT activities were observed in drought stressed plants. Reduction in peroxidation of lipids and H2O2 content in the plants treated with both 24-EBL and drought stress was observed. Based on our results it seems that brassinosteroids considerably alleviated oxidative damage that occurred under drought stress. Increase in activity of antioxidant enzymes (POD, CAT, APX, GR, and SOD) and change in isoenzymes pattern with higher intensity as well as increases in proline and protein content in drought stressed plants treated with BR will probably show the role of brassinosteroids in increased tolerance of plants to water stress. Therefore, 24-epibrassinolide may have a role in the mitigation of damage caused by water stress.