Effect of 28-homobrassinolide on the drought stress-induced changes in photosynthesis and antioxidant system of Brassica juncea L.

To investigate the effect of exogenously applied 28-homobrassinolide (HBL) on drought-stressed plants, photosynthesis and antioxidant systems were examined in Indian mustard (Brassica juncea L.). Seedlings of Indian mustard were subjected to drought stress for 7 days at the 8-14 (DS1)/15-21 (DS2) days' stage of growth and then returned to normal conditions of growth. These seedlings were sprayed with HBL (0.01 mu M) at the 30-day stage and were sampled at 60 days to assess the changes in growth, photosynthesis and antioxidant enzymes. Plants exposed to stress at either of the stages of growth exhibited a significant decrease in growth and photosynthesis. The exposure of plants to stress at an earlier stage (DS1) was more inhibitory than that at a later stage (DS2). However, the follow-up treatment with HBL significantly improved the values of these parameters and also overcame the inhibitory effect of water stress. The activity of antioxidant enzymes [catalase (E.C. 1.11.1.6), peroxidase (E.C. 1.11.1.7) and superoxide dismutase (E.C. 1.15.1.1)] and proline content in leaves exhibited an increase in response to both the treatment factors, where their interaction had an additive effect. It was, therefore, concluded that the elevated antioxidant system, at least in part, was responsible for amelioration of the drought stress.