Amelioration of Lead Toxicity in Radish (Raphanus sativus L) Plants by Brassinolide

Abstract

The present study was designed to evaluate the effect of lead (Pb) and combine effect of Pb with brassinolide (BL) on the
growth, metabolite contents and enzyme activities in radish plants. Pb suppressed the growth of the radish plants, reduced net
photosynthesis rate and soluble sugar levels. Activities of nitrate reductase in radish plants were also reduced under Pb stress.
However seed treatment with BL mitigated the adverse effects of Pb and stimulated the growth of radish plants. The growth
promotion was associated with enhanced rate of photosynthesis and elevated levels of reducing and total sugars and nitrate
reductase activities in radish plants under Pb stress. Under Pb stress, reactive oxygen species (ROS) levels and lipid peroxidation
were increased in radish plants, which were significantly inhibited by BL application. The activities of antioxidant enzymes such
as peroxidase, ascorbate peroxidase and superoxide dismutase were increased during metal stress. Treatment with BL further
increased the activity of ascorbate peroxidase, catalase and superoxide dismutase. The BL treatment also enhanced glutathione
reductase activity under stress. From the results it can be concluded that BL could play a positive role in the alleviation of oxidative
stress caused by ROS by enhancing antioxidant defense system, thus improving the tolerance of radish plants to Pb stress