Effects of exogenous brassinosteroid on Cd tolerance in Solanum nigrum seedlings

Cadmium (Cd) is one of the most toxic heavy metals with a strong inhibitory effect on plant growth. Although the effects of auxin on Cd tolerance and accumulation has been reported, the role of brassinosteroid (BR) on Cd stress response has remained unclear. In this study, the physiological effects of BR on Cd stress in Solanum nigrum seedlings were investigated. Cd toxicity induced oxidative damage and decreased the activities of SOD, CAT, and APX in S. nigrum seedlings. Treatment with epibrassinolide (eBL, a synthetic BR) increased Cd sensitivity in S. nigrum seedlings. On the contrary, supplementation with brassinazole (Brz, a specific inhibitor of BR biosynthesis) increased anti-oxidative enzyme activities and reduced reactive oxygen species (ROS) accumulation and oxidative damage. This improved Cd tolerance in S. nigrum seedlings exposed to Cd stress. After treatment with Brz, plant height and root length increased by 29% and 28%, respectively. Also MDA level and Evans blue staining decreased by 37% and 20%, respectively compared with Cd treatment alone. This suggested that BR increased Cd-induced oxidative damage and growth inhibition in S. nigrum seedlings. The results suggest that enhanced Cd sensitivity by BR was correlated with decreasing activities of anti-oxidative capacity in S. nigrum seedling. These results suggested that manipulation of BR level was an effective approach to improve Cd tolerance in plants. It modulated anti-oxidative enzyme activity and ROS accumulation, and provided detailed insights into novel phytoremediation strategies.