Exogenous brassinosteroids increase lead stress tolerance in seed germination and seedling growth of Brassica juncea L.

Lead (Pb) is a highly toxic heavy metal to plants, animals, and human beings. The use of growth regulators has reversed the effects of heavy metal stress on germination and early plant development. The aim of this study was to evaluate the effect of brassinosteroids on seed germination and seedling growth of Brassica juncea (L.) Czern. & Coss. under Pb stress conditions. Two forms of application of 24-epibrassinolide (EBL) were evaluated, application on seeds in pre-soaking and on germination paper, using EBL concentrations of 0, 10-10, 10-8, and 10-6 M. Germination and seedling growth parameters were evaluated during the germination test. The activity of the enzymes superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase were determined, as well as the lead content in the seeds and seedlings. The EBL applied at the 10-8 M concentration was the most effective in overcoming Pb stress in both forms of application. The antioxidant enzyme defense system was compromised by Pb exposure. However, 10-8 M EBL increased the activity of antioxidant enzymes such as catalase and peroxidase to overcome the toxic effects caused by Pb. In addition, EBL at the concentration of 10-8 M increased Pb content in seedlings without affecting seedling growth.