28‑Homobrassinolide Alters Protein Content and Activities of Glutathione‑S‑Transferase and Polyphenol Oxidase in Raphanus Sativus L. Plants Under Heavy Metal Stress

Objectives: The application of brassinosteroids (BRs), the plant steroidal hormones, results in an increased tolerance toward stress and thus helps improving the yield of crop plants. The present study was carried out to investigate the effect of 28‑homobrassinolide (28‑HBL) on the protein content as well as activities of antioxidant enzymes viz., glutathione‑s‑transferase (GST) and polyphenol oxidase (PPO) in radish plants grown under Cadmium (Cd) and Mercury (Hg) metal stress. Materials and Methods: Shoots of 60 and 90 days old radish plants, grown under Cd and Hg metal stress (0, 0.5, 1.0, 1.5 mM) and given the presowing treatment of 28‑HBL (0, 10–7, 10–9, 10–11 M) to seeds for 8 h, were analyzed for protein content and GST and PPO enzyme activities. Results: Protein content showed decrease in plants given Cd and Hg metal treatment alone, while treatment with 28‑HBL enhanced the protein content, suggesting its stress protective role. An increase in the activity of antioxidative enzymes was also observed in plants stressed with heavy metals as well as in those supplemented with 28‑HBL. Conclusions: In the present investigation, the activity of antioxidative enzymes was found to increase due to metal stress and a further increase was noticed in plants given both metal and 28‑HBL treatment, suggesting the stress protective role of 28‑HBL via modulating the antioxidative enzymes.