Brassica juncea L. plants were subjected to cobalt (Co) ion (0, 5 × 10⁻⁴, 10⁻³, 1.5 × 10⁻³ and 2 × 10⁻³ M) toxicity and were sprayed with different concentrations of 24-epibrassinolide (24-EBL) (0, 10⁻¹⁰, 10⁻⁸ and 10⁻⁶ M) at 15-day stage after sowing. They were sampled at 30 and 60 days after sowing and analyzed for growth parameters in terms of shoot length and number of leaves. Thereafter, leaves were excised and content of proteins and the activities of antioxidative enzymes (superoxide dismutase (SOD) (EC 1.15.1.1) catalase (CAT) (EC 1.11.1.6), ascorbate peroxidase (APOX) (EC 1.11.1.11), guaiacol peroxidase (POD) (EC 1.11.1.7) glutathione reductase (GR) (EC 1.6.4.2), monodehydroascorbate reductase (MDHAR) (EC 1.1.5.4) and dehydroascorbate reductase (DHAR) (EC 1.8.5.1)) were analyzed. The plants exposed to cobalt ion exhibited a significant decline in growth in terms of shoot length and number of leaves. However, foliar spray treatment with 24-EBL was able to alleviate the stress generated by cobalt ion and significantly improved the above parameters. The activities of antioxidative enzymes (SOD, CAT, POD, GR, APOX,MDHAR and DHAR) and protein content were also regulated considerably in leaves of plants treated with 24-EBL alone, 10⁻⁸ M concentration being the most effective. The activities of antioxidative enzymes also increased in leaves of B. juncea plants by the application of cobalt ion to soil and consequently sprayed with 24-EBL. Similarly, the protein content was also regulated in leaves of B. juncea plants treated with 24-EBL as compared to untreated control plants, thereby revealing stress-protective properties of 24-EBL.
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