Co-application of 6-ketone type brassinosteroid and metal chelator alleviates cadmium toxicity in B. juncea L.

Plant growth regulator-assisted phytoremediation has been assessed as a novel strategy to improve phytoremediation potential of plants. In the present work, potential of castasterone, a plant growth regulator, combined with citric acid was explored for phytoremediation of cadmium in Brassica juncea seedlings. The seedlings were raised under controlled laboratory conditions for 7 days. Results revealed that 0.6 mM cadmium exposure induced toxicity in the seedlings, which was reflected through root growth inhibition, accumulation of hydrogen peroxide and malondialdehyde, and loss of cell viability. Pre-sowing treatment of castasterone supplemented with citric acid enhanced cadmium accumulation in the roots (from 752 µg/g DW to 1192 µg/g DW) and shoots (from 88 µg/g DW to 311 µg/g DW) and also improved root length, shoot length, fresh weight, and dry weight of seedlings by 81, 17, 39, and 35 %, respectively. The co-application reduced malondialdehyde accumulation by 39 % and reduced oxidative stress by enhancing the activities of antioxidant enzymes (superoxide dismutase, guaiacol peroxidase, catalase, ascorbate peroxidase, dehydroascorbate, glutathione reductase, glutathione peroxidase, glutathione-S-transferase, polyphenol oxidase), maximum enhancement (82 %) being in polyphenol oxidase. Similarly, the contents of water- and lipid-soluble antioxidants were found to increase by 31 and 4 %, respectively. Confocal microscopy revealed enhanced content of NO. Results suggested that binary combination of castasterone and citric acid is helpful in improving cadmium accumulation and ameliorating metal toxicity in B. juncea seedlings.