Role of earthworms in phytoremediation of cadmium (Cd) by modulating the antioxidative potential of Brassica juncea L.

Earthworms are important soil organisms known to affect soil nutrients and microbial properties. Role of earthworms in modulating the antioxidative potential of plants during phytoremediation of cadmium (Cd) was analyzed in this study. The effect of earthworms on growth, metal chelating compounds and antioxidants during accumulation of Cd was observed in 15 d old Brassica juncea seedlings. The seeds were grown under controlled conditions in plastic pots containing soil and partially decomposed cow dung (1:1). The soil was treated with different Cd concentrations i.e. 56 mg kg−1, 84 mg kg−1, 112 mg kg−1 and 140 mg kg−1 (C0, C1, C2, C3 and C4 respectively) and a set of each treatment was inoculated with earthworms. Significant improvement in growth and Cd uptake was observed after inoculation of earthworms by 28.7% in roots and 31.3% in shoots in seedlings grown in C4 concentration. Metal chelating compounds, i.e., total thiols, protein bound thiols and organic acids were also found to increase with increased Cd accumulation. The expression of genes encoding various enzymes responsible for organic acid metabolism, i.e., CS (citrate synthase), SUCLG1 (succinyl Co-A ligase,), SDH (succinate dehydrogenase), FH (fumarate hydratase) was also studied. Enhanced antioxidative potential of plants supplemented with earthworms was observed in Cd treated soils. Total antioxidative capacity (water soluble and lipid soluble antioxidants) was increased maximally by 100.6% and 139% in C4 treatment, respectively. Content of various phenolic compounds, i.e., total phenols, flavonoids, anthocyanin and polyphenols followed the same trend and were found to accumulate in metal treated soil amended with earthworms.