Genotypic variation in phytoremediation potential of Brassica juncea cultivars exposed to Cd stress

Problem of heavy metal contamination in agricultural lands, in part, is responsible for limiting the crop productivity. In India, Brassica juncea is cultivated as a major oilseed crop. This crop may further be useful in soil reclamation through the process of phytoremediation including phytoextraction of toxic heavy metals such as Zn, Pb, Cd, etc. from the soil. However, selection of B. juncea cultivar (cv.) with high Cd-extraction potential amongst the higher yielding cultivars would be of great importance to reclaim the soil with lesser impact on plant metabolism and hence the yield. Ten such B. juncea cultivars (V-1-V-10) commonly grown in India were selected for the present study to determine their Cd extraction potential and degree.of resistance to Cd stress. Ten-day-old seedlings of B. juncea cultivars were exposed to various levels of cadmium chloride (0.0-2.0 mM) for 72 h in hydroponics culture and leaf samples were analyzed at 24, 48 and 72 h after treatment (HAT) for the changes in the rate of lipid peroxidation, plant length, biomass accumulation, cadmium accumulation and activities of catalase (CAT, 1.11.1.6), superoxide dismutase (SOD, 1.15.1.1), ascorbate peroxidase (APX, 1.11.1.11) and glutathione reductase (GR, 1.6.4.2) along with ascorbate (Asc) and glutathione contents. A reduction in the plant length, biomass accumulation, CAT activity and ascorbate content was noted in all the cultivars, however, a significant increase in lipid peroxidation rate, Cd accumulation, activities of APX, GR, SOD and glutathione content was observed. B. juncea cv. Pusa Jai Kisan (V-5) showed the least increase in the rate of lipid peroxidation but accumulated highest levels of biomass, Cd and glutathione contents among the cultivars studied. These results indicate that cv. Pusa Jai Kisan possesses a better Cd-sequestering and antioxidant system. High increase in the levels of glutathione suggests its possible incorporation in synthesis of the phytochelatins and metallothioneins to sequester Cd and combat Cd-stress. (C) 2004 Elsevier Ireland Ltd. All rights reserved.