Genotypic variation in Brassica juncea (L.) Czern. cultivars in growth, nitrate assimilation, antioxidant responses and phytoremediation potential during cadmium stress.

Four cultivars of Brassica juncea i.e. TM-4, TM-2, RH-30 and T-59 were screened for seed germination and seedling growth up to 15 days in the presence of 0.5-1.5 mM cadmium (Cd). The exposure to Cd reduced seed germination and seedling growth (root and shoot length and dry weight) in all four cultivars; the effect being more severe in TM-2 and RH-30 than in TM-4 and T-59 and at 3 d than at 7 d and 15 d. The cultivars TM-4 and T-59, with higher tolerance to Cd toxicity, were selected for further analysis including the estimation of nitrate reductase (NR) and peroxidase (POD) activities, total organic nitrogen (TON), total soluble proteins, proline levels and Cd accumulation. The NR activity and total soluble proteins decreased upon Cd exposure in a concentration dependent manner, whereas TON increased significantly in 3 d seedlings upon Cd exposure. The activity of POD and proline level increased significantly as compared to the respective controls. The level of Cd accumulation was higher in T-59 than in TM-4. Therefore, T-59 was found to be the most tolerant cultivar to Cd than other three cultivars possibly due to a better capacity to transport Cd in their vacuolar sink. The variety T-59, thus, appears to be suitable for Cd phytoremediation.