Photosynthesis, Growth and Antioxidant Metabolism in Mustard (Brassica juncea L.) Cultivars Differing in Cadmium Tolerance

Two mustard (Brassica juncea L. Czern and Coss) cultivars, Pusa Jai Kisan and SS2 differing in cadmium (Cd) tolerance were treated with 0, 25 and 50 mu mol L-1 Cd to study the physiological basis of difference in Cd tolerance Cultivar SS2 (Cd sensitive) accumulated greater Cd in leaves than Pusa Jai Kisan (Cd tolerant) Further, SS2 also exhibited higher contents of thiobarbituric acid reactive substances (TBARS) and H2O2 and electrolyte leakage However, the activities of antioxidant enzymes, catalase (CAT), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), and glutathione reductase (GR) were higher in Pusa Jai Kisan than those in SS2 Contrarily, the activity of superoxide dismutase (SOD) was higher in SS2 than that in Pusa Jai Kisan and was the greatest at 25 mu mol L-1 Cd Treatment of 25 mu mol L-1 Cd induced the maximum activity of enzymes However, the activity of GR increased up to 50 mu mol L-1 Cd in both the cultivars. The non-enzymatic antioxidants ascorbate (AsA) and glutathione (GSH) were higher in Pusa Jai Kisan than that in SS2, whereas dehydroascorbate (DHA) and oxidized glutathione (GSSG) were higher in SS2 Photosynthesis and growth were adversely and maximally decreased by 50 mu mol L-1 Cd treatment in both the cultivars, but SS2 exhibited greater reductions The protection of photosynthesis and growth and lesser reduction in Pusa Jai Kisan were associated with its capacity to restrict accumulation of Cd in leaves resulting in lower level of TBARS and H2O2 and electrolyte leakage. Moreover, Pusa Jai Kisan exhibited efficient antioxidant metabolism for removal of Cd-induced reactive oxygen species