Relative tolerance of different species of Brassica to cadmium toxicity: Coordinated role of antioxidant defense and glyoxalase systems

The present study was carried out to examine the metal accumulation and tolerance abilities of three 'Brassica' species ('B. napus, B. campestris, and B. juncea') seedlings exposed to two levels of cadmium (Cd) stress (0.25 and 0.5 mM CdCl2 for three days). Of the 'Brassica' species studied, 'B. juncea' accumulated the highest amount of Cd in a dose-dependent manner, and in every case, the Cd content was higher in the roots than the shoots. Cadmium stress reduced seedlings biomass, leaf relative water content (RWC), and chlorophyll (chl) content, whereas proline (Pro), MDA, and H2O2 content and lipoxygenase (LOX) activity increased in all species. Under Cd stress, ascorbate (AsA) content reduction was lower and glutathione (GSH) content increase was higher in 'B. juncea' compared with other species. Monodehydroascorbate reductase (MDHAR), glutathione reductase (GR), and superoxide dismutase (SOD) activities increased significantly in 'B. juncea' under Cd stress compared with the other species. Catalase (CAT) activity did not decrease in 'B. juncea' due to Cd stress, compared with the other species. Dehydroascorbate reductase (DHAR) activity decreased with both levels of Cd stress in all species except for 'B. juncea' under 0.25 mM CdCl2 stress. Glyoxalase system components performed better in 'B. juncea' than the other species under Cd stress. Methylglyoxal (MG) increased substantially under both levels of Cd stress, but MG content was lower in 'B. juncea' compared with the others. Considering the antioxidant defense and glyoxalase systems performance B. juncea is relatively tolerant species to Cd toxicity though it accumulated highest Cd.