Solanum nigrum L. antioxidant defence system isozymes are regulated transcriptionally and posttranslationally in Cd-induced stress

Solanum nigrum L. plants were grown for 45 days in increasing cadmium (Cd) levels (0-30 μM) in a hydroponic system to analyse the antioxidant defence response. There was a significant decrease in fresh weight and photosynthetic pigments and an increase in malondialdehyde and proline along the increasing Cd level applied. Cd levels in roots and leaves increased in a dose-dependent manner, the highest Cd concentration occurring in roots. The specific activity and mRNA accumulation of each superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) isozymes, in plants subjected to 0 and 15 μM Cd, suggest that specific isozymes play more important roles than others against Cd-induced oxidative stress. Mn-SOD and Fe-SOD are transcriptionally regulated while CuZn-SOD and both APX and CAT isozymes are regulated posttranscriptionally. The overall antioxidant defence activity increased mainly in roots, which contributed for the plant tolerance to this heavy metal.