Response of antioxidant defence system in soybean nodules and roots subjected to cadmium stress

The antioxidant defence system of soybean (Glycine max L.) nodules and root s was studied in plants subjected to three different concentrations (50, 10 0 and 200 muM) of CdCl2. Cadmium (Cd)-induced oxidative stress was determin ed by lipid peroxidation, which remained unaltered in nodules and roots tre ated with 50 muM Cd(II). No changes were observed in nodules treated with 1 00 muM Cd(II), while a 20% increase was found in roots and 200 muM Cd(II) p roduced an increase of about 55% in both tissues. The soluble antioxidant d efence, reduced glutathione (GSH) and the corresponding reduced/oxidised gl utathione (GSH/GSSG) ratio showed different behaviour in both tissues, decr easing in roots with 100 and 200 muM Cd(II). No changes were observed in th e GSH/GSSG ratio in nodules under the three Cd treatments. However, ascorba te content and ascorbate/dehydroascorbate (As/DAs) ratio were diminished in nodules and roots subjected to the three Cd concentrations. Regarding the antioxidant enzymes, it was found that, except for catalase, a general decr ease in nodule enzyme activities was produced only under the 200 muM Cd( II ) treatment. Nevertheless, root enzymatic antioxidant defences showed signi ficant increments in L-ascorbate peroxidase (APOX), dehydroascorbate reduct ase (DHAR) and glutathione reductase (GR) activities under lower Cd treatme nt, while the enzyme activities decreased with the two higher concentration s of CdCl2. These results suggest that soybean roots were more affected tha n nodules by Cd treatments, although the higher Cd concentration produced o xidative stress and deleterious effects in antioxidant defence system in bo th tissues.