Comparative studies of H2O2 detoxifying enzymes in green and greening barley seedlings under cadmium stress

Cadmium(Cd) stress induced alterations in the activities of several represe ntatives of the enzymatic antioxidant defense system such as guiacol peroxi dase (POD), catalase (CAT) and ascorbate peroxidase (APX) were comparativel y studied in green and greening barley seedlings that represent two differe nt stages of plant development. Although roots were the main site of Cd acc umulation, 1.5-3% of Cd was translocated into leaves and it induced oxidati ve damage which was indicated by the reduced chlorophyll and increased malo ndialdehyde content of the leaves. In roots of both types of seedlings expo sed to various Cd concentrations, the APX activity was enhanced without any increase in the activity of POD. In leaves, however, elevated activities o f both POD and APX could be observed. In roots of green seedlings at high c oncentration of Cd, the APX activity was reduced on the fourth day of cultu re but no inhibition was found in the POD activity. Leaf CAT which mainly r epresented the peroxisomal enzyme activity did not display any changes unde r Cd stress. Our results show that at both developmental stages barley seed lings exhibit a well-defined activity of the enzymatic antioxidant system, which operates differentially in roots and shoots subjected to Cd stress. ( C) 2001 Elsevier Science Ireland Ltd. All rights reserved.