Cadmium and H2O2-induced oxidative stress in Populus × canescens roots

Clonal, hydroponically grown poplar plants (Populus × canescens, a hybrid of Populus tremula × Populus alba) were exposed to Cd or H2O2 to find out whether Cd-induced injury was related to the disturbance of the cellular redox control in root tips. Cd exposure resulted in an inhibition of antioxidative enzymes (superoxide dismutase, EC 1.15.1.1; catalase, EC 1.11.1.6; ascorbate peroxidase, EC 1.11.1.11; monodehydroascorbate radical reductase, EC 1.1.5.4; glutathione reductase, EC 1.6.4.2) but had fewer effects on dehydroascorbate reductase (EC 1.8.5.1) activities. Glutathione concentrations decreased, whereas ascorbate remained unaffected by Cd. Five micromoles of Cd were subinjurious in short-term experiments and stimulated root growth. Fifty micromoles of Cd retarded shoot growth faster than root growth, caused a more severe loss in antioxidative capacity than 5 μM Cd and resulted in an accumulation of H2O2 in roots. Exposure to H2O2 had an effect on antioxidative enzymes similar to that found under the influence of Cd, but caused GSH accumulation, and loss of ascorbate. The present data indicate that both agents acted via the disturbance of the cellular redox control.