Differences in oxidative stress in heavy metal resistant and sensitive clones of Salix viminalis

Many stress mechanisms, such as antioxidative mechanisms, are known to be activated by heavy metals. The aim of this work was to investigate whether oxidative stress and related mechanisms were expressed differently in plants with different resistances to heavy metals. Different clones of Salix viminalis with different resistances to Cd, Cu, and Zn were cultivated hydroponically in the presence of 7 μmol/L Cd, 3 μmol/L Cu or 70 μmol/L Zn for 20 days. The clones were then compared with regard to the concentrations of free radicals, estimated by measuring thiobarbituric acid-reactive material (TBA-rm) and glutathione (GSH). The activity of the enzymes, aspartate peroxidase (APX), guaiacol peroxidase (GPX), superoxide dismutase (SOD), and catalase (CAT) was also analysed. Salicylic acid was also measured since it is known to be involved in antioxidative activities. The results showed that some differences could be observed between resistant and sensitive clones. The SOD activity was higher in untreated resistant clones compared with the sensitive ones. Under metal treatment, however, the SOD activity was similar. Furthermore, TBA-rm was higher in shoots of resistant clones compared to sensitive ones, while the opposite was found in roots.