ANTIOXIDANT RESPONSES TO SIMULATED ACID-RAIN AND HEAVY-METAL DEPOSITION IN BIRCH SEEDLINGS

This study measured the responses of different antioxidants in 2-year- old birch (Betula pendula Roth) seedlings subjected to simulated acid rain (pH 4.0) and heavy metals (Cu/Ni), applied alone or in combinatio n for 2 months. The applied concentrations of pollutants did not signi ficantly affect seedling biomass or total glutathione levels. Acid rai n alone increased superoxide dismutase (SOD) activity both in leaves a nd roots, while heavy metals alone inhibited SOD activity in roots. Bo th acid rain and heavy metals applied singly increased ascorbate perox idase (APX) and guaiacol peroxidase (GPX) activities in leaves but dec reased activities in roots. In contrast, acid rain and heavy metal tre atments increased glutathione reductase (GR) activity in roots but not in leaves. Spraying birch seedlings with a mixture of acid rain and h eavy metals increased SOD, APX and GPX activities in leaves and GR act ivity in roots. However, the effects of mixed pollutants on enzyme act ivities usually were less than the summed effects of individual pollut ants. Enzyme responses also depended on where pollutants were applied: spraying pollutants onto the shoots initiated higher responses in SOD , APX and GPX than did application to the soil surface, while the oppo site was true for GR. (C) 1997 Elsevier Science Ltd. All rights reserv ed.