Antioxidative defense system in lupin roots exposed to increasing concentrations of lead
Yellow lupin (Lupinus luteus) cv. Juno seedlings exposed to increasing concentrations of Pb2+ (50-350 mg l-1) were analysed in respect to its effect on the degradation of lipids, the content of antioxidants (ascorbate, α-tocopherol) and the activity of the ascorbate glutathione cycle enzymes (dehydroascorbate reductase DAR; EC 22.214.171.124 and glutathione reductase GR; EC 126.96.36.199). Lipid peroxidation, expressed as the content of TBArm (thiobarbituric acid reactive metabolites), increased only at 50 and 100 mg l-1 Pb2+, whereas at higher lead concentrations it decreased as compared with the control. The level of free fatty acids was not significantly affected as a result of Pb2+ exposure, except for 300 mg l-1 Pb2+. The content of α-tocopherol increased significantly at the range of concentrations between 150 and 300 mg l-1 and at these concentrations lipid peroxidation was inhibited. Ascorbic acid (AA) and dehydroascorbic acid (DHA) content increased considerably in roots treated with 100 and 150 mg l-1 Pb2+. In general the activity of DHAR and GR was stimulated by lead, however at higher Pb2+ concentrations (300 and 350 mg l-1) GR revealed lower enzymatic activity. Our results suggest that in lead-treated roots lipids might be protected against reactive oxygen species (ROS) by lipid-soluble molecules of α-tocopherol and this direct defense seems to be supported by AA as well as the enzymes: DHAR and GR.