The activity and localization of lipoxygenases in Arabidopsis thaliana under cadmium and copper stresses

The regulation of lipoxygenases (LOX) activity was studied in Arabidopsis thaliana grown under excess Cd and Cu (0.0, 5.0, 50.0 mu M) in solution cultures for 7 days. The LOX activity was determined spectrophotometrically at 234 nm in the leaves of mature plants using linoleic and linolenic acids as substrates, while their cellular localization was assessed by immunogold-labelling. The LOX mainly occurred in the cytoplasm as well as inside the chloroplasts. Two bands of LOX were found in the leaves of A. thaliana, but one more band appeared in plants treated with 50.0 mu M Cu. Despite the lower amount of enzymatic protein in plants exposed to heavy metals, the enzyme activity was significantly higher than that in the control; it was especially high at pH 8.0 when linolenic acid was used as a substrate. The role of the redox state of plant cells in modifying the LOX activity was also discussed. The changes in ultra-structure of the leaf parenchyma cells were more evident in A. thaliana plants treated with Cd than those treated with Cu.