Localization and activity of lipoxygenase in Cd-treated seedlings of Phaseolus coccineus

Lipoxygenase was localized in the primary leaves of Phaseolus coccineus (L.), seedlings treated with 25 µM Cd and in control plants using the immunogold method. The enzyme was localized mainly in the peripheral parts of protoplast of control plant cells. It was found in the cell wall, along the ER elements, at plastid lamellae and inside the mitochondria. In Cd-treated seedlings the elements of parenchyma cells showed an atypical inner structure. The immunolabelling of LOX was less intensive in comparison with control. The enzyme was found in the cytoplasm, at the cell wall area, vacuoles and in the plastid stroma as single gold particles. LOX activity optima were determined at pH 7.0 and 8.0 for both linoleic and linolenic acid used as substrates. After 2 days of seedlings exposure to Cd the activity of LOX decreased at pH 7.0 and 8.0 when linoleic acid was used as substrate, and strongly declined at pH 7.0 after 4 days of the metal treatment. When linolenic acid was the substrate LOX activity slightly increased after 2 days of the plants exposure to Cd, but after 4 days it rapidly decreased at pH 7.0. The changes in LOX activity are discussed.