Lipoxygenase Forms Located at the Plant Plasma Membrane

In cucumber cotyledons (Cucumis sativus L.) containing several soluble and particulate forms of lipoxygenase (LOX), the location of LOX forms in microsomes has been studied. We concentrated on the question whether the plasma membrane contains one or more forms of LOX. As methodology, we applied both the two-phase partition with polyethylene glycol/dextran and density gradient flotation of plasma membrane-enriched membrane fractions. Both methods show that a high percentage of the microsomal LOX can be attributed to the plasma membrane. Emphasis was put on the findings that the LOX located at the plasma membrane consisted of a species behaving as an integral membrane protein and another form characterized as a peripheral membrane protein by solubilization with carbonate. With long distance SDS-PAGE and immunodecoration using anti-lipid body LOX antiserum, it is possible to distinguish between microsomal LOX forms by small but significant differences in size. Treatment of seedlings with methyl jasmonate led to an enhanced level of LOX at the plasma membrane.