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 form s in microsomes has been studied. We concentrated on the question whet her the plasma membrane contains one or more forms of LOX. As methodol ogy, we applied both the two-phase partition with polyethylene glycol/ dextran and density gradient flotation of plasma membrane-enriched mem brane fractions. Both methods show that a high percentage of the micro somal LOX can be attributed to the plasma membrane. Emphasis was put o n the findings that the LOX located at the plasma membrane consisted o f 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 micro somal LOX forms by small but significant differences in size. Treatmen t of seedlings with methyl jasmonate led to an enhanced level of LOX a t the plasma membrane.