Immunogold Localization of the L3 Protein of Maize Lipid Bodies during Germination and Seedling Growth

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Abstract
We have used antibodies directed against the 16.5 kilodalton protein L3, the most abundant integral protein of maize (Zea mays L. cv Mo 17) lipid bodies, to follow the fate of this protein in scutellar parenchyma cells of maize during germination and subsequent seedling growth. Using gel electrophoresis and immunoblotting as well as immunocytochemical electron microscopy, we found that the amount of L3 decreases gradually during the first 3 to 4 days of seedling growth and more rapidly over the course of the next several days. Immunogold localization of the protein on thin sections indicated that L3 is found exclusively in the surface phospholipid monolayer of lipid bodies. The density of L3 in the surface layer of individual lipid bodies does not change during seedling growth; therefore, the decrease in the amount of L3 can be attributed to a decrease in the number of lipid bodies rather than to selective removal of protein components from the surface of all lipid bodies. Thus, L3 is apparently degraded at the same time as the matrix lipid of each lipid body. Unlike lipase, L3 does not appear to be transferred to other cellular compartments such as vacuoles during late stages of seedling growth.