The incorporation of 3H-palmitic acid into Ornithogalum umbellatum lipotubuloids, which are a cytoplasmic domain rich in lipid bodies and microtubules. Light and EM autoradiography

In the ovary epidermis of Ornithogalum umbellatum L. lipotubuloids were found, i.e. distinguished cytoplasmic domain with an agglomeration of half unit membrane-surrounded lipid bodies, entwined and held together by a system of microtubules (Protoplasma 75: 345-357; 77: 473-476). Using light and EM-autoradiography with 3H-palmitic acid (25 μCi/ml) it was found that lipotubuloids were the site of intense incorporation of this isotope. After extraction of lipids with lipid solvent the lipotubuloids were not labeled. Localization of autoradiographic grains after 15-h postincubation with isotope-free medium indicated a migration of the labeled substances from the lipotubuloids to the whole cells. Ultrastructural studies demonstrated that most autoradiographic grains after 2-h incubation were localized over the site of the microtubules adjoining closely the half unit membranes of lipid bodies. These observations suggest, that the surface of lipid bodies may be the active site in lipid synthesis and involvement of the microtubules in these processes is possible.