Electron dense markers of a size suitable for transmission electron microscopy and scanning electron microscopy have been prepared with gold granules labeled with a monolayer of specific macromolecules. The optimum conditions for preparing the markers have been ascertained. The method is simple, rapid and seems to be general since gold granules have been labeled with polysaccharides and proteins. As homogeneous populations of gold granules having different sizes can be prepared, the method is also suitable for double marking experiments. The gold technique is illustrated by the localization of polysaccharides and glycoproteins on yeast cell walls and erythrocyte membranes by transmission electron microscopy and on yeast cells and intact erythrocytes by scanning electron microscopy. Good spatial resolution of the marker was achieved in all cases. The method is also suitable for marking thin sections. Spectrophotometric measurements were used to determine the number of gold granules adsorbed per cell.

The location of galactomannan on the surface of Schizosaccharomyces pombe cells was reexamined by scanning electron microscopy by an indirect but specific method using gold markers. The polysaccharide was found on the cell surface and at the end beginning to grow but not on the wall established by division. Galactomannan was also localized on S. pombe thin sections by transmission electron microscopy using the same method. The polysaccharide was found deposited in two layers in the cell wall, i.e. at the periphery of the wall and near the plasmalemma. The septum was also marked but mainly near the plasmalemma. These results indicated that the polysaccharide is elaborated onto the outside of the wall during extension but not during septum formation. When thin sections of S. pombe were marked with gold granules labeled with wheat germ agglutinin, marking was found in vacuoles but not in the cell wall. This confirmed that S. pombe cell wall is devoid of chitin.

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Galactomannan was localized by scanning and transmission electron microscopy on the cells and cell walls of Schizosaccharomyces pombe. The markers were prepared from colloidal gold granules labelled with an alpha-galactopyranosyl-binding lectin isolated from the seeds of Bandeiraea simplicifolia. Part or all of this alpha-galactomannan was present in the outer layer of the cell wall and was uniformly distributed even on the fission scars.

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