Use of ruthenium red for visualization of the regenerating cell wall in yeast protoplasts

Ruthenium red was used to stain the surface of fresh and regenerating protoplasts in Saccharomyces cerevisiae. The presence of a dense layer, 10--40 nm wide, was demonstrated on the surface of most of the fresh protoplasts. This layer could be removed neither by repeated washings of protoplasts nor ;by their centrifugation. Ruthenium red proved to be a very useful dye for regenerating walls since it stained both the amorphous and the fibrillar components, but to a different degree, thus permitting their easy differentiation.