Yeast protoplasts from stationary and starved cells: preparation, ultrastructure and vacuolar development

The conversion of stationary and starved yeast cells into protoplasts is described. The method is rapid, simple and can be applied to a variety of stationary yeast cells. Preincubation of yeast cells in the presence of pronase was essential for effective conversion into protoplasts. Baker's yeast and seven defined yeast strains, including one "petite", were studied. All of them were efficiently transformed into protoplasts in 60 to 90 min, depending on the strain culture conditions and the age of the culture. Protoplasts may be obtained even from late-stationary cells which contain spores. Saccharomyces cerevisiae cells subjected to complete starvation conditions in water, could also be completely transformed into protoplasts, even after 48 h of starvation. Electron microscope examination of stationary protoplasts from three different yeast strains showed no evidence of a remaining cell-wall. S. cerevisiae stationary cells show a very developed vacuolar system, a number of "lipid granules" and a few altered mitochondria. Endomycopsis fibuligera and Candida tropicalis stationary protoplasts show a similar fine structure, but "lipid granules" were completely absent.