PASSIVE RESPONSE OF SACCHAROMYCES-CEREVISIAE TO OSMOTIC SHIFTS - CELL-VOLUME VARIATIONS DEPENDING ON THE PHYSIOLOGICAL-STATE

The passive osmoregulation phase of S. cerevisiae has been characteriz ed for different physiological states. The relative cell volume decrea se of exponential cells was found to be greater than the volume decrea se of stationary ones during the hyperosmotic shock. The application o f a slow and linear increase in osmotic pressure has allowed the disti nguishing of two phases in the passive osmoregulatory response of cell s and to calculate the turgor pressure of S. cerevisiae. Cells in the exponential phase have a weak turgor pressure (0.05 MPa) compared to t he turgor pressure of stationary phase cells (0.2 MPa). Nevertheless, the turgor pressure and the relative decrease in volume were found to be independent of the size of cells for the same physiological state. (C) 1996 Academic Press, Inc.