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 characterized for different physiological states. The relative cell volume decrease of exponential cells was found to be greater than the volume decrease of stationary ones during the hyperosmotic shock. The application of a slow and linear increase in osmotic pressure has allowed the distinguishing of two phases in the passive osmoregulatory response of cells and to calculate the turgor pressure of S. cerevisiae. Cells in the exponential phase have a weak turgor pressure (0.05 MPa) compared to the 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.