In the model yeast Saccharomyces cerevisiae, two uptake systems, Trk1 and Trk2, are responsible for the accumulation of a relatively high intracellular potassium content (200–300 mM) and the efflux of surplus potassium is mediated by the Tok1 channel and active exporters Ena ATPase and Nha1 cation/proton antiporter. Using a series of deletion mutants, we studied the role of individual potassium transporters in yeast cell resistance to dehydration. The Trk2 transporter (whose role in S. cerevisiae physiology was not clear) is important for cell viability in the stationary phase of growth and, moreover, it
plays a crucial role in the yeast survival of dehydration/rehydration LY294002 nmr treatments. Mutants lacking the TRK2 gene accumulated significantly lower amounts of potassium ions in the stationary culture growth phase, and these lower amounts correlated with decreased resistance to dehydration/rehydration stress. Our results showed Trk2 to be the major potassium uptake system in stationary cells, and potassium content to be a crucial parameter for desiccation survival. In a natural environment, most microorganisms, including yeasts, may be periodically subjected to quite intense dehydration, MG-132 in vitro resulting in the state of anhydrobiosis. This unique state of live organisms is linked with a temporary reversible suspension of metabolism for the periods of unfavorable environmental
conditions. Upon rehydration, the cell functions can be restored and the cells start to grow and divide. This ability is widely utilized, mainly in food-related biotechnology processes producing or employing so-called ‘dry yeast’. Detailed studies of anhydrobiosis in yeasts revealed structural and functional changes in the main cellular organelles Dynein as well as a number of protective intracellular reactions which take place in the cells upon their dehydration and subsequent rehydration/reactivation (Beker & Rapoport, 1987). One of the most important factors to determine the maintenance of cell viability
under these conditions is linked with the maximal preservation of the molecular organization of cell membranes, including the plasma membrane (Crowe et al., 1989; Rapoport et al., 1997). The transfer of yeast cells into the state of anhydrobiosis results in a very significant decrease in cell volume (up to 60%). Such a huge decrease in cell volume is accompanied by the formation of large invaginations of the plasma membrane inside the cytosol (Beker & Rapoport, 1987). Cell volume and the normal shape of the plasma membrane is restored during a rather long process of cell reactivation that follows the rehydration process (Beker & Rapoport, 1987; Gervais & Beney, 2001). Besides the importance of trehalose and polyols for membrane protection under conditions of dehydration-rehydration (Panek et al., 1987; Krallish et al., 1997; Rapoport et al.
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