OSMOTIC ACCLIMATION AND TURGOR PRESSURE REGULATION IN ALGAE

Salinity, together with light, temperature, and nutrients, is one of the abiotic factors affecting algal growth and distribution. Changes in salinity result in immediate water fluxes according to the osmotic gradients. This rapid response is followed by osmotic acclimation through adjustment of the cellular solute concentrations. As a result of these processes, a more or less constant turgor pressure is maintained or, in the case of wall-less cells, the cell volume is regained. Ions, mainly Na+, K+, and Cl-, and low-molecular-weight organic compounds are the major osmolytes. Possible mechanisms of sensing turgor pressure and the signal transduction during osmotic acclimation, which most likely involve Ca2+, are discussed for microalgae and charophytes as examples.