[Cell turgor and selective ion transport of Chaetomorpha linum].

The littoral alga Chaetomorpha linum is especially able to maintain a constant turgor pressure in the cell by regulating the internal osmotic pressure, if the salt content of the sea water changes. Experiments in artificial isotonic sea water with a constant sodium concentration, but variable potassium concentrations (from 1 to 50 mMol/1) prove, that the decrease or increase of the potassium concentration in the medium (CKa) is an essential cause for this regulation of the turgor pressure besides the change of the osmotic pressure of the medium, which was thought to be the predominant cause till now. In the examined concentration range the ratio CKa to CK1 (potassium concentration in the cell) depends linear on CKa in the steady state. At low values of CKa (< 10 mMol/1) the decrease in CK1 is compensated by a reversible sodium uptake only in part, and this leads to partly high changes in the cell turgor pressure, although the osmotic pressure of the medium remains constant. The results are discussed on the basis of carrier models.