FIG. 1.

Depletion of external Na⁺ by P. sorbitophila and U. maydis. K⁺-starved cells of S. cerevisiae, P. sorbitophila, and U. maydis were suspended in testing buffer, with Na⁺ or Na⁺ plus K⁺ added to the suspension, and the variations of the external concentration of Na⁺ were recorded at intervals in the absence of K⁺ (closed circles) or in the presence of 50 μM K⁺ (open circles). The cell densities (dry weight, in milligrams per milliliter) in the experiments were as follows: S. cerevisiae, 0.7; P. sorbitophila, 0.9; and U. maydis, 0.7.