K+-Dependent Deplasmolysis of a Marine Pseudomonad Plasmolyzed in a Hypotonic Solution1

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RESUMO

When cells of a marine pseudomonad were washed with a solution consisting of 0.3 m NaCl, 0.05 m MgSO4, and 0.01 m KCl (complete salts), they maintained their normal morphology. When washed with a solution of 0.05 m MgSO4, they became plasmolyzed as indicated by both phase and electron microscopy. Suspensions of cells washed with 0.05 m MgSO4 showed an increase in optical density (OD) when 0.3 m NaCl was added, and this was followed by a decrease in OD upon the further addition of 0.01 m KCl. Salts of other monovalent cations were not effective in replacing K+ in producing the OD decrease. Phase-contrast microscopy revealed that the increase in OD was accompanied by a decrease in cell size, and the decrease in OD, by an increase in the cell size. Both phase and electron microscopy showed that the K+-dependent decrease in OD was accompanied by deplasmolysis of the cells. Na+ was required in the suspending medium in addition to K+ to obtain deplasmolysis. The intracellular K+ concentration in cells which had been washed with complete salts and which had retained their normal morphology was found to be 0.290 m. In cells plasmolyzed by washing with 0.05 m MgSO4, the intracellular K+ concentration was 0.004 m. Deplasmolyzed cells contained 0.330 m K+. The membrane profile of plasmolyzed cells was retained when protoplasts were formed. The protoplasts became spherical if incubated in a solution permitting the deplasmolysis of the parent cells. The evidence obtained indicates that plasmolysis and deplasmolysis under the conditions described was due to the loss and gain, respectively, of K+ by the cells. The effect of Na+ could be ascribed to its capacity to control the porosity of the cytoplasmic membrane of this organism.

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