A more complete study of ionic concentrations and fluxes in the giant internodal cells of Nitella translucens has been made. The vacuolar concentrations were 76 mM K and 170 mM Cl. The content of the chloroplast layer was 135 mµmoles K/cm2 and 215 mµmoles Cl/cm2; in a layer 9 µ thick these correspond to concentrations of 150 mM K and 240 mM Cl. Such a high level of chloride requires active transport of chloride into the cytoplasm, either at the plasmalemma or at the membranes bounding the cytoplasmic particles; it cannot be achieved by active transport of chloride only at the tonoplast. With concentrations of 0.1 mM K and 1.3 mM Cl outside, the fluxes into the cytoplasm had mean values of 1.0 to 1.4 µµmoles K/cm2sec. and 2.1 to 2.8 µµmoles Cl/cm2sec.; the corresponding fluxes from the cytoplasm to the vacuole were about 110 µµmoles K/cm2sec. and 175 µµmoles Clcm2sec. The transfer of both potassium and chloride to the vacuole under different conditions appeared to be correlated with the uptake of chloride into the cytoplasm. It is suggested that two separate processes are involved in the active accumulation of salts in the vacuole—an active uptake of chloride in the cytoplasm and a subsequent transfer of salt to the vacuole. It may be that the second process involves the formation of small vesicles in the cytoplasm and their subsequent discharge into the central vacuole.

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