Factors Affecting the Fluxes of Potassium and Chloride Ions in WiteUa translucens

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 C1. The content of the chloroplast layer was 135 m#moles K/cm 2 and 215 m/~moles C1/cm2; in a layer 9 # thick these correspond to concentrations of 150 mM K and 240 rn~ C1. 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 C1 outside, the fluxes into the cytoplasm had mean values of 1.0 to 1.4 ##moles K/cm~sec. and 2.1 to 2.8 #/~moles C1/cm2sec.; the corresponding fluxes from the cytoplasm to the vacuole were about 110 #/zmoles K/cm2sec. and 175 ##moles C1/cmSsec. 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. I t has previously been shown that the normal ionic state of the giant internodal ceils of the fresh water characean Nitella translucens is maintained by active transport of both cations and anions; the high potassium/sodium ratio is maintained by an active influx of potassium and an active efflux of sodium at the outer membrane, the plasmalemma, whereas the high total salt concentration arises by an active uptake of chloride (MacRobbie, 1962). The site of the chloride transport was not established, although it was argued that osmotic equilibrium between cytoplasm and vacuole required the chloride transport to be at the tonoplast, the inner protoplasmic membrane. This paper reports work on the chloride concentrations and fluxes in