Ionic relations of marine algae

Measurements were made of ionic fluxes in cells of the marine algae G. monile and G. pulvinata. The data for sodium and chloride fluxes appear to be consistent with the usually proposed model for the plant cell in which the vacuolar, cytoplasmic, and external compartments are in series, with the cytoplasm bounded on the inside by the tonoplast and on the outside by the plasmalemma. However, there are difficulties in explaining the results for potassium fluxes on this model. At the plasmalemma, the passive fluxes of potassium, sodium, and chloride were 50-380, 15, and 5 p.moles cm-2 sec-I respectively. There was also an active chloride influx of 0-35 p·moles cm-2 sec-I and an active sodium efflux of about 15 p.moles cm-2 sec-I. The fluxes at the tonoplast, on the basis of the compartments-in-series model, were potassium 300-1000, sodium 10 p-moles cm-2 sec-I, and chloride at least 30 p-moles cm-2 sec-I. Electrochemical data (Findlay, Hope, and Williams 1969) indicate that there is an active flux of potassium across the tonoplast from the cytoplasm into the vacuole. The large fluxes of potassium and chloride at the tonoplast are difficult to reconcile with the electrical resistance of 5000 Qcm2, which suggests that a large part of the tonoplast potassium flux is exchange diffusion, or that vesicular movement of potassium and chloride ion pairs occurs. The influxes ofK+, Rb+, Cs+, and Na+ ions at the plasmalemma were measured and the following order of permeability obtained: P K > P Rb > PCs > P Na? This order agrees with that obtained from measurements of depolarization of the plasmalemma potential.