EFFECTS OF ELECTRON-ACCEPTORS ON ANION UPTAKE IN HYDRODICTYON-RETICULATUM

The artificial electron acceptors, potassium ferricyanide and tetrahia fulvalene cation radical, are shown to inhibit uptakes of chloride, ni trate and sulphate anions in the green fresh-water alga Hydrodictyon r eticulatum. The same is true about the phosphate anion in an alkaline medium, where its divalent form prevails. The unidirectional efflux of these anions was not inhibited. TTF+, the more potent of the two inhi bitors, appears to be partly located in the plasma membrane. An electr on-anion antiport (a redox pump) is suggested as the mechanism of the active uptake of most of the physiologically important anions in the a lga. Notable exceptions to this rule are represented by bicarbonate, t he carbon source for photosynthesis at air levels of CO2, and by phosp hate (probably univalent) in a medium buffered to pH 6.