CALCIUM-IONS STIMULATE THE ALGAL ANION REDOX PUMP BY SHIELDING NEGATIVE SURFACE-CHARGES

Calcium (and, still more, lanthanum) ions are shown to exert significa nt effect on the anion redox pump in the freshwater alga Hydrodictyon reticulatum. Both the transport of electrons by the pump to an artific ial electron acceptor in the medium and the uptake of chloride and nit rate anions are increased. The uptake of calcium ions itself does not seem to be responsible for these events which can rather be explained by a reduction or repolarisation of the outer surface potential of the plasmalemma.