Net efflux of Cl− during hypotonic turgor regulation in a brackish water alga Lamprothamnium*

Abstract

Abstract. Net efflux of Cl− was measured potentiometrically (Ag/AgCl electrode) during turgor regulation which was induced by hypotonic treatment (hypotonic turgor regulation) in the alga Lamprothamnium succinctum. The efflux of Cl− reached the peak value (11 μmol m −2s−1) several minutes after the hypotonic treatment was started and then declined. The efflux of Cl− and inhibition of the cytoplasmic streaming [reflection of an increase in cytoplasmic concentration of free Ca2+([Ca2+]c)] were blocked under a low external concentration of Ca2+ ([Ca2+]e) (0·01 mol m−3) and resumed after raising [Ca2+]e to the normal value (3·9 mol m−3). The decrease in cell‐osmotic pressure upon hypotonic treatment was inhibited by lowering either turgor pressure or [Ca2h]e. The inhibition was reflected in decreases of both the efflux of Cl− and the membrane conductance. Recovery of the cytoplasmic streaming from the inhibition was also accelerated by the same treatments. It is concluded that an increase in turgor pressure is continuously sensed by the cells and that continuous presence of external Ca2+ is necessary for the hypotonic turgor regulation.