| Abstract: | The contribution of K+ accumulation to cell turgor pressurewas investigated in the gas-vacuolate blue-green alga Anabaenaflos-aquae. The cell turgor pressure, measured by the gas vesiclemethod, drops in cells suspended in culture medium depletedof K+ but rapidly rises again, by 100 kPa or more, when K+ isresupplied. A similar though rather slower rise in turgor pressureis supported by an equivalent concentration of Rb+. The internalK+ concentration rose from 66 to 91 mM when K+ was suppliedat an external concentration of 0.4 mM. This rise was light-dependent.Greater increases in internal K+ concentration and turgor pressureoccurred when K+ was supplied at a higher concentration, 3.6mM. In both cases over 60% of the observed turgor pressure risecould be accounted for by accumulation of K+. The turgor pressurerise supported by light-stimulated K+ uptake can cause collapseof enough of the alga's gas vesicles to destroy its buoyancy.The effect of K+ availability on buoyancy regulation by planktonicblue-green algae is discussed. |
