Changes in potassium fluxes in cells of carrot storage tissue related to turgor pressure

The effect of increasing external osmotic pressure on potassium fluxes in aged and fresh‐cut discs of Daucus carota L. storage tissue was investigated. An increase of the external osmotic pressure by 5 bars of mannitol solution increased the rate of K+ net uptake of aged discs to 180% of their control rate. At 3°C and in 0.1 mM azide, in which a net efflux of potassium was observed, the mannitol treatment caused a reduction in the net efflux. In fresh‐cut discs, in which the capability of net influx was rather low and a substantial net release of potassium was noted, the increase in the external osmotic pressure by mannitol caused a 70% inhibition in the net efflux. This effect was also observed at 3°C. Measurements of separate fluxes confirmed the assumption that the mannitol treatment brought about two distinct effects on K+ fluxes: (a) raised the metabolically‐dependent influx and (b) lowered the membrane permeability‐dependent efflux. When a permeating solute (ethylene glycol) was used instead of mannitol, no effect on K+ flux was detectable. Reasons are given for relating the observed changes in K+ fluxes to the reduction in turgor pressure of the cells.