Turgor‐ dependent membrane permeability in relation to calcium level

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Abstract
The relationship between the inhibiting effect of Ca2+ and of low turgor pressure on K+ release from fresh‐cut discs of carrot (Daucus carota var. Nantes) storage tissue was studied. A range of Ca2+ concentrations in the tissue was obtained by adding 0.5 mM EDTA or CaSO4 at different concentrations to the medium. Calcium inhibited K+ release in fully turgid cells (2.5 μmol K+ g−1 h−1 in 0.5 mM EDTA vs 0.4 μmol K+ g−1 h−1 in 10 mM CaSO4). Less turgid cells, obtained by equilibration with 0.2 M mannitol, released K+ at only 30% of the rate of the turgid cells, yet the pattern of K+ release as a function of Ca2+ level was similar in both turgid and non‐turgid cells. Removal of calcium by EDTA occasionally injured cell membranes in the fully turgid discs but never in the less turgid ones. In view of the additive effect of Ca2+ and low turgor on K+ release regardless of the treatment order, it is suggested that the two factors exert their effect on membrane permeability independently of each other.