Potassium ion uptake by swelling Commelina communis guard cell protoplasts

Commelina communis L. guard cell protoplasts were induced to swell under low CO 2 conditions in the light while incubated in media containing KCl. Precise measurements of changes in the volume of the protoplasts were made including estimates of protoplast non‐osmotic volume by Boyle‐van't Hoff analysis. The amount of K + which accumulated during the treatment was measured. The observed changes in osmotic volume could be accounted for by the uptake of K + which appeared to be balanced by an anion or anions with an effective mean charge of – 1.63. The K + flux rates occurring in guard cell protoplasts were sufficient to explain guard cell turgor regulation in vivo.