Effects of external potassium supply on stomatal closure induced by abscisic acid

Epidermal strips of Commelina communis with ‘isolated’ stomata were incubated on Trizma‐maleate buffer containing 0‐500 mM KCL, with or without 10 −4 M ABA, for 2.5 h. The resulting stomatal apertures indicate that there is no absolute requirement for live epidermal and subsidiary cells for ABA‐mediated closure. This implies that ABA has a direct effect on influx or efflux of K + into or out of the guard cells rather than on uptake of K + by the subsidiary cells. The possible in vivo role of subsidiary cells in stomatal closure is discussed.