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The effects of 2 x 10−3 M ABA on ion fluxes in isolated guard cells of Commelina communis L. have been studied, using 86RbCl and K82Br, in epidermal strips in which all cells other than guard cells have been killed by treatment at low pH. The effect of ABA on influx is small, if present, and the major effect is a marked transient stimulation of the efflux of both 86Rb and 82Br at the plasmalemma; there is also an increase in the flux of 82Br from vacuole to cytoplasm. The stimulation is transient, and the cells do not simply become more leaky. The results are not consistent with previous speculations on the mechanism by which ABA reduces aperture.
E. A. C. MACROBBIE (Thu,) studied this question.