The effect of xanthoxylin (2-oxy 4,6- dimethoxyacetophenone) on potassium dependent acid extrusion in wheat and maize root segments.

Abstract. Xanthoxylin is a cytotoxic and fungicidal compound with the characteristics of a typical phytoalexin. At a concentration of 0.3 mol m-3 it inhibits K+-dependent acid extrusion and K+ net uptake (or uptake of equivalent alkaline cations such as Rb+ and CS+) by up to about 80% and hyperpolarizes by about 20% the membrane electrical potential. Its inhibition of the acid extrusion does not depend on altered ion exchange involving the anions in the media, a reduction of the metabolic energy available, or detectable changes in the permeability of the cell membrane to H+ ions. The drop in K+ net uptake depends on a decrease in the influx of K+ into the cell. In functional terms, xanthoxylin is an inhibitor of the K+ permeation mechanism and does not appear to interact with the mechanisms creating the electrochemical energy gradient.