Stimulation of proton extrusion by K+ and divalent cations (Ni2+, Co2+ Zn2+) in maize root segments

Entry of the divalent cations Ni2+, Co2+ and Zn2+ into cells of maize (Zea mays L. cv. Dekalb XL 85) root tissue is accompanied by an acidification of the incubation medium, a decrease in both the pH of the cell sap and the level of malate in the cells, and by an inhibition of dark fixation of CO2. K+, on the contrary, induces only a very low acidification of the incubation medium, does not change either the pH of the cell sap or the malate level in the cells, and induces an increase in CO2 dark fixation. Different mechanisms are postulated for the stimulation of proton extrusion by divalent cations and K+.