Typical changes in proton and potassium fluxes from S. peruvianum leaf tissue induced by 100 nm systemin. A, pH of the unstirred layer and proton flux. B, K⁺ concentration of the unstirred layer and K⁺ flux. Continuous lines, pH or K⁺ concentration at 10 and 50 μm from the cell wall (left y axis). Dotted lines, Calculated H⁺ or K⁺ flux based on the pH at 10 and 50 μm (right y axis). A vertical line indicates the moment of the addition of 100 nm systemin. When the flux becomes more positive, this means either an increase of the influx or a reduction of the efflux. Typical experiments of at least three experiments are shown. The insert in A shows a magnification of the pH trace between 40 and 55 min and between pH values 7.20 and 7.35, which shows the saw-tooth-like trace due to the movement of the electrode through the pH gradient in the unstirred layer.