Electrical Membrane Properties of Leaves, Roots, and Single Root Cap Cells of Susceptible Avena sativa

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Abstract
The effect of the purified host-selective toxin victorin C, a cyclized penta peptide, was compared to that of CCCP and vanadate on membrane functions of susceptible leaves, roots, and single root cap cells of Avena sativa with conventional electrophysiology. The plasmalemma depolarized irreversibly by about 80 millivolts and to below the diffusion potential within 1 hour. Concentrations as low as 12.5 picomolar were effective in the susceptible but not the resistant cultivar. Electrical membrane potential difference changes were independent of pH and could not be prevented by fusicoccin or Ca2+. Membranes began to depolarize after a lag phase that never was shorter than 6.5 minutes, even with concentrations as high as 1.25 micromolar. Membrane depolarization was accompanied by a distinct decrease in specific membrane resistance from 4.5 to 1.0 ohm times square meter on average. These changes were followed by K+ and Cl− efflux and extracellular alkalinization. ATP level and O2 uptake did not decrease within 2 hours. It is concluded that the victorin-induced deleterious membrane alterations are not caused by direct interaction with the plasmalemma H+-ATPase, K+ channels, lipid structure, nor energy metabolism, but they seem to be triggered by a cascade of events leading to an unspecific increase in membrane permeability.