Depolarization of Cell Membrane Potential during Trans-Plasma Membrane Electron Transfer to Extracellular Electron Acceptors in Iron-Deficient Roots of Phaseolus vulgaris L.

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Abstract
Transfer of electrons from the cytosol of bean (P. vulgaris L.) root cells to extracellular acceptors such as ferricyanide and Fe(III) EDTA causes a rapid depolarization of the membrane potential. This effect is most pronounced (30-40 mV) with root cells of Fe-deficient plants, which have an increased capacity to reduce extracellular ferric salts. Ferrocyanide has no effect. In the state of ferricyanide reduction, H+ (1H+/2 electrons) and K+ ions are excreted. The reduction of extracellular ferric salts by roots of Fe-deficient bean plants is driven by cellular NADPH (Sijmons et al, 1984). From this and from the membrane potential depolarization, trans-plasma membrane electron transfer from NADPH apparently is the primary process in the reduction of extracellular ferric salts.