Generation of a Membrane Potential by Electron Transport in Plasmalemma-Enriched Vesicles of Cotton and Radish

Plasmalemma-enriched vesicles were isolated from cotton roots (Gossypium hirsutum L. cv Acala San Jose 2) and from germinating radish seeds (Raphanus sativa L. cv Tondo Rosso Quarantino). When 100 millimolar ascorbate was added to the grinding medium, the addition of ferricyanide to either preparation led to an inside positive membrane potential as measured by the accumulation of thiocyanate. It is suggested that electrons from ascorbate were being transported electrogenically across the membrane to ferricyanide, resulting in an accumulation of protons within the vesicle. The redox activity of the vesicles has some similarities to that occurring in intact cells, thus providing a simpler system to study the components and effects of transmembrane electron transport.