Light induced polarity of redox reactions in leaves of Elodea canadensis Michx

This paper reports that extracellular reductase activity in leaves of Elodea canadensis, hitherto never associated with polar processes thought to be involved in bicarbonate utilization, also shows a very marked polarity in light. The effect of ferricyanide, applied to the lower side of illuminated leaves, was a depolarization of the membrane electrical potential of up to 110 millivolts, while no depolarization was induced when ferricyanide was applied to the upper side. In the dark ferricyanide induced a depolarization when applied to either the upper or to the lower side of the leaf. Staining with tetrazolium salts, specific indicators for reductase activity, resulted in the formation of a precipitate on the lower side of the leaf when illuminated and on both sides in the dark. The precipitate was only located along the plasmalemma.