Sucrose and proton cotransport in Ricinus cotyledons

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Abstract
In Ricinus cotyledons, evidence for proton extrusion came from observation of direct acidification of the medium in the presence of potassium salts. Increasing K+ influx with increasing pH suggested a link between K+ influx and H+ efflux by an H+ pump. The kinetics of K+ influx and H+ efflux were consistent with a 1:1 stoichiometry K+:H+, which may indicate either electrical coupling or carrier mediated exchange. The results were consistent with an H+ pump setting up an electrochemical potential gradient which provides the driving force for an H+-sucrose cotransport and the movement of K+. With reference to this, a model for phloem loading is suggested.