Abstract
Loading of 14C-labelled sugars from the hollow petiole of Ricinus communis L. was stimulated by potassium and by low pH in that both the 14C-activity and the sugar concentration of phloem sap collected from a nearby incision increased. A pH drop was observed in the solution perfusing a hollow petiole. This pH drop was greater in the presence of potassium and less in the presence of sugars, while the uncoupler CCCP induced a pH rise in the perfusing solution. Sugars were detected in the perfusing solution when it was buffered at pH>9. A model is proposed for a proton co-transport of sugars from the free space driven by a linked proton efflux/potassium influx pump.
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References
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Malek, F., Baker, D.A. Proton co-transport of sugars in phloem loading. Planta 135, 297–299 (1977). https://doi.org/10.1007/BF00384903
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DOI: https://doi.org/10.1007/BF00384903