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.
Similar content being viewed by others
References
Geiger, D.R.: Phloem loading. In: Encyclopedia of plant physiology, vol. 1 Zimmermann, M.H. Milburn, J.A. eds., pp. 395–431. Berlin-Heidelberg-New York: Springer 1975
Gilder, J., Cronshaw, J.: The distribution of adenosine triphosphatase activity in differentiating and mature phloem cells of Nicotiana tabacum and its relationship to phloem transport. J. Ultrastruct. Res. 44, 388–404 (1973)
Hall, S.M., Baker, D.A.: The chemical composition of Ricinus phloem exudate. Planta (Berl.) 106, 131–140 (1972)
Heinz, E.: Na+-linked transport of organic solutes. Berlin-Heidelberg-New York: Springer 1972
Komor, E.: Proton-coupled hexose transport in Chlorella vulgaris. F.E.B.S. Letters 38, 16–18 (1973)
West, I.C.: Lactose transport coupled to proton movements in Escherichia coli. Biochem. Biophys. Res. Commun. 41, 655–661 (1970)
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Malek, F., Baker, D.A. Proton co-transport of sugars in phloem loading. Planta 135, 297–299 (1977). https://doi.org/10.1007/BF00384903
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00384903