title: Sorption of copper and zinc to the plasma membrane of wheat root.
abstract: Sorption of Cu(2+) and Zn(2+) to the plasma membrane (PM) of wheat root (Triticum aestivum L cv. Scout 66) vesicles was measured at different pH values and in the presence of organic acids and other metals. The results were analyzed using a Gouy-Chapman-Stem model for competitive sorption (binding and electrostatic attraction) to a negative binding site. The binding constants for the two investigated cations as evaluated from the sorption experiments were 5 M(-1) for Zn(2+) and 400 M(-1) for Cu(2+). Thus, the sorption affinity of Cu(2+) to the PM is considerably larger than that of Ca(2+), Mg(2+) or Zn(2+). The greater binding affinity of Cu(2+) was confirmed by experiments in which competition with La(3+) for sorption sites was followed. The amount of sorbed Cu(2+) decreased with increasing K(+), Ca(2+), or La(3+) concentrations, suggesting that all these cations competed with Cu(2+) for sorption at the PM binding sites, albeit with considerable differences among these cations in effectiveness as competitors with Cu(2+). The sorption of Cu(2+) and Zn(2+) to the PM decreased in the presence of citric acid or malic acid. Citric acid (as well as pH) affected the sorption of Cu(2+) or Zn(2+) to PM more strongly then did malic acid.
authors.affiliation: Agricultural Research Organization, Gilat Research Center, D.N. Negev 2 85280, Israel. uri4@volcani.agri.gov.il
authors.forename: R
authors.initials: R
authors.lastname: Vulkan
authors.forename: U
authors.initials: U
authors.lastname: Yermiyahu
authors.forename: U
authors.initials: U
authors.lastname: Mingelgrin
authors.forename: G
authors.initials: G
authors.lastname: Rytwo
authors.forename: T B
authors.initials: TB
authors.lastname: Kinraide
mesh_terms: D002412:Cations / Q000378:metabolism / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism*; D003164:Competitive Bidding; D003300:Copper / Q000493:pharmacokinetics*; D008293:Malates / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism*; D014908:Triticum / Q000378:metabolism*; D015032:Zinc / Q000493:pharmacokinetics*
chemical_list: D002412:Cations; D008293:Malates; D003300:Copper; C030298:malic acid; D015032:Zinc