Sorption of Copper and Zinc to the Plasma Membrane of Wheat Root

• Published in: The Journal of membrane biology 2004-11, Vol.202 (2), p.97-104
• Main Authors: Vulkan, R, Yermiyahu, U, Mingelgrin, U, Rytwo, G, Kinraide, T.B
• Format: Article
• Language: English
• Subjects: Cations - metabolism; Cations - pharmacology; Cell Membrane - metabolism; Competitive Bidding; copper; Copper - pharmacokinetics; Malates - metabolism; metal ions; nutrient uptake; Plant Roots - metabolism; plasma membrane; root systems; Triticum - metabolism; Triticum aestivum; wheat; zinc; Zinc - pharmacokinetics
• ISSN: 1432-1424; 0022-2631; 1432-1424
• DOI: 10.1007/s00232-004-0722-7

Sorption of Cu2+ and Zn2+ to the plasma membrane (PM) of wheat root (Triticum aestivum Lcv. 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 Zn2+ and 400 M-1 for Cu2+. Thus, the sorption affinity of Cu2+ to the PM is considerably larger than that of Ca2+, Mg2+ or Zn2+. The greater binding affinity of Cu2+ was confirmed by experiments in which competition with La3+ for sorption sites was followed. The amount of sorbed Cu2+ decreased with increasing K+, Ca2+, or La3+ concentrations, suggesting that all these cations competed with Cu2+ for sorption at the PM binding sites, albeit with considerable differences among these cations in effectiveness as competitors with Cu2+. The sorption of Cu2+ and Zn2+ to the PM decreased in the presence of citric acid or malic acid. Citric acid (as well as pH) affected the sorption of Cu2+ or Zn2+ to PM more strongly then did malic acid.