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Title: SORPTION OF COPPER AND ZINC TO THE PLASMA MEMBRANE OF WHEAT ROOT

Author
item VULCAN, R - AG RES ORG, ISRAEL
item YERMIYAHU, U - AG RES ORG, ISRAEL
item MINGELGRIN, U - AG RES ORG, ISRAEL
item RYTWO, G - TEL HAI ACAD COLLEGE, ISR
item Kinraide, Thomas

Submitted to: Journal of Membrane Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2004
Publication Date: 12/15/2004
Citation: Vulcan, R., Yermiyahu, U., Mingelgrin, U., Rytwo, G., Kinraide, T.B. 2004. Sorption of copper and zinc to the plasma membrane of wheat root. Journal of Membrane Biology, 202:97-104.

Interpretive Summary: Copper and zinc are essential trace nutrients for plants and animals, but excessive amounts are toxic to both. These elements are present in appropriate amounts in most soils, but in some cases the amounts are too small or too great, especially in polluted areas in the case of the latter. The present study is part of an ongoing effort to characterize the interaction between important elements and the cell surface. (Previous studies by our group have characterized interactions with calcium, magnesium, aluminum, sodium, hydrogen, and others.) The principal objective was to determine a coefficient for binding of the elements to the plant cell membranes. Such coefficients are needed for a comprehensive view of cell-surface electrical effects that enable an understanding of plant interactions with various elements. These interactions include plant acquisition of essential nutrients or harmful pollutants, plant intoxication by the elements, and the alleviation of intoxication by ameliorative elements.

Technical Abstract: Sorption of Cu2+ and Zn2+ 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-Stern 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.