Plant and Soil

, Volume 316, Issue 1, pp 177–192

Effects of Zn-complexes on zinc uptake by wheat (Triticum aestivum) roots: a comprehensive consideration of physical, chemical and biological processes on biouptake

Regular Article

DOI: 10.1007/s11104-008-9769-z

Cite this article as:
Wang, P., Zhou, D.M., Luo, X.S. et al. Plant Soil (2009) 316: 177. doi:10.1007/s11104-008-9769-z


Commonly used equilibrium models for metal biouptake, such as the Free Ion Activity Model (FIAM) and the Biotic Ligand Model (BLM), are limited to the cases in which mass diffusive transport is not the flux-determining step. In analyses of metal biouptake from a complexing medium, all the physical (diffusion), chemical (dissociation kinetics of metal complexes), and biological (transport and internalization) processes have to be taken into account. A short-term zinc uptake by wheat (Triticum aestivum) roots from culture solutions in the absence or presence of synthetic ligands (NTA, nitrilotriacetic acid, and EDTA, ethylenediaminetetraacetate) was studied. At the same free Zn2+ concentration \(\left( {\left\{ {{\text{Zn}}^{{\text{2 + }}} } \right\} = 1.5 \times 10^{ - 8} {\text{M}}} \right)\) , the uptake of Zn was significantly enhanced in the presence of ligands and was larger when Zn complexes have a quicker dissociation rate. The diffusional fluxes in the same culture solution were determined with the differential pulse anodic stripping voltammetry (DPASV) method, and the diffusive gels in thin film (DGT) technique. The contribution from Zn complexes to root Zn uptake was in better agreement with the degree of Zn complex labilities measured with DPASV than with DGT. The diffusion of free Zn2+ ion to the root surface is a rate-controlling step for Zinc biouptake when the free Zn2+ concentration is low. Based on the comprehensive consideration of the diffusion and dissociation processes of Zn2+ ion and Zn complexes and the existence of high- and low-affinity uptake systems in the root surface, a two-pathway Zn uptake model was developed to predict the resulting Zn uptake fluxes into roots in the overall range of exposure.


Biotic ligand modelDiffusive gels in thin film (DGT)DiffusionDissociationDifferential pulse anodic stripping voltammetry (DPASV)BioavailabilityMetal complex



free ion activity model


biotic ligand model


differential pulse anodic stripping voltammetry


diffusive gels in thin film


singular pathway uptake Best equation model


two-pathway uptake Best equation model


root fresh weight


the characteristic bioaffinity parameter of roots

\(J_{u,i}^* \)

limiting uptake flux of roots

\(c_M^0 \) and \(c_M^* \)

the concentration of the species M at the biosurface and in the bulk solution, respectively


the degree of metal complex lability

ka and kd

the association and dissociation rate, respectively


the conditional stability constant of complexation equilibrium

DM and DML

the diffusion coefficients of the free metal M and complex ML, respectively


the steady-state diffusion layer thickness


the reaction layer thickness

Copyright information

© Springer Science+Business Media B.V. 2008

Authors and Affiliations

  • P. Wang
    • 1
    • 2
  • D. M. Zhou
    • 1
  • X. S. Luo
    • 1
    • 2
  • L. Z. Li
    • 1
    • 2
  1. 1.State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil ScienceChinese Academy of SciencesNanjingChina
  2. 2.Graduate School of Chinese Academy of SciencesBeijingChina