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

Abstract

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.

Keywords

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

Abbreviations

FIAM

free ion activity model

BLM

biotic ligand model

DPASV

differential pulse anodic stripping voltammetry

DGT

diffusive gels in thin film

SPUB-Model

singular pathway uptake Best equation model

TPUB-Model

two-pathway uptake Best equation model

RFW

root fresh weight

KM,i

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

ξ

the degree of metal complex lability

ka and kd

the association and dissociation rate, respectively

K

the conditional stability constant of complexation equilibrium

DM and DML

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

δM

the steady-state diffusion layer thickness

µ

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