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Plant and Soil

, Volume 334, Issue 1–2, pp 277–288 | Cite as

Evaluating mechanisms for plant-ion (Ca2+, Cu2+, Cd2+ or Ni2+) interactions and their effectiveness on rhizotoxicity

  • Peng Wang
  • Dong-Mei Zhou
  • Willie J. G. M. Peijnenburg
  • Lian-Zhen Li
  • Nanyan Weng
Regular Article

Abstract

Electrical properties of plant cell membranes (CMs) provide a new avenue for exploring the mechanisms of plant-ion interactions and the biotic effects of ions. The modulating effect of Ca2+ on rhizotoxicity of metallic ions was studied to evaluate the mechanisms of plant-ion interaction in terms of the electrical potential at the CM exterior surface CMSe 0 o ). Adding Ca2+ to root bathing media (BM) reduced the negativity of ψ 0 o at the CMSe. This reduction caused decreases in the activities of toxic metal ions at the CMSe and hence alleviated the toxicity (denoted as Mechanism I). Calcium is an essential element for growth and adding Ca2+ could also restore metal-displaced Ca2+ at the CMSe and alleviated Ca2+ deficiency (Mechanism II). The reduced surface negativity increased the surface-to-surface transmembrane potential difference (E m,surf), thus increasing the electrical driving force for transport of toxic metallic ions across the CM (Mechanism III). The Mechanism III would increase toxicity, but did not offset the alleviation by Mechanisms I and II. Regression analysis of relative root elongation in appropriate nonlinear equations incorporating the effects of above mechanisms provided evidence that under the current experimental conditions, Mechanism I is the most important mechanism for plant-ion interactions. In addition, the intracellular concentration of metals in root was a better predictor of toxicity than the free metal ion activity in the BM and could be predicted with an electrostatic uptake model developed previously. Based on the intracellular concentration and the EUM, the toxicity threshold (EC50, activities producing 50% growth inhibition) could be predicted generally within a factor of 2 of the observed values, indicting its potential utility in risk assessment of toxic metals.

Keywords

Metal toxicology Mechanism Cell membrane surface electrical potential Electrostatic uptake model 

Abbreviations

CMSe

cell membrane exterior surface

BM

bathing medium

EUM

electrostatic uptake model

BLM

biotic ligand model

G-C-S model

Gouy-Chapman-Stern model

RRL

relative root length

T

toxicant intensity

ψ0o

cell membrane surface electrical potential

Em,surf

the electrical potential difference from membrane surface to membrane surface

Em

transmembrane electrical potential difference between the cell interior and bathing medium

σ0

membrane surface charge densities

{IZ}b

the activity of ion I Z in the bathing medium

{IZ}0o

the activity of ion I Z at the cell membrane exterior surface

Notes

Acknowledgments

The authors are grateful for the help and discussion from Dr. Thomas Kinraide (U.S. Department of Agriculture). This work was supported financially by the National Natural Science Foundation (Grant No. 40871115; 40930739), the Natural Science Foundation of Jiangsu Province (Grant No. BK 2009339) and the Graduate Innovative Program of Graduate School of Chinese Academy of Sciences.

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Copyright information

© Springer Science+Business Media B.V. 2010

Authors and Affiliations

  • Peng Wang
    • 1
    • 4
  • Dong-Mei Zhou
    • 1
  • Willie J. G. M. Peijnenburg
    • 2
    • 3
  • Lian-Zhen Li
    • 1
    • 4
  • Nanyan Weng
    • 1
    • 4
  1. 1.State Key Laboratory of Soil and Sustainable AgricultureInstitute of Soil Science, Chinese Academy of SciencesNanjingChina
  2. 2.Institute of Environmental Science (CML)Leiden UniversityLeidenThe Netherlands
  3. 3.RIVM-Laboratory for Ecological Risk AssessmentNational Institute of Public Health and the EnvironmentBilthovenThe Netherlands
  4. 4.Graduate School of Chinese Academy of SciencesBeijingChina

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