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Surface Electrical Potentials of Root Cell Plasma Membranes: Implications for Ion Interactions, Rhizotoxicity, and Uptake

1
Key Laboratory of Soil Environment & Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China
2
University of Chinese Academy of Sciences, Beijing 100049, China
3
Agricultural Research Service, United States Department of Agriculture, Collaborating Scientist, Plant Science Research Unit, Raleigh, NC 27695, USA
4
The University of Queensland, School of Agriculture and Food Sciences, St. Lucia, Queensland 4072, Australia
*
Author to whom correspondence should be addressed.
Int. J. Mol. Sci. 2014, 15(12), 22661-22677; https://doi.org/10.3390/ijms151222661
Received: 14 September 2014 / Revised: 28 November 2014 / Accepted: 1 December 2014 / Published: 8 December 2014
(This article belongs to the Section Biochemistry)
Many crop plants are exposed to heavy metals and other metals that may intoxicate the crop plants themselves or consumers of the plants. The rhizotoxicity of heavy metals is influenced strongly by the root cell plasma membrane (PM) surface’s electrical potential (ψ0). The usually negative ψ0 is created by negatively charged constituents of the PM. Cations in the rooting medium are attracted to the PM surface and anions are repelled. Addition of ameliorating cations (e.g., Ca2+ and Mg2+) to the rooting medium reduces the effectiveness of cationic toxicants (e.g., Cu2+ and Pb2+) and increases the effectiveness of anionic toxicants (e.g., SeO42− and H2AsO4). Root growth responses to ions are better correlated with ion activities at PM surfaces ({IZ}0) than with activities in the bulk-phase medium ({IZ}b) (IZ denotes an ion with charge Z). Therefore, electrostatic effects play a role in heavy metal toxicity that may exceed the role of site-specific competition between toxicants and ameliorants. Furthermore, ψ0 controls the transport of ions across the PM by influencing both {IZ}0 and the electrical potential difference across the PM from the outer surface to the inner surface (Em,surf). Em,surf is a component of the driving force for ion fluxes across the PM and controls ion-channel voltage gating. Incorporation of {IZ}0 and Em,surf into quantitative models for root metal toxicity and uptake improves risk assessments of toxic metals in the environment. These risk assessments will improve further with future research on the application of electrostatic theory to heavy metal phytotoxicity in natural soils and aquatic environments. View Full-Text
Keywords: plasma membrane; surface electrical potential; heavy metal; rhizotoxicity; metal uptake; risk assessment plasma membrane; surface electrical potential; heavy metal; rhizotoxicity; metal uptake; risk assessment
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Wang, Y.-M.; Kinraide, T.B.; Wang, P.; Hao, X.-Z.; Zhou, D.-M. Surface Electrical Potentials of Root Cell Plasma Membranes: Implications for Ion Interactions, Rhizotoxicity, and Uptake. Int. J. Mol. Sci. 2014, 15, 22661-22677.

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