Calcium and magnesium enhance arsenate rhizotoxicity and uptake in Triticum aestivum

Authors

  • Peng Wang,

    1. Key Laboratory of Soil Environment & Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, China
    2. Graduate School of Chinese Academy of Sciences, Beijing, China
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  • Dongmei Zhou,

    Corresponding author
    1. Key Laboratory of Soil Environment & Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, China
    • Key Laboratory of Soil Environment & Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, China.
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  • Nanyan Weng,

    1. Key Laboratory of Soil Environment & Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, China
    2. Graduate School of Chinese Academy of Sciences, Beijing, China
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  • Dengjun Wang,

    1. Key Laboratory of Soil Environment & Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, China
    2. Graduate School of Chinese Academy of Sciences, Beijing, China
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  • Willie J.G.M. Peijnenburg

    1. National Institute of Public Health and the Environment, Laboratory for Ecological Risk Assessment, Bilthoven, The Netherlands
    2. Leiden University, Leiden, The Netherlands
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Abstract

Cations such as calcium (Ca) and magnesium (Mg) alleviate toxicities of cationic toxicants and increase those of anionic toxicants such as arsenic (As) present as arsenate under aerobic conditions. Increasing evidence exists that these phenomena are related to the outer surface electrical potential (ψmath image) of the root cell plasma membrane (PM). Short-term (48-h) nutrient culture experiments with wheat (Triticum aestivum L.) seedlings investigated Ca and Mg effects on arsenate rhizotoxicity and uptake. Increased Ca and Mg in solution from 0.2 to 3.5 mM equally reduced the negativity of ψmath image from −45 to −15 mV. This increased arsenate activity at the PM surface from 0.3 to 0.9 µM at the same bulk concentration of 2.0 µM NaH2AsO4 consequently increased arsenate uptake and rhizotoxicity. However, increased Mg was more effective than Ca in enhancing As uptake by roots, especially with the activity of As in the range of 0.5 to 1.5 µM in the bulk medium. This was explained by a modified electrostatic uptake model which indicated a mechanism other than through an effect on ψmath image. Subcellular fractionation of roots indicated that > 95% of As was associated with cellular debris and heat-stable protein (HSP). The results of the present study show that Ca and Mg reduce the negativity of ψmath image, increasing arsenate uptake and rhizotoxicity, and suggest that Mg is more efficient than Ca in enhancing the uptake of As due, in large part, to inducing greater As binding by peptides in the HSP fraction. Environ. Toxicol. Chem. 2011; 30:1642–1648. © 2011 SETAC

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