Determining the fluxes of ions (Pb2+, Cu2+ and Cd2+) at the root surface of wetland plants using the scanning ion-selective electrode technique
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Background and aims
Measuring specific ion fluxes from different regions of the root under practical physiological conditions is crucial for understanding metal uptake mechanisms by plants.
We developed and tested a neutral carrier-based liquid-membrane Pb2+ and Cu2+ ion selective microelectrode (ISME) to investigate ion-transport processes along the roots of three common wetland plant species.
The Pb2+ and Cu2+ ISME exhibited a Nernstian response with Pb2+ and Cu2+ activities as low as 1.0 nM and 1.0 μM in deionized water and simulated soil solution, respectively. Phragmites australis had a region of Cu2+ release for approximately the first 200 μm, while it exhibited Pb2+ and Cd2+ outward net flux up to the first 500 μm. Although in older sections of the root of Phragmites australis there were areas of influx of Cu2+, Pb2+ and Cd2+, the overall influx was much smaller than that of Typha latifolia or Canna indica. Such a reduced uptake and/or an increased efflux of metal ions across the root-cell plasma-membrane might explain the higher resistance of Phragmites australis to metals, at least in part.
The Pb2+ and Cu2+ ISMEs are shown to permit detailed investigation of heavy-metal ion transport in plant roots, especially for plants used for phytoremediation.
KeywordsCadmium Wetland plants Ion selective microelectrode Scanning ion-selective electrode technique Metal uptake
This study is supported by the National Natural Science Foundation (No. Y311111031 and 41230858), a grant from the National High Technology Research and Development Program of China (863 Program) (2012AA06A204-4) and the Scientific Research Equipments Development Program of CAS (YZ201558). This is also supported by the project of “Research on Migration/Transformation and Safety Threshold of Heavy Metals in Farmland Systems” (2016YFD0800405), National Key Research and Development Program of China. We want to thank Dr. Ian Newman and Dr. Sergey Shabala from University of Tasmania, Australia and Prof. Peter J S Smith from University of Southampton, UK for their valuable comments in the improvement of the manuscript. The authors also thank Prof. Michael O’Donnell from McMaster University for his constructive comments on an earlier version of the manuscript.
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