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Development, Characterization, and Application of a Cadmium-Selective Microelectrode for the Measurement of Cadmium Fluxes in Roots of Thlaspi Species and Wheat1
United States Plant, Soil, and Nutrition Laboratory, United States Department of Agriculture-Agricultural Research Service, Cornell University, Ithaca, New York 14853 A Cd2+-selective vibrating microelectrode was constructed using a neutral carrier-based Cd ionophore to investigate ion-transport processes along the roots of wheat (Triticum aestivum L.) and two species of Thlaspi, one a Zn/Cd hyperaccumulator and the other a related nonaccumulator. In simple Cd(NO3)2 solutions, the electrode exhibited a Nernstian response in solutions with Cd2+ activities as low as 50 nm. Addition of Ca2+ to the calibration solutions did not influence the slope of the calibration curve but reduced the detection limit to a solution activity of 1 µm Cd2+. Addition of high concentrations of K+ and Mg2+ to the calibration solution to mimic the ionic composition of the cytoplasm affected neither the slope nor the sensitivity of the electrode, demonstrating the pH-insensitive electrode's potential for intracellular investigations. The electrode was assayed for selectivity and was shown to be at least 1000 times more selective for Cd2+ than for any of those potentially interfering ions tested. Flux measurements along the roots of the two Thlaspi species showed no differences in the pattern or the magnitude of Cd2+ uptake within the time frame considered. The Cd2+-selective microelectrode will permit detailed investigations of heavy-metal ion transport in plant roots, especially in the area of phytoremediation. 1 This work was supported by a grant from the U.S. Department of Energy-Division of Energy Biosciences (interagency agreement DE-A I02-95ER 21097). * Corresponding author; e-mail lvk1{at}cornell.edu; fax 1-607-255-2459.
Plant Physiol. (1998) 116: 1393-1401
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