DEVELOPMENT, CHARACTERIZATION, AND APPLICATION OF A CADMIUM-SELECTIVEMICROELECTRODE FOR THE MEASUREMENT OF CADMIUM FLUXES IN ROOTS OF THLASPI SPECIES AND WHEAT

A Cd2+-selective vibrating microelectrode was constructed using a neut ral carrier-based Cd ionophore to investigate ion-transport processes along the roots of wheat (Triticum aestivum L.) and two species of Thl aspi, one a Zn/Cd hyperaccumulator and the other a related nonaccumula tor. In simple Cd(NO3)(2) solutions, the electrode exhibited a Nernsti an response in solutions with Cd2+ activities as low as 50 nM. Additio n of Ca2+ to the calibration solutions did not influence the slope of the calibration curve but reduced the detection limit to a solution ac tivity of 1 mu M Cd2+. Addition of high concentrations of K+ and Mg2to the calibration solution to mimic the ionic composition of the cyto plasm affected neither the slope nor the sensitivity of the electrode, demonstrating the pH-insensitive electrode's potential for intracellu lar investigations. The electrode was assayed for selectivity and was shown to be at least 1000 times more selective for Cd2+ than for any o f those potentially interfering ions tested. Flux measurements along t he roots of the two Thlaspi species showed no differences in the patte rn or the magnitude of Cd2+ uptake within the time frame considered. T he Cd2+-selective microelectrode will permit detailed investigations o f heavy-metal ion transport in plant roots, especially in the area of phytoremediation.