Development, Characterization, and Application of a
Cadmium-Selective Microelectrode for the Measurement of Cadmium Fluxes
in Roots of Thlaspi Species and
Wheat1
Miguel A. Piñeros,
Jon E. Shaff, and
Leon V. Kochian*
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
Copyright Clearance Center: 0032-0889/98/116/1393/09
© 1998 American Society of Plant Physiologists
