Potentiometric sensor for the measurement of Cd 2+ transport in yeast and plants Sonia Plaza a,1 , Zso ´ fia Szigeti b,1 , Markus Geisler a, * , Enrico Martinoia a , Beat Aeschlimann c , Detlef Gu ¨ nther c , Erno ¨ Pretsch b, * a Molecular Plant Physiology, Institute of Plant Biology, University of Zurich, CH-8006 Zurich, Switzerland b Laboratorium fu ¨ r Organische Chemie, ETH Ho ¨ nggerberg, CH-8093 Zurich, Switzerland c Laboratorium fu ¨ r Anorganische Chemie, ETH Ho ¨ nggerberg, CH-8093 Zurich, Switzerland Received 29 January 2005 Available online 11 October 2005 Abstract Research on heavy metals, and especially on transport of Cd 2+ , has attracted much interest during the past decade. An optimized Cd 2+ -selective electrode for the continuous potentiometric monitoring of Cd 2+ fluxes in biological systems is presented. The selectivity of the electrode for Cd 2+ was further improved, and it now has very good long-term stability. The utility of this simple and inexpensive method is demonstrated by studying the Cd 2+ transport with model organisms, such as the yeast Saccharomyces cerevisiae and Arabid- opsis cell cultures, frequently used in plant science. Its lower detection limits in the presence of commonly used growth media for yeast and plant cells are improved by approximately three orders of magnitude and are 10 10 and 10 8 M Cd 2+ , respectively. Control exper- iments using atomic absorption spectrophotometry confirm that the decrease in Cd 2+ activities in the cell cultures is indeed due to the uptake of these metal ions by the cells. Both model systems can be easily transformed; therefore, in combination with the new electrode, they are very promising tools for the investigation of any protein of interest that might be involved in Cd 2+ transport. Ó 2005 Elsevier Inc. All rights reserved. Keywords: Ion-selective electrode; Potentiometric sensor; Cadmium ion uptake; Yeast; Arabidopsis cell cultures Plants are often exposed to heavy metals present in soils, which may be deposited by anthropogenic activities but also may be of geogenic origin. One of the most toxic heavy metals for animals and plants is cadmium. In most cases, it is released into the environment by power stations, heating systems, metal-working industries, waste incinerators, ur- ban traffic, and cement factories and also as a contaminant present in some phosphate fertilizers [1]. Exposure to high amounts of a heavy metal may result in increased uptake, lead to toxicity symptoms, and enter the food chain. This risk and the idea of cleaning up soils contaminated by hea- vy metals using a phytoremediation approach have in- creased the interest of the plant community in the elucidation of processes involved in heavy metal tolerance and transport [2]. Several analytical methods, including atomic absorption spectrophotometry (AAS), 2 inductively coupled plasma–mass spectrometry (ICP–MS) [3], the www.elsevier.com/locate/yabio Analytical Biochemistry 347 (2005) 10–16 ANALYTICAL BIOCHEMISTRY 0003-2697/$ - see front matter Ó 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.ab.2005.09.030 * Corresponding authors. Fax: +41 1 634 8204 (M. Geisler), +41 1 632 1164 (E. Pretsch). E-mail addresses: markus.geisler@botinst.unizh.ch (M. Geisler), pretsch@org.chem.ethz.ch (E. Pretsch). 1 These authors contributed equally and are listed in alphabetical order. 2 Abbreviations used: AAS, atomic absorption spectrophotometry; ICP–MS, inductively coupled plasma–mass spectrometry; ETH 5435, N,N,N 0 ,N 0 -tetradodecyl-3,6-dioxaoctanedithioamide; PVC, poly(vinyl chloride); DOS, bis(2-ethylhexyl) sebacate; NaTFPB, sodium tetra- kis[3,5-bis(trifluoromethyl)phenyl]borate; ETH 500, tetradodecylammo- nium tetrakis(4-chlorophenyl)borate; THF, tetrahydrofuran; Et 4 NNO 3 , tetraethylammonium nitrate; MS, Murashige and Skoog; EMF, electro- motive force; SD, synthetically defined; EDTA, ethylenediaminetetra- acetic acid; ABC, ATP-binding cassette.