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ENVIRONMENTAL STRESS AND ADAPTATION

The Nature of Arsenic-Phytochelatin Complexes in Holcus lanatus and Pteris cretica¹

Department of Chemistry, University of Aberdeen, Meston Building, Meston Walk, Aberdeen AB24 3UE, United Kingdom (A.R., J.F.); and School of Biological Sciences, University of Aberdeen, Cruickshank Building, St. Machar Drive, Aberdeen, AB24 3UU, United Kingdom (A.A.M.).

We have developed a method to extract and separate phytochelatins (PCs)—metal(loid) complexes using parallel metal(loid)-specific (inductively coupled plasma-mass spectrometry) and organic-specific (electrospray ionization-mass spectrometry) detection systems—and use it here to ascertain the nature of arsenic (As)-PC complexes in plant extracts. This study is the first unequivocal report, to our knowledge, of PC complex coordination chemistry in plant extracts for any metal or metalloid ion. The As-tolerant grass Holcus lanatus and the As hyperaccumulator Pteris cretica were used as model plants. In an in vitro experiment using a mixture of reduced glutathione (GS), PC₂, and PC₃, As preferred the formation of the arsenite [As^(III)]-PC₃ complex over GS-As^(III)-PC₂, As^(III)-(GS)₃, As^(III)-PC₂, or As^(III)-(PC₂)₂ (GS: glutathione bound to arsenic via sulphur of cysteine). In H. lanatus, the As^(III)-PC₃ complex was the dominant complex, although reduced glutathione, PC₂, and PC₃ were found in the extract. P. cretica only synthesizes PC₂ and forms dominantly the GS-As^(III)-PC₂ complex. This is the first evidence, to our knowledge, for the existence of mixed glutathione-PC-metal(loid) complexes in plant tissues or in vitro. In both plant species, As is dominantly in non-bound inorganic forms, with 13% being present in PC complexes for H. lanatus and 1% in P. cretica.

¹ This work was supported by the Biotechnology and Biological Science Research Council (grant no. I/REI 18479) and by the College of Engineering and Physical Sciences, Aberdeen, Aberdeenshire, UK.

^* Corresponding author; e-mail a.meharg{at}abdn.ac.uk; fax 44–0–1224–272703.

Received September 17, 2003; returned for revision October 19, 2003; accepted December 4, 2003.

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