JXB Advance Access originally published online on February 5, 2007
Journal of Experimental Botany 2007 58(6):1333-1338; doi:10.1093/jxb/erl300
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© 2007 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)
RESEARCH PAPER |
Can arsenic–phytochelatin complex formation be used as an indicator for toxicity in Helianthus annuus?
1Department of Chemistry, University of Aberdeen, Meston Building, Meston Walk, Aberdeen AB24 3UE, UK
2School of Biological Sciences, University of Aberdeen, Cruickshank Building, St Machar Drive, Aberdeen AB24 3UU, UK
* To whom correspondence should be addressed. E-mail: j.feldmann{at}abdn.ac.uk
The formation of arsenic–phytochelatin (As–PC) complexes is thought to be part of the plant detoxification strategy for arsenic. This work examines (i) the arsenic (As) concentration-dependent formation of As–PC complex formation and (ii) redistribution and metabolism of As after arrested As uptake in Helianthus annuus. HPLC with parallel ICP-MS/ES-MS detection was used to identify and quantify the species present in plant extracts exposed to arsenate (As(V)) (between 0 and 66.7 µmol As l–1 for 24 h). At As concentrations below the EC50 value for root growth (22 µmol As l–1) As uptake is exponential, but it is reduced at concentrations above. Translocation between root and shoot seemed to be limited to the uptake phase of arsenic. No redistribution of As between root and shoot was observed after arresting As exposure. The formation of As–PC complexes was concentration-dependent. The amount and number of As–PC complexes increased exponentially with concentration up to 13.7 µmol As l–1. As(III)–PC3 and GS–As(III)–PC2 complexes were the dominant species in all samples. The ratio of PC-bound As to unbound As increased up to 1.3 µmol As l–1 and decreased at higher concentrations. Methylation of inorganic As was only a minor pathway in H. annuus with about 1% As methylated over a 32 d period. The concentration dependence of As–PC complex formation, amount of unbound reduced and oxidized PC2, and the relative uptake rate showed that As starts to influence the cellular metabolism of H. annuus negatively at As concentrations well below the EC50 value determined by more traditional means. Generally, As–PC complexes and PC-synthesis rate seem to be the more sensitive parameters to be studied when As toxicity values are to be estimated.
Key words: Arsenic, arsenic–phytochelatin complex, arsenic speciation, ES-MS, Helianthus annuus, ICP-MS, methylation, phytochelatin
Received 25 September 2006; Revised 11 December 2006 Accepted 15 December 2006