Uptake, Translocation and Transformation of Arsenate and Arsenite in Sunflower (Helianthus annuus): Formation of Arsenic-Phytochelatin Complexes during Exposure to High Arsenic Concentrations

$\bullet$) The aim of the study was to determine the time-dependent formation of arsenic-phytochelatin (As-PC) complexes in the roots, stems and leaves of an arsenic-nontolerant plant (Helianthus annuus) during exposure to $66 \mu mol l^{-1}$ arsenite $(As^{(III)})$) or arsenate $(As^{(V)})$. $\bull...

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Published inThe New phytologist Vol. 168; no. 3; pp. 551 - 558
Main Authors Raab, Andrea, Schat, Henk, Meharg, Andrew A., Feldmann, Jörg
Format Journal Article
LanguageEnglish
Published Oxford, UK Blackwell Science 01.12.2005
Blackwell Science Ltd
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Summary:$\bullet$) The aim of the study was to determine the time-dependent formation of arsenic-phytochelatin (As-PC) complexes in the roots, stems and leaves of an arsenic-nontolerant plant (Helianthus annuus) during exposure to $66 \mu mol l^{-1}$ arsenite $(As^{(III)})$) or arsenate $(As^{(V)})$. $\bullet$ We used our previously developed method of simultaneous element-specific (inductively coupled plasma mass spectrometry, ICP-MS) and molecular-specific (electrospray-ionization mass spectrometry, ES-MS) detection systems interfaced with a suitable chromatographic column and eluent conditions, which enabled us to identify and quantify As-PC complexes directly. $\bullet$ Roots of As-exposed H. annuus contained up to 14 different arsenic species, including the complex of arsenite with two ($(\gamma-Glu-Cys)_2-Gly$ molecules $\lbrack As^{(III)}-(PC_2)_2\rbrack$, the newly identified monomethylarsonic phytochelatin-2 or $(\gamma-Glu-Cys)_2-Gly CH_3As (MA^{(III)}-PC_2)$ and at least eight not yet identified species. The complex of arsenite with $(\gamma-Glu-Cys)_3-Gly (As^{(III)}-PC_3)$ and the complex of arsenite with glutathione (GSH) and $(\gamma-Glu-Cys)_2-Gly (GS-As^{(III)}-PC_2)$ were present in all samples (roots, stems and leaves) taken from plants exposed to As. The $GS-As^{(III)}-PC_2$ complex was the dominant complex after 1 h of exposure. $As^{(III)}-PC_3$ became the predominant As-PC complex after 3 h, binding up to 40% of the As present in the exposed plants. $\bullet$ No As-PC complexes were found in sap (mainly xylem sap from the root system), in contrast to roots, stems and leaves, which is unequivocal evidence that As-PC complexes are not involved in the translocation of As from root to leaves of H. annuus.
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ISSN:0028-646X
1469-8137
DOI:10.1111/j.1469-8137.2005.01519.x