Uptake, translocation and transformation of arsenate and arsenite in sunflower (Helianthus annuus): formation of arsenic–phytochelatin complexes during exposure to high arsenic concentrations

Authors


Author for correspondence: Jörg Feldmann Tel: +44 (0)1224 272911 Fax: +44 (0)1224 272703 Email: j.feldmann@abdn.ac.uk

Summary

  • • 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 mol l−1 arsenite (As(III)) or arsenate (As(V)).
  • • 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.
  • • Roots of As-exposed H. annuus contained up to 14 different arsenic species, including the complex of arsenite with two (γ-Glu-Cys)2-Gly molecules [As(III)–(PC2)2], the newly identified monomethylarsonic phytochelatin-2 or (γ-Glu-Cys)2-Gly CH3As (MA(III)–PC2) and at least eight not yet identified species. The complex of arsenite with (γ-Glu-Cys)3-Gly (As(III)–PC3) and the complex of arsenite with glutathione (GSH) and (γ-Glu-Cys)2-Gly (GS–As(III)–PC2) were present in all samples (roots, stems and leaves) taken from plants exposed to As. The GS–As(III)–PC2 complex was the dominant complex after 1 h of exposure. As(III)–PC3 became the predominant As–PC complex after 3 h, binding up to 40% of the As present in the exposed plants.
  • • 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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