The nature of arsenic-phytochelatin complexes in Holcus lanatus and Pteris cretica.
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), PC(2), and PC(3), As preferred the formation of the arsenite [As((III))]-PC(3) complex over GS-As((III))-PC(2), As((III))-(GS)(3), As((III))-PC(2), or As((III))-(PC(2))(2) (GS: glutathione bound to arsenic via sulphur of cysteine). In H. lanatus, the As((III))-PC(3) complex was the dominant complex, although reduced glutathione, PC(2), and PC(3) were found in the extract. P. cretica only synthesizes PC(2) and forms dominantly the GS-As((III))-PC(2) 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.
Raab
Andrea
A
Department of Chemistry, University of Aberdeen, Meston Building, Meston Walk, Aberdeen AB24 3UE, United Kingdom.
Feldmann
Jörg
J
Meharg
Andrew A
AA
D001151:Arsenic / Q000302:isolation & purification / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D004355:Drug Stability; D005978:Glutathione; D031752:Holcus / Q000378:metabolism*; D008667:Metalloproteins / Q000302:isolation & purification / Q000378:metabolism*; D054811:Phytochelatins; D032495:Pteris / Q000378:metabolism*; D021241:Spectrometry, Mass, Electrospray Ionization
D008667:Metalloproteins; D054811:Phytochelatins; D005978:Glutathione; D001151:Arsenic