title: Arsenic speciation in tissues of the hyperaccumulator P. calomelanos var. austroamericana using X-ray absorption spectroscopy.
abstract: The fate and chemical speciation of arsenic (As) during uptake, translocation, and storage by the As hyperaccumulating fern Pityrogramma calomelanos var. austroamericana (Pteridaceae) were examined using inductively coupled plasma-atomic emission spectrometry (ICP-AES) and synchrotron-based micro-X-ray absorption near edge structure (micro-XANES) and micro-X-ray fluorescence (micro-XRF) spectroscopies. Chemical analysis revealed total As concentration was ca. 6.5 times greater in young fronds (5845 mg kg(-1) dry weight (DW)) than in old fronds (903 mg kg(-1) DW). In pinnae, As concentration decreased from the base (6822 mg kg(-1) DW) to the apex (4301 mg kg(-1) DW) of the fronds. The results from micro-XANES and micro-XRF of living tissues suggested that more than 60% of arsenate (As(V)) absorbed was reduced to arsenite (As(III)) in roots, prior to transport through vascular tissues as As(V) and As(III). In pinnules, As(III) was the predominant redox species (72-90%), presumably as solvated, oxygen coordinated compounds. The presence of putative As(III)-sulphide (S(2-)) coordination throughout the fern tissues (4-25%) suggests that S(2-) functional groups may contribute in the biochemical reduction of As(V) to As(III) during uptake and transport at a whole-plant level. Organic arsenicals and thiol-rich compounds were not detected in the species and are unlikely to play a role in As hyperaccumulation in this fern. The study provides important insights into homeostatic regulation of As following As uptake in P. calomelanos var. austroamericana.
authors.affiliation: Faculty of Agriculture, Food and Natural Resources, The University of Sydney, New South Wales 2006, Australia. anthony.kachenko@ngia.com.au
authors.forename: Anthony G
authors.initials: AG
authors.lastname: Kachenko
authors.forename: Markus
authors.initials: M
authors.lastname: Gräfe
authors.forename: Balwant
authors.initials: B
authors.lastname: Singh
authors.forename: Steve M
authors.initials: SM
authors.lastname: Heald
mesh_terms: D001151:Arsenic / Q000378:metabolism*; D029624:Ferns / Q000378:metabolism*; D014018:Tissue Distribution; D056928:X-Ray Absorption Spectroscopy
chemical_list: D001151:Arsenic