title: Chemical form and distribution of selenium and sulfur in the selenium hyperaccumulator Astragalus bisulcatus.
abstract: In its natural habitat, Astragalus bisulcatus can accumulate up to 0.65% (w/w) selenium (Se) in its shoot dry weight. X-ray absorption spectroscopy has been used to examine the selenium biochemistry of A. bisulcatus. High concentrations of the nonprotein amino acid Se-methylseleno-cysteine (Cys) are present in young leaves of A. bisulcatus, but in more mature leaves, the Se-methylseleno-Cys concentration is lower, and selenate predominates. Seleno-Cys methyltransferase is the enzyme responsible for the biosynthesis of Se-methylseleno-Cys from seleno-Cys and S-methyl-methionine. Seleno-Cys methyltransferase is found to be expressed in A. bisulcatus leaves of all ages, and thus the biosynthesis of Se-methylseleno-Cys in older leaves is limited earlier in the metabolic pathway, probably by an inability to chemically reduce selenate. A comparative study of sulfur (S) and Se in A. bisulcatus using x-ray absorption spectroscopy indicates similar trends for oxidized and reduced Se and S species, but also indicates that the proportions of these differ significantly. These results also indicate that sulfate and selenate reduction are developmentally correlated, and they suggest important differences between S and Se biochemistries.
authors.affiliation: Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: Ingrid J
authors.initials: IJ
authors.lastname: Pickering
authors.forename: Carrie
authors.initials: C
authors.lastname: Wright
authors.forename: Ben
authors.initials: B
authors.lastname: Bubner
authors.forename: Danielle
authors.initials: D
authors.lastname: Ellis
authors.forename: Michael W
authors.initials: MW
authors.lastname: Persans
authors.forename: Eileen Y
authors.initials: EY
authors.lastname: Yu
authors.forename: Graham N
authors.initials: GN
authors.lastname: George
authors.forename: Roger C
authors.initials: RC
authors.lastname: Prince
authors.forename: David E
authors.initials: DE
authors.lastname: Salt
mesh_terms: D027883:Astragalus Plant / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D001711:Biotransformation; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D008780:Methyltransferases / Q000235:genetics / Q000378:metabolism; D018515:Plant Leaves / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D012643:Selenium / Q000737:chemistry / Q000378:metabolism*; D013455:Sulfur / Q000737:chemistry / Q000378:metabolism*; D013997:Time Factors
chemical_list: D013455:Sulfur; D008780:Methyltransferases; C100751:selenocysteine methyltransferase; D012643:Selenium