Chemical form and distribution of selenium and sulfur in the selenium hyperaccumulator Astragalus bisulcatus.
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.
Pickering
Ingrid J
IJ
Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, Indiana 47907, USA.
Wright
Carrie
C
Bubner
Ben
B
Ellis
Danielle
D
Persans
Michael W
MW
Yu
Eileen Y
EY
George
Graham N
GN
Prince
Roger C
RC
Salt
David E
DE
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
D013455:Sulfur; D008780:Methyltransferases; C100751:selenocysteine methyltransferase; D012643:Selenium