title: Localizing the chemical forms of sulfur in vivo using X-ray fluorescence spectroscopic imaging: application to onion (Allium cepa) tissues.
abstract: Sulfur has a particularly rich biochemistry and fills a number of important roles in biology. In situ information on sulfur biochemistry is generally difficult to obtain because of a lack of biophysical techniques that have sufficient sensitivity to molecular form. We have recently reported that sulfur K-edge X-ray absorption spectroscopy can be used as a direct probe of the sulfur biochemistry of living mammalian cells [Gnida, M., et al. (2007) Biochemistry 46, 14735-14741]. Here we report an extension of this work and develop sulfur K-edge X-ray fluorescence spectroscopic imaging as an in vivo probe of sulfur metabolism in living cells. For this work, we have chosen onion (Allium cepa) as a tractable model system with well-developed sulfur biochemistry and present evidence of the localization of a number of different chemical forms. X-ray absorption spectroscopy of onion sections showed increased levels of lachrymatory factor (LF) and thiosulfinate and decreased levels of sulfoxide (LF precursor) following cell breakage. In intact cells, X-ray fluorescence spectroscopic imaging showed elevated levels of sulfoxides in the cytosol and elevated levels of reduced sulfur in the central transport vessels and bundle sheath cells.
authors.affiliation: Department of Geological Sciences, University of Saskatchewan, 114 Science Place, Saskatoon, Saskatchewan S7N 5E2, Canada. ingrid.pickering@usask.ca
authors.forename: Ingrid J
authors.initials: IJ
authors.lastname: Pickering
authors.forename: Eileen Yu
authors.initials: EY
authors.lastname: Sneeden
authors.forename: Roger C
authors.initials: RC
authors.lastname: Prince
authors.forename: Eric
authors.initials: E
authors.lastname: Block
authors.forename: Hugh H
authors.initials: HH
authors.lastname: Harris
authors.forename: Gregory
authors.initials: G
authors.lastname: Hirsch
authors.forename: Graham N
authors.initials: GN
authors.lastname: George
mesh_terms: D015335:Molecular Probes; D019697:Onions; D013050:Spectrometry, Fluorescence / Q000379:methods*; D013455:Sulfur / Q000737:chemistry*; D014965:X-Rays
chemical_list: D015335:Molecular Probes; D013455:Sulfur