title: Iron (Fe) speciation in xylem sap by XANES at a high brilliant synchrotron X-ray source: opportunities and limitations.
abstract: The development of highly brilliant synchrotron facilities all around the world is opening the way to new research in biological sciences including speciation studies of trace elements in plants. In this paper, for the first time, iron (Fe) speciation in xylem sap has been assessed by X-ray absorption near-edge structure (XANES) spectroscopy at the highly brilliant synchrotron PETRA III, beamline P06. Both standard organic Fe-complexes and xylem sap samples of Fe-deficient tomato plants were analyzed. The high photon flux provided by this X-ray synchrotron source allows on one side to obtain good XANES spectra in a reasonable amount of time (approx. 15 min for 200 eV scan) at low Fe concentrations (sub parts-per-million), while on the other hand may cause radiation damage to the sample, despite the sample being cooled by a stream of liquid nitrogen vapor. Standard Fe-complexes such as Fe(III)-succinate, Fe(III)-α-ketoglutarate, and Fe(III)-nicotianamine are somehow degraded when irradiated with synchrotron X-rays and Fe(III) can undergo photoreduction. Degradation of the organic molecules was assessed by HPLC-UV/Vis analyses on the same samples investigated by X-ray absorption spectroscopy (XAS). Fe speciation in xylem sap samples revealed Fe(III) to be complexed by citrate and acetate. Nevertheless, artifacts created by radiation damage cannot be excluded. The use of highly brilliant synchrotrons as X-ray sources for XAS analyses can dramatically increase the sensitivity of the technique for trace elements thus allowing their speciation in xylem sap. However, great attention must be paid to radiation damage, which can lead to biased results.
authors.affiliation: Department of Soil, Plant and Food Sciences, University of Bari Aldo Mor", Via Amendola 165/A, 70126 Bari, Italy. roberto.terzano@uniba.it
authors.forename: Roberto
authors.initials: R
authors.lastname: Terzano
authors.forename: Tanja
authors.initials: T
authors.lastname: Mimmo
authors.forename: Bart
authors.initials: B
authors.lastname: Vekemans
authors.forename: Laszlo
authors.initials: L
authors.lastname: Vincze
authors.forename: Gerald
authors.initials: G
authors.lastname: Falkenberg
authors.forename: Nicola
authors.initials: N
authors.lastname: Tomasi
authors.forename: Magali
authors.initials: M
authors.lastname: Schnell Ramos
authors.forename: Roberto
authors.initials: R
authors.lastname: Pinton
authors.forename: Stefano
authors.initials: S
authors.lastname: Cesco
mesh_terms: D000085:Acetates / Q000737:chemistry / Q000378:metabolism; D001383:Azetidinecarboxylic Acid / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism; D002951:Citrates / Q000737:chemistry / Q000378:metabolism; D004867:Equipment Design; D005290:Ferric Compounds / Q000032:analysis / Q000378:metabolism; D007501:Iron / Q000032:analysis* / Q000378:metabolism; D007656:Ketoglutaric Acids / Q000737:chemistry / Q000378:metabolism; D018551:Solanum lycopersicum / Q000737:chemistry / Q000378:metabolism; D013386:Succinates / Q000737:chemistry / Q000378:metabolism; D017356:Synchrotrons; D056928:X-Ray Absorption Spectroscopy / Q000295:instrumentation / Q000379:methods*; D014965:X-Rays; D052584:Xylem / Q000737:chemistry / Q000378:metabolism*
chemical_list: D000085:Acetates; D002951:Citrates; D005290:Ferric Compounds; D007656:Ketoglutaric Acids; D013386:Succinates; C082893:nicotianamine; D001383:Azetidinecarboxylic Acid; D007501:Iron