title: Element distribution and iron speciation in mature wheat grains (Triticum aestivum L.) using synchrotron X-ray fluorescence microscopy mapping and X-ray absorption near-edge structure (XANES) imaging.
abstract: Several studies have suggested that the majority of iron (Fe) and zinc (Zn) in wheat grains are associated with phytate, but a nuanced approach to unravel important tissue-level variation in element speciation within the grain is lacking. Here, we present spatially resolved Fe-speciation data obtained directly from different grain tissues using the newly developed synchrotron-based technique of X-ray absorption near-edge spectroscopy imaging, coupling this with high-definition μ-X-ray fluorescence microscopy to map the co-localization of essential elements. In the aleurone, phosphorus (P) is co-localized with Fe and Zn, and X-ray absorption near-edge structure imaging confirmed that Fe is chelated by phytate in this tissue layer. In the crease tissues, Zn is also positively related to P distribution, albeit less so than in the aleurone. Speciation analysis suggests that Fe is bound to nicotianamine rather than phytate in the nucellar projection, and that more complex Fe structures may also be present. In the embryo, high Zn concentrations are present in the root and shoot primordium, co-occurring with sulfur and presumably bound to thiol groups. Overall, Fe is mainly concentrated in the scutellum and co-localized with P. This high resolution imaging and speciation analysis reveals the complexity of the physiological processes responsible for element accumulation and bioaccessibility.
authors.affiliation: Laboratory of Food Chemistry and Biochemistry, Leuven Food Science and Nutrition Research Centre (LFoRCe), KU Leuven, Leuven, B-3001, Belgium.
authors.forename: Niels
authors.initials: N
authors.lastname: De Brier
authors.affiliation: Laboratory of Food Chemistry and Biochemistry, Leuven Food Science and Nutrition Research Centre (LFoRCe), KU Leuven, Leuven, B-3001, Belgium.
authors.forename: Sara V
authors.initials: SV
authors.lastname: Gomand
authors.affiliation: Centre for Environmental Risk Assessment and Remediation, University of South Australia, Mawson Lakes, South Australia, 5095, Australia.
authors.forename: Erica
authors.initials: E
authors.lastname: Donner
authors.affiliation: Australian Synchrotron, Clayton, Victoria, 3168, Australia.
authors.forename: David
authors.initials: D
authors.lastname: Paterson
authors.affiliation: Division of Soil and Water Management, KU Leuven, Leuven, B-3001, Belgium.
authors.forename: Erik
authors.initials: E
authors.lastname: Smolders
authors.affiliation: Laboratory of Food Chemistry and Biochemistry, Leuven Food Science and Nutrition Research Centre (LFoRCe), KU Leuven, Leuven, B-3001, Belgium.
authors.forename: Jan A
authors.initials: JA
authors.lastname: Delcour
authors.affiliation: Centre for Environmental Risk Assessment and Remediation, University of South Australia, Mawson Lakes, South Australia, 5095, Australia.
authors.forename: Enzo
authors.initials: E
authors.lastname: Lombi
mesh_terms: D002523:Edible Grain / Q000378:metabolism*; D007501:Iron / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D010940:Plant Proteins / Q000378:metabolism; D014908:Triticum / Q000378:metabolism*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D010940:Plant Proteins; C000624173:aleurone; D007501:Iron
keywords: Aleurone; crease region; embryo; nutrient elements