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Iron and zinc complexation in wild-type and ferritin-expressing wheat grain: implications for mineral transport into developing grain

DOI: 10.1007/s00775-013-1000-x DOI Help

Authors: Andrew L. Neal (Rothamsted Research) , Tina Geraki (Diamond Light Source) , Søren Borg (Aarhus University) , Paul Quinn (Diamond Light Source) , Fred Mosselmans (Diamond Light Source) , Henrik Brinch-pedersen (Aarhus University) , Peter R. Shewry (Rothamsted Research)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Jbic Journal Of Biological Inorganic Chemistry

State: Published (Approved)
Published: April 2013
Diamond Proposal Number(s): 2952 , 923

Abstract: We have used synchrotron-based X-ray fluorescence and absorption techniques to establish both metal distribution and complexation in mature wheat grains. In planta, extended X-ray absorption fine structure (EXAFS) spectroscopy reveals iron phytate and zinc phytate structures in aleurone cells and in modified aleurone cells in the transfer region of the grain: iron is coordinated octahedrally by six oxygen atoms and fewer than two phosphorous atoms. Zinc is coordinated tetrahedrally by four oxygen atoms and approximately 1.5 phosphorus atoms in an asymmetric coordination shell. We also present evidence of modified complexation of both metals in transgenic grain overexpressing wheat ferritin. For zinc, there is a consistent doubling of the number of complexing phosphorus atoms. Although there is some EXAFS evidence for iron phytate in ferritin-expressing grain, there is also evidence of a structure lacking phosphorus. This change may lead to an excess of phosphorus within the storage regions of grain, and in turn to the demonstrated increased association of phosphorus with zinc in ferritin-expressing grains. Derivative X-ray absorption spectra also suggest that mineral complexation in the transfer region of ferritin-expressing grains is quite different from that in wild-type grain. This may explain why the raised levels of minerals transported to the developing grain accumulate within the crease region of the transgenic grain.

Journal Keywords: Wheat; grain; Iron Zinc; Phytate; X-ray fluorescence

Subject Areas: Food Science, Chemistry, Biology and Bio-materials


Instruments: I18-Microfocus Spectroscopy