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

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  • Andrew L Neal, Rothamsted Research, Storbritannien
  • Kalotina Geraki, Diamond Light Source, Harwell Science and Innovation Campus, Storbritannien
  • Søren Borg
  • Paul Quinn, Diamond Light Source, Harwell Science and Innovation Campus, Storbritannien
  • J Fred Mosselsmans, Diamond Light Source, Harwell Science and Innovation Campus, Storbritannien
  • Henrik Brinch-Pedersen
  • Peter R Shewry, Rothamsted Research, Storbritannien
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.
OriginalsprogEngelsk
TidsskriftJournal of Biological Inorganic Chemistry
Vol/bind18
Nummer5
Sider (fra-til)557-570
Antal sider14
ISSN0949-8257
DOI
StatusUdgivet - 2013

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