Iron insufficiency is a worldwide problem in human diets. In cereals like wheat, the bran layer of the grains is an important source of iron. However, the dietary availability of iron in wheat flour is limited due to the loss of the iron-rich bran during milling and processing and the presence of anti-nutrients like phytic acid that keep iron strongly chelated in the grain. The present study investigated the localization of iron and phosphorus in grain tissues of wheat genotypes with contrasting grain iron content using synchrotron-based micro-X-ray fluorescence (micro-XRF) and micro-proton-induced X-ray emission (micro-PIXE). X-ray absorption near-edge spectroscopy (XANES) was employed to determine the proportion of divalent and trivalent forms of Fe in the grains. It revealed the abundance of oxygen, phosphorus, and sulphur in the local chemical environment of Fe in grains, as Fe-O-P-R and Fe-O-S-R coordination. Contrasting differences were noticed in tissue-specific relative localization of Fe, P, and S among the different genotypes, suggesting a possible effect of localization pattern on iron bioavailability. The current study reports the shift in iron distribution from maternal to filial tissues of grains during the evolution of wheat from its wild relatives to the present-day cultivated varieties, and thus suggests the value of detailed physical localization studies in varietal improvement programmes for food crops.
Bibliographical noteFunding Information:
This work was supported by the Department of Biotechnology (DBT, Government of India), the Slovenian Research Agency research programme (P1-0112, P-0212) and DESY and the European Community’s Seventh Framework Programme (FP7/2007–2013) under grant agreement CALIPSO n_ 312284 (EU Support of Access to Synchrotrons/FELs in Europe). Micro-PIXE methodology and instrumentation at JSI was upgraded within the project 7FP EU No. 227012 ‘SPIRIT’. Access to synchrotron radiation facilities of CLS (project 14–3657), HASYLAB (project I-20110511 EC) and Elettra (projects 20110086 and 20115112) is acknowledged. IAEA framework of coordinated research project 16796 “Applications of synchrotron radiation for environmental sciences and materials research for development of environmentally friendly resources” (CSI, KV) is acknowledged. Renfei Feng of CLS, Giuliana Aquilanti and Luca Olivi of Elettra, and Roman Chernikov and Edmund Welter of HASYLAB are acknowledged for expert advice on beamline operation. Harcharan S. Dhaliwal of Eternal University is acknowledged for providing the grains. S.P.S. acknowledges DBT for supporting visit to CLS, Canada. R.T. acknowledges J. C. Bose fellowship, Department of Science and Technology, Government of India.
- Triticum aestivum
- grain iron distribution