Spatially resolved distributions of the mineral elements in the grain of tartary buckwheat (Fagopyrum tataricum)

• Tissue and cell-specific distributions of mineral elements are presented.
• Most mineral elements are highest in cotyledons, with Ca mainly in the pericarp.
• P localisation correlates strongly with Mg and Fe, in the mesophyll of cotyledons.
• Binding sites other than phytate are indicated for Mn, Cu and Zn in the mesophyll.

The different buckwheat species are gluten-free pseudocereals, and they are amongst the most important alternative foodstuffs as they have an excellent nutrient profile. The grain of tartary buckwheat (Fagopyrum tataricum Gaertn.) is known to be rich in antioxidants (especially rutin) and mineral elements. In addition to the spatial distributions of Mg, P, S, K, Ca, Mn, Fe, Cu and Zn at the tissue level that have been determined using micro-proton-induced X-ray emission, we have also assessed the distributions of C, O, Mg, P, Mn, Fe, Cu and Zn at the cellular and sub-cellular levels using synchrotron radiation-based low-energy X-ray fluorescence. The highest concentrations of all of the studied mineral elements were in the cotyledons, except for Ca, which dominated in the pericarp. The relative mineral-element distributions calculated on dry weight basis confirm the observed mineral distribution profiles. In the cotyledons, P clearly partitions to the mesophyll and is mainly ascribed to phytate. In the mesophyll, the P spatial distribution strongly correlates with Mg and, in decreasing order, with Cu > Fe > Mn > Zn. These spatial distributions of the mineral elements, their concentrations and their co-localisation are discussed in relation to other pseudocereal and cereal grain.