The location of iron and zinc in grain of conventional and biofortified lines of sorghum

Sorghum is an important source of dietary iron (Fe) and zinc (Zn) in parts of Africa and India, but there is a need to increase their concentrations to meet dietary requirements. Grains of a genetically biofortified sorghum line (Parbhani Shakti) had higher concentrations of Fe and Zn than a control line (M35-1). Analysis at the tissue level by histochemical staining and at the cellular level using NanoSIMS showed that both minerals are concentrated in the aleurone layer and in the scutellum of the embryo, with Zn also being concentrated in the embryonic axis. However, NanoSIMS showed that “hot spots” of 56Fe+ and 64Zn+ were also present in the sub-aleurone and starchy endosperm cells. Most of these hot spots also contained 31P16O+ indicating that the Fe and Zn are present as phytates, as in the aleurone and scutellum cells. Low concentrations of 56Fe+ and 64Zn+ were also observed in the protein matrix of these cells.