Micronutrient deficiencies have a negative impact in the lives of millions of people worldwide. Most affected are children and pregnant women in developing regions. Biofortification is a sustainable way to alleviate micronutrient deficiencies in at-risk populations. To optimize the biofortification approach, it is important to consider both the quantities and bioavailability of the target micronutrients. Both the speciation and the localization of the micronutrients within the seed can have an impact on bioavailability. In this study we use the sensitive and non-destructive micro-PIXE technique to reveal the distribution of iron, zinc, manganese and phosphorus within soybean seeds. We show that high concentrations of iron accumulate in the seed coats of mature soybean seeds. This iron accounted for 20 to 40% of the total seed iron. Furthermore, manganese and iron accumulated in close proximity to each other in the provascular tissue of the soybean radicle. No regions with increased accumulation of iron, zinc, or manganese were observed in the cotyledons. The concentrations of both phosphorus and zinc were higher in the radicle compared to the cotyledons, and zinc accumulated primarily near the radicle tip.

Our study provides a thorough description of the distribution of important micronutrients within the mature soybean seed.