A first glance at the micro-ZnO coating of maize (Zea mays L.) seeds: a study of the elemental spatial distribution and Zn speciation analysis

An adequate concentration of zinc in seeds can help in the initial development of plants. ZnO-coating can provide this nutrient to plants from the early stages of growth. However, there is a pressing need for additional studies to enable its safe use. This study aimed to evaluate the elemental distribution over ZnO-treated maize seeds stored for up to 12 months, as well as to map Zn species in the internal seed tissues. Synchrotron radiation micro-X-ray fluorescence spectrometry (SR mu-XRF) and micro-X-ray absorption near-edge spectroscopy (mu-XANES) were used as analytical tools for this purpose. The highest Zn accumulation site in micro-sized ZnO treated maize seeds is the embryo, mainly close to the black layer. The distribution pattern of Zn, S and P does not change in maize seeds treated with ZnO. Zn mass fractions in the embryo, pericarp and endosperm suggest that after 12 months of storage, Zn absorption is observed in ZnO-treated seeds. In the Zn hotspot, this element is in the form of phytate and in more readily bioavailable forms, such as Zn-3(PO4)(2) and cysteine. These findings can yield valuable insights into the advantages of using advanced microanalytical tools to provide important information regarding potential nutrient bioavailability to those interested in biofortification studies.