Mature developed seeds are physiologically and biochemically committed to store nutrients, principally as starch, protein, oils, and minerals. The composition and distribution of elements inside the aleurone cell layer reflect their biogenesis, structural characteristics, and physiological functions. It is therefore of primary importance to understand the mechanisms underlying metal ion accumulation, distribution, storage, and bioavailability in aleurone subcellular organelles for seed fortification purposes. Synchrotron radiation soft X-ray full-field imaging mode (FFIM) and low-energy X-ray fluorescence (LEXRF) spectromicroscopy were applied to characterize major structural features and the subcellular distribution of physiologically important elements (Zn, Fe, Na, Mg, Al, Si, and P). These direct imaging methods reveal the accumulation patterns between the apoplast and symplast, and highlight the importance of globoids with phytic acid mineral salts and walls as preferential storage structures. C, N, and O chemical topographies are directly linked to the structural backbone of plant substructures. Zn, Fe, Na, Mg, Al, and P were linked to globoid structures within protein storage vacuoles with variable levels of co-localization. Si distribution was atypical, being contained in the aleurone apoplast and symplast, supporting a physiological role for Si in addition to its structural function. These results reveal that the immobilization of metals within the observed endomembrane structures presents a structural and functional barrier and affects bioavailability. The combination of high spatial and chemical X-ray microscopy techniques highlights how in situ analysis can yield new insights into the complexity of the wheat aleurone layer, whose precise biochemical composition, morphology, and structural characteristics are still not unequivocally resolved.

Biological systems are unique matter with very complex morphology and highly heterogeneous chemical composition dominated by light elements. Discriminating qualitatively at the sub-micrometer level the lateral distribution of constituent elements, and correlating it to the sub-cellular biological structure, continues to be a challenge. The low-energy X-ray fluorescence microspectroscopy, recently implemented in TwinMic scanning transmission mode, has opened up new opportunities for mapping the distribution of the light elements, complemented by morphology information provided by simultaneous acquisition of absorption and phase contrast images. The important new information that can be obtained in bio-related research domains is demonstrated by two pilot experiments with specimens of interest for marine biology and food science. They demonstrate the potential to yield important insights into the structural and compositional enrichment, distribution and correlation of essential trace elements in the lorica of Tintinnopsis radix , and the lateral distribution of trace nutrients in the seeds of wheat Triticum aestivum .