The elemental composition of specific fractions of cereal and pseudocereal grains can be roughly estimated after milling. Alternatively, the elemental localization of cross-sectioned grains can be quantitatively analyzed by microproton induced X-ray emission (micro-PIXE), taking advantage of high elemental sensitivity and low lateral resolution. We present a micro-PIXE study on buckwheat (Fagopyrum esculentum) grain, with a detailed description of the elemental distributions. Elements such as Mg, P, S, K, Fe, Ni, Cu, and Zn were preferentially localized in the cotyledons and embryonic axis; however, significant amounts of K and Fe were also found in the pericarp. The aleurone layer covering the cotyledons was especially enriched in S and P, while testa, a thin layer above the aleurone did not show any significant element enrichments. The highest concentrations of Al, Si, Cl, Ca, and Ti were found in the pericarp. A detailed element localization study of pericarp layers revealed that the inner layer was enriched in K, Mn, Ca, and Fe, while the outer layer showed enrichments in Na, Mg, P, S, and Al. On the basis of the data obtained, milling techniques can be adapted to obtain milling fractions with targeted nutritional values.
COBISS.SI-ID: 6591097
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 ion metals 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 of Si besides its structural function. These results reveal that the immobilization of metals within the observed endomembrane structures present a structural and functional barrier and affect 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
COBISS.SI-ID: 6626169
Information on localization of Al in tea leaf tissues is required in order to better understand Al tolerance mechanism in this Al-accumulating plant species. Here, we have used low-energy X-ray fluorescence spectro-microscopy (LEXRF) to study localization of Al and other low Z-elements, namely C, O, Mg, Si and P, in fully developed leaves of the tea plant [Camellia sinensis (L.) O. Kuntze]. Plants were grown from seeds for 3 months in a hydroponic solution, and then exposed to 200 micro M AlCl3 for 2 weeks. Epidermal-mesophyll and xylem phloem regions of 20 micro m thick cryo-fixed freeze-dried tea-leaf cross-sections were raster scanned with 1.7 and 2.2 keV excitation energies to reach the Al–K and P–K absorption edges. Al was mainly localized in the cell walls of the leaf epidermal cells, while almost no Al signal was obtained from the leaf symplast. The results suggest that the retention of Al in epidermal leaf apoplast represent the main tolerance mechanism to Al in tea plants. In addition LEXRF proved to be a powerful tool for localization of Al in plant tissues, which can help in our understanding of the processes of Al uptake, transport and tolerance in plants.
COBISS.SI-ID: 2235215