Morphological analysis of the seeds of three pseudocereals by using light microscopy and ESEM-EDS

The seed morphology of three pseudocereal grains (PSCg), i.e. quinoa (Chenopodium quinoa Willd, Chenopodiaceae), buckwheat (Fagopyrum esculentum Moench, Polygonaceae) and amaranth (Amaranthus caudatus L., Amaranthaceae) was studied by light microscopy (LM) and Environmental Scanning Electron Microscopy coupled with Energy Dispersive Spectroscopy (ESEM-EDS). LM was used in bright field to eval- uate either unstained sections or sections stained with Azan mixture, and in fluorescence. The aim of the study was to compare the architecture of the three seeds in order to connect their morphology with nutrient localiza- tion. The Azan staining allowed for the visualization of the seed coat, the embryo - with its shoot apical meris- tem - and the radicle cell layers, whereas the use of fluorescence microscopy identified the cells rich in phenolic compounds. Finally, the ESEM-EDS analysis revealed that the seed coat of the quinoa was thinner than that of amaranth or buckwheat. In all PSCg, starch granules appeared to be located in large polygonal cells, surrounded by a thin cell wall. Several globoids of proteins were observed in the embryo cells. In the radicle section, the vascular bundles of the procambium were evident, while Amaranth only showed a consistent layer of calcium crystals, located between the embryo and the perisperm. The morphological differences of the three PSCg were discussed in the context of their structural resistance to processing technologies which impact on nutritional value of derived foods.