Selenium hyperaccumulators are plants able to accumulate over 1000 μg selenium g−1 in their shoots while growing in their natural environments. The most studied selenium hyperaccumulators are Astragalus bisulcatus, Neptunia amplexicaulis (Fabaceae), and Stanleya pinnata (Brassicaceae). To date, several studies have investigated selenium distribution in these species, most of which have focused on the leaves and roots. Other plant organs, such as seeds, remain poorly investigated. In this study, we determined selenium distribution in the seeds of these three key hyperaccumulating species using X-ray fluorescence microscopy computed tomography (XFM-CT). Seeds of A. bisulcatus, S. pinnata, and N. amplexicaulis were also analyzed for total elemental content. Single seeds of each species were examined using XFM-CT at beamline P06 of PETRA III (Deutsches Elektronen-Synchrotron, DESY) to generate detailed elemental maps. Selenium concentrations were 1800 ± 180, 1240 ± 170, and 870 ± 100 μg g−1 DW in N. amplexicaulis, A. bisulcatus, and S. pinnata seeds, respectively. In general, selenium is enriched in the cotyledon parenchyma and radicle cortex of all seeds. Selenium is generally absent from the seed coat and endosperm. Seleni is present in the inner part of the seed coat (tegmen). The distribution of selenium in tissues that are especially sensitive to herbivory appears to support the defense function of this metalloid in hyperaccumulator plants.
Salinitro et al. (Thu,) studied this question.