Differences and similarities in selenium biopathways in Astragalus, Neptunia (Fabaceae) and Stanleya (Brassicaceae) hyperaccumulators
Antony van der Ent, Mirko Salinitro, Dennis Brueckner, Kathryn M Spiers, Sofia Montanari, Annalisa Tassoni, Michela Schiavon- Plant Science
SUMMARY
Background and aims
Selenium hyperaccumulator species are of primary interest for studying the evolution of hyperaccumulation and biofortification as selenium is an essential element in human nutrition. We aimed to determine whether the distributions of selenium in Astragalus bisulcatus, Stanleya pinnata and Neptunia amplexicaulis are similar or contrasting to infer the underlying physiological mechanisms.
Methods
This study used synchrotron-based X-ray Fluorescence Microscopy techniques to visualize the distribution of selenium and other elements in fresh hydrated plant tissues of Astragalus racemosus, Stanleya pinnata and Neptunia amplexicaulis.
Results
Selenium distribution widely differs in the three species: in the leaves of the A. racemosus and N. amplexicaulis Se is mainly concentrated in pulvini, whereas in S. pinnata it is located in leaf margins. In roots and stems of all species selenium was absent in xylem cells, while it was particularly concentrated in pith rays of S. pinnata and phloem cells of A. racemosus and N. amplexicaulis.
Conclusions
This study shows that Astragalus, Stanleya and Neptunia have evolved different selenium handling physiologies, resulting in different mechanisms for translocation and storage of excess selenium. Important dissimilarities among the three analyzed species suggests that Se hyperaccumulation has likely evolved multiple times under similar environmental pressures.