Annals of Botany

Life on the high Se...S

In many western countries a visit to a so-called health-food shop will often reveal fashionable food supplements aimed at satisfying equally fashionable anxieties about dietary deficiencies. Amongst these supplements are those offering selenium (Se) as a key ingredient, reflecting a view that modern diets do not contain enough. This is not to say that we do not need Se. We do need it, but only as a trace element (approx. 50 g d^–1); too much Se is actually toxic. Understanding the mechanism and kinetics of Se uptake by plants is thus important on two counts – the dietary need for small amounts of Se and the toxic effects of any excess. Further, there is the possibility that plants that take up Se may be used in bioremediation of contaminated soil. All this forms the background to the work of White et al. (Dundee, Warwick and Nottingham, UK, pp. 111–118). Se is very similar chemically to sulphur (S); selenate and sulphate are generally taken up by the same plasma-membrane high-affinity sulphate transporters (HASTs). However, an earlier survey by the research group revealed that some plants select in favour of sulphate while a few are able to select in favour of selenate. The authors have now surveyed 39 angiosperm species across the range of Se-accumulation phenotypes, grown them hydroponically and studied their ability to take up Se and S. Most of the species did not discriminate between S and Se but two species, Astragalus recemosus (Fabaceae) and Stanleya pinnata (Brassicaceae) were very obviously Se accumulators, with concentrations of Se in leaves and leaf Se/S quotients very markedly higher than the other species. This ability to discriminate in favour of Se probably lies in the molecular structure of one or more root-located HASTs, which now become important research targets.