Selenium uptake, translocation, assimilation and metabolic fate in plants

Abstract

The chemical and physical resemblance between selenium (Se) and sulfur (S) establishes that both these elements share common metabolic pathways in plants. The presence of isologous Se and S compounds indicates that these elements compete in biochemical processes that affect uptake, translocation and assimilation throughout plant development. Yet, minor but crucial differences in reactivity and other metabolic interactions infer that some biochemical processes involving Se may be excluded from those relating to S. This review examines the current understanding of physiological and biochemical relationships between S and Se metabolism by highlighting their similarities and differences in relation to uptake, transport and assimilation pathways as observed in Se hyperaccumulator and non-accumulator plant species. The exploitation of genetic resources used in bioengineering strategies of plants is illuminating the function of sulfate transporters and key enzymes of the S assimilatory pathway in relation to Se accumulation and final metabolic fate. These strategies are providing the basic framework by which to resolve questions relating to the essentiality of Se in plants and the mechanisms utilized by Se hyperaccumulators to circumvent toxicity. In addition, such approaches may assist in the future application of genetically engineered Se accumulating plants for environmental renewal and human health objectives.

The effect of catch crop species on selenium availability for succeeding crops

“…In Experiment II, S fertilisation decreased Se uptake by onions when Se fertilisation was applied. The S status of the plant regulates the expression of the high affinity sulfate transporter genes as high concentrations of sulfate decreases transcription and potentially decreases Se uptake by plants (Sors et al 2005).…”

Characterization of selenium-enriched wheat by agronomic biofortification

“…In general, selenate is readily absorbed and transported within plants due to its similarity with sulphate; on the other hand, selenite is faster transformed into selenoaminoacids (Pedrero and Madrid 2009). Some of the Se-organic compounds identified in plant tissues are: selenomethionine, selenocysteine, selenocystathione, selenomethylselenomethionine, selenomethylselenocysteine, s e l e n o h o m o c y s t e i n e a n d g a m m a -g l u t a m y lselenomethylselenocysteine (Terry et al 2000;Sors et al 2005). Selenocysteine and selenomethionine can replace their sulphur analogues into the proteins, which may lead to phytotoxicity.…”

Molecular Mechanisms of Selenium Tolerance and Hyperaccumulation in Stanleya pinnata

“…Indistinguishable to most S enzymes, Se can be found in most S-containing metabolites (Leustek, 2002). In chloroplasts, the S assimilation pathway first reduces selenate to selenite, then selenide, which is enzymatically incorporated into selenocysteine (SeCys) and selenomethionine (SeMet; for review, see Terry et al, 2000;Ellis and Salt, 2003;Sors et al, 2005b). These two seleno-amino acids can be misincorporated into proteins, replacing Cys and Met, which causes Se toxicity Shrift, 1981, 1982;Stadtman, 1996).…”

“…Like A. bisulcatus, the Brassicaceae hyperaccumulator S. pinnata accumulates mainly MeSeCys Freeman et al, 2006b). In addition to the specific methylation of SeCys by SMT, it is not clear at this point which mechanisms may contribute to Se hyperaccumulation and tolerance in A. bisulcatus or other hyperaccumulators (Sors et al, 2005a(Sors et al, , 2005b(Sors et al, , 2009. Se hyperaccumulators do possess some unexplained physiological traits associated with growing on Se-enriched soils.…”