Se Accumulation (se + accumulation)

Distribution by Scientific Domains

Selected Abstracts

Rapid microalgal metabolism of selenate to volatile dimethylselenide

ABSTRACT An axenically cultured isolate of single-celled freshwater microalgae (Chlorella sp.) metabolized toxic selenate to volatile dimethylselenide at exceptionally high rates when transferred from mineral-nutrient solution to water for 24 h. The Se-volatilization rates were orders of magnitude higher than those similarly measured for wetland macroalgae and higher plants. Ninety percent of 20 µm selenate supplied to the microalgae incubated without nutrients was removed through accumulation and volatilization. Additions of 1 mm sulphate but not nitrate, inhibited Se accumulation and volatilization so that only 1.8% of the supplied selenate was removed. The microalgae cultured in nutrient solution without sulphate showed increased 35S-sulphate-transporter activity. Selenium K-edge X-ray absorption spectroscopy of selenate-treated microalgae cultured with or without mineral nutrients, showed that 87% of the selenate accumulated during 24 h was reductively metabolized to intermediate organic compounds such as selenomethionine and selenocystine. This is in complete contrast to higher plants that show very limited reduction of selenate. It appears that high rates of Se accumulation and volatilization by the sulphate-deprived microalgae resulted from reduced competition with chemically analogous sulphate ions for selenate uptake via up-regulated sulphate/selenate transporters and rapid reductive metabolism of selenate. Hyper-volatilization of selenate by microalgal cells may provide a novel detoxification response. [source]

Analysis of sulfur and selenium assimilation in Astragalus plants with varying capacities to accumulate selenium

Thomas G. Sors
Summary Several Astragalus species have the ability to hyperaccumulate selenium (Se) when growing in their native habitat. Given that the biochemical properties of Se parallel those of sulfur (S), we examined the activity of key S assimilatory enzymes ATP sulfurylase (ATPS), APS reductase (APR), and serine acetyltransferase (SAT), as well as selenocysteine methyltransferase (SMT), in eight Astragalus species with varying abilities to accumulate Se. Se hyperaccumulation was found to positively correlate with shoot accumulation of S -methylcysteine (MeCys) and Se -methylselenocysteine (MeSeCys), in addition to the level of SMT enzymatic activity. However, no correlation was observed between Se hyperaccumulation and ATPS, APR, and SAT activities in shoot tissue. Transgenic Arabidopsis thaliana overexpressing both ATPS and APR had a significant enhancement of selenate reduction as a proportion of total Se, whereas SAT overexpression resulted in only a slight increase in selenate reduction to organic forms. In general, total Se accumulation in shoots was lower in the transgenic plants overexpressing ATPS, PaAPR, and SAT. Root growth was adversely affected by selenate treatment in both ATPS and SAT overexpressors and less so in the PaAPR transgenic plants. Such observations support our conclusions that ATPS and APR are major contributors of selenate reduction in planta. However, Se hyperaccumulation in Astragalus is not driven by an overall increase in the capacity of these enzymes, but rather by either an increased Se flux through the S assimilatory pathway, generated by the biosynthesis of the sink metabolites MeCys or MeSeCys, or through an as yet unidentified Se assimilation pathway. [source]

Hyperaccumulation of selenium in hybrid striped bass: a functional food for aquaculture?

Abstract One method of increasing the value of aquacultured product is to produce fillets that are fortified with minerals that are beneficial to human health , that is enhance the functionality of an already healthy product. A good candidate mineral in this regard is selenium (Se) which is of vital importance to normal metabolism in humans. In order to evaluate the dose response and tissue accumulation of supplemental dietary Se, a study was undertaken with hybrid striped bass (HSB). Animals were fed diets supplemented with either organic (0,3.2 mg kg,1 as SelPlex®) or inorganic (0.2 and 0.4 mg kg,1 as sodium selenite) Se for 6 weeks. Because basal fishmeal-based diets contained 1.22 mg Se kg,1, doses of Se delivered equated to 1.22,4.42 mg kg,1. At trial end, greatest weight gain was observed in fish receiving 0.2 mg Se kg,1, irrespective of form (organic/inorganic). Se accumulation in HSB liver and fillet revealed a classical dose-response once a threshold level of 0.2 mg Se kg,1 was surpassed. Greatest tissue accumulation of Se was observed in fish fed the 3.2 mg Se kg,1 level (P > 0.0001). A 100 g portion of Se-enhanced HSB fillet would contain between 33 and 109 ,g Se, amounting to a dietary intake of between 25 and 80 ,g Se; a level that would satisfy present daily intake recommendations. Comparison of tissue Se levels indicated that the muscle provides a more conspicuous gauge of dietary Se dose-response than does liver. Dietary treatments of between 0.4 and 1.6 mg organic Se kg,1 reduced (P < 0.024) plasma glutathione peroxidase (GSH-Px) activity. No differences were observed in ceruloplasmin, lysozyme or GSH-Px activities between organic and inorganic Se when delivered at the 0.2 mg Se kg,1 level. Ceruloplasmin, lysozyme and GSH-Px levels were elevated (P , 0.025) in fish fed the diet containing 0.4 mg inorganic Se kg,1. [source]