Seleno-Amino Acid Found in
            <i>Astragalus bisulcatus</i>

Trelease, Sam F.; Somma, August A. Di; Jacobs, Allen L.

doi:10.1126/science.132.3427.618

Cited by 82 publications

(26 citation statements)

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“…The Se hyperaccumulator Astragalus species, such as Astragalus bisulcatus, may be an excellent source of genetic material from which to isolate genes to develop such plants. In the wild, A. bisulcatus can accumulate Se levels of up to 0.65% (w/w) dry weight in the shoots (Byers, 1936), predominantly as Se-methylseleno-Cys (Trelease et al, 1960), and similar results are readily obtained in plants grown hydroponically in the laboratory (Orser et al, 1999). Understanding Se uptake in A. bisulcatus might also allow the development of highly effective cultivars for phytoremediation (Salt et al, 1998).…”

mentioning

confidence: 84%

“…2A), whereas the spectra of the younger tissues show predominantly lower energy features that correspond to organic Se. We modeled this species using the spectrum of seleno-Met, but in the tissues, the organic form is most likely Se-methyl seleno-Cys (Trelease et al, 1960), which has a nearly identical near-edge spectrum to seleno-Met (because the immediate local environment of Se is identical). Fitting the tissue x-ray absorption spectra to spectra of selected standard compounds, together with estimation of total Se, allowed the quantitative estimation of the relative content of Se chemical forms in the different A. bisulcatus tissues (Fig.…”

Section: Se Speciation In a Bisulcatus Tissuesmentioning

confidence: 99%

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Chemical Form and Distribution of Selenium and Sulfur in the Selenium Hyperaccumulator Astragalus bisulcatus

et al. 2003

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In its natural habitat, Astragalus bisulcatus can accumulate up to 0.65% (w/w) selenium (Se) in its shoot dry weight. X-ray absorption spectroscopy has been used to examine the selenium biochemistry of A. bisulcatus. High concentrations of the nonprotein amino acid Se-methylseleno-cysteine (Cys) are present in young leaves of A. bisulcatus, but in more mature leaves, the Se-methylseleno-Cys concentration is lower, and selenate predominates. Seleno-Cys methyltransferase is the enzyme responsible for the biosynthesis of Se-methylseleno-Cys from seleno-Cys and S-methyl-methionine. Seleno-Cys methyltransferase is found to be expressed in A. bisulcatus leaves of all ages, and thus the biosynthesis of Se-methylselenoCys in older leaves is limited earlier in the metabolic pathway, probably by an inability to chemically reduce selenate. A comparative study of sulfur (S) and Se in A. bisulcatus using x-ray absorption spectroscopy indicates similar trends for oxidized and reduced Se and S species, but also indicates that the proportions of these differ significantly. These results also indicate that sulfate and selenate reduction are developmentally correlated, and they suggest important differences between S and Se biochemistries.Many selenium (Se) compounds are toxic to mammals at high concentrations, but Se is also an essential micronutrient, and low doses have been implicated in cancer prevention (Clark et al., 1996; Combs et al., 1997). Not all diets provide adequate Se, and an obvious and inexpensive way to provide Se may be to engineer food plants to accumulate higher levels of the element (Ip et al., 1994). The Se hyperaccumulator Astragalus species, such as Astragalus bisulcatus, may be an excellent source of genetic material from which to isolate genes to develop such plants. In the wild, A. bisulcatus can accumulate Se levels of up to 0.65% (w/w) dry weight in the shoots (Byers, 1936), predominantly as Se-methylseleno-Cys (Trelease et al., 1960), and similar results are readily obtained in plants grown hydroponically in the laboratory (Orser et al., 1999). Understanding Se uptake in A. bisulcatus might also allow the development of highly effective cultivars for phytoremediation (Salt et al., 1998).A critical step in the biotransformation of selenate is the initial two-electron reduction to selenite. Hyperaccumulating plants might achieve this in at least three different ways: by substituting selenate into the sulfate reduction pathway (reduction by ATP sulfurylase/adenyl sulfate (APS) reductase; Shrift, 1969;Setya et al., 1996), by substituting selenate into the nitrate uptake pathway (microbial nitrate reductases can reduce selenate; Sabaty et al., 2001), or by a specific selenate reductase. For nonhyperaccumulating plants, there is good evidence that selenate reduction occurs via substitution for sulfate in the ATP sulfurylase/APS reductase system, and that this is the ratelimiting step in selenate transformation (Shrift, 1969;Shaw and Anderson, 1974; Burnell, 1981; Pilon-Smits et al., 1999). In these spe...

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mentioning

confidence: 84%

Section: Se Speciation In a Bisulcatus Tissuesmentioning

confidence: 99%

Chemical Form and Distribution of Selenium and Sulfur in the Selenium Hyperaccumulator Astragalus bisulcatus

et al. 2003

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“…(12,13). In A. lenitiginosuls, about 19 % of the radioactivity in the ethanol extract emerged in the neutral or basic fraction and probably contained Se-nmetlhvlseleiionoethionine wvhich has been idlentified in leaves of this nonaccumulator species (17).…”

Section: Discussionmentioning

confidence: 99%

Transport of Selenate and Selenite into Astragalus Roots

Shrift

Ulrich

1969

Plant Physiol.

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Abstract. After giveln an accumiiulation ratio greater thani one, but evidence for an active transport of this ionl is unclear because of siome apparent non-biological uptake (15). Since selenate and selenite are both assimilable ions (1,9,10,11,12,16,17), accunmulationi of selenium by these roots could be either ani accumulation of the ions against an electrochemical gradient or an accumulation of seleno-metabolites whose synthesis is energy dependent. The data presented here will show that selenate can accumulate largely unchanged in excised roots of 2 species of Astragaluts; much of the selenite however, is changed into other selenium comll)ounds or possibly adsorbed. Materials and MethodsPreparationi a(id Growth of Seedlings. Techni(quies described earlier for the preparation and growth of seedlings (15) were used in these 'experiments but moldified as follows: after germination in the dark for 2 days, (21-22°), the seedlings were laterally illunminated before a bank of fluorescent lights at an intensity of 4300 ft-c for 3 more days (22-25°).This research w-as supported by Public Health Research Grant GM 09086 from the National Institutes of Healtlh.ion Absorption Procedure. The preparation of root tips and the conditions for the uptake of selenate and selenite were identical with the procedures de-scribed earlier (15).Fractionation of Radioactive Tissues. At the end of thle uptake period, roots were blotted on filter paper and weighed rapidly. For nleasurement of the total radioactivity abs,orbed, roots were prepared as described earlier (15). For measurement of the ethanol insoluble fraction, the weighed roots were suiccessively extracted with 70 % (v/v) ethanol 6 to 8 times until the radioactivity in the ethanol extract was approximately 1 % of the radioactivity in the first extraction. The acid digestion mixture was slowly added to the extracted roots to avoid foaming, and the extracted roots were digested as described earlier (15). A precipitate which formed in the digest of the ethanol-extracted roots had no effect on the counts. Samples for total and ethanol-insoluble radioactivity were run in triplicate.For biochemical analysis of soluble radioactive components, weighed roots from 24 colanders were pooled and extracted with 48 ml of 70 % ethanol.Column Chromatography. The use of Dowex-1-Cl coltumns for identification of selenite and selenate has been described previously ( 12).Paper Chromatographiy. XVhatman No. 1 was used throughout. The following solvent systems were used: No.

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“…Toxicity symptoms include chlorosis, stunting and yellowing of the leaves. The mechanism of toxicity is thought to be indiscriminate replacement of S by Se in proteins and nucleic acids with disruptions in metabolism (Trelease et al 1960). Wan et al (1988) measured 30 to 85% reductions in shoot weight of alfalfa grown in soils containing 1.5 ppm Se.…”

Section: F1-29mentioning

confidence: 99%

Remedial investigation/feasibility study of the Clinch River/Poplar Creek Operable Unit. Volume 3. Risk assessment information. Appendixes E, F

1996

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Seleno-Amino Acid Found in Astragalus bisulcatus

Abstract: Ion-exchange and filter-paper columns were used in a separation of amino acids from an extract of Astragalus bisulcatus. Two amino acids were identified, S-methylcysteine and Se-methylselenocysteine.

Cited by 82 publications

References 4 publications

Chemical Form and Distribution of Selenium and Sulfur in the Selenium Hyperaccumulator Astragalus bisulcatus

Chemical Form and Distribution of Selenium and Sulfur in the Selenium Hyperaccumulator Astragalus bisulcatus

Transport of Selenate and Selenite into Astragalus Roots

Remedial investigation/feasibility study of the Clinch River/Poplar Creek Operable Unit. Volume 3. Risk assessment information. Appendixes E, F

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