Characterization of Selenium Accumulation, Localization and Speciation in Buckwheat–Implications for Biofortification

Abstract

Buckwheat is an important crop species in areas of selenium (Se) deficiency. To obtain better insight into their Se metabolic properties, common buckwheat (Fagopyrum esculentum) and tartary buckwheat (F. tataricum) were supplied with different concentrations of Se, supplied as selenate, selenite, or Astragalus bisulcatus plant extract (methyl-selenocysteine). Se was supplied at different developmental stages, with different durations, and in the presence or absence of potentially competing ions, sulfate, and phosphate. The plants were analyzed for growth, Se uptake, translocation, accumulation, as well as for Se localization and chemical speciation in the seed. Plants of both buckwheat species were supplied with 20 μM of either of the three forms of Se twice over their growth period. Both species accumulated 15–40 mg Se kg−1 DW in seeds, leaves and stems, from all three selenocompounds. X-ray microprobe analysis showed that the Se in seeds was localized in the embryo, in organic C-Se-C form(s) resembling selenomethionine, methyl-selenocysteine, and γ-glutamyl-methylselenocysteine standards. In short-term (2 and 24 h) Se uptake studies, both buckwheat species showed higher Se uptake rate and shoot Se accumulation when supplied with plant extract (methyl-selenocysteine), compared to selenite or selenate. In long-term (7 days) uptake studies, both species were resistant to selenite up to 50 μM. Tartary buckwheat was also resistant to selenate up to 75 μM Se, but >30 μM selenate inhibited common buckwheat growth. Selenium accumulation was similar in both species. When selenite was supplied, Se levels were 10–20-fold higher in root (up to 900 mg Se kg−1 DW) than shoot, but 4-fold higher in shoot (up to 1,200 mg Se kg−1 DW) than root for selenate-supplied plants. Additionally, sulfate and phosphate supply affected Se uptake, and conversely selenate enhanced S and P accumulation in both species. These findings have relevance for crop Se biofortification applications.

Agronomic biofortification with selenium improves the yield and nutraceutical quality in tomato under soilless conditions

“…The greatest absorption of this element might have taken place because it is chemically similar to sulfur. Thus, the roots easily absorb and metabolize them through high affinity sulfate transporters in the plasmatic membrane (Chomchan et al, 2017) and incorporate routes with plant proteins to form selenocysteine (SeCys) and seleno-methyonine (Se-Met) (White, 2016); then, they move without chemical modification through the xylem up to the leaves before reducing to other compounds (Jiang et al, 2018;Alves et al, 2020). Similar results were reported (Andrade et al, 2018) when increased Se content was found in fruit as a result of adding it in the nutritional solution.…”

Selenium in cereals: Insight into species of the element from total amount

“…In addition to increasing the total Se content, some attention has also been given to the effects of biofortification approaches on Se species and their bioaccessibilities (Gong et al., 2018). All three Se species, selenate, selenite, and Astragalus bisulcatus plant extract (MeSeCys), accumulated 15 to 40 mg Se kg −1 DW in the seeds of both common and tartary buckwheats, and the Se localized in the seed embryo was in the forms of SeMet, MeSeCys, and γ‐Glu‐MeSeCys (Jiang, El Mehdawi, et al., 2018). It is proposed that selenate is the most effective Se form for biofortification in soil, as selenite is rapidly adsorbed on clay colloids, rendering it poorly available to plants in many soils, and selenate is usually also more effective than selenite in foliar application (Lyons, 2018; Wang et al., 2020).…”

“…(Jiang, El Mehdawi, et al. (2018) obtained the Se K‐edge μXANES spectra of buckwheat seeds and performed least‐squares linear combination fitting (LCF) of the spectra at a range of 12,630 to 12,850 eV using a standard library including 52 Se compounds, and the resultant data indicated that organic Se species predominated (96% to 100%) in the buckwheat seeds, with the C‐Se‐C configuration attributed to SeMet, MeSeCys, and γ‐Glu‐MeSeCys. The XANES and HPLC‐ICP‐MS techniques had a good agreement in the analysis of SeMet in Se speciation for bulked rice grains.…”

Effects of selenium application concentration, period and method on the selenium content and grain yield of Tartary buckwheat of different varieties

“…Buckwheat is a potential selenium‐biofortified crop with rich nutrition and good health functions 8 . China is one of the main buckwheat‐producing countries.…”