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Selenium speciation and content of oat kernels in response to foliar and soil selenium fertilization
Published in Gary Bañuelos, Zhi-Qing Lin, Dongli Liang, Xue-bin Yin, Selenium Research for Environment and Human Health: Perspectives, Technologies and Advancements, 2019
J.H. Li, A.N. Guo, Q. Xia, X.J. Dai, Zh.Q. Gao, Z.H.P. Yang*, C.H.Y. Wang*
Selenium content was between 40 and 125 μg/kg in Se-enriched oats. This level was an appropriate concentration of Se in oat kernels according to the National Standard (DB/T 22499-2008) of 100–300 μg/kg and recommended human intake of 50 μg per day. Results showed that foliar and soil application of Se strongly influenced the total Se contents in kernels (Table 1). The lowest total Se content in kernels was found in control, and the highest Se accumulation was recorded in the SA+FA treatment. The FA treatment had higher grain total Se contents than the SA treatment. There were four identified peaks in the chromatograph of the sample, including selenocystine (SeCys2), methyl-selenocysteine (MeSeCys), Se4+, and selenomethionine (SeMet). The peak at retention time of 350,000 s was not identified, because it did not match with any one of the Se standard compounds (Fig. 1). Inorganic Se species, such as selenate (SeO42−) and selenite (SeO32−), are generally considered to be the most bioavailable and potentially toxic Se species (Fordyce et al. 2005). Organic Se species such as SeCys2, SeMet, and MeSeCys are generally considered less toxic (Rayman et al. 2008, Zhu et al. 2009). Furthermore, Se bioaccessibility greatly depends on Se chemical species (Fairweathertait et al. 2010). It is well known that selenocysteine methyltransferase (SMT) catalyzes the methylation reaction of selenocysteine (SeCys) and Se-methylselenocysteine. Se-methylselenocysteine is a natural Se-containing amino acid, and a preferred source of Se intake for human health according to recommendation by CFDA (GB 14880-2012, National Standard for Nutritional Fortification Substances by Industries, Ministry of Health of P.R. China). Previous studies also suggested that Se-methyl-selenocysteine has higher anti-cancer activity, because it can induce apoptosis of cancer cells, inhibit tumor vascular development, and prevent early cancer cell expansion (Chen et al. 2012, Cao et al. 2014). Therefore, future research on Se-methyl-selenocysteine accumulation in oat kernels will be beneficial.
Understanding selenium metabolism in plants and its role as a beneficial element
Published in Critical Reviews in Environmental Science and Technology, 2019
Reshu Chauhan, Surabhi Awasthi, Sudhakar Srivastava, Sanjay Dwivedi, Elizabeth A. H. Pilon-Smits, Om P. Dhankher, Rudra D. Tripathi
Crops are the major source of dietary Se intake for many of the human populations worldwide and thus, Se enriched crops might be envisioned as a tool to counteract Se deficiency (Schiavon & Pilon-Smits, 2017). Plants readily take up and metabolize Se. Different plant species have been found to accumulate a number of Se containing metabolites (Figure 1): selenomethionine (SeMet), SeCys, Seleno-methylselenocysteine (SeMeSeCys), methylselenocysteine (MeSeCys), selenotaurine, selenobetaine, selenoecholine, dimethylselenine, dimethyldiselenide (DMDSe), and trimethylselenium (Kabata-Pendias, 2011). However, the present knowledge states that Se is not an essential part of proteins in plants (Pilon-Smits, Quinn, Tapken, Malagoli, & Schiavon, 2009) and hence, plants Se metabolism in plants occurs nonspecifically via sulfur metabolic pathways (Schiavon & Pilon-Smits, 2017). It cannot be excluded that in future studies some plant species might be found to require Se, or to contain essential selenoproteins. The essentiality of Se for plants could be conclusively proven in experiments where plants are shown not to survive under totally Se-free conditions (Stadtman, 1996), or if proteins/enzymes containing SeCys as an integral amino acid (incorporated via translation process) can be discovered (De Filippis, 2010). There are several green (eukaryotic) algae, including Chlamydomonas reinhardtii that possess a GPx homolog with SeCys and also have UGA opal codon decoding SeCys tRNA (Fu et al., 2002). Algae contain several selenoproteins as evidenced by identification of 12 selenoproteins in C. reinhardtii (Grossman et al., 2007). Other algae (about 33 algae) are also known to require Se for selenoproteins, such as Cyanidioschyzon (Cyanidiaceae), Ostreococcus (Prasinophyceae) and Emiliania huxleyi (Haptophytes) (Schiavon & Pilon-Smits, 2017). The alga Ulva australis also has specific SeVI transport system (Schiavon et al., 2012). However, algae have been classified in different ways either exclusively or partly in Protista and Plantae Kingdoms (Whittaker & Margulis, 1978). Hence, essentiality of Se in algae cannot be considered as a hint of Se being essential in plants too. It appears that higher plants might have lost essential Se metabolism or the identification of selenoproteins might still be awaiting in plants (Lobanov et al., 2009).