Selenium Species Determination in Selenium-Enriched Pumpkin (Cucurbita pepo L.) Seeds by HPLC-UV-HG-AFS

Implementing micronutrient fortification programs as a potential practical contribution to achieving sustainable diets

Due to sustainability concerns related to current diets and environmental challenges, it is crucial to have sound policies to protect human and planetary health. It is proposed that sustainable diets will improve public health and food security and decrease the food system's effect on the environment. Micronutrient deficiencies are a well-known major public health concern. One-third to half of the world's population suffers from nutrient deficiencies, which have a negative impact on society in terms of unrealised potential and lost economic productivity. Large-scale fortification with different micronutrients has been found to be a useful strategy to improve public health. As a cost-effective strategy to improve micronutrient deficiency, this review explores the role of micronutrient fortification programmes in ensuring the nutritional quality (and affordability) of diets that are adjusted to help ensure environmental sustainability in the face of climate change, for example by replacing some animal-sourced foods with nutrient-dense, plant-sourced foods fortified with the micronutrients commonly supplied by animal-sourced foods. Additionally, micronutrient fortification considers food preferences based on the dimensions of a culturally sustainable diet. Thus, we conclude that investing in micronutrient fortification could play a significant role in preventing and controlling micronutrient deficiencies, improving diets and being environmentally, culturally and economically sustainable.

Selenium Species and Fractions in the Rock-Soil-Plant Interface of Maize (Zea mays L.) Grown in a Natural Ultra-Rich Se Environment

Selenium (Se) enrichments or deficiency in maize (Zea mays L.), one of the world's most important staple foods and livestock feeds, can significantly affect many people's diets, as Se is essential though harmful in excess. In particular, Se-rich maize seems to have been one of the factors that led to an outbreak of selenosis in the 1980s in Naore Valley in Ziyang County, China. Thus, this region's geological and pedological enrichment offers some insight into the behavior of Se in naturally Se-rich crops. This study examined total Se and Se species in the grains, leaves, stalks, and roots of 11 maize plant samples, Se fractions of soils around the rhizosphere, and representative parent rock materials from Naore Valley. The results showed that total Se concentrations in the collected samples were observed in descending order of soil > leaf > root > grain > stalk. The predominant Se species detected in maize plants was SeMet. Inorganic Se forms, mainly Se(VI), decreased from root to grain, and were possibly assimilated into organic forms. Se(IV) was barely present. The natural increases of Se concentration in soils mainly affected leaf and root dry-weight biomasses of maize. In addition, Se distribution in soils markedly correlated with the weathered Se-rich bedrocks. The analyzed soils had lower Se bioavailability than rocks, with Se accumulated predominantly as recalcitrant residual Se. Thus, the maize plants grown in these natural Se-rich soils may uptake Se mainly from the oxidation and leaching of the remaining organic-sulfide-bound Se fractions. A viewpoint shift from natural Se-rich soils as menaces to possibilities for growing Se-rich agricultural products is also discussed in this study.

Exploring the new dimensions of selenium research to understand the underlying mechanism of its uptake, translocation, and accumulation

Selenium (Se) is a vital mineral for both plants and animals. It is widely distributed on the earth's crust and is taken up by the plants as selenite or selenate. Plants substantially vary in their physiological response to Se. The amount of Se in edible plants is genetically controlled. Its availability can be determined by measuring its phytoavailability in soil. The low concentration of Se in plants can help them in combating stress, whereas higher concentrations can be detrimental to plant health and in most cases it is toxic. Thus, solving the double-edged sword problem of nutritional Se deficiency and its elevated concentrations in environment requires a better understanding of Se uptake and metabolism in plants. The studies on Se uptake and metabolism can help in genetic biofortification of Se in plants and also assist in phytoremediation. Moreover, Se uptake and transport, especially biochemical pathways of assimilation and incorporation into proteins, offers striking mechanisms of toxicity and tolerance. These developments have led to a revival of Se research in higher plants with significant break throughs being made in the previous years. This review explores the new dimensions of Se research with major emphasis on key research events related to Se undertaken in last few years. Further, we also discussed future possibilities in Se research for crop improvement.

The use of biofortification for production of selenium enriched garden pea

Biofortification of crops with selenium is one of the possible manners on how to increase selenium intake by humans. The effect of selenium fertilization in relation to selenium enrichment of pea and following the phytotoxicity symptoms in garden pea plants was studied. Pot experiments were established with a control variant without selenium addition and four variants where selenium was applied as sodium selenate into the soil in four different concentrations (1 - 6 mg Se.kg-1) before seeding. Garden pea was grown in pots for 60 days and then plant material was dried and submitted to analysis. The total content of selenium was determined by the ZET-AAS method in the roots, above-ground parts of the plant (stems, leaves, extracted pods), and in seeds of a pea. Dean-Dixon´s test and paired t-test (α = 0.05) were used for statistical evaluation of the results. Transfer factors were calculated as a ratio between selenium content (mg.kg-1) in individual plant material and soil. Transfer indexes were calculated as a ratio between selenium content (mg.kg-1) in seeds and roots. The results showed that with the increasing addition of the Se to the soil, its contents in all parts of the plant proportionally increased. The content of the Se increased in the roots 43 to 173-fold, in the above-ground parts 79 to 372-fold, and in the seeds Se was accumulated 130 to 415 times more compared to control. Transfer factors and transport indexes were expressed. Transfer factors for pea varied from 11.05 to 19.25 in the case of Se transfer to the whole pea biomass. In the case of the Se transfer from soil to pea seeds, the highest transfer showed variant with addition 1 mg Se.kg-1 and the transfer factor gradually decreased with increasing addition of Se. Based on the amount of biomass produced, the experiments statistically confirmed the phytotoxicity of higher doses (4 and 6 mg Se.kg-1) of selenium to plants. The highest transport index values are shown variants with the Se addition 1 and 2 mg Se.kg-1 (2.03 and 1.77, respectively). In these variants, Se was used the most efficiently. Our results showed that the best biofortification results were obtained in experimental variants with the lower selenium additions (1 and 2 mg Se.kg-1).

Response of Pumpkin to Different Concentrations and Forms of Selenium and Iodine, and their Combinations

The elements selenium (Se) and iodine (I) are both crucial for the normal functioning of the thyroid. Biofortification with these elements is particularly feasible in areas where they show a deficit. Iodine and selenium can have positive effects on different plants when applied at the correct concentrations. The effects of their simultaneous addition on plant physiology and biochemistry, as well as on seed germination and sprout biomass, were studied in pumpkin (Cucurbita pepo L. ssp. pepo). To study the effect of Se and I on sprouts, sprouts were grown from seeds soaked in solutions of different forms of Se, I and their combination in the growth chamber experiment. In the field experiment, pumpkins plants were foliarly treated with the same concentrations and forms of Se and I. The combination of Se and I treatments enhanced the germination of the soaked seeds, with no significant differences between Se and I treatments for sprout mass. The yield of pumpkins and seed production were unaffected by Se and I foliar application. The anthocyanin levels and respiratory potential measured via the electron transport system's activity showed different patterns according to treatments and plant parts (sprouts, leaves, seeds). The redistribution of Se and I from seeds to sprouts was significant. The accumulation of Se was higher in sprouts from the seeds treated with Se together with I, compared to sprouts from the seeds treated with Se alone. Interactions between Se and I were also noted in the seeds, which developed in the treated plants.

Legume biofortification is an underexploited strategy for combatting hidden hunger

Legumes are the world's primary source of dietary protein and are particularly important for those in developing economies. However, the biofortification potential of legumes remains underexploited. Legumes offer a diversity of micronutrients and amino acids, exceeding or complementing the profiles of cereals. As such, the enhancement of legume nutritional composition presents an appealing target for addressing the "hidden hunger" of global micronutrient malnutrition. Affecting ~2 billion people, micronutrient malnutrition causes severe health effects ranging from stunted growth to reduced lifespan. An increased availability of micronutrient-enriched legumes, particularly to those in socio-economically deprived areas, would serve the dual functions of ameliorating hidden hunger and increasing the positive health effects associated with legumes. Here, we give an updated overview of breeding approaches for the nutritional improvement of legumes, and crucially, we highlight the importance of considering nutritional improvement in a wider ecological context. Specifically, we review the potential of the legume microbiome for agronomic trait improvement and highlight the need for increased genetic, biochemical, and environmental data resources. Finally, we state that such resources should be complemented by an international and multidisciplinary initiative that will drive crop improvement and, most importantly, ensure that research outcomes benefit those who need them most.

Selenium accumulation by plants

BACKGROUND

Selenium (Se) is an essential mineral element for animals and humans, which they acquire largely from plants. The Se concentration in edible plants is determined by the Se phytoavailability in soils. Selenium is not an essential element for plants, but excessive Se can be toxic. Thus, soil Se phytoavailability determines the ecology of plants. Most plants cannot grow on seleniferous soils. Most plants that grow on seleniferous soils accumulate <100 mg Se kg(-1) dry matter and cannot tolerate greater tissue Se concentrations. However, some plant species have evolved tolerance to Se, and commonly accumulate tissue Se concentrations >100 mg Se kg(-1) dry matter. These plants are considered to be Se accumulators. Some species can even accumulate Se concentrations of 1000-15 000 mg Se kg(-1 )dry matter and are called Se hyperaccumulators.

SCOPE

This article provides an overview of Se uptake, translocation and metabolism in plants and highlights the possible genetic basis of differences in these between and within plant species. The review focuses initially on adaptations allowing plants to tolerate large Se concentrations in their tissues and the evolutionary origin of species that hyperaccumulate Se. It then describes the variation in tissue Se concentrations between and within angiosperm species and identifies genes encoding enzymes limiting the rates of incorporation of Se into organic compounds and chromosomal loci that might enable the development of crops with greater Se concentrations in their edible portions. Finally, it discusses transgenic approaches enabling plants to tolerate greater Se concentrations in the rhizosphere and in their tissues.

CONCLUSIONS

The trait of Se hyperaccumulation has evolved several times in separate angiosperm clades. The ability to tolerate large tissue Se concentrations is primarily related to the ability to divert Se away from the accumulation of selenocysteine and selenomethionine, which might be incorporated into non-functional proteins, through the synthesis of less toxic Se metabilites. There is potential to breed or select crops with greater Se concentrations in their edible tissues, which might be used to increase dietary Se intakes of animals and humans.

Selenium species in the roots and shoots of chickpea plants treated with different concentrations of sodium selenite

The trace element selenium has an essential role for human health. It is involved in redox center functions, and it is related to the immune system response. Legumes are among the main suppliers of selenium into the human food chain. Not only Se concentration as such but also more the chemical species of Se is of higher importance for successful Se supply to the human diet and its bioavailability. The current study was focused on the investigation of the Se species present in chickpea plants exposed to 0, 10, 25, 50, and 100 μM selenite in short- and long-term treatment studies. The linear increase of total Se concentration could be linked to the increased concentrations of Se exposure. The selenium species (SeMet, SeCys, selenite, selenate, GPx) detected in varying concentrations in shoots and roots depend on the exposure's concentration and duration. The investigation showed that chickpea can accumulate Se in favorable concentrations and its transformation to bioavailable Se species may have positive impacts on human health and aid to implement Se into the diet.

Selenium species and their distribution in freshwater fish from Argentina

The distribution and speciation of selenium (Se) in freshwater fish (muscle and liver tissue) from lakes in Argentina was investigated. Three introduced species, brown trout (Salmo trutta), rainbow trout (Oncorhynchus mykiss) and brook trout (Salvelinus fontinalis), and one native species, creole perch (Percichthys trucha), were investigated. Values for total selenium in muscle ranged from 0.66 to 1.61 μg/g, while in the liver, concentrations were much higher, from 4.46 to 73.71 μg/g on a dry matter basis. Separation of soluble Se species (SeCys(2), selenomethionine (SeMet), SeMeSeCys, selenite and selenate) was achieved by ion exchange chromatography and detection was performed by inductively coupled plasma-mass spectrometry. The results showed that in fish muscle, from 47 to 55 % of selenium was soluble and the only Se species identified was SeMet, which represented around 80 % of soluble Se, while in the liver, the amount of soluble Se ranged from 61 to 76 % and the percentage of species identified (SeMet and SeCys(2)) was much lower and ranged from 8 to 17 % of soluble Se.

Bioavailability of selenium from selenium-enriched green onions (Allium fistulosum) and chives (Allium schoenoprasum) after ‘in vitro’ gastrointestinal digestion

Three sample preparation methods--proteolysis to determine the initial species distribution, and an in vitro gastric and gastrointestinal digestion to assess the bioavailability of selenium--were applied to extract the selenium from selenized green onion and chive samples. Ion exchange chromatography was coupled to a high-performance liquid chromatography-ICP-MS system to analyze the selenium species of Allium samples. The difference in the selenium accumulation capability of green onions and chives was significant. Chive accumulated a one order of magnitude higher amount of selenium than did green onion. After proteolysis of both types of Allium plants, high amounts of organic selenium species such as MeSeCys, SeCys2 and SeMet became accessible. In the case of Se(VI)-enrichment, selenate was the main species in the proteolytic extract. After simulating the human digestion, the organic species were just slightly bioavailable compared with the results from proteolysis. The inorganic selenium content of the selenized samples increased significantly and SeOMet could be detected from the extracts. As an effect of the significant pH change between the gastric and the intestinal tracts, two oxidation processes took place: selenite oxidized to selenate, while SeMet oxidized to SeOMet.

Food-chain selenium and human health: spotlight on speciation

There is a growing appreciation that it is not just the total intake of dietary Se that is important to health but that the species of Se ingested may also be important. The present review attempts to catalogue what is known about Se species in foods and supplements and the health effects in which they are implicated. The biosynthetic pathways involved in Se assimilation by plants and the way in which Se species are metabolised in animals are presented in order to give an insight into the species likely to be present in plant and animal foods. Known data on the species of Se in the food chain and in food supplements are tabulated along with their concentrations and the analytical methodology used. The latter is important, since identification that is only based on retention-time matching with authentic standards must be considered as tentative: for evidence of structural confirmation, fragmentation of the molecular ion in addition to MS data is required. Bioavailability, as normally defined, is higher for organic Se species. Health effects, both beneficial and toxic, thought to be associated with specific Se species are described. Potent anti-tumour effects have been attributed to the low-molecular-weight species,Se-methyl-selenocysteine and its γ-glutamyl-derivative, found in a number of edible plants of theAlliumandBrassicafamilies. There remain considerable gaps in our knowledge of the forms of Se that naturally occur in foods. Without adequate knowledge of Se speciation, false conclusions may be drawn when assessing Se requirements for optimal health.