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• How cadmium (Cd) tolerance in rice is regulated remains poorly understood. We used a forward genetic approach to investigate Cd tolerance in rice. • Using a root elongation assay, we isolated a rice mutant with enhanced Cd tolerance, cadt1, from an ethyl methanesulphonate (EMS)-mutagenized population of a widely grown Indica cultivar. The mutant accumulated more Cd in roots but not in shoots and grains. Using genomic resequencing and complementation, we identified OsCADT1 as the causal gene for the mutant phenotype, which encodes a putative serine hydroxymethyltransferase. • OsCADT1 protein was localized to the nucleus and the OsCADT1 gene was expressed in both roots and shoots. OsCADT1 mutation resulted in higher sulphur and selenium accumulation in the shoots and grains. Selenate influx in cadt1 was 2.4 times that of the wild-type. The mutant showed higher expression of the sulphate/selenate transporter gene OsSULTR1;1 and the sulphur-deficiency-inducible gene OsSDI1. Thiol compounds including cysteine, glutathione and phytochelatins were significantly increased in the mutant, underlying its increased Cd tolerance. Growth and grain biomass were little affected. • The results suggest that OsCADT1 acts as a negative regulator of sulphate/selenate uptake and assimilation. OsCADT1 mutation increases Cd tolerance and enriches selenium in rice grains, providing a novel solution for selenium biofortification.

The importance of selenium (Se) for medicine, industry and the environment is increasingly apparent. Se is essential for many species, including humans, but toxic at elevated concentrations. Plant Se accumulation and volatilization may be applied in crop biofortification and phytoremediation. Topics covered here include beneficial and toxic effects of Se on plants, mechanisms of Se accumulation and tolerance in plants and algae, Se hyperaccumulation, and ecological and evolutionary aspects of these processes. Plant species differ in the concentration and forms of Se accumulated, Se partitioning at the whole-plant and tissue levels, and the capacity to distinguish Se from sulfur. Mechanisms of Se hyperaccumulation and its adaptive significance appear to involve constitutive up-regulation of sulfate/selenate uptake and assimilation, associated with elevated concentrations of defense-related hormones. Hyperaccumulation has evolved independently in at least three plant families, probably as an elemental defense mechanism and perhaps mediating elemental allelopathy. Elevated plant Se protects plants from generalist herbivores and pathogens, but also gives rise to the evolution of Seresistant specialists. Plant Se accumulation affects ecological interactions with herbivores, pollinators, neighboring plants, and microbes. Hyperaccumulation tends to negatively affect Sesensitive ecological partners while facilitating Se-resistant partners, potentially affecting species composition and Se cycling in seleniferous ecosystems.

Key messageKnowledge of genetic variation, genetics, physiology/molecular basis and breeding (including biotechnological approaches) for biofortification and bioavailability for Zn, Fe and Se will help in developing nutritionally improved wheat.Biofortification of wheat cultivars for micronutrients is a priority research area for wheat geneticists and breeders. It is known that during breeding of wheat cultivars for productivity and quality, a loss of grain micronutrient contents occurred, leading to decline in nutritional quality of wheat grain. Keeping this in view, major efforts have been made during the last two decades for achieving biofortification and bioavailability of wheat grain for micronutrients including Zn, Fe and Se. The studies conducted so far included evaluation of gene pools for contents of not only grain micronutrients as above, but also for phytic acid (PA) or phytate and phytase, so that, while breeding for the micronutrients, bioavailability is also improved. For this purpose, QTL interval mapping and GWAS were carried out to identify QTLs/genes and associated markers that were subsequently used for marker-assisted selection (MAS) during breeding for biofortification. Studies have also been conducted to understand the physiology and molecular basis of biofortification, which also allowed identification of genes for uptake, transport and storage of micronutrients. Transgenics using transgenes have also been produced. The breeding efforts led to the development of at least a dozen cultivars with improved contents of grain micronutrients, although land area occupied by these biofortified cultivars is still marginal. In this review, the available information on different aspects of biofortification and bioavailability of micronutrients including Zn, Fe and Se in wheat has been reviewed for the benefit of those, who plan to start work or already conducting research in this area.

Selenium (Se) is an essential trace element for humans and other animals. The human body mainly acquires Se from plant foods, especially cereal grains. Rice is the staple food for more than half of the world’s population. Increasing the Se concentration of rice grains can increase the average human dietary Se intake. This review summarizes recent advances in the molecular mechanisms of Se uptake, transport, subcellular distribution, retranslocation, volatilization, and Se-containing protein degradation in plants, especially rice. The strategies for improving Se concentration in rice grains by increasing Se accumulation, reducing Se volatilization, and optimizing Se form were proposed, which provide new insight into Se biofortification in rice by improving the utilization efficiency of Se.

Selenium (Se) is an essential micronutrient for diverse organisms such as mammals, bacteria, some insects and nematodes, archaea, and algae, as it is involved in a large number of physiological and metabolic processes and is part of approximately 25 selenoproteins in mammals. In plants, Se has no essential metabolic role, high concentrations of inorganic Se can lead to the formation of Se-amino acids, and its incorporation into selenoproteins can generate toxicity. Conversely, low doses of Se can trigger a variety of beneficial effects as an antioxidant, antimicrobial, or stress-modulating agent without being an essential element. Therefore, Se can generate toxicity depending on the dose and the chemical form in which it is supplied. Selenium nanoparticles (SeNPs) have emerged as an approach to reduce this negative effect and improve its biological properties. In turn, SeNPs have a wide range of potential advantages, making them an alternative for areas such as agriculture and food technology. This review focuses on the use of SeNPs and their different applications as antimicrobial agents, growth promoters, crop biofortification, and nutraceuticals in agriculture. In addition, the utilization of SeNPs in the generation of packaging with antioxidant and antimicrobial traits and Se enrichment of animal source foods for human consumption as part of food technology is addressed. Additionally, possible action mechanisms and potential adverse effects are discussed. The concentration, size, and synthesis method of SeNPs are determining factors of their biological properties.

There are a lack of systematic studies comparing the effects of foliar-applied selenium (Se) with different Se sources at different growth stages in wheat. Herein, we biofortified wheat via the foliar application of selenite and selenate at different rates and different stages under field conditions. Results showed that foliar-applied selenate and selenite had no significant effect either on wheat biomass or grain yield ( p < 0.05). Selenium distribution in different parts of wheat plant ranked decrease as leaf > root > grain > glume > stem with selenite treatment, and it appeared in the decline order as leaf > grain > glume > stem > root with selenate treatment. These results suggested that biofortification with selenate caused, relatively to selenite, a higher accumulation of Se in grains. Foliar application of Se of either selenate or selenite at pre-filling stage was superior in improving the Se concentration of wheat grains than application at pre-flowering stage. Meanwhile, organic Se comprised about 72–93% of total Se in wheat grains, which was reduced by 5.8% at high Se rate (100 g ha −1 ), irrespective of the forms of Se or stages applied. The organic Se proportion in wheat grains was 9% higher with the selenate treatment than with the selenite treatment. Selenomethionine (SeMet) was the main organic species (67–86%) in wheat grains, followed by selenocysteine (SeCys 2 ). In summary, our results indicate that Se biofortification of wheat is most effective with 20 g ha −1 selenate foliar-applied at pre-filling stage.

The diets of over two-thirds of the world's population lack one or more essential mineral elements. This can be remedied through dietary diversification, mineral supplementation, food fortification, or increasing the concentrations and/or bioavailability of mineral elements in produce (biofortification). This article reviews aspects of soil science, plant physiology and genetics underpinning crop biofortification strategies, as well as agronomic and genetic approaches currently taken to biofortify food crops with the mineral elements most commonly lacking in human diets: iron (Fe), zinc (Zn), copper (Cu), calcium (Ca), magnesium (Mg), iodine (I) and selenium (Se). Two complementary approaches have been successfully adopted to increase the concentrations of bioavailable mineral elements in food crops. First, agronomic approaches optimizing the application of mineral fertilizers and/or improving the solubilization and mobilization of mineral elements in the soil have been implemented. Secondly, crops have been developed with: increased abilities to acquire mineral elements and accumulate them in edible tissues; increased concentrations of 'promoter' substances, such as ascorbate, f-carotene and cysteine-rich polypeptides which stimulate the absorption of essential mineral elements by the gut; and reduced concentrations of 'antinutrients', such as oxalate, polyphenolics or phytate, which interfere with their absorption. These approaches are addressing mineral malnutrition in humans globally.

Selenium (Se) is an essential trace element, which represents an integral part of glutathione peroxidase and other selenoproteins involved in the protection of cells against oxidative damage. Selenomethionine (SeMet), selenocysteine (SeCys), and methylselenocysteine (MeSeCys) are the forms of Se that occur in living systems. Se-containing compounds have been found to reduce carcinogenesis of animal models, and dietary supplemental Se might decrease cancer risk. Se is mainly taken up by plant roots in the form of selenate via high-affinity sulfate transporters. Consequently, owing to the chemical similarity between Se and sulfur (S), the availability of S plays a key role in Se accumulation owing to competition effects in absorption, translocation, and assimilation. Moreover, naturally occurring S-containing compounds have proven to exhibit anticancer potential, in addition to other bioactivities. Therefore, it is important to understand the interaction between Se and S, which depends on Se/S ratio in the plant or/and in the growth medium. Brassicaceae (also known as cabbage or mustard family) is an important family of flowering plants that are grown worldwide and have a vital role in agriculture and populations’ health. In this review we discuss the distribution and further interactions between S and Se in Brassicaceae and provide several examples of Se or Se/S biofortifications’ experiments in brassica vegetables that induced the chemopreventive effects of these crops by enhancing the production of Se- or/and S-containing natural compounds. Extensive further research is required to understand Se/S uptake, translocation, and assimilation and to investigate their potential role in producing anticancer drugs.

Selenium (Se) is an essential nutrient for humans, due to its antioxidant properties, whereas, to date, its essentiality to plants still remains to be demonstrated. Nevertheless, if added to the cultivation substrate, plants growth resulted enhanced. However, the concentration of Se in agricultural soils is very variable, ranging from 0.01 mg kg up to 10 mg kg in seleniferous areas. Therefore several studies have been performed aimed at bio-fortifying crops with Se and the approaches exploited were mainly based on the application of Se fertilizers. The aim of the present research was to assess the biofortification potential of Se in hydroponically grown strawberry fruits and its effects on qualitative parameters and nutraceutical compounds. The supplementation with Se did not negatively affect the growth and the yield of strawberries, and induced an accumulation of Se in fruits. Furthermore, the metabolomic analyses highlighted an increase in flavonoid and polyphenol compounds, which contributes to the organoleptic features and antioxidant capacity of fruits; in addition, an increase in the fruits sweetness also was detected in biofortified strawberries. In conclusion, based on our observations, strawberry plants seem a good target for Se biofortification, thus allowing the increase in the human intake of this essential micronutrient.

Selenium (Se) biofortified wheat could enhance human health by providing essential Selenium. Different nitrogen application rates (0, 60, 120, 180, 240 and 300 kg N ha –1 ) on soil Se speciations and contents, the differences of Se accumulation and yield of triticales were investigated. The concerntration of total Se, water-soluble Se (SOL Se ), and exchangeable Se (EXC Se ) in 0–20 cm and 20–40 cm soil layers showed an increasing trend from anthesis to maturity, and decreasing tendency as nitrogen application increasing. TZ-8293 compared to TH-3 exhibited the highest grain Se content and accumulation at the maturity, measured 77.00 μg kg –1 and 73.11%, respectively. Compared to the control, the concentration of flour Se in TH-3, and TZ-8293 under the 240 kg N ha –1 treatment significantly increased by 90.97 and 91.67%, respectively, and the yield of TH-3 under 240 kg N ha –1 treatment was significantly the highest, measuring 7889.84 kg ha –1 . Following anthesis, net photosynthetic rate ( P n ) showed an significantly increasing tendency with the application of nitrogen increased, however, transpiration rate ( T r ), intercellular CO 2 and stomatal conductance ( C i ), and g s in flag leaf decreased significantly with the increase of nitrogen application rate. The correlation analysis showed that there were (extremely) significant negative correlations among Se content, yield and yield components (–0.30 ≤ R 2 ≤ –0.89), excessive nitrogen application may hinder the formation of soil available Se, which can have a negative impact on the absorption of Se, finally impede the biofortification of Se in triticale. In conclusion for locally Se-enriched triticale cultivation, it was recommended to apply nitrogen fertilizer rate of 120–240 kg N ha –1 on TH-3.