Impact of selenium supply on Se-methylselenocysteine and glucosinolate accumulation in selenium-biofortified Brassica sprouts

Selenium biofortification of microgreens: Influence on phytochemicals, pigments and nutrients

Kale (Brassica oleracea L. var. sabellica L.), kohlrabi (Brassica oleracea L. var. gongylodes L.) and wheat (Triticum aestivum L. cv. Bancal) microgreens were cultivated in presence of selenium 20 μmol L-1 as sodium selenite and sodium selenate mixture. The influence of this biofortification process was evaluated in terms of biomass production, total Se, macro- and micronutrients concentration, polyphenols, antioxidant activity, chlorophylls and carotenoids levels and total soluble proteins content. The results obtained have shown a significant concentration of total Se in the biofortified microgreens of kale (133 μg Se·g-1 DW) and kohlrabi (127 μg Se·g-1 DW) higher than that obtained for wheat (28 μg Se·g-1 DW). The Se uptake in all the species did not produce oxidative damage to the plants reflected in the bioactive compounds, antioxidant capacity or pigments concentration. These Se-enriched microgreens may contribute to the recommended intake of this nutrient in human diet as to overcome Se-deficiency.

Integrated non-targeted and targeted metabolomics analysis reveals the mechanism of inhibiting lignification and optimizing the quality of pea sprouts by combined application of nano-selenium and lentinans

BACKGROUND

Lignification causes a detrimental impact on the quality of edible sprouts. However, the mechanism of inhibition of lignification of edible sprouts by nano-selenium and lentinans remains unclear.

RESULTS

To reveal the mechanism of lignification regulation of sprouts by nano-selenium and lentinans, this study investigated the changes in antioxidant indicators, phytohormones, polyphenols, and metabolites in the lignin biosynthesis in pea sprouts following sprays of nano-selenium or/and lentinans twice. There was an overall increase in the aforementioned indices following treatment. In particular, the combined application of 5 mg L-1 nano-selenium and 20 mg L-1 lentinans was more effective than their individual applications in enhancing peroxidase, catalase, DPPH free-radical scavenging rate, luteolin, and sinapic acid, as well as inhibiting malondialdehyde generation and lignin accumulation. Combined with the results from correlation analysis, nano-selenium and lentinans may inhibit lignification by enhancing antioxidant systems, inducing phytohormone-mediated signaling, and enriching precursor metabolites (caffeyl alcohol, sinapyl alcohol, 4-coumaryl alcohol). In terms of the results of non-targeted metabolomics, the combined application of 5 mg L-1 nano-selenium and 20 mg L-1 lentinans mainly affected biosynthesis of plant secondary metabolites, biosynthesis of phenylpropanoids, phenylpropanoid biosynthesis, arginine and proline metabolism, and linoleic acid metabolism pathways, which supported and complemented results from targeted screenings.

CONCLUSION

Overall, the combined sprays of nano-selenium and lentinans showed synergistic effects in delaying lignification and optimizing the quality of pea sprouts. This study provides a novel and practicable technology for delaying lignification in the cultivation of edible sprouts. © 2023 Society of Chemical Industry.

I2/DMSO-Promoted Synthesis of Diaryl Sulfide- and Selenide-Embedded Arylhydrazones

Functionalization and derivatization of arylhydrazones are important in pharmaceutical, medicinal, material, and coordination chemistry. In this regard, a facile I₂/DMSO-promoted cross-dehydrogenative coupling (CDC) for direct sulfenylation and selenylation of arylhydrazones has been accomplished utilizing arylthiols/arylselenols at 80 °C. This method provides a metal-free benign route for the synthesis of a variety of arylhydrazones embedded with diverse diaryl sulfide and selenide moieties in good to excellent yield. In this reaction, molecular I₂ acts as a catalyst, and DMSO is utilized as a mild oxidant as well as solvent to produce several sulfenyl and selenyl arylhydrazones through a CDC-mediated catalytic cycle.

Formation, immunomodulatory activities, and enhancement of glucosinolates and sulforaphane in broccoli sprouts: a review for maximizing the health benefits to human

Broccoli sprouts have been considered as functional foods which have received increasing attention because they have been highly prized for glucosinolates, phenolics, and vitamins in particular glucosinolates. One of hydrolysates-sulforaphane from glucoraphanin is positively associated with the attenuation of inflammatory, which could reduce diabetes, cardiovascular and cancer risk. In recent decades, the great interest in natural bioactive components especially for sulforaphane promotes numerous researchers to investigate the methods to enhance glucoraphanin levels in broccoli sprouts and evaluate the immunomodulatory activities of sulforaphane. Therefore, glucosinolates profiles are different in broccoli sprouts varied with genotypes and inducers. Physicochemical, biological elicitors, and storage conditions were widely studied to promote the accumulation of glucosinolates and sulforaphane in broccoli sprouts. These inducers would stimulate the biosynthesis pathway gene expression and enzyme activities of glucosinolates and sulforaphane to increase the concentration in broccoli sprouts. The immunomodulatory activity of sulforaphane was summarized to be a new therapy for diseases with immune dysregulation. The perspective of this review served as a potential reference for customers and industries by application of broccoli sprouts as a functional food and clinical medicine.

Iodine Biofortification and Seaweed Extract-Based Biostimulant Supply Interactively Drive the Yield, Quality, and Functional Traits in Strawberry Fruits

The horticultural sector is seeking innovative and sustainable agronomic practices which could lead to enhanced yield and product quality. Currently, plant biofortification is recognized as a valuable technique to improve microelement concentrations in plant tissues. Among trace elements, iodine (I) is an essential microelement for human nutrition. Concomitantly, the application of biostimulants may improve overall plant production and quality traits. With the above background in mind, an experiment was designed with the aim of assessing the interactive impact of a seaweed extract-based biostimulant (SwE) (0 mL L^-1 (served as control) or 3 mL L^-1 (optimal dosage)) and 0, 100, 300, or 600 mg L^-1 I on the growth parameters, yield, fruit quality, minerals, and functional characteristics of the tunnel-grown "Savana" strawberry. SwE foliar application improved the plant growth-related traits, total and marketable yield, fruit color parameters, soluble solids content, nitrogen (N), potassium (K), and magnesium (Mg) fruit concentrations. Furthermore, an enhancement in the fruit dry matter content, ascorbic acid, and I concentration in fruits was detected when the SwE supply interacted with a mild I dose (100 or 300 mg L^-1). The research underlined that combining SwE application and I biofortification increased the strawberry yield and quality and enhanced the plant nutritional status variation, thereby, determining a boosted strawberry I tolerance.

Joint Cultivation of Allium ursinum and Armoracia rusticana under Foliar Sodium Selenate Supply

Despite the high value of ramson (Allium ursinum) in medicine and nutrition, it is not cultivated in open fields due to the need for shading as well as weeding during the early crop stages. Research was carried out in an open field with the aim to improve A. ursinum growth, through its intercropping with Armoracia rusticana (horseradish). In the latter context, with and without sodium selenate application, ramson and horseradish showed reciprocal growth stimulation, as ramson biomass increased by 1.28 times and horseradish root biomass by 1.7 times. The biofortification level of horseradish roots increased from 5.9 to 9.6 times due to joint plant growth under selenium (Se) supply. The opposite phenomenon was recorded for ramson leaves, as the biofortification level decreased from 11.7 in the case of Se supplementation to 6.7 in plants supplied with sodium selenate when jointly cultivated with horseradish. Among the tested antioxidants, the highest increase due to joint cultivation and/or Se supply was recorded for ascorbic acid by 1.69 times in ramson leaves and 1.48 and 1.37 times in horseradish roots and leaves, respectively. All treatments significantly increased the total antioxidant activity (AOA) of horseradish leaves (by 1.33-1.49 times) but not roots. Comparison of the results obtained in field conditions with those obtained earlier for the Se biofortification of ramson in the natural habitat (forest) revealed significantly higher levels of the plant's antioxidant status under environmental stress (field) and a decrease in the correspondent differences as a consequence of Se biofortification. The estimation of allelopathic beneficial interaction between ramson and horseradish implies the efficiency of ramson growth and production of functional food with high levels of Se (Se-ramson leaves and Se-horseradish roots).

Exogenous Selenium Treatment Promotes Glucosinolate and Glucoraphanin Accumulation in Broccoli by Activating Their Biosynthesis and Transport Pathways

Supplementation using selenium (Se) on plants is an effective and widely used approach. It can not only be converted to more Se rich compounds but promote the accumulation of glucosinolates (GSLs) with anti-carcinogenic properties. However, the molecular mechanism of Se in regulating GSLs synthesis remains unclear. In the present study, we analyzed the effects of Se treatment (50 μM sodium selenite) on GSLs, glucoraphanin (4MSOB), and sulforaphane compounds in broccoli tissues. The transcript levels of genes involved in sulfur absorption and transport, GSLs biosynthesis, translocation, and degradation pathways were also evaluated. The study showed that Se treatment remarkably promoted the accumulation of total sulfur and total Se contents and increased Trp-derived GSLs levels in roots by 2 times. The 4MSOB concentration and sulforaphane content in fresh leaves was increased by 67% and 30% after Se treatment, respectively. For genes expressions, some genes involved in sulfate uptake and transporters, GSLs biosynthesis, and transporters were induced strongly upon Se exposure. Results revealed that exogenous Se treatment promotes the overaccumulation of GSLs and 4MSOB content in broccoli by activating the transcript levels of genes involved in sulfur absorption, GSLs biosynthesis, and translocation pathways.

Seleno-Amino Acids in Vegetables: A Review of Their Forms and Metabolism

Seleno-amino acids are safe, health-promoting compounds for humans. Numerous studies have focused on the forms and metabolism of seleno-amino acids in vegetables. Based on research progress on seleno-amino acids, we provide insights into the production of selenium-enriched vegetables with high seleno-amino acids contents. To ensure safe and effective intake of selenium, several issues need to be addressed, including (1) how to improve the accumulation of seleno-amino acids and (2) how to control the total selenium and seleno-amino acids contents in vegetables. The combined use of plant factories with artificial lighting and multiple analytical technologies may help to resolve these issues. Moreover, we propose a Precise Control of Selenium Content production system, which has the potential to produce vegetables with specified amounts of selenium and high proportions of seleno-amino acids.

Elicitation: a new perspective into plant chemo-diversity and functional property

Sprouts are consumed as fresh foods or their flours can be added in processed products as determinants of sensory perception, product differentiation, and shelf life. Elicitation technique can be used to accumulate phytochemicals in plant sprouts thereby improving their functionality. This review summarized the recent state of knowledge on the use of elicitors to produce sprouts with improved functional properties. Elicitation using abiotic or biotic elicitors has been applied to increase the yield of sprout secondary metabolites (glucosinolates, aminobutyric acid, phenolic compounds), biological activities (antioxidant, anti-obesity, antidiabetic properties), and growth. Elicitors trigger the synthesis of plant metabolites by changing enzyme activities or gene expression related to the plant defence system. They also promote sprout growth by enhancing the levels of plant growth hormones. Elicitation is an effective method to produce sprouts with improved health benefits, and enhance their growth. Future studies are needed to identify early plant signaling pathways to fully understand elicitors' mechanisms on plant metabolites. Moreover, further investigation can be impetus in revealing the lower and upper limits of elicitor that can be applied in sprouts without compromising health and environmental safety.

Combination of Selenium and UVA Radiation Affects Growth and Phytochemicals of Broccoli Microgreens

Addition of selenium or application of ultraviolet A (UVA) radiation for crop production could be an effective way of producing phytochemical-rich food. This study was conducted to investigate the effects of selenium and UVA radiation, as well as their combination on growth and phytochemical contents in broccoli microgreens. There were three treatments: Se (100 μmol/L Na₂SeO₃), UVA (40 μmol/m²/s) and Se + UVA (with application of Se and UVA). The control (CK) was Se spraying-free and UVA radiation-free. Although treatment with Se or/and UVA inhibited plant growth of broccoli microgreens, results showed that phytochemical contents increased. Broccoli microgreens under the Se treatment had higher contents of total soluble sugars, total phenolic compounds, total flavonoids, ascorbic acid, Fe, and organic Se and had lower Zn content. The UVA treatment increased the contents of total chlorophylls, total soluble proteins, total phenolic compounds, and FRAP. However, the Se + UVA treatment displayed the most remarkable effect on the contents of total anthocyanins, glucoraphanin, total aliphatic glucosinolates, and total glucosinolates; here, significant interactions between Se and UVA were observed. This study provides valuable insights into the combinational selenium and UVA for improving the phytochemicals of microgreens grown in an artificial lighting plant factory.

Selenium Fortification Alters the Growth, Antioxidant Characteristics and Secondary Metabolite Profiles of Cauliflower (Brassica oleracea var. botrytis) Cultivars in Hydroponic Culture

Nowadays the importance of selenium for human health is widely known, but most of the plants are poor in terms of selenium storage and accumulation because of the low selenium mineralization potential of the soil. For this purpose, foliar application of different sodium selenate concentrations (0, 5, 10, 15, 20 mg/L) was used to treat the cauliflower cultivars "Clapton" and "Graffiti". Higher yields and other related vegetative attributes were improved at 10 and 15 mg/L sodium selenate application. At a concentration of 10 mg/L sodium selenate, photosynthetic pigments, total phenolic compounds and antioxidant capacity were enhanced in both cultivars, but the "Graffiti" cultivar responded stronger than the "Clapton" cultivar. The glucosinolates were accumulated in response to selenium fortification and the highest amounts were found in the "Graffiti" cultivar at 10 mg/L. Selenium accumulated concentration-dependently and rose with higher fertilization levels. In general, foliar application of selenium at 10 mg/L led to an accumulation of secondary metabolites and also positively affected the growth and yield of florets.

Selenium yeast promoted the Se accumulation, nutrient quality and antioxidant system of cabbage (Brassica oleracea var. capitata L.)

The application of Se yeast as a Se source to cultivate Se-rich cabbage has a significant effect on cabbage growth and quality indices. Results showed that total plant weight, head weight, and head size in cabbage were notably increased by 48.4%, 88.3%, and 25.4% under 16 mg/kg Se yeast treatment, respectively. Compare with the control, a high proportion of 3874% of Se accumulation in cabbage head was also detected in 16 mg/kg Se yeast treatment. Selenocystine (SeCys₂) and Methyl-selenocysteine (MeSeCys) were the main Se speciations in the cabbage head. Application of 8 mg/kg Se yeast improved cabbage quality and antioxidant system indices, including free amino acid, soluble sugar, ascorbic acid, phenolic acid, glucosinolates, and SOD activity, which had 81.6%, 46.5%, 34.9%, 12.3%, 44.8%, 25.2% higher than that of the control, respectively. In summary, considering 8 mg/kg Se yeast as the appropriate level of Se enrichment during cabbage cultivation. These findings enhanced our understanding of the effects of Se yeast on the growth and quality of cabbage and provided new insights into Se-enrichment vegetable cultivation.

Effects of selenate on Se, flavonoid, and glucosinolate in broccoli florets by combined transcriptome and metabolome analyses

Broccoli is a nutritious vegetable popular all over the world. This study investigated the effects of different concentrations of selenate (0, 0.1, 0.2, 0.4, 0.8, and 1.6 mmol/L) on the selenium (Se), glucosinolate, and flavonoid contents of broccoli florets. Results showed that the total Se, selenomethionine, and methyl selenocysteine contents increased following selenate dosage. Interestingly, selenate treatment of 0.4 mmol/L decreased the flavonoid but increased the glucosinolate content. Metabolome analysis revealed changes in the individual contents of glucosinolates and flavonoids. Conjoint analysis of transcriptome and metabolome showed that the glucosinolate and flavonoid compounds were potentially regulated by two sulfate transporter genes (Sultr3;1 and Sultr4;2) and several cytochrome P450 genes (e.g., CYP71B21, CYP72C1, and CYP81F1). These new findings indicated that Se treatment may influence glucosinolate and flavonoid accumulation by regulating the expression of these genes. The results of this study provide some novel insights into the effects of Se on glucosinolates and flavonoids in broccoli florets and deepen our understanding of the regulatory network between some specific genes and these compounds.

Nutritional quality and sensory acceptance of biofortified cassava

Abstract It is estimated that the global number of people affected by micronutrient deficiency, known worldwide as hidden hunger, is over two billion and also considered a public health problem. Therefore, this study aimed to evaluate biofortified cassava cultivars in relation to their physical-chemical composition, total carotenoids and to verify their sensory acceptance by schoolchildren. The study was conducted in Santa Maria, in the state of Rio Grande do Sul (RS), Brazil, with four cassava cultivars, two biofortified with yellow pulp (BRS 399 and BRS 396); two non-biofortified varieties: one with yellow pulp (“Gema de ovo”) and another with white pulp (“Vassourinha”). After cooking the roots, the nutritional composition (moisture, protein, lipid, ash, and total starch), the total carotenoid content, and the sensory acceptance of the roots by the children at school, in the countryside of Julio de Castilhos and Dilermando de Aguiar, was determined. The contents of moisture, protein, lipids, ash, and starch showed significant variations between the cultivars analyzed. The highest levels of total carotenoids were found in biofortified cultivars (12.85 µg g-1). In the non-biofortified cultivars, “Gema de ovo” and “Vassourinha”, the levels were 12.01 µg g-1 and 3.30 µg g-1, respectively. Sensory acceptance was 78.7%, demonstrating the potential for the insertion of biofortified roots in school meals.

Regulation of Selenium/Sulfur Interactions to Enhance Chemopreventive Effects: Lessons to Learn from Brassicaceae

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.

Phosphorus and sulfur in a tropical soil and their effects on growth and selenium accumulation in Leucaena leucocephala (Lam.) de Wit

Selenium (Se) is an essential metalloid element for mammals. Nonetheless, both deficiency and excess of Se in the environment are associated with several diseases in animals and humans. Here, we investigated the interaction of Se, supplied as selenate (Se⁺⁶) and selenite (Se⁺⁴), with phosphorus (P) and sulfur (S) in a weathered tropical soil and their effects on growth and Se accumulation in Leucaena leucocephala (Lam.) de Wit. The P-Se interaction effects on L. leucocephala growth differed between the Se forms (selenate and selenite) supplied in the soil. Selenate was prejudicial to plants grown in the soil with low P dose, while selenite was harmful to plants grown in soil with high P dose. The decreasing soil S dose increased the toxic effect of Se in L. leucocephala plants. Se tissue concentration and total Se accumulation in L. leucocephala shoot were higher with selenate supply in the soil when compared with selenite. Therefore, selenite proved to be less phytoavailable in the weathered tropical soil and, at the same time, more toxic to L. leucocephala plants than selenate. Thus, it is expected that L. leucocephala plants are more efficient to phytoextract and accumulate Se as selenate than Se as selenite from weathered tropical soils, for either strategy of phytoremediation (decontamination of Se-polluted soils) or purposes of biofortification for animal feed (fertilization of Se-poor soils).

Biochemical basis of differential selenium tolerance in arugula (Eruca sativa Mill.) and lettuce (Lactuca sativa L.)

Selenium (Se) biofortification in crops provides a valuable strategy to enhance human Se intake. However, crops vary greatly with their capacity in tolerating and metabolizing/accumulating Se, and the basis underlying such variations remains to be fully understood. Here, we compared the effects of Se and its analog S treatments on plant growth and biochemical responses between a Se accumulator (arugula) and a non-accumulator (lettuce). Arugula exhibited an increased biomass production in comparison with untreated controls at a higher selenate concentration than lettuce (20 μM vs. 10 μM Na2SeO4), showing better tolerance to Se. Arugula accumulated 3-folds more Se and S than lettuce plants under the same treatments. However, the Se/S assimilation as assessed by ATP sulfurylase and O-acetylserine (thiol)lyase activities was comparable between arugula and lettuce plants. Approximately 4-fold higher levels of Se in proteins under the same doses of Se treatments were observed in arugula than in lettuce, indicating that Se accumulators have better tolerance to selenoamino acids in proteins. Noticeably, arugula showed 6-fold higher ascorbate peroxidase activity and produced over 5-fold more glutathione and non-protein thiols than lettuce plants, which suggest critical roles of antioxidants in Se tolerance. Taken together, our results show that the elevated Se tolerance of arugula compared to lettuce is most likely due to an efficient antioxidant defense system. This study provides further insights into our understanding of the difference in tolerating and metabolizing/accumulating Se between Se accumulators and non-accumulators.

Effect of selenium-sulfur interaction on the anabolism of sulforaphane in broccoli

The effects of S (as sulphate) and Se (as selenite) treatment (S mM/Se μM: 1/0, 1/50, 1/100, 1/150, 4/0, 4/50, 4/100, and 4/150) on the production of sulforaphane (an anticancer compound), the accumulation of its precursor substance, and the expression of genes related to glucoraphanin biosynthesis in broccoli were examined. Sulforaphane yield and myrosinase activity increased significantly with the combined application of 4 mM S and 100 μM Se on broccoli. Furthermore, the concentrations of glucoraphanin (a sulforaphane precursor) and methionine (a glucoraphanin substrate) slightly changed after Se application. And the strong anticancer activity of compound Se-SMC was further improved. Analysis of related gene expression showed that MY, which encodes myrosinase, was strongly induced by Se treatment. Thus, the myrosinase activity induced by Se treatment is the dominant factor affecting sulforaphane yield from glucoraphanin hydrolyzation. Selenium-sulfur biofortification provides a technical support for the cultivation of broccoli with high sulforaphane and high anti-cancer selenium compounds.

Searching for Low Molecular Weight Seleno-Compounds in Sprouts by Mass Spectrometry

A fit for purpose analytical protocol was designed towards searching for low molecular weight seleno-compounds in sprouts. Complementary analytical techniques were used to collect information enabling the characterization of selenium speciation. Conceiving the overall characterization of the behavior of selenium, inductively plasma optical mass spectrometry (ICP-MS) was used to determine the total selenium content in entire sprouts as well as in selected extracts or chromatographic fractions. Then, high-performance liquid chromatography combined with ICP-MS (HPLC-ICP-MS) was used to evaluate the presence of inorganic and organic seleno-compounds, with the advantages of being very sensitive towards selenium, but limited by available selenium standard compounds. Finally, ultra-high performance liquid chromatography electrospray ionization triple quadrupole mass spectrometry (UHPLC-ESI-QqQ-MS/MS) and UHPLC-ESI-Orbitrap-MS/MS were used for the confirmation of the identity of selected compounds and identification of several unknown compounds of selenium in vegetable sprouts (sunflower, onion, radish), respectively. Cultivation of plants was designed to supplement sprouts with selenium by using solutions of selenium (IV) at the concentration of 10, 20, 40, and 60 mg/L. The applied methodology allowed to justify that vegetable sprouts metabolize inorganic selenium to a number of organic derivatives, such as seleno-methylselenocysteine (SeMetSeCys), selenomethionine (SeMet), 5′-seleno-adenosine, 2,3-DHP-selenolanthionine, Se-S conjugate of cysteine-selenoglutathione, 2,3-DHP-selenocysteine-cysteine, 2,3-DHP-selenocysteine-cysteinealanine, glutathione-2,3-DHP-selenocysteine, gamma-Glu-MetSeCys or glutamyl-glycinyl-N-2,3-DHP-selenocysteine.

Selenium in plant foods: speciation analysis, bioavailability, and factors affecting composition

Interest in selenium has been increasing over the past few decades with growing knowledge of its importance to overall health. The ability of several plants to accumulate and transform inorganic selenium forms into its bioactive organic compounds has important implications for human nutrition and health. In this review, we present the studies carried out during the last decade to characterize selenium species produced by different plant foods. Attention is also paid to the effect of selenium treatment on chemical composition and antioxidant properties of plants.

Does selenium fortification of kale and kohlrabi sprouts change significantly their biochemical and cytotoxic properties?

BACKGROUND

The sprouts of Brassica vegetables are known from their nutritional and chemopreventive values. Moreover, sprouts fortification with some trace elements, like selenium, may increase their importance in human diet. Thus, the aim of our study was to examine if selenium enrichment of kale and kohlrabi sprouts may influence their biochemical properties (phenolic acids and L-tryptophan content, antioxidant potential) or cytotoxic activity. Additional aim of the study was to evaluate the profile of selenium compounds and to describe the multidimensional interactions between the mentioned parameters.

METHODS

Selenium content in the sprouts was evaluated by double-channel atomic fluorescence spectrometer AFS-230 with the flow hydride-generation system. Separation of selenium species in water soluble fraction was performed by size-exclusion LC-ICP-MS. The identification and quantification of phenolic acids and L-tryptophan was performed by HPLC. For antioxidant activity DPPH and FRAP methods were used. Cytotoxic activity of the sprouts extracts on a panel of human metastatic carcinoma cells was evaluated by MTT test.

RESULTS

Selenium content in the fortified sprouts was several orders of magnitude higher than in the unfortified ones. Only small percentage of supplemented selenium (ca. 10 %) was incorporated into the sprouts as seleno-L-methionine, while the other detected selenium species remained unidentified. Selenium fortification differently stimulated the production of phenolic acids (sinapic, chlorogenic, isochlorogenic and caffeic acid) in the tested sprouts, depending on the particular species, selenium dose and the investigated compound. PCA analysis revealed strong correlation between antioxidant parameters and phenolic acids and L-tryptophan, while Se correlated only with caffeic acid. The sprouts extracts (≥1 mg/mL) showed cytotoxic potency to all the studied cancer cell lines (SW480, SW620, HepG2, SiHa), regardless the selenium supplementation.

CONCLUSION

Se-fortified kale and kohlrabi sprouts are good candidates for functional food ingredients. Moreover, these results indicate that the sprouts enriched with sodium selenite show higher nutritional value, without significant changes in their cytotoxic activity.

Current Knowledge on Selenium Biofortification to Improve the Nutraceutical Profile of Food: A Comprehensive Review

Selenium (Se) is an important micronutrient for living organisms, since it is involved in several physiological and metabolic processes. Se intake in humans is often low and very seldom excessive, and its bioavailability depends also on its chemical form, with organic Se as the most available after ingestion. The main dietary source of Se for humans is represented by plants, since many species are able to metabolize and accumulate organic Se in edible parts to be consumed directly (leaves, flowers, fruits, seeds, and sprouts) or after processing (oil, wine, etc.). Countless studies have recently investigated the Se biofortification of plants to produce Se-enriched foods and elicit the production of secondary metabolites, which may benefit human health when incorporated into the diet. Moreover, feeding animals Se-rich diets may provide Se-enriched meat. This work reviews the most recent literature on the nutraceutical profile of Se-enriched foods from plant and animal sources.

Selenium biofortification in the 21st century: status and challenges for healthy human nutrition

BACKGROUND

Selenium (Se) is an essential element for mammals and its deficiency in the diet is a global problem. Plants accumulate Se and thus represent a major source of Se to consumers. Agronomic biofortification intends to enrich crops with Se in order to secure its adequate supply by people.

SCOPE

The goal of this review is to report the present knowledge of the distribution and processes of Se in soil and at the plant-soil interface, and of Se behaviour inside the plant in terms of biofortification. It aims to unravel the Se metabolic pathways that affect the nutritional value of edible plant products, various Se biofortification strategies in challenging environments, as well as the impact of Se-enriched food on human health.

CONCLUSIONS

Agronomic biofortification and breeding are prevalent strategies for battling Se deficiency. Future research addresses nanosized Se biofortification, crop enrichment with multiple micronutrients, microbial-integrated agronomic biofortification, and optimization of Se biofortification in adverse conditions. Biofortified food of superior nutritional quality may be created, enriched with healthy Se-compounds, as well as several other valuable phytochemicals. Whether such a food source might be used as nutritional intervention for recently emerged coronavirus infections is a relevant question that deserves investigation.

Selenium Biofortification of Agricultural Crops and Effects on Plant Nutrients and Bioactive Compounds Important for Human Health and Disease Prevention - a Review

Selenium supplementation in humans has been suggested for the prevention of chronic diseases including cardiovascular disease, cancer, and neurodegenerative diseases. Selenium biofortification of plants has been explored as a method for increasing selenium content of food and dietary selenium intake in humans. However, the effects of selenium biofortification on other dietary nutrients is often a secondary discussion. These effects are especially important to explore considering selenium-biofortified foods contain many other nutrients important to human health, such as other minerals and antioxidant compounds, which can make these foods superior to selenium supplementation alone. Investigation of selenium biofortification's effect on these nutrients is necessary for a comprehensive human nutrition perspective on biofortification strategies. This review considers the effects of selenium biofortification on selenium content, other minerals, and antioxidant compounds as they pertain to human health in order to suggest optimal strategies for biofortification. Pre-clinical and clinical studies assessing the effects of consumption of selenium biofortified foods are also discussed.

Selenium Application During Radish (Raphanus sativus) Plant Development Alters Glucosinolate Metabolic Gene Expression and Results in the Production of 4-(methylseleno)but-3-enyl glucosinolate

Selenium (Se) is an essential micronutrient for human health, entering the diet mainly through the consumption of plant material. Members of the Brassicaceae are Se-accumulators that can accumulate up to 1g Se kg⁻¹ dry weight (DW) from the environment without apparent ill effect. The Brassicaceae also produce glucosinolates (GSLs), sulfur (S)-rich compounds that benefit human health. Radish (Raphanussativus) has a unique GSL profile and is a Se-accumulating species that is part of the human diet as sprouts, greens and roots. In this report we describe the effects of Se-fertilisation on GSL production in radish during five stages of early development (from seed to mature salad greens) and on the transcript abundance of eight genes encoding enzymes involved in GSL metabolism. We tentatively identified (by tandem mass spectrometry) the selenium-containing glucosinolate, 4-(methylseleno)but-3-enyl glucosinolate, with the double bond geometry not resolved. Two related isothiocyanates were tentatively identified by Gas Chromatography-Mass Spectrometry as (E/Z?) isomers of 4-(methylseleno)but-3-enyl isothiocyanate. Se fertilisation of mature radish led to the presence of selenoglucosinolates in the seed. While GSL concentration generally reduced during radish development, GSL content was generally not affected by Se fertilisation, aside from the indole GSL, indol-3-ylmethyl glucosinolate, which increased on Se treatment, and the Se-GSLs, which significantly increased during development. The transcript abundance of genes involved in aliphatic GSL biosynthesis declined with Se treatment while that of genes involved in indole GSL biosynthesis tended to increase. APS kinase transcript abundance increased significantly in three of the four developmental stages following Se treatment. The remaining genes investigated were not significantly changed following Se treatment. We hypothesise that increased APS kinase expression in response to Se treatment is part of a general protection mechanism controlling the uptake of S and the production of S-containing compounds such as GSLs. The upregulation of genes encoding enzymes involved in indole GSL biosynthesis and a decrease in those involved in aliphatic GSL biosynthesis may be part of a similar mechanism protecting the plant’s GSL complement whilst limiting the amount of Se-GSLs produced.

Production of selenium-biofortified microgreens from selenium-enriched seeds of basil

BACKGROUND

Microgreens (i.e. tender immature greens) are a popular alternative to sprouts (i.e. germinating seeds) because of their higher content of vitamins, carotenoids and phenols, as well as their lower content of nitrates. Their nutritional value can be improved by biofortification, which increases micronutrient levels during plant growth. Because selenium (Se) plays a significant role in antioxidant defense, biofortification with Se is a good way of improving the nutritional quality of sprouts and microgreens. The present study investigated the production of Se-fortified microgreens from Se-enriched seeds of sweet basil (Ocimum basilicum L.). These microgreens could be used as new beneficial dietary supplements.

RESULTS

Basil plants were grown in a nutrient solution, containing 0 (control), 4 or 8 mg Se L^-1 as sodium selenate, to full maturity. Seeds accumulated a high amount of Se and were then used to produce microgreens. The germination index was higher in the seeds from Se-treated plants and the microgreens were enriched in Se. The antioxidant capacity of Se-fortified microgreens was higher compared to the control.

CONCLUSION

The production of microgreens from Se-enriched seeds could comprise a good system for obtaining microgreens with a high nutritional value. Basil plants treated with Se could be used to produce both Se-fortified leaves and microgreens. © 2019 Society of Chemical Industry.

Hydroponic Solutions for Soilless Production Systems: Issues and Opportunities in a Smart Agriculture Perspective

Soilless cultivation represent a valid opportunity for the agricultural production sector, especially in areas characterized by severe soil degradation and limited water availability. Furthermore, this agronomic practice embodies a favorable response toward an environment-friendly agriculture and a promising tool in the vision of a general challenge in terms of food security. This review aims therefore at unraveling limitations and opportunities of hydroponic solutions used in soilless cropping systems focusing on the plant mineral nutrition process. In particular, this review provides information (1) on the processes and mechanisms occurring in the hydroponic solutions that ensure an adequate nutrient concentration and thus an optimal nutrient acquisition without leading to nutritional disorders influencing ultimately also crop quality (e.g., solubilization/precipitation of nutrients/elements in the hydroponic solution, substrate specificity in the nutrient uptake process, nutrient competition/antagonism and interactions among nutrients); (2) on new emerging technologies that might improve the management of soilless cropping systems such as the use of nanoparticles and beneficial microorganism like plant growth-promoting rhizobacteria (PGPRs); (3) on tools (multi-element sensors and interpretation algorithms based on machine learning logics to analyze such data) that might be exploited in a smart agriculture approach to monitor the availability of nutrients/elements in the hydroponic solution and to modify its composition in realtime. These aspects are discussed considering what has been recently demonstrated at the scientific level and applied in the industrial context.

Selenium Biofortification Differentially Affects Sulfur Metabolism and Accumulation of Phytochemicals in Two Rocket Species (Eruca Sativa Mill. and Diplotaxis Tenuifolia) Grown in Hydroponics

Biofortification can be exploited to enrich plants in selenium (Se), an essential micronutrient for humans. Selenium as selenate was supplied to two rocket species, Eruca sativa Mill. (salad rocket) and Diplotaxis tenuifolia (wild rocket), at 0–40 μM in hydroponics and its effects on the content and profile of sulphur (S)-compounds and other phytochemicals was evaluated. D. tenuifolia accumulated more total Se and selenocysteine than E. sativa, concentrating up to ~300 mg Se kg⁻¹ dry weight from 10–40 μM Se. To ensure a safe and adequate Se intake, 30 and 4 g fresh leaf material from E. sativa grown with 5 and 10–20 μM Se, respectively or 4 g from D. tenuifolia supplied with 5 μM Se was estimated to be optimal for consumption. Selenium supplementation at or above 10 μM differentially affected S metabolism in the two species in terms of the transcription of genes involved in S assimilation and S-compound accumulation. Also, amino acid content decreased with Se in E. sativa but increased in D. tenuifolia and the amount of phenolics was more reduced in D. tenuifolia. In conclusion, selenate application in hydroponics allowed Se enrichment of rocket. Furthermore, Se at low concentration (5 μM) did not significantly affect accumulation of phytochemicals and plant defence S-metabolites.

Selenium forms and methods of application differentially modulate plant growth, photosynthesis, stress tolerance, selenium content and speciation in Oryza sativa L

Selenium (Se) is an essential microelement for humans and a beneficial element for plants. Recently, biofortification with Se has emerged as a key strategy to increase crop Se content. Nonetheless, Se species matters a lot as inorganic Se species is mostly toxic to human health. In this study, we investigated the effects of different forms and mode of Se application on Se accumulation and speciation in rice. The results showed that root application of Se remarkably increased Se accumulation, photosynthetic rate, biomass accumulation and tolerance to cadmium stress in rice as compared to foliar application. However, the stimulatory effects of Se varied depending on the Se species used for root feeding. At vegetative stage, root application of Se-(Methyl) selenocysteine caused the highest water extractable Se content in leaves with major contribution from organic Se species such as Se-amino acid and non-amino acid organic Se. Further investigation at reproductive stage revealed that foliar application of sodium selenite (Na₂SeO₃) resulted in the highest total Se content in rice seeds which was largely attributed to inorganic Se. In contrast, the root application of Na₂SeO₃ led to the maximum accumulation of organic Se compounds which are advantageous to human health. Moreover, the root application of Se increased antioxidant capacity and selectively enhanced amino acids and essential element content in rice grain. This study deepens our understanding of the Se species in Se-enriched rice and suggests that root application of Se may ensure the safe intake of Se through rice.

Speciation Analysis of Selenium in Candida utilis Yeast Cells Using HPLC-ICP-MS and UHPLC-ESI-Orbitrap MS Techniques

Selenium plays a key role in the proper metabolism of living organisms. The search for new selenium compounds opens up new possibilities for understanding selenometabolome in yeast cells. This study was aimed at the identification of compounds containing selenium in the feed yeasts Candida utilis ATCC 9950. Yeast biomass was kept in aqueous solutions enriched with inorganic selenium (20 mg·L−1) for 24 h. Speciation analysis of the element was performed using the HPLC-ICP-MS and UHPLC-ESI-Orbitrap MS techniques. The obtained selenium value in the yeast was 629 μg·g−1, while the selenomethionine value was 31.57 μg·g−1. The UHPLC-ESI-Orbitrap MS analysis conducted allowed for the identification of six selenium compounds: dehydro-selenomethionine-oxide, selenomethionine, selenomethionine-NH3, a Se-S conjugate of selenoglutathione-cysteine, methylthioselenoglutathione, and 2,3-DHP-selenocysteine-cysteine. In order to explain the structure of selenium compounds, the selected ions were subjected to fragmentation. The selenium compounds obtained with a low mass play a significant role in the metabolism of the compound. However, the bioavailability of such components and their properties have not been fully understood. The number of signals indicating the presence of selenium compounds obtained using the UHPLC-ESI-Orbitrap MS method was characterized by higher sensitivity than when using the HPLC-ICP-MS method. The obtained results will expand upon knowledge about the biotransformation of selenium in eukaryotic yeast cells. Future research should focus on understanding the entire selenium metabolism in cells and on the search for new transformation pathways for this element. This opens up new possibilities for obtaining functional food, rich in easily absorbable selenium sources, and constituting an alternative to dietary supplements based on this compound found primarily in inorganic form.

Effects of Selenium Supplementation on Glucosinolate Biosynthesis in Broccoli

Selenium (Se)-enriched broccoli has health-beneficial selenium-containing compounds, but it may contain reduced amounts of chemopreventive glucosinolates. To investigate the basis by which Se treatment influences glucosinolate levels, we treated two broccoli cultivars with 25 μM Na₂SeO₄. We found that Se supplementation suppressed the accumulation of total glucosinolates, particularly glucoraphanin, the direct precursor of a potent anticancer compound, in broccoli florets and leaves. We showed that the suppression was not associated with plant sulfur nutrition. The levels of the glucosinolate precursors methionine and phenylalanine as well as the expression of genes involved in glucosinolate biosynthesis were greatly decreased following Se supplementation. Comparative proteomic analysis identified proteins in multiple metabolic and cellular processes that were greatly affected and detected an enzyme affecting methionine biosynthesis that was reduced in the Se-biofortified broccoli. These results indicate that Se-conferred glucosinolate reduction is associated with negative effects on precursor amino acid biosynthesis and glucosinolate-biosynthetic-gene expression and provide information for a better understanding of glucosinolate accumulation in response to Se supplementation in broccoli.

Selenium Accumulation Characteristics and Biofortification Potentiality in Turnip (Brassica rapa var. rapa) Supplied with Selenite or Selenate

Selenium (Se) is an essential trace element for humans. About 70% of the regions in China, including most of the Tibetan Plateau, are faced with Se deficiency problems. Turnip is mainly distributed around the Tibetan Plateau and is one of the few local crops. In the present study, we compared the absorption and translocation differences of Se (IV) selenite and Se (VI) selenate in turnip. The results showed that Se treatment, either by soil addition (0.2-2 mg Se kg^-1 dry soil) or by foliar spraying (50-200 mg L^-1 Se), could significantly increase the Se concentrations in turnips, and 0.5 mg Se (IV) or Se (VI) kg^-1 dry matter in soils could improve the biomasses of turnips. Moreover, turnip absorbed significantly more Se (VI) than Se (IV) at the same concentration and also transferred much more Se (VI) from roots to leaves. Based on the Se concentrations, as well as the bioconcentration factors and translocation coefficients, we considered that turnip might be a potential Se indicator plant. Subsequently, we estimated the daily Se intake for adults based on the Se concentrations in turnip roots. The results indicated that Se (IV) should be more suitable as an artificial Se fertilizer for turnips, although the levels found in most samples in this study could cause selenosis to humans. In addition, we also estimated the optimum and maximum Se concentrations for treating turnips based on the linear relations between Se concentrations in turnip roots and Se treatment concentrations. The results provided preliminary and useful information about Se biofortification in turnips.

Antitumor and Immunoregulatory Activities of Seleno-β-Lactoglobulin on S180 Tumor-Bearing Mice

Degeneration of immune organs like thymus and spleen has been discovered in tumor-bearing mice; which increases the difficulties on oncotherapy. More effective drugs which target the protection of immune organs are expected to be researched. In this study; we aim to analyze the antitumor and immunoregulatory activities of seleno-β-lactoglobulin (Se-β-lg) on S180 tumor-bearing mice. Results indicated that Se-β-lg exhibited a remarkable inhibitory effect on S180 solid tumors with the inhibition rate of 48.38%; and protected the thymuses and spleens of S180-bearing mice. In addition, Se-β-lg could also balance the proportions of CD4⁺ and CD8⁺ T cells in spleens; thymuses and peripheral bloods; and improve Levels of IL-2; IFN-γ; TNF-α in mice serums. β-lg showed weaker bioactivities while SeO₂ showed stronger toxicity on mice. Therefore our results demonstrated that Se-β-lg possessed stronger antitumor and immunoregulatory activities with lower side effects and had the potential to be a novel immunopotentiator and antitumor agent.

Selenium Biofortification in Fragaria × ananassa: Implications on Strawberry Fruits Quality, Content of Bioactive Health Beneficial Compounds and Metabolomic Profile

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-1 up to 10 mg kg-1 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.

Modelling of the effect of selenium fertilization on the content of bioactive compounds in broccoli heads

Selenium (Se) exerts many effects beneficial to health. Broccoli is a Se-hyperaccumulator plant, with Se-fertilization increasing its potential as a functional food. We studied the effect of dose, and the developmental stage at the beginning of Se-fortification, on antioxidant capacity, phenolics, glucosinolates, sulphoraphane, Se-methyl selenocysteine and myrosinase in broccoli. Se-fortification decreased the antioxidant properties and sulphur-containing compounds, but increased Se-methyl-selenocysteine content. Regression models gave r>0.77 confirming that Se dose and developmental stage largely determine the behaviour of the system. Correlation models gave r>0.95, allowing estimation of saturation concentration of Se-methyl-selenocysteine in broccoli cv. Traditional (3.13µmolg^-1DM) and the concentration (2-mmol sodium selenate) above which the content of phenolic compounds decreases significantly. Sulphoraphane and glucosinolates' dependence on total Se supply was consistent with myrosinase activity below 3.5-mmol sodium selenate. Our results would enable design of optimal fertilization strategies to enrich broccoli in Se with minimal impairment of antioxidants properties.

Electrochemical Oxidation of l-selenomethionine and Se-methylseleno-l-cysteine at a Thiol-Compound-Modified Gold Electrode: Its Application in a Flow-Through Voltammetric Sensor

A flow-electrolytic cell that consists of a bare gold wire or of different thiol-compound-modified gold electrodes (such as 2,4-thiazolidinedione, 2-mercapto-5-thiazoline, 2-mercaptothiazoline, l-cysteine, thioglycolic acid) was designed to be used in a voltammetric detector to identify l-selenomethionine and Se-methylseleno-l-cysteine using high-performance liquid chromatography. Both l-selenomethionine and Se-methylseleno-l-cysteine are more efficiently electrochemically oxidized on a thiol/gold than on a bare gold electrode. For the DC mode, and for measurements with suitable experimental parameters, a linear concentration from 10 to 1600 ng·mL⁻¹ was found. The limits of quantification for l-selenomethionine and Se-methylseleno-l-cysteine were below 10 ng·mL⁻¹. The method can be applied to the quantitative determination of l-selenomethionine and Se-methylseleno-l-cysteine in commercial selenium-containing supplement products. Findings using high-performance liquid chromatography with a flow-through voltammetric detector and ultraviolet detector are comparable.

Selenium Biofortification and Phytoremediation Phytotechnologies: A Review

The element selenium (Se) is both essential and toxic for most life forms, with a narrow margin between deficiency and toxicity. Phytotechnologies using plants and their associated microbes can address both of these problems. To prevent Se toxicity due to excess environmental Se, plants may be used to phytoremediate Se from soil or water. To alleviate Se deficiency in humans or livestock, crops may be biofortified with Se. These two technologies may also be combined: Se-enriched plant material from phytoremediation could be used as green fertilizer or as fortified food. Plants may also be used to "mine" Se from seleniferous soils. The efficiency of Se phytoremediation and biofortification may be further optimized. Research in the past decades has provided a wealth of knowledge regarding the mechanisms by which plants take up, metabolize, accumulate, and volatilize Se and the role plant-associated microbes play in these processes. Furthermore, ecological studies have revealed important effects of plant Se on interactions with herbivores, detrivores, pollinators, neighboring vegetation, and the plant microbiome. All this knowledge can be exploited in phytotechnology programs to optimize plant Se accumulation, transformation, volatilization, and/or tolerance via plant breeding, genetic engineering, and tailored agronomic practices.

Mechanisms of Selenium Enrichment and Measurement in Brassicaceous Vegetables, and Their Application to Human Health

Selenium (Se) is an essential micronutrient for human health. Se deficiency affects hundreds of millions of people worldwide, particularly in developing countries, and there is increasing awareness that suboptimal supply of Se can also negatively affect human health. Selenium enters the diet primarily through the ingestion of plant and animal products. Although, plants are not dependent on Se they take it up from the soil through the sulphur (S) uptake and assimilation pathways. Therefore, geographic differences in the availability of soil Se and agricultural practices have a profound influence on the Se content of many foods, and there are increasing efforts to biofortify crop plants with Se. Plants from the Brassicales are of particular interest as they accumulate and synthesize Se into forms with additional health benefits, such as methylselenocysteine (MeSeCys). The Brassicaceae are also well-known to produce the glucosinolates; S-containing compounds with demonstrated human health value. Furthermore, the recent discovery of the selenoglucosinolates in the Brassicaceae raises questions regarding their potential bioefficacy. In this review we focus on Se uptake and metabolism in the Brassicaceae in the context of human health, particularly cancer prevention and immunity. We investigate the close relationship between Se and S metabolism in this plant family, with particular emphasis on the selenoglucosinolates, and consider the methodologies available for identifying and quantifying further novel Se-containing compounds in plants. Finally, we summarize the research of multiple groups investigating biofortification of the Brassicaceae and discuss which approaches might be most successful for supplying Se deficient populations in the future.

Selenium-Induced Toxicity Is Counteracted by Sulfur in Broccoli (Brassica oleracea L. var. italica)

Selenium (Se) is an essential micronutrient for humans. Increasing Se content in food crops offers an effective approach to enhance the consumption of Se in human diets. A thoroughly understanding of the effects of Se on plant growth is important for Se biofortification in food crops. Given that Se is an analog of sulfur (S) and can be toxic to plants, its effect on plant growth is expected to be greatly affected by S nutrition. However, this remains to be further understood. Here, we evaluated the influence of Se treatments on broccoli (Brassica oleracea L. var. italica) growth when S was withheld from the growth nutrient solution. We found that Se was highly toxic to plants when S nutrition was poor. In contrast to Se treatments with adequate S nutrition that slightly reduced broccoli growth, the same concentration of Se treatments without S supplementation dramatically reduced plant sizes. Higher Se toxicity was observed with selenate than selenite under low S nutrition. We examined the bases underlying the toxicity. We discovered that the high Se toxicity in low S nutrition was specifically associated with an increased ratio of Se in proteins verse total Se level, enhanced generation of reactive oxygen species, elevated lipid peroxidation causing increased cell membrane damage, and reduced antioxidant enzyme activities. Se toxicity could be counteracted with increased supplementation of S, which is likely through decreasing non-specific integration of Se into proteins and altering the redox system. The present study provides information for better understanding of Se toxicity and shows that adequate S nutrition is important to prevent Se toxicity during biofortification of crops by Se fertilization.