Excess Se Research Articles

Effect of Paenibacillus favisporus CHP14 inoculation on selenium accumulation and tolerance of Pakchoi (Brassica chinensis L.) under exogenous selenite treatments

The effects of Paenibacillus favisporus CHP14 inoculation on selenium (Se) accumulation and Se tolerance of Pakchoi were studied by a pot experiment conducted in greenhouse. The results revealed that the growth traits such as plant height, root length, and biomass were significantly elevated during CHP14 treatment at 0 ∼ 8.0 mg·kg−1 Se(IV) levels. CHP14-inoculated plants accumulated more Se in root and shoot, which were 24.1%∼57.3% and 7.5%∼50.9% higher than those of non-inoculated plants. The contents of leaf nitrogen (N), phosphorus (P), magnesium (Mg), and iron (Fe), as well as the ratio of indoleacetic acid and abscisic acid contents (IAA/ABA) were increased by CHP14 inoculation, and positively associated with photosynthetic pigment contents (p < 0.05). At ≥ 4.0 mg·kg−1 Se(IV) levels, superoxide dismutase, peroxidase, and glutathione peroxidase activities of Pakchoi roots were increased with CHP14 inoculation, by 9.9%∼17.1%, 28.4%∼40.7%, and 7.4%∼15.3%, respectively. Moreover, CHP14 inoculation enhanced ascorbate-glutathione (AsA-GSH) metabolism in roots by upregulating the related enzymes activities and antioxidant contents under excess Se(IV) stress. These findings suggest that CHP14 is beneficial to improve plant growth and enhance Se(IV) resistance of Pakchoi, and can be exploited as potential inoculants for phytoremediation process in Se contaminated soil.

Selenium spatial distribution and bioavailability of soil-plant systems in China: a comprehensive review.

Selenium (Se) has a dual nature, with beneficial and harmful effects on plants, essential for both humans and animals, playing a crucial role in ecosystem regulation. Insufficient Se in specific terrestrial environments raises concerns due to its potential to cause diseases, while excess Se can lead to severe toxicity. Thus, maintaining an optimal Se level is essential for living organisms. This review focuses first on Se transformation, speciation, and geochemical properties in soil, and then provides a concise overview of Se distribution in Chinese soil and crops, with a focus on the relationship between soil Se levels and parent materials. Additionally, this paper explores Se bioavailability, considering parent materials and soil physicochemical properties, using partial least squares path modeling for analysis. This paper aimed to be a valuable resource for effectively managing Se-enriched soil resources, contributing to a better understanding of Se role in ecosystems.

Hydrogen exposure-enhanced superconductivity transition in FeSe/SrTiO3 monolayer

Interface-enhanced superconductivity in FeSe/SrTiO3 (FeSe/STO) monolayers provides the record for the highest transition temperature (Tc) in iron-based compounds. Long-term post annealing is the commonly adopted recipe to induce the superconductivity transition in the not-superconductive as-grown FeSe/STO monolayer. Here, we developed a kinetic method, i.e., hydrogen exposure followed by gentle annealing, to enhance the superconductivity of the FeSe/STO monolayer. Our approach is more efficient than the long-term post annealing. Scanning tunneling microscopy (STM) characterization demonstrated the so far largest superconducting gap of ∼22 mV, indicating an enhanced superconductivity. We believe that the hydrogen-induced lattice Fe diffusion facilitates to remove the interfacial excess Se atoms fatal to the superconductivity, resulting in the formation of a second layer FeSe. The subsequent annealing helps to annihilate the generated Fe vacancies and, thus, enhance the superconductivity in the FeSe/STO monolayer.

Influence of soil properties on selenium concentration in paddy soil and rice grains in the hilly regions of southern China

BackgroundSelenium (Se) is essential for human health and is predominantly obtained from dietary sources, particularly rice in Hunan Province, a significant rice-producing region in southern China. Investigating the relationship between Se levels in paddy soil and rice grains, along with the associated influencing factors, is critical for enhancing Se-enriched food security.ResultsAnalysis of 128,992 samples collected between 2019 and 2022 revealed that the soil Se concentration in Hunan exceeded the global average, with rice grains showing promising potential for Se enrichment. Various analytical methods, including statistical analyses, co-occurrence networks, and correlation heatmaps, were utilized to scrutinize the extensive dataset. Additionally, partial least squares path analysis elucidated the interactive effects of influencing factors on soil Se concentration, rice grain Se concentration, and Se bioconcentration factor (BCF). Soil parent materials significantly affected soil Se concentration, rice grain Se concentration, and Se BCF (p < 0.01). Factors such as soil cation exchange capacity, soil organic matter, slope, and soil concentrations of Cu, Mn, and Zn demonstrated positive correlations with soil Se concentration. Similarly, these factors exhibited positive associations with rice grain Se concentration. Conversely, negative correlations were observed between certain factors and Se BCF. As a result, predictive models were developed for soil Se, rice grain Se concentration, and Se BCF.ConclusionsThis study contributes valuable insights to inform policy-making for Se-enriched food production and to ensure regional nutritional equilibrium. Caution is recommended in areas with excessive Se levels to prevent potential poisoning risks.

High Concentrations of Se Inhibited the Growth of Rice Seedlings.

Selenium (Se) is crucial for both plants and humans, with plants acting as the main source for human Se intake. In plants, moderate Se enhances growth and increases stress resistance, whereas excessive Se leads to toxicity. The physiological mechanisms by which Se influences rice seedlings' growth are poorly understood and require additional research. In order to study the effects of selenium stress on rice seedlings, plant phenotype analysis, root scanning, metal ion content determination, physiological response index determination, hormone level determination, quantitative PCR (qPCR), and other methods were used. Our findings indicated that sodium selenite had dual effects on rice seedling growth under hydroponic conditions. At low concentrations, Se treatment promotes rice seedling growth by enhancing biomass, root length, and antioxidant capacity. Conversely, high concentrations of sodium selenite impair and damage rice, as evidenced by leaf yellowing, reduced chlorophyll content, decreased biomass, and stunted growth. Elevated Se levels also significantly affect antioxidase activities and the levels of proline, malondialdehyde, metal ions, and various phytohormones and selenium metabolism, ion transport, and antioxidant genes in rice. The adverse effects of high Se concentrations may directly disrupt protein synthesis or indirectly induce oxidative stress by altering the absorption and synthesis of other compounds. This study aims to elucidate the physiological responses of rice to Se toxicity stress and lay the groundwork for the development of Se-enriched rice varieties.

Hydrogen sulfide activates calcium signaling to confer tolerance against selenium stress in Brassica rapa

BackgroundSe (selenium) pollution is an emerging environmental concern. Excessive Se induces phytotoxicity. The endogenous H2S (hydrogen sulfide) was involved in plant adaptation to Se stress, but the signaling player of H2S remains unclear.MethodsThe study was conducted in a hydroponic system with different chemicals added to the treatment solution. Fluorescent tracking was performed to detect endogenous signaling molecules in plant tissues. Physiological changes were determined based on pharmaceutics and histochemical experiments. Gene expression was analyzed using qRT-PCR. The data were summarized using hierarchical cluster and Pearson correlation analysis.ResultsSe stress inhibited B. rapa growth (e.g. root elongation, shoot height, and seedling fresh weight and dry weight) in both dose- and time-dependent manners, with approximately 50% of root growth inhibition occurred at 20 µM Se. Se stress induced ROS (reactive oxygen species) accumulation and oxidative injury in B. rapa. Se exposure resulted in the upregulation of LCDs (L-cysteine desulfhydrase) and DCDs (D-cysteine desulfhydrase) encoding enzymes for H2S production in B. rapa at early stage of Se exposure, followed by downregulation of these genes at late stage. This was consistent with the change of endogenous H2S in B. rapa. Enhancing endogenous H2S level with NaHS (H2S donor) stimulates endogenous Ca2+ in B. rapa upon Se exposure, accompanied the attenuation of growth inhibition, ROS accumulation, oxidative injury, and cell death. The beneficial effects of H2S on detoxifying Se were blocked by decreasing endogenous Ca2+ level with Ca2+ channel blocker or Ca2+ chelator. Finally, hierarchical cluster combined with correlation analysis revealed that Ca2+ might acted as downstream of H2S to confer Se tolerance in B. rapa.ConclusionCa2+ was an important player of H2S in the regulation of plant physiological response upon Se stress. Such findings extend our knowledge of the mechanism for Se-induced phytotoxicity.Graphical

Defect induced Raman shifts and bandgap engineering in layered SnSe2+δ bulks

In the context of the extensive application prospect of two-dimensional (2D) chalcogenides, we synthesized layered SnSe2+δ bulks with defects employing a hybrid chemical vapor transport-melt approach. Both the Eg and A1g Raman characteristic peaks in SnSe2+δ are dominated by cubic anharmonicity, coupled with nonlinear temperature dependencies below 140 K. Notably, the reduction in phonon energy observed in these vibrational modes can be ascribed to defect-mediated Raman scattering, irrespective of deficient or excess Se defects. However, the lower consistency in the Raman shifts of the in-plane Eg vibrations compared to the out-of-plane A1g modes suggests that the defects predominantly entail the absence of Se atoms and the substitutions of Sn by Se, delineating a continuum of Se-deficient and Se-enriched compositions. Furthermore, Se defects induce the contraction of the indirect bandgaps, facilitating a transition from medium to narrow bandgap semiconductors in SnSe2+δ, which underscores the tunable nature of the bandgaps through the incorporation of Se defects. These discoveries present an avenue for bandgap engineering and foster a deeper comprehension of the phonon and thermal properties of layered chalcogenides for further advanced technologies.

Effects of Selenium and Cadmium on Human Liver and Kidney Functions in Exposed Black Shale Areas.

Animal experiments suggest that selenium (Se) may alleviate cadmium (Cd) toxicity in animal liver and kidneys, but its effect on human liver and kidneys remains uncertain. In China, areas with black shale have shown elevated levels of Se and Cd. According to the USEPA (U.S. Environmental Protection Agency) evaluation method, the soil and rice in these areas pose significant risks. In black shale regions such as Enshi and Zhuxi County, residents who long-term consume local rice may surpass safe Se and Cd intake levels. Significantly high median blood Se (B-Se) and urine selenium (U-Se) levels were detected in these areas, measuring 416.977μg/L and 352.690μg/L and 104.527μg/L and 51.820μg/L, respectively. Additionally, the median blood Cd (B-Cd) and urine Cd (U-Cd) levels were markedly elevated at 4.821μg/L and 3.848μg/L and at 7.750μg/L and 7.050μg/L, respectively, indicating substantial Cd exposure. Nevertheless, sensitive liver and kidney biomarkers in these groups fall within healthy reference ranges, suggesting a potential antagonistic effect of Se on Cd in the human body. Therefore, the USEPA method may not accurately assess Cd risk in exposed black shale areas. However, within the healthy ranges, residents in the Enshi study area had significantly greater median levels of serum creatinine and cystatin C, measuring 67.3μmol/L and 0.92mg/L, respectively, than those in Zhuxi did (53.6μmol/L and 0.86mg/L). In cases of excessive Se and Cd exposure, high Se and Cd levels impact the filtration function of the human kidney to some extent.

Occurrence, bioaccumulation, and risk evaluation of selenium in typical Chinese aquatic ecosystems

Selenium (Se), a trace element, is essential for biological growth; however, excess Se in water can harm aquatic organisms, including fish. Thus, increasing attention is being paid to the risk of Se in aquatic ecosystems. However, there has been little research regarding the protection of aquatic organisms from excess Se in China. To comprehensively ensure China's ecological safety, research on the water quality criteria (WQC) of Se is urgently required. Herein, water and fish samples were collected from Taihu Lake and Yellow River estuary to investigate Se distribution characteristics and bioaccumulation factors (BAFs) in aquatic ecosystems. Tissue-based toxicity data and BAFs were used to derive the WQC for Se. Quotient and probabilistic methods were used to assess the ecological risk of Se to aquatic life. The results revealed that the average levels of Se in the water samples were 1.54 and 1.07 μg/L and that the average Se levels in the fish samples were 0.87 and 0.66 mg/kg in Taihu Lake and the Yellow River estuary, respectively. Furthermore, the calculated BAF for Se in fish was 618.69 L/kg, and the calculated WQC for Se to protect aquatic organisms was 0.29 μg/L. The high levels of ecological risk associated with Se in Taihu Lake and the Yellow River estuary indicate that the aquatic risk of Se warrants further attention. This study provides scientific guidance for setting Se water quality standards to protect aquatic organisms and ensure environmental management in China.

Structural and electronic properties of MoS2 and MoSe2 monolayers grown by chemical vapor deposition on Au(111).

The exceptional electronic and photonic properties of the monolayers of transition metal dichalcogenides including the spin-orbit splitting of the valence and conduction bands at the K points of the Brillouin zone make them promising for novel applications in electronics, photonics and optoelectronics. Scalable growth of these materials and understanding of their interaction with the substrate is crucial for these applications. Here we report the growth of MoS2 and MoSe2 monolayers on Au(111) by chemical vapor deposition at ambient pressure as well as the analysis of their structural and electronic properties down to the atomic scale. To this aim, we apply ultrahigh vacuum surface sensitive techniques including scanning tunneling microscopy and spectroscopy, low-energy electron diffraction, X-ray and angle-resolved ultraviolet photoelectron spectroscopy in combination with Raman spectroscopy at ambient conditions. We demonstrate the growth of high-quality epitaxial single crystalline MoS2 and MoSe2 monolayers on Au(111) and show the impact of annealing on the monolayer/substrate interaction. Thus, as-grown and moderately annealed (<100 °C) MoSe2 monolayers are decoupled from the substrate by excess Se atoms, whereas annealing at higher temperatures (>250 °C) results in their strong coupling with the substrate caused by desorption of the excess Se. The MoS2 monolayers are strongly coupled to the substrate and the interaction remains almost unchanged even after annealing up to 450 °C.

Dietary selenium and mercury intakes from fish consumption during pregnancy: Seychelles Child Development Study Nutrition Cohort 2

Some health agencies have issued precautionary principle fish advisories to pregnant women based on the presence of methylmercury (MeHg) in fish that could possibly be harmful to the developing fetus. Fish, however, is a rich source of selenium (Se) and other nutrients essential for normal brain development. Selenium is also thought to have a key role in alleviating MeHg toxicity. We estimated the dietary Se and MeHg intakes and dietary Se:Hg molar ratios from the fish consumed in a high fish-eating pregnant cohort where no adverse associations of fish consumption and outcomes has been reported. We used dietary data collected as part of the Seychelles Child Development Study Nutrition Cohort 2 (n = 1419). In this cohort 98% of participants consumed fish, with an average intake of 106.2 g per day. Daily Se intakes from fish consumption were 61.6 µg/ d, within the range recommended during pregnancy. The mean dietary Se:Hg molar ratios was 6. These findings demonstrate that fish consumption exposes pregnant Seychellois women to Se in excess of MeHg. Based on these findings, fish consumption, especially fish with Se:Hg ratios above 1, may help pregnant women achieve optimum dietary Se intakes, which may protect against MeHg toxicity.

Molecular insights into the bonding mechanisms between selenium and dissolved organic matter

Natural organic matter (NOM) plays a critical role in the mobilization and bioavailability of metals and metalloids in the aquatic environment. Selenium (Se), an environmental contaminant of aquatic systems, has drawn increasing attention over the years. While Se is a vital micronutrient to human beings, animals and plants, excess Se intake may pose serious long-term risks. However, the interaction between Se and dissolved organic matter (DOM) remains relatively unexplored, especially the reaction mechanisms and interactions of specific NOM components of certain molecular weight and the corresponding functional group change. Herein, we report an investigation on the interactions between Se and DOM by focusing on the mass distribution profile change of operationally defined molecular weight fractions of humic acid (HA) and fulvic acid (FA). The results showed that across all molecular weights studied, HA fractions were more prone to enhanced aggregation upon introduction of Se into the system. For FA, the presence of Se species results in aggregation, dissociation, and redox reactions with the first two being the major mechanisms. Total organic carbon analysis (TOC), UV–vis spectroscopy (UV–vis), and Orbitrap MS data showed that [10, 30] kDa MW fraction had the largest aromatic decrease (CRAM-like, lignin-like and tannin-like) upon addition of SeO2 via dissociation as the dominant mechanism. Fourier transform infrared spectroscopy (FT-IR) revealed that Se based bridging or chelation of functional groups from individual DOM components through hydrogen bonding in the form of SeO⋯H and possibly Se⋯H and/or attractive electrostatic interactions lead to aggregated DOM1⋯Se⋯DOM2. It was concluded from two-dimensional correlation analyses of excitation emission matrix (EEM) and FT-IR that the preferred Se-binding follows lipid ➔ peptide ➔ tannin ➔ aromatic functionalities. These results provide new understanding of Se interactions with various NOM components in aquatic environments and provide insight for Se assessing health risk and/or treatment of Se contaminated water.

2H-2M Phase Control of WSe2 Nanosheets by Se Enrichment Toward Enhanced Electrocatalytic Hydrogen Evolution Reaction.

The phase control of transition metal dichalcogenides (TMDs) is an intriguing approach for tuning the electronic structure toward extensive applications. In this study, WSe2 nanosheets synthesized via a colloidal reaction exhibit a phase conversion from semiconducting 2H to metallic 2M under Se-rich growth conditions (i.e., increasing the concentration of Se precursor or lowering the growth temperature). High-resolution scanning transmission electron microscopy images are used to identify the stacking sequence of the 2M phase, which is distinctive from that of the 1T' phase. First-principles calculations employing various Se-rich models (intercalation and substitution) indicated that Se enrichment induces conversion to the 2M phase. The 2M phase WSe2 nanosheets with the Se excess exhibited enhanced electrocatalytic performance in the hydrogen evolution reaction (HER). In situ X-ray absorption fine structure studies suggested that the excess Se atoms in the 2M phase WSe2 enhanced the HER catalytic activity, which is supported by the Gibbs free energy (ΔGH* ) of H adsorption and the Fermi abundance function. These results provide an appealing strategy for phase control of TMD catalysts.

Thermal and Spectral Characterization of a Binary Mixture of Medazepam and Citric Acid: Eutectic Reaction and Solubility Studies

Medazepam, citric acid and their binary mixtures were studied using differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) for thermal and structural properties. The DSC data show a simple eutectic peak at 370 K. To determine the exact mole fraction at which the eutectic occurs, Tamman’s triangle was used. The obtained results show that the eutectic mixture appears at a molar fraction of medazepam of approximately 0.85. The excess thermodynamic functions GE, SE and μE were calculated, and the results were interpreted to evaluate the interactions that occur between the components of the mixture. The FTIR results were used to confirm the eutectic formation. Solubility tests in deionized water show a 40-times increase in the medazepam solubility from the eutectic mixture, from 0.73 μg/mL to 28.61 μg/mL. However, further tests showed that the acidic character of the sample was the main factor responsible for this increase.

Selenate triggers diverse oxidative responses in Astragalus species with diverse selenium tolerance and hyperaccumulation capacity

Selenium (Se) hyperaccumulators are capable of uptake and tolerate high Se dosages. Excess Se-induced oxidative responses were compared in Astragalus bisulcatus and Astragalus cicer. Plants were grown on media supplemented with 0, 25 or 75 μM selenate for 14 days. Both A. bisulcatus and A. cicer accumulated >2000 μg/g dry weight Se to the shoot but the translocation factors of A. cicer were below 1 suggesting its non hyperaccumulator nature. A. cicer showed Se sensitivity indicated by reduced seedling fresh weight, root growth and root apical meristem viability, altered element homeostasis in the presence of Se. In Se-exposed A. bisulcatus, less toxic organic Se forms (mainly MetSeCys, γ-Glu-MetSeCys, and a selenosugar) dominated, while these were absent from A. cicer suggesting that the majority of the accumulated Se may be present as inorganic forms. The glutathione-dependent processes were more affected, while ascorbate levels were not notably influenced by Se in either species. Exogenous Se triggered more intense accumulation of malondialdehyde in the sensitive A. cicer compared with the tolerant A. bisulcatus. The extent of protein carbonylation in the roots of the 75 μM Se-exposed A. cicer exceeded that of A. bisulcatus indicating a correlation between selenate sensitivity and the degree of protein carbonylation. Overall, our results reveal connection between oxidative processes and Se sensitivity/tolerance/hyperaccumulation and contribute to the understanding of the molecular responses to excess Se.

Urinary essential and toxic metal mixtures, and type 2 diabetes mellitus: Telomere shortening as an intermediary factor?

The joint effect of metal mixtures on telomere function and type 2 diabetes mellitus (T2DM) is unclear. This large-scale cross-sectional study sought to assess the role of telomere length (TL) in the relationship between urinary essential and toxic metal mixtures, and T2DM in 7410 Chinese adults ≥ 60 years of age. Essential (Cr, Cu, Zn, Se) and non-essential metals (V, Al, Sb, Sn, Cd, Pb) in urine samples were quantified, while leukocyte TL was measured from blood samples. Restricted cubic splines regression showed nonlinear relationships between single metal and T2DM, and between TL and T2DM. Bayesian kernel machine regression and quantile-based g-computation showed that the overall status of urinary metals was positively associated with risk of developing T2DM, which was mainly explained by exposure to Pb, Cd, and Sb, excessive Se intake, and high excretion of Zn. Mediation analyses showed that shortened TL mediated 27.9% of the overall positive effect of metal exposure on T2DM, and this mediation was mainly explained by toxic metal exposure and excessive Se intake. Tobacco smoke exposure, extensive cooking at home, and black tea consumption were found to be important contributors of toxic metal exposures. Further studies are needed to explore the recommended Zn dosage for T2DM patients at different stages, which may ameliorate pancreatic senescence and glycemic progression.

Porous Zn1-xCdxSe/ZnO Nanorod Photoanode Fabricated from ZnO Building Blocks Grown on Zn Foil for Photoelectrochemical Solar Hydrogen Production.

Solar energy is the most promising, efficient, environmentally friendly energy source with the potential to meet global demand due to its non-polluting nature. Herein, a porous Zn1-xCdxSe/ZnO nanorod (NR) heterojunction was synthesized by hydrothermal and low-temperature solvothermal methods. First, the ZnO NR was grown on a Zinc foil, and an inorganic-organic hybrid ZnSe(en)0.5 material was developed by the low-temperature solvothermal method. In this work, the ZnO NR acted as a base material and a building block for the growth of ZnSe(en)0.5. Moreover, after the solvothermal process, the reduced Se2- reacts with the ZnO NR and forms inorganic-organic hybrid ZnSe(en)0.5. After the selenization process, the obtained material shows a red brick color due to the absorbance of excessive Se metal particles during the solvothermal process. Furthermore, in order to enhance the photoelectrochemical properties, the Cd2+ ion exchange method was applied at various temperatures (140, 160, and 180 °C for 3 h) to produce a precursor material to a porous Zn1-xCdxSe/ZnO NR nanostructure. The optimum Zn1-xCdxSe/ZnO NR-160 photoanode showed a high photocurrent density of 7.8 mA·cm-2 at -0.5 V vs. Ag/AgCl with a hydrogen evolution rate of 199 μmol·cm-2/3 h. The improved photocurrent performance was attributed to effective light absorption and prolonged recombination lifetime.

Rapid and user-friendly detection of selenium-rich foods using a THEATER colorimetric device with Pt-Co-N-C as viewing glasses

The consumption of Se-rich foods is a highly effective means of augmenting a person’s intake of Se, which plays a critical role in human health; however, excessive Se consumption can be toxic. The determination of Se levels is therefore of paramount importance to ensure the safety of both the production and consumption of selenium-rich foods. In this study, a rapid and user-friendly method is developed for the analysis of selenium-rich foods wherein the detection process is similar to watching three-dimensional movies in a theater. A portable 3D-printed colorimetric device called the Detection THEATER (Time-saving, High-sensitive, Easy, Accurate, Telling, Economical, and Rapid) is first constructed for the rapid and visually accessible colorimetric analysis of samples in nonlaboratory settings. Subsequently, the Co-N-C nanozyme is doped with Pt to produce a Pt-Co-N-C nanozyme with superior peroxidase-like activity, which serves as the viewing glasses for signal amplification in the Detection THEATER. The Detection THEATER exhibits excellent sensitivity and accuracy, including a linear range of 0.5–1.2 μg/mL and a low detection limit of 0.026 μg/mL. The pretreatment of food samples is also optimized and simplified, thereby reducing processing times three-fold and enhancing accessibility and usability. The Pt-Co-N-C nanozyme-based Detection THEATER, demonstrated outstanding specificity and practicality, opening up a new avenue for the analysis of selenium-rich foods.

Glutathione is involved in selenium detoxification and suppresses the selenate-induced SULTR1;1 gene expression in plants

Selenium (Se) as a sulfur (S) analog is beneficial to plants. However, excessive Se is toxic. Glutathione (GSH) can protect plant cells from metal toxicity. In this study, we investigated the role of GSH in resistance to Se toxicity and in regulating sulfate/selenate transporter gene expression. We also examined the effects of Se and S treatments on GSH production and growth of Arabidopsis thaliana (a non-Se-accumulator) and broccoli (Brassica oleracea var. italica, a secondary-Se-accumulator). By treating the Arabidopsis wild-type and the glutathione-deficient mutant pad2–1 plants with and without selenate, reduced glutathione, or GSH synthesis inhibitor L-buthionine sulfoximine, we demonstrated that GSH is involved in Se detoxification. The pad2–1 mutant exhibited lower selenate tolerance, and GSH supply alleviated the toxicity. However, selenate treatment reduced GSH levels in a dose-dependent manner, which was further augmented in low sulfur (S) conditions as shown in broccoli plants. Interestingly, the selenate-induced SULTR1;1 gene expression was negatively associated with GSH levels in plants. The pad2–1 mutant showed a much higher AtSULTR1;1 expression than WT under excess Se supply, and GSH supply partially inhibited its expression. Moreover, selenate conferred higher toxicity than selenite under a low S supply in broccoli plants. In contrast, S alleviated selenate toxicity, which was associated with GSH levels. These findings demonstrate the critical role of GSH in resistance to Se toxicity and provide insights into processes related to Se toxicity resistance in plants, which enhances our understanding of metal tolerance for Se biofortification in crops.

Se(IV) reduction and extracellular biosynthesis of Nano-Se(0) by Shewanella oneidensis MR-1 and Shewanella putrefaciens

Microbial reduction of Se(IV) to Se(0) is extremely important for the detoxification of selenium oxyanion, but the reductive mechanism is still controversial. In this study, the reduction of Se(IV) by Shewanella oneidensis MR-1 and Shewanella putrefaciens was systematically investigated. The results showed that excessive Se(IV) severely inhibited the growth of microorganisms and Se(IV) reduction. The extracellular accumulation of Nano-Se(0) particles was shown to be approximately 250–650 nm in diameter. Riboflavin facilitated Se(IV) reduction, while rotenone, as an electron inhibitor, could completely inhibit Se(IV) reduction, validating the extracellular electron transport process for biosynthesized Nano-Se(0). Importantly, the amorphous Nano-Se(0) synthesized by S. oneidensis MR-1 were mixtures of helical chains and Se8 rings, while those synthesized by S. putrefaciens were mainly composed of helical chains. FTIR results demonstrated that Nano-Se(0) particles were wrapped by some proteins, organic substances and lipids, exhibiting superior dispersibility and biocompatibility. Biogenic Nano-Se(0) particles can also be considered for technological applications in various fields.