Selenium-Functionalized Corn Starch as a Biodegradable GPx Mimic with High Catalytic Performance.

Selenium-functionalized starch (Se-starch80) is one of the main functional foods used for selenium supplementation. In traditional agriculture, Se-starch has some deficiencies such as long growth cycle and unstable selenium content that prevent its antioxidant performance. In this study, Se-starch was prepared by the nucleophilic addition between NaSeH and carbon-carbon double bond of octenyl succinic anhydride waxy corn starch ester (OSA starch). Some techniques such as 1HNMR, XPS, SEM-EDS, XRD and FT-IR were used to characterize the relevant samples and the results showed that the modification did not destroy the starch framework significantly and the catalytic center (negative divalent selenium) was anchored on the starch framework. The intensive distribution of catalytic center on the starch surface and the hydrophobic microenvironments derived from the OSA chains furnished the Se-starch80 with a high GPx-like catalytic activity (initial reaction rate = 3.64 µM/min). This value was about 1.5 × 105 times higher than that of a typical small-molecule GPx mimic (PhSeSePh). In addition, the Se-starch80, without any cytotoxicity, showed a saturated kinetic catalytic behavior that is similar to a typical enzyme. This work exemplifies a biodegradable selenium-functionalized polymer platform for the high-performing GPx mimic.

Evaluation of selenium bioavailability to Brassica juncea in representative Chinese soils based on diffusive gradients in thin-films (DGT) and chemical extraction methods.

Selenium (Se) is an essential micronutrient for humans but is toxic when consumed in excess through the food chain, such as vegetables. Therefore, it is imperative to understand the relationship between the bioavailability of Se in soil and its uptake in edible parts of vegetables. This study investigated Se bioavailability of Brassica juncea in six representative Chinese soils treated with different concentrations of exogenous selenate fertilizer (0-2 mg·kg-1) by comparing diffusive gradients in thin-films (DGT) and chemical extraction methods. The correlation coefficients between the Se uptake by Brassica juncea and soil available Se determined by different extraction methods was as follows: DGT > KCl > Water > EDTA > KH2PO4 > NaHCO3 extractions. In addition, soil properties were correlated between Brassica juncea and soil Se concentrations determined by chemical extraction methods, while the DGT method was independent of soil properties. DGT was more suitable for the measurement of Se thresholds for Udic Ferrisols, Mollisols, Stagnic Anthrosols, Fluviogenic Loamy Paddy soil, Silty Loam soil, and Calcaric Regosols with values of 373.34, 648.68, 436.29, 589.84, 295.35, and 464.95 µg·L-1, respectively. Thus, DGT may be an effective method for the prediction and evaluation of Se bioavailability to Brassica juncea in different soil types.

DOM derivations determine the distribution and bioavailability of DOM-Se in selenate applied soil and mechanisms.

Straw amendment and plant root exudates modify the quality and quantities of soil dissolved organic matter (DOM) and then manipulate the fractions of soil selenium (Se) and its bioavailability. Two typical soils with distinct pH were selected to investigate the effect of different contributors on DOM-Se in soil. The mechanisms relying on the variation in DOM characteristics (quality, quantity and composition) were explored by UV-Vis, ATR-FTIR and 3D-EEM. Straw amendment significantly (p < 0.05) suppressed the selenate bioavailability. The reduction in wheat Se content was greater in krasnozems than in Lou soil, as more HA fraction appeared in krasnozems. The root exudates of wheat mainly elevated the low molecular hydrophilic compounds (Hy) in soil, which contributed to the SOL-Hy-Se fractions and thus grain Se in soils (p < 0.01). However, straw amendment promoted DOM transforming from small molecules (Hy and FA) to aromatic large molecules (HA), when accompanied with the reduction and retention of Se associated with these molecules. As a result, selenium bioavailability and toxicity reduced with DOM amendment and DOM-Se transformation.

Nitric oxide alleviates selenium toxicity in rice by regulating antioxidation, selenium uptake, speciation and gene expression.

In plants, excess selenium (Se) causes toxicity, while the beneficial effects of nitric oxide (NO) have verified in plants under various abiotic conditions. In order to ensure safely Se-enriched rice production, the objective of the research was to clarify how exogenous NO alleviated high Se toxicity in rice. Under high Se (25 µM) stress, the effects of exogenous NO (by applying sodium nitroprusside, an exogenous NO donor) on growth parameters, Se content, Se speciation, photosynthesis, antioxidant system, expressions of Se transport and metabolism-related genes (phosphate transporter, OsPT2; S-adenosylmethionine synthase 1, OsSAMS1; cysteine synthase, OsCS; Se-binding protein gene, OsSBP1) in rice seedlings were investigated by a hydroponic experiment. The results showed that exogenous NO alleviated high Se-induced irreversible damage to root morphology, growth, photosynthesis, antioxidant capacity and decreased the contents of MDA, H2O2 and proline significantly in rice seedlings. Compared with high Se treatment, application of exogenous NO reduced root Se content (10%), and the Se(VI) decreased by 100% in root and shoot. Besides, exogenous NO decreased the accumulation of inorganic Se speciation in rice roots and shoots. Also, the qRT-PCR analysis showed that down-regulated gene expressions of OsPT2, OsSAMS1 and OsCS affected significantly via exogenous NO. So, the exogenous NO could effectively decrease the toxicity of high Se treatment in rice.

Prediction of selenium uptake by pak choi in several agricultural soils based on diffusive gradients in thin-films technique and single extraction.

The accurate assessment of soil selenium (Se) bioavailability is crucial for Se biofortification in Se-deficient areas and risk assessment in selenosis areas. However, a universally accepted approach to evaluate Se bioavailability in soil is currently lacking. This research investigated Se bioavailability in six soils treated with selenite (Se(IV)) or selenate (Se(VI)) by comparing diffusive gradients in thin-films (DGT) technique and chemical extraction methods through pot experiments. A bioindicator method was used to evaluate Se concentrations in pak choi and compare the results with the Se concentration measured by other methods. Results showed that chemical extraction methods presented different extraction efficiencies for available Se over a range of soil types, and the same extraction method had various extraction efficiencies for different Se species in the same soil. DGT measured Se concentrations (CDGT-Se) for Se(VI) treatment were 2.3-34.1 times of those for Se(IV) treatment. KH2PO4-K2HPO4 and AB-DTPA extractable Se could predict the bioavailability of soil Se, but they were disturbed by soil properties. HAc extraction was unsuitable for evaluating Se bioavailability in different Se(IV)-treated soils. By contrast, DGT technique was preferable for predicting plant uptake of Se(IV) over chemical extraction methods. Although DGT technique was independent of soil properties, KH2PO4-K2HPO4 extraction provided the best fitting regression equation for Se(VI) when it was dependent on soil organic matter. Thus, KH2PO4-K2HPO4 extraction may be preferred to assess Se(VI) bioavailability in different soil types on a large scale.

Impact of land use/land cover change on the topsoil selenium concentration and its potential bioavailability in a karst area of southwest China.

Selenium (Se) is an essential micronutrient for human health, and its abundance and potential bioavailability in the soil are of increasing concern worldwide. To date, how total soil Se and its bioavailability would respond to human disturbance or future environmental change is not yet clear, and associated controlling factors remain incompletely understood. Here, we collected soil samples (0-15 cm) from different land use/land cover types, including active cropland, grassland, shrubland, and secondary forest, in a Se-enriched area of Guangxi, southwest China. Total Se concentration and its potential bioavailability, as estimated by phosphate extractability, were investigated. Total soil Se concentration (Setotal) for all samples ranged from 220 to 1820 µg kg-1, with an arithmetic average value of 676 ± 24 µg kg-1 (Mean ± SE, the same below). The concentration of phosphate extractable Se (Sephosphate) varied between 1 and 257 µg kg-1, with an arithmetic mean value of 79 ± 5 µg kg-1, accounting for on average 13 ± 1% of the Setotal. Among the four land use/land cover types, Setotal and Sephosphate were generally more enriched in the secondary forest than those in the grassland and cropland. The content of soil organic carbon (SOC) was the overriding edaphic factor controlling the abundance and potential bioavailability of Se in topsoils. In addition, climatic variables such as mean annual precipitation and mean annual temperature were also key factors affecting the abundance and potential bioavailability of soil Se. Our results suggest that changes in land use/land cover types may deeply influence Se biogeochemistry likely via alterations in soil properties, particularly SOC content.

Assessing the uptake of selenium from naturally enriched soils by maize (Zea mays L.) using diffusive gradients in thin-films technique (DGT) and traditional extractions.

A generally accepted method to predict selenium (Se) bioavailability of long-term contaminated soils has not yet been established, even if risk assessments in selenosis areas are crucial. In this study, a set of methods were tested to assess the bioavailability of Se to field maize. Fifty maize (Zea mays L.) samples and corresponding soils were collected from a selenosis area (Ziyang, China). The diffusive gradients in thin-films (DGT) technique and the traditional chemical extraction methods, including seven single-step extraction procedures and a five-step sequential extraction were used to predict the bioaccumulation of Se in plant. The result verified the presence of 50% of total Se in the form of residual Se fraction, followed by organic-bound and Fe-Mn oxide-bound Se fractions in soil. In addition, Se6+, Se4+, and Se2- were all detected in the solution extracted by H2O, KCl, phosphate-buffered solution (PBS), NaHCO3, ethylenediaminetetraacetic acid-2Na (EDTA-2Na) and ammonium bicarbonate-diethylenetriaminepentaacetic acid (AB-DTPA), but Se6+ was not extracted by NaOH. The Se extracted by single-step extraction methods was weakly correlated with the Se uptake by plants with relatively high Se concentration (>3 mg·kg-1). The abilities of the tested methods to predict Se bioavailability in naturally Se-enriched soils declined in the following order: DGT > soil solution > PBS > KCl > H2O > NaHCO3 > EDTA > DTPA > NaOH. The ratio of CDGT to soil solution Se (Csoln) totaled 0.13, indicating an extremely low Se supply from the soil solid phase to the soil solution. Se measured by DGT was mainly derived from the soluble and exchangeable Se fractions that can accurately reflect the plant-absorbed Se pool. Therefore, the DGT technique is highly applicable in the simultaneous prediction of Se bioavailability in naturally Se-enriched soils.

Spatial variations in soil selenium and residential dietary selenium intake in a selenium-rich county, Shitai, Anhui, China.

Shitai, a selenium (Se)-rich county in Anhui, China, has been reported for its resident longevity in the last 20 years. A recent survey by the Anhui Bureau of Geological Survey showed that soil Se contents in the Shitai area ranged from 0.05 to 51.20 mg/kg, with an average of 0.56 mg/kg. To explore the potential relationship between longevity and natural-occurring Se contents in Shitai county, Se concentrations were determined in Shitai's food chain (including soils and foods) and the daily Se intakes and hair Se contents were calculated for the residents. In the present study, 33 soil samples, 66 food samples and 82 hair samples were randomly collected from field sites, local food markets and male and female residents in downtown Shitai and in four nearby villages (Dashan, Xianyu, Yongfu and Yuantou). The total Se contents in all samples and the levels of water soluble, exchangeable, acid soluble, organic bound and residual Se in soil samples were determined with hydride generation - atomic fluorescence spectrometry. The total Se contents in soils ranged from 227 to 2603 µg/kg, with the averages of 1607 ±â€¯242 µg/kg in Dashan, 1149 ±â€¯118 µg/kg in Xianyu, 521 ±â€¯157 µg/kg in Yongfu, and 363 ±â€¯140 µg/kg in Yuantou. The soil bioavailable Se content (soluble and exchangeable Se) in Dashan was highest (14.98%), followed by Xianyu (13.69%), Yongfu (13.18%) and Yuantou (9.38%). For food samples, the highest Se concentration of grains was 468.5 µg/kg in Dashan, while lowest was observed in downtown (41.7 µg/kg). The estimated daily Se intake of residents in Dashan reached 298.4 µg/d/adult, which is about 5 times higher than the recommend nutrient intake in China (60 µg/d/adult), and 6-10 times higher than the levels observed in Xianyu (47.6 µg/d/adult), Yuantou (46.1 µg/d/adult), Yongfu (40.0 µg/d/adult), and downtown (30.0 µg/d/adult). Although hair Se contents in Dashan (male: 709.2 µg/kg; female: 589.2 µg/kg) were significantly higher than those at the other study sites, no significant relationships between daily Se intakes and hair Se contents were observed. The present study demonstrated that Se levels in soils, foods, resident dietary intake and human hairs in Shitai County varied significantly; therefore, the region could be a unique field site to study the direct relationship between Se and human health.

Selenium Accumulation, Antioxidant Enzyme Levels, and Amino Acids Composition in Chinese Mitten Crab (Eriocheir sinensis) Fed Selenium-Biofortified Corn.

The effects of selenium (Se)-biofortified corn on the total Se contents, the antioxidant enzyme levels, and the amino acids composition in Chinese mitten crab (Eriocheir sinensis) during the stage of the fifth shelling to maturity were investigated in the present study. The culture density of crabs was 600 per 667 m², and they were continuously fed 120.4 mg Se from Se-biofortified corn per 667 m² every two days for 90 days. The results showed that the total muscle Se levels in the crabs were significantly increased (p < 0.05). Activities of hemolymph supernatant enzymes including alkaline phosphatase (AKP), lysozyme (LZM), glutathione peroxidase (GPx), and superoxide dismutase (SOD) were also enhanced (p < 0.05). The protein and crude fat levels at maturity were higher than those at the fourth molt. The levels of total essential amino acids (∑EAAs) and total delicious amino acids (∑DAAs) were significantly increased (p < 0.05). We demonstrate that the feeding of Se-biofortified corn could significantly improve total muscle Se concentrations and hemolymph supernatant antioxidant enzyme activities in Chinese mitten crab, and slow down the rapid decline of ∑EAAs and ∑DAAs at maturity, thus improving the nutritional quality of Chinese mitten crab.

Design, synthesis, anti-TMV, fungicidal, and insecticidal activity evaluation of 1,2,3,4-tetrahydro-ß-carboline-3-carboxylic acid derivatives based on virus inhibitors of plant sources.

By drawing the creation ideas of botanical pesticides, a series of tetrahydro-ß-carboline-3-carboxylic acid derivatives were designed and synthesized, and first evaluated for their anti-TMV, fungicidal and insecticidal activities. Most of these derivatives exhibited good antiviral activity against TMV both in vitro and in vivo. Especially, the activities of compounds 8 and 15 in vivo were higher than that of ribavirin. The compound 8 exhibited more than 70% fungicidal activities against Cercospora arachidicola Hori, Alternaria solani, Bipolaris maydis, and Rhizoctonia solani at 50mg/kg, compounds 16 and 20 exhibited more than 60% insecticidal activities against Mythimna separate and Ostrinia nubilalis.