Se Availability Research Articles

Improving soil selenium availability as a strategy to promote selenium uptake by high-Se rice cultivar

The aim of this research was to investigate the mechanism of selenium (Se) utilization by roots between two rice genotypes. The plant Se concentration, root organic acids secretion, soil Se fractions, soil pH, and infrared spectrum of soil were all determined through a root box experiment to clarify the differences in Se availability of rhizosphere soils between high- and low-Se rice cultivars. The results revealed that the grain Se concentration of the high-Se cultivar was significantly higher than that of the low-Se cultivar. The concentration of available Se, e.g. water-soluble and exchangeable, in the rhizosphere soil of the high-Se rice cultivar was dramatically higher than that of the low-Se rice cultivar, and the opposite result was observed in non-rhizosphere soil. The organic acids secretion of the high-Se rice cultivar showed a greater degree of reduction than that of the low-Se rice cultivar in response to the increase of Se application rates, while the infrared spectrum intensity of clay mineral in the rhizosphere of the high-Se rice cultivar exhibited a greater degree of increase than that of the low-Se rice cultivar. In addition, the pH of the rhizosphere soil of the high-Se rice cultivar was significantly higher than that of the low-Se rice cultivar at 0 mg kg−1 Se treatment. The results demonstrated that the high-Se rice cultivar could obtain more Se than the low-Se rice cultivar by mass flow, which is limited by the concentration of mobile Se in soil; The high-Se rice cultivar had a greater ability to activate Se by increasing soil pH than the low-Se rice cultivar; The secretion of organic acids could activate Se by degrading clay minerals, while the high-Se rice cultivar may have a greater ability to regulate the secretion of organic acids. The present study suggests the high-Se rice cultivar has stronger ability to increase Se availability of rhizosphere soil than the low-Se rice cultivar.

Selenium supplementation suppresses immunological and serological features of lupus in B6.Sle1b mice

Systemic lupus erythematosus (SLE) is a debilitating multi-factorial immunological disorder characterized by increased inflammation and development of anti-nuclear autoantibodies. Selenium (Se) is an essential trace element with beneficial anti-cancer and anti-inflammatory immunological functions. In our previous proteomics study, analysis of Se-responsive markers in the circulation of Se-supplemented healthy men showed a significant increase in complement proteins. Additionally, Se supplementation prolonged the life span of lupus prone NZB/NZW-F1 mice. To better understand the protective immunological role of Se in SLE pathogenesis, we have investigated the impact of Se on B cells and macrophages using in vitro Se supplementation assays and the B6.Sle1b mouse model of lupus with an oral Se or placebo supplementation regimen. Analysis of Se-treated B6.Sle1b mice showed reduced splenomegaly and splenic cellularity compared to untreated B6. Sle1b mice. A significant reduction in total B cells and notably germinal center (GC) B cell numbers was observed. However, other cell types including T cells, Tregs, DCs and pDCs were unaffected. Consistent with reduced GC B cells there was a significant reduction in autoantibodies to dsDNA and SmRNP of the IgG2b and IgG2c subclass upon Se supplementation. We found that increased Se availability leads to impaired differentiation and maturation of macrophages from mouse bone marrow derived progenitors in vitro. Additionally, Se treatment during in vitro activation of B cells with anti-CD40L and LPS inhibited optimal B cell activation. Overall our data indicate that Se supplementation inhibits activation, differentiation and maturation of B cells and macrophages. Its specific inhibitory effect on B cell activation and GC B cell differentiation could be explored as a potential therapeutic supplement for SLE patients.

Apparent availability of zinc, selenium and manganese as inorganic metal salts or organic forms in plant-based diets for Atlantic salmon (Salmo salar)

The composition of salmonid diets has changed from the use of mainly marine ingredients to increased use of plant ingredients, and this has an impact on the mineral content and availability. Minerals, like zinc (Zn), selenium (Se) and manganese (Mn), are supplemented to diets as inorganic or organic forms to cover the nutritional requirements of fish. This study compared the apparent availability (AA) of Zn, Se and Mn from inorganic metal salts and their organic forms in Atlantic salmon. Sixteen diets were prepared based on a two-level factorial design (24). The tested factors were Zn additive source (A), Se additive source (B), Mn additive source (C) and phytic acid level (D). The diets were fed to Atlantic salmon for 11 days, faeces were collected by stripping, and the total content of mineral and yttrium in diets and faeces were determined by inductively coupled plasma mass spectrometry. Data obtained were used to estimate the AA for the minerals. Zinc additive source had no significant effect on the AA of Zn. However, the Se and Mn additive source had significant effects on the AA of Se and Mn, respectively. Higher AA of Se was achieved with selenomethionine than with selenite, and Mn sulphate was more available than Mn chelate of glycine. The phytic acid level did not significantly affect the AA of Zn, Se or Mn. However, several interactions between mineral additive sources and the phytic acid level significantly affected the AA of Zn, Se and Mn.

Effects of straw amendment on selenium aging in soils: Mechanism and influential factors

Soil dissolved organic matter (DOM) alters heavy metal availability, but whether straw amendment can manipulate soil selenium (Se) speciation and availability through DOM mineralization remains unclear. In this study, allochthonous maize straw and selenate were incubated together in four different soils for 1 y. The transformation and availability of DOM associated Se (DOM-Se) was investigated during aging. Results indicated that soil solution and soil particle surfaces were dominated by hexavalent hydrophilic acid-bound Se (Hy-Se). The amount of fulvic acid bound Se in soil solution (SOL-FA-Se) was higher than humic acid bound Se in soil solution (SOL-HA-Se), except in krasnozems, and mainly existed as hexavalent Se (Se(VI)). Tetravalent Se (Se(IV)) was the main valence state of FA-Se adsorbed on soil particle surfaces (EX-FA-Se) after 5 w of aging. The proportion of soil-available Se (SOL + EX-Se) decreased with increasing straw rate. However, under an application rate of 7500 kg·hm−2, soluble Se fraction (SOL-Se) reduction was minimal in acidic soils (18.7%–34.7%), and the organic bound Se fraction (OM-Se) was maximally promoted in alkaline soils (18.2%–39.1%). FA and HON could enhance the availability of Se in the soil solution and on particle surfaces of acidic soil with high organic matter content. While Se incorporation with HA could accelerate the fixation of Se into the solid phase of soil. Three mechanisms were involved in DOM-Se aging: (1) Reduction, ligand adsorption, and inner/outer-sphere complexation associated with the functional groups of straw-derived DOM, including hydroxyls, carboxyl, methyl, and aromatic phenolic compounds; (2) interconnection of EX-FA-Se between non-residual and residual Se pools; and (3) promotion by soil electrical conductivity (EC), clay, OM, and straw application. The dual effect of DOM on Se aging was highly reliant on the characteristics of the materials and soil properties. In conclusion, straw amendment could return selenium in soil and reduce soluble Se loss.

Lettuce Biofortification with Selenium in Chitosan-Polyacrylic Acid Complexes

Selenium (Se) is an essential element of the human diet. Therefore, it is necessary to implement Se in selenium-deficient soils and in the nutrient solution of soilless system culture. Although it is not considered as an essential element for plants, Se provides benefits at the level of redox metabolism, increasing the resistance of plants to various stress factors. The increase of the availability of Se, with the use of biopolymer complexes, was sought in Lactuca sativa var. Great Lakes, grown in substrate pots treated with SeO2 (5 mg Se/plant), chitosan-polyacrylic acid complex + Se (Cs-PAA + Se) (5 mg Se/plant), and chitosan-polyacrylic acid complex (Cs-PAA). The redox metabolism was modified by increasing the enzymatic activity of catalase and glutathione peroxidase. The use of Cs-PAA + Se biopolymer complexes increased Se up to 24 mg/Kg dry weight (DW) in plant tissues.

Effects of selenium fertilization on selenium availability in rice soil.

Selenium (Se) is easy to be fixed in acidic rice soil of South China, and thus its availability is low. The aim of this study was to investigate the influence of Se fertilizer on Se availability in rice rhizosphere and non-rhizosphere soils. The results showed that Se application increased yield and rice Se concentration. The water soluble, exchangeable, Fe/Mn oxide-bound, organic matter/sulfide-bound, and residual Se contents of the rhizosphere soil were lower than those of the non-rhizosphere soil. There was no significant difference in the migration coefficient of Se between the rhizosphere and non-rhizosphere soils. Se application had no significant effect on the migration coefficient of Se between roots and leaves but improved its migration coefficient between leaves and grains. The secretion of organic acids was increased by the application of 0.5 mg·kg-1 and decreased by the application of 1.0 and 5.0 mg·kg-1 Se. The secretion of organic acids had no significant effect on the rhizosphere soil pH. The pH of rhizosphere soil was higher than that of the non-rhizosphere soil, while the application of Se decreased the pH of the rhizosphere soil. With the increases of Se application, the intensity of the infrared absorption of clay mineral (kaolinite) in the rhizosphere soil showed an increasing trend. In this study, most of the Se was transformed into forms that were difficult to be absorbed and utilized by rice and difficult to move to rhizosphere soil. The enhancement of soil Se availability following the secretion of organic acids was not due to its effects on soil pH.

Soil management and ionic strength on selenite retention in oxidic soils

ABSTRACT Sorption of selenium (Se) on soils may be influenced by factors that are changed though agricultural practices usually performed for crop production, such as soil pH, competing anion and organic matter contents, among others. This study aimed to evaluate the influence of soil management and ionic strength (IS) on Se retention in Brazilian soils, which is important to predict Se availability in both systems, native and cultivated soils. For that, adsorption and desorption reactions of Se were evaluated in 16 soil samples (eight from cultivated soils and eight from native soils), using solutions containing 100 and 500 µg L-1 Se in the form of sodium selenate and in two IS, 15 and 150 mM. Se adsorption varied as a function of IS for most soils, which may indicate that the adsorption mechanism by outer-sphere complex is important for selenate retention in the studied soils, but future studies involving other techniques, such as spectroscopic studies, are needed to more clearly confirm the adsorption mechanism. In general, adsorption varied in relation to soil characteristics, and native soils adsorbed larger Se amounts than the cultivated soils. In terms of desorption, soils which had larger Se adsorbed amounts also presented larger desorbed amounts. Finally, IS and soil management influenced the availability of selenate in the studied soils.

Assessing the mobilization of As, Cr, Mo, and Se in Egyptian lacustrine and calcareous soils using sequential extraction and biogeochemical microcosm techniques

The mobilization of As, Cr, Mo, and Se in four soil profiles representing Sodic Fluvisols (lacustrine deposits) and Haplic Calcisols (calcareous deposits) in Egypt were assessed using sequential extraction and an advanced biogeochemical microcosm technique. The concentrations of total and AB-DTPA-extractable elements were determined. The geochemical fractions (acid soluble (F1), reducible (F2), oxidizable (F3), and residual (F4) fraction) of the elements were extracted using the Commission of the European Communities Bureau of Reference (BCR) procedure. An automated biogeochemical microcosm apparatus was used to assess the redox-induced mobilization of As, Cr, Mo, and Se in the lacustrine soil as affected by the changes of redox potential (EH) and the EH-dependent changes on pH, Fe, Mn, SO42−, and dissolved organic carbon (DOC). The lacustrine soils showed higher total concentrations (mg kg−1) of As (38–70), Cr (58–85), Mo (6–13), and Se (22–45) than the calcareous soils. The pollution load index was higher than unity (3.0–11.3) and Se was the major contributor to the soil pollution followed by Mo, As, and Cr. The residual fraction was dominant for the four elements in the two soils. The acid soluble fraction and AB-DTPA extractable concentrations of As and Cr were below the detection limits, while Se and Mo were detected in the studied profiles. The reducible fraction was the dominant non-residual fraction for As and Se in the two soils and for Mo in the lacustrine soils, while the oxidizable fraction was the dominant non-residual fraction for Cr in the two soils and for Mo in the calcareous soils. The acid soluble fraction, availability, and potential mobility (PMF = ∑F1-F3) of Se and Mo were higher in the calcareous than the lacustrine soils. Selenium showed the highest redox-induced mobilization, followed by Mo and As, while dissolved Cr was lower than the detection limit under both reducing and oxidizing conditions. Mobilization of Se, Mo, and As increased under reducing conditions. Mobilization of As and Se was positively affected by the chemistry of Fe, Mn, SO42− and DOC. Dissolved Mo was affected by the EH dependent changes of pH and the chemistry of S and SO42−. The results of the biogeochemical microcosm supported the sequential extractions data. Increasing the dissolved concentrations of As, Mo, and Se under reducing conditions in the temporally flooded lacustrine rice soil might increase their release and transfer into the groundwater and the food chain which might increase the potential environmental risks.

Effect of selenium-enriched organic material amendment on selenium fraction transformation and bioavailability in soil

To exploit the plant byproducts from selenium (Se) biofortification and reduce environmental risk of inorganic Se fertilizer, pot experiment was conducted in this study. The effects of Se-enriched wheat (Triticum aestivum L.) straw (WS + Se) and pak choi (Brassica chinensis L.) (P + Se) amendment on organo-selenium speciation transformation in soil and its bioavailability was evaluated by pak choi uptake. The Se contents of the cultivated pak choi in treatments amended with the same amount of Se-enriched wheat straw and pak choi were 1.7 and 9.7 times in the shoots and 2.3 and 6.3 times in the roots compared with control treatment. Soil respiration rate was significantly increased after all organic material amendment in soil (p < 0.05), which accelerated the mineralization of organic materials and thus resulted in soluble Se (SOL-Se), exchangeable Se (EX-Se), and fulvic acid-bound Se (FA-Se) fraction increasing by 25.2–29.2%, 9–13.8%, and 4.92–8.28%, respectively. In addition, both Pearson correlation and cluster analysis showed that EX-Se and FA-Se were better indicators for soil Se availability in organic material amendment soils. The Marquardt–Levenberg Model well described the dynamic kinetics of FA-Se content after Se-enriched organic material amendment in soil mainly because of the mineralization of organic carbon and organo-selenium. The utilization of Se in P + Se treatment was significantly higher than those in WS + Se treatment because of the different mineralization rates and the amount of FA-Se in soil. Se-enriched organic materials amendment can not only increase the availability of selenium in soil but also avoid the waste of valuable Se source.

Selenium behavior in the soil environment and its implication for human health

ABSTRACT Selenium (Se) is an important element that was discovered in 1817, and since the 1960s, it has been regarded as an essential micronutrient for both animals and humans, playing among other functions a relevant role in the antioxidant system of mammals. Inadequate blood Se levels in the human body is a well-known concern in many parts of the world. This malnutrition problem is often due to Se-poor diet, probably as a result of the low Se availability in soils where crops are growing. Nowadays, it is known that not only the total content, but also the inorganic and organic forms of Se contained in foods are important for human nutrition. However, paradoxically some regions of the world present high Se levels in soils causing several functional disorders and diseases in people who live in seleniferous areas. As essential micronutrient, Se should be supplied in controlled amounts to avoid harmful effects. Therefore, taking into account the importance of the soils as a way to ensure the adequate Se supply for the population, this review has dealt with Se behavior in soil environment (e.g., Se forms and adsorption and desorption reactions) and its relevance for the human health. As a final message, the further understanding of Se behavior in soils to predict its availability for crops in different systems will be a significant approach in future studies to establish forms and safe doses of Se to be added in fertilizers. Agronomic and genetic biofortification of staple crops with Se has been suggested as an important tool to improve Se intake by population in Se-poor sites.

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.

Aminoglycoside-driven biosynthesis of selenium-deficient Selenoprotein P

Selenoprotein biosynthesis relies on the co-translational insertion of selenocysteine in response to UGA codons. Aminoglycoside antibiotics interfere with ribosomal function and may cause codon misreading. We hypothesized that biosynthesis of the selenium (Se) transporter selenoprotein P (SELENOP) is particularly sensitive to antibiotics due to its ten in frame UGA codons. As liver regulates Se metabolism, we tested the aminoglycosides G418 and gentamicin in hepatoma cell lines (HepG2, Hep3B and Hepa1-6) and in experimental mice. In vitro, SELENOP levels increased strongly in response to G418, whereas expression of the glutathione peroxidases GPX1 and GPX2 was marginally affected. Se content of G418-induced SELENOP was dependent on Se availability, and was completely suppressed by G418 under Se-poor conditions. Selenocysteine residues were replaced mainly by cysteine, tryptophan and arginine in a codon-specific manner. Interestingly, in young healthy mice, antibiotic treatment failed to affect Selenop biosynthesis to a detectable degree. These findings suggest that the interfering activity of aminoglycosides on selenoprotein biosynthesis can be severe, but depend on the Se status, and other parameters likely including age and general health. Focused analyses with aminoglycoside-treated patients are needed next to evaluate a possible interference of selenoprotein biosynthesis by the antibiotics and elucidate potential side effects.

Dynamic Differences of Uptake and Translocation of Exogenous Selenium by Different Crops and Its Mechanism

The study aimed to find out the dynamic changes of selenium (Se) uptake with crops growing and to provide better understanding on the translocation of Se in soil-plant system. Pot experiments and laboratory analysis were carried out, in which 6 crops were planted for eight weeks in the soils treated with selenite and selenate. The results showed that there was a significant difference in the plant dynamic uptake pattern for selenite and selenate. Se concentration in shoots and roots of all tested plants continuously declined with growth since the third week after planting for selenate treatment; while Se concentration in roots of plants gradually increased with the growth, and that for shoots firstly increased and then leveled off or decreased for selenite treatment. Crops could accumulate Se throughout the whole growing period, while 80% of the Se in plants was uptaken in the first 6 weeks. Among the 6 tested plants, the Se concentration in the shoots and roots of mustard was the highest, followed by the shoots of wheat for selenate treatment. The Se concentration in shoots of carrot was the highest, while that in roots was the lowest for selenite treatment. For the same Se treatment, the Se concentrations in both roots and shoots of broccoli, purple cabbage and flowering Chinese cabbage were similar. Broccoli, purple cabbage, flowering Chinese cabbage, mustard and wheat had higher translocation ability to transport selenate than selenite from roots to shoots, whereas carrot had the same ability for translocating selenite and selenate. Biological dilution affected the dynamic changes of the Se content in crops, especially for selenate treatment, and a significant negative correlation between Se concentration of plants and their biomass further verified this. However, the changes of biomass of plants with growing period couldn't explain the total inverse dynamic uptake pattern for selenite and selenate. A significant positive correlation was observed between Se accumulations amount in six crops with available Se changes in soil during the corresponding growing period for selenate treatment, while no such correlation was found for selenite treatment. Se accumulation in crops grown on selenite-treated soil accounted for 0.5%-18.1% of soil available Se, whereas that in selenate treatment was 1.1-4.5 times of soil available Se except for carrot. In conclusion, the dynamic changes of Se uptake with crop growth were the comprehensive results of the absorption and transport capacity of crops, Se availability in soil and biological dilution. It should be considered as a whole in the selenium biofortification.

Effects of Initial Selenium Status on Apparent Dietary Selenium Requirements in Rodents

Robust biomarkers – that are specific for the nutrient, fall dramatically in deficiency, and reach well‐defined plateaus – are essential for the careful determination of dietary nutrient requirements (Adv Nutr 2016;7:1129). A second key component of dietary nutrient requirement studies is initial status at the start of an experiment. Se‐adequate male weanling rats fed Se‐deficient diets supplemented with graded levels of Se (as selenite) for 4 wk result in sigmoidal Se response curves with well‐defined plateaus for glutathione peroxidase (Gpx) activity, and with plateau breakpoints indicating minimum Se requirements of 0.06, 0.06, and 0.09 μg Se/g diet based on liver Gpx4, plasma Gpx3 and liver Gpx1 activity, respectively. Underlying these requirements, the Se requirement for liver Gpx1 mRNA is 0.06 μg Se/g diet. When second‐generation Se‐deficient weanling male rats were fed graded Se levels for 4 wk, apparent dietary Se requirements increased to 0.08, 0.1 and 0.14 μg Se/g for liver Gpx4, plasma Gpx3, and liver Gpx1 activities, respectively. The Se requirement for liver Gpx1 mRNA was 0.08 μg Se/g diet, which is 25% higher than when starting with Se‐adequate pups (Biol Trace Elem Res 2016, in press). Clearly, repleting Se‐deficient rats using an identical paradigm increased apparent dietary Se requirements by 33–67%, showing that limited dietary Se was being diverted to replete deeper body pools of Se. The higher dietary Se required to protect liver Gpx1 mRNA from nonsense mediated decay further substantiates this shift of Se from liver to other tissues. To explore in a preliminary study the role of Gpx1 mRNA and selenoprotein expression on restoration of Se status, Gpx1 wildtype (Gpx1+/+), heterozygote (Gpx1+/−), and knockout (Gpx1−/−) mice were fed Se‐deficient diets for 16 wk, then re‐supplemented with graded levels of dietary Se (0–0.3 μg Se/g) for 7 days to partially replete Gpx activities. Liver Gpx1 activity in Gpx1+/+ mice reached a plateau with 0.15 μg Se/g, whereas in Gpx1+/− mice, liver Gpx1 activity increased linearly over the full dietary range from 0 to 0.3 μg Se/g, showing the effect of limited Gpx1 mRNA as well as Se availability; there was no increase in Gpx1 activity in Gpx1−/− mice, as expected. In contrast, red blood cell (RBC) Gpx1 activity was little altered by 0 to 0.15 μg Se/g in both Gpx1+/+ and Gpx1+/− mice, but then reached a similar level for both genotypes at 0.3 μg Se/g, suggesting that Se availability but not mRNA was controlling level of RBC Gpx1. The plasma Gpx3 activity Se response curve for Gpx1+/+ mice was similar to the Se response curve for RBC Gpx1 activity for Gpx1+/+ mice, only reaching a maximum at 0.3 μg Se/g. Surprisingly, the Se response curve for plasma Gpx3 activity in Gpx1−/− mice overlay the response curve for Gpx1+/+ mice, indicating that similar quantities of Se were transported to kidney for Gpx3 synthesis, whereas Gpx1+/− mice fed 0.3 μg Se/g had considerable less Gpx3 activity than Gpx1+/+ or Gpx1−/− mice, again suggesting that Se was diverted to other tissues. Collectively, these studies illustrate that diversion of nutrient to depleted stores can result in higher apparent nutrient requirements when starting with initially depleted animals.Support or Funding InformationWisconsin Alumni Foundation Selenium Nutrition Research Fund (No. 2046295)

Assessment of bioavailability of selenium in different plant-soil systems by diffusive gradients in thin-films (DGT)

Uptake of selenium (Se) by plants largely depend on the availability of Se in soil. Soils and plants were sampled four times within 8 weeks of plant growth in pot experiments using four plant species. Sequential extraction and diffusive gradients in thin-films (DGT) method were employed to measure Se concentrations in potted soils in selenite- or selenate-amended soils. Results showed that DGT-measured Se concentrations (CDGT−Se) were generally several folds higher for selenate than selenite amended soils, which were obviously affected by the plant species and the duration of their growth. For example, the folds in soil planted with mustard were 1.49–3.47 and those in soils planted with purple cabbage and broccoli, which grew for 3 and 4 weeks after sowing, were 1.06–2.14 and only 0.15–0.62 after 6 weeks of growth. The selenate-amended soil planted with wheat showed an extremely high CDGT−Se compared with selenite-amended soil, except the last harvest. Furthermore, minimal changes in CDGT−Se and soluble Se(IV) were found in selenite-amended soils during plant growth, whereas significant changes were observed in selenate-amended soils (p < 0.05). Additionally, Se distribution in various fractions of soil remarkably changed; the soils planted with purple cabbage and broccoli showed the most obvious change followed by wheat and mustard. Soluble Se(VI) and exchangeable Se(VI) were likely the major sources of CDGT−Se in selenate-amended soils, and soluble Se(IV) was the possible source of CDGT−Se in selenite-amended soils. In selenate-amended soils, soluble Se(VI) and exchangeable Se(VI) were significantly correlated with Se concentrations in purple cabbage, broccoli, and mustard; in wheat, Se concentration was significantly correlated only with soluble Se(VI) but not with exchangeable Se. CDGT−Se eventually became positively correlated with Se concentrations accumulated by different plants, indicating that DGT is a feasible method in predicting plant uptake of selenate but not of selenite.

Effects of selenite and selenate application on distribution and transformation of selenium fractions in soil and its bioavailability for wheat (Triticum aestivum L.).

This study investigated the effect of selenate and selenite application on the distribution, transformation of selenium (Se) fractions in soil, as well as the accumulation and availability of Se in each part of wheat plants. A pot experiment was conducted using different concentrations of exogenous selenite or selenate (0.5, 1, 2.5, 5, and 10mgSekg-1 soil). Sequential extraction was used to determine the Se fractions in soil, and different models were used to study the behavior of Se in soil and its availability to wheat. Results showed that the distribution and availability of Se in soil and its accumulation in wheat affected both by Se concentrations and forms of exogenous Se. In selenite-treated soil, the proportion of exchangeable and carbonate-bound Se (EXC-Se) (21-42%) fraction increased compared to that in control (12%), while organic matter-bound Se (OM-Se) (23-33%) and Fe-Mn oxide-bound Se (FMO-Se) (11-15%) fractions decreased compare with those in control (37 and 32%, respectively). In selenate-treated soil, soluble-Se (SOL-Se) fraction (30-54%) increased and the OM-Se (9.8-20%) and FMO-Se (4.7-14.2%) fractions decreased compared with those in control. Residual Se (RES-Se) fraction was increased for selenite (7.4-13.4%) and selenate (12-20%) treatments compared with that in control (6.5%). In comparison with control, the available Se (SOL-Se+EXC-Se) fraction increased for both selenite (32-47%) or selenate (54-72%) treatments. Moreover, at the same rate of Se application, Se availability was higher in wheat grown in selenate-treated soils than that in selenite-treated soils. The redistribution index (U ts) of Se increased from 1 (in control) to 1.2-1.9 and 1.5-2 for selenite and selenate treatments, respectively; additionally, the mobility factor (MF) in selenate-treated soil was 40-90% higher than that in selenite-treated soil. Furthermore, relative bonding intensity (I R ) for both selenite (0.38-0.45) and selenate treatment (0.33-0.41) decreased compared with that in control (0.55). These differences indicated that selenite and selenate varied in terms of fixation capacities in soil, in transformation and distribution of Se in soil fractions, and in their availability to plants. The results of Michaelis-Menten equation demonstrated the high affinity of leaf to selenate, and the high affinity of roots and grains to selenite. Selenate was dominant in nearly all parts of wheat plants and in each application level. However, the affinity of selenite to wheat grains suggests that selenite is a useful Se fertilizer that must be considered in biofortification programs. In-depth studies at the pot and field scales by using different wheat varieties and application methods of Se in different ecological zones must be conducted to elucidate the mechanism and biochemical properties of Se in soil-plant system and ultimately produce Se-rich staple foods.

Adsorption-desorption reactions of selenium (VI) in tropical cultivated and uncultivated soils under Cerrado biome

Soil management may affect selenium (Se) adsorption capacity. This study investigated adsorption and desorption of Se (VI) in selected Brazilian soils from the Cerrado biome, an area of ever increasing importance for agriculture expansion in Brazil. Soil samples were collected from cultivated and uncultivated soils, comprising clayed and sandy soils. Following chemical and mineralogical characterization, soil samples were subjected to Se adsorption and desorption tests. Adsorption was evaluated after a 72-h reaction with increasing concentrations of Se (0–2000 μg L−1) added as Na2SeO4 in a NaCl electrolyte solution (pH 5.5; ionic strength 15 mmol L−1). Desorption, as well as distribution coefficients (Kd) for selenate were also assessed. Soil management affected Se adsorption capacity, i.e., Se adsorbed amounts were higher for uncultivated soils, when compared to cultivated ones. Such results were also supported by data of Kd and maximum adsorption capacity of Se. This fact was attributed mainly to the presence of greater amounts of competing anions, especially phosphate, in cultivated soils, due to fertilizer application. Phosphate may compete with selenate for adsorption sites, decreasing Se retention. For the same group of soils (cultivated and uncultivated), Se adsorption was greater in the clayed soils compared to sandy ones. Our results support the idea that adding Se (VI) to the soil is a good strategy to increase Se levels in food crops (agronomic biofortification), especially when crops are grown in soils that have been cultivated over the time due to their low Se adsorption capacity (high Se availability).

Modeling and gene knockdown to assess the contribution of nonsense-mediated decay, premature termination, and selenocysteine insertion to the selenoprotein hierarchy.

The expression of selenoproteins, a specific group of proteins that incorporates selenocysteine, is hierarchically regulated by the availability of Se, with some, but not all selenoprotein mRNA transcripts decreasing in abundance with decreasing Se. Selenocysteine insertion into the peptide chain occurs during translation following recoding of an internal UGA stop codon. There is increasing evidence that this UGA recoding competes with premature translation termination, which is followed by nonsense-mediated decay (NMD) of the transcript. In this study, we tested the hypothesis that the susceptibility of different selenoprotein mRNAs to premature termination during translation and differential sensitivity of selenoprotein transcripts to NMD are major factors in the selenoprotein hierarchy. Selenoprotein transcript abundance was measured in Caco-2 cells using real-time PCR under different Se conditions and the data obtained fitted to mathematical models of selenoprotein translation. A calibrated model that included a combination of differential sensitivity of selenoprotein transcripts to NMD and different frequency of non-NMD related premature translation termination was able to fit all the measurements. The model predictions were tested using SiRNA to knock down expression of the crucial NMD factor UPF1 (up-frameshift protein 1) and selenoprotein mRNA expression. The calibrated model was able to predict the effect of UPF1 knockdown on gene expression for all tested selenoproteins, except SPS2 (selenophosphate synthetase), which itself is essential for selenoprotein synthesis. These results indicate an important role for NMD in the hierarchical regulation of selenoprotein mRNAs, with the exception of SPS2 whose expression is likely regulated by a different mechanism.

Effect of Intensive Greenhouse Vegetable Cultivation on Selenium Availability in Soil

Soil properties dramatically change after long-term greenhouse vegetable cultivation, which further affects soil selenium (Se) nutritional status and plant Se uptake. An evaluation of Se availability after long-term greenhouse vegetable cultivation (GVC) can help in better understanding its influential factors under GVC conditions and will also facilitate further regulation of soil Se nutrition in GVC systems. Two typical GVC bases were chosen: one with clayey and acidic soil in Nanjing, southern China, and the other with sandy alkaline soil in Shouguang, northern China. Twenty-seven surface soil samples at the Nanjing base and 61 surface soil samples at the Shouguang base were collected according to cultivation duration and cultivation intensity. Soil properties including soil available Se (PO3−4-Se) and total Se (T-Se) were analyzed. The results showed that soil PO3−4-Se was significantly and negatively correlated with soil Olsen-P, available K (A-K), and electrical conductivity (EC) at the Nanjing base. At the Shouguang base, however, no significant correlation was found between soil PO3−4-Se and Olsen-P and EC, and soil PO3−4-Se increased with increasing soil organic matter (OM). Intensively utilized greenhouse vegetable cultivation caused significant changes in soil properties and further affected soil Se availability. Due to different management practices, the dominant factors affecting Se availability varied between the two GVC bases. At the Nanjing base, the dominant influential factor on soil Se availability was soil nutritional status, especially Olsen-P and A-K status. At the Shouguang base, where organic fertilizers were applied at high rates, soil OM was the dominant influential factor.

Improving selenium status in plant nutrition and quality

Abstract Selenium (Se) is an essential micronutrient for human health due to its antioxidant capabilities. The Se content around the world is highly variable from 0.005 mg kg -1 in areas from China and Finland to 8,000 mg kg in seleniferous soils from Tuva-Russia. However, about one billion of people in the world wide are Se deficient. During the last decade, studies related with strategies for Se biofortification in food plants for human nutrition have significantly increased because this metalloid is incorporated into human metabolism mainly as a constituent of food plants. Similarly, Se biofortification is important in pastures for increasing the Se content in cattle to enrich meat and to prevent disease associated to Se deficiency as white muscle disease. In China, two endemic diseases have been related to Se deficiency: Keshan and Keshin–Beck diseases.Agronomic biofortification by using inorganic Se sources is a current practice in countries as China, Finland, and USA. In Chile, fertilization by using chemical compounds with Se is an uncommon practice due the edaphoclimatic characteristics of Andisols, which represent around 60% of agricultural soils of southern Chile. Recent studies showed that microorganisms as bacteria and arbuscular mycorrhizal fungi play an important role in the transformations and Se availability, representing an interesting biotechnological alternative to Se biofortification.This review is focalized to describing Se behavior in soil-plant system and the possible strategies to improving Se content, including the use of microorganisms as biotechnological tools for increasing plant nutrition and quality. Specific attention will be devoted to volcanic soils of Southern Chile, where different factors concur to enhance the Se-deficiency problem.