Se Absorption Research Articles

The role of selenium and nano selenium on physiological responses in plant: a review.

Selenium (Se), being an essential micronutrient, enhances plant growth and development in trace amounts. It also protects plants against different abiotic stresses by acting as an antioxidant or stimulator in a dose-dependent manner. Knowledge of Se uptake, translocation, and accumulation is crucial to achieving the inclusive benefits of Se in plants. Therefore, this review discusses the absorption, translocation, and signaling of Se in plants as well as proteomic and genomic investigations of Se shortage and toxicity. Furthermore, the physiological responses to Se in plants and its ability to mitigate abiotic stress have been included. In this golden age of nanotechnology, scientists are interested in nanostructured materials due to their advantages over bulk ones. Thus, the synthesis of nano-Se or Se nanoparticles (SeNP) and its impact on plants have been studied, highlighting the essential functions of Se NP in plant physiology. In this review, we survey the research literature from the perspective of the role of Se in plant metabolism. We also highlight the outstanding aspects of Se NP that enlighten the knowledge and importance of Se in the plant system.

Effect of Nano-Selenium on Nutritional Quality of Cowpea and Response of ABCC Transporter Family.

It is an important way for healthy Selenium (Se) supplement to transform exogenous Se into organic Se through crops. In the present study, Vigna unguiculata was selected as a test material and sprayed with biological nano selenium (SeNPs) and Na2SeO3, and its nutrient composition, antioxidant capacity, total Se and organic Se content were determined, respectively. Further, the response of ABC transporter family members in cowpea to different exogenous Se treatments was analyzed by transcriptome sequencing combined with different Se forms. The results show that the soluble protein content of cowpea increased after twice Se treatment. SeNPs treatment increased the content of cellulose in cowpea pods. Na2SeO3 treatment increased the content of vitamin C (Vc) in cowpea pods. Se treatments could significantly increase the activities of Peroxidase (POD), polyphenol oxidase (PPO) and catalase (CAT) in cowpea pods and effectively maintain the activity of Superoxide dismutase (SOD). SeNPs can reduce the content of malondialdehyde (MDA) in pods. After Se treatment, cowpea pods showed a dose-effect relationship on the absorption and accumulation of total Se, and Na2SeO3 treatment had a better effect on the increase of total Se content in cowpea pods. After treatment with SeNPs and Na2SeO3, the Se species detected in cowpea pods was mainly SeMet, followed by MeSeCys. Inorganic Se can only be detected in the high concentration treatment group. Analysis of transcriptome data of cowpea treated with Se showed that ABC transporters could play an active role in response to Se stress and Se absorption, among which ABCB, ABCC and ABCG subfamilies played a major role in Se absorption and transportation in cowpea. Further analysis by weighted gene co-expression network analysis (WGCNA) showed that the content of organic Se in cowpea treated with high concentration of SeNPs was significantly and positively correlated with the expression level of three transporters ABCC11, ABCC13 and ABCC10, which means that the ABCC subfamily may be more involved in the transmembrane transport of organic Se in cells.

Selenium accumulation in plant foods and selenium intake of residents in a moderately selenium-enriched area of Mingyueshan, Yichun, China

The aim of this study was to investigate the levels of total, organic and inorganic selenium (Se) in edible plants and surrounding soils of a moderately Se-enriched area of Mingyueshan (Yichun, China). The absorption and transport capacity of Se in plants as well as the total daily intake Se by local residents consuming the studied plants were investigated. A total of 167 samples were collected from 31 plants and their surrounding soils and measured by inductively coupled plasmamass spectrometry (ICPMS) and atomic fluorescence spectrophotometry. Selenium, mainly in organic form, was detected in most samples. Most plants were found to easily absorb inorganic Se from the soil, and based on the absorption and transport capacity, the Se distribution was as follows: root > leaf > stem or rhizome > fruit. The total daily intake of Se by local residents consuming the studied plans was 50 µg, mainly owing to Oryza sativa and leafy vegetables.

Effect of Enterobacter sp. EG16 on Selenium biofortification and speciation in pak choi (Brassica rapa ssp. chinensis)

Using plant growth promoting rhizobacteria (PGPR) to boost Se uptake and accumulation in crops is a promising recent approach to biofortification. Most studies, however, have focused on a certain dose of PGPR or Se, while the synergistic effects of simultaneously changing the concentration of both exogenous Se and PGPR on plant growth and Se bioaccumulation are rarely explored. In this study, the combined treatments of 0-2 mg L−1 Se and (3.83-11.3) ×107 CFU mL−1 PGPR strain Enterobacter sp. EG16 were used for the hydroponic experiments of pak choi (Brassica rapa) to investigate the mutual effects on plant growth and Se absorption. The growth of pak choi, in terms of plant height, number of leaves and root tips, was promoted by combining 7.65×107 CFU mL−1 EG16 and no more than 1 mg L−1 of Se. Growth was significantly inhibited when the concentration of EG16 was raised to 11.3×107 CFU mL−1. Chlorophyll content, superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities were also boosted under the same combination of Se and EG16 concentrations. In addition, the Se content of aboveground part and intact plants significantly increased with rising concentrations of EG16 and Se. Selenomethionine (SeMet), methylselenocysteine (SeMeCys) and selenocystine (SeCys2) were the main organo-Se compounds detected in pak choi, accounting for almost 90% when supplied with selenite. Among these compounds, SeMet accounted for a high proportion and SeCys2 for a relatively low percentage in most treatments. The two forms were inversely related, probably because the transformation was driven by EG16. On the other hand, the proportion of SeMeCys was significantly affected by different concentrations of exogenous Se and EG16. Selenate was also detected, indicative of selenite oxidation. In terms of both plant biomass and nutritional quality, the combined formulation of 1 mg L−1 Se and 7.65×107 CFU mL−1 of EG16 is a promising means of producing Se-enriched vegetables.

Metabonomic analysis of the haemolymph reveals the dual effects of dietary selenium supplementations on growth of silkwormBombyx mori

Selenium (Se) is a vital micronutrient for the growth and development of organisms; however, its deficiency and toxicity pose worldwide challenges. Herein, we investigated the absorption, accumulation effect, and distribution of Se in silkworms, and tested the effect of Se feeding on the antioxidant indexes of silkworm haemolymph. Results showed that low concentrations of Se (50 μM and 100 μM) significantly increased the enzyme activities of catalase, glutathione peroxidase, glutathione S-transferase and superoxide dismutase in the silkworm haemolymph compared to control and 200 μM group. In addition, metabonomic analysis could reveal the metabolic changes in silkworm haemolymph after treatment with different concentrations (50 μM, and 200 μM) of Se. Compared to un-treatment group, the amount of 90 metabolites in both of 50 μM and the 200 μM Se-treated groups displayed significant differences, with 50 up-regulated and 40 down-regulated in 50 μM group, 36 up-regulated and 54 down-regulated in 200 μM group, respectively. The main different metabolites were amino acids, carbohydrates, lipids, nucleotide metabolites and their derivatives. These results suggest that Se could affect the carbohydrate metabolism in silkworms. The difference in metabolites was subject to different changes under different concentrations of Se and consequently altered their metabolic functions to meet the required energy demands under the Se toxic stress conditions.

Dual RNA and 16S ribosomal DNA sequencing reveal arbuscular mycorrhizal fungi-mediated mitigation of selenate stress in Zea mays L. and reshaping of soil microbiota

Excessively high concentrations of selenium (Se) in soil are toxic to crop plants, and inoculation with arbuscular mycorrhizal fungi (AMF) can reverse Se stress in maize (Zea mays L.). To investigate the underlying mechanisms, maize seedlings were treated with sodium selenate (5 mg Se[VI] kg-1) and/or AMF (Funneliformis mosseae and Claroideoglomus etunicatum). Dual RNA sequencing in mycorrhiza and 16 S ribosomal DNA sequencing in soil were performed. The results showed that Se(VI) application alone decreased plant dry weight, but increased plant Se concentration, total Se content (mainly selenocysteine), and root superoxide content. Inoculation with either F. mosseae or C. etunicatum increased plant dry weight, decreased Se accumulation and selenocysteine proportion, enhanced root peroxidase activity, and alleviated oxidative stress in Se(VI)-treated plants. Inoculation also downregulated the expression of genes encoding Se transporters, assimilation enzymes, and cysteine-rich receptor-like kinases in Se(VI)-stressed plants, similar to plant–pathogen interaction and glutathione metabolism related genes. Conversely, genes encoding selenium-binding proteins and those related to phenylpropanoid biosynthesis were upregulated in inoculated plants under Se(VI) stress. Compared with Se(VI)-free plants, Se tolerance index, symbiotic feedback percentage on plant dry weight, and root colonization rate were all increased in inoculated plants under Se(VI) stress, corresponding to upregulated expression of ‘key genes’ in symbiosis. AMF inoculation increased bacterial diversity, decreased the relative abundances of selenobacteria related to plant Se absorption (e.g., Proteobacteria and Firmicutes), and improved bacterial network complexity in Se(VI)-stressed soils. We suggest that stress-mediated enhancement of mycorrhizal symbiosis contributed to plant Se(VI) tolerance, whereas AMF-mediated reshaping of soil bacterial community structure prevented excessive Se accumulation in maize.

Effects of abscisic acid on growth and selenium uptake in medicinal plant Perilla frutescens.

The aim of the present study was to explore the effects of abscisic acid (ABA) on growth and selenium (Se) absorption of the medicinal plant, Perilla frutescens. A pot experiment was conducted to evaluate the effects of different ABA concentrations (0, 1, 5, 10 and 20 μmol/L) on the physiological characteristics and Se absorption capacity of P. frutescens. Application of 5, 10 and 20 μmol/L ABA increased the shoot biomass of P. frutescens, and only 5 and 10 μmol/L ABA increased the root biomass. Application of 5, 10, and 20 μmol/L ABA increased the contents of photosynthetic pigments (chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid), superoxide dismutase activity, peroxidase activity, and soluble protein content of P. frutescens, and decreased the malondialdehyde content in P. frutescens. Only 5 and 10 μmol/L ABA used in the present study increased the catalase activity of P. frutescens. For the Se uptake, only 5 μmol/L ABA increased the Se content, Se extraction and Se bioconcentration factor of both roots and shoots. The findings of the present study indicate that 5 and 10 μmol/L ABA promotes the growth of P. frutescens, whereas 5 μmol/L ABA enhances the Se accumulation capacity in P. frutescens.

New horizons for selenium in animal nutrition and functional foods.

Selenium (Se), one of the indispensable nutrients for both human health and animal growth, participates in various physiological functions, such as antioxidant and immune responses and metabolism. The role of dietary Se, in its organic and inorganic forms, has been well documented in domestic animals. Furthermore, many feeding strategies for different animals have been developed to increase the Se concentration in animal products to address Se deficiency and even as a potential nutritional strategy to treat free radical-associated diseases. Nevertheless, studies on investigating the optimum addition of Se in feed, the long-term consequences of Se usage in food for animal nutrition, the mechanism of metallic Se nanoparticle (SeNP) transformation in vivo, and the nutritional effects of SeNPs on feed workers and the environment are urgently needed. Starting from the absorption and metabolism mechanism of Se, this review discusses the antioxidant role of Se in detail. Based on this characteristic, we further investigated the application of Se in animal health and described some unresolved issues and unanswered questions warranting further investigation. This review is expected to provide a theoretical reference for improving the quality of food animal meat as well as for the development of Se-based biological nutrition enhancement technology.

Embracing nanotechnology for selenium application in aquafeeds

AbstractSelenium (Se) is an important micronutrient that has been used in aquafeeds for the normal growth, welfare and health of aquatic animals. Through nanotechnology, Se can be converted into nanoparticles that are more bioavailable, utilized and absorbed by aquatic animals. However, this is still a new and emerging area of research in aquafeeds. This paper aims to review the effect of Se and Se nanoparticles (Se‐NPs) application in aquafeeds on aquatic animals. Specifically, different compounds of Se, requirement levels by different species, effects on animal growth, physiology, antioxidant capacity and immune response have been highlighted. The review shows that the application of Se in aquafeeds could improve the growth performance, physiology, antioxidant enzymes, immunity and disease resistance in aquatic animals. However, the effectiveness could be highly influenced by the source of Se, aquaculture species and administration quantity. Through nanotechnology, the utilization and absorption of Se could be improved while reducing its toxicity. Therefore, Se‐NPs present an efficient way to utilize nutrients in aquafeeds. Important gaps, however, exist in the current knowledge, particularly with regard to the response of shrimps and crustaceans to dietary supplementation of Se and Se‐NPs as most of the existing studies have focused on fish species. Also, some species of economic importance and life stages have not been investigated, which hinders the embracement of nanotechnology in aquafeeds production.

First-principles investigations of metal chalcogenides Tl2Hg3X4(X=S,Se,Te) for advanced optoelectronic and thermoelectric applications

The crystalline metal chalcogenides materials have got great attraction due to their narrow bandgap materials for renewable energy applications. In the present work, we have broadly explored the optoelectronic and thermoelectric properties of Tl2Hg3X4(X ​= ​S, Se, Te) using first-principle calculations. The Tl2Hg3S4, Tl2Hg3Se4, and Tl2Hg3Te4 have a monoclinic crystal structure and exhibit semiconducting nature with band gaps of 2.0 ​eV, 1.5 ​eV, and 0.8 ​eV, respectively. In the visible region, a minimum absorption occurred for the S dopant, but as we replace S with Se/Te a halted absorption is seen in the visible region that confirming their nominal employment in optoelectronic applications (solar cells). Optical absorption of Se and Te dopant in Tl2Hg3X4 is found in I.R and the visible region of the radiation, making them promising candidates for optoelectronics. Further, the thermoelectric parameters versus carrier concentration are studied for these materials using the BoltzTraP code. The drifts of thermoelectric parameters for the Te dopant diverge from the tendencies of S and Se dopants at specific temperatures i.e., at 300, 500, and 700 ​K. The power factor (PF) of Tl2Hg3S4 and Tl2Hg3Se4 (Tl2Hg3Te4) favor n-type (p-type) doping, indicating higher mobility of electrons(holes) as compared with the holes (electrons). These findings suggest the practical realization of these compounds for emerging optoelectronic and renewable energy device applications.

Combined metabolome and transcriptome analysis reveal the mechanism of selenate influence on the growth and quality of cabbage (Brassica oleracea var. capitata L.)

Selenium is an essential trace element for human and animal health, and an appropriate amount of Se can promote the growth and development of plants. Cabbage is a popular cruciferous vegetable with a good ability to accumulate Se, and Se-enriched cabbage can be used as an important Se source for humans. However, the effects of Se-enriched cultivation and the Se accumulation mechanism in cabbage are still unclear. In this study, the effects of different concentrations (0, 0.1, 0.2, 0.4, 0.8, and 1.6 mmol/L) of selenate on cabbage growth and quality were explored. A low concentration of selenate (0.1 mmol/L) promoted growth and nutritional quality. The contents of total Se, S, selenocystine, and selenomethionine significantly increased following selenate application. Important secondary metabolites, namely glucosinolates, phenolic acids, and flavonoids, participate in the response to selenate in cabbage. Comparative transcriptome and metabolomics analysis revealed that SULTR2.2, SULTR3.1, APS, APK2, HMT, MMT, and NTR2 played important roles in Se absorption and conversion. Additionally, the SUR1, UGT74B1, and ST5b genes and cytochrome P450 family genes CYP83A1, CYP79A2, and CYP79F1 may be the crucial genes in the glucosinolates biosynthesis and regulation pathway. The PAL, 4CL, CAD, CHS3, FLS, and CYP73A5 genes were involved in flavonoid and phenolic acid accumulation under selenate treatment. These results reveal the internal relationships in the regulatory network of Se metabolism and secondary metabolite biosynthesis in cabbage and help further the understanding of the physiological and molecular mechanism of how Se biofortification affects cabbage quality, thereby providing genetic resources and a technical basis for the breeding and cultivation of Se-enriched cabbage with excellent nutritional quality.

Integrative Transcriptome and Proteome Analysis Reveals the Absorption and Metabolism of Selenium in Tea Plants [Camellia sinensis (L.) O. Kuntze

Certain tea plants (Camellia sinensis) have the ability to accumulate selenium. In plants, the predominant forms of bioavailable Se are selenite (SeO32–) and selenate (SeO42–). We applied transcriptomics and proteomics to hydroponically grown plants treated with selenite or selenate for 48 h in the attempt to elucidate the selenium absorption and assimilation mechanisms in tea. A total of 1,844 differentially expressed genes (DEGs) and 691 differentially expressed proteins (DEPs) were obtained by comparing the Na2SeO3 and Na2SeO4 treatments against the control. A GO analysis showed that the genes related to amino acid and protein metabolism and redox reaction were strongly upregulated in the plants under the Na2SeO3 treatment. A KEGG pathway analysis revealed that numerous genes involved in amino acid and glutathione metabolism were upregulated, genes and proteins associated with glutathione metabolism and ubiquinone and terpenoid-quinone biosynthesis were highly expressed. Genes participating in DNA and RNA metabolism were identified and proteins related to glutathione metabolism were detected in tea plants supplemented with Na2SeO4. ABC, nitrate and sugar transporter genes were differentially expressed in response to selenite and selenate. Phosphate transporter (PHT3;1a, PHT1;3b, and PHT1;8) and aquaporin (NIP2;1) genes were upregulated in the presence of selenite. Sulfate transporter (SULTR1;1 and SULTR2;1) expression increased in response to selenate exposure. The results of the present study have clarified Se absorption and metabolism in tea plants, and play an important theoretical reference significance for the breeding and cultivation of selenium-enriched tea varieties.

Duckweed (Lemna minor L.) Successfully Accumulates Selenium from Selenium-Impacted Water

The absorption of selenium (Se) from water by Lemna minor L. and the influence of different concentrations and forms of Se on its biochemical and morphological characteristics were studied. Plants were exposed to various concentrations of Se: 1 mg Se L−1, 2 mg Se L−1 and 5 mg Se L−1 in sodium selenite and sodium selenate solutions and in a combination of selenite (2 mg Se L−1) and selenate (2 mg Se L−1). When the Se was added in the form of selenate, plants accumulated higher amounts of Se compared to plants exposed to selenite. Comparisons of the combined addition of selenite and selenate (2 + 2 mg Se L−1) with their individual applications (2 and 5 mg Se L−1) showed that for the combination, the L. minor fronds accumulated more Se than in selenite alone. Plants exposed to any of the concentrations of sodium selenate or sodium selenite, or the combination of selenite and selenate, showed inferior physiological performances, and lower concentrations of photosynthetic pigments, compared to control plants. Consequently, growth was also suppressed under the stress conditions caused by higher concentrations of Se in any form. The efficient absorption of Se from the water by L. minor indicates the potential use of this species in phytoremediation processes for waters polluted with Se.

Influence of arbuscular mycorrhizal fungi on selenium uptake by winter wheat depends on the level of selenate spiked in soil

Selenium (Se) deficiency has been a public health concern for years. Arbuscular mycorrhizal fungi (AMF) play an essential role in improving Se uptake in crops, but related mechanisms still remain unclear. To explore the influence of AMF on uptake of Se in winter wheat, a pot experiment was conducted to inoculate wheat with Funneliformis mosseae (F.m) or not under different levels of selenate in soil. The present results indicated that inoculation of F.m significantly (p < 0.05) increased Se concentration in shoots and roots of wheat under low level of selenate (≤5.0 mg kg−1) treatments, while the contrary pattern was recorded under high level of selenate (15 and 20 mg kg−1) treatments. Moreover, inoculation of F.m significantly increased concentration of available Se in soil by 4.68–34.05%. Under selenate ≤5 mg kg−1 treatments, the expression of TaeSultr1;1 and TaeSultr1;3 in roots of mycorrhizal wheat was significantly up-regulated by 3.06–5.53 and 0.63–5.12 times, while reached saturation under selenate >5 mg kg−1 treatments. In addition, partial least squares path modeling (PLS-PM) showed that inoculation of AMF directly affected the expression of sulfate transporter and that both sulfate transporter and soil Se fractions played a significant positive effect on plant Se content. The present study indicated that AMF on Se concentration in winter wheat depends on the level of selenate spiked in soil and added to our understanding of the functions and applications of AMF on crop Se absorption.

Using 77Se-Labelled Foliar Fertilisers to Determine How Se Transfers Within Wheat Over Time.

Foliar selenium (Se) fertilisation has been shown to be more efficient than soil-applied fertilisation, but the dynamics of absorption and translocation have not yet been explored. An experiment was undertaken to investigate time-dependent changes in the absorption, transformation, and distribution of Se in wheat when 77Se-enriched sodium selenate (Sefert) was applied to the leaves at a rate of 3.33 μg Se per kg soil (equivalent to 10 g ha−1) and two growth stages, namely stem elongation, Zadoks stage 31/32 (GS1), and heading stage, Zadoks stage 57 (GS2). The effect of urea inclusion in foliar Se fertilisers on the penetration rates of Se was also investigated. Wheat was harvested at 3, 10, and 17 days and 3, 10, and 34 days after Se applications at GS1 and GS2, respectively. Applying foliar Se, irrespective of the formulation, brought grain Se concentration to a level high enough to be considered adequate for biofortification. Inclusion of N in the foliar Se solution applied at an early growth stage increased recoveries in the plants, likely due to improved absorption of applied Se through the young leaves. At a later growth stage, the inclusion of N in foliar Se solutions was also beneficial as it improved the assimilation of applied inorganic Se into bioavailable selenomethionine, which was then rapidly translocated to the grain. The practical knowledge gained about the optimisation of Se fertiliser formulation, method, and timing of application will be of importance in refining biofortification programs across different climatic regimes.

143 Effect of Supplementary Selenium Source on Dairy Cow Performance, Antioxidant Status, and Apparent Absorption and Retention

Abstract The objective of this experiment was to determine how source of selenium (Se) affects dairy cow performance, antioxidant status, and apparent absorption and retention. Multiparous Holstein cows (n = 24; 597 ± 49 kg BW) were blocked by days in milk (161 ± 18) and randomly assigned to receive 0.3 mg/kg of either: 1) organic Se (selenized yeast; ORG; Sel-Plex-Alltech); or, 2) inorganic Se (sodium selenite; INO) premix, top dressed and mixed into a ration daily. After an 11-week adaptation period (blood and milk sampled monthly), cows received an intraruminal dose of Se77 (either Se77 yeast or NaSe77O3) followed by a 4-day period of blood and rumen fluid sampling, and total collection of feces, urine, and milk. Data were analyzed using PROC GLIMMIX in SAS with fixed effects of treatment, time, and their interaction, and random effect of block. Daily DMI (23 ± 0.6 kg), milk yield (35 ± 1.2 kg), plasma glutathione peroxidase (64 ± 4.2 U), and serum Se (0.11 ± 0.003 µg/g) were not different between treatments during the adaptation period. Serum Se77 maximum concentration and area under the curve (AUC) were not different between treatments for 72 hours following infusion, but rumen fluid Se77 AUC was higher (P = 0.02) for ORG cows. Apparent absorption (64 ± 1.3%) and retention (44 ± 1.5%) of the Se77 dose did not differ between treatments. The ORG cows had lower urinary excretion (13 vs. 17 ± 0.6%; P &amp;lt; 0.01), higher milk excretion (6 vs. 2 ± 0.3%; P &amp;lt; 0.01), and similar fecal excretion (36 ± 1.3%; P = 0.9) of Se77 compared to INO cows. These results indicate that ORG Se increased Se content of milk and decreased Se excretion in urine, but did not alter performance, antioxidant status, and apparent absorption and retention of Se in mid-lactation cows.

Selenium in Soil-Plant-Microbe: A Review.

Selenium (Se) plays an important role in geochemistry and is an essential trace element for humans and animals. This review summarizes the transformation and accumulation of Se in the plant-soil-microbe system. As one of the important reservoirs of Se, soil is an important material basis of its entry into the food chain through plants. Soil with an appropriate amount of Se is beneficial for plant growth and plays a valuable role in a stress-resistant environment. Among the many migration and transformation pathways, the transformation of Se by microorganisms is particularly important and is the main form of Se transformation in the soil environment. In this review, the role and form transformation of Se in plants, soil, and microorganisms; the role of Se in plants; the form, input, and output of Se in soil; the absorption and transformation of Se by plants; and the role of microorganisms in Se transformation are presented. In addition to describing the migration and transformation laws of Se in the environment, this review expounds on the main directions and trends of Se research in the agricultural field as well as current gaps and difficulties in Se-related research. Overall, this reviews aims to provide necessary information and theoretical references for the development of Se-rich agriculture.

Microbes: a potential tool for selenium biofortification.

Selenium (Se) is a component of many enzymes and indispensable for human health due to its characteristics of reducing oxidative stress and enhancing immunity. Human beings take Se mainly from Se-containing crops. Taking measures to biofortify crops with Se may lead to improved public health. Se accumulation in plants mainly depends on the content and bioavailability of Se in soil. Beneficial microbes may change the chemical form and bioavailability of Se. This review highlights the potential role of microbes in promoting Se uptake and accumulation in crops and the related mechanisms. The potential approaches of microbial enhancement of Se biofortification can be summarized in the following four aspects: (1) microbes alter soil properties and impact the redox chemistry of Se to improve the bioavailability of Se in soil; (2) beneficial microbes regulate root morphology and stimulate the development of plants through the release of certain secretions, facilitating Se uptake in plants; (3) microbes upregulate the expression of certain genes and proteins that are related to Se metabolism in plants; and (4) the inoculation of microbes give rise to the generation of certain metabolites in plants contributing to Se absorption. Considering the ecological safety and economic feasibility, microbial enhancement is a potential tool for Se biofortification. For further study, the recombination and establishment of synthesis microbes is of potential benefit in Se-enrichment agriculture.

Accumulation and translocation of selenium in a soil–rice system in Guangxi, China

ABSTRACT Selenium (Se) is an essential element for the human body. Humans meet their basic Se requirements primarily through food consumption. The largest Se-rich contiguous area in China is located in the southeast of Guangxi. In this study, the Se accumulation and translocation in the Guangxi rice–soil system was assessed. Organically bound Se (O-Se) was found to be the main type of soil Se (72.5%), and had a good linear relationship with soil total Se (TSe) and soil organic matter (SOM); the three forms were closely related and thus, affected each other. The contents of Se in the various plant organs were highly correlated. The roots had the greatest Se concentration, followed by the stems, grains, and lastly the leaves. The distribution coefficient of grain/stem (0.74) was greater than that of grain/leaf (0.54), suggesting that the migration of Se in plants may have apical dominance and/or reproductive advantages. Ligand-exchangeable Se, water-soluble Se, and residual Se had little effect on the accumulation of Se in the soil and plants. The soil S content showed no significant correlation with the various types of soil Se and TSe, but showed a low correlation with the Se content in various plant organs. SOM played a special role in the translocation of Se between the soil and plants, which affected the absorption and accumulation of Se by plants. SOM can affect the content of O-Se and, consequently, of TSe in the soil. SOM can also directly or indirectly affect the Se content in various plant organs, especially the Se concentration in rice grains.

Selenium-oxidizing Agrobacterium sp. T3F4 steadily colonizes in soil promoting selenium uptake by pak choi (Brassica campestris)

Selenium (Se) deficiency in soil is linked to its low content in edible crops, resulting in adverse impacts on the health of 15% of the global population. The crop mainly absorbs oxidized selenate and selenite from soil, then converts them into organic Se. However, the role of Se-oxidizing bacteria in soil Se oxidation, Se bioavailability and Se absorption into plants remains unclear. The strain Agrobacterium sp. T3F4, isolated from seleniferous soil, was able to oxidize elemental Se into selenite under pure culture conditions. The green fluorescent protein (gfp)-gene-marked strain (T3F4-GFP) and elemental Se or selenite (5 mg·kg−1) were added to pak choi (Brassica campestris ssp. chinensis) pot cultures. Observation of the fluorescence and viable counting indicated that GFP-expressing bacterial cells steadily colonized the soil in the pots and the leaves of the pak choi, reaching up to 6.6 × 106 and 2.0 × 105 CFU g−1 at 21 days post cultivation, respectively. Moreover, the total Se content (mostly organic Se) was significantly increased in the pak choi under T3F4 inoculated pot culture, with elemental Se(0) being oxidized into Se(IV), and soil Se(IV) being dissolved before being absorbed by the crop. After strain T3F4 was inoculated, no significant differences in microbial diversity were observed in the soils and roots, whereas the abundance of Rhizobium spp. was significantly increased. To our knowledge, this is the first time that Se-oxidizing Agrobacterium sp. T3F4 has been found to steadily colonize soil and plant tissues, and that its addition to soil increases the absorption of Se in plants. This study provides a potential strategy for Se biofortification.