Interactions between selenium and sulphur nutrition in Arabidopsis thaliana

Variation in the mineral element concentration of Moringa oleifera Lam. and M. stenopetala (Bak. f.) Cuf.: Role in human nutrition

BACKGROUND

Moringa oleifera (MO) and M. stenopetala (MS) (family Moringaceae; order Brassicales) are multipurpose tree/shrub species. They thrive under marginal environmental conditions and produce nutritious edible parts. The aim of this study was to determine the mineral composition of different parts of MO and MS growing in their natural environments and their potential role in alleviating human mineral micronutrient deficiencies (MND) in sub-Saharan Africa.

METHODS

Edible parts of MO (n = 146) and MS (n = 50), co-occurring cereals/vegetables and soils (n = 95) underneath their canopy were sampled from localities in southern Ethiopia and Kenya. The concentrations of seven mineral elements, namely, calcium (Ca), copper (Cu), iodine (I), iron (Fe), magnesium (Mg), selenium (Se), and zinc (Zn) in edible parts and soils were determined using inductively coupled plasma-mass spectrometry.

RESULTS

In Ethiopian crops, MS leaves contained the highest median concentrations of all elements except Cu and Zn, which were greater in Enset (a.k.a., false banana). In Kenya, Mo flowers and MS leaves had the highest median Se concentration of 1.56 mg kg-1 and 3.96 mg kg-1, respectively. The median concentration of Se in MS leaves was 7-fold, 10-fold, 23-fold, 117-fold and 147-fold more than that in brassica leaves, amaranth leaves, baobab fruits, sorghum grain and maize grain, respectively. The median Se concentration was 78-fold and 98-fold greater in MO seeds than in sorghum and maize grain, respectively. There was a strong relationship between soil total Se and potassium dihydrogen phosphate (KH2PO4)-extractable Se, and Se concentration in the leaves of MO and MS.

CONCLUSION

This study confirms previous studies that Moringa is a good source of several of the measured mineral nutrients, and it includes the first wide assessment of Se and I concentrations in edible parts of MO and MS grown in various localities. Increasing the consumption of MO and MS, especially the leaves as a fresh vegetable or in powdered form, could reduce the prevalence of MNDs, most notably Se deficiency.

Selenium and Sulfur to Produce Allium Functional Crops

Selenium is an element that must be considered in the nutrition of certain crops since its use allows the obtaining of biofortified crops with a positive impact on human health. The objective of this review is to present the information on the use of Se and S in the cultivation of plants of the genus Allium. The main proposal is to use Allium as specialist plants for biofortification with Se and S, considering the natural ability to accumulate both elements in different phytochemicals, which promotes the functional value of Allium. In spite of this, in the agricultural production of these species, the addition of sulfur is not realized to obtain functional foods and plants more resistant; it is only sought to cover the necessary requirements for growth. On the other hand, selenium does not appear in the agronomic management plans of most of the producers. Including S and Se fertilization as part of agronomic management can substantially improve Allium crop production. Allium species may be suitable to carry out biofortification with Se; this practice can be combined with the intensive use of S to obtain crops with higher production and sensory, nutritional, and functional quality.

The fascinating facets of plant selenium accumulation - biochemistry, physiology, evolution and ecology

Contents 1582 I. 1582 II. 1583 III. 1588 IV. 1590 V. 1592 1592 References 1592 SUMMARY: The importance of selenium (Se) for medicine, industry and the environment is increasingly apparent. Se is essential for many species, including humans, but toxic at elevated concentrations. Plant Se accumulation and volatilization may be applied in crop biofortification and phytoremediation. Topics covered here include beneficial and toxic effects of Se on plants, mechanisms of Se accumulation and tolerance in plants and algae, Se hyperaccumulation, and ecological and evolutionary aspects of these processes. Plant species differ in the concentration and forms of Se accumulated, Se partitioning at the whole-plant and tissue levels, and the capacity to distinguish Se from sulfur. Mechanisms of Se hyperaccumulation and its adaptive significance appear to involve constitutive up-regulation of sulfate/selenate uptake and assimilation, associated with elevated concentrations of defense-related hormones. Hyperaccumulation has evolved independently in at least three plant families, probably as an elemental defense mechanism and perhaps mediating elemental allelopathy. Elevated plant Se protects plants from generalist herbivores and pathogens, but also gives rise to the evolution of Se-resistant specialists. Plant Se accumulation affects ecological interactions with herbivores, pollinators, neighboring plants, and microbes. Hyperaccumulation tends to negatively affect Se-sensitive ecological partners while facilitating Se-resistant partners, potentially affecting species composition and Se cycling in seleniferous ecosystems.

An Overview of Selenium Uptake, Metabolism, and Toxicity in Plants

Selenium (Se) is an essential micronutrient for humans and animals, but lead to toxicity when taken in excessive amounts. Plants are the main source of dietary Se, but essentiality of Se for plants is still controversial. However, Se at low doses protects the plants from variety of abiotic stresses such as cold, drought, desiccation, and metal stress. In animals, Se acts as an antioxidant and helps in reproduction, immune responses, thyroid hormone metabolism. Selenium is chemically similar to sulfur, hence taken up inside the plants via sulfur transporters present inside root plasma membrane, metabolized via sulfur assimilatory pathway, and volatilized into atmosphere. Selenium induced oxidative stress, distorted protein structure and function, are the main causes of Se toxicity in plants at high doses. Plants can play vital role in overcoming Se deficiency and Se toxicity in different regions of the world, hence, detailed mechanism of Se metabolism inside the plants is necessary for designing effective Se phytoremediation and biofortification strategies.

Selenium Biofortification and Phytoremediation Phytotechnologies: A Review

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

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

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

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

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

Titanium as a Beneficial Element for Crop Production

Titanium (Ti) is considered a beneficial element for plant growth. Ti applied via roots or leaves at low concentrations has been documented to improve crop performance through stimulating the activity of certain enzymes, enhancing chlorophyll content and photosynthesis, promoting nutrient uptake, strengthening stress tolerance, and improving crop yield and quality. Commercial fertilizers containing Ti, such as Tytanit and Mg-Titanit, have been used as biostimulants for improving crop production; however, mechanisms underlying the beneficial effects still remain unclear. In this article, we propose that the beneficial roles Ti plays in plants lie in its interaction with other nutrient elements primarily iron (Fe). Fe and Ti have synergistic and antagonistic relationships. When plants experience Fe deficiency, Ti helps induce the expression of genes related to Fe acquisition, thereby enhancing Fe uptake and utilization and subsequently improving plant growth. Plants may have proteins that either specifically or nonspecifically bind with Ti. When Ti concentration is high in plants, Ti competes with Fe for ligands or proteins. The competition could be severe, resulting in Ti phytotoxicity. As a result, the beneficial effects of Ti become more pronounced during the time when plants experience low or deficient Fe supply.

Development of an algal treatment system for Se removal: Effects of light regimes, nutrients, sulfate and hypersalinity

Selenium (Se) exposure poses potential risks to wildlife at the Salton Sea. Our previous research suggests Chlorella sp. be highly efficient at absorbing and volatilizing Se. In developing an algal treatment system for Se removal, this study further evaluated the performance under the conditions to be encountered in the field using Chlorella pyrenoidosa and Chlorella vulgaris. The results show the algal Se removal efficiency was little affected by photoperiod, yet volatilization became relatively greater in dark/light cycles over a longer term. The rates of Se absorption and volatilization by C. vulgaris were 88% and 77% more, respectively, in the DI water, while C. pyrenoidosa acted oppositely, indicating C. vulgaris will perform better in Se removal if nutrient levels are reduced in advance. The presence of sulfate reduced biomass Se, especially through volatilization, by 8% for C. vulgaris, lessening potential ecotoxicity. Finally, C. vulgaris released biomass Se back to the water column under hypersaline conditions, leading to a 6% increase in water Se concentrations. These results suggest C. vulgaris be the best alga for the treatment of Se laden river water in the Salton Sea area, yet a filtering system is required to prevent Se containing algae from entering food chains.

Sulphur interferes with selenium accumulation in Tartary buckwheat plants

Tartary buckwheat (Fagopyrum tataricum Gaertn.) and common buckwheat (Fagopyrum esculentum Moench.) plants grown in the field were treated foliarly with 126 μM solutions of selenate and/or sulphate in order to study the effect of sulphur (S) on selenium (Se) concentration in plants. In both species, the concentration of Se in all plant parts was similar in control and S treated plants. In Tartary buckwheat the concentration of Se was higher in S and Se treated plants than in plants treated with Se alone. S was shown to enhance Se accumulation in Tartary buckwheat. It was also shown that it is possible to produce grain and herb of Tartary and common buckwheat containing appropriate amounts of Se for food without affecting the yield of the plants.

Nitric oxide-cytokinin interplay influences selenite sensitivity in Arabidopsis

Selenite oppositely modifies cytokinin and nitric oxide metabolism in Arabidopsis organs. A mutually negative interplay between the molecules exists in selenite-exposed roots; and their overproduction causes selenite insensitivity. Selenium-induced phytotoxicity is accompanied by developmental alterations such as primary root (PR) shortening. Growth changes are provoked by the modulation of hormone status and signalling. Cytokinin (CK) cooperates with the nitric oxide (NO) in many aspects of plant development; however, their interaction under abiotic stress has not been examined. Selenite inhibited the growth of Arabidopsis seedlings and reduced root meristem size through cell division arrest. The CK-dependent pARR5::GUS activity revealed the intensification of CK signalling in the PR tip, which may be partly responsible for the root meristem shortening. The selenite-induced alterations in the in situ expressions of cytokinin oxidases (AtCKX4::GUS, AtCKX5::GUS) are associated with selenite-triggered changes of CK signalling. In wild-type (WT) and NO-deficient nia1nia2 root, selenite led to the diminution of NO content, but CK overproducer ipt-161 and -deficient 35S:CKX2 roots did not show NO decrease. Exogenous NO (S-nitroso-N-acetyl-DL-penicillamine, SNAP) reduced the pARR5::GFP and pTCS::GFP expressions. Roots of the 35S:CKX and cyr1 plants suffered more severe selenite-triggered viability loss than the WT, while in ipt-161 and gsnor1-3 no obvious viability decrease was observed. Exogenous NO ameliorated viability loss, but benzyladenine intensified it. Based on the results, selenite impacts development by oppositely modifying CK signalling and NO level. In the root system, CK signalling intensifies which possibly contributes to the nitrate reductase-independent NO diminution. A mutually negative CK-NO interplay exists in selenite-exposed roots; however, overproduction of both molecules worsens selenite sensing. Hereby, we suggest novel regulatory interplay and role for NO and CK in abiotic stress signalling.

Essential and Beneficial Trace Elements in Plants, and Their Transport in Roots: a Review

The essentiality of 14 mineral elements so far have been reported in plant nutrition. Eight of these elements were known as micronutrients due to their lower concentrations in plants (usually ≤100 mg/kg/dw). However, it is still challenging to mention an exact number of plant micronutrients since some elements have not been strictly proposed yet either as essential or beneficial. Micronutrients participate in very diverse metabolic processes, including from the primary and secondary metabolism to the cell defense, and from the signal transduction to the gene regulation, energy metabolism, and hormone perception. Thus, the attempt to understand the molecular mechanism(s) behind their transport has great importance in terms of basic and applied plant sciences. Moreover, their deficiency or toxicity also caused serious disease symptoms in plants, even plant destruction if not treated, and many people around the world suffer from the plant-based dietary deficiencies or metal toxicities. In this sense, shedding some light on this issue, the 13 mineral elements (Fe, B, Cu, Mn, Mo, Si, Zn, Ni, Cl, Se, Na, Al, and Co), required by plants at trace amounts, has been reviewed with the primary focus on the transport proteins (transporters/channels) in plant roots. So, providing the compiled but extensive information about the structural and functional roles of micronutrient transport genes/proteins in plant roots.

Selenium Biofortification in Radish Enhances Nutritional Quality via Accumulation of Methyl-Selenocysteine and Promotion of Transcripts and Metabolites Related to Glucosinolates, Phenolics, and Amino Acids

Two selenium (Se) fertilization methods were tested for their effects on levels of anticarcinogenic selenocompounds in radish (Raphanus sativus), as well as other nutraceuticals. First, radish was grown on soil and foliar selenate applied 7 days before harvest at 0, 5, 10, and 20 mg Se per plant. Selenium levels were up to 1200 mg Se/kg DW in leaves and 120 mg Se/kg DW in roots. The thiols cysteine and glutathione were present at 2-3-fold higher levels in roots of Se treated plants, and total glucosinolate levels were 35% higher, due to increases in glucoraphanin. The only seleno-aminoacid detected in Se treated plants was Se-methyl-SeCys (100 mg/kg FW in leaves, 33 mg/kg FW in roots). The levels of phenolic aminoacids increased with selenate treatment, as did root total nitrogen and protein content, while the level of several polyphenols decreased. Second, radish was grown in hydroponics and supplied with 0, 5, 10, 20, or 40 μM selenate for 1 week. Selenate treatment led to a 20-30% increase in biomass. Selenium concentration was 242 mg Se/kg DW in leaves and 85 mg Se/kg DW in roots. Cysteine levels decreased with Se in leaves but increased in roots; glutatione levels decreased in both. Total glucosinolate levels in leaves decreased with Se treatment due to repression of genes involved in glucosinolates metabolism. Se-methyl-SeCys concentration ranged from 7-15 mg/kg FW. Aminoacid concentration increased with Se treatment in leaves but decreased in roots. Roots of Se treated plants contained elevated transcript levels of sulfate transporters (Sultr) and ATP sulfurylase, a key enzyme of S/Se assimilation. No effects on polyphenols were observed. In conclusion, Se biofortification of radish roots may be achieved via foliar spray or hydroponic supply. One to ten radishes could fulfill the daily human requirement (70 μg) after a single foliar spray of 5 mg selenate per plant or 1 week of 5-10 μM selenate supply in hydroponics. The radishes metabolized selenate to the anticarcinogenic compound Se-methyl-selenocysteine. Selenate treatment enhanced levels of other nutraceuticals in radish roots, including glucoraphanin. Therefore, Se biofortification can produce plants with superior health benefits.

Selenium promotes sulfur accumulation and plant growth in wheat (Triticum aestivum)

Selenium (Se) is an essential micronutrient for animals and humans and a target for biofortification in crops. Sulfur (S) is a crucial nutrient for plant growth. To gain better understanding of Se and S nutrition and interaction in plants, the effects of Se dosages and forms on plant growth as well as on S level in seven wheat lines were examined. Low dosages of both selenate and selenite supplements were found to enhance wheat shoot biomass and show no inhibitory effect on grain production. The stimulation on plant growth was correlated with increased APX antioxidant enzyme activity. Se forms were found to exert different effects on S metabolism in wheat plants. Selenate treatment promoted S accumulation, which was not observed with selenite supplement. An over threefold increase of S levels following selenate treatment at low dosages was observed in shoots of all wheat lines. Analysis of the sulfate transporter gene expression revealed an increased transcription of SULTR1;1, SULTR1;3 and SULTR4;1 in roots following 10 μM Na2 SeO4 treatment. Mass spectrometry-based targeted protein quantification confirmed the gene expression results and showed enhanced protein levels. The results suggest that Se treatment mimics S deficiency to activate specific sulfate transporter expression to stimulate S uptake, resulting in the selenate-induced S accumulation. This study supports that plant growth and nutrition benefit from low dosages of Se fertilization and provides information on the basis underlying Se-induced S accumulation in plants.

Effects of selenium on biological and physiological properties of the duckweed Landoltia punctata

Duckweed can be used for bioremediation of selenium (Se) polluted water because of its capability of absorbing minerals from growing media. However, the presence of Se in the media may affect the growth of the duckweed. Landoltia punctata 7449 has been studied for its changes in chemical and biological properties with the presence of Se in the media. The duckweed was cultivated over a 12-day period at different initial concentrations of selenite (Na2 SeO3 ) from 0 to 80 μmol·l(-1) . The growth rate, the organic and total Se contents, the activity of antioxidant enzymes, the photosynthetic pigment contents, the chlorophyll a fluorescence OJIP transient, and the ultrastructure of the duckweed were monitored during the experiment. The results have shown that Se at low concentrations of ≤20 μmol·l(-1) promoted the growth of the L. punctata and inhibited lipid peroxidation. Substantial increases in duckweed growth rate and organic Se content in the duckweed were observed at low Se concentrations. The anti-oxidative effect occurred likely with the increases in guaiacol peroxidase, catalase and superoxide dismutase activities as well as the amount of photosynthetic pigments. However, negative impact to the duckweed was observed when the L. punctata was exposed to high Se concentrations (≥40 μmol·l(-1) ), in which the duckweed growth was inhibited by the selenium. The results indicate that L. punctata 7449 can be used for bioremediation of selenium (Se) polluted water when the Se concentration is ≤20 μmol·l(-1) .

Comparative effects of selenate and selenite on selenium accumulation, morphophysiology, and glutathione synthesis in Ulva australis

The capacity of Ulva australis Areschoug to tolerate and accumulate selenium (Se) supplied in the form of selenate or selenite was investigated. The macroalga was provided for 3 and 7 days with concentrations of selenate (Na2SeO4) or selenite (Na2SeO3) ranging from 0 to 400 μM. U. australis exhibited the highest ability to accumulate selenium when fed with 100 μM selenate and 200 μM selenite after 7 days, and accumulation values were respectively 25 and 36 ppm Se. At the same concentrations, stimulation of the synthesis of chlorophylls and carotenoids was observed. Elevated doses of selenate or selenite decreased Se accumulation inside algal cells, perhaps through repression of membrane transporters. This effect was more pronounced in thalli cultivated with selenate. There were no morphological and ultrastructural alterations in thalli exposed to Se. However, selenite induced the increase of the oxidized fraction of glutathione (GSSG), perhaps because of its capacity to bind the thiol group of reduced glutathione (GSH). In conclusion, this study highlights the capacity of U. australis to resist to very high concentrations of selenite and selenate, which are normally toxic to other organisms. Also, the lack of bioconcentration in U. australis indicates that this alga does not facilitate delivery of Se in the food chain and remains safe for consumption when it grows in water bodies contaminated with Se. Its potential for the removal of excess Se from water bodies appears limited.

Interactions of Sulfate with Other Nutrients As Revealed by H2S Fumigation of Chinese Cabbage

Sulfur deficiency in plants has severe impacts on both growth and nutrient composition. Fumigation with sub-lethal concentrations of H2S facilitates the supply of reduced sulfur via the leaves while sulfate is depleted from the roots. This restores growth while sulfate levels in the plant tissue remain low. In the present study this system was used to reveal interactions of sulfur with other nutrients in the plant and to ascertain whether these changes are due to the absence or presence of sulfate or rather to changes in growth and organic sulfur. There was a complex reaction of the mineral composition to sulfur deficiency, however, the changes in content of many nutrients were prevented by H2S fumigation. Under sulfur deficiency these nutrients accumulated on a fresh weight basis but were diluted on a dry weight basis, presumably due to a higher dry matter content. The pattern differed, however, between leaves and roots which led to changes in shoot to root partitioning. Only the potassium, molybdenum and zinc contents were strongly linked to the sulfate supply. Potassium was the only nutrient amongst those measured which showed a positive correlation with sulfur content in shoots, highlighting a role as a counter cation for sulfate during xylem loading and vacuolar storage in leaves. This was supported by an accumulation of potassium in roots of the sulfur-deprived plants. Molybdenum and zinc increased substantially under sulfur deficiency, which was only partly prevented by H2S fumigation. While the causes of increased molybdenum under sulfur deficiency have been previously studied, the relation between sulfate and zinc uptake needs further clarification.

Selenium accumulation by plants

BACKGROUND

Selenium (Se) is an essential mineral element for animals and humans, which they acquire largely from plants. The Se concentration in edible plants is determined by the Se phytoavailability in soils. Selenium is not an essential element for plants, but excessive Se can be toxic. Thus, soil Se phytoavailability determines the ecology of plants. Most plants cannot grow on seleniferous soils. Most plants that grow on seleniferous soils accumulate <100 mg Se kg(-1) dry matter and cannot tolerate greater tissue Se concentrations. However, some plant species have evolved tolerance to Se, and commonly accumulate tissue Se concentrations >100 mg Se kg(-1) dry matter. These plants are considered to be Se accumulators. Some species can even accumulate Se concentrations of 1000-15 000 mg Se kg(-1 )dry matter and are called Se hyperaccumulators.

SCOPE

This article provides an overview of Se uptake, translocation and metabolism in plants and highlights the possible genetic basis of differences in these between and within plant species. The review focuses initially on adaptations allowing plants to tolerate large Se concentrations in their tissues and the evolutionary origin of species that hyperaccumulate Se. It then describes the variation in tissue Se concentrations between and within angiosperm species and identifies genes encoding enzymes limiting the rates of incorporation of Se into organic compounds and chromosomal loci that might enable the development of crops with greater Se concentrations in their edible portions. Finally, it discusses transgenic approaches enabling plants to tolerate greater Se concentrations in the rhizosphere and in their tissues.

CONCLUSIONS

The trait of Se hyperaccumulation has evolved several times in separate angiosperm clades. The ability to tolerate large tissue Se concentrations is primarily related to the ability to divert Se away from the accumulation of selenocysteine and selenomethionine, which might be incorporated into non-functional proteins, through the synthesis of less toxic Se metabilites. There is potential to breed or select crops with greater Se concentrations in their edible tissues, which might be used to increase dietary Se intakes of animals and humans.

Shoot ionome to predict the synergism and antagonism between nutrients as affected by substrate and physiological status

The elemental composition of a tissue or organism is defined as ionome. However, the combined effects on the shoot ionome determined by the taxonomic character, the nutrient status and different substrates have not been investigated. This study tests the hypothesis that phylogenetic variation of monocots and dicots grown in iron deficiency can be distinguished by the shoot ionome. We analyzed 18 elements in barley, cucumber and tomato and in two substrates (hydroponic vs soil) with different nutritional regimes. Multivariate analysis evidenced a clear separation between the species. In hydroponic conditions the main drivers separating the species are non essential-nutrients as Ti, Al, Na and Li, which were positively correlated with macro- (P, K) and micronutrients (Fe, Zn, Mo, B). The separation between species is confirmed when plants are grown on soil, but the distribution is determined especially by macronutrients (S, P, K, Ca, Mg) and micronutrients (B). A number of macro (Mg, Ca, S, P, K) and micronutrients (Fe, Mn, Zn, Cu, Mo, B) contribute to plant growth and several other important physiological and metabolic plant activities. The results reported here confirmed that the synergism and antagonism between them and other non-essential elements (Ti, Al, Si, Na) define the plant taxonomic character. The ionome profile might thus be exploited as a tool for the diagnosis of plants physiological/nutritional status but also in defining biofortification strategies to optimize both mineral enrichment of staple food crops and the nutrient input as fertilizers.

Selenium cycling across soil-plant-atmosphere interfaces: a critical review

Selenium (Se) is an essential element for humans and animals, which occurs ubiquitously in the environment. It is present in trace amounts in both organic and inorganic forms in marine and freshwater systems, soils, biomass and in the atmosphere. Low Se levels in certain terrestrial environments have resulted in Se deficiency in humans, while elevated Se levels in waters and soils can be toxic and result in the death of aquatic wildlife and other animals. Human dietary Se intake is largely governed by Se concentrations in plants, which are controlled by root uptake of Se as a function of soil Se concentrations, speciation and bioavailability. In addition, plants and microorganisms can biomethylate Se, which can result in a loss of Se to the atmosphere. The mobilization of Se across soil-plant-atmosphere interfaces is thus of crucial importance for human Se status. This review gives an overview of current knowledge on Se cycling with a specific focus on soil-plant-atmosphere interfaces. Sources, speciation and mobility of Se in soils and plants will be discussed as well as Se hyperaccumulation by plants, biofortification and biomethylation. Future research on Se cycling in the environment is essential to minimize the adverse health effects associated with unsafe environmental Se levels.

Possible role of NAD-dependent glyceraldehyde-3-phosphate dehydrogenase in growth promotion of Arabidopsis seedlings by low levels of selenium

We explored functional significance of selenium (Se) in Arabidopsis physiology. Se at very low concentrations in cultivation exerted a considerable positive effect on Arabidopsis growth with no indication of oxidative stress, whereas Se at higher concentrations significantly suppressed the growth and brought serious oxidative damage. Respiration, ATP levels, and the activity of NAD-dependent glyceraldehyde-3-phosphate dehydrogenase (NAD-GAPDH) were enhanced in Arabidopsis grown in the medium containing 1.0 μM Se. Addition of an inhibitor of glutathione (GSH) synthesis to the medium abolished both of the Se-dependent growth promotion and NAD-GAPDH up-regulation. Assay of NAD-GAPDH purified from seedlings subjected to Se interventions raised the possibility of a direct connection between the activity of this enzyme and Arabidopsis growth. These results reveal that trace amounts of Se accelerate Arabidopsis growth, and suggest that this pro-growth effect of Se arises enhancing mitochondrial performance in a GSH-dependent manner, in which NAD-GAPDH may serve as a key regulator.

Uptake kinetics and translocation of selenite and selenate as affected by iron plaque on root surfaces of rice seedlings

Iron plaque on root surfaces greatly influenced selenium uptake and played different roles in selenite and selenate uptake. Iron plaque commonly forms on rice root surfaces under flooded conditions, but little is known about the relationship between iron plaque and selenium (Se) accumulation. Here, we investigate the effects of iron plaque on Se uptake by and translocation within rice (Oryza sativa) seedlings, and the kinetics of selenite and selenate influx into rice roots (with or without iron plaque) were determined in short-term (30 min) experiments. Rice seedlings were planted in nutrient solutions containing different levels of ferrous ion for 3 days and then transplanted into nutrient solutions with selenite or selenate. Se concentrations in iron plaque were positively associated with the amounts of iron plaque in both selenite and selenate treatments and iron plaque had a higher affinity for selenite than selenate. Results showed that iron plaque on root surfaces greatly influenced Se uptake and played different roles in selenite and selenate uptake. The selenite and selenate uptake kinetics results demonstrated that the presence of iron plaque enhanced selenite uptake, but decreased selenate uptake. In addition, root-Se concentrations increased with the increasing amounts of iron plaque, but Se translocation from roots to shoots was reduced with the increasing amounts of iron plaque in the +selenite treatment. Iron plaque significantly influenced selenite uptake and might act as a pool to selenite accumulation in rice plants. However, iron plaque had no significant effect on selenate uptake or even as a barrier to selenate uptake.

Interactions between Cs, Sr, and other nutrients and trace element accumulation in Amaranthus shoot in response to variety effect

Aiming at clarifying the interactions between Cs, Sr, and other mineral elements in the genus Amaranthus, this study adopted 33 different varieties of Amaranthus and investigated the concentrations of 23 mineral elements in shoots grown in the fields of Iino in Fukushima prefecture. Significant varietal effects were detected for all elements except Se, and degree of interspecies variation was highly element dependent. Among 23 elements, amaranths were less sensitive to the accumulation of Cs and Sr than most other mineral elements to the species level. There are six elements showing significant correlation with Cs, positive correlations between As, Rb, Al, Fe, Ni, and Cs, and negative correlation between Ba and Cs. Significant correlations between Ca, Mg, Mn, Zn, B, Ba, Cd, and Sr were detected, and all of the coefficients were positive. Cs and Sr did not present significant correlation, but they were both significantly correlated with Ba. By principal component analysis (PCA), the first and second principal components (PC1 and PC2) accounted for 23.2 and 20.3% of the total variance and associated with Cs and Sr, respectively. Both of the two species took up more Cs by promoting the influx of elements positively correlated with Cs into shoot, but at the same time, Amaranthus hypochondriacus (L.) Mapes 847 decreased the K and Ba uptake and Amaranthus powellii (S. Wats) subsp. Powellii inhibited the accumulation of Rb, Sr, and significantly correlated elements of Sr in shoot. This study is the first to pave the way for comprehension on ionome in amaranth shoot at the variety level. The results of this research provide the ionomic basis for implementing countermeasures in the field against the translocation of Cs (and potentially Sr) toward crops and food.

Selenium and sulfur influence ethylene formation and alleviate cadmium-induced oxidative stress by improving proline and glutathione production in wheat

We have studied the influence of selenium (Se) and sulfur (S) in the protection of photosynthetic capacity of wheat (Triticum aestivum) against cadmium (Cd) stress. The involvement of ethylene and its interaction with proline and antioxidant metabolism in the tolerance of plants to Cd stress was evaluated. Application of Se or S alleviated Cd-induced oxidative stress by increasing proline accumulation as a result of increased activity of glutamyl kinase (GK) and decreased activity of proline oxidase (PROX). These nutrients also induced the activity of ATP-sulfurylase and serine acetyl transferase and the content of cysteine (Cys), a precursor for the synthesis of both reduced glutathione (GSH) and ethylene. Further, application of Se and S to plants under Cd stress reduced ethylene level and increased the activity of glutathione reductase (GR) and glutathione peroxidase (GPX), reduced oxidative stress and improved photosynthesis and growth. The involvement of ethylene in Se and S-mediated alleviation of Cd stress was substantiated with the use of ethylene biosynthesis inhibitor aminoethoxyvinylglycine (AVG). The use of AVG reversed the effects of Se and S on ethylene, content of proline and GSH and photosynthesis. The results suggested that Se and S both reversed Cd-induced oxidative stress by regulating ethylene formation, proline and GSH metabolism. Thus, Se or S-induced regulatory interaction between ethylene and proline and GSH metabolism may be used for the reversal of Cd-induced oxidative stress.

Exploring the importance of sulfate transporters and ATP sulphurylases for selenium hyperaccumulation-a comparison of Stanleya pinnata and Brassica juncea (Brassicaceae)

Selenium (Se) hyperaccumulation, the capacity of some species to concentrate Se to levels upwards of 0.1% of dry weight, is an intriguing phenomenon that is only partially understood. Questions that remain to be answered are: do hyperaccumulators have one or more Se-specific transporters? How are these regulated by Se and sulfur (S)? In this study, hyperaccumulator Stanleya pinnata was compared with related non-hyperaccumulator Brassica juncea with respect to S-dependent selenate uptake and translocation, as well as for the expression levels of three sulfate/selenate transporters (Sultr) and three ATP sulphurylases (APS). Selenium accumulation went down ~10-fold with increasing sulfate supply in B. juncea, while S. pinnata only had a 2-3-fold difference in Se uptake between the highest (5 mM) and lowest sulfate (0 mM) treatments. The Se/S ratio was generally higher in the hyperaccumulator than the non-hyperaccumulator, and while tissue Se/S ratio in B. juncea largely reflected the ratio in the growth medium, S. pinnata enriched itself up to 5-fold with Se relative to S. The transcript levels of Sultr1;2 and 2;1 and APS1, 2, and 4 were generally much higher in S. pinnata than B. juncea, and the species showed differential transcript responses to S and Se supply. These results indicate that S. pinnata has at least one transporter with significant selenate specificity over sulfate. Also, the hyperaccumulator has elevated expression levels of several sulfate/selenate transporters and APS enzymes, which likely contribute to the Se hyperaccumulation and hypertolerance phenotype.

Biochemical and biophysical characterization of the selenium-binding and reducing site in Arabidopsis thaliana homologue to mammals selenium-binding protein 1

The function of selenium-binding protein 1 (SBP1), present in almost all organisms, has not yet been established. In mammals, SBP1 is known to bind the essential element selenium but the binding site has not been identified. In addition, the SBP family has numerous potential metal-binding sites that may play a role in detoxification pathways in plants. In Arabidopsis thaliana, AtSBP1 over-expression increases tolerance to two toxic compounds for plants, selenium and cadmium, often found as soil pollutants. For a better understanding of AtSBP1 function in detoxification mechanisms, we investigated the chelating properties of the protein toward different ligands with a focus on selenium using biochemical and biophysical techniques. Thermal shift assays together with inductively coupled plasma mass spectrometry revealed that AtSBP1 binds selenium after incubation with selenite (SeO3(2-)) with a ligand to protein molar ratio of 1:1. Isothermal titration calorimetry confirmed the 1:1 stoichiometry and revealed an unexpectedly large value of binding enthalpy suggesting a covalent bond between selenium and AtSBP1. Titration of reduced Cys residues and comparative mass spectrometry on AtSBP1 and the purified selenium-AtSBP1 complex identified Cys(21) and Cys(22) as being responsible for the binding of one selenium. These results were validated by site-directed mutagenesis. Selenium K-edge x-ray absorption near edge spectroscopy performed on the selenium-AtSBP1 complex demonstrated that AtSBP1 reduced SeO3(2-) to form a R-S-Se(II)-S-R-type complex. The capacity of AtSBP1 to bind different metals and selenium is discussed with respect to the potential function of AtSBP1 in detoxification mechanisms and selenium metabolism.

Selenium accumulation in unicellular green alga Chlorella vulgaris and its effects on antioxidant enzymes and content of photosynthetic pigments

The aim of the present study was to investigate selenite effects in the unicellular green algae Chlorella vulgaris as a primary producer and the relationship with intracellular bioaccumulation. The effects of selenite were evaluated by measuring the effect of different selenite concentrations on algal growth during a 144 h exposure period. It was found that lower Se concentrations (≤ 75 mg L(-1)) positively promoted C. vulgaris growth and acted as antioxidant by inhibiting lipid peroxidation (LPO) and intracellular reactive oxygen species (ROS). The antioxidative effect was associated with an increase in guaiacol peroxidase (GPX), catalase (CAT), superoxide dismutase (SOD) and photosynthetic pigments. Meanwhile, significant increase in the cell growth rate and organic Se content was also detected in the algae. In contrast, these changes were opposite in C. vulgaris exposed to Se higher than 100 mg L-1. The antioxidation and toxicity appeared to be correlated to Se bioaccumulation, which suggests the appropriate concentration of Se in the media accumulation of C. vulgaris should be 75 mg L-1. Taken together, C. vulgaris possesses tolerance to Se, and Se-Chlorella could be developed as antioxidative food for aquaculture and human health.

Roles of rhizobial symbionts in selenium hyperaccumulation in Astragalus (Fabaceae)

PREMISE OF THE STUDY

Are there dimensions of symbiotic root interactions that are overlooked because plant mineral nutrition is the foundation and, perhaps too often, the sole explanation through which we view these relationships? In this paper we investigate how the root nodule symbiosis in selenium (Se) hyperaccumulator and nonaccumulator Astragalus species influences plant selenium (Se) accumulation.

METHODS

In greenhouse studies, Se was added to nodulated and nonnodulated hyperaccumulator and nonaccumulator Astragalus plants, followed by investigation of nitrogen (N)-Se relationships. Selenium speciation was also investigated, using x-ray microprobe analysis and liquid chromatography-mass spectrometry (LC-MS).

KEY RESULTS

Nodulation enhanced biomass production and Se to S ratio in both hyperaccumulator and nonaccumulator plants. The hyperaccumulator contained more Se when nodulated, while the nonaccumulator contained less S when nodulated. Shoot [Se] was positively correlated with shoot N in Se-hyperaccumulator species, but not in nonhyperaccumulator species. The x-ray microprobe analysis showed that hyperaccumulators contain significantly higher amounts of organic Se than nonhyperaccumulators. LC-MS of A. bisulcatus leaves revealed that nodulated plants contained more γ-glutamyl-methylselenocysteine (γ-Glu-MeSeCys) than nonnodulated plants, while MeSeCys levels were similar.

CONCLUSIONS

Root nodule mutualism positively affects Se hyperaccumulation in Astragalus. The microbial N supply particularly appears to contribute glutamate for the formation of γ-Glu-MeSeCys. Our results provide insight into the significance of symbiotic interactions in plant adaptation to edaphic conditions. Specifically, our findings illustrate that the importance of these relationships are not limited to alleviating macronutrient deficiencies.

Constraint on selenium bioavailability caused by its geochemical behavior in typical Kaschin-Beck disease areas in Aba, Sichuan Province of China

Kaschin-Beck disease (KBD), an endemic osteoarthropathy, is distributed in the low-selenium (Se)-belt that stretches from northeast to southwest China. However, very few studies have investigated the relationship between low bioavailabitity of Se and KBD. The present study examined the behavior of Se and other elements in areas with varying levels of KBD prevalence using pedological and geochemical methods. Rhizosphere soil samples obtained from the KBD-stricken Aba area were classified into Ustic Isohumisols (J2), Udic Luvisols (L4), Stagnic Gleysols (I2), and Cryic Cambisols (M1) and the integrated constraints on selenium bioavailability in these soils were analyzed. We found that Se concentration in soil profiles from a typical KBD area ranged between 0.08 μg · g(-1) and 0.215 μg · g(-1), indicating absent and marginal bioavailability, respectively. This suggested that low Se bioavailability may be a feature that soils inherit from their Se-deficient parent materials. Moreover, the soil types examined showed different geochemical behaviors such as eluviation for soluble Se(VI), migration of Se(IV) for its adsorption on clay and sesquioxide, and extreme redox conditions. In conclusion, a higher level of Se bioavailability in environment might be related to a lower risk of KBD, and our results offer a foundation for scientific theory on ecological geochemistry and improve our understanding of KBD.

Analysis of selenium accumulation, speciation and tolerance of potential selenium hyperaccumulator Symphyotrichum ericoides

Symphyotrichum ericoides was shown earlier to contain hyperaccumulator levels of selenium (Se) in the field (>1000 mg kg(-1) dry weight (DW)), but only when growing next to other Se hyperaccumulators. It was also twofold larger next to hyperaccumulators and suffered less herbivory. This raised two questions: whether S. ericoides is capable of hyperaccumulation without neighbor assistance, and whether its Se-derived benefit is merely ecological or also physiological. Here, in a comparative greenhouse study, Se accumulation and tolerance of S. ericoides were analyzed in parallel with hyperaccumulator Astragalus bisulcatus, Se accumulator Brassica juncea and related Asteraceae Machaeranthera tanacetifolia. Symphyotrichum ericoides and M. tanacetifolia accumulated Se up to 3000 and 1500 mg Se kg(-1) DW, respectively. They were completely tolerant to these Se levels and even grew 1.5- to 2.5-fold larger with Se. Symphyotrichum ericoides showed very high leaf Se/sulfur (S) and shoot/root Se concentration ratios, similar to A. bisulcatus and higher than M. tanacetifolia and B. juncea. Se X-ray absorption near-edge structure spectroscopy showed that S. ericoides accumulated Se predominantly (86%) as C-Se-C compounds indistinguishable from methyl-selenocysteine, which may explain its Se tolerance. Machaeranthera tanacetifolia accumulated 55% of its Se as C-Se-C compounds; the remainder was inorganic Se. Thus, in this greenhouse study S. ericoides displayed all of the characteristics of a hyperaccumulator. The larger size of S. ericoides when growing next to hyperaccumulators may be explained by a physiological benefit, in addition to the ecological benefit demonstrated earlier.

OsPT2, a phosphate transporter, is involved in the active uptake of selenite in rice

• Selenite is a predominant form of selenium (Se) available to plants, especially in anaerobic soils, but the molecular mechanism of selenite uptake by plants is not well understood. • ltn1, a rice mutant previously shown to have increased phosphate (Pi) uptake, was found to exhibit higher selenite uptake than the wild-type in both concentration- and time-dependent selenite uptake assays. Respiratory inhibitors significantly inhibited selenite uptake in the wildtype and the ltn1 mutant, indicating that selenite uptake was coupled with H(+) and energy-dependent. Selenite uptake was greatly enhanced under Pi-starvation conditions, suggesting that Pi transporters are involved in selenite uptake. • OsPT2, the most abundantly expressed Pi transporter in the roots, is also significantly up-regulated in ltn1 and dramatically induced by Pi starvation. OsPT2-overexpressing and knockdown plants displayed significantly increased and decreased rates of selenite uptake, respectively, suggesting that OsPT2 plays a crucial role in selenite uptake. Se content in rice grains also increased significantly in OsPT2-overexpressing plants. • These data strongly demonstrate that selenite and Pi share similar uptake mechanisms and that OsPT2 is involved in selenite uptake, which provides a potential strategy for breeding Se-enriched rice varieties.

Stability of solid-phase selenium species in fly ash after prolonged submersion in a natural river system

Selenium (Se) chemistry can be very complex in the natural environment, exhibiting different valence states (-2, 0, +4, +6) representing multiple inorganic, methylated, or complexed forms. Since redox associated shifts among most of known Se species can occur at environmentally relevant conditions, it is important to identify these species in order to assess their potential toxicity to organisms. In June of 2009, researchers from the US Army Engineer Research & Development Center (ERDC) conducted investigations of the fly ash spilled 6 months previously into the Emory River at the TVA Kingston Fossil Plant, TN. Ash samples were collected on site from both the original ash pile (that did not move during the levee failure), from the spill zone (including the Emory River), and from the ash recovery ditch (ARD) containing ash removed during dredging cleanup operations. The purpose of this work was to determine the state of Se in the spilled fly ash and to assess its potential for transformation and resultant chemical stability from its prolonged submersion in the river and subsequent dredging. Sequential chemical extractions suggested that the river environment shifted Se distribution toward organic/sulfide species. Speciation studies by bulk XANES analysis on fly ash samples showed that a substantial portion of the Se in the original ash pile had transformed from inorganic selenite to a mixture of Se sulfide and reduced (organo)selenium (Se(-II)) species over the 6-month period. μ-XRF mapping data showed that significant trends in the co-location of Se domains with sulfur and ash heavy metals. Ten-d extended elutriate tests (EETs) that were bubbled continuously with atmospheric air to simulate worst-case oxidizing conditions during dredging showed no discernible change in the speciation of fly ash selenium. The enhanced stability of the organo- and sulfide-selenium species coincided with the mixture of the ash material with humic materials in the river, corresponding with notable shifts in the ash carbon- and nitrogen-functionality.

Selenium fertilization alters the chemical composition and antioxidant constituents of tomato (Solanum lycopersicon L.)

Although selenium (Se) is a known anticarcinogen, little is known regarding how Se affects other nutritional qualities in crops. Tomato ( Solanum lycopersicon ) was supplied with 0-50 μM selenate and analyzed for elemental composition and antioxidant compounds. When supplied at low doses (5 and 10 μM) via the roots, Se stimulated the synthesis of phenolic compounds in leaves and reduced the levels of Mo, Fe, Mn, and Cu in roots. At higher doses (25 and 50 μM Se) leaf glutathione levels were 3-5-fold enhanced. Supply of selenate via foliar spray (0, 2, or 20 mg Se plant(-1)) resulted in Se-biofortified tomato fruits, with Se levels low enough not to pose a health risk. The Se-biofortified fruits showed enhanced levels of the antioxidant flavonoids naringenin chalcone and kaempferol and a concomitant decrease of cinnamic acid derivatives. Thus, tomato fruits can be safely enriched with Se, and Se biofortification may enhance levels of other neutraceutical compounds.

Evaluation of germplasm effect on Fe, Zn and Se content in wheat seedlings

Micronutrients are essential for human health and crucial for plant survival. The capacity of food crops in acquiring mineral nutrients affects plant growth and potentially the yield and nutrient content in edible tissues/organs. In this study, we selected 20 wheat (Triticum aestivum L.) accessions and evaluated genotypic variations of the young seedlings in response to iron (Fe), zinc (Zn), and selenium (Se) treatments. Wheat accessions exhibited different growth responses to these minerals and possessed various abilities to accumulate them. Wheat seedlings in general were less tolerable to excess of Fe and benefits from increased levels of Zn supply. They were sensitive to selenite and profited from selenate treatment at low dosages. Limited mineral interactions were observed between Fe or Zn with other nutrients. In contrast, selenate supply enhanced Fe, Zn, sulfur (S), molybdenum (Mo), magnesium (Mg), calcium (Ca) and manganese (Mn) content in wheat seedlings, supporting its beneficial role in promoting plant growth; Selenite supplement reduced Zn, S, Mo, Mg, Ca and Mn levels in the plants, consisting with its detrimental role in inhibiting seedling growth. Based on nutrient accumulation, plant growth, and mineral interaction, a number of accessions such as EMB 38 and BRS 264 appeared to be good lines for breeding wheat cultivars with better plant health and potential to accumulate essential micronutrients in edible grains.

A novel selenocystine-accumulating plant in selenium-mine drainage area in Enshi, China

Plant samples of Cardamine hupingshanesis (Brassicaceae), Ligulariafischeri (Ledeb.) turcz (Steraceae) and their underlying top sediments were collected from selenium (Se) mine drainage areas in Enshi, China. Concentrations of total Se were measured using Hydride Generation-Atomic Fluorescence Spectrometry (HG-AFS) and Se speciation were determined using liquid chromatography/UV irradiation-hydride generation-atomic fluorescence spectrometry (LC-UV-HG-AFS). The results showed that C. hupingshanesis could accumulate Se to 239±201 mg/kg DW in roots, 316±184 mg/kg DW in stems, and 380±323 mg/kg DW in leaves, which identifies it as Se secondary accumulator. Particularly, it could accumulate Se up to 1965±271 mg/kg DW in leaves, 1787±167 mg/kg DW in stem and 4414±3446 mg/kg DW in roots, living near Se mine tailing. Moreover, over 70% of the total Se accumulated in C. hupingshanesis were in the form of selenocystine (SeCys2), increasing with increased total Se concentration in plant, in contrast to selenomethionine (SeMet) in non-accumulators (eg. Arabidopsis) and secondary accumulators (eg. Brassica juncea), and selenomethylcysteine (SeMeCys) in hyperaccumulators (eg. Stanleya pinnata). There is no convincing explanation on SeCys2 accumulation in C. hupingshanesis based on current Se metabolism theory in higher plants, and further study will be needed.

Responses of Portulaca oleracea Linn. to selenium exposure

The present study was investigated to evaluate the uptake and accumulation of selenium (Se) by the stem cuttings of Portulaca oleracea L. grown in alfisol amended with various concentrations of Se. P. oleracea accumulated a maximum of 63.4 µg g−1 dry weight in a short growth period of 42 days. The order of accumulation of Se among the plant parts was leaves (31.5 μg g−1) > stems (16.4 μg g−1) > roots (15.5 μg g−1). The accumulation potential was fourfold higher than the plant available concentration of 15.2 μg g−1 of Se g−1 of soil (diethylenetriaminepentaacetic acid extracted). Although the plant was able to accumulate Se in their tissues, increase in Se concentrations in soil caused a concentration-dependent decrease in the growth rate of plants (regeneration of leaves, number of leaves, number of roots, root length, stem length and biomass).

Effects of selenium accumulation on phytotoxicity, herbivory, and pollination ecology in radish (Raphanus sativus L.)

Selenium (Se) has contaminated areas in the western USA where pollination is critical to the functioning of both agricultural and natural ecosystems, yet we know little about how Se can impact pollinators. In a two-year semi-field study, the weedy plant Raphanus sativus (radish) was exposed to three selenate treatments and two pollination treatments to evaluate the effects on pollinator-plant interactions. Honey bee (Apis mellifera L.) pollinators were observed to readily forage on R. sativus for both pollen and nectar despite high floral Se concentrations. Se treatment increased both seed abortion (14%) and decreased plant biomass (8-9%). Herbivory by birds and aphids was reduced on Se-treated plants, indicating a potential reproductive advantage for the plant. Our study sheds light on how pollutants such as Se can impact the pollination ecology of a plant that accumulates even moderate amounts of Se.

A dual role of Se on Cd toxicity: evidences from the uptake of Cd and some essential elements and the growth responses in paddy rice

This study was carried out to investigate the effects of selenium (Se) on the uptake and translocation of cadmium (Cd) and essential elements in paddy rice (Oryza sativa L., Shuangyou 998). Selenium could alleviate/aggravate Cd toxicity in paddy rice, which depended on the dosages of Se and/or Cd. When Cd treatment level was as low as 35.6 μM, ≤12.7 μM Se could inhibit the uptake of Cd in paddy rice and increase the biomass of paddy rice; however, with Cd levels reaching 89-178 μM, the addition of Se resulted in increases in Cd uptake and exacerbated the growth of paddy rice. Cd always inhibited the uptake of Se. Cd alone suppressed the uptake of Ca, Mg, Mn, Cu, and Zn; however, Se reversed the decreases in the concentrations of the said elements, suggesting an element regulation mechanism to relieve Cd toxicity. Without Cd in the solution, low doses of Se increased the biomasses of shoots and roots at the expense of the more or less decreases in the concentrations of Ca, Mg, K, Fe, Mn, Cu, and shoot Zn, indicating an antagonistic effect of Se on these cations. The presence of Cd could also reverse these decreases especially at the highest treatment levels for both Se and Cd, also suggesting an element regulation mechanism responsible for the detoxification of high dosages of Se. Consequently, when Se is used to alleviate Cd toxicity, attention must be paid to the Cd pollution extent and doses of Se supplement.

Selenium reduces cadmium uptake and mitigates cadmium toxicity in rice

Hydroponic experiments were performed to investigate physiological mechanisms of selenium (Se) mitigation of Cd toxicity in rice. Exogenous Se markedly reduced Cd concentration in leaves, roots, and stems. Addition or pretreatment of 3 μM Se in 50 μM Cd solution significantly addressed Cd-induced growth inhibition, recovered root cell viability, and dramatically depressed O(2)(-), H(2)O(2), and malondialdehyde (MDA) accumulation. Supplemental Se counteracted 50 μM Cd-induced alterations of certain antioxidant enzymes, and uptake of nutrients, e.g. depressed Cd-induced increase in leaf and root superoxide dismutase (SOD) and leaf peroxidase (POD) activities, but elevated depressed catalase (CAT) activity; decreased Cd-induced high S and Cu concentrations in both leaves and roots. External Se counteracted the pattern of alterations in ATPase activities induced by Cd, e.g. significantly elevated the depressed root H(+)- and Ca(2+)-ATPase activities, but decreased the ascent root Na(+)K(+)-ATP activity. Results indicate that alleviated Cd toxicity by Se application is related to reduced Cd uptake and ROS accumulation, balanced nutrients, and increased H(+)- and Ca(2+)-ATPase activities in rice.

Testing the distinctness of shoot ionomes of angiosperm families using the Rothamsted Park Grass Continuous Hay Experiment

• The ionome is the elemental composition of a tissue or organism. Phylogenetic variation in the ionomes of plant shoots has been widely reported based on controlled experiments, vegetation surveys and literature meta-analyses. However, environmental effects on phylogenetic variation in shoot ionomes have not been quantified. This study tests the hypothesis that phylogenetic variation in shoot ionomes is robust to environmental perturbation and that plant families can be distinguished by their shoot ionomes. • Herbage was sampled from six subplots of the Rothamsted Park Grass Experiment. Subplots had received contrasting fertilizer treatments since 1856. Herbage was separated into its constituent species (n = 21) and concentrations of eleven mineral elements were determined in dried shoot material. • Shoot concentrations of calcium (Ca), zinc (Zn), manganese (Mn), magnesium (Mg) and sodium (Na) showed significant variation associated with plant species, and responded similarly to fertilizer treatments in diverse plant species. Species × treatment interactions were indicated for phosphorus (P), potassium (K), nickel (Ni), copper (Cu) and iron (Fe). Plant families could be distinguished by their shoot ionomes. The most informative elements for discriminant analysis were Ca > Mg > Ni > S > Na > Zn > K > Cu > Fe > Mn > P. • Whilst shoot ionomes were sensitive to fertilizer treatment, phylogenetic variation in a subset of the shoot ionome (Ca, Zn, Mn, Mg) was robust to this environmental perturbation.