The protective role of selenium in rape seedlings subjected to cadmium stress

Genome-Wide Characterization of DNA Demethylase Genes and Their Association with Salt Response in Pyrus

DNA methylation plays important roles in genome protection and the regulation of gene expression and it is associated with plants’ responses to environments. DNA demethylases are very important proteins in DNA methylation regulation. In this study, we performed genome-wide and deep analysis of putative demethylases (DMEs) in pear. Seven DME genes were found in the pear genome and were defined as PbDME1–7 based on their domain organization. Results were supported by the gene structural characteristics and phylogenetic analysis. The gene structure of the DME genes were relatively complex and the DME7 proteins didn’t contain the Perm_CXXC domain. The DME genes experienced a whole genome duplication event (WGD) that occurred in the ancestor genome of pear and apple before their divergence based on the Ks values. Expression results showed that high salinity stress could influence the expression level of DMEs and salt-responsive genes in Pyrus betulaefolia. Furthermore, the methylation levels of salt-responsive genes changed under salt stress treatment. Results suggested important roles of PbDME genes in response to salt stress and are useful for better understanding the complex functions of this DME genes, which will facilitate epigenetic studies in pear trees salt tolerance.

Foliar spraying with silicon and selenium reduces cadmium uptake and mitigates cadmium toxicity in rice

Foliar spraying with silicon (Si) and selenium (Se) can regulate the accumulation of cadmium (Cd) in rice (Oryza sativa L.), but the effects on different cultivars and the main determining factors remain unknown. Field experiments were conducted to investigate the ability of foliar spraying with Si, Se, and mixture of Si and Se to decrease Cd accumulation and translocation in rice cultivars WYHZ, NJ5055, and ZF1Y. All three spray treatments significantly decreased the Cd concentration in WYHZ brown rice, but had no such effect in NJ5055 or ZF1Y, relative to controls. WYHZ had a higher ability to translocate Cd than the other two cultivars. Foliar spraying changed this pattern by decreasing Cd translocation from roots to stems and from stems to brown rice, and increasing Cd translocation from stems to leaves. Foliar spraying also increased the photosynthetic rate, stomatal conductance, and transpiration efficiency in WYHZ. Structural equation modelling revealed the negative effects of photosynthetic rate, transpiration efficiency, and leaf Cd concentration, and the positive effects of stem and root Cd concentration on brown rice Cd concentration. Structural equation modelling further highlighted the significant role of stem Cd concentration in determining brown rice Cd concentration, which had the highest standardized total effects (direct plus indirect effects). These findings demonstrate that foliar spraying with Si and Se is effective in reducing Cd accumulation in rice cultivars with high Cd translocation ability, mainly by reducing stem Cd concentrations and ameliorating plant photosynthetic processes.

Cadmium phytoremediation potential of Brassica crop species: A review

Cadmium (Cd) is a highly toxic metal released into the environment through anthropogenic activities. Phytoremediation is a green technology used for the stabilization or remediation of Cd-contaminated soils. Brassica crop species can produce high biomass under a range of climatic and growing conditions, allowing for considerable uptake and accumulation of Cd, depending on species. These crop species can tolerate Cd stress via different mechanisms, including the stimulation of the antioxidant defense system, chelation, compartmentation of Cd into metabolically inactive parts, and accumulation of total amino-acids and osmoprotectants. A higher Cd-stress level, however, overcomes the defense system and may cause oxidative stress in Brassica species due to overproduction of reactive oxygen species and lipid peroxidation. Therefore, numerous approaches have been followed to decrease Cd toxicity in Brassica species, including selection of Cd-tolerant cultivars, the use of inorganic and organic amendments, exogenous application of soil organisms, and employment of plant-growth regulators. Furthermore, the coupling of genetic engineering with cropping may also help to alleviate Cd toxicity in Brassica species. However, several field studies demonstrated contrasting results. This review suggests that the combination of Cd-tolerant Brassica cultivars and the application of soil amendments, along with proper agricultural practices, may be the most efficient means of the soil Cd phytoattenuation. Breeding and selection of Cd-tolerant species, as well as species with higher biomass production, might be needed in the future when aiming to use Brassica species for phytoremediation.

Can Selenium and Molybdenum Restrain Cadmium Toxicity to Pollen Grains in Brassica napus?

Cadmium (Cd) is highly toxic, even at very low concentrations, to both animals and plants. Pollen is extremely sensitive to heavy metal pollutants; however, less attention has been paid to the protection of this vital part under heavy metal stress. A pot experiment was designed to investigate the effect of foliar application of Se (1 mg/L) and Mo (0.3 mg/L) either alone or in combination on their absorption, translocation, and their impact on Cd uptake and its further distribution in Brassica napus, as well as the impact of these fertilizers on the pollen grains morphology, viability, and germination rate in B. napus under Cd stress. Foliar application of either Se or Mo could counteract Cd toxicity and increase the plant biomass, while combined application of Se and Mo solutions on B. napus has no significant promotional effect on plant root and stem, but reduces the seeds' weight by 10⁻11%. Se and Mo have decreased the accumulated Cd in seeds by 6.8% and 9.7%, respectively. Microscopic studies, SEM, and pollen viability tests demonstrated that pollen grains could be negatively affected by Cd, thus disturbing the plant fertility. Se and Mo foliar application could reduce the toxic symptoms in pollen grains when the one or the other was sprayed alone on plants. In an in vitro pollen germination test, 500 μM Cd stress could strongly inhibit the pollen germination rate to less than 2.5%, however, when Se (10 μM) or Mo (1.0 μM) was added to the germination medium, the rate increased, reaching 66.2% and 39.4%, respectively. At the molecular level, Se and Mo could greatly affect the expression levels of some genes related to Cd uptake by roots (IRT1), Cd transport (HMA2 and HMA4), Cd sequestration in plant vacuoles (HMA3), and the final Cd distribution in plant tissue at the physiological level (PCS1).

Selenium and silicon reduce cadmium uptake and mitigate cadmium toxicity in Pfaffia glomerata (Spreng.) Pedersen plants by activation antioxidant enzyme system

Cadmium (Cd) is toxic to plants and animals, making it necessary to develop strategies that seek to reduce its introduction into food chains. Thus, the aim of this study was to investigate whether silicon (Si) and selenium (Se) reduce Cd concentrations in Pfaffia glomerata medicinal plant and attenuate the oxidative stress promoted by this metal. These plants were cultivated in hydroponics under the following treatments: control (nutrient solution), 2.5 μM Se, 2.5 mM Si, 50 μM Cd, 50 μM Cd + 2.5 μM Se, 50 μM Cd + 2.5 mM Si. After 14 days of exposure to treatments, leaves and roots were collected for the determination of dry weight of shoot and roots, Cd concentrations, chlorophyll and carotenoids content, and biochemical parameters (lipid peroxidation and guaiacol peroxidase and superoxide dismutase activities). The data were submitted to analysis of variance and means were compared with Scott-Knott test at 5% error probability. Roots of P. glomerata plants showed a significant reduction on dry weight accumulation when exposed to Cd. However, both Se and Si promoted a significant reduction of deleterious effects of Cd. The Cd concentrations in the tissues were reduced in the presence of Se or Si. Plants treated with Cd together with Se or Si presented higher pigment content than those with only Cd, thus showing a reduction in the negative effects caused by this element. In the treatments in which Se and Si were added in the growth medium together with Cd, an activation of superoxide dismutase and guaiacol peroxidase enzymes was observed in the roots and shoot, which may have contributed to lower lipid peroxidation. Thus, Se and Si reduce Cd concentrations and have potential to ameliorate Cd toxicity in P. glomerata plants, which can be used to increase productivity and quality of medicinal plants.

Selenium biofortification enhances the growth and alters the physiological response of lamb's lettuce grown under high temperature stress

We examined the possibility to enhance the growth and the physiological tolerance of lamb's lettuce (Valerianella locusta L.) grown under heat stress (HS) by biofortification with selenium (Se). The plants were grown at optimal (22/19 °C; day/night) or high (35/22 °C; day/night) temperature and Se was applied via foliar or soil treatment. The HS reduced plant biomass and photosynthetic pigment concentration and impaired some parameters of chlorophyll a fluorescence. The lamb's lettuce grown under HS accumulated large amounts of H2O2 in the leaves, especially in younger ones. The Se fertilization (both foliar and soil) at HS was beneficial to plant growth, whilst the concentration of photosynthetic pigments and the analysed parameters of chlorophyll a fluorescence were unaffected by the Se supply. The application of Se enhanced the thermo-tolerance of plants through cooperative action of antioxidant enzymes, such as guaiacol peroxidase (GPOX; EC 1.11.1.7) and catalase (CAT; EC 1.11.1.6), and reduced glutathione (GSH) among low-molecular-weight non-enzymatic antioxidants, in removal of excess of H2O2. Although under HS the content of different phenolic compounds in the leaves was higher than under normal temperature (NT), the application of Se did not affect their concentration at stress conditions. On the other hand, at NT the Se-biofortified plants accumulated significantly more phenolic compounds with health-promoting properties than Se-untreated plants. Therefore, biofortification of lamb's lettuce with Se can be beneficial in terms of plants yield and their nutritional value under both NT and HS.

Soil Selenium (Se) Biofortification Changes the Physiological, Biochemical and Epigenetic Responses to Water Stress in Zea mays L. by Inducing a Higher Drought Tolerance

Requiring water and minerals to grow and to develop its organs, Maize (Zea mays L.) production and distribution is highly rainfall-dependent. Current global climatic changes reveal irregular rainfall patterns and this could represent for maize a stressing condition resulting in yield and productivity loss around the world. It is well known that low water availability leads the plant to adopt a number of metabolic alterations to overcome stress or reduce its effects. In this regard, selenium (Se), a trace element, can help reduce water damage caused by the overproduction of reactive oxygen species (ROS). Here we report the effects of exogenous Se supply on physiological and biochemical processes that may influence yield and quality of maize under drought stress conditions. Plants were grown in soil fertilized by adding 150 mg of Se (sodium selenite). We verified the effects of drought stress and Se treatment. Selenium biofortification proved more beneficial for maize plants when supplied at higher Se concentrations. The increase in proline, K concentrations and nitrogen metabolism in aerial parts of plants grown in Se-rich substrates, seems to prove that Se-biofortification increased plant resistance to water shortage conditions. Moreover, the increase of SeMeSeCys and SeCys2 forms in roots and aerial parts of Se-treated plants suggest resistance strategies to Se similar to those existing in Se-hyperaccumulator species. In addition, epigenetic changes in DNA methylation due to water stress and Se treatment were also investigated using methylation sensitive amplified polymorphism (MSAP). Results suggest that Se may be an activator of particular classes of genes that are involved in tolerance to abiotic stresses. In particular, PSY (phytoene synthase) gene, essential for maintaining leaf carotenoid contents, SDH (sorbitol dehydrogenase), whose activity regulates the level of important osmolytes during drought stress and ADH (alcohol dehydrogenase), whose activity plays a central role in biochemical adaptation to environmental stress. In conclusion, Se-biofortification could help maize plants to cope with drought stress conditions, by inducing a higher drought tolerance.

A critical review of selenium biogeochemical behavior in soil-plant system with an inference to human health

Selenium (Se) is an essential trace element for humans and animals, although controversial for different plant species. There exists a narrow line between essential, beneficial and toxic levels of Se to living organisms which greatly varies with Se speciation, as well as the type of living organisms. Therefore, it is crucial to monitor its solid- and solution-phase speciation, exposure levels and pathways to living organisms. Consumption of Se-laced food (cereals, vegetables, legumes and pulses) is the prime source of Se exposure to humans. Thus, it is imperative to assess the biogeochemical behavior of Se in soil-plant system with respect to applied levels and speciation, which ultimately affect Se status in humans. Based on available relevant literature, this review traces a plausible link among (i) Se levels, sources, speciation, bioavailability, and effect of soil chemical properties on selenium bioavailability/speciation in soil; (ii) role of different protein transporters in soil-root-shoot transfer of Se; and (iii) speciation, metabolism, phytotoxicity and detoxification of Se inside plants. The toxic and beneficial effects of Se to plants have been discussed with respect to speciation and toxic/deficient concentration of Se. We highlight the significance of various enzymatic (catalase, peroxidase, superoxide dismutase, ascorbate peroxidase, glutathione peroxidase) and non-enzymatic (phytochelatins and glutathione) antioxidants which help combat Se-induced overproduction of reactive oxygen species (ROS). The review also delineates Se accumulation in edible plant parts from soils containing low or high Se levels; elucidates associated health disorders or risks due to the consumption of Se-deficient or Se-rich foods; discusses the potential role of Se in different human disorders/diseases.

Selenium mitigates cadmium-induced oxidative stress in tomato (Solanum lycopersicum L.) plants by modulating chlorophyll fluorescence, osmolyte accumulation, and antioxidant system

Pot experiments were conducted to investigate the role of selenium in alleviating cadmium stress in Solanum lycopersicum seedlings. Cadmium (150 mg L^-1) treatment caused a significant reduction in growth in terms of height and biomass accumulation and affected chlorophyll pigments, gas exchange parameters, and chlorophyll fluorescence. Selenium (10 μM) application mitigated the adverse effects of cadmium on growth, chlorophyll and carotenoid contents, leaf relative water content, and other physiological attributes. Lipid peroxidation and electrolyte leakage increased because of cadmium treatment and selenium-treated plants exhibited considerable reduction because of the decreased production of hydrogen peroxide in them. Cadmium-treated plants exhibited enhanced activity of antioxidant enzymes that protected cellular structures by neutralizing reactive free radicals. Supplementation of selenium to cadmium-treated plants (Cd + Se) further enhanced the activity of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) by 19.69, 31.68, 33.14, and 54.47%, respectively. Osmolytes, including proline and glycine betaine, increased with selenium application, illustrating their role in improving the osmotic stability of S. lycopersicum under cadmium stress. More importantly, selenium application significantly reduced cadmium uptake. From these results, it is clear that application of selenium alleviates the negative effects of cadmium stress in S. lycopersicum through the modifications of osmolytes and antioxidant enzymes.

Phenological application of selenium differentially improves growth, oxidative defense and ion homeostasis in maize under salinity stress

The underlying mechanism of selenium (Se) mediating plant salt tolerance is not well understood and information on how plant growth and development is regulated by phenological Se application (20 and 40 mg/L) under salinity stress is scarce. In present study, we have appraised the impact of phenological Se application on growth, antioxidant defense system and ionic imbalance in maize under salinity. Salinity (12 dS m^-1) reduced growth, concentration of chlorophyll and K⁺ in root and leaf. Contrarily, salinity increased toxic Na⁺, malondialdehyde (MDA) and H₂O₂ concentration that resulted in oxidative damage. Lower level of Se application (20 mg/L) increased growth and chlorophyll by reducing oxidative damage due to high cell concentrations of MDA and H₂O₂. Se reduced endogenous levels of H₂O₂ and MDA under salinity. Moreover, Se regulated antioxidant defense system by increasing the activities of antioxidant enzymes (SOD, POD and CAT) and influenced the concentrations of non-enzymatic antioxidants (phenolics and flavonoids). Se-induced better antioxidant system protected plants from oxidative damage. We have also recorded substantial increase in K⁺ and decrease in Na⁺ concentration in plants treated with 20 mg/L Se under salinity stress. The impact of Se on plant growth and development is linked with the growth stage of exogenous application. Foliar Se at reproductive and both vegetative and reproductive stages improved salinity tolerance in maize compared with vegetative stage.

Effect of selenium application on arsenic uptake in rice (Oryza sativa L.)

Alluvial aquifers of the agrarian state of Punjab of southwestern arid zone used for irrigation of rice crops are rich in arsenic concentration. In the present study, rice (Oryza sativa L.) crops were raised in pots in a greenhouse with a purpose to study whether selenium (Se) application was effective in ameliorating As uptake. The rice crop was irrigated with arsenic laced water (0, 2.5, 5.0, 10.0 μM As L^-1) throughout the growing period, without and with selenium (0.05 and 0.10 mg kg^-1) added through mustard biomass, grown ex situ in seleniferous soil. Arsenic uptake and dry matter yield in different parts of the rice crop were assayed after application of As alone and simultaneous supplementations (As + Se). An antagonistic interaction between Se and As was observed. Addition of As through irrigation water significantly reduced yield of rice grain, straw and root. However, subsequent addition of Se helped in mitigating the harmful effect of As and countered the yield reduction caused due to As toxicity. The effect of Se on dry matter yield was more pronounced at its higher dose (0.10 mg kg^-1) as compared to its lower dose (0.05 mg kg^-1). The presence of Se either alone or added along with As significantly reduced the As concentration and its uptake by different parts of rice and higher reduction in As concentration was observed with addition of the highest level of applied Se (0.10 mg kg^-1). Our observations indicated that Se supplementation might be favourable to reduce As accumulation and toxicity in rice crops.

Underlying mechanisms and effects of hydrated lime and selenium application on cadmium uptake by rice (Oryza sativa L.) seedlings

A pot experiment was conducted to investigate the effects of selenium (Se) and hydrated lime (Lime), applied alone or simultaneously (Se+Lime), on growth and cadmium (Cd) uptake and translocation in rice seedlings grown in an acid soil with three levels of Cd (slight, mild, and moderate contamination). In the soil with 0.41 mg kg^-1 Cd (slight Cd contamination), Se addition alone significantly decreased Cd accumulation in the root and shoot by 35.3 and 40.1%, respectively, but this tendency weakened when Cd level in the soil increased. However, Se+Lime treatment effectively reduced Cd accumulation in rice seedlings in the soil with higher Cd levels. The results also showed that Se application alone strongly increased Cd concentration in the iron plaque under slight Cd contamination, which was suggested as the main reason underlying the inhibition of Cd accumulation in rice seedlings. Se+Lime treatment also increased the ability of the iron plaques to restrict Cd uptake by rice seedlings across all Cd levels and dramatically decreased the available Cd concentration in the soil. These results suggest that Se application alone would be useful in the soil with low levels of Cd, and the effect would be enhanced when Se application is combined with hydrated lime at higher Cd levels.

Allium cepa L. Response to Sodium Selenite (Se(IV)) Studied in Plant Roots by a LC-MS-Based Proteomic Approach

Liquid chromatography-high-resolution mass spectrometry was used for the first time to investigate the impact of Se(IV) (10 mgSe L^-1 as sodium selenite) on Allium cepa L. root proteome. Using MaxQuant platform, more than 600 proteins were found; 42 were identified based on at least 2 razor + unique peptides, score > 25, and were found to be differentially expressed in the exposed versus control roots with t-test difference > ±0.70 (p < 0.05, Perseus). Se(IV) caused growth inhibition and the decrease of total RNA in roots. Different abundances of proteins involved in transcriptional regulation, protein folding/assembly, cell cycle, energy/carbohydrate metabolism, stress response, and antioxidant defense were found in the exposed vs nonexposed roots. New evidence was obtained on the alteration of sulfur metabolism due to S-Se competition in A. cepa L. which, together with the original analytical approach, is the main scientific contribution of this study. Specifically, proteins participating in assimilation and transformation of both elements were affected; formation of volatile Se compounds seemed to be favored. Changes observed in methionine cycle suggested that Se(IV) stress might repress methylation capability in A. cepa L., potentially limiting accumulation of Se in the form of nonprotein methylated species and affecting adversely transmethylation-dependent signaling pathways.

Salinity induced differential methylation patterns in contrasting cultivars of foxtail millet (Setaria italica L.)

Genome-wide methylation analysis of foxtail millet cultivars contrastingly differing in salinity tolerance revealed DNA demethylation events occurring in tolerant cultivar under salinity stress, eventually modulating the expression of stress-responsive genes. Reduced productivity and significant yield loss are the adverse effects of environmental conditions on physiological and biochemical pathways in crop plants. In this context, understanding the epigenetic machinery underlying the tolerance traits in a naturally stress tolerant crop is imperative. Foxtail millet (Setaria italica) is known for its better tolerance to abiotic stresses compared to other cereal crops. In the present study, methylation-sensitive amplified polymorphism (MSAP) technique was used to quantify the salt-induced methylation changes in two foxtail millet cultivars contrastingly differing in their tolerance levels to salt stress. The study highlighted that the DNA methylation level was significantly reduced in tolerant cultivar compared to sensitive cultivar. A total of 86 polymorphic MSAP fragments were identified, sequenced and functionally annotated. These fragments showed sequence similarity to several genes including ABC transporter, WRKY transcription factor, serine threonine-protein phosphatase, disease resistance, oxidoreductases, cell wall-related enzymes and retrotransposon and transposase like proteins, suggesting salt stress-induced methylation in these genes. Among these, four genes were chosen for expression profiling which showed differential expression pattern between both cultivars of foxtail millet. Altogether, the study infers that salinity stress induces genome-wide DNA demethylation, which in turn, modulates expression of corresponding genes.

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.

Indications of Selenium Protection against Cadmium and Lead Toxicity in Oilseed Rape (Brassica napus L.)

The present study investigated the beneficial role of selenium (Se) in protecting oilseed rape (Brassica napus L.) plants from cadmium (Cd+2) and lead (Pb+2) toxicity. Exogenous Se markedly reduced Cd and Pb concentration in both roots and shoots. Supplementation of the medium with Se (5, 10, and 15 mg kg-1) alleviated the negative effect of Cd and Pb on growth and led to a decrease in oxidative damages caused by Cd and Pb. Furthermore, Se-enhanced superoxide free radicals ([Formula: see text]), hydrogen peroxide (H2O2), and lipid peroxidation, as indicated by malondialdehyde accumulation, but decreased superoxide dismutase and glutathione peroxidase activities. Meanwhile, the presence of Cd and Pb in the medium affected Se speciation in shoots. The results suggest that Se could alleviate Cd and Pb toxicity by preventing oxidative stress in oilseed rape plant.

Chromatin-Based Epigenetic Regulation of Plant Abiotic Stress Response

Plants are continuously exposed to various abiotic and biotic factors limiting their growth and reproduction. In response, they need various sophisticated ways to adapt to adverse environmental conditions without compromising their proper development, reproductive success and eventually survival. This requires an intricate network to regulate gene expression at transcriptional and post-transcriptional levels, including epigenetic switches. Changes in chromatin modifications such as DNA and histone methylation have been observed in plants upon exposure to several abiotic stresses. In the present review, we highlight the changes of DNA methylation in diverse plants in response to several abiotic stresses such as salinity, drought, cold and heat. We also discuss the progresses made in understanding how these DNA methylation changes might contribute to the abiotic stress tolerance.

Root application of selenite can simultaneously reduce arsenic and cadmium accumulation and maintain grain yields, but show negative effects on the grain quality of paddy rice

Most current technologies can hardly simultaneously reduce the accumulation of arsenic (As) and cadmium (Cd) in crops. In this study, root application of selenite [Se (IV)] and selenate [Se (VI)] was used to assess their abilities to reduce the accumulation of As and Cd, and maintain the yields and quality of rice grains. The results show that Se (IV) showed a weaker ability than Se (VI) to maintain the grain contents of many essential elements, but a stronger ability to decrease As and Cd contents in rice grains, and maintain the yields, photosynthesis rate and stomatal conductance, and increase the grain contents of several amino acids (AAs), total Se, selenomethionine (SeMet) and selenocysteine (SeCys). The best outcomes resulted at a relatively high application of 5 mg kg^-1 Se (IV), reflecting in the highest total Se, SeCys and SeMet content (14.95, 118.70 and 864.73 μg kg^-1, respectively) in the grains, highest grain yield, and lowest grain As and Cd content (0.36 and 0.07 mg kg^-1, respectively). In addition, the application of 1-5 mg kg^-1 Se (IV) seemed to facilitate the formation of SeMet in the grains, but most inorganic Se in the grains were transformed into SeCys and SeMet under Se (VI) treatments. This study provides a new idea to resolve the problems of high accumulation of As and Cd in rice grains and insufficiency of Se intake in China.

The importance of glutathione and phytochelatins on the selenite and arsenate detoxification in Arabidopsis thaliana

We investigated the role of glutathione (GSH) and phytochelatins (PCs) on the detoxification of selenite using Arabidopsis thaliana. The wild-type (WT) of Arabidopsis thaliana and its mutants (glutathione deficient Cad 2-1 and phytochelatins deficient Cad 1-3) were separately exposed to varying concentrations of selenite and arsenate and jointly to both toxicants to determine their sensitivities. The results of the study revealed that, the mutants were about 20-fold more sensitive to arsenate than the WT, an indication that the GSH and PCs affect arsenate detoxification. On the contrary, the WT and both mutants showed a similar level of sensitivity to selenite, an indication that the GSH and PCs do not significantly affect selenite detoxification. However, the WT is about 8 times more sensitive to selenite than to arsenate, and the mutants were more resistant to selenite than arsenate by a factor of 2. This could not be explained by the accumulation of both elements in roots and shoots in exposure experiments. The co-exposure of the WT indicates a synergistic effect with regards to toxicity since selenite did not induce PCs but arsenic and selenium compete in their PC binding as revealed by speciation analysis of the root extracts using HPLC-ICP-MS/ESI-MS. In the absence of PCs an antagonistic effect has been detected which might suggest indirectly that the formation of Se glutathione complex prevent the formation of detrimental selenopeptides. This study, therefore, revealed that PC and GSH have only a subordinate role in the detoxification of selenite.

Cadmium uptake dynamics and translocation in rice seedling: Influence of different forms of selenium

Selenium (Se) can alleviate the toxicity of cadmium (Cd), but little is known about its mechanism in Cd uptake and translocation in plants. We investigated the effects of exogenous selenite, selenate, and selenomethionine (SeMet) on Cd uptake and translocation within rice (Oryza sativa L., Zhunliangyou 608) seedlings, and the concentration-dependent uptake kinetics of Cd into rice roots (with or without Se) were determined. The effect of the endogenous Se pool on Cd uptake was also investigated. Results of uptake kinetics showed that selenite slightly promoted Cd influx during 1h of exposure, compared with no selenite addition; Vmax of Cd uptake increased by 13.8% in 10μM selenite treatment; while the presence of selenate had no effect on the influx of Cd. When exposed to Cd (5μM) over 20h (with selenite) or 30h (with selenate or SeMet), Se addition (5μM) decreased Cd uptake and root-to-shoot translocation; after 30h selenite, selenate, or SeMet addition decreased Cd uptake by roots by 28.6%, 17.7% or 12.1%, respectively. Besides, as the selenite levels in the treatment solutions (1μMCd) increased (0, 0.1, 1, and 5μM, Se), Cd uptake and translocation were both significantly reduced, while the inhibitive effect was more significant at lower levels of selenate. Pretreatment of selenite or selenate (5μM) also decreased Cd uptake by 24.9% or 15.7%, and reduced the root-to-shoot transfer factor by 41.4% or 36.2% after 144h of subjection to Cd (5μM), respectively. The presence of selenite decreased Cd content more effectively than did selenate. Our results demonstrated that Se can effectively reduce the Cd translocation from roots to shoots in rice seedlings.

Selenate mitigates arsenite toxicity in rice (Oryza sativa L.) by reducing arsenic uptake and ameliorates amino acid content and thiol metabolism

Arsenic (As) is a toxic element with the potential to cause health effects in humans. Besides rice is a source of both amino acids (AAs) and mineral nutrients, it is undesired source of As for billions of people consuming rice as the staple food. Selenium (Se) is an essential metalloid, which can regulate As toxicity by strengthening antioxidant potential. The present study was designed to investigate As(III) stress mitigating effect of Se(VI) in rice. The level of As, thiolic ligands and AAs was analyzed in rice seedlings after exposure to As(III)/Se(VI) alone and As(III)+Se(VI) treatments. Selenate supplementation (As(III) 25μM+Se(VI) 25μM) decreased total As accumulation in both root and shoot (179 & 144%) as compared to As(III) alone treatment. The As(III)+Se(VI) treatment also induced the levels of non-protein thiols (NPTs), glutathione (GSH) and phytochelatins (PCs) as compared to As(III) alone treatment and also modulated the activity of enzymes of thiol metabolism. The content of amino acids (AAs) was significantly altered with Se(VI) supplementation. Importantly, essential amino acids (EAAs) were enhanced in As(III)+Se(VI) treatment as compared to As(III) alone treatment. In contrast, stress related non-essential amino acids (NEAAs) like GABA, Glu, Gly, Pro and Cys showed enhanced levels in As(III) alone treatment. In conclusion, rice supplemented with Se(VI) tolerated As toxicity with reduced As accumulation and increased the nutrition quality by increasing EAAs.

Internalization and Phytotoxic Effects of CuO Nanoparticles in Arabidopsis thaliana as Revealed by Fatty Acid Profiles

Internalization and phytotoxic effects of CuO nanoparticles (nCuO) in plants were studied at the cellular level. Arabidopsis thaliana was hydroponically challenged by nCuO (100 mg/L), as compared to Cu²⁺ ions (1.2 mg/L), to account for nCuO dissolution for 96 h and 28 days to monitor Cu accumulation in the plant as well as the fatty acid (FA) profiles of the plant cell membrane. Under the same growing conditions, the nCuO exposure resulted in more Cu accumulation than did the Cu²⁺ exposure. Multiple microscopic techniques confirmed the internalization and sequestration of nCuO in root cell vacuoles, where transformation of Cu(II) to Cu(I)Cl occurred. Short and long exposures (96 h versus 28 days) to both nCuO and Cu²⁺ elevated FA saturation degrees in plant cells through oxidative stress, as verified by in situ detection of superoxide radicals, with conversions mostly from C18:3, C16:3, and C18:2 to C16:0. Only the long exposure to nCuO significantly brought about an additional elevation of FA saturation degree in root cells. These results demonstrated that the acute effects of plant exposure to nCuO were mainly produced from the stress of Cu²⁺ ions released from nCuO dissolution, while the chronic effects in roots were significantly developed by the nCuO particle stress. The findings in this work are novel and may offer significant implications in better understanding nanoparticle-induced phytotoxicity and potential risks in ecosystems.

Efficiency evaluation for remediating paddy soil contaminated with cadmium and arsenic using water management, variety screening and foliage dressing technologies

Paddy soils in many regions of China have been seriously polluted by multiple heavy metals or metalloids, such as arsenic (As), cadmium (Cd) and lead (Pb). In order to ensure the safety of food and take full advantage of the limited farmland resources of China, exploring an effective technology to repair contaminated soils is urgent and necessary. In this study, three technologies were employed, including variety screening, water management and foliage dressing, to assess their abilities to reduce the accumulation of Cd and As in the grains of different rice varieties, and meanwhile monitor the related yields. The results of variety screening under insufficient field drying condition showed that the As and Cd contents in the grains of only four varieties [Fengliangyouxiang 1 (P6), Zhongzheyou 8 (P7), Guangliangyou 1128 (P10), Y-liangyou 696 (P11)] did not exceed their individual national standard. P6 gained a relatively high grain yield but accumulated less As and Cd in the grains despite of the relatively high As and Cd concentrations in the rhizosphere soil. However, long-playing field drying in water management trial significantly increased Cd but decreased As content in the grains of all tested three varieties including P6, suggesting an important role of water supply in controlling the accumulation of grain As and Cd. Selenium (Se) showed a stronger ability than silicon (Si) to reduce As and Cd accumulation in the grains of Fengliangyou 4 (P2) and Teyou 524 (P13), and keep the yields. The results of this study suggest that combined application of water management and foliage dressing may be an efficient way to control As and Cd accumulation in the grains of paddy rice exposing to As- and Cd-contaminated soils.

Heavy Metal Tolerance in Plants: Role of Transcriptomics, Proteomics, Metabolomics, and Ionomics

Heavy metal contamination of soil and water causing toxicity/stress has become one important constraint to crop productivity and quality. This situation has further worsened by the increasing population growth and inherent food demand. It has been reported in several studies that counterbalancing toxicity due to heavy metal requires complex mechanisms at molecular, biochemical, physiological, cellular, tissue, and whole plant level, which might manifest in terms of improved crop productivity. Recent advances in various disciplines of biological sciences such as metabolomics, transcriptomics, proteomics, etc., have assisted in the characterization of metabolites, transcription factors, and stress-inducible proteins involved in heavy metal tolerance, which in turn can be utilized for generating heavy metal-tolerant crops. This review summarizes various tolerance strategies of plants under heavy metal toxicity covering the role of metabolites (metabolomics), trace elements (ionomics), transcription factors (transcriptomics), various stress-inducible proteins (proteomics) as well as the role of plant hormones. We also provide a glance of some strategies adopted by metal-accumulating plants, also known as "metallophytes."

Isobolographic analysis of the interaction between cadmium (II) and sodium sulphate: toxicological consequences

Sulphate is an essential nutrient for autotrophic organisms and has been shown to have important implications in certain processes of tolerance to cadmium toxicity. Sodium sulphate is the main salt of sulphate in the natural environments. The concentration of this salt is increasing in the aquatic environments due to environmental pollution. The aim of this study was to investigate, using an analysis of isobolograms, the type and the degree of the interaction between Cd(II) and sodium sulphate in the freshwater microalga Chlamydomonas moewusii. Two blocks of experiments were performed, one at sub-optimal sodium sulphate concentrations (<14.2 mg/L) and the other at supra-optimal concentrations (>14.2 mg/L). Three fixed ratios (2:1, 1:1, and 1:2) of the individual EC50 for cadmium and sodium sulphate were used within each block. The isobolographic analysis of interaction at sub-optimal concentrations showed a stronger antagonistic effect with values of interaction index (γ) between 1.46 and 3.4. However, the isobologram with sodium sulphate at supra-optimal concentrations revealed a slight but significant synergistic effect between both chemicals with an interaction index between 0.54 and 0.64. This synergic effect resulted in the potentiation of the toxic effects of cadmium, synergy that was related to the increase of the ionic strength and of two species of cadmium, CdSO4 (aq), and Cd(SO4)2(2-) , in the medium. Results of the current study suggest that sodium sulphate is able to perform a dual antagonist/synergist effect on cadmium toxicity. This role was concentration dependent.

Exogenously applied selenium reduces oxidative stress and induces heat tolerance in spring wheat

Heat stress (HS) is a worldwide threat to productivity of wheat, especially in arid and semiarid regions of the world. Earlier studies suggested the beneficial effects of selenium (Se) on the growth of some crop species grown under stressful environments. In the present study, we assessed whether Se application could increase antioxidative potential, and thus enhance tolerance to heat in wheat at the sensitive stage i.e., heading stage. At the heading stage, after foliar application of sodium selenate solutions (0, 2 and 4 mg Se L(-1)), the plants of wheat cultivars, namely Chakwal-97 (drought tolerant) and Faisalabad-08 (drought sensitive), were subjected to HS (38 ± 2 °C). The HS significantly altered antioxidative potential, affected growth, photosynthetic pigments and grain yield in both cultivars. Exogenous application of low (2 mg L(-1)) Se increased chlorophyll a and total chlorophyll contents and modulated the growth of wheat plants under HS. However, high concentration (4 mg L(-1)) of Se was much more effective in increasing grains per spike and grain yield in heat stressed plants of both wheat cultivars. Exogenous Se increased both enzymatic (catalase and ascorbate peroxidase activities) and non-enzymatic (carotenoids, anthocyanins and ascorbic acid contents) antioxidants while decreased oxidants (hydrogen peroxide and malondialdehyde contents) under HS in both wheat cultivars. In conclusion, foliar application of Se (4 mg L(-1)) was much more effective in mitigating the deleterious effects of HS on grain yield of wheat plants. The results suggested that Se-mediated up-regulation of antioxidative system (both enzymatic and non-enzymatic) helped the wheat plants to increase fertility, and hence avoid reduction of grain yield under HS.

Effects of selenium and silicon on enhancing antioxidative capacity in ramie (Boehmeria nivea (L.) Gaud.) under cadmium stress

Hydroponic experiments were performed to investigate the ameliorating effects and mitigation mechanisms of selenium and silicon on Cd toxicity in Boehmeria nivea (L.) Gaud. Metal accumulation, chlorophyll content, activities of antioxidant enzymes, and antioxidant contents in ramie were evaluated. The results revealed that cadmium was mainly accumulated in the roots of plants rather than in the aerial parts. Additionally, under 5 mg L(-1) Cd stress, both Se (1 μmol L(-1)) and Si (1 mmol L(-1)) treatments decreased the Cd concentrations in plants. Besides, the treatments also inhibited the translocation ability of Cd from roots to the aboveground parts, which might be related to the decline of generation of reactive oxygen species (ROS). The application of Se and/or Si ameliorated Cd toxicity via stimulating the activities of antioxidant enzymes such as superoxide dismutase (SOD), guaiacol peroxidase (POD), and ascorbate peroxidase (APX), which resulted in the significant decrease of the contents of malondialdialdehyde (MDA) and hydrogen peroxide (H2O2) in ramie leaves. In addition, the content of nonenzymatic antioxidant such as glutathione (GSH) was increased significantly through the addition of selenite and silicate. Also, ascorbate (AsA) and vitamin E played a crucial role in scavenging excess ROS within plants. On the whole, appropriate doses of Se and Si were found to benefit plant growth and enhance the ability of ramie to alleviate Cd-induced stress. Moerover, the effects of combination of Se and Si appeared to be more superior compared to addition separately in response to Cd stress.

The effect of selenium on the subcellular distribution of antimony to regulate the toxicity of antimony in paddy rice

Selenium (Se) can alleviate the toxicity of antimony (Sb) in plants; however, the associated mechanisms have not been fully clarified. In this study, we hypothesize that Se can affect the subcellular distribution of Sb to regulate Sb toxicity. To test our hypothesis, two nested hydroponic experiments were performed by using paddy rice (Fengmeizhan). The results showed that Sb exerted toxic effects on the growth of paddy rice, and Se caused beneficial effects that were limited to the shoot growth. In general, Se and Sb mutually showed antagonistic effects on their uptake and concentrations in different subcellular fractions. However, in some cases, the stimulation effects of Sb on the Se concentration in chlorophyll (Chl) and cytosol (Cy) fractions or of Se on the Sb concentration in the cell wall fraction (Cw) were also observed in the shoots, which might suggest that Sb detoxification by Se is also related to the migration of both Se and Sb in cells. Selenium and Sb were primarily concentrated in the Cw and Cy, suggesting the important roles of these two fractions in detoxifying Se and Sb. When paddy rice was subjected to increasing Sb concentrations and a fixed Se concentration, most of the Se in the shoots was sequestered in the Cy (59.81-79.51% of total Se) and more Se was transferred into the inner cell from Cw; however, in the roots, Se was primarily concentrated in the Cw (53.28-72.10%). When paddy rice was exposed to increasing Se concentrations with a fixed Sb concentration, the Cw in both the shoots and roots might play an important role in binding Se, especially in the roots where up to 78.92% of the total Se was sequestered in the Cw.

Selenium alleviates chromium toxicity by preventing oxidative stress in cabbage (Brassica campestris L. ssp. Pekinensis) leaves

The beneficial role of selenium (Se) in alleviation of chromium (Cr)-induced oxidative stress is well established. However, little is known about the underlying mechanism. The impacts of exogenous Se (0.1mg/L) on Cr(1mg/L)-induced oxidative stress and antioxidant systems in leaves of cabbage (Brassica campestris L. ssp. Pekinensis) were investigated by using cellular and biochemical approaches. The results showed that supplementation of the medium with Se was effective in reducing Cr-induced increased levels of lipid peroxides and superoxide free radicals (O(-)2(·)), as well as increasing activities of superoxide dismutase (SOD) and peroxidase (POD). Meanwhile, 1mg/L Cr induced loss of plasma membrane integrity, growth inhibition, as well as ultrastructural changes of leaves were significantly reversed due to Se supplementation in the medium. In addition, Se application significantly altered the subcellular distribution of Cr which transported from mitochondria, nucleus and the cell-wall material to the soluble fraction and chloroplasts. However, Se application did no significant alteration of Cr effects on osmotic adjustment accumulating products. The study suggested that Se is able to protect leaves of cabbage against Cr toxicity by alleviation of Cr induced oxidative stress, and re-distribution of Cr in the subcellular of the leaf. Furthermore, free radicals, lipid peroxides, activity of SOD and POD, and subcellular distribution of Cr can be considered the efficient biomarkers to indicate the efficiency of Se to detoxification Cr.

Modulation of antioxidant machinery and the methylglyoxal detoxification system in selenium-supplemented Brassica napus seedlings confers tolerance to high temperature stress

We investigated the protective role of selenium (Se) in minimizing high temperature-induced damages to rapeseed (Brassica napus L. cv. BINA Sarisha 3) seedlings. Ten-day-old seedlings which had been supplemented with Se (25 μM Na2SeO4) or not were grown separately under control temperature (25 °C) or high temperature (38 °C) for a period of 24 or 48 h in nutrient solution. Heat stress caused decrease in chlorophyll and leaf relative water content (RWC) and increased malondialdehyde (MDA), hydrogen peroxide (H2O2), proline (Pro), and methylglyoxal (MG) contents. Ascorbate (AsA) content decreased at any duration of heat treatment. The content of reduced glutathione (GSH) increased only at 24 h of stress, while glutathione disulfide (GSSG) markedly increased at both duration of heat exposure with associated decrease in GSH/GSSG ratio. Upon heat treatment the activities of ascorbate peroxidase (APX), glutathione S-transferase (GST) and glyoxalase I (Gly I) were increased, while the activities of monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and catalase (CAT) were decreased. The activities of glutathione reductase (GR) and glutathione peroxidase (GPX) remained unchanged under heat stress. However, heat-treated seedlings which were supplemented with Se significantly decreased the lipid peroxidation, H2O2, and MG content and enhanced the content of chlorophyll, Pro, RWC, AsA, and GSH as well as the GSH/GSSG ratio. Selenium supplemented heat-treated seedlings also showed enhanced activities of MDHAR, DHAR, GR, GPX, CAT, Gly I, and Gly II as compared to heat-treated seedlings without Se supplementation. This study concludes that exogenous Se application confers heat stress tolerance in rapeseed seedlings by upregulating the antioxidant defense mechanism and methylglyoxal detoxification system.

OsACA6, a P-type 2B Ca(2+) ATPase functions in cadmium stress tolerance in tobacco by reducing the oxidative stress load

MAIN CONCLUSION

The present study demonstrates the first direct evidence of the novel role of OsACA6 in providing Cd (2+) stress tolerance in transgenic tobacco by maintaining cellular ion homeostasis and modulating ROS-scavenging pathway. Cadmium, a non-essential toxic heavy metal, interferes with the plant growth and development. It reaches the leaves through xylem and may become part of the food chain, thus causing detrimental effects to human health. Therefore, there is an urgent need to develop strategies for engineering plants for Cd(2+) tolerance and less accumulation. The members of P-type ATPases family transport metal ions including Cd(2+), and thus play important role an ion homeostasis. The present study elucidates the role of P-type 2B Ca(2+) ATPase (OsACA6) in Cd(2+) stress tolerance. The transcript levels of OsACA6 were up-regulated upon Cd(2+), Zn(2+) and Mn(2+) exposure. Transgenic tobacco expressing OsACA6 showed tolerance towards Cd(2+) stress as demonstrated by several physiological indices including root length, biomass, chlorophyll, malondialdehyde and hydrogen peroxide content. The roots of the transgenic lines accumulated more Cd(2+) as compared to shoot. Further, confocal laser scanning microscopy showed that Cd(2+) exposure altered Ca(2+) uptake in OsACA6 transgenic plants. OsACA6 expression in tobacco also protected the transgenic plants from oxidative stress by enhancing the activity of enzymatic (SOD, CAT, APX, GR) and non-enzymatic (GSH and AsA) antioxidant machinery. Transgenic lines also tolerated Zn(2+) and Mn(2+) stress; however, tolerance for these ions was not as significant as observed for Cd(2+) exposure. Thus, overexpression of OsACA6 confers Cd(2+) stress tolerance in transgenic lines by maintaining cellular ion homeostasis and modulating reactive oxygen species (ROS)-scavenging pathway. The results of the present study will help to develop strategies for engineering Cd(2+) stress tolerance in economically important crop plants.

Selenium ameliorates arsenic induced oxidative stress through modulation of antioxidant enzymes and thiols in rice (Oryza sativa L.)

Arsenic (As) contamination of rice is a major problem for South-East Asia. In the present study, the effect of selenium (Se) on rice (Oryza sativa L.) plants exposed to As was studied in hydroponic culture. Arsenic accumulation, plant growth, thiolic ligands and antioxidative enzyme activities were assayed after single (As and Se) and simultaneous supplementations (As + Se). The results indicated that the presence of Se (25 µM) decreased As accumulation by threefold in roots and twofold in shoots as compared to single As (25 µM) exposed plants. Arsenic induced oxidative stress in roots and shoots was significantly ameliorated by Se supplementation. The observed positive response was found associated with the increased activities of ascorbate peroxidase (APX; EC 1.11.1.11), catalase (CAT; EC 1.11.1.6) and glutathione peroxidase (GPx; EC 1.11.1.9) and induced levels of non-protein thiols (NPTs), glutathione (GSH) and phytochelatins (PCs) in As + Se exposed plants as compared to single As treatment. Selenium supplementation modulated the thiol metabolism enzymes viz., γ-glutamylcysteine synthetase (γ-ECS; EC 6.3.2.2), glutathione-S-transferase (GST; EC 2.5.1.18) and phytochelatin synthase (PCS; EC 2.3.2.15). Gene expression analysis of several metalloid responsive genes (LOX, SOD and MATE) showed upregulation during As stress, however, significant downregulation during As + Se exposure as compared to single As treatment. Gene expressions of enzymes of antioxidant and GSH and PC biosynthetic systems, such as APX, CAT, GPx, γ-ECS and PCS were found to be significantly positively correlated with their enzyme activities. The findings suggested that Se supplementation could be an effective strategy to reduce As accumulation and toxicity in rice plants.

Comparison of the heat stress induced variations in DNA methylation between heat-tolerant and heat-sensitive rapeseed seedlings

DNA methylation is responsive to various biotic and abiotic stresses. Heat stress is a serious threat to crop growth and development worldwide. Heat stress results in an array of morphological, physiological and biochemical changes in plants. The relationship between DNA methylation and heat stress in crops is relatively unknown. We investigated the differences in methylation levels and changes in the cytosine methylation patterns in seedlings of two rapeseed genotypes (heat-sensitive and heat-tolerant) under heat stress. Our results revealed that the methylation levels were different between a heat-tolerant genotype and a heat-sensitive one under control conditions. Under heat treatment, methylation increased more in the heat-sensitive genotype than in the heat-tolerant genotype. More DNA demethylation events occurred in the heat-tolerant genotype, while more DNA methylation occurred in the heat-sensitive genotype. A large and diverse set of genes were affected by heat stress via cytosine methylation changes, suggesting that these genes likely play important roles in the response and adaption to heat stress in Brassica napus L. This study indicated that the changes in DNA methylation differed between heat-tolerant and heat-sensitive genotypes of B. napus in response to heat stress, which further illuminates the molecular mechanisms of the adaption to heat stress in B. napus.

Selenium alleviates cadmium toxicity by preventing oxidative stress in sunflower (Helianthus annuus) seedlings

The present study investigated the possible mediatory role of selenium (Se) in protecting plants from cadmium (Cd) toxicity. The exposure of sunflower seedlings to 20μM Cd inhibited biomass production, decreased chlorophyll and carotenoid concentrations and strongly increased accumulation of Cd in both roots and shoots. Similarly, Cd enhanced hydrogen peroxides content and lipid peroxidation as indicated by malondialdehyde accumulation. Pre-soaking seeds with Se (5, 10 and 20μM) alleviated the negative effect of Cd on growth and led to a decrease in oxidative injuries caused by Cd. Furthermore, Se enhanced the activities of catalase, ascorbate peroxidase and glutathione reductase, but lowered that of superoxide dismutase and guaiacol peroxidase. As important antioxidants, ascorbate and glutathione contents in sunflower leaves exposed to Cd were significantly decreased by Se treatment. The data suggest that the beneficial effect of Se during an earlier growth period could be related to avoidance of cumulative damage upon exposure to Cd, thus reducing the negative consequences of oxidative stress caused by heavy metal toxicity.

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.

Exogenous selenium pretreatment protects rapeseed seedlings from cadmium-induced oxidative stress by upregulating antioxidant defense and methylglyoxal detoxification systems

The protective effect of selenium (Se) on antioxidant defense and methylglyoxal (MG) detoxification systems was investigated in leaves of rapeseed (Brassica napus cv. BINA sharisha 3) seedlings under cadmium (Cd)-induced oxidative stress. Two sets of 11-day-old seedlings were pretreated with both 50 and 100 μM Se (Na(2)SeO(4), sodium selenate) for 24 h. Two concentrations of CdCl(2) (0.5 and 1.0 mM) were imposed separately or on the Se-pretreated seedlings, which were grown for another 48 h. Cadmium stress at any levels resulted in the substantial increase in malondialdehyde and H(2)O(2) levels. The ascorbate (AsA) content of the seedlings decreased significantly upon exposure to Cd stress. The amount of reduced glutathione (GSH) increased only at 0.5 mM CdCl(2), while glutathione disulfide (GSSG) increased at any level of Cd, with concomitant decrease in GSH/GSSG ratio. The activities of ascorbate peroxidase (APX) and glutathione S-transferase (GST) increased significantly with increased concentration of Cd (both at 0.5 and 1.0 mM CdCl(2)), while the activities of glutathione reductase (GR) and glutathione peroxidase (GPX) increased only at moderate stress (0.5 mM CdCl(2)) and then decreased at 1.0 mM severe stress (1.0 mM CdCl(2)). Monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), catalase (CAT), glyoxalase I (Gly I), and glyoxalase II (Gly II) activities decreased upon exposure to any levels of Cd. Selenium pretreatment had little effect on the nonenzymatic and enzymatic components of seedlings grown under normal conditions; i.e., they slightly increased the GSH content and the activities of APX, GR, GST, and GPX. On the other hand, Se pretreatment of seedlings under Cd-induced stress showed a synergistic effect; it increased the AsA and GSH contents, the GSH/GSSG ratio, and the activities of APX, MDHAR, DHAR, GR, GPX, CAT, Gly I, and Gly II which ultimately reduced the MDA and H(2)O(2) levels. However, in most cases, pretreatment with 50 μM Se showed better results compared to pretreatment with 100 μM Se. The results indicate that the exogenous application of Se at low concentrations increases the tolerance of plants to Cd-induced oxidative damage by enhancing their antioxidant defense and MG detoxification systems.

Phytotoxicity by Lead as Heavy Metal Focus on Oxidative Stress

In the recent years, search for better quality of life in urban areas has been provoking an increase in urban agriculture. However, this new way of agriculture can bring risks to human health since this land is highly contaminated, due to anthropogenic activities. This way, lead (Pb) phytotoxicity approach must be taken into consideration since it can be prejudicial to human health through food chain. Pb is a common environmental contaminant, which originate numerous disturbances in plant physiological processes due to the bioacummulation of this metal pollutant in plant tissues. This review, focus on the uptake and interaction of lead by plants and how it can be introduced in food chain. Special attention was taken to address the oxidative stress by lead regarding the effects produced in plant physiological and biochemical processes. Furthermore, the antioxidant defence system was taken into consideration. Phytoremediation is applied on site or chronic polluted soils. This emerging technique is useful to bioaccumulate, degrade or decrease risks associated with contaminants in soils, water or air through the use of hyperaccumulaters. In addition, the impact of nanoparticles in plant science was also focused in this article since some improving properties in plants have been increasingly investigated.

The influence of selenium on root growth and oxidative stress induced by lead in Vicia faba L. minor plants

The effect of selenium (Se) on Vicia faba L. minor roots subjected to lead (Pb) stress was studied by investigating root growth, root viability, and antioxidant enzyme activity. The experiments were carried out on plants grown for 2 weeks on Hoagland medium supplied with 50 μM Pb in the form of lead nitrate Pb(NO(3))(2) and/or Se concentrations of 1.5 and 6 μM in the form of sodium selenite Na(2)SeO(3). It was shown that Pb reduced the root growth and caused serious damage in the roots, which was accompanied by metal accumulation in these tissues. The exposition of roots to Pb led to significant changes in the biochemical parameters: the MDA and T-SH content and glutathione peroxidase (GSH-Px) activity increased but the guaiacol peroxidase (GPOX) activity decreased. Moreover, Pb intensified O(2)(·-) production in the roots. Selenium at a lower concentration alleviated Pb toxicity which was accompanied by a decreased O(2)(·-) production in the apical parts of roots and increased the T-SH content and GPOX activity. However, higher Se concentration intensified MDA and T-SH accumulation and GPOX and GSH-Px activity in Pb-treated plant roots. At low concentration, Se improved cell viability whereas at high concentration it was pro-oxidant and enhanced the lipid peroxidation and cell membrane injury.

Selenium and spermine alleviate cadmium induced toxicity in the red seaweed Gracilaria dura by regulating antioxidants and DNA methylation

The protective role of exogenously supplied selenium (Se) and polyamines (PAs) such as putrescine (Put) and spermine (Spm) in detoxifying the cadmium (Cd) induced toxicity was studied in the marine red alga Gracilaria dura in laboratory conditions. The Cd exposure (0.4 mM) impede the growth of alga while triggering the reactive oxygen species (ROS viz. O(2)(•-) and H(2)O(2)) generation, inhibition of antioxidant system, and enhancing the lipoxygenase (LOX) activity, malondialdehyde (MDA) level and demethylation of DNA. Additions of Se (50 μM) and/or Spm (1 mM) to the culture medium in contrast to Put, efficiently ameliorated the Cd toxicity by decreasing the accumulation of ROS and MDA contents, while restoring or enhancing the level of enzymatic and nonenzymatic antioxidants and their redox ratio, phycobiliproteins and phytochelatins, over the controls. The isoforms of antioxidant enzymes namely superoxide dismutase (Mn-SOD, ~150 kDa; Fe-SOD ~120 kDa), glutathione peroxidase (GSH-Px, ~120 and 140 kDa), glutathione reductase (GR, ~110 kDa) regulated differentially to Se and/or Spm supplementation. Furthermore, it has also resulted in enhanced levels of endogenous PAs (specially free and bound insoluble Put and Spm) and n-6 PUFAs (C20-3, n-6 and C20-4, n-6). This is for the first time wherein Se and Spm were found to regulate the stabilization of DNA methylation by reducing the events of cytosine demethylation in a mechanism to alleviate the Cd stress in marine alga. The present findings reveal that both Se and Spm play a crucial role in controlling the Cd induced oxidative stress in G. dura.

Established Principles and Emerging Concepts on the Interplay between Mitochondrial Physiology and S-(De)nitrosylation: Implications in Cancer and Neurodegeneration

S-nitrosylation is a posttranslational modification of cysteine residues that has been frequently indicated as potential molecular mechanism governing cell response upon redox unbalance downstream of nitric oxide (over)production. In the last years, increased levels of S-nitrosothiols (SNOs) have been tightly associated with the onset of nitroxidative stress-based pathologies (e.g., cancer and neurodegeneration), conditions in which alterations of mitochondrial homeostasis and activation of cellular processes dependent on it have been reported as well. In this paper we aim at summarizing the current knowledge of mitochondria-related proteins undergoing S-nitrosylation and how this redox modification might impact on mitochondrial functions, whose impairment has been correlated to tumorigenesis and neuronal cell death. In particular, emphasis will be given to the possible, but still neglected implication of denitrosylation reactions in the modulation of mitochondrial SNOs and how they can affect mitochondrion-related cellular process, such as oxidative phosphorylation, mitochondrial dynamics, and mitophagy.