Comparative proteomic analysis in Miscanthus sinensis exposed to antimony stress

Managing antimony pollution: Insights into Soil-Plant system dynamics and remediation Strategies

Researchers are increasingly concerned about antimony (Sb) in ecosystems and the environment. Sb primarily enters the environment through anthropogenic (urbanization, industries, coal mining, cars, and biosolid wastes) and geological (natural and chemical weathering of parent material, leaching, and wet deposition) processes. Sb is a hazardous metal that can potentially harm human health. However, no comprehensive information is available on its sources, how it behaves in soil, and its bioaccumulation. Thus, this study reviews more than 160 peer-reviewed studies examining Sb's origins, geochemical distribution and speciation in soil, biogeochemical mechanisms regulating Sb mobilization, bioavailability, and plant phytotoxicity. In addition, Sb exposure effects plant physio-morphological and biochemical attributes were investigated. The toxicity of Sb has a pronounced impact on various aspects of plant life, including a reduction in seed germination and impeding plant growth and development, resulting from restricted essential nutrient uptake, oxidative damages, disruption of photosynthetic system, and amino acid and protein synthesis. Various widely employed methods for Sb remediation, such as organic manure and compost, coal fly ash, biochar, phytoremediation, microbial-based bioremediation, micronutrients, clay minerals, and nanoremediation, are reviewed with a critical assessment of their effectiveness, cost-efficiency, and suitability for use in agricultural soils. This review shows how plants deal with Sb stress, providing insights into lowering Sb levels in the environment and lessening risks to ecosystems and human health along the food chain. Examining different methods like bioaccumulation, bio-sorption, electrostatic attraction, and complexation actively works to reduce toxicity in contaminated agricultural soil caused by Sb. In the end, the exploration of recent advancements in genetics and molecular biology techniques are highlighted, which offers valuable insights into combating Sb toxicity. In conclusion, the findings of this comprehensive review should help develop innovative and useful strategies for minimizing Sb absorption and contamination and thus successfully managing Sb-polluted soil and plants to reduce environmental and public health risks.

Enzymes Involved in Antioxidant and Detoxification Processes Present Changes in the Expression Levels of Their Coding Genes under the Stress Caused by the Presence of Antimony in Tomato

Currently, there is an increasing presence of heavy metals and metalloids in soils and water due to anthropogenic activities. However, the biggest problem caused by this increase is the difficulty in recycling these elements and their high permanence in soils. There are plants with great capacity to assimilate these elements or make them less accessible to other organisms. We analyzed the behavior of Solanum lycopersicum L., a crop with great agronomic interest, under the stress caused by antimony (Sb). We evaluated the antioxidant response throughout different exposure times to the metalloid. Our results showed that the enzymes involved in the AsA-GSH cycle show changes in their expression level under the stress caused by Sb but could not find a relationship between the NITROSOGLUTATHIONE REDUCTASE (GSNOR) expression data and nitric oxide (NO) content in tomato roots exposed to Sb. We hypothesize that a better understanding of how these enzymes work could be key to develop more tolerant varieties to this kind of abiotic stress and could explain a greater or lesser phytoremediation capacity. Moreover, we deepened our knowledge about Glutathione S-transferase (GST) and Glutathione Reductase (GR) due to their involvement in the elimination of the xenobiotic component.

Effect of endophytic bacteria on the phytoremediation potential of halophyte Tamarix smyrnensis for Sb-contaminated soils

Phytoremediation, including bacteria-assisted phytoremediation, presents a promising technology for treating shooting range soils contaminated with toxic metalloids. In this study, a pot experiment was performed using the halophyte Tamarix smyrnensis and soil collected from a shooting range and artificially spiked at two different antimonite (Sb(III)) concentrations (50 mg/kg and 250 mg/kg) with the aim to explore the Sb phytoremediation of the halophyte. The effect of salt (0.3%) and Mn addition (300 ppm) on its remediation capacity was also investigated. Moreover, the root endophytic community of the halophyte was found able to remove Sb(III) and was periodically inoculated to the plants. The consortium application increased the Sb bioavailable fraction in the soil and enhanced the Sb accumulation in root and aerial parts (up to 50% and 55% respectively at high Sb(III) concentration) compared to the uninoculated plants. Moreover, the presence of Mn increased the translocation factor (21% increase for inoculated and 46% increase for uninoculated plants) while lower TF was observed at high Sb concentrations (0,2 and 0,07 was the lowest value at low and high Sb treatments respectively). The addition of salt, Mn and root endophytic bacteria aided the halophyte to cope with elevated Sb concentrations. The total chlorophyll concentration was higher in inoculated plants compared to the uninoculated ones in all treatments, implying the positive effects of endophytic inoculation. The halophyte T. smyrnensis with the aid of endophytic community presents a promising alternative for remediating shooting range soils especially in areas impacted by salinity.

Uptake, tolerance, and detoxification mechanisms of antimonite and antimonate in Boehmeria nivea L

Boehmeria nivea L. (ramie) is a promising phytoremediation plant for antimony (Sb)-contaminated soils. However, the uptake, tolerance, and detoxification mechanisms of ramie to Sb, which are the basis for finding efficient phytoremediation strategies, remain unclear. In the present study, ramie was exposed to 0, 1, 10, 50, 100, and 200 mg/L of antimonite (Sb(III)) or antimonate (Sb(V)) for 14 days in hydroponic culture. The Sb concentration, speciation, subcellular distribution, and antioxidant and ionomic responses in ramie were investigated. The results illustrated that ramie was more effective in the uptake of Sb(III) than Sb(V). Most of the Sb accumulated in ramie roots, with the highest level reaching 7883.58 mg/kg. Sb(V) was the predominant species in leaves, with 80.77-96.38% and 100% in the Sb(III) and Sb(V) treatments, respectively. Immobilization of Sb on the cell wall and leaf cytosol was the primary mechanism of accumulation. Superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) contributed significantly to root defense against Sb(III), while CAT and glutathione peroxidase (GPX) were the major antioxidants in leaves. CAT and POD played crucial roles in the defense against Sb(V). B, Ca, K, Mg, and Mn in Sb(V)-treated leaves and K and Cu in Sb(III)-treated leaves may be related to the biological processes of Sb toxicity mitigation. This study is the first to investigate the ionomic responses of plants toward Sb and could provide valuable information for the phytoremediation of Sb-polluted soils.

Evaluation of Pollution Level, Spatial Distribution, and Ecological Effects of Antimony in Soils of Mining Areas: A Review

The first global-scale assessment of Sb contamination in soil that was related to mining/smelting activities was conducted based on 91 articles that were published between 1989 and 2021. The geographical variation, the pollution level, the speciation, the influencing factors, and the environmental effects of Sb that were associated with mining/smelting-affected soils were analyzed. The high Sb values mainly occurred in developed (Poland, Italy, Spain, Portugal, New Zealand, Australia) and developing (China, Algeria, Slovakia) countries. Sb concentrations of polluted soil from mining areas that were reported in most countries significantly exceeded the maximum permissible limit that is recommended by WHO, except in Turkey and Macedonia. The soil Sb concentrations decreased in the order of Oceania (29,151 mg/kg) > North Africa (13,022 mg/kg) > Asia (1527 mg/kg) > Europe (858 mg/kg) > South America (37.4 mg/kg). The existing extraction methods for Sb speciation have been classified according to the extractant, however, further research is needed in the standardization of these extraction methods. Modern analytical and characterization technologies, e.g., X-ray absorption spectroscopy, are effective at characterizing chemical speciation. Conditional inference tree (CIT) analysis has shown that the clay content was the major factor that influenced the soil Sb concentration. Non-carcinogenic risks to the public from soil Sb pollution were within the acceptable levels in most regions. An Sb smelter site at the Endeavour Inlet in New Zealand, an abandoned open-pit Sb mine in Djebel Hamimat, Algeria, an old Sb-mining area in Tuscany, Italy, and Hillgrove mine in Australia were selected as the priority control areas. Cynodon dactylon, Boehmeria, Pteris vittata, and Amaranthus paniculatus were found to be potential Sb accumulators. All of the values of bioaccumulation factors for the crops were less than one. However, ingestion of Sb through crop consumption posed potential non-carcinogenic health risks, which should not be neglected. The soil variables (pH, Eh, total sulfur, carbon nitrogen ratio, total organic carbon, and sulfate), the total Sb and the bioavailable Sb, and heavy metal(loid)s (As, Pb, and Fe) were the major parameters affecting the microbial community compositions.

Toxic effects of antimony in plants: Reasons and remediation possibilities-A review and future prospects

Antimony (Sb) is a dangerous heavy metal (HM) that poses a serious threat to the health of plants, animals, and humans. Leaching from mining wastes and weathering of sulfide ores are the major ways of introducing Sb into our soils and aquatic environments. Crops grown on Sb-contaminated soils are a major reason of Sb entry into humans by eating Sb-contaminated foods. Sb toxicity in plants reduces seed germination and root and shoot growth, and causes substantial reduction in plant growth and final productions. Moreover, Sb also induces chlorosis, causes damage to the photosynthetic apparatus, reduces membrane stability and nutrient uptake, and increases oxidative stress by increasing reactive oxygen species, thereby reducing plant growth and development. The threats induced by Sb toxicity and Sb concentration in soils are increasing day by day, which would be a major risk to crop production and human health. Additionally, the lack of appropriate measures regarding the remediation of Sb-contaminated soils will further intensify the current situation. Therefore, future research must be aimed at devising appropriate measures to mitigate the hazardous impacts of Sb toxicity on plants, humans, and the environment and to prevent the entry of Sb into our ecosystem. We have also described the various strategies to remediate Sb-contaminated soils to prevent its entry into the human food chain. Additionally, we also identified the various research gaps that must be addressed in future research programs. We believe that this review will help readers to develop the appropriate measures to minimize the toxic effects of Sb and its entry into our ecosystem. This will ensure the proper food production on Sb-contaminated soils.

Toxicity of different forms of antimony to rice plants: Photosynthetic electron transfer, gas exchange, photosynthetic efficiency, and carbon assimilation combined with metabolome analysis

Antimony (Sb) is a toxic metalloid, and excess Sb causes damage to the plant photosynthetic system. However, the underlying mechanisms of Sb toxicity in the plant photosynthetic system are not clear. Hydroponic culture experiments were conducted to illustrate the toxicity differences of antimonite [Sb(III)] and antimonate [Sb(V)] to the photosynthetic system in a rice plant (Yangdao No. 6). The results showed that Sb(III) showed a higher toxicity than Sb(V), judging from (1) lower shoot and root biomass, leaf water moisture content, water use efficiency, stomatal conductance, net photosynthetic rate, and transpiration rate; (2) higher water vapor deficit, soluble sugar content, starch content, and oligosaccharide content (sucrose, stachyose, and 1-kestose). To further analyze the direction of the photosynthetic products, we conducted a metabonomic analysis. More glycosyls were allocated to the synthesis pathways of oligosaccharides (sucrose, stachyose, and 1-kestose), anthocyanins, salicylic acid, flavones, flavonols, and lignin under Sb stress to quench excess oxygen free radicals (ROS), strengthen the cell wall structure, rebalance the cell membrane, and/or regulate cell permeability. This study provides a complete mechanism to elucidate the toxicity differences of Sb(III) and Sb(V) by exploring their effects on photosynthesis, saccharide synthesis, and the subsequent flow directions of glycosyls.

Effects of arbuscular mycorrhizal fungi on frond antimony enrichment, morphology, and proteomics in Pteris cretica var. nervosa during antimony phytoremediation

Pteris cretica var. nervosa is a dominant fern species found in antimony (Sb) mining areas, capable of forming symbiosis with arbuscular mycorrhizal fungi (AMF), especially with those members of the Glomus genus. Despite this fern's relevance and the potential contribution of mycorrhizal symbiosis to phytoremediation, the AMF's impact on P. var. nervosa phytoremediation of Sb remains unknown. Here, we exposed P. var. nervosa to different concentrations of Sb for 6 months. Our results showed that Sb reduced shoot biomass, enlarged the root/shoot ratio, and disrupted the fronds' intracellular structure. AMF inoculation, however, was able to moderate these phenotypic changes and increased the accumulation level of Sb in plants. From a proteomics analysis of this plant's fronds, a total of 283 proteins were identified. Notably, those proteins with catalytic function, carbon fixing and ATP metabolic function were highly enriched. K-means clustering demonstrated protein-changing patterns involved in multiple metabolic pathways during exposure to Sb. Further, these patterns can be moderated by AMF inoculation. Pearson correlations were used to assess the plant biomarkers-soil Sb relationships; This revealed a strong correlation between ribosome alteration and the root/shoot ratio when inoculated with AMF, and a positive correlation between photosynthesis proteins and chlorophyll (SPAD value). Our results indicate AMF could moderate the fronds impairment by maintaining the sufficient protein levels for ribosomal functioning, photosynthesis activity and to counter ROS production. We demonstrate the effective use of AMF associated with P. cretica var. nervosa for Sb phytoremediation and the potential of applying proteomics to better understand the mechanism behind this symbiotic plant physiological response.

Response to Antimony Toxicity in Dittrichia viscosa Plants: ROS, NO, H2S, and the Antioxidant System

Dittrichia viscosa plants were grown hydroponically with different concentrations of Sb. There was preferential accumulation of Sb in roots. Fe and Cu decreased, while Mn decreased in roots but not in leaves. Chlorophyll content declined, but the carotenoid content increased, and photosynthetic efficiency was unaltered. O₂^●− generation increased slightly, while lipid peroxidation increased only in roots. H₂O₂, NO, ONOO⁻, S-nitrosothiols, and H₂S showed significant increases, and the enzymatic antioxidant system was altered. In roots, superoxide dismutase (SOD) and monodehydroascorbate reductase (MDAR) activities declined, dehydroscorbate reductase (DHAR) rose, and ascorbate peroxidase (APX), peroxidase (POX), and glutathione reductase (GR) were unaffected. In leaves, SOD and POX increased, MDAR decreased, and APX was unaltered, while GR increased. S-nitrosoglutathione reductase (GSNOR) and l-cysteine desulfhydrilase (l-DES) increased in activity, while glutathione S-transferase (GST) decreased in leaves but was enhanced in roots. Components of the AsA/GSH cycle decreased. The great capacity of Dittrichia roots to accumulate Sb is the reason for the differing behaviour observed in the enzymatic antioxidant systems of the two organs. Sb appears to act by binding to thiol groups, which can alter free GSH content and SOD and GST activities. The coniferyl alcohol peroxidase activity increased, possibly to lignify the roots’ cell walls. Sb altered the ROS balance, especially with respect to H₂O₂. This led to an increase in NO and H₂S acting on the antioxidant system to limit that Sb-induced redox imbalance. The interaction NO, H₂S and H₂O₂ appears key to the response to stress induced by Sb. The interaction between ROS, NO, and H₂S appears to be involved in the response to Sb.

Transcriptome characterization of candidate genes related to chromium uptake, transport and accumulation in Miscanthus sinensis

Miscanthus sinensis is a C4 perennial grass species that is widely used as forage, ornamental grass and bioenergy crop due to its broad adaption and great biological traits. Recent studies indicated that M. sinensis could also grow in marginal lands which were contaminated with heavy metals, and exhibited important ecological restoration potential. In this study, transcriptome characterization of candidate genes related to chromium (Cr) uptake, transport and accumulation in M. sinensis were employed to investigate the molecular mechanism of plant tolerance to heavy metal stress. The result showed that following treatment of 200 mg/L of Cr, plant roots could accumulate most Cr and localize mainly in cell walls and soluble fractions, whereas Cr in stems and leaves was primarily in soluble fractions. A total of 83,645 differentially expressed genes (DEGs) were obtained after the treatment. Many genes involved in heavy metal transport, metal ion chelation and photosynthesis were found to be Cr-induced DEGs. Co-expression and weighted correlation network analysis revealed that Glutathion metabolism and ABC transporters pathways play an important role in Cr tolerance of M. sinensis. A hypothesis schematic diagram for the Cr uptake, transport and accumulation of M. sinensis cells were suggested, which could provide a molecular and genetic basis for future candidate genes validation and breeding of such crops.

Synergistic effects of antimony and arsenic contaminations on bacterial, archaeal and fungal communities in the rhizosphere of Miscanthus sinensis: Insights for nitrification and carbon mineralization

The impacts of metal(loids) on soil microbial communities are research focuses to understand nutrient cycling in heavy metal-contaminated environments. However, how antimony (Sb) and arsenic (As) contaminations synergistically affect microbially-driven ecological processes in the rhizosphere of plants is poorly understood. Here we examined the synergistic effects of Sb and As contaminations on bacterial, archaeal and fungal communities in the rhizosphere of a pioneer plant (Miscanthus sinensis) by focusing on soil carbon and nitrogen cycle. High contamination (HC) soils showed significantly lower levels of soil enzymatic activities, carbon mineralization and nitrification potential than low contamination (LC) environments. Multivariate analysis indicated that Sb and As fractions, pH and available phosphorus (AP) were the main factors affecting the structure and assembly of microbial communities, while Sb and As contaminations reduced the microbial alpha-diversity and interspecific interactions. Random forest analysis showed that microbial keystone taxa provided better predictions for soil carbon mineralization and nitrification under Sb and As contaminations. Partial least squares path modeling indicated that Sb and As contaminations could reduce the carbon mineralization and nitrification by influencing the microbial biomass, alpha-diversity and soil enzyme activities. This study enhances our understanding of microbial carbon and nitrogen cycling affected by Sb and As contaminations.

Root-associated (rhizosphere and endosphere) microbiomes of the Miscanthus sinensis and their response to the heavy metal contamination

The plant root-associated microbiomes, including both the rhizosphere and the root endosphere microbial community, are considered as a critical extension of the plant genome. Comparing to the well-studied rhizosphere microbiome, the understanding of the root endophytic microbiome is still in its infancy. Miscanthus sinensis is a pioneering plant that could thrive on metal contaminated lands and holds the potential for phytoremediation applications. Characterizing its root-associated microbiome, especially the root endophytic microbiome, could provide pivotal knowledge for phytoremediation of mine tailings. In the current study, M. sinensis residing in two Pb/Zn tailings and one uncontaminated site were collected. The results demonstrated that the metal contaminant fractions exposed strong impacts on the microbial community structures. Their influences on the microbial community, however, gradually decreases from the bulk soil through the rhizosphere soil and finally to the endosphere, which resulting in distinct root endophytic microbial community structures compared to both the bulk and rhizosphere soil. Diverse members affiliated with the order Rhizobiales was identified as the core microbiome residing in the root of M. sinensis. In addition, enrichment of plant-growth promoting functions within the root endosphere were predicted, suggesting the root endophytes may provide critical services to the host plant. The current study provides new insights into taxonomy and potential functions of the root-associated microbiomes of the pioneer plant, M. sinensis, which may facilitate future phytoremediation practices.

Effect of antimony in soils of an Sb mine on the photosynthetic pigments and antioxidant system of Dittrichia viscosa leaves

Antimony is a toxic element whose concentration in soil and water has been rising due to anthropogenic activities. This study focuses on its accumulation in leaves of Dittrichia viscosa growing in soils of an abandoned Sb mine, and the effect on oxidant/antioxidant systems and photosynthetic efficiency. The results showed leaves to have a high Sb accumulation capacity. The amount of total chlorophyll decreased depending on Sb concentration and of carotenoids increased slightly, with a consequent increase in carotenoid/chlorophyll ratio. Photosynthetic efficiency was unaffected. The amount of O ₂ ^.- rose, although there was no increase in cell membrane damage, with lipid peroxidation levels being similar to normal. This response may be due to considerable increases that were observed in total phenolics, PPO activity, and enzymatic antioxidant system. SOD, POX, and DHAR activities increased in response to increased Sb amounts in leaves. The ascorbate/glutathione cycle was also affected, with strong increases observed in all of its components, and consequent increases in total contents of the ascorbate and glutathione pools. However, the ratio between reduced and oxidized forms declined, reflecting an imbalance between the two, especially that between GSH and GSSG. Efficient detoxification of Sb may take place either through increases in phenolics, carotenoids, and components of the glutathione-ascorbate cycle or through the enzymatic antioxidant system. Since Dittrichia viscosa accumulates large amounts of Sb without suffering oxidative damage, it could be used for phytoremediation.

Physico-Chemical Characteristics and In Vitro Gastro-Small Intestinal Digestion of New Zealand Ryegrass Proteins

Being widely abundant, grass proteins could be a novel source of plant proteins for human foods. In this study, ryegrass proteins extracted using two different approaches-chemical and enzymatic extraction, were characterised for their physico-chemical and in vitro digestion properties. A New Zealand perennial ryegrass cultivar Trojan was chosen based on its higher protein and lower dry matter contents. Grass protein concentrate (GPC) with protein contents of approximately 55 and 44% were prepared using the chemical and enzymatic approach, respectively. The thermal denaturation temperature of the GPC extracted via acid precipitation and enzymatic treatment was found to be 68.0 ± 0.05 °C and 66.15 ± 0.03 °C, respectively, showing significant differences in protein’s thermal profile according to the method of extraction. The solubility of the GPC was highly variable, depending on the temperature, pH and salt concentration of the dispersion. The solubility of the GPC extracted via enzymatic extraction was significantly lower than the proteins extracted via the chemical method. Digestion of raw GPC was also studied via a gastro-small intestinal in vitro digestion model and was found to be significantly lower, in terms of free amino N release, for the GPC prepared through acid precipitation. These results suggest that the physico-chemical and digestion characteristics of grass proteins are affected by the extraction method employed to extract the proteins. This implies that selection of an appropriate extraction method is of utmost importance for achieving optimum protein functionality during its use for food applications.

Factors influencing the uptake and speciation transformation of antimony in the soil-plant system, and the redistribution and toxicity of antimony in plants

Antimony (Sb) is not an essential element for humans and plants although it can be used to treat some human diseases, such as schistosomiasis. Sb contamination has been documented in many regions around the world, particularly in China. The Sb contamination in the environment often stems from anthropogenic activities such as mining, smelting, and shooting. Within the latest decade, great progress has been made in research examining the physiochemical behavior of Sb in the environment, including 1) the extent of Sb pollution around the world particularly in China; 2) the mechanisms and factors influencing Sb migration in soils, especially the adsorption/desorption of Sb by minerals or organic materials; 3) the transformations influencing speciation catalyzed by soil microbes; 4) to a lesser extent, the toxicity of Sb to plants and soil animals. In this review, we highlighted the current knowledge with respect to 1) how soil physicochemical properties (including water regimes, pH, organic materials and Eh), and soil organisms will affect the soil bioavailability of Sb, and subsequently the uptake of Sb by plants; 2) the uptake pathway of antimonite and antimonate, the translocation of Sb from roots to shoots, and the redistribution and toxicity of Sb in plants.

Effects of Antimony on Reactive Oxygen and Nitrogen Species (ROS and RNS) and Antioxidant Mechanisms in Tomato Plants

This research studies the effects that Sb toxicity (0.0, 0.5, and 1.0 mM) has on the growth, reactive oxygen and nitrogen species, and antioxidant systems in tomato plants. Sb is accumulated preferentially in the roots, with little capacity for its translocation to the leaves where the concentration is much lower. The growth of the seedlings is reduced, with alteration in the content in other nutrients. There is a decrease in the content of Fe, Mg, and Mn, while Cu and Zn increase. The contents in chlorophyll a and b decrease, as does the photosynthetic efficiency. On the contrary the carotenoids increase, indicating a possible action as antioxidants and protectors against Sb. The phenolic compounds do not change, and seem not to be involved in the defense response of the tomato against the stress by Sb. The water content of the leaves decreases while that of proline increases in response to the Sb toxicity. Fluorescence microscopy images and spectrofluorometric detection showed increases in the production of O2.-, H2O2, NO, and ONOO-, but not of nitrosothiols. The Sb toxicity induces changes in the SOD, POX, APX, and GR antioxidant activities, which show a clear activation in the roots. In leaves, only the SOD and APX increase. The DHAR activity is inhibited in roots but undergoes no changes in the leaves, as is also the case for the POX and GR activities. Ascorbate increases while GSH decreases in the roots. The total AsA + DHA content increases in the roots, but the total GSH + GSSG content decreases, while neither is altered in the leaves. Under Sb toxicity increases the expression of the SOD, APX, and GR genes, while the expression of GST decreases dramatically in roots but increases in leaves. In addition, an alteration is observed in the pattern of the growth of the cells in the elongation zone, with smaller and disorganized cells. All these effects appear to be related to the ability of the Sb to form complexes with thiol groups, including GSH, altering both redox homeostasis and the levels of auxin in the roots and the quiescent center.

The potential role of brassinosteroids (BRs) in alleviating antimony (Sb) stress in Arabidopsis thaliana

Brassinosteroids (BRs) play a crucial role in improving plant resistance to various environmental stresses. In this study, we aimed to explore the potential role of BRs in protecting plants from antimony (Sb) toxicity. In the in vitro agar-plate culture experiments, the level changes of BR in wide-type plants and BR biosynthesis mutant dwrf4-1 significantly affected the corresponding response of Arabidopsis to Sb stress. Increasing the BR content significantly enhanced Sb-induced root growth inhibition and lowering the BR level appeared to reduce the plant sensitivity to Sb stress. Foliar application of eBL, however, significantly decreased the Sb accumulation and peroxidation of membrane lipids, increased the contents of chlorophyll and proline, and further boosted and strengthened the antioxidant enzymes activities. These experiments demonstrated that BRs played an important role in regulating heavy metal stress responses in plants and exogenous foliar spray of eBL was an important method for alleviating toxicity of Sb.

Uptake, translocation and phytotoxicity of antimonite in wheat (Triticum aestivum)

Antimony (Sb) contamination of soils and its potential negative impact on crop yields have been recently recognized. To explore the effects of Sb(III) on wheat, responses of physical growth properties, enzyme activities and gene expression were examined. The root length was the most relevant indicator to exposure concentration, the root fresh weight was the most sensitive endpoint according to the comparison of the EC₅₀ (50% inhibitory effect concentration) values, and NRAMP1 gene expression at 1 mg L^-1 was more sensitive than other genes. The genes HMA2 and IRT1 were upregulated but less sensitive than NRAMP1. Additionally, the antioxidant enzyme response was examined to explore Sb toxicity toward wheat. The glutathione (GSH) content in roots exposed to high concentrations of Sb(III) was higher than that in the control group, which indicated that GSH is involved in protecting wheat against the effects of Sb(III). Comparing the different antioxidant responses and correlations with malondialdehyde (MDA) in different tissues, super oxide dismutase (SOD) exhibited the main contribution to defense Sb(III) in roots; SOD and peroxidase (POD) were the major antioxidants in shoots. Gene expression of transporter proteins was a highly sensitive indicator of Sb toxicity in wheat and allowed for understanding the defense mechanism in wheat. The upregulation of HMA2 under Sb(III) expression was one kind of defense mechanism, which can induce efflux of heavy metals into the apoplast or vacuoles. Biomass and plant height results suggested that wheat may grow better than other crops under similar exposure due to the lower degree of Sb uptake. This work is the first to provide a wheat uptake model of Sb(III) under a wide concentration range as well as a perspective on the response to this stress at the molecular level.

Antimony speciation in the environment: Recent advances in understanding the biogeochemical processes and ecological effects

Antimony (Sb) is a toxic metalloid, and its pollution has become a global environmental problem as a result of its extensive use and corresponding Sb-mining activities. The toxicity and mobility of Sb strongly depend on its chemical speciation. In this review, we summarize the current knowledge on the biogeochemical processes (including emission, distribution, speciation, redox, metabolism and toxicity) that trigger the mobilization and transformation of Sb from pollution sources to the surrounding environment. Natural phenomena such as weathering, biological activity and volcanic activity, together with anthropogenic inputs, are responsible for the emission of Sb into the environment. Sb emitted in the environment can adsorb and undergo redox reactions on organic or inorganic environmental media, thus changing its existing form and exerting toxic effects on the ecosystem. This review is based on a careful and systematic collection of the latest papers during 2010-2017 and our research results, and it illustrates the fate and ecological effects of Sb in the environment.

Biochemical profile of non-enzymatic stress markers in the plant species "Urginea maritima" in a Mediterranean natural reserve exposed to oxidative stress

Protected areas decrease degrading natural ecosystems due to pollution such as air pollution. In 1981, the inhabitants founded Bentael natural reserve in Byblos, Lebanon, to secure their region against urbanization projects, like the recently constructed road that threatens the biodiversity of the reserve. This study was conducted to determine the oxidative stress resulting from this pollution and that menaces 360 floral species among them a rare species "Urginea maritima." In this research, the biomonitoring approach was experienced to assess the oxidative stress. Biomonitoring possesses has the advantage to be low cost and a constructive method to generate valuable data for further examinations. The studied parameters were air pollutants, ascorbic acid, photosynthetic pigments, leave's pH, relative water content, proline, carbohydrates, and hydrogen peroxide, in three chosen spots, near the pollution source (P1), opposite the latter spot (P2), and in an area relatively far from the source of contamination and which was chosen as the control site (Ctrl). The results showed in P1 detection of air pollutants higher of about 80% than in Ctrl, modifications in stress markers: increased concentration of the reactive oxygen species "hydrogen peroxide," rise in the concentration of the osmoregulator amino acid "proline," and depletion in chlorophyll content, in contrast to an increase in pheophytin. All these findings can be exploited as early diagnosis of air pollution and confirmed the ability to use such biomonitor ("Urginea maritima") as a way to assess the environmental pollution levels and consequently affirm the danger of such landscape activities on natural reserves.

Effects of antimony on redox activities and antioxidant defence systems in sunflower (Helianthus annuus L.) plants

The alterations induced by the toxicity of antimony (Sb) in the roots and leaves of sunflower plants were determined. The plants were grown hydroponically with different concentrations of Sb, a heavy metal which reduces biomass production and growth. There was preferential accumulation of Sb in the tissues of the roots, with the concentrations in the leaves being much lower. The accumulation of other mineral elements was also altered, especially that of Fe and Zn. Chlorophyll content declined, as also did the photosynthetic efficiency, but the carotenoid content remained unaltered. The total content of phenolics, flavonoids, and phenylpropanoid glycosides rose, evidence of their participation in the defence response. Increases were observed in the amount of superoxide anion in both roots and leaves, and in lipid peroxidation levels, especially with the highest Sb concentration of 1.0 mM. The induced oxidative stress leads to a strong increase in the SOD, POX and APX antioxidant activities, while the GR activity was only increased in the leaves and at the 1.0 mM Sb concentration. In contrast, the DHAR activity increased considerably in both organs. The GSNOR activity increased only in roots, and the total RSNOs increased. The total amount of AsA + DHA increased in roots and remained unaltered in leaves, whereas that of GSH + GSSG decreased considerably in all cases. As a whole, these results are evidence for the development of a strong oxidative stress induced by Sb, with there being a clear imbalance in the content of the compounds that constitute the AsA/GSH cycle. 0.5 mM Sb enhances GST expression, especially in leaves. This, together with the increase that was observed in the amount of GSH, may play an important part in detoxification. This oxidative stress affects both the phenolic and the ROS/RNS metabolic processes, which seems to implicate their involvement in the plant's defence and response to the stress.

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.

Insights into the molecular mechanism of the responses for Cyperus alternifolius to PhACs stress in constructed wetlands

Cyperus alternifolius has been widely reported to be an effective phytoremediation plant in constructed wetland systems (CWs). In this context, an integrated biochemical and proteomic analysis of C. alternifolius leaves exposed to pharmaceutically active compounds (PhACs) in CWs was conducted to understand the mechanism of phytoremediation. The obtained results showed the antioxidant enzyme activities were induced throughout the experiment; however over time, the malondialdehyde content is not significantly different from the control and the photosynthetic pigment contents in plant were subsequently slowly recovered. Therefore, we concluded that reactive oxygen species could be effectively counteracted by the enhanced antioxidant enzyme activities, and therefore the photosynthetic pigments were ultimately restored. Leaf extract proteome maps were obtained through 2-DE, and an average of 55, 49, and 24 spots were significantly altered by 30, 100, and 500 μg/L of PhACs over the control, respectively. Protein expression patterns showed that proteins in C. alternifolius leaves are associated with photosynthesis, energy metabolism, defense, and protein synthesis. Moreover, the most relevant pathways modulated by PhACs were photosynthesis and energy metabolism. The protein expression involved in antioxidant defense and stress response generally increased in all the PhAC treatments. The regulated proteins may favor PhAC degradation in CWs; however, the role of these proteins in degrading PhACs remains unknown; further biochemical studies should be conducted. This study indicated that C. alternifolius can tolerate multiple PhACs.

Microbial Antimony Biogeochemistry: Enzymes, Regulation, and Related Metabolic Pathways

Antimony (Sb) is a toxic metalloid that occurs widely at trace concentrations in soil, aquatic systems, and the atmosphere. Nowadays, with the development of its new industrial applications and the corresponding expansion of antimony mining activities, the phenomenon of antimony pollution has become an increasingly serious concern. In recent years, research interest in Sb has been growing and reflects a fundamental scientific concern regarding Sb in the environment. In this review, we summarize the recent research on bacterial antimony transformations, especially those regarding antimony uptake, efflux, antimonite oxidation, and antimonate reduction. We conclude that our current understanding of antimony biochemistry and biogeochemistry is roughly equivalent to where that of arsenic was some 20 years ago. This portends the possibility of future discoveries with regard to the ability of microorganisms to conserve energy for their growth from antimony redox reactions and the isolation of new species of "antimonotrophs."