Oxidative stress and arsenic toxicity: role of NADPH oxidases

OsbHLH6, a basic helix-loop-helix transcription factor, confers arsenic tolerance and root-to-shoot translocation in rice

Arsenic (As) is extremely toxic to plants, posing a serious concern for food safety. Identification of genes responsive to As is significative for figuring out this issue. Here, we identified a bHLH transcription factor OsbHLH6 that was involved in mediating the processes of As tolerance, uptake, and root-to-shoot translocation in rice. The expression of OsbHLH6 gene was strongly induced after 3 and 48 h of arsenite [As(III)] treatment. The OsbHLH6-overexpressed transgenic rice (OE-OsbHLH6) was sensitive to, while the knockout mutant of OsbHLH6 gene (Osbhlh6) was tolerant to As(III) stress by affecting the contents of reactive oxygen species (ROS) and non-protein thiols (NPT), etc. Knockout of OsbHLH6 gene increased significantly the As concentration in roots, but decreased extensively As accumulation in shoots, compared to that in OE-OsbHLH6 and WT plants. The transcripts of phytochelatins (PCs) synthetase encoding genes OsPCS1 and OsPCS2, as well as As(III) transporter encoding genes OsLsi1 and OsABCC1 were greatly abundant in Osbhlh6 mutants than in OE-OsbHLH6 and WT plants under As(III) stress. In contrast, the expression of OsLsi2 gene was extensively suppressed by As(III) in Osbhlh6 mutants. OsbHLH6 acted as a transcriptional activator to bind directly to the promoter and regulate the expression of OsPrx2 gene that encodes a peroxidase precursor. Moreover, overexpression of OsbHLH6 gene resulted in significant change of expression of amounts of abiotic stress-related genes, which might partially contribute to the As sensitivity of OE-OsbHLH6 plants. These findings may broaden our understanding of the molecular mechanism of OsbHLH6-mediated As response in rice and provide novel useful genes for rice As stress-resistant breeding.

Metalloproteomics Reveals Multi-Level Stress Response in Escherichia coli When Exposed to Arsenite

The arsRBC operon encodes a three-protein arsenic resistance system. ArsR regulates the transcription of the operon, while ArsB and ArsC are involved in exporting trivalent arsenic and reducing pentavalent arsenic, respectively. Previous research into Agrobacterium tumefaciens 5A has demonstrated that ArsR has regulatory control over a wide range of metal-related proteins and metabolic pathways. We hypothesized that ArsR has broad regulatory control in other Gram-negative bacteria and set out to test this. Here, we use differential proteomics to investigate changes caused by the presence of the arsR gene in human microbiome-relevant Escherichia coli during arsenite (AsIII) exposure. We show that ArsR has broad-ranging impacts such as the expression of TCA cycle enzymes during AsIII stress. Additionally, we found that the Isc [Fe-S] cluster and molybdenum cofactor assembly proteins are upregulated regardless of the presence of ArsR under these same conditions. An important finding from this differential proteomics analysis was the identification of response mechanisms that were strain-, ArsR-, and arsenic-specific, providing new clarity to this complex regulon. Given the widespread occurrence of the arsRBC operon, these findings should have broad applicability across microbial genera, including sensitive environments such as the human gastrointestinal tract.

The effects of cadmium on selected oxidative stress parameters and the content of photosynthetic pigments in cucumber Cucumis sativus L

BACKGROUND

Environmental pollution by cadmium (Cd) is currently a common problem in many countries, especially in highly industrialised areas. Cd present in the soil can be absorbed by plants through the root system.

AIM

The aim of the present study was to investigate the effects of cadmium on the metabolic activity of cucumber plants (Cucumis sativus L.) and the accumulation and distribution of Cd in the organs of the plants.

METHODS

Cucumber seeds (3 g) were exposed to 0.76, 1.58 or 4.17 mg Cd/L (applied as CdCl2 solutions). The activity of selected antioxidant enzymes - glutathione peroxidase (GSH-Px), superoxide dismutase (SOD) and catalase (CAT), lipid peroxidation and the content of photosynthetic pigments were determined in 6-week-old cucumber plants. In addition, intake of Cd has been determined by flame atomic absorption spectrometry (F-AAS).

RESULTS

The results show that the applied cadmium concentrations affected the activity of antioxidant enzymes. An increase in CAT activity and a decrease in SOD activity were observed in all cucumber organs analysed. GSH-Px activity increased in the roots and stems. Surprisingly, GSH-Px activity decreased in the leaves. The level of lipid peroxidation was usually unchanged (the only one statistically significant change was a decrease in the concentration of malondialdehyde in the leaves which was observed after exposure to the highest Cd concentration). The applied Cd concentrations had no effect on the content of photosynthetic pigments. The highest cadmium content was found in the roots of cucumber plants. Cd tends to accumulate in the roots and a small amount was translocated to the stems and leaves, which was confirmed with the translocation factor (TF).

CONCLUSIONS

The results indicate that the range of cadmium concentrations used, corresponding to the level of environmental pollution recorded in Europe, effectively activates the antioxidant enzyme system, without intensifying lipid peroxidation or reducing the content of photosynthetic pigments.

Synergistic influence of selenium and silicon supplementation prevents the oxidative effects of arsenic stress in wheat

Influence of supplementation of selenium (Se, 1 and 5 µM) and silicon (Si, 0.1 and 0.5 mM) was investigated in wheat under arsenic (30 µM As) stress. Plants grown under As stress exhibited a significant decline in growth parameters however, Se and Si supplementation mitigated the decline significantly. Treatment of Se and Si alleviated the reduction in the intermediate components of chlorophyll biosynthesis pathway and the content of photosynthetic pigments. Arsenic stressed plants exhibited increased reactive oxygen species accumulation and the NADPH oxidase activity which were lowered significantly due to Se and Si treatments. Moreover, Se and Si supplementation reduced lipid peroxidation and activity of lipoxygenase and protease under As stress. Supplementation of Se and Si significantly improved the antioxidant activities and the content of cysteine, tocopherol, reduced glutathione and ascorbic acid. Treatment of Se and Si alleviated the reduction in nitrate reductase activity. Exogenously applied Se and Si mitigated the reduction in mineral elements and reduced As accumulation. Hence, supplementation of Se and Si is beneficial in preventing the alterations in growth and metabolism of wheat under As stress.

Arsenic(III) sorption on organo-ferrihydrite coprecipitates: Insights from maize and rape straw-derived DOM

The mobility of arsenic (As) specie in agricultural soils is significantly impacted by the interaction between ferrihydrite (Fh) and dissolved organic material (DOM) from returning crop straw. However, additional research is necessary to provide molecular evidence for the interaction of toxic and mobile As (As(III)) specie and crop straw-based organo- Fh coprecipitates (OFCs). This study investigated the As(III) sorption behaviours of OFCs synthesized with maize or rape derived-DOM under various environmental conditions and the primary molecular sorption mechanisms using As K-edge X-ray absorption near edge structure (XANES) spectroscopy. According to our findings, pure Fh adsorbed more As(III) relative to the other two OFCs, and the presence of natural organic matter in the OFCs induced more As(III) adsorption at pH 5.0. Findings from this study indicated a maximum As(III) sorption on Ma (53.71 mg g⁻1) and Ra OFC (52.46 mg g⁻1) at pH 5.0, with a sharp decrease as the pH increased from 5.0 to 8.0. Additionally, As K-edge XANES spectroscopy indicated that ∼30% of adsorbed As(III) on the OFCs undergoes transformation to As(V) at pH 7-8. Functional groups from the DOM, such as O-H, COOH, and CO, contributed to As(III) desorption and its oxidation to As(V), whereas ionic strength analysis revealed inner complexation as the dominant As(III) sorption mechanism on the OFCs. Overall, the results indicate that the interaction of natural organic matter (NOM) with As(III) at higher pH promotes As(III) mobility, which is crucial when evaluating As migration and bioavailability in alkaline agricultural soils.

Analysis of Genetic Diversity in Adzuki Beans (Vigna angularis): Insights into Environmental Adaptation and Early Breeding Strategies for Yield Improvement

Adzuki beans are widely cultivated in East Asia and are one of the earliest domesticated crops. In order to gain a deeper understanding of the genetic diversity and domestication history of adzuki beans, we conducted Genotyping by Sequencing (GBS) analysis on 366 landraces originating from Korea, China, and Japan, resulting in 6586 single-nucleotide polymorphisms (SNPs). Population structure analysis divided these 366 landraces into three subpopulations. These three subpopulations exhibited distinctive distributions, suggesting that they underwent extended domestication processes in their respective regions of origin. Phenotypic variance analysis of the three subpopulations indicated that the Korean-domesticated subpopulation exhibited significantly higher 100-seed weights, the Japanese-domesticated subpopulation showed significantly higher numbers of grains per pod, and the Chinese-domesticated subpopulation displayed significantly higher numbers of pods per plant. We speculate that these differences in yield-related traits may be attributed to varying emphases placed by early breeders in these regions on the selection of traits related to yield. A large number of genes related to biotic/abiotic stress resistance and defense were found in most quantitative trait locus (QTL) for yield-related traits using genome-wide association studies (GWAS). Genomic sliding window analysis of Tajima's D and a genetic differentiation coefficient (Fst) revealed distinct domestication selection signatures and genotype variations on these QTLs within each subpopulation. These findings indicate that each subpopulation would have been subjected to varied biotic/abiotic stress events in different origins, of which these stress events have caused balancing selection differences in the QTL of each subpopulation. In these balancing selections, plants tend to select genotypes with strong resistance under biotic/abiotic stress, but reduce the frequency of high-yield genotypes to varying degrees. These biotic/abiotic stressors impact crop yield and may even lead to selection purging, resulting in the loss of several high-yielding genotypes among landraces. However, this also fuels the flow of crop germplasms. Overall, balancing selection appears to have a more significant impact on the three yield-related traits compared to breeder-driven domestication selection. These findings are crucial for understanding the impact of domestication selection history on landraces and yield-related traits, aiding in the improvement of adzuki bean varieties.

Differential effects of arsenite and arsenate on rice (Oryza sativa) plants differing in glutathione S-transferase gene expression

Contamination of paddy soils with arsenic (As) can cause phytotoxicity in rice and increase the accumulation of arsenic in grains. The uptake and accumulation of As in rice depends on the different As species present in the soil. Plants detoxify As by conjugating and sequestering xenobiotic compounds into vacuoles using various enzymes. However, the severity of damage induced by arsenite (As(III)) and arsenate (As(V)), as well as the roles of glutathione S-transferase in detoxifying these As species in rice, are not fully understood. In this study, we developed plant materials overexpressing a glutathione S-transferase gene OsGSTU40 under the control of the maize UBIL promoter. Through systematic investigations of both wild-type Nipponbare (Oryza sativa L., ssp. japonica) and OsGSTU40 overexpression lines under chronic or acute stress of As, we aimed to understand the toxic effects of both As(III) and As(V) on rice plants at the vegetative growth stage. We hypothesized that (i) As(III) and As(V) have different toxic effects on rice plants and (ii) OsGSTU40 played positive roles in As toxicity tolerance. Our results showed that As(III) was more detrimental to plant growth than As(V) in terms of plant growth, biomass, and lipid peroxidation in both chronic and acute exposure. Furthermore, overexpression of OsGSTU40 led to better plant growth even though uptake of As(V), but not As(III), into shoots was enhanced in transgenic plants. In acute As(III) stress, transgenic plants exhibited a lower level of lipid peroxidation than wild-type plants. The element composition of plants was dominated by the different As stress treatments rather than by the genotype, while the As concentration was negatively correlated with phosphorus and silicon. Overall, our findings suggest that As(III) is more toxic to plants than As(V) and that glutathione S-transferase OsGSTU40 differentially affects plant reactions and tolerance to different species of arsenic.

Citicoline ameliorates arsenic-induced hepatotoxicity and diabetes in mice by overexpression of VAMP2, PPAR-γ, As3MT, and SIRT3

The use of arsenic in arsenic-based pesticides has been common in many countries in the past and today. There is considerable evidence linking arsenic exposure to hepatotoxicity and diabetes. Destructive phenomena such as hepatic oxidative stress and inflammation can interfere with glucose uptake and insulin function. In the present study, the antioxidant, anti-inflammatory, and molecular mechanism of citicoline against sodium arsenite-induced hepatotoxicity and glucose intolerance were investigated in mice. Citicoline improved glucose tolerance impaired by sodium arsenite. Citicoline increased the hepatic activity of catalase, superoxide dismutase, and glutathione peroxidase enzymes. Moreover, we found that citicoline prevents an increase in the levels of thiobarbituric acid reactive substances. Citicoline reduced levels of caspase 3, tumor necrosis factor-alpha, and interleukin 6 in sodium arsenite intoxicated groups. It was shown that citicoline increased the expression of arsenite methyltransferase, vesicle-associated membrane protein 2, peroxisome proliferator-activated receptor gamma, and sirtuin 3 to combat sodium arsenite toxicity. Citicoline reduced glucose intolerance, which was disrupted by sodium arsenite, by affecting the pancreatic and extra-pancreatic pathways involved in insulin production, secretion, and action. Based on our results, citicoline can be considered a modulating agent against arsenic-induced hepatotoxicity and hyperglycemia. Considering the relationship between arsenic exposure and the occurrence of side effects such as liver toxicity and diabetes, it is necessary to monitor and awareness of arsenic residues from sources such as drinking water.

Physiological response of adult Salix aurita in wetland vegetation affected by flooding with As-rich fine pyrite particles

An uncontrolled, natural episode of flooding with waters contaminated with As-rich pyrite (FeAsS) particles caused serious ecological damage leading to necrosis of plants growing in a fresh wet meadow located in an area characterized by unique geological structures rich in arsenopyrites. One of the few plant species capable of surviving this event was Salix aurita L., which grew in numbers in the analyzed area, but individual plants were affected differently by toxic flooding. No significant phenotypic changes (Group I), through partial leaf and/or stem necrosis (Group II) up to necrosis of the whole parental plant and root suckers (Group III), were observed for various willow clumps. These varied phenotypic responses of S. aurita to As-rich sediments were compared with the biochemical status of the foliage of willow trees, and with their rhizosphere physiological parameters. Our in situ study revealed that the biochemical status of leaves reflects the phenotypic damage incurred by adult willows growing in their natural environment and affected by the flooding. In leaves of willows with increasingly negative phenotypic changes (Groups I → II → III) as well as increasing levels of reactive oxygen species, malondialdehyde and decreased levels of glutathione and thiol groups were detected. Phytochelatins, commonly considered major As chelators, were not detected in S. aurita leaves. Despite a decrease in the size of leaves with the intensity of tree damage, all leaves expressed a normal level of leaf pigments. Phenotypic changes observed for particular willow clumps were only partly related to soil As levels. Moreover, As and S (but not Fe) foliar levels were related but did not correspond strictly with foliar biochemical features, or with soil As levels, soil pH or soil microbial activity, with the latter two drastically decreased in the rhizospheres of willows from Groups II and III.

The chemical journey of Europium(III) through winter rye (Secale cereale L.) - Understanding through mass spectrometry and chemical microscopy

A combination of biochemical preparation methods with microscopic, spectroscopic, and mass spectrometric analysis techniques as contemplating state of the art application, was used for direct visualization, localization, and chemical identification of europium in plants. This works illustrates the chemical journey of europium (Eu(III)) through winter rye (Secale cereale L.), providing insight into the possibilities of speciation for Rare Earth Elements (REE) and trivalent f-elements. Kinetic experiments of contaminated plants show a maximum europium concentration in Secale cereale L. after four days. Transport of the element through the vascular bundle was confirmed with Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray analysis (EDS). For chemical speciation, plants were grown in a liquid nutrition medium, whereby Eu(III) species distribution could be measured by mass spectrometry and luminescence measurements. Both techniques confirm the occurrence of Eu malate species in the nutrition medium, and further analysis of the plant was performed. Luminescence results indicate a change in Eu(III) species distribution from root tip to plant leaves. Microscopic analysis show at least three different Eu(III) species with potential binding to organic and inorganic phosphate groups and a Eu(III) protein complex. With plant root extraction, further europium species could be identified by using Electrospray Ionization Mass Spectrometry (ESI MS). Complexation with malate, citrate, a combined malate-citrate ligand, and aspartate was confirmed mostly in a 1:1 stoichiometry (Eu:ligand). The combination of the used analytical techniques opens new possibilities in direct species analysis, especially regarding to the understanding of rare earth elements (REE) uptake in plants. This work provides a contribution in better understanding of plant mechanisms of the f-elements and their species uptake.

Melatonin alleviates arsenite toxicity by decreasing the arsenic accumulation in cell protoplasts and increasing the antioxidant capacity in rice

Arsenic (As) is a common environmental pollutant that seriously interferes with the normal growth of organisms. There is an urgent need to take environment-safe and efficient strategies to mitigate As toxicity. Melatonin (MT) is a pleiotropic molecule that regulates plant growth and organ development and alleviates heavy metal stresses. The experiment aims to explore the mechanism of MT in reducing arsenite toxicity by hydroponic rice seedlings. The results showed that MT application reduced the As content in rice roots and shoots by 26.4% and 37.5%, respectively, and mainly decreased As content in the soluble fractions of the rice root cell. MT application also increased the As content of chelated-soluble pectin and alkali-soluble pectin in the cell wall by 14.7% and 74.4%, respectively. It promoted the generation of the functional group of the root cell walls by the FTIR analysis, indicating that MT may promote the fixation of As on the cell wall. Meanwhile, MT contributed to scavenging excess H₂O₂, reducing MDA content, and maintaining normal morphology of root cells by stimulating SOD, POD and CAT activities and increasing the level of GSH. The research deepens our understanding of how MT participates in maintaining redox homeostasis in rice cells, reducing As toxicity, and decreasing As concentration in rice seedlings, thereby providing more possibilities for reducing As accumulation in rice.

A review of mechanisms underlying the protective effects of natural compounds against arsenic-induced neurotoxicity

Arsenic (As) is a toxic metalloid that is widely distributed in the earth's crust. People are continuously exposed to this toxicant in their food and drinking water. Inorganic arsenic occurs in two oxidation states, arsenite 3⁺ (iAs³⁺) and arsenate 5⁺ (iAs⁵⁺). The most toxic form is its trivalent form which interferes with the electron transfer cycle and induces overproduction of reactive oxygen species, leading to depletion of the antioxidant defense system, as well as altering fatty acid levels and mitochondrial action. Since arsenic crosses the blood-brain barrier, it can damage cells in different regions of the brain, causing neurological disorders through the induction of oxidative stress, inflammation, DNA damage, and cell death. Hydroxytyrosol, taurine, alpha-lipoic acid, ellagic acid, and thymoquinone have been shown to effectively alleviate arsenic-induced neurotoxicity. The protective effects are the result of the anti-oxidative and anti-inflammatory properties of the phytochemicals and in particular their anti-apoptotic function via the Nrf2 and PI3/Akt/SIRT1 signaling pathways.

The role of NADPH oxidases in regulating leaf gas exchange and ion homeostasis in Arabidopsis plants under cadmium stress

NADPH oxidase, an enzyme associated with the plasma membrane, constitutes one of the main sources of reactive oxygen species (ROS) which regulate different developmental and adaptive responses in plants. In this work, the involvement of NADPH oxidases in the regulation of photosynthesis and cell ionic homeostasis in response to short cadmium exposure was compared between wild type (WT) and three RBOHs (Respiratory Burst Oxidase Homologues) Arabidopsis mutants (AtrbohC, AtrbohD, and AtrbohF). Plants were grown under hydroponic conditions and supplemented with 50 µM CdCl₂ for 24 h. Cadmium treatment differentially affected photosynthesis, stomatal conductance, transpiration, and antioxidative responses in WT and Atrbohs mutants. The loss of function of RBOH isoforms resulted in higher Cd²⁺ influx, mainly in the elongation zone of roots, which was more evident in AtrbohD and AtrbohF mutants. In the mature zone, the highest Cd²⁺ influx was observed in rbohC mutant. The lack of functional RBOH isoforms also resulted in altered patterns of net K⁺ transport across cellular membranes, both in the root epidermis and leaf mesophyll. The analysis of expression of metal transporters by qPCR demonstrated that a loss of functional RBOH isoforms has altered transcript levels for metal NRAMP3, NRAMP6 and IRT1 and the K⁺ transporters outward-rectifying K⁺ efflux GORK channel, while RBOHD specifically regulated transcripts for high-affinity K⁺ transporters KUP8 and HAK5, and IRT1 and RBOHD and F regulated the transcription factors TGA3 and TGA10. It is concluded that RBOH-dependent H₂O₂ regulation of ion homeostasis and Cd is a highly complex process involving multilevel regulation from transpirational water flow to transcriptional and posttranslational modifications of K/metals transporters.

Harnessing plant microbiome for mitigating arsenic toxicity in sustainable agriculture

Heavy metal toxicity has become an impediment to agricultural productivity, which presents major human health concerns in terms of food safety. Among them, arsenic (As) a non-essential heavy metal has gained worldwide attention because of its noxious effects on agriculture and public health. The increasing rate of global warming and anthropogenic activities have promptly exacerbated As levels in the agricultural soil, thereby causing adverse effects to crop genetic and phenotypic traits and rendering them vulnerable to other stresses. Conventional breeding and transgenic approaches have been widely adapted for producing heavy metal resilient crops; however, they are time-consuming and labor-intensive. Hence, finding new mitigation strategies for As toxicity would be a game-changer for sustainable agriculture. One such promising approach is harnessing plant microbiome in the era of 'omics' which is gaining prominence in recent years. The use of plant microbiome and their cocktails to combat As metal toxicity has gained widespread attention, because of their ability to metabolize toxic elements and offer an array of perquisites to host plants such as increased nutrient availability, stress resilience, soil fertility, and yield. A comprehensive understanding of below-ground plant-microbiome interactions and their underlying molecular mechanisms in exhibiting resilience towards As toxicity will help in identifying elite microbial communities for As mitigation. In this review, we have discussed the effect of As, their accumulation, transportation, signaling, and detoxification in plants. We have also discussed the role of the plant microbiome in mitigating As toxicity which has become an intriguing research frontier in phytoremediation. This review also provides insights on the advancements in constructing the beneficial synthetic microbial communities (SynComs) using microbiome engineering that will facilitate the development of the most advanced As remedial tool kit in sustainable agriculture.

Evaluation of mutagenesis, necrosis and apoptosis induced by omeprazole in stomach cells of patients with gastritis

BACKGROUND

Gastritis is a superficial and prevalent inflammatory lesion that is considered a public health concern once can cause gastric ulcers and gastric cancer, especially when associated with Helicobacter pylori infection. Proton pump inhibitors, such as omeprazole, are the most widely used drugs to treat this illness. The aim of the study was evaluate cytogenetic effects of omeprazole in stomach epithelial cells of patients with gastritis in presence and absence of H. pylori, through cytogenetic biomarkers and catalse and superoxide dismutase analysis.

METHODS

The study included 152 patients from the Gastroenterology Outpatient Clinic of Hospital Getúlio Vargas, Teresina-Brazil, that reported continuous and prolonged omeprazole use in doses of 20, 30 and 40 mg/kg. The participants were divided into groups: (1) patients without gastritis (n = 32); (2) patients without gastritis but with OME use (n = 24); (3) patients with gastritis (n = 26); (4) patients with gastritis undergoing OME therapy (n = 26); (5) patients with gastritis and H. pylori (n = 22) and (6) patients with gastritis and H. pylori on OME therapy (n = 22).

RESULTS

OME induced cytogenetic imbalance in the stomach epithelium through the formation of micronuclei (group 6 > 1, 2, 3, 4, 5; group 5 > 1, 2, 3; group 4 > 1, 2, 3); bridges (groups 4 and 6 > 1, 2, 3, 5 and group 2 > 3, 5); buds (groups 2,4,6 > , 1, 3, 5); binucleated cells (group 6 > 1, 2, 3, 4, 5; group 4 > 1, 2, 3); (groups 2 and 3 > 1); picnoses (group 6 > 1, 2, 3, 4, 5), groups 2 and 5 > 1, 3; group 4 > 1, 2, 3, 5); cariorrexis (groups 6 and 4 > 1, 2, 3, 5; groups 2, 3, 5 > 1) and karyolysis (groups 2, 4, and 6 > 1, 3, 5; groups 3 and 5 > 1). The OME cytogenetic instability was associated with H. pylori infection, indicating clastogenic/aneugenic effects, chromosomes alterations, gene expression changes, cytotoxicity and apoptosis.

CONCLUSIONS

The cytogenetic changescan be attributed to several mechanisms that are still unclear, including oxidative damage, as observed by increased catalase and superoxide dismutase expresion. Positive correlations between antioxidant enzymes were found with micronuclei formation, and were negative for picnoses. Thus, the continuous and prolonged omeprazole use induces genetic instability, which can be monitored through cytogenetic analyzes, as precursor for gastric cancer.

Antioxidants as modulators of arsenic-induced oxidative stress tolerance in plants: An overview

Arsenic (As) is a highly toxic contaminant in the environment. Although both inorganic and organic types of arsenic exist in the environment, the most common inorganic forms of As that adversely affect plants are arsenite (As III) and arsenate (As V). Despite no evidence for As being essential for plant growth, exposure of roots to this element can cause its uptake primarily via transporters responsible for the transport of essential mineral nutrients. Arsenic exposure even at low concentrations disturbs the plant normal functioning via excessive generation of reactive oxygen species, a condition known as oxidative stress leading to an imbalance in the redox system of the plant. This is associated with considerable damage to the cell components thereby impairing normal cellular functions and activation of several cell survival and cell death pathways. To counteract this oxidative disorder, plants possess natural defense mechanisms such as chemical species and enzymatic antioxidants. This review considers how different types of antioxidants participate in the oxidative defense mechanism to alleviate As stress in plants. Since the underlying phenomena of oxidative stress tolerance are not yet fully elucidated, the potential for "Omics" technologies to uncover molecular mechanisms are discussed. Various strategies to improve As-induced oxidative tolerance in plants such as exogenous supplementation of effective growth regulators, protectant chemicals, transgenic approaches, and genome editing are also discussed thoroughly in this review.

Arsenic-Induced Oxidative Stress and Antioxidant Defense in Plants

The non-essential metalloid arsenic (As) is widely distributed in soil and underground water of many countries. Arsenic contamination is a concern because it creates threat to food security in terms of crop productivity and food safety. Plants exposed to As show morpho-physiological, growth and developmental disorder which altogether result in loss of productivity. At physiological level, As-induced altered biochemistry in chloroplast, mitochondria, peroxisome, endoplasmic reticulum, cell wall, plasma membrane causes reactive oxygen species (ROS) overgeneration which damage cell through disintegrating the structure of lipids, proteins, and DNA. Therefore, plants tolerance to ROS-induced oxidative stress is a vital strategy for enhancing As tolerance in plants. Plants having enhanced antioxidant defense system show greater tolerance to As toxicity. Depending upon plant diversity (As hyperaccumulator/non-hyperaccumulator or As tolerant/susceptible) the mechanisms of As accumulation, absorption or toxicity response may differ. There can be various crop management practices such as exogenous application of nutrients, hormones, antioxidants, osmolytes, signaling molecules, different chelating agents, microbial inoculants, organic amendments etc. can be effective against As toxicity in plants. There is information gap in understanding the mechanism of As-induced response (damage or tolerance response) in plants. This review presents the mechanism of As uptake and accumulation in plants, physiological responses under As stress, As-induced ROS generation and antioxidant defense system response, various approaches for enhancing As tolerance in plants from the available literatures which will make understanding the to date knowledge, knowledge gap and future guideline to be worked out for the development of As tolerant plant cultivars.

A tau class glutathione-S-transferase (OsGSTU5) confers tolerance against arsenic toxicity in rice by accumulating more arsenic in root

Arsenic (As) considered as one of the hazardous metalloid that hampers various physiological activities in rice. To study the mechanism of As tolerance in rice, one differentially expressed tau class glutathione-S-transferase (OsGSTU5) has been selected and transgenic rice plants with knockdown (KD) and overexpressing (OE) OsGSTU5 were generated. Our results suggested that KD lines became less tolerant to As stress than WT plants, while OE lines showed enhanced tolerance to As. Under As toxicity, OE and KD lines showed enhanced and reduced antioxidant activities such as, SOD, PRX and catalase, respectively indicating its role in ROS homeostasis. In addition, higher malondialdehyde content, poor photosynthetic parameters and higher reactive oxygen species (ROS) in KD plant, suggests that knockdown of OsGSTU5 renders KD plants more susceptible to oxidative damage. Also, the relative expression profile of various transporters such as OsABCC1 (As sequestration), Lsi2 and Lsi6 (As translocaters) and GSH dependent activity of GSTU5 suggests that GSTU5 might help in chelation of As with GSH and sequester it into the root vacuole using OsABCC1 transporter and thus limits the upward translocation of As towards shoot. This study suggests the importance of GSTU5 as a good target to improve the As tolerance in rice.

Arsenic and Human Health: Genotoxicity, Epigenomic Effects, and Cancer Signaling

Arsenic is a well-known element because of its toxicity. Humans as well as plants and animals are negatively affected by its exposure. Some countries suffer from high levels of arsenic in their tap water and soils, which is considered a primary arsenic-linked risk factor for living beings. Humans generally get exposed to arsenic by contaminated drinking waters, resulting in many health problems, ranging from cancer to skin diseases. On the other hand, the FDA-certified drug arsenic trioxide provides solutions for various diseases, including several types of cancers. This issue emphasizes the importance of speciation of the metalloid elements in terms of impacts on health. When species get exposed to arsenic, it affects the cells altering their involvement. It can lead to abnormalities in inflammatory mechanisms and the immune system which contribute to the negative impacts generated on the body. The poisoning originating from arsenic gives rise to various biological signs on the body which can be useful for the diagnosis. It is important to find true biomarkers for the detection of arsenic poisoning. In view of its application in medicine and biology, studies on understanding the biological activity of arsenic have increased. In this review, we aim at summarizing the current state of knowledge of arsenic and the mechanism behind its toxicity including genotoxicity, oxidative insults, epigenomic changes, and alterations in cellular signaling.

The Effect of Broccoli Extract in Arsenic-Induced Experimental Poisoning on the Hematological, Biochemical, and Electrophoretic Parameters of the Liver and Kidney of Rats

Heavy metals such as arsenic contribute to environmental pollution that can lead to systemic effects in various body organs. Some medicinal plants such as broccoli have been shown to reduce the harmful effects of these heavy metals. The main aim of the present study is to evaluate the effects of broccoli extract on liver and kidney toxicity, considering hematological and biochemical changes. The experimental study was performed in 28 days on 32 male Wistar rats classified into four groups: the control group (C), a group receiving 5 mg/kg oral arsenic (AS), a group receiving 300 mg/kg broccoli (B), and a group receiving arsenic and broccoli combination (AS + B). Finally, blood samples were taken to evaluate the hematological and biochemical parameters of the liver and kidney, as well as serum proteins' concentration. Liver and kidney tissue were fixed and stained by H&E and used for histopathological diagnosis. The results demonstrated a significant decrease in white blood cells (WBC), red blood cells (RBC), and hemoglobin (Hb) in the AS group compared to other groups. However, in the B group, a significant increase in RBC and WBC was observed compared to the AS and C groups (P < 0.05). Moreover, RBC and WBC levels increased significantly in the AS + B group compared to the AS group (P = 0.046). However, in the AS group, aspartate aminotransferase (AST), alanine aminotransferase (ALT), urea, and creatinine levels increased, while total protein, albumin, and globulin decreased. This can be a result of liver and kidney damage, which was observed in the AS group. Furthermore, the increase in the concentration of albumin and globulin in the AS + B group was higher than that in the AS group. Infiltration of inflammatory cells and necrosis of the liver and kidney tissue in the pathological evaluation of the AS group were significantly higher than other groups. There was an increase in superoxide dismutases (SOD), glutathione peroxidase (GPx), and total antioxidant capacity (TAC); however, a decrease in malondialdehyde (MDA) concentration was seen in the AS + B group compared to the AS group. It seems that broccoli is highly effective at reducing liver and kidney damage and improving the hematological and biochemical factors in arsenic poisoning conditions.

Arsenic contamination, impact and mitigation strategies in rice agro-environment: An inclusive insight

Arsenic (As) contamination and its adverse consequences on rice agroecosystem are well known. Rice has the credit to feed more than 50% of the world population but concurrently, rice accumulates a substantial amount of As, thereby compromising food security. The gravity of the situation lays in the fact that the population in theAs uncontaminated areas may be accidentally exposed to toxic levels of As from rice consumption. In this review, we are trying to summarize the documents on the impact of As contamination and phytotoxicity in past two decades. The unique feature of this attempt is wide spectrum coverages of topics, and that makes it truly an interdisciplinary review. Aprat from the behaviour of As in rice field soil, we have documented the cellular and molecular response of rice plant upon exposure to As. The potential of various mitigation strategies with particular emphasis on using biochar, seed priming technology, irrigation management, transgenic variety development and other agronomic methods have been critically explored. The review attempts to give a comprehensive and multidiciplinary insight into the behaviour of As in Paddy -Water - Soil - Plate prospective from molecular to post-harvest phase. From the comprehensive literature review, we may conclude that considerable emphasis on rice grain, nutritional and anti-nutritional components, and grain quality traits under arsenic stress condition is yet to be given. Besides these, some emerging mitigation options like seed priming technology, adoption of nanotechnological strategies, applications of biochar should be fortified in large scale without interfering with the proper use of biodiversity.

Arsenic transport and interaction with plant metabolism: Clues for improving agricultural productivity and food safety

Arsenic (As) is a ubiquitous metalloid that is highly toxic to all living organisms. When grown in As-contaminated soils, plants may accumulate significant amounts of As in the grains or edible shoot parts which then enter a food chain. Plant growth and development per se are also both affected by arsenic. These effects are traditionally attributed to As-induced accumulation of reactive oxygen species (ROS) and a consequent lipid peroxidation and damage to cellular membranes. However, this view is oversimplified, as As exposure have a major impact on many metabolic processes in plants, including availability of essential nutrients, photosynthesis, carbohydrate metabolism, lipid metabolism, protein metabolism, and sulfur metabolism. This review is aimed to fill this gap in the knowledge. In addition, the molecular basis of arsenic uptake and transport in plants and prospects of creating low As-accumulating crop species, for both agricultural productivity and food safety, are discussed.

Targeting redox metabolism of the maize-Azospirillum brasilense interaction exposed to arsenic-affected groundwater

Arsenic in groundwater constitutes an agronomic problem due to its potential accumulation in the food chain. Among the agro-sustainable tools to reduce metal(oid)s toxicity, the use of plant growth-promoting bacteria (PGPB) becomes important. For that, and based on previous results in which significant differences of As translocation were observed when inoculating maize plants with Az39 or CD Azospirillum strains, we decided to decipher the redox metabolism changes and the antioxidant system response of maize plants inoculated when exposed to a realistic arsenate (As^V ) dose. Results showed that As^V caused morphological changes in the root exodermis. Photosynthetic pigments decreased only in CD inoculated plants, while oxidative stress evidence was detected throughout the plant, regardless of the assayed strain. The antioxidant response was strain-differential since only CD inoculated plants showed an increase in superoxide dismutase, glutathione S-transferase (GST), and glutathione reductase (GR) activities while other enzymes showed the same behavior irrespective of the inoculated strain. Gene expression assays reported that only GST23 transcript level was upregulated by arsenate, regardless of the inoculated strain. As^V diminished the glutathione (GSH) content of roots inoculated with the Az39 strain, and CD inoculated plants showed a decrease of oxidized GSH (GSSG) levels. We suggest a model in which the antioxidant response of the maize-diazotrophs system is modulated by the strain and that GSH plays a central role acting mainly as a substrate for GST. These findings generate knowledge for a suitable PGPB selection, and its scaling to an effective bioinoculant formulation for maize crops exposed to adverse environmental conditions.

Role of potassium transporter KUP8 in plant responses to heavy metals

Heavy metal concentrations, which have been increasing over the last 200 years, affect soil quality and crop yields. These elements are difficult to eliminate from soils and may constitute a human health hazard by entering the food chain. Recently, we obtained a selection of mutants with different degrees of tolerance to a mixture of heavy metals (HMmix) in order to gain a deeper insight into the underlying mechanism regulating plant responses to these elements. In this study, we characterized the mutant obtained Atkup8 (in this work, Atkup8-2), which showed one of the most resistant phenotypes, as determined by seedling root length. Atkup8-2 is affected in the potassium transporter KUP8, a member of the high-affinity K⁺ uptake family KUP/HAK/KT. Atkup8-2 mutants, which are less affected as measured by seedling root length under HMmix conditions, showed a resistant phenotype with respect to WT seedlings which, despite their delayed growth, are able to develop true leaves at levels similar to those under control conditions. Adult Atkup8-2 plants had a higher fresh weight than WT plants, a resistant phenotype under HMmix stress conditions and lower levels of oxidative damage. KUP8 did not appear to be involved in heavy metal or macro- and micro-nutrient uptake and translocation from roots to leaves, as total concentrations of these elements were similar in both Atkup8-2 and WT plants. However, alterations in cellular K⁺ homeostasis in this mutant cannot be ruled out.

Arsenic uptake and toxicity in wheat (Triticum aestivum L.): A review of multi-omics approaches to identify tolerance mechanisms

Arsenic (As) due to its widespread has become a primary concern for sustainable food production, especially in Southeast Asian countries. In that context, the present review presented a comprehensive detail of the available literature marking an assortment of As-induced impacts on wheat. The conclusive findings of past research suggest that As tends to grossly affect the germination, elongation, biomass, grain yield, and induce oxidative stress. Several human studies are suggestive of higher cancer risks (>1 × 10^-6) due to the ingestion of wheat grains. However, the body of proof is limited and the scarcity of information limited understanding about tolerance mechanism in wheat against As. Therefore, the paper provided a reference from tolerance mechanism based studies in other crops like rice and maize. The generated knowledge of arsenomics would pave the way for plant breeders to develop resistant varieties for As to ensure sustainable food production.

Mitigation of arsenate toxicity by indole-3-acetic acid in brinjal roots: Plausible association with endogenous hydrogen peroxide

The role of indole-3-acetic acid (IAA) and hydrogen peroxide (H₂O₂) crosstalk in regulating metal stress is still less known. Herein, role of IAA in alleviating arsenate (As^V) toxicity in brinjal seedlings along with its probable relation with endogenous H₂O₂ was investigated. Arsenate hampered root growth due to greater accumulation of As and decrease in phosphorus uptake that resulted into inhibited photosynthesis and cell death. Further, As^V induced oxidative stress markers and damage to macromolecules (lipids and proteins) due to alterations in redox status of glutathione as a result of inhibition in activity of glutathione synthetase and glutathione reductase. However, application of IAA with As^V improved root growth by significantly declining As accumulation and oxidative stress markers, sequestrating As into vacuoles, and improving redox status of glutathione which collectively protected roots from cell death. Interestingly, addition of diphenylene iodonium (DPI, an inhibitor of NADPH oxidase) further increased As^V toxicity even in the presence of IAA. However, application of H₂O₂ rescued negative effect of DPI. Overall, the results suggested that in IAA-mediated mitigation of As^V toxicity in brinjal roots, endogenous H₂O₂ might have acted as a downstream signal.

The effect of NADPH oxidase inhibitor diphenyleneiodonium (DPI) and glutathione (GSH) on Isatis cappadocica, under Arsenic (As) toxicity

The present work was conducted to assess the effects of arsenic (As, 1000 µM), diphenyleneiodonium (DPI, 10 µM) and reduced glutathione (GSH, 500 µM) on Isatis cappadocica. As treatment decreased plant growth and fresh and dry weight of shoot and root and also enhanced the accumulation of As. As stress also enhanced the oxidative stress biomarkers, hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) content. However, the application of GSH decreased the content of H₂O₂ and MDA by 43% and 55%, respectively, as compared to As treatment. The antioxidants like superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), glutathione reductase (GR) and glutathione S-transferase (GST) also enhanced with As stress. NADPH oxidase inhibitor, the DPI, enhances the effect of As toxicity by increasing the accumulation of As, H₂O₂, MDA. DPI also enhances the activity of antioxidant enzymes except GR and GST, However, the application GSH increased the plant growth and biomass yield, decreases accumulation of As, H₂O₂ and MDA content in As as well as As + DPI treated plants. The thiols content [total thiol (TT), non-protein thiol (NPT) protein thiols (PT), and glutathione (GSH)] were decreased in the As + DPI treatment but supplementation of GSH enhanced them. Novelty statement: The study reveals the beneficial role of GSH in mitigating the deleterious effects of Arsenic toxicity through its active involvement in the antioxidant metabolism, thiol synthesis and osmolyte accumulation. Apart from As, We provided the plants NADPH oxidase inhibitor, the diphenyleneiodonium (DPI), which boosts the As toxicity. At present, there is dearth of information pertaining to the effects of DPI on plants growth and their responses under heavy metal stress.GSH application reversed the effect of diphenyleneiodonium (DPI) under As stress preventing the oxidative damage to biomolecules through the modulation of different antioxidant enzymes. The application of GSH for As stressed soil could be a sustainable approach for crop production.

Unraveling the impact of arsenic on the redox response of peanut plants inoculated with two different Bradyrhizobium sp. strains

Arsenic (As) can be present naturally in groundwater from peanut fields, constituting a serious problem, as roots can accumulate and mobilize the metalloid to their edible parts. Understanding the redox changes in the legume exposed to As may help to detect potential risks to human health and recognize tolerance mechanisms. Thirty-days old peanut plants inoculated with Bradyrhizobium sp. strains (SEMIA6144 or C-145) were exposed to a realistic arsenate concentration, in order to unravel the redox response and characterize the oxidative stress indexes. Thus, root anatomy, reactive oxygen species detection by fluorescence microscopy and, ROS histochemical staining along with the NADPH oxidase activity were analyzed. Besides, photosynthetic pigments and damage to lipids and proteins were determined as oxidative stress indicators. Results showed that at 3 μM As^V, the cross-section areas of peanut roots were augmented; NADPH oxidase activity was significantly increased and O₂˙¯and H₂O₂ accumulated in leaves and roots. Likewise, an increase in the lipid peroxidation and protein carbonyls was also observed throughout the plant regardless the inoculated strain, while chlorophylls and carotenes were increased only in those inoculated with Bradyrhizobium sp. C-145. Interestingly, the oxidative burst, mainly induced by the NADPH oxidase activity, and the consequent oxidative stress was strain-dependent and organ-differential. Additionally, As modifies the root anatomy, acting as a possibly first defense mechanism against the metalloid entry. All these findings allowed us to conclude that the redox response of peanut is conditioned by the rhizobial strain, which contributes to the importance of effectively formulating bioinoculants for this crop.

Remodeling of Root Growth Under Combined Arsenic and Hypoxia Stress Is Linked to Nutrient Deprivation

Root architecture responds to environmental stress. Stress-induced metabolic and nutritional changes affect the endogenous root development program. Transcriptional and translational changes realize the switch between stem cell proliferation and cell differentiation, lateral root or root hair formation and root functionality for stress acclimation. The current work explores the effects of stress combination of arsenic toxicity (As) and hypoxia (Hpx) on root development in Arabidopsis thaliana. As revealed previously, combined As and Hpx treatment leads to severe nutritional disorder evident from deregulation of root transcriptome and plant mineral contents. Both As and Hpx were identified to pose stress-specific constraints on root development that lead to unique root growth phenotype under their combination. Besides inhibition of root apical meristem (RAM) activity under all stresses, As induced lateral root growth while root hair density and lengths were strongly increased by Hpx and HpxAs-treatments. A dual stimulation of phosphate (Pi)-starvation response was observed for HpxAs-treated plant roots; however, the response under HpxAs aligned more with Hpx than As. Transcriptional evidence along with biochemical data suggests involvement of PHOSPHATE STARVATION RESPONSE 1; PHR1-dependent systemic signaling. Pi metabolism-related transcripts in close association with cellular iron homeostasis modulate root development under HpxAs. Early redox potential changes in meristematic cells, differential ROS accumulation in root hair zone cell layers and strong deregulation of NADPH oxidases, NADPH-dependent oxidoreductases and peroxidases signify a role of redox and ROS signaling in root architecture remodeling under HpxAs. Differential aquaporin expression suggests transmembrane ROS transport to regulate root hair induction and growth. Reorganization of energy metabolism through NO-dependent alternate oxidase, lactate fermentation, and phosphofructokinase seems crucial under HpxAs. TOR and SnRK-signaling network components were potentially involved in control of sustainable utilization of available energy reserves for root hair growth under combined stress as well as recovery on reaeration. Findings are discussed in context of combined stress-induced signaling in regulation of root development in contrast to As and Hpx alone.

Metals and Mechanisms of Carcinogenesis

Metal exposure is pervasive and not limited to sporadic poisoning events or toxic waste sites. Hundreds of millions of people around the globe are affected by chronic metal exposure, which is associated with serious health concerns, including cancer, as demonstrated in a variety of studies at the molecular, systemic, and epidemiologic levels. Metal-induced toxicity and carcinogenicity are sophisticated and complex in nature. This review provides a broad context and holistic view of currently available studies on the mechanisms of metal-induced carcinogenesis. Specifically, we focus on the five most prevalent carcinogenic metals, arsenic, nickel, cadmium, chromium, and beryllium, and their potential to drive carcinogenesis in humans. A comprehensive understanding of the mechanisms behind the development of metal-induced cancer can provide valuable insights for therapeutic intervention involving molecular targets in metal-induced carcinogenesis.

Mycoremediation affects antioxidative status in winter rye plants grown at Chernobyl exclusion zone site in Ukraine

Soil contaminated with heavy metals in general and radionuclides in particular represents an escalating problem for all living organisms. Since, Chernobyl nuclear power plant accident in 1986 in Ukraine, an exclusion zone of 30 km around the former power plant is uninhabitable land due to severe contamination. Two most notable beta emitters contributing to dose hazards for decades is radioactive ¹³⁷Cs/⁹⁰Sr. However, large parts of the zone are also highly contaminated with uranium particles (hot particles) bearing trace amounts of highly alpha-emitting radionuclides. We established an experiment at exclusion zone with the aim to investigate the influence of two macro fungi (Schizophyllum commune (S.C.) and Leucoagaricus naucinus (L.N.)) on oxidative status and antioxidative responses in winter rye plants; from this, we wanted to test the radionuclide/heavy metals retention capacity of both fungi, and probe their further potential for mycoremediation.Result shows some differences in the concentrations of radionuclides/heavy metals and micro/macronutrients uptake in plants. As a biomarker of oxidative status, lipid peroxidation (LPO) levels and other antioxidative parameters were determined, i.e., superoxide-dismutase (SOD) isoenzymes, cysteine (CYS), and ascorbic acid (AA) concentrations as well as catalase (CAT) and glutathione reductase (GR) activities in winter rye shoots. LPO showed no significant differences between controls and plants cultivated with macro fungi. However, CAT activities were elevated in the presence of S.C/L.N compared with control, while GR activity was significantly higher only in presence of S.C. In contrast, isozyme of SOD (Cu,Zn-SOD) was the most prominent in control. Likewise, CYS content was lower in plants grown with both fungi, while AA concentration was only lower in the presence of L.N. The results showed that presence of fungi in radionuclide contaminated soil caused induction of antioxidative response in shoots of winter rye and that the response depended on the type of fungi used.

NADPH Oxidases: The Vital Performers and Center Hubs during Plant Growth and Signaling

NADPH oxidases (NOXs), mostly known as respiratory burst oxidase homologs (RBOHs), are the key producers of reactive oxygen species (ROS) in plants. A lot of literature has addressed ROS signaling in plant development regulation and stress responses as well as on the enzyme's structure, evolution, function, regulation and associated mechanisms, manifesting the role of NOXs/RBOHs as the vital performers and center hubs during plant growth and signaling. This review focuses on recent advances of NOXs/RBOHs on cell growth, hormone interaction, calcium signaling, abiotic stress responses, and immunity. Several primary particles, including Ca2+, CDPKs, BIK1, ROPs/RACs, CERK, FER, ANX, SnRK and SIK1-mediated regulatory mechanisms, are fully summarized to illustrate the signaling behavior of NOXs/RBOHs and their sophisticated and dexterous crosstalks. Diverse expression and activation regulation models endow NOXs/RBOHs powerful and versatile functions in plants to maintain innate immune homeostasis and development integrity. NOXs/RBOHs and their related regulatory items are the ideal targets for crop improvement in both yield and quality during agricultural practices.

Uranium accumulation and its phytotoxicity symptoms in Pisum sativum L

Environmental contamination by uranium (U) and other radionuclides is a serious problem worldwide, especially due to, e.g. mining activities. Ultimate accumulation of released U in aquatic systems and soils represent an escalating problem for all living organisms. In order to investigate U uptake and its toxic effects on Pisum sativum L., pea plantlets were hydroponically grown and treated with different concentrations of U. Five days after exposure to 25 and 50 μM U, P. sativum roots accumulated 2327.5 and 5559.16 mg kg-1 of U, respectively, while in shoots concentrations were 11.16 and 12.16 mg kg-1, respectively. Plants exposed to both U concentrations showed reduced biomass of shoots and reduced content of photosynthetic pigments (total chlorophyll and carotenoids) relative to control. As a biomarker of oxidative stress, lipid peroxidation (LPO) levels were determined, while antioxidative response was determined by catalase (CAT) and glutathione reductase (GR) activities as well as cysteine (Cys) and non-protein thiol (NP-SH) concentrations, both in roots and shoots. Both U treatments significantly increased LPO levels in roots and shoots, with the highest level recorded at 50 μM U, 50.38% in shoots and 59.9% in roots relative to control. U treatment reduced GR activity in shoots, while CAT activity was increased only in roots upon treatment with 25 μM U. In pea roots, cysteine content was significantly increased upon treatment with both U concentrations, for 19.8 and 25.5%, respectively, compared to control plants, while NP-SH content was not affected by the applied U. This study showed significant impact of U on biomass production and biochemical markers of phytotoxicity in P. sativum, indicating presence of oxidative stress and cellular redox imbalance in roots and shoots. Obtained tissue-specific response to U treatment showed higher sensitivity of shoots compared to roots. Much higher accumulation of U in pea roots compared to shoots implies potential role of this species in phytoremediation process.

Nitric oxide improves tolerance to arsenic stress in Isatis cappadocica desv. Shoots by enhancing antioxidant defenses

Arsenic (As) is a toxic metalloid that severely hampers plant growth and also poses health risks for humans through the food chain. Although nitric oxide (NO) is known to improve plant resistance to multiple stresses including metal toxicity, little is known about its role in the As tolerance of hyperaccumulator plants. This study investigates the role of the exogenously applied NO donor, sodium nitroprusside (SNP), in improving the As tolerance of Isatis cappadocica, which has been reported to hyperaccumulate As. Exposure to toxic As concentrations significantly increases NO production and damages the cell membrane, as indicated by increased hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) concentrations, thereby reducing plant growth. However, the addition of SNP improves growth and alleviates As-induced oxidative stress by enhancing the activity of superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR), glutathione S-transferase (GST), glutathione (GSH), as well as proline and thiol concentrations, thereby confirming the beneficial role played by NO in increasing As stress tolerance. Furthermore, the As-induced decrease in growth and the increase in oxidative stress were more marked in the presence of bovine hemoglobin (Hb; a NO scavenger) and N(G)-nitro-l-arginine methyl ester (l-NAME; a NO synthase inhibitor), thus demonstrating the protective role of NO against As toxicity. The reduction in NO concentrations by l-NAME suggests that NOS-like activity is involved in the generation of NO in response to As in I. cappadocica.

Variations in grain cadmium and arsenic concentrations and screening for stable low-accumulating rice cultivars from multi-environment trials

In order to help mitigate widespread cadmium (Cd) and arsenic (As) co-contamination in paddy soils in China, screening and breeding of low-accumulating rice (Oryza sativa L.) cultivars (excluders) have been widely adopted. However, the performance of rice cultivars for grain Cd and As accumulation may vary in different growing environments. The inability to identify stable low-accumulating cultivars has largely hindered their application. In this study, 51 rice cultivars were evaluated at four Cd- and As-contaminated paddy sites in two crop seasons in northern Guangdong Province, China. The aim was to investigate the effects of cultivar, environment and their interactions in determining grain Cd and As concentrations, and so to identify stable low-accumulating cultivars. Results showed that environment effects dominated the Cd and As concentrations in rice grains, explaining 87% of the total variations. The crop season played a vital role; compared to early season, grain Cd levels increased and As levels lowered significantly in late season. Large variations in grain Cd, total As, inorganic As concentrations and the percentage of inorganic As were observed between different cultivars. Conventional japonica cultivars exhibited lower Cd levels but higher As levels in the grains than did indica cultivars. The cultivar × environment interaction (CEI) was significant, and its importance was comparable to the cultivar effect. By measuring and interpreting such an interaction, stable Cd and As excluder cultivars were identified based upon the yield, grain Cd and As levels as well as the stabilities of cultivars across the trial environments. Two stable Cd and As co-excluders were found among the hybrid indica cultivars. These results demonstrated that the variations in grain Cd and As concentrations could mainly be attributed to the environment effects and cultivar selection practices should include the analysis of CEI to identify stable low-accumulating rice cultivars.

Prospects of genetic engineering utilizing potential genes for regulating arsenic accumulation in plants

The rapid pace of industrial, agricultural and anthropogenic activities in the 20^th century has resulted in contamination of heavy metals across the globe. Arsenic (As) is a ubiquitous, naturally occurring toxic metalloid, contaminating the soil and water and affecting human health in several countries. Several physicochemical methods exist for the cleanup of As contamination but these are expensive and disastrous to microbes and soil. Plant based remediation approaches are low cost and environmentally safe. Hence, extensive biochemical, molecular and genetic experiments have been conducted to understand plants' responses to As stress and have led to the identification of potential genes. The available knowledge needs to be utilized to either reduce As accumulation in crop plants (rice) or to enhance As levels in shoots of hyperaccumulators (Pteris vittata). Gene manipulation using biotechnological tools can be an effective approach to exploit the potential genes (plasmamembrane and vacuolar transporters, glutathione and phytochelatin biosynthetic enzymes, etc.) playing pivotal roles in uptake, translocation, transformation, complexation, and compartmentalization of As in plants. The transgenic plants with increased tolerance to As and altered (increased/decreased) As accumulation have been developed. The need, however, exists to design plants with altered expression of two or more genes for harmonizing various events (like arsenate reduction, arsenite complexation, sequestration and translocation) so as to achieve desirable reduction (crop plants) or increase (phytoremediator plants) in As content. This review sheds light on transgenic approaches adopted to modulate As levels in plants and proposes future directions to achieve desirable results.

Effects of Olive Oil supplementation on Sodium Arsenate-induced Hepatotoxicity in Mice

Background:

Sodium arsenate (As), a toxic substance with induced oxidative stress, lead to hepatotoxicity. Olive oil (OO) with antioxidant property has protective effect on toxicity. The aim of this study was to investigate protective effect of OO on sodium As-induced hepatotoxicity in mice.

Subjects and Methods:

In this experimental study, 32 adult male BALB/c mice were divided randomly into four groups: control group (received only normal saline, the same volume as other groups), OO (0.4 mL/day, gavage), sodium As (15 mg/kg, gavage), and OO + sodium As (received OO 1 h before sodium As). Drugs were given for 30 consecutive days. After the last receipt of the drugs, oxidative stress parameters [malondialdehyde (MDA), glutathione (GSH)] in tissue, liver function parameters [alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatase (ALP)] in serum, ferric reducing ability of plasma (FRAP) in plasma, and histopathological assays were performed.

Results:

Sodium As induced hepatic injury as indicated by significant increase in AST, ALT, ALP, and LDH in serum and pathologic evidences. It also induces hepatic oxidative stress biomarkers as indicated by significant increase in levels of MDA and significant decrease in FRAP and GSH concentration. OO administration significantly improved oxidative stress parameters, histopathological changes, and enzymatic markers of liver injury.

Conclusions:

It was concluded that antioxidant activity of OO has hepatoprotective effect on As-induced hepatic injury.

Analysis of 28 trace elements in the blood and serum antioxidant status in chickens under arsenic and/or copper exposure

This study aimed to evaluate the 28 trace elements in the blood and serum antioxidant status in chickens under arsenic (As) and/or copper (Cu) exposure. A total of 200 1-day-old male Hy-Line chickens were fed either a commercial diet (C-group) or arsenic trioxide (30 mg/kg) and/or cupric sulfate (300 mg/kg) for 90 days. The 28 trace element levels in the blood were analyzed by inductively coupled plasma mass spectrometry (ICP-MS). The concentrations of As in the blood of chickens were elevated approximately 17.15-fold, 2.30-fold, and 13.37-fold in the As-group, Cu-group, and As + Cu-group, respectively, at 90 days. The concentrations of Cu did not change in the As-group and increased approximately 29.53 and 23.37% in the Cu-group and As + Cu-group, respectively, at 90 days. Moreover, As exposure caused ion profile disorders in the blood, including increased concentrations of Na, Mg, Si, K, Cr, Fe, and Se and reduced B, Ca, Ti, V, Mn, Co, Ni, Zn, Sr, and Mo. Cu exposure increased the contents of Mg, Si, Ca, Ti, V, Cr, Mn, Fe, Co, Zn, and Se and decreased the content of B, Ca, Al, Ni, and Mo. As + Cu exposure increased the contents of Mg, Si, Cr, Fe, Zn, and Se and decreased the content of B, Ca, Ti, Co, Ni, Sr, and Mo. Moreover, As and/or Cu exposure induced oxidative stress in the blood of chickens. In conclusion, the results indicated that the mixture of As and Cu caused a synergistic effect via disturbing homeostasis of trace elements and oxidative stress in the blood of chickens.

Genomics of Metal Stress-Mediated Signalling and Plant Adaptive Responses in Reference to Phytohormones

INTRODUCTION

As a consequence of a sessile lifestyle, plants often have to face a number of life threatening abiotic and biotic stresses. Plants counteract the stresses through morphological and physiological adaptations, which are imparted through flexible and well-coordinated network of signalling and effector molecules, where phytohormones play important role. Hormone synthesis, signal transduction, perception and cross-talks create a complex network. Omics approaches, which include transcriptomics, genomics, proteomics and metabolomics, have opened new paths to understand such complex networks.

OBJECTIVE

This review concentrates on the importance of phytohormones and enzymatic expressions under metal stressed conditions.

CONCLUSION

This review sheds light on gene expressions involved in plant adaptive and defence responses during metal stress. It gives an insight of genomic approaches leading to identification and functional annotation of genes involved in phytohormone signal transduction and perception. Moreover, it also emphasizes on perception, signalling and cross-talks among various phytohormones and other signalling components viz., Reactive Oxygen Species (ROS) and Reactive Nitrogen Species (RNS).

Uptake of Plutonium-238 into Solanum tuberosum L. (potato plants) in presence of complexing agent EDTA

Bioavailability and plant uptake of radionuclides depend on various factors. Transfer into different plant parts depends on chemical and physical processes, which need to be known for realistic ingestion dose modelling when these plants are used for food. Within the scope of the present work, the plutonium uptake by potato plants (Solanum tuberosum L.) was investigated in hydroponic solution of low concentration [Pu] = 10^-9 mol L^-1. Particular attention was paid to the speciation of radionuclides in the solution which was modelled by the speciation code PHREEQC. The speciation, the solubility and therefore the plant availability of radionuclides mainly depend on the pH value and the redox potential of the solution. During the contamination period, the redox potential did not change significantly. In contrast, the pH value showed characteristic changes depending on exudates excreted by the plants. Plant roots took up high amounts of plutonium (37%-50% of the added total amount). In addition to the uptake into the roots, the radionuclides can also adsorb to the exterior root surface. The solution-to-plant transfer factor showed values between 0.03 and 0.80 (Bq kg^-1/ Bq L^-1) for the potato tubers. By addition of the complexing agent EDTA (10^-4 mol L-1), the plutonium uptake from solution increased by 58% in tubers and by 155% in shoots/leaves. The results showed that excreted substances by plants affect bioavailability of radionuclides at low concentration, on the one hand. On the other hand, the uptake of plutonium by roots and the accumulation in different plant parts can lead to non-negligible ingestion doses, even at low concentration. We are aware of the limited transferability of data obtained in hydroponic solutions to plants growing in soil. However, the aim of this study is twofold: First we want to investigate the influence of Pu speciation on plant uptake in a rather well defined system which can be modelled using available thermodynamic data. Second, techniques developed here shall be applied to the investigation of plants growing in soil in the future. The present work contributes to the basic understanding how plant induced effects on nutrient solution influence bioavailability of radionuclides and fosters the need for more detailed investigations of the complex uptake and accumulation processes of radionuclides into plants.

NF-κB-mediated inflammation correlates with calcium overload under arsenic trioxide-induced myocardial damage in Gallus gallus

Arsenic is a known environmental pollutant and highly hazardous toxin to human health. Due to the biological accumulation, arsenic produces a variety of cardiovascular diseases. However, the exact mechanism is still unclear. Here, our objective was to evaluate myocardial damage and determine the potential mechanism under arsenic exposure in chickens. Arsenic trioxide (As₂O₃) (1.25 mg/kg BW, corresponding 15 mg/kg feed) was administered as basal diet to male Hy-line chickens (one-day-old) for 4, 8 and 12 weeks. The results showed that As₂O₃-induced histological and ultrastructural damage in heart accompanied with significantly Ca²⁺ overload and increased the activities of myocardial enzymes. Moreover, As₂O₃ exposure significantly increased (P < 0.05) the mRNA levels of ITPR3, PMCA, TRPC1, TRPC3, STIM1, ORAI1 and pro-inflammatory genes, while the mRNA levels of ITPR1, ITPR2, RyR1, RyR3, SERCA, SLC8A1, CACNA1S and interleukin-10 were decreased (P < 0.05) by As₂O₃ exposure at 4, 8 and 12 weeks as compared with the corresponding control group. Western blot results showed that As₂O₃ exposure decreased the expression of SERCA and SLC8A1 protein, while the expression of TNF-α, NF-κB, iNOS and PMCA1 increased compared with the corresponding control group. Additionally, correlation analysis and protein-protein interaction prediction shown that NF-κB-mediated inflammatory response have a function correlation with calcium (Ca) regulation-related genes. In conclusion, this study indicated that As₂O₃-induced inflammatory response might dependent on Ca overload in myocardial damage of chickens. Our work has implications for the development of potential therapeutic approaches by resisting Ca overload for arsenic-induced myocardial damage.

Does low uranium concentration generates phytotoxic symptoms in Pisum sativum L. in nutrient medium?

Due to excessive mining and use of radionuclide especially uranium (U) and its fission products, numerous health hazards as well as environmental contamination worldwide have been created. The present study focused on demonstrating whether low concentration of U treatment in liquid nutient medium may translocate traces of U in plants and in fruits of Pisum sativum after 30 and 60 days of exposure for the safe use as a food supplement for human/animals. Hydroponically grown plants (in amended Hoagland medium) were treated with two different concentrations of uranium ([U] = 100 and 500 nM, respectively). Plants showed a decrease in total chlorophyll after 60 days of treatment. On the other hand, Eh of the nutrient medium was not affected from the initial days till 60 days of treatment, but pH of nutrient medium was increased upon durations, highest at 60 days of treatment. In seeds, micro/macro elements were under limit as well as U concentration was also under detection limit. We did not observe any U in the above ground parts (shoots/seeds) of the plant, i.e., under detection limit. Our observation suggests that P. sativum plants may be useful to grow at low radionuclide [U]-contaminated areas for safe human/animal use, but for other fission products, we have to investigate further for the safe human/animal use.

Screening Arabidopsis mutants in genes useful for phytoremediation

Emissions of heavy metals have risen over the past 200 years and significantly exceed those from natural sources. Phytoremediation strategies may be able to recover soil productivity in self-sustaining ecosystems; however, our knowledge of the molecular mechanisms involved in plant heavy-metal perception and signalling is scarce. The aim of this study was to assemble a "molecular tool box" of genes useful for phytoremediation. To identify mutants with different heavy-metal-tolerance, we first selected a medium from mixtures containing three metals based on their presence in two Spanish mining areas and then screened about 7000 lines of Arabidopsis T-DNA mutants and found 74 lines more resistant and 56 more susceptible than the wild type (WT). Classification of the genes showed that they were mainly linked to transport, protein modification and signalling, with RNA metabolism being the most representative category in the resistant phenotypes and protein metabolism in the sensitive ones. We have characterized one resistant mutant, Athpp9 and one sensitive, Atala4. These mutants showed differences in growth and metal translocation. Additionally, we found that these mutants keep their phenotype in amended former soils, suggesting that these genes may be useful for phytoremediation and the recovery of contaminated soils.

Protection of Nrf2 against arsenite-induced oxidative damage is regulated by the cyclic guanosine monophosphate-protein kinase G signaling pathway

Arsenite has been shown to induce a variety of oxidative damage in mammalian cells. However, the mechanisms underlying cellular responses to its adverse effects remain unknown. We previously showed that the level of Nrf2, a nuclear transcription factor significantly increased in arsenite-treated human bronchial epithelial (HBE) cells suggesting that Nrf2 is involved in responding to arsenite-induced oxidative damage. To explore how Nrf2 can impact arsenite-induced oxidative damage, in this study, we examined Nrf2 activation and its regulation upon cellular arsenite exposure as well as its effects on arsenite-induced oxidative damage in HBE cells. We found that Nrf2 mRNA and protein levels were significantly increased by arsenite in a dose- and time-dependent manner. Furthermore, we showed that over-expression of Nrf2 significantly reduced the level of arsenite-induced oxidative damage in HBE cells including DNA damage, chromosomal breakage, lipid peroxidation and depletion of antioxidants. This indicates a protective role of Nrf2 against arsenite toxicity. This was further supported by the fact that activation of Nrf2 by its agonists, tertiary butylhydroquinone (t-BHQ) and sulforaphane (SFN) resulted in the same protective effects against arsenite toxicity. Moreover, we demonstrated that arsenite-induced activation of Nrf2 was mediated by the cyclic guanosine monophosphate (cGMP)-protein kinase G (PKG) signaling pathway. This is the first evidence showing that Nrf2 protects against arsenite-induced oxidative damage through the cGMP-PKG pathway. Our study suggests that activation of Nrf2 through the cGMP-PKG signaling pathway in HBE cells may be developed as a new strategy for prevention of arsenite toxicity. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 2004-2020, 2017.

Arsenic Hyperaccumulation Strategies: An Overview

Arsenic (As) pollution, which is on the increase around the world, poses a growing threat to the environment. Phytoremediation, an important green technology, uses different strategies, including As uptake, transport, translocation, and detoxification, to remediate this metalloid. Arsenic hyperaccumulator plants have developed various strategies to accumulate and tolerate high concentrations of As. In these plants, the formation of AsIII complexes with GSH and phytochelatins and their transport into root and shoot vacuoles constitute important mechanisms for coping with As stress. The oxidative stress induced by reactive oxygen species (ROS) production is one of the principal toxic effects of As; moreover, the strong antioxidative defenses in hyperaccumulator plants could constitute an important As detoxification strategy. On the other hand, nitric oxide activates antioxidant enzyme and phytochelatins biosynthesis which enhances As stress tolerance in plants. Although several studies have focused on transcription, metabolomics, and proteomic changes in plants induced by As, the mechanisms involved in As transport, translocation, and detoxification in hyperaccumulator plants need to be studied in greater depth. This review updates recent progress made in the study of As uptake, translocation, chelation, and detoxification in As hyperaccumulator plants.

Comparative effect of calcium and EDTA on arsenic uptake and physiological attributes of Pisum sativum

In this study, we determined the effect of ethylenediaminetetraacetic acid (EDTA) and calcium (Ca) on arsenic (As) uptake and toxicity to Pisum sativum. Plants were treated with three levels of As (25, 125, and 250 µM) in the presence and absence of three levels of Ca (1, 5, and 10 mM) and EDTA (25, 125, and 250 µM). Exposure to As caused an overproduction of hydrogen peroxide (H2O2) in roots and leaves, which induced lipid peroxidation and decreased pigment contents. Application of both Ca and EDTA significantly reduced As accumulation by pea, Ca being more effective in reducing As accumulation. Both Ca and EDTA enhanced As-induced H2O2 production, but reduced lipid peroxidation. In the case of pigment contents, EDTA significantly reduced pigment contents, whereas Ca significantly enhanced pigment contents compared to As alone. The effect of As treatment in the presence and absence of EDTA and Ca was more pronounced in younger leaves compared to older leaves. The effect of amendments varied greatly with their applied levels, as well as type and age of plant organs. Importantly, due to possible precipitation of Ca-As compounds, the soils with higher levels of Ca ions are likely to be less prone to food chain contamination.

Investigation of low-level 242Pu contamination on nutrition disturbance and oxidative stress in Solanum tuberosum L

Plutonium associated with higher molecular weight molecules is presumed to be poorly mobile and hardly plant available. In our present study, we investigate the uptake and effects of Pu treatments on Solanum tuberosum plants in amended Hoagland medium at concentrations of [²⁴²Pu] = 100 and 500 nm, respectively. We found a direct proof of oxidative stress in the plants caused by these rather low concentrations. For the confirmation of oxidative stress, we explored the production of nitric oxide (NO) and hydrogen peroxide (H₂O₂) by epifluorescence microscopy. Oxidative stress markers like lipid peroxidation and superoxide radicals (O₂^•-) are monitored through histochemical analysis. The biochemical parameters i.e. chlorophyll and carotenoids are measured as an indicator of cellular damage in the tested plants including the enzymatic parameters such as catalase and glutathione reductase. From our work, we conclude that Pu in low concentration has no significant effects on the uptake of many trace and macroelements. In contrast, the content of O₂^•- , malondialdehyde (MDA), and H₂O₂ increases with increasing Pu concentration in the solution, while the opposite effects was found for NO, catalase, and glutathione reductase. These findings prove that even low concentration of Pu regulates ROS production and generate oxidative stress in S. tuberosum L.

The Involvement of Nitric Oxide in Integration of Plant Physiological and Ultrastructural Adjustments in Response to Arsenic

High arsenic (As) concentrations are toxic to all the living organisms and the cellular response to this metalloid requires the involvement of cell signaling agents, such as nitric oxide (NO). The As toxicity and NO signaling were analyzed in Pistia stratiotes leaves. Plants were exposed to four treatments, for 24 h: control; SNP [sodium nitroprusside (NO donor); 0.1 mg L-1]; As (1.5 mg L-1) and As + SNP (1.5 and 0.1 mg L-1, respectively). The absorption of As increased the concentration of reactive oxygen species and triggered changes in the primary metabolism of the plants. While photosynthesis and photorespiration showed sharp decrease, the respiration process increased, probably due to chemical similarity between arsenate and phosphate, which compromised the energy status of the cell. These harmful effects were reflected in the cellular structure of P. stratiotes, leading to the disruption of the cells and a possible programmed cell death. The damages were attenuated by NO, which was able to integrate central plant physiological processes, with increases in non-photochemical quenching and respiration rates, while the photorespiration level decreased. The increase in respiratory rates was essential to achieve cellular homeostasis by the generation of carbon skeletons and metabolic energy to support processes involved in responses to stress, as well to maintaining the structure of organelles and prevent cell death. Overall, our results provide an integrated view of plant metabolism in response to As, focusing on the central role of NO as a signaling agent able to change the whole plant physiology.