Toxic Heavy Metal and Metalloid Accumulation in Crop Plants and Foods

Identification of novel arsenic resistance genes in yeast

Arsenic is a toxic metalloid that affects human health by causing numerous diseases and by being used in the treatment of acute promyelocytic leukemia. Saccharomyces cerevisiae (budding yeast) has been extensively utilized to elucidate the molecular mechanisms underlying arsenic toxicity and resistance in eukaryotes. In this study, we applied a genomic DNA overexpression strategy to identify yeast genes that provide arsenic resistance in wild-type and arsenic-sensitive S. cerevisiae cells. In addition to known arsenic-related genes, our genetic screen revealed novel genes, including PHO86, VBA3, UGP1, and TUL1, whose overexpression conferred resistance. To gain insights into possible resistance mechanisms, we addressed the contribution of these genes to cell growth, intracellular arsenic, and protein aggregation during arsenate exposure. Overexpression of PHO86 resulted in higher cellular arsenic levels but no additional effect on protein aggregation, indicating that these cells efficiently protect their intracellular environment. VBA3 overexpression caused resistance despite higher intracellular arsenic and protein aggregation levels. Overexpression of UGP1 led to lower intracellular arsenic and protein aggregation levels while TUL1 overexpression had no impact on intracellular arsenic or protein aggregation levels. Thus, the identified genes appear to confer arsenic resistance through distinct mechanisms but the molecular details remain to be elucidated.

The Response of Cd Chemical Fractions to Moisture Conditions and Incubation Time in Arable Land Soil

Heavy metal pollution in soils is an issue of global concern, and many scholars have focused on Cadmium (Cd) because of its strong biological migration and toxicity. This study explored arable land soil, changes in external Cd contamination processes and its response to soil moisture conditions, and indoor simulation. After adding an external source of 5 mg/kg d.w., the distribution of soil Cd fractions content, EXC-Cd, CAB-Cd, FMO-Cd, OM-Cd, and RES-Cd, were continuously monitored under different water management regimes, and correlation analysis and regression equations were calculated. The results show that after external Cd entered arable land soils, the binging strength of pollutants and soil gradually increased with incubation time, and the distribution of Cd chemical forms was more stable under different water management regimes. The oversaturated water content promotes the transformation of EXC-Cd to other forms. The transformation of CAB-Cd fractions can be accelerated to other fractions by field capacity, and the active conversion period was 30–60 d. Not all Cd fractions correlated between each other, under the four water management regimes, but it seems that the reducibility of the soil environment was more conducive to external Cd fixation and stability. The response surface design method (RSM) was used to establish quantitative regimes between Cd fractions with incubation time and soil moisture, and the soil moisture content and incubation time had an obvious effect on FMO-Cd content, with R2 = 0.9542.

Transcriptome analysis provides new insight into the distribution and transport of selenium and its associated metals in selenium-rich rice

Selenium is an essential trace element for humans and obtained from diary diets. The consumption of selenium-rich agricultural food is an efficient way to obtain selenium, but the quality and safety of selenium-rich agro-food are always affected by their associated heavy metals, even poses a potential threaten to human health. In this research, a sampling survey of heavy metals contents in selenium-rich rice was conducted, 182 sets of selenium-rich rice samples were collected from five selenium-rich rice-producing areas of China, and the accumulation of selenium and cadmium were found to be associated in rice and soil. Subsequently, a pot experiment was performed in the greenhouse via treating the soil samples with 12 different concentrations of selenium and heavy metals, and the contents of selenium and cadmium in rice grain were confirmed to be significantly associated. Moreover, transcriptome analysis revealed that the up-regulation of transporter-coding may promote the absorption of selenium and cadmium. The expression of antioxidant-coding genes and cadmium chelator transporter coding-genes was up-regulated to reduce the toxicity of cadmium. Meanwhile, the up-regulation of key genes of the ascorbic acid-glutathione metabolic pathway were responsible for the association between selenium and cadmium in Se-rich rice. Our work suggested the correlation between selenium and cadmium accumulation in selenium-rich rice, clarified their accumulation mechanism, provides a direction for the scientific production of selenium-rich agro-foods.

A review on bioremediation approach for heavy metal detoxification and accumulation in plants

Nowadays, the accumulation of toxic heavy metals in soil and water streams is considered a serious environmental problem that causes various harmful effects on plants and animals. Phytoremediation is an effective, green, and economical bioremediation approach by which the harmful heavy metals in the contaminated ecosystem can be detoxified and accumulated in the plant. Hyperaccumulators exude molecules called transporters that carry and translocate the heavy metals present in the soil to different plant parts. The hyperaccumulator plant genes can confine higher concentrations of toxic heavy metals in their tissues. The efficiency of phytoremediation relies on various parameters such as soil properties (pH and soil type), organic matters in soil, heavy metal type, nature of rhizosphere, characteristics of rhizosphere microflora, etc. The present review comprehensively discusses the toxicity effect of heavy metals on the environment and different phytoremediation mechanisms for the transport and accumulation of heavy metals from polluted soil. This review gave comprehensive insights into plants tolerance for the higher heavy metal concentration their responses for heavy metal accumulation and the different mechanisms involved for heavy metal tolerance. The current status and the characteristic features that need to be improved in the phytoremediation process are also reviewed in detail.

Synergetic modulation of plant cadmium tolerance via MYB75-mediated ROS homeostasis and transcriptional regulation

KEY MESSAGE

MYB75 enhances plant cadmium tolerance by mediating ROS homeostasis and cadmium tolerance-related genes expression. Cadmium (Cd) is a heavy metal with biological toxicity, which can be detoxified through chelation and compartmentation in plants. Transcriptional regulation mediates plant Cd tolerance by modulating these processes. However, the mechanism remains to be studied. Our results showed a previously unknown function of MYB75 transcription factor in the regulation of Cd tolerance. Cd exposure stimulates anthocyanin accumulation by raising MYB75 expression. Enhanced Cd tolerance was observed in the MYB75-overexpressing plants, whereas increased Cd sensitivity was found in the MYB75 loss-of-function mutants. Under Cd stress conditions, lower reactive oxygen species (ROS) levels were detected in MYB75-overexpressing plants than in wild type plants. In contrast, higher ROS levels were found in MYB75 loss-of-function mutants. Overexpression of MYB75 was associated with increased glutathione (GSH) and phytochelatin (PC) content under Cd exposure. Furthermore, the expression of Cd stress-related gene including ACBP2 and ABCC2 was elevated in MYB75-overexpressing plants, and this upregulation was mediated through the mechanism by which MYB75 directly bind to the promoter of ACBP2 and ABCC2. Our findings reveal an important role for MYB75 in the regulation of plant Cd tolerance via anthocyanin-mediated ROS homeostasis, and through upregulation of Cd stress-related gene at the transcriptional level.

Alleviation of cadmium stress in rice by inoculation of Bacillus cereus

Heavy metal resistant bacteria are of great importance because they play a crucial role in bioremediation. In the present study, 11 bacterial strains isolated from industrial waste were screened under different concentrations of cadmium (Cd) (100 µM and 200 µM). Among 11 strains, the Cd tolerant Bacillus cereus (S₆D_1-105) strain was selected for in vitro and in vivo studies. B. cereus was able to solubilize potassium, and phosphate as well as produce protease and siderophores during plate essays. Moreover, we observed the response of hydroponically grown rice plants, inoculated with B. cereus which was able to promote plant growth, by increasing plant biomass, chlorophyll contents, relative water content, different antioxidant enzymatic activity such as catalase, superoxide dismutase, ascorbate peroxidase, polyphenol oxidase and phenylalanine ammonia-lyase and reducing malondialdehyde content in both roots and leaves of rice plants under Cd stress. Our results showed that the B. cereus can be used as a biofertilizer which might be beneficial for rice cultivation in Cd contaminated soils.

Comparative transcriptomics provide new insights into the mechanisms by which foliar silicon alleviates the effects of cadmium exposure in rice

Silicon (Si) has been shown to alleviate Cd stress in rice. Here, we investigated the beneficial effects of foliar Si in an indica rice Huanghuazhan (HHZ). Our results showed that foliar Si increases the dry weight and decreases Cd translocation in Cd-exposed rice at the grain-filling stage only, implying that the filling stage is critical for foliar Si to reduce Cd accumulation. We also investigated the transcriptomics in flag leaves (FLs), spikelets (SPs), and node Is (NIs) of Cd-exposed HHZ after foliar Si application at the filling stage. Importantly, the gene expression profiles associated with the Si-mediated alleviation of Cd stress were tissue specific, while shared pathways were mediated by Si in Cd-exposed rice tissues. Furthermore, after the Si treatment of Cd-exposed rice, the ATP-binding cassette (ABC)-transporters were mostly upregulated in FL and SP, while the bivalent cation transporters were mostly downregulated in FL and NI, possibly helping to reduce Cd accumulation. The genes associated with essential nutrient transporters, carbohydrate and secondary metabolite biosynthesis, and cytochrome oxidase activity were mostly upregulated in Cd-exposed FL and SP, which may help to alleviate oxidative stress and improve plant growth under Cd exposure. Interestingly, genes responsible for signal transduction were negatively regulated in FL, but positively regulated in SP, by foliar Si. Our results provide transcriptomic evidence that foliar Si plays an active role in alleviating the effects of Cd exposure in rice. In particular, foliar Si may alter the expression pattern of genes associated with transport, biosynthesis and metabolism, and oxidation reduction.

Interactive effect of glycine, alanine, and calcium nitrate Ca(NO3)2 on wheat (Triticum aestivum L.) under lead (Pb) stress

Aim of this study was to evaluate the interactive effects of glycine, alanine, calcium nitrate [Ca(NO₃)₂], and their mixture on the growth of two wheat (Triticum aestivum L.) varieties, i.e., var. Punjab-2011 and var. Anaj-2017 under lead [0.5 mM Pb(NO₃)₂] stress. A pot experiment was conducted for this purpose. Pre-sowing seed treatment with 1 mM glycine, alanine, and calcium nitrate [Ca(NO₃)₂] was applied under two levels of lead nitrate [Pb(NO₃)₂] stress, i.e., control and 0.5 mM Pb(NO₃)₂. Lead (0.5 mM) stress significantly decreased root and shoot lengths, fresh and dry weights of root and shoot, and chlorophyll contents, while it increased activities of antioxidant enzymes such as catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX), and peroxidase (POD) in both wheat varieties. Lead (0.5 mM) stress increased the accumulation of free proline, glycinebetaine, total free amino acids, and total soluble protein contents. Although var. Punjab-2011 was higher in root fresh and dry weights, shoot length, and total leaf area per plant, however, var. Anaj-2017 showed less reduction in shoot dry weight, root fresh weight, and shoot length under lead stress. Under lead stress, Punjab-2011 was higher in grain yield and number of grain plant^-1, chlorophyll a contents, membrane permeability (%), POD activity, total free amino acids, and glycinebetaine (GB) contents as compared to Anaj-2017. Pre-sowing seed treatments with glycine, alanine, calcium nitrate, and their mixture (1 mM of each) increased shoot dry weight, number of grains per plants, 100-grain weight, number of spikes, and chlorophyll a contents under normal and lead-stressed conditions. Wheat var. Anaj-2017 showed higher growth and yield attributes as compared to var. Punjab-2011. Results of the current study have shown that pre-sowing seed treatments with glycine, alanine, calcium nitrate, and their mixture (1 mM of each) can overcome the harmful effects of lead (Pb) stress in wheat plants.

Identifying the dose response relationship between seminal metal at low levels and semen quality using restricted cubic spline function

Environmental exposure to metals, including essential and nonessential elements, may be related to semen quality. Our goal was to explore the continuous relationship between seminal metals and sperm parameters. A restricted cubic spline (RCS) was applied to automatic selection criteria to ascertain the optimal smoothing degree. We recruited 841 male volunteers from Henan Province, China. Eighteen seminal metals, namely Al, Cr, Mn, Cu, Zn, Se, As, Ni, Cd, Pb, Co, V, Rb, Ag, Ba, TI, Fe, and Li, and 21 semen parameters were detected. Seminal malondialdehyde (MDA) was also detected to express oxidative stress. We revealed a non-linear relationship of the vanadium and chromium exposure to semen parameters. There were inverse 'U' shapes found between seminal Cr and sperm concentrations, total sperm count, and semen quality. The best semen quality was observed when the seminal Cr concentration was 5.05 ppb, and an increase or decrease in chromium concentration led to decreased semen quality. The V concentration was associated with reduced sperm concentration, total sperm count, normal morphology, and progressive motility at high doses (V > 0.58 ppb). Seminal MDA had a strong adverse association with sperm motility parameters, such as curve line velocity (VCL) (P < 0.001), straight line velocity (VSL) (P = 0.004), velocity of average path (VAP) (P < 0.001), and lateral head movement (ALH) (P = 0.001), whereas it was adversely associated with seminal Zn (β [95% confidence interval (CI)], -0.28(-0.41-0.16), P < 0.001) after adjusting for confounding factors. Our findings represent the curves of the dose-response relationship between seminal Cr, seminal V, and semen quality, in which seminal MDA was a good indicator of sperm movement. These models provide new insight into the dose-relationship between metal exposure and semen quality, and further investigation is needed to validate this.

Genome-Wide Identification and Expressional Profiling of the Metal Tolerance Protein Gene Family in Brassica napus

The Cation Diffusion Facilitator (CDF) family, also named Metal Tolerance Protein (MTP), is one of the gene families involved in heavy metal transport in plants. However, a comprehensive study of MTPs in Brassica napus has not been reported yet. In the present study, we identified 33 BnMTP genes from the rapeseed genome using bioinformatic analyses. Subsequently, we analyzed the phylogenetic relationship, gene structure, chromosome distribution, conserved domains, and motifs of the BnMTP gene family. The 33 BnMTPs were phylogenetically divided into three major clusters (Zn-CDFs, Fe/Zn-CDFs, and Mn-CDFs) and seven groups (group 1, 5, 6, 7, 8, 9, and 12). The structural characteristics of the BnMTP members were similar in the same group, but different among groups. Evolutionary analysis indicated that the BnMTP gene family mainly expanded through whole-genome duplication (WGD) and segmental duplication events. Moreover, the prediction of cis-acting elements and microRNA target sites suggested that BnMTPs might be involved in plant growth, development, and stress responses. In addition, we found the expression of 24 BnMTPs in rapeseed leaves or roots could respond to heavy metal ion treatments. These results provided an important basis for clarifying the biological functions of BnMTPs, especially in heavy metal detoxification, and will be helpful in the phytoremediation of heavy metal pollution in soil.

The rice heavy-metal transporter OsNRAMP1 regulates disease resistance by modulating ROS homoeostasis

Crop diseases threaten food security and sustainable agriculture. Consumption of crops containing nonessential toxic metals leads to health risks for humans. Therefore, cultivation of disease-resistant and toxic metal-safe crops is a double-gain strategy that can contribute to food security. Here, we show that rice heavy-metal transporter OsNRAMP1 plays an important role in plant immunity by modulating metal ion and reactive oxygen species (ROS) homoeostasis. OsNRAMP1 expression was induced after pathogenic bacteria and fungi infections. The osnramp1 mutants had an increased content of H₂ O₂ and activity of superoxide dismutase, but decreased activity of catalase, showing enhanced broad-spectrum resistance against bacterial and fungal pathogens. RNA-seq analysis identified a number of differentially expressed genes that were involved in metal ion and ROS homoeostasis. Altered expression of metal ion-dependent ROS-scavenging enzymes genes and lower accumulation of cations such as Mn together induced compromised metal ion-dependent enzyme-catalysing activity and modulated ROS homoeostasis, which together contributed towards disease resistance in osnramp1 mutants. Furthermore, the osnramp1 mutants contained lower levels of toxic heavy metals Cd and Pb and micronutrients Ni and Mn in leaves and grains. Taken together, a proof of concept was achieved that broad-spectrum disease-resistant and toxic heavy-metal-safe rice was engineered by removal of the OsNRAMP1 gene.

Urinary element profiles and associations with cardiometabolic diseases: A cross-sectional study across ten areas in China

BACKGROUND

Existing evidence on the associations of urinary element profiles with related food intake and cardiometabolic diseases has been limited in China.

OBJECTIVES

To examine the associations of urinary toxic metals and other elements with food intakes and with the prevalence of cardiometabolic diseases.

METHODS

Inductively coupled plasma mass spectrometry was used to measure the concentrations of cadmium (Cd), arsenic (As), nickel (Ni), aluminum (Al), copper (Cu), and 16 other elements in spot urine samples collected from 19,380 adults in 10 geographically diverse areas of China during 2013-2014. The levels of creatinine-corrected elements were used to analyze their correlations with self-reported dietary intake and associations with prevalent diabetes (n = 1862), stroke (n = 1322) and ischemic heart disease (IHD) (n = 1690).

RESULTS

Overall, the mean (SD) age was 59.2 (10.1) years with a mean BMI of 24.2 (3.5) kg/m². Of the 21 elements, the median (IQR) concentrations varied from 0.49 (0.31-0.82) μg/g creatinine for vanadium (V) to 1666 (1189-2321) mg/g creatinine for potassium (K). Nine urinary elements [Cd, As, Ni, lead (Pb), boron (B), magnesium (Mg), rubidium (Rb), strontium (Sr), and cesium (Cs); all rs > 0.20, p < 0.001] were positively correlated with staple food intake, five [Cd, As, selenium (Se), Rb, and Cs; all rs > 0.20, p < 0.001] with animal-sourced food group, and one (Cd; r = 0.21, p < 0.05) with pickled vegetable intake. For diabetes, adjusted prevalence ratios (PRs) per SD of specific element levels were 1.10 [95% confidence interval (CI): 1.03-1.18] for Cd, 1.24 (1.18-1.31) for As, 1.33 (1.27-1.39) for Ni, 1.14 (1.09-1.20) for Al, and 1.24 (1.18-1.30) for Cu. Cd was positively associated with stroke (PR per SD = 1.13, 1.04-1.23), while none of the elements were significantly associated with IHD.

CONCLUSION

In China, the urinary levels of several toxic metals were significantly associated with the consumption of specific food groups and the risk of cardiometabolic diseases including diabetes and stroke.

Various potentially toxic element tolerances in different rice genotypes correlate with distinct physiological responses and alterations in DNA methylation

Potentially toxic elements (PTEs) are harmful to plant growth and reduce crop productivity. In this work, we studied three rice genotypes (T-35, RZ-1, and RZ-2) to quantify the diverse PTE effects and tolerances by examining morphology, physiology, and DNA methylation patterns. Morphological results showed that T-35 exhibits the highest tolerance to all studied PTE stressors (Cu, Cd, Cr). Physiological responses under PTE stresses confirmed earlier findings, where T-35 showed a higher potassium (K⁺) content and more peroxidase (POD) accumulation in the roots than the other two rice genotypes. The differences in PTE tolerance levels observed among the three rice genotypes were also associated with variations in the heavy metal transportation (HMT) gene expression level. Moreover, methylation-sensitive blotting analysis of the selected genes showed that the DNA methylation changes occurring due to PTE treatments are mainly CHG hypomethylation in T-35 but hypermethylation in RZ-1 and RZ-2. Our results demonstrate a tight relationship among physiological response, expression levels of the HMT genes, and DNA methylation pattern under PTEs stresses. It is also indicated that plants use generic mechanisms to tolerate stresses; however, different genotypes employ different combinations of such tactics to confer tolerance, which results in diverse PTE stress tolerances. These findings shed light on the PTE stresses tolerance mechanism and help direct future breeding activities in rice.

A Systematic Review on Amaranthus-Related Research

Leafy vegetables promote reparation of energy loss due to oxidative stress, and they have the potential to alleviate hunger and malnutrition as well as other forms of metabolic imbalance ravaging the world. However, these vegetables are underutilized, despite the fact that they harbor essential minerals needed for critical cellular activities. As amaranth is one of the earliest vegetables reputed for its high nutraceutical and therapeutic value, in this study, we explored research on the Amaranthus species, and identified areas with knowledge gaps, to harness the various biological and economic potentials of the species. Relevant published documents on the plant were retrieved from the Science Citation Index Expanded accessed through the Web of Science from 2011 to 2020; while RStudio and VOSviewer were used for data analysis and visualization, respectively. Publications over the past decade (dominated by researchers from the USA, India, and China, with a collaboration index of 3.22) showed that Amaranthus research experienced steady growth. Findings from the study revealed the importance of the research and knowledge gaps in the underutilization of the vegetable. This could be helpful in identifying prominent researchers who can be supported by government funds, to address the malnutrition problem in developing countries throughout the world.

Whole-cell biosensors for determination of bioavailable pollutants in soils and sediments: Theory and practice

The bioavailability of pollutants is a key factor affecting environmental risk. Whole-cell bioreporters are a demonstratedly effective tool for the investigation of pollutant bioavailability in water and soil/sediment. Unlike aqueous samples, transmittance of bioreporter optical signal is reduced in direct-contact assays with soil/sediment, which affects the accuracy of bioreporter-detected pollutant bioavailability. No studies have measured the magnitude and variability of soil/sediment effects on signal in direct-contact assays or how associated uncertainties influence results. In this study, we investigate the optical effects of soil/sediment particles in suspensions on bioreporter signal transmittance and quantify how variable these optical effects are from sample-to-sample. We find that neglecting bioreporter signal diminution by soil/sediment, as many studies do, can lead to order-of-magnitude errors in results, underestimating risk. Correction based on methods in ad hoc use (e.g. comparison to signal from non-inducible reporter or use of reference soil/sediment) are also problematic for some types of experiment, and could lead to errors in excess of 30%. Our findings have a sound basis in theory, and we provide recommendations concerning the most suitable type of approach to use for different experimental settings. Generally, if best accuracy is not needed to quantify bioavailability, for samples that have been ground, sieved, and are of reasonably uniform color, it may be possible to use a single or average correction factor, particularly for experiments performed at a single slurry concentration. For investigations studying bioavailability under varying solid-phase:water ratios (e.g., sorption/desorption), detailed compensation measurements are needed for independent variables, including each specific soil/sediment sample, slurry concentration, and in some cases bioreporter signal intensity. Our measurements and calculations indicate that best results are obtained when working in the region of ballistic photon transmittance. Findings herein will be useful in areas that require information on bioavailability, such as ecotoxicology and environmental risk assessment.

Mechanistic Impact of Zinc Deficiency in Human Development

Zinc (Zn) deficiency in humans is an emerging global health issue affecting approximately two billion people across the globe. The situation prevails due to the intake of Zn deficient grains and vegetables worldwide. Clinical identification of Zn deficiency in humans remains problematic because the symptoms do not appear until impair the vital organs, such as the gastrointestinal track, central nervous system, immune system, skeletal, and nervous system. Lower Zn body levels are also responsible for multiple physiological disorders, such as apoptosis, organs destruction, DNA injuries, and oxidative damage to the cellular components through reactive oxygen species (ROS). The oxidative damage causes chronic inflammation lead toward several chronic diseases, such as heart diseases, cancers, alcohol-related malady, muscular contraction, and neuro-pathogenesis. The present review focused on the physiological and growth-related changes in humans under Zn deficient conditions, mechanisms adopted by the human body under Zn deficiency for the proper functioning of the body systems, and the importance of nutritional and nutraceutical approaches to overcome Zn deficiency in humans and concluded that the biofortified food is the best source of Zn as compared to the chemical supplementation to avoid their negative impacts on human.

Ammonium has stronger Cd detoxification ability than nitrate by reducing Cd influx and increasing Cd fixation in Solanum nigrum L

Cadmium (Cd) is a harmful heavy metal that affects the growth and development of plants. Nitrogen (N) is an essential nutrient for plants, and appropriate N management can improve Cd tolerance. The aim of our study was to explore the effects of different forms of N on the molecular and physiological responses of the hyperaccumulator Solanum nigrum to Cd toxicity. Measurement of biomass, photosynthetic parameters, and Cd²⁺ fluxes using non-invasive micro-test technique, Cd fluorescent dying, biochemical methods and quantitative real-time PCR analysis were performed in our study. Our results showed that ammonium (NH₄⁺) has stronger Cd detoxification ability than nitrate (NO₃^-), which are likely attributed to the following three reasons: (1) NH₄⁺ decreased the influx and accumulation of Cd²⁺ by regulating the transcription of Cd transport-related genes; (2) the ameliorative effects of NH₄⁺ were accompanied by the increased retention of Cd in the cell walls of roots; and (3) NH₄⁺ up-regulated SnExp expression.

AMPK pathway is implicated in low level lead-induced pubertal testicular damage via disordered glycolysis

Lead (Pb) is a common environmental pollutant. It has been demonstrated that long-term exposure to Pb at environmental levels may cause severe and irreversible damage to the male reproductive system. Of note, the impairments may originate from environmental Pb exposure at puberty. However, the underlying mechanisms remain unclear. In this study, we administrated male ICR mice with 200 mg/L Pb through the drinking water for 30-, 60-, 90-day from postnatal day 28. RNA sequencing was performed in the control group and the 90-day Pb exposure group. It was found that Pb exposure induced testicular damage, increased oxidative stress levels and poor sperm quality. Bioinformatic analysis displayed 199 genes up-regulated (such as GLUT1 and MCT4 genes) and 156 genes down-regulated (such as GLUT3, PFK1, LDH, CD147 and AMPK genes) in the Pb exposure group compared to the control group. Gene ontology (GO) terms enrichment analysis showed differentially expressed genes (DEGs) are involved in the protein catabolic, cellular catabolic and triglyceride catabolic processes. KEGG pathways enrichment analysis indicated glycerolipid metabolism and AMPK signaling were significantly enriched. Furthermore, experimental verification showed that Pb exposure induces energy dysmetabolism and decreases glycolysis products in mice testicular tissue. The AMPK signaling pathway was found to be deactivated after Pb exposure. The GLUT1, GLUT3, PFK1 and LDH proteins, which play a critical role in the cell glycolysis process, also were decreased. Besides, the expression of CD147 was decreased and the location of CD147 was altered upon Pb exposure. Together, these findings indicated the implication of the AMPK signaling pathway in Pb exposure induced pubertal testicular damage and poor sperm quality by inhibiting cell glycolysis and disordering lactate transportation in testicular cells.

The role of roots and rhizosphere in providing tolerance to toxic metals and metalloids

Human activity and natural processes have led to the widespread dissemination of metals and metalloids, many of which are toxic and have a negative impact on plant growth and development. Roots, as the first point of contact, are essential in endowing plants with tolerance to excess metal(loid) in the soil. The most important root processes that contribute to tolerance are: adaptation of transport processes that affect uptake efflux and long-distance transport of metal(loid)s; metal(loid) detoxification within root cells via conjugation to thiol rich compounds and subsequent sequestration in the vacuole; plasticity in root architecture; the presence of bacteria and fungi in the rhizosphere that impact on metal(loid) bioavailability; the role of root exudates. In this review, we provide details on these processes and assess their relevance on the detoxification of arsenic, cadmium, mercury and zinc in crops. Furthermore, we assess which of these strategies have been tested in field conditions and whether they are effective in terms of improving crop metal(loid) tolerance.

Characterization of a novel arsenite long-distance transporter from arsenic hyperaccumulator fern Pteris vittata

Pteris vittata is an arsenic (As) hyperaccumulator that can accumulate several thousand mg As kg^-1 DW in aboveground biomass. A key factor for its hyperaccumulation ability is its highly efficient As long-distance translocation system. However, the underlying molecular mechanisms remain unknown. We isolated PvAsE1 through the full-length cDNA over-expression library of P. vittata and characterized it through a yeast system, RNAi gametophytes and sporophytes, subcellular-location and in situ hybridization. Phylogenomic analysis was conducted to estimate the appearance time of PvAsE1. PvAsE1 was a plasma membrane-oriented arsenite (AsIII) effluxer. The silencing of PvAsE1 reduced AsIII long-distance translocation in P. vittata sporophytes. PvAsE1 was structurally similar to solute carrier (SLC)13 proteins. Its transcripts could be observed in parenchyma cells surrounding the xylem of roots. The appearance time was estimated at c. 52.7 Ma. PvAsE1 was a previously uncharacterized SLC13-like AsIII effluxer, which may contribute to AsIII long-distance translocation via xylem loading. PvAsE1 appeared late in fern evolution and might be an adaptive subject to the selection pressure at the Cretaceaou-Paleogene boundary. The identification of PvAsE1 provides clues for revealing the special As hyperaccumulation characteristics of P. vittata.

The E3 Ubiquitin Ligase Gene Sl1 Is Critical for Cadmium Tolerance in Solanum lycopersicum L

Heavy metal cadmium (Cd) at high concentrations severely disturbs plant growth and development. The E3 ubiquitin ligase involved in protein degradation is critical for plant tolerance to abiotic stress, but the role of E3 ubiquitin ligases in Cd tolerance is largely unknown in tomato. Here, we characterized an E3 ubiquitin ligase gene Sl1, which was highly expressed in roots under Cd stress in our previous study. The subcellular localization of Sl1 revealed that it was located in plasma membranes. In vitro ubiquitination assays confirmed that Sl1 had E3 ubiquitin ligase activity. Knockout of the Sl1 gene by CRISPR/Cas9 genome editing technology reduced while its overexpression increased Cd tolerance as reflected by the changes in the actual quantum efficiency of PSII photochemistry (Φ_PSII) and hydrogen peroxide (H₂O₂) accumulation. Cd-induced increased activities of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) were compromised in sl1 mutants but were enhanced in Sl1 overexpressing lines. Furthermore, the content of Cd in both shoots and roots increased in sl1 mutants while reduced in Sl1 overexpressing plants. Gene expression assays revealed that Sl1 regulated the transcript levels of heavy metal transport-related genes to inhibit Cd accumulation. These findings demonstrate that Sl1 plays a critical role in regulating Cd tolerance by relieving oxidative stress and resisting heavy metal transportation in tomato. The study provides a new understanding of the mechanism of plant tolerance to heavy metal stress.

(De)Activation (Ir)Reversibly or Degradation: Dynamics of Post-Translational Protein Modifications in Plants

The increasing dynamic functions of post-translational modifications (PTMs) within protein molecules present outstanding challenges for plant biology even at this present day. Protein PTMs are among the first and fastest plant responses to changes in the environment, indicating that the mechanisms and dynamics of PTMs are an essential area of plant biology. Besides being key players in signaling, PTMs play vital roles in gene expression, gene, and protein localization, protein stability and interactions, as well as enzyme kinetics. In this review, we take a broader but concise approach to capture the current state of events in the field of plant PTMs. We discuss protein modifications including citrullination, glycosylation, phosphorylation, oxidation and disulfide bridges, N-terminal, SUMOylation, and ubiquitination. Further, we outline the complexity of studying PTMs in relation to compartmentalization and function. We conclude by challenging the proteomics community to engage in holistic approaches towards identification and characterizing multiple PTMs on the same protein, their interaction, and mechanism of regulation to bring a deeper understanding of protein function and regulation in plants.

Arsenic Transformation in Soil-Rice System Affected by Iron-Oxidizing Strain (Ochrobactrum sp.) and Related Soil Metabolomics Analysis

Iron-oxidizing bacteria (FeOB) could oxidize Fe(II) and mediate biomineralization, which provides the possibility for its potential application in arsenic (As) remediation. In the present study, a strain named Ochrobactrum EEELCW01 isolated previously, was inoculated into paddy soils to investigate the effect of FeOB inoculation on the As migration and transformation in paddy soils. The results showed that inoculation of Ochrobactrum sp. increased the proportion of As in iron-aluminum oxide binding fraction, which reduced the As bioavailability in paddy soils and effectively reduced the As accumulation in rice tissues. Moreover, the inoculation of iron oxidizing bacteria increased the abundance of KD4-96, Pedosphaeraceae and other bacteria in the soils, which could reduce the As toxicity in the soil through biotransformation. The abundance of metabolites such as carnosine, MG (0:0/14:0/0:0) and pantetheine 4'-phosphate increased in rhizosphere soils inoculated with FeOB, which indicated that the defense ability of soil-microorganism-plant system against peroxidation caused by As was enhanced. This study proved that FeOB have the potential application in remediation of As pollution in paddy soil, FeOB promotes the formation of iron oxide in paddy soil, and then adsorbed and coprecipitated with arsenic. On the other hand, the inoculation of Ochrobactrum sp. change soil microbial community structure and soil metabolism, increase the abundance of FeOB in soil, promote the biotransformation process of As in soil, and enhance the resistance of soil to peroxide pollution (As pollution).

Cadmium oral bioavailability is affected by calcium and phytate contents in food: Evidence from leafy vegetables in mice

To test high cadmium (Cd) concentration may not be high in health risk when considering Cd bioavailability, we assessed variation of Cd relative bioavailability (RBA, relative to CdCl₂) using a mouse assay for 14 vegetables of water spinach, amaranth, and pakchoi. Cadmium concentration varied from 0.13 ± 0.01-0.37 ± 0.00 μg g^-1 fw. Cadmium-RBA also varied significantly from 22.9 ± 2.12-77.2 ± 4.46%, however, the variation was overall opposite to that of Cd concentration, as indicated by a strong negative correlation between Cd-RBA and Cd concentration (R² = 0.43). Based on both Cd concentration and bioavailability, the identified high-Cd pakchoi variety resulted in significantly lower Cd intake than the high-Cd varieties of water spinach and amaranth (4.74 ± 0.05 vs. 10.1 ± 0.54 and 8.03 ± 0.04 μg kg^-1 bw week^-1) due to significantly lower Cd-RBA (22.9 ± 2.12 vs. 77.2 ± 4.46 and 51.3 ± 2.93%). The lower Cd-RBA in pakchoi was due to its significantly higher Ca and lower phytate concentrations, which facilitated the role of Ca in inhibiting intestinal Cd absorption. This was ascertained by observation of decreased Cd-RBA (90.5 ± 12.0% to 63.5 ± 5.53%) for a water spinach when elevating its Ca concentration by 30% with foliar Ca application. Our results suggest that to assess food Cd risk, both total Cd and Cd bioavailability should be considered.

Brassinosteroids and metalloids: Regulation of plant biology

Metalloid contamination in the environment is one of the serious concerns posing threat to our ecosystems. Excess of metalloid concentrations (including antimony, arsenic, boron, selenium etc.) in soil results in their over accumulation in plant tissues, which ultimately causes phytotoxicity and their bio-magnification. So, it is very important to find some ecofriendly approaches to counter negative impacts of above mentioned metalloids on plant system. Brassinosteroids (BRs) belong to family of plant steroidal hormones, and are considered as one of the ecofriendly way to counter metalloid phytotoxicity. This phytohormone regulates the plant biology in presence of metalloids by modulating various key biological processes like cell signaling, primary and secondary metabolism, bio-molecule crosstalk and redox homeostasis. The present review explains the in-depth mechanisms of BR regulated plant responses in presence of metalloids, and provides some biotechnological aspects towards ecofriendly management of metalloid contamination.

Changeable effects of coexisting heavy metals on transfer of cadmium from soils to wheat grains

Cadmium (Cd) and other heavy metals usually coexist in soils. Effects of coexisting heavy metals on the accumulation and transfer of Cd in field soils by wheat remain poorly understood. Here we revealed changeable effects of coexisting Pb, Zn and Cu on the Cd transfer from soils to wheat grains. Soil burdens of Cd were found to exhibit positive correlations (r = 0.459-0.946) with those of coexisting Pb, Zn and Cu (particularly Pb). Effects of three coexisting metals on to the uptake of Cd by wheat varied in the directions and/or extents with types of metals and transfer processes of Cd. Coexisting Zn inhibited the uptake of Cd by wheat grains to higher extent than Pb and Cu. Soil Zn, along with soil Cd, soil pH and soil Ca, was used to construct the predictive model of grain Cd (R² = 0.868). External verifications of the model on 572 datasets of large representation performed well. The predictive accuracy was about 54%, 73% and 89% for a factor of 1, 2 and 5 above and below the ideal fit, respectively. This finding has practical interest in risk assessments and remediation measures of Cd-contaminated soil sites in regional scales.

Foliar application of silica sol alleviates boron toxicity in rice (Oryza sativa) seedlings

Boron (B) toxicity is one of the limiting factors affecting plant growth. Previous studies showed that silicon (Si) application could alleviate B toxicity. However, there is limited information on how Si alleviates B toxicity in rice, particularly nano-silicon (SiNP). Therefore, the current study aimed to explore the foliar function of SiNP in the reduction of B toxicity in rice. The results showed that B toxicity significantly hampered root and shoot development. However, SiNP application increased root and shoot lengths by 14.29% and 29.67%, respectively, compared to B toxicity treatment. Moreover, SiNP increased fresh weight (FW) of root (28.02%) and shoot (34%) and enhanced dry weight (DW) of root (65.13%), and shoot (26.87%), compared to B toxicity treatment. The application of SiNP decreased the translocation of B to leaves and promoted B adsorption to leaf cell wall. In roots, SiNP triggered high B accumulation and Fourier infrared spectroscopy (FTIR) also suggested higher peak values of functional groups (pectin), indicating that cell wall polysaccharides can adsorb high concentration of B. Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM) investigations showed that SiNP treated roots had a well-arranged structure of alkali-soluble pectin (ASP), and ultrastructure of root was well organized. Cell wall adsorbed more than 80% of total B. All of these results suggest that SiNP can alleviate B toxicity in rice seedlings.

Transcriptome-wide m6A methylation profile reveals regulatory networks in roots of barley under cadmium stress

Cadmium (Cd) pollutants restrict crop yield and food security in long-term agricultural activities. Crops have evolved adaptive strategies under Cd condition, however, the transcriptional regulatory mechanism of Cd-tolerant genes remains to be largely illustrated. In this study, barley roots were exposed to 5 µM CdCl₂ for physiological response and transcriptome-wide m6A methylation profile. Cd stress inhibited root growth after 7 d Cd treatment, which is mainly associated with inhibited absorption of Mn. After Cd treatment, 8151 significantly modified m6A sites and 3920 differentially expressed genes were identified. Transcriptome-wide m6A hypermethylation was widely induced by Cd stress and enriched near the stop codon and 3' UTR regions. Among 435 m6A modified DEGs, 319 hypermethylated genes were up-regulated and 84 hypomethylated genes were down-regulated, respectively, indicating a positive correlation of m6A methylation and expression. But well-known Cd transporter genes (HvNramp5, HvIRT1, HvHMA3, etc.) were not modified by m6A methylation, except for ABC transporters. We further found key Cd-responding regulatory genes were positively modulated with m6A methylation, including MAPK, WRKY and MYB members. This study proposed a transcriptional regulatory network of Cd stress response in barley roots, which may provide new insight into gene manipulation of controlling low Cd accumulation for crops.

Cadmium uptake and transport processes in rice revealed by stable isotope fractionation and Cd-related gene expression

Multiple processes are involved in Cd transfer in rice plants, including root uptake, xylem loading, and immobilization. These processes can be mediated by membrane transporters and can alter Cd speciation by binding Cd to different organic ligands. However, it remains unclear which processes control Cd transport in rice in response to different watering conditions in soil. Herein, Cd isotope fractionation and Cd-related gene expression were employed to investigate the key regulatory mechanisms during uptake, root-to-shoot, and stem-to-leaf transport of Cd in rice grown in pot experiments with Cd-contaminated soil under flooded and non-flooded conditions, respectively. The results showed that soil flooding decreased the Cd concentration in soil porewater and, thereby, Cd uptake and transport in rice. Cd isotopes fractionated negatively from soil porewater to the whole rice (flooded: ∆^114/110Cd_{rice-porewater} = -0.15‰, non-flooded: ∆^114/110Cd_{rice-porewater} = -0.39‰), suggesting that Cd transporters preferentially absorbed light Cd isotopes. The non-flooded treatment revealed an upregulated expression of OsNRAMP1 and OsNRAMP5 genes compared to the flooded treatment, which may partially contribute to its more pronounced porewater-to-rice fractionation. Cd isotopes fractionated positively from roots to shoots under flooded conditions (∆^114/110Cd_shoot-root = 0.19‰). However, a reverse direction of fractionation was observed under non-flooded conditions (∆^114/110Cd_shoot-root = -0.67‰), which was associated with the substantial upregulation of CAL1 in roots, facilitating xylem loading of Cd-CAL1 complexes with lighter isotopes. After being transported to the shoots, the majority of Cd were detained in stems (44%-55%), which were strongly enriched in lighter isotopes than in the leaves (∆^114/110Cd_leaf-stem = 0.77 to 1.01‰). Besides the Cd-CAL1 transported from the roots, the expression of OsPCS1 and OsHMA3 in the stems could also favor the enrichment of Cd-PCs with lighter isotopes, leaving heavier isotopes to be transported to the leaves. The higher expression levels of OsMT1e in older leaves than in younger leaves implied that Cd immobilization via binding to metallothioneins like OsMT1e may favor the enrichment of lighter isotopes in older leaves. The non-flooded treatment showed lighter Cd isotopes in younger leaves than the flooded treatment, suggesting that more Cd-CAL1 in the stems and Cd-PCs in the older leaves might be transported to the younger leaves under non-flooded conditions. Our results demonstrate that isotopically light Cd can be preferentially transported from roots to shoots when more Cd is absorbed by rice under non-flooded conditions, and isotope fractionation signature together with gene expression quantification has the potential to provide a better understanding of the key processes regulating Cd transfer in rice.

Effect of temperature on PTEs deportment and ecological risks of the biochars obtained from sewage sludge

Sewage sludge-derived biochars (SSBCs) were obtained at temperatures of 300, 500, and 700 °C to investigate the potentially toxic elements (PTEs) behaviors and assess the environmental acceptability for the possible application in the environment. Results indicated that PTEs exhibited diversely in the distribution of chemical speciation, while all elements tended to be immobilized in biochar matrix and the total amount elevated during the pyrolysis. The risk assessment of biochars implied a low degree of environmental risk for the utilization of SSBCs prepared at high temperatures. In addition, higher pyrolysis temperature alleviated the inhibition on the early seedling growth of Triticum aestivum L., with root elongation more sensitive to the biochar addition. PTEs, especially Cr, contributed much to the phytotoxicity of biochars as revealed by the principle component analysis (PCA) and leaner correlation analysis. Findings from this work illustrated that SSBCs prepared at higher temperatures might be more conductive to a wide range of applications with acceptable environmental risk.

Associations of blood and urinary heavy metals with rheumatoid arthritis risk among adults in NHANES, 1999-2018

Heavy metals exposure has been widely recognized as a risk factor for human health. However, limited information is available about the impacts of heavy metals on rheumatoid arthritis (RA). Herein, we estimated the associations of 3 blood and 11 urinary metals with the risk of RA among 49830 U.S. adults from the National Health and Nutrition Examination Survey (NHANES), 1999-2018. In the single-exposure model, blood cadmium (Cd) and lead (Pb), urinary Cd, Pb, antimony (Sb), tungsten (Tu), and uranium (Ur) were identified to be positively associated with RA risk. Furthermore, weighted quantile sum (WQS) regression, quantile-based g computation (qgcomp), and Bayesian kernel machine regression (BKMR) analyses consistently showed that both blood and urinary metals-mixed exposure were positively correlated with the risk of RA, and highlighted that Cd and Pb were responsible for the outcomes. Such associations were more evident in the young and middle-aged population. These findings indicated that exposure to heavy metals increased RA risk, and advanced the identification of risk factors for RA.

Association Between Low-Level Blood Cadmium Exposure and Hyperuricemia in the American General Population: a Cross-sectional Study

Heavy metals, including cadmium, are suspected to increase serum uric acid levels and hyperuricemia in both gender, but the evidences about this are inconclusive. To determine whether serum cadmium in American adults(≥19 years old) is associated with uric acid levels and risk of hyperuricemia, 2620 participants from the US National Health and Nutrition Examination Survey were recruited. Hyperuricemia was defined as a serum UA concentration ≥ 416.4 μmol/L for men and ≥ 356.9 μmol/L for women. Regression analyses were used to analyze the association of cadmium with serum UA and hyperuricemia. The threshold effect explored using two-piecewise linear regression model by the smoothing plot. The overall median of blood cadmium was 0.27 μg/L in men and 0.33μg/L in women. After adjusting for the covariates (race; age; education; BMI; smoke status; alcohol consumption; blood lead; hypertension; diabetes mellitus; hemoglobin; eGFR; triglyceride; and cholesterol), a non-linear relationship between hyperuricemia and cadmium among men was detected; and there was a positive line correlation between them for women (OR = 1.58; 95%CI (1.08, 2.31)). No significant association between uric acid and cadmium in either gender was found. Blood cadmium levels in the range currently considered acceptable were positively associated with increased prevalence of hyperuricemia in women, but inversely associated in men (cadmium <0.77μg/L).

Water and soil contaminated by arsenic: the use of microorganisms and plants in bioremediation

Owing to their roles in the arsenic (As) biogeochemical cycle, microorganisms and plants offer significant potential for developing innovative biotechnological applications able to remediate As pollutions. This possible use in bioremediation processes and phytomanagement is based on their ability to catalyse various biotransformation reactions leading to, e.g. the precipitation, dissolution, and sequestration of As, stabilisation in the root zone and shoot As removal. On the one hand, genomic studies of microorganisms and their communities are useful in understanding their metabolic activities and their interaction with As. On the other hand, our knowledge of molecular mechanisms and fate of As in plants has been improved by laboratory and field experiments. Such studies pave new avenues for developing environmentally friendly bioprocessing options targeting As, which worldwide represents a major risk to many ecosystems and human health.

Genome-Wide Association Study Reveals Complex Genetic Architecture of Cadmium and Mercury Accumulation and Tolerance Traits in Medicago truncatula

Heavy metals are an increasing problem due to contamination from human sources that and can enter the food chain by being taken up by plants. Understanding the genetic basis of accumulation and tolerance in plants is important for reducing the uptake of toxic metals in crops and crop relatives, as well as for removing heavy metals from soils by means of phytoremediation. Following exposure of Medicago truncatula seedlings to cadmium (Cd) and mercury (Hg), we conducted a genome-wide association study using relative root growth (RRG) and leaf accumulation measurements. Cd and Hg accumulation and RRG had heritability ranging 0.44 - 0.72 indicating high genetic diversity for these traits. The Cd and Hg trait associations were broadly distributed throughout the genome, indicated the traits are polygenic and involve several quantitative loci. For all traits, candidate genes included several membrane associated ATP-binding cassette transporters, P-type ATPase transporters, oxidative stress response genes, and stress related UDP-glycosyltransferases. The P-type ATPase transporters and ATP-binding cassette protein-families have roles in vacuole transport of heavy metals, and our findings support their wide use in physiological plant responses to heavy metals and abiotic stresses. We also found associations between Cd RRG with the genes CAX3 and PDR3, two linked adjacent genes, and leaf accumulation of Hg associated with the genes NRAMP6 and CAX9. When plant genotypes with the most extreme phenotypes were compared, we found significant divergence in genomic regions using population genomics methods that contained metal transport and stress response gene ontologies. Several of these genomic regions show high linkage disequilibrium (LD) among candidate genes suggesting they have evolved together. Minor allele frequency (MAF) and effect size of the most significant SNPs was negatively correlated with large effect alleles being most rare. This is consistent with purifying selection against alleles that increase toxicity and abiotic stress. Conversely, the alleles with large affect that had higher frequencies that were associated with the exclusion of Cd and Hg. Overall, macroevolutionary conservation of heavy metal and stress response genes is important for improvement of forage crops by harnessing wild genetic variants in gene banks such as the Medicago HapMap collection.

Use of Air-Classification Technology to Manage Mycotoxin and Arsenic Contaminations in Durum Wheat-Derived Products

Mycotoxins are the most common natural contaminants and include different types of organic compounds, such as deoxynivalenol (DON) and T-2 and HT-2 toxins. The major toxic inorganic elements include those commonly known as heavy metals, such as cadmium, nickel, and lead, and other minerals such as arsenic. In this study, micronisation and air classification technologies were applied to durum wheat (Triticum turgidum ssp. durum L.) samples to mitigate inorganic (arsenic) and organic contaminants in unrefined milling fractions and final products (pasta). The results showed the suitability of milling plants, providing less refined milling products for lowering amounts of mycotoxins (DON and the sum of T-2 and HT-2 toxins) and toxic inorganic elements (As, Cd, Ni, and Pb). The results showed an As content (in end products) similar to that obtained using semolina as raw material. In samples showing high organic contamination, the contamination rate detected in the more bran-enriched fractions ranged from 74% to 150% (DON) and from 119% to 151% (sum of T2 and HT-2 toxins) as compared to the micronised samples. Therefore, this technology may be useful for manufacturing unrefined products with reduced levels of organic and inorganic contaminants, minimising the health risk to consumers.

Caesium-133 Accumulation by Freshwater Macrophytes: Partitioning of Translocated Ions and Enzyme Activity in Plants and Microorganisms

The potential of aquatic plants to accumulate Cs may be of notable importance in the environmental monitoring of radioactive wastes. This study aimed to evaluate the accumulation of Cs-133 by freshwater macrophytes Bacopa amplexicaulis, Elodea densa, Ceratophyllum submersum, and Limnobium laevigantum after a 10-day incubation period with CsCl (1–1000 μM). The partitioning of Cs and other elements, including 21 metals, such as P, B, and As, was analyzed using inductively coupled plasma mass spectrometry combined with principal component analysis (PCA). The enzymatic activity of plant crude extracts and aquatic microorganisms was characterized. The transfer factor (TF) reached the highest values of 0.13 and 0.10 for C. submersum and L. laevigantum, respectively, at 1000 μM Cs. The TFs in the other sets were below 0.1. In the presence of Cs-133, there was a significant increase in dehydrogenase activity (p < 0.05) and a decrease in the activity of the Folin–Ciocalteu assay. A three-fold decrease in culturable microorganisms was found in plants with 1000 μM Cs. PCA analysis revealed the species-specific elemental distribution in plant biomass and the aquatic phase. A negative correlation between Na, Ca (2.0–2.5, PC1) and Mg, K, and P (−2, PC1) was found. Certain enzyme groups can serve as bioindicators of Cs pollution in aquatic ecosystems.

Microbiome-wide association studies between phyllosphere microbiota and ionome highlight the beneficial symbiosis of Lactococcus lactis in alleviating aluminium in cassava

The phyllosphere is one of the most abundant habitats for global microbiota. The ionome is the composition of mineral elements in plants. The correlation between phyllosphere microbiota and the ionome remains elusive in plants, especially in the most important tropical crop cassava. In this study, microbiome-wide association studies (MWASs) of thirty varieties were performed to reveal the association between phyllosphere microbiota and ionomic variations in cassava. Annotation of metagenomic species identified some species that were significantly correlated with ionomic variations in cassava. Among them, Lactococcus lactis abundance was negatively associated with leaf aluminium (Al) levels but positively related to leaf potassium (K) levels. Notably, both the reference and isolated L. lactis showed strong binding capacity to Al. Further bacterial transplantation of isolated L. lactis could significantly decrease endogenous Al levels but increase K levels in cassava, and it can also lead to increased citric acid and lactic acid levels as well as higher transcript levels of K uptake-related genes. Taken together, this study reveals the involvement of phyllosphere microbiota in ionomic variation in cassava, and the correlation between L. lactis abundance and Al and K levels provides novel insights into alleviating Al accumulation and promoting K uptake simultaneously.

Excess Zinc Supply Reduces Cadmium Uptake and Mitigates Cadmium Toxicity Effects on Chloroplast Structure, Oxidative Stress, and Photosystem II Photochemical Efficiency in Salvia sclarea Plants

Salvia sclarea L. is a Cd2+ tolerant medicinal herb with antifungal and antimicrobial properties cultivated for its pharmacological properties. However, accumulation of high Cd2+ content in its tissues increases the adverse health effects of Cd2+ in humans. Therefore, there is a serious demand to lower human Cd2+ intake. The purpose of our study was to evaluate the mitigative role of excess Zn2+ supply to Cd2+ uptake/translocation and toxicity in clary sage. Salvia plants were treated with excess Cd2+ (100 μM CdSO4) alone, and in combination with Zn2+ (900 μM ZnSO4), in modified Hoagland nutrient solution. The results demonstrate that S. sclarea plants exposed to Cd2+ toxicity accumulated a significant amount of Cd2+ in their tissues, with higher concentrations in roots than in leaves. Cadmium exposure enhanced total Zn2+ uptake but also decreased its translocation to leaves. The accumulated Cd2+ led to a substantial decrease in photosystem II (PSII) photochemistry and disrupted the chloroplast ultrastructure, which coincided with an increased lipid peroxidation. Zinc application decreased Cd2+ uptake and translocation to leaves, while it mitigated oxidative stress, restoring chloroplast ultrastructure. Excess Zn2+ ameliorated the adverse effects of Cd2+ on PSII photochemistry, increasing the fraction of energy used for photochemistry (ΦPSII) and restoring PSII redox state and maximum PSII efficiency (Fv/Fm), while decreasing excess excitation energy at PSII (EXC). We conclude that excess Zn2+ application eliminated the adverse effects of Cd2+ toxicity, reducing Cd2+ uptake and translocation and restoring chloroplast ultrastructure and PSII photochemical efficiency. Thus, excess Zn2+ application can be used as an important method for low Cd2+-accumulating crops, limiting Cd2+ entry into the food chain.

Calcium Oxide Nanoparticles Have the Role of Alleviating Arsenic Toxicity of Barley

Arsenic (As) contamination in agricultural soils has become a great threat to the sustainable development of agriculture and food safety. Although a lot of approaches have been proposed for dealing with soil As contamination, they are not practical in crop production due to high cost, time-taking, or operational complexity. The rapid development of nanotechnology appears to provide a novel solution to soil As contamination. This study investigated the roles of calcium oxide nanoparticles (CaO NPs) in alleviating As toxicity in two barley genotypes (LJZ and Pu-9) differing in As tolerance. The exposure of barley seedlings to As stress showed a significant reduction in plant growth, calcium and chlorophyll content (SPAD value), fluorescence efficiency (Fv/m), and a dramatic increase in the contents of reactive oxygen species (ROS), malondialdehyde (MDA) and As, with LJZ being more affected than Pu-9. The exogenous supply of CaO NPs notably alleviated the toxic effect caused by As in the two barley genotypes. Moreover, the expression of As transporter genes, that is, HvPHT1;1, HvPHT1;3, HvPHT1;4 and HvPHT1;6, was dramatically enhanced when barley seedlings were exposed to As stress and significantly reduced in the treatment of CaO NPs addition. It may be concluded that the roles of CaO NPs in alleviating As toxicity could be attributed to its enhancement of Ca uptake, ROS scavenging ability, and reduction of As uptake and transportation from roots to shoots.

Argon Plasma Treated Phosphatic Clays for Efficient Heavy Metal Pb(II) Immobilization

Phosphatic clays, one type of phosphorite industry wastes, could induce environmental issues and geological disasters when they are piled in the open air. Previous research demonstrated that phosphatic clays usually exhibit poor performance in heavy metal immobilization mostly due to low phosphate content. Thus, phosphatic clays could not be applied in practical heavy metal remediation without pretreatment. If the adsorption performance of phosphatic clays could be improved, employing phosphatic clays for heavy metal immobilization may act as an eco-friendly, economic way to not only reutilize phosphorite industry wastes but also remedy environmental heavy metal pollution at the same time. In this study, we propose an argon plasma treatment approach to remarkably improve the effectiveness of phosphatic clay performances in heavy metal immobilization. The optimal Pb(II) sorption capacity of 66.7 mg g^-1 can be obtained at pH 6 and 25°C by using 15-min argon plasma treated phosphatic clays, which is two times as large as those of the untreated phosphatic clays and almost reaches those of raw apatite minerals. Moreover, the Pb(II) desorption ratios of Pb(II)-adsorbed phosphatic clays are also reduced by 30%-60% at different pH conditions. Therefore, applying argon-plasma technique to transform waste phosphatic clays into efficient heavy-metal sorbents is a promising road to phosphorite waste reclamation and environmental remediation.

Effects of soil cadmium exposure on physio-ecological characteristics of Bletilla striata

Bletilla striata (Thunb.) Reichb.f. has shown rather extraordinary medicinal and economic value in recent years. However, the artificial cultivation of B. striata faces quite a lot of obstacles, especially the quality degradation and heavy metal pollution problems. Cadmium (Cd) in particular, is reported to generally exceed the standard in the artificial cultivation of B. striata. So far, little attention has been paid to analyze the effects of heavy metals on the growth and the medicinal treatment efficacy of B. striata. Herein, we investigate the physio-ecological response of B. striata under gradient Cd concentration treatment: Control (0.285 mg kg^-1); Tr-1 (0.655 mg kg^-1); Tr-2 (1.285 mg kg^-1); Tr-3 (7.675 mg kg^-1); Tr-4 (54.885 mg kg^-1), so as to provide a reference for the study of the Cd response regulation on B. striata. In this work, we examined the biomass, total carbon, total nitrogen, and content of B. striata polysaccharides (BSP, the functional component of B. striata), as well as the absorption proportion of Cd in B. striata. Based on the preliminary research, ecological risk assessment and human health risk assessment were allocated. Experiments were conducted in two batches (2018 and 2019, sampling in the same season) with the following findings: (1) The biomass showed no pronounced differences between the treatments or the sampling dates, only reached significant decrease at 54.885 mg kg^-1 (Tr-4) soil Cd concentration in 2019; (2) The total carbon of B. striata under Cd treatment was in line with the Hormesis effect and reached a peak at 0.655 mg kg^-1 (Tr-1) soil Cd concentration; (3) The total nitrogen content was generally promoted under Cd treatment with the highest content at 1.225 mg kg^-1 (Tr-2); (4) The total BSP content in two sampling years are both sorted in decreasing order: Tr-4 < Tr-3 < Tr-2 < Tr-1 < Control; (5) The Cd content in Bletillae Rhizoma (tuber of B. striata) under 0.655 mg kg^-1 soil Cd treatment was within the threshold stipulated in Chinese Pharmacopoeia in 2018 batch and in 2019 batch, only the control group was qualified with a safe plantation limit of Cd. The results of ecological risk assessment showed moderate toxic risk under Tr-1 (0.655 mg Cd kg^-1) and the human health risk assessment indicated negligible toxic effects on human health. Overall, the soil Cd concentration should be lower than 0.655 mg kg^-1, if safe cultivation, medicinal effect of B. striata and human health risk are taken into consideration.

Anthocyanin-mediated arsenic tolerance in plants

Plants detoxify toxic metal(loid)s by accumulating diverse metabolites. Beside scavenging excess reactive oxygen species (ROS) induced by metal(loid)s, some metabolites chelate metal(loid) ions. Classically, thiol-containing compounds, especially glutathione (GSH) and phytochelatins (PCs) are thought to be the major chelators that conjugate with metal(loid)s in the cytoplasm followed by transport and sequestration in the vacuole. In addition to this classical detoxification pathway, a role for secondary metabolites in metal(loid) detoxification has recently emerged. In particular, anthocyanins, a kind of flavonoids with ROS scavenging potential, contribute to enhanced arsenic tolerance in several plant species. Evidence is accumulating that, in analogy to GSH and PCs, anthocyanins may conjugate with arsenic followed by vacuolar sequestration in the detoxification event. Exogenous application or endogenous accumulation of anthocyanins enhances arsenic tolerance, leading to improved plant growth and productivity. The application of some plant hormones and signaling molecules stimulates endogenous anthocyanin synthesis which confers tolerance to arsenic stress. Anthocyanin biosynthesis is transcriptionally regulated by several transcription factors, including myeloblastosis (MYBs). The light-regulated transcription factor elongated hypocotyl 5 (HY5) also affects anthocyanin biosynthesis, but its role in arsenic tolerance remains elusive. Here, we review the mechanism of arsenic detoxification in plants and the potential role of anthocyanins in arsenic tolerance beyond the classical points of view. Our analysis proposes that anthocyanin manipulation in crop plants may ensure sustainable crop yield and food safety in the marginal lands prone to arsenic pollution.

Novel Quantitative Trait Loci for Grain Cadmium Content Identified in Hard White Spring Wheat

Cadmium (Cd) is a heavy metal that can cause a variety of adverse effects on human health, including cancer. Wheat comprises approximately 20% of the human diet worldwide; therefore, reducing the concentrations of Cd in wheat grain will have significant impacts on the intake of Cd in food products. The tests for measuring the Cd content in grain are costly, and the content is affected significantly by soil pH. To facilitate breeding for low Cd content, this study sought to identify quantitative trait loci (QTL) and associated molecular markers that can be used in molecular breeding. One spring wheat population of 181 doubled haploid lines (DHLs), which was derived from a cross between two hard white spring wheat cultivars "UI Platinum" (UIP) and "LCS Star" (LCS), was assessed for the Cd content in grain in multiple field trials in Southeast Idaho, United States. Three major QTL regions, namely, QCd.uia2-5B, QCd.uia2-7B, and QCd.uia2-7D, were identified on chromosomes 5B, 7B, and 7D, respectively. All genes in these three QTL regions were identified from the NCBI database. However, three genes related to the uptake and transport of Cd were used in the candidate gene analysis. The sequences of TraesCS5B02G388000 (TaHMA3) in the QCd.uia2-5B region and TraesCS7B02G320900 (TaHMA2) and TraesCS7B02G322900 (TaMSRMK3) in the QCd.uia2-7B region were compared between UIP and LCS. TaHMA2 on 7B is proposed for the first time as a candidate gene for grain Cd content in wheat. A KASP marker associated with this gene was developed and it will be further validated in near-isogenic lines via a gene-editing system in future studies.

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.

Knockout of FER decreases cadmium concentration in roots of Arabidopsis thaliana by inhibiting the pathway related to iron uptake

Identifying the genes that affect cadmium (Cd) accumulation in plants is a prerequisite for minimizing dietary Cd uptake from contaminated edible parts of plants by genetic engineering. This study showed that Cd stress inhibited the expression of FERONIA (FER) gene in the roots of wild-type Arabidopsis. Knockout of FER in fer-4 mutants downregulated the Cd-induced expression of several genes related to iron (Fe) uptake, including IRT1, bHLH38, NRAMP1, NRAMP3, FRO2 andFIT. In addition, the Cd concentration in fer-4 mutant roots reduced to approximately half of that in the wild-type seedlings. As a result, the Cd tolerance of fer-4 was higher. Furthermore, increased Fe supplementation had little effect on the Cd tolerance of fer-4 mutants, but clearly improved the Cd tolerance of wild-type seedlings, showing that the alleviation of Cd toxicity by Fe depends on the action of FER. Taken together, the findings demonstrate that the knockout of FER might provide a strategy to reduce Cd contamination and improve the Cd tolerance in plants by regulating the pathways related to Fe uptake.

Short-term effects of cadmium on leaf growth and nutrient transport in rice plants

Consumption of rice grains contaminated with high concentrations of cadmium (Cd) can cause serious long-term health problems. Moreover, even low Cd concentrations present in the soil can result in the abatement of plant performance, leading to lower grain yield. Studies examining the molecular basis of plant defense against Cd-induced oxidative stress could pave the way in creating superior rice varieties that display an optimal antioxidative defense system to cope with Cd toxicity. In this study, we showed that after one day of Cd exposure, hydroponically grown rice plants exhibited adverse shoot biomass and leaf growth effects. Cadmium accumulates especially in the roots and the leaf meristematic region, leading to a disturbance of manganese homeostasis in both the roots and leaves. The leaf growth zone showed an increased amount of lipid peroxidation indicating that Cd exposure disturbed the oxidative balance. We propose that an increased expression of genes related to the glutathione metabolism such as glutathione synthetase 2, glutathione reductase and phytochelatin synthase 2, rather than genes encoding for antioxidant enzymes, is important in combating early Cd toxicity within the leaves of rice plants. Furthermore, the upregulation of two RESPIRATORY BURST OXIDASE HOMOLOG genes together with a Cd concentration-dependent increase of abscisic acid might cause stomatal closure or cell wall modification, potentially leading to the observed leaf growth reduction. Whereas abscisic acid was also elevated at long term exposure, a decrease of the growth hormone auxin might further contribute to growth inhibition and concomitantly, an increase in salicylic acid might stimulate the activity of antioxidative enzymes after a longer period of Cd exposure. In conclusion, a clear interplay between phytohormones and the oxidative challenge affect plant growth and acclimation during exposure to Cd stress.

Are Grasses Really Useful for the Phytoremediation of Potentially Toxic Trace Elements? A Review

The pollution of soil, water, and air by potentially toxic trace elements poses risks to environmental and human health. For this reason, many chemical, physical, and biological processes of remediation have been developed to reduce the (available) trace element concentrations in the environment. Among those technologies, phytoremediation is an environmentally friendly in situ and cost-effective approach to remediate sites with low-to-moderate pollution with trace elements. However, not all species have the potential to be used for phytoremediation of trace element-polluted sites due to their morpho-physiological characteristics and low tolerance to toxicity induced by the trace elements. Grasses are prospective candidates due to their high biomass yields, fast growth, adaptations to infertile soils, and successive shoot regrowth after harvest. A large number of studies evaluating the processes related to the uptake, transport, accumulation, and toxicity of trace elements in grasses assessed for phytoremediation have been conducted. The aim of this review is (i) to synthesize the available information on the mechanisms involved in uptake, transport, accumulation, toxicity, and tolerance to trace elements in grasses; (ii) to identify suitable grasses for trace element phytoextraction, phytostabilization, and phytofiltration; (iii) to describe the main strategies used to improve trace element phytoremediation efficiency by grasses; and (iv) to point out the advantages, disadvantages, and perspectives for the use of grasses for phytoremediation of trace element-polluted soils.

Phytohormones Producing Acinetobacter bouvetii P1 Mitigates Chromate Stress in Sunflower by Provoking Host Antioxidant Response

Different physical and chemical techniques are used for the decontamination of Cr+6 contaminated sites. The techniques are expensive, laborious, and time-consuming. However, remediation of Cr+6 by microbes is viable, efficient, and cost-effective. In this context, plant growth-promoting rhizobacteria Acinetobacter bouvetii P1 isolated from the industrial zone was tested for its role in relieving Cr+6 induced oxidative stress in sunflower. At the elevated Cr+6 levels and in the absence of P1, the growth of the sunflower plants was inhibited. In contrast, the selected strain P1 restored the sunflower growth under Cr+6 through plant growth-promoting interactions. Specifically, P1 biotransformed the Cr+6 into a stable and less toxic Cr+3 form, thus avoiding the possibility of phytotoxicity. On the one hand, the P1 strengthened the host antioxidant system by triggering higher production of enzymatic antioxidants, including catalases, ascorbate peroxidase, superoxide dismutase, and peroxidase. Similarly, P1 also promoted higher production of nonenzymatic antioxidants, such as flavonoids, phenolics, proline, and glutathione. Apart from the bioremediation, P1 solubilized phosphate and produced indole acetic acid, gibberellic acid, and salicylic acid. The production of phytohormones not only helped the host plant growth but also mitigated the harsh condition posed by the elevated levels of Cr+6. The findings mentioned above suggest that P1 may serve as an excellent phyto-stimulant and bio-remediator in a heavy metal-contaminated environment.

Mutation in OsFWL7 Affects Cadmium and Micronutrient Metal Accumulation in Rice

Micronutrient metals, such as Mn, Cu, Fe, and Zn, are essential heavy metals for plant growth and development, while Cd is a nonessential heavy metal that is highly toxic to both plants and humans. Our understanding of the molecular mechanisms underlying Cd and micronutrient metal accumulation in plants remains incomplete. Here, we show that OsFWL7, an FW2.2-like (FWL) family gene in Oryza sativa, is preferentially expressed in the root and encodes a protein localized to the cell membrane. The osfwl7 mutation reduces both the uptake and the root-to-shoot translocation of Cd in rice plants. Additionally, the accumulation of micronutrient metals, including Mn, Cu, and Fe, was lower in osfwl7 mutants than in the wildtype plants under normal growth conditions. Moreover, the osfwl7 mutation affects the expression of several heavy metal transporter genes. Protein interaction analyses reveal that rice FWL proteins interact with themselves and one another, and with several membrane microdomain marker proteins. Our results suggest that OsFWL7 is involved in Cd and micronutrient metal accumulation in rice. Additionally, rice FWL proteins may form oligomers and some of them may be located in membrane microdomains.