Toxic metal accumulation, responses to exposure and mechanisms of tolerance in plants

Blue Light Enhances Cadmium Tolerance of the Aquatic Macrophyte Potamogeton crispus

Cadmium (Cd) is highly toxic and widely distributed in aquatic systems due to its high solubility and mobility in water, which can severely inhibit the survival of aquatic macrophytes. The phytotoxicity of Cd depends on environmental factors; however, it remains unclear whether and how light quality affects its toxicity on aquatic macrophytes. In this study, we investigated the effects of Cd on aquatic macrophytes Potamogeton crispus under different light qualities (white, blue, and red light). We evaluated morphological and photo-physiological traits, as well as the cellular antioxidant defense system. Our findings indicate that P. crispus under Cd stress showed notable damage in leaf morphology, decreased photosynthetic efficiency, inhibited HCO₃^- uptake, and reduced antioxidant enzyme activities, as well as oxidative damage indicated by MDA accumulation and superoxide (O₂^-) overproduction. However, compared with white or red light under Cd stress, blue light reduced structural damage and oxidative stress caused by Cd while increasing pigment synthesis and photosynthetic efficiency, as well as increasing ascorbate peroxidase (APX) activity. In conclusion, the changes induced by blue light in P. crispus's photosynthesis and antioxidant system strengthen its tolerance to Cd. Further research on signal transmission in relation to light quality in Cd-exposed aquatic plants is still needed.

Expression of TaNCL2-A ameliorates cadmium toxicity by increasing calcium and enzymatic antioxidants activities in arabidopsis

Cadmium (Cd) is a heavy metal that occurs naturally in the environment and is toxic to both animals and plants. The impact of Cd toxicity is shown to be reduced by the exogenous application of calcium (Ca) in crop plants. The sodium/calcium exchanger-like (NCL) protein is involved in Ca enrichment in the cytoplasm by transporting it from the vacuole in the exchange of cytosolic sodium (Na). However, it has not been utilized to ameliorate the Cd toxicity, to date. An elevated expression of TaNCL2-A gene in the root and shoot tissues of bread wheat seedlings, and a higher growth rate of recombinant yeast cells, suggested its role in Cd stress response. The TaNCL2-A expressing transgenic Arabidopsis lines exhibited significant Cd tolerance with increased Ca (∼10-fold) accumulation. The proline content and antioxidant enzymes activities were increased while oxidative stress-related molecules such as H₂O₂ and MDA were reduced in the transgenic lines. In addition, the growth and yield parameters of transgenic lines such as seed germination rate, root length, leaf biomass, leaf area index, rosette diameter, leaf length and width, and silique count, along with various physiological indicators like chlorophyll, carotenoid, and relative water contents were also improved in comparison to the control plants. Further, the transgenic lines exhibited significant salinity and osmotic stress tolerance, as well. Taken together, these results suggested that the TaNCL2-A could mitigate Cd toxicity along with salinity and osmotic stress. This gene may also be utilized for phytoremediation and Cd sequestration in future studies.

Silicon in Plants: Alleviation of Metal(loid) Toxicity and Consequential Perspectives for Phytoremediation

For the majority of higher plants, silicon (Si) is considered a beneficial element because of the various favorable effects of Si accumulation in plants that have been revealed, including the alleviation of metal(loid) toxicity. The accumulation of non-degradable metal(loid)s in the environment strongly increased in the last decades by intensified industrial and agricultural production with negative consequences for the environment and human health. Phytoremediation, i.e., the use of plants to extract and remove elemental pollutants from contaminated soils, has been commonly used for the restoration of metal(loid)-contaminated sites. In our viewpoint article, we briefly summarize the current knowledge of Si-mediated alleviation of metal(loid) toxicity in plants and the potential role of Si in the phytoremediation of soils contaminated with metal(loid)s. In this context, a special focus is on metal(loid) accumulation in (soil) phytoliths, i.e., relatively stable silica structures formed in plants. The accumulation of metal(loid)s in phytoliths might offer a promising pathway for the long-term sequestration of metal(loid)s in soils. As specific phytoliths might also represent an important carbon sink in soils, phytoliths might be a silver bullet in the mitigation of global change. Thus, the time is now to combine Si/phytolith and phytoremediation research. This will help us to merge the positive effects of Si accumulation in plants with the advantages of phytoremediation, which represents an economically feasible and environmentally friendly way to restore metal(loid)-contaminated sites.

Transcriptome analysis reveals different mechanisms of selenite and selenate regulation of cadmium translocation in Brassica rapa

Selenium (Se) inhibits cadmium (Cd) root-to-shoot translocation and accumulation in the shoots of pak choi; however, the mechanism by which Se regulates Cd retention in roots is still poorly understood. A time-dependent hydroponic experiment was conducted to compare the effects of selenite and selenate on Cd translocation and retention in the roots. The underlying mechanisms were investigated regarding Se biotransformation and metal transportation in roots using HPLC and transcriptome analyses. Selenite showed reducing effects on Cd translocation and accumulation in shoots earlier than selenate. Selenite is mainly biotransformed into selenomethionine (80% of total Se in roots) at 72 h, while SeO42- was the dominant species in the selenate treatments (68% in shoots). Selenite up-regulated genes involved in the biosynthesis of lignin, suberin, and phytochelatins and those involved in stress signaling, thereby helping to retain Cd in the roots, whereas essentially, selenate had opposite effects and impaired the symplastic and apoplastic retention of Cd. These results suggest that cell-wall reinforcement and Cd retention in roots may be the key processes by which Se regulates Cd accumulation, and faster biotransformation into organic seleno-compounds could lead to earlier effects.

Response and Tolerance of Macleaya cordata to Excess Zinc Based on Transcriptome and Proteome Patterns

Macleaya cordata is a dominant plant of mine tailings and a zinc (Zn) accumulator with high Zn tolerance. In this study, M. cordata seedlings cultured in Hoagland solution were treated with 200 μmol·L^-1 of Zn for 1 day or 7 days, and then, their leaves were taken for a comparative analysis of the transcriptomes and proteomes between the leaves of the control and Zn treatments. Differentially expressed genes included those that were iron (Fe)-deficiency-induced, such as vacuolar iron transporter VIT, ABC transporter ABCI17 and ferric reduction oxidase FRO. Those genes were significantly upregulated by Zn and could be responsible for Zn transport in the leaves of M. cordata. Differentially expressed proteins, such as chlorophyll a/b-binding proteins, ATP-dependent protease, and vacuolar-type ATPase located on the tonoplast, were significantly upregulated by Zn and, thus, could be important in chlorophyll biosynthesis and cytoplasm pH stabilization. Moreover, the changes in Zn accumulation, the production of hydrogen peroxide, and the numbers of mesophyll cells in the leaves of M. cordata were consistent with the expression of the genes and proteins. Thus, the proteins involved in the homeostasis of Zn and Fe are hypothesized to be the keys to the tolerance and accumulation of Zn in M. cordata. Such mechanisms in M. cordata can suggest novel approaches to genetically engineering and biofortifying crops.

Investigation of the role of TmMYB16/123 and their targets (TmMTP1/11) in the tolerance of Taxus media to cadmium

The toxicity and stress caused by heavy metal contamination has become an important constraint to the growth and flourishing of trees. In particular, species belonging to the genus Taxus, which are the only natural source for the anti-tumor medicine paclitaxel, are known to be highly sensitive to environmental changes. To investigate the response of Taxus spp. to heavy metal stress, we analyzed the transcriptomic profiles of Taxus media trees exposed to cadmium (Cd2+). In total, six putative genes from the metal tolerance protein (MTP) family were identified in T. media, including two Cd2+ stress inducible TMP genes (TmMTP1, TmMTP11 and Taxus media). Secondary structure analyses predicted that TmMTP1 and TmMTP11, which are members of the Zn-CDF and Mn-CDF subfamily proteins, respectively, contained six and four classic transmembrane domains, respectively. The introduction of TmMTP1/11 into the ∆ycf1 yeast cadmium-sensitive mutant strain showed that TmMTP1/11 might regulate the accumulation of Cd2+ to yeast cells. To screen the upstream regulators, partial promoter sequences of the TmMTP1/11 genes were isolated using the chromosome walking method. Several myeloblastosis (MYB) recognition elements were identified in the promoters of these genes. Furthermore, two Cd2+-induced R2R3-MYB TFs, TmMYB16 and TmMYB123, were identified. Both in vitro and in vivo assays confirmed that TmMTB16/123 play a role in Cd2+ tolerance by activating and repressing the expression of TmMTP1/11 genes. The present study elucidated new regulatory mechanisms underlying the response to Cd stress and can contribute to the breeding of Taxus species with high environmental adaptability.

Regulatory mechanisms of sulfur metabolism affecting tolerance and accumulation of toxic trace metals and metalloids in plants

Soil contamination with trace metals and metalloids can cause toxicity to plants and threaten food safety and human health. Plants have evolved sophisticated mechanisms to cope with excess trace metals and metalloids in soils, including chelation and vacuolar sequestration. Sulfur-containing compounds, such as glutathione and phytochelatins, play a crucial role in their detoxification, and sulfur uptake and assimilation are regulated in response to the stress of toxic trace metals and metalloids. This review focuses on the multi-level connections between sulfur homeostasis in plants and responses to such stresses, especially those imposed by arsenic and cadmium. We consider recent progress in understanding the regulation of biosynthesis of glutathione and phytochelatins and of the sensing mechanism of sulfur homeostasis for tolerance of trace metals and metalloids in plants. We also discuss the roles of glutathione and phytochelatins in controlling the accumulation and distribution of arsenic and cadmium in plants, and possible strategies for manipulating sulfur metabolism to limit their accumulation in food crops.

Effects of exogenous calcium on cadmium accumulation in amaranth

Calcium oxalate (CaOx) crystals in plants act as a sink for excess Ca and play an essential role in detoxifying heavy metals (HMs). However, the mechanism and related influencing factors remain unclear. Amaranth (Amaranthus tricolor L.) is a common edible vegetable rich in CaOx and a potential Cd hyperaccumulation species. In this study, the hydroponic experiment was carried out to investigate the effect of exogenous Ca concentrations on Cd uptake by amaranth. The results showed that either insufficient or excess Ca supply inhibited amaranth growth, while the Cd bioconcentration factor (BCF) increased with Ca concentration. Meanwhile, the sequence extraction results demonstrated that Cd mainly accumulated as pectate and protein-bound species (NaCl extracted) in the root and stem, compared to pectate, protein, and phosphate-bound (acetic acid extractable) species in the leaf. Correlation analysis showed that the concentration of exogenous Ca was positively correlated with amaranth-produced CaOx crystals but negatively correlated with insoluble oxalate-bound Cd in the leaf. However, since the accumulated insoluble oxalate-bound Cd was relatively low, Cd detoxification via the CaOx pathway in amaranth is limited.

New Insight into the Function of Dopamine (DA) during Cd Stress in Duckweed (Lemna turionifera 5511)

Dopamine (DA), a kind of neurotransmitter in animals, has been proven to cause a positive influence on plants during abiotic stress. In the present study, the function of DA on plants under cadmium (Cd) stress was revealed. The yellowing of duckweed leaves under Cd stress could be alleviated by an exogenous DA (10/20/50/100/200 μM) supplement, and 50 μM was the optimal concentration to resist Cd stress by reducing root breakage, restoring photosynthesis and chlorophyll content. In addition, 24 h DA treatment increased Cd content by 1.3 times in duckweed under Cd stress through promoting the influx of Cd2+. Furthermore, the gene expression changes study showed that photosynthesis-related genes were up-regulated by DA addition under Cd stress. Additionally, the mechanisms of DA-induced Cd detoxification and accumulation were also investigated; some critical genes, such as vacuolar iron transporter 1 (VIT1), multidrug resistance-associated protein (MRP) and Rubisco, were significantly up-regulated with DA addition under Cd stress. An increase in intracellular Ca2+ content and a decrease in Ca2+ efflux induced by DA under Cd stress were observed, as well as synchrony with changes in the expression of cyclic nucleotide-gated ion channel 2 (CNGC2), predicting that, in plants, CNGC2 may be an upstream target for DA action and trigger the change of intracellular Ca2+ signal. Our results demonstrate that DA supplementation can improve Cd resistance by enhancing duckweed photosynthesis, changing intracellular Ca2+ signaling, and enhancing Cd detoxification and accumulation. Interestingly, we found that exposure to Cd reduced endogenous DA content, which is the result of a blocked shikimate acid pathway and decreased expression of the tyrosine aminotransferase (TAT) gene. The function of DA in Cd stress offers a new insight into the application and study of DA to Cd phytoremediation in aquatic systems.

Impacts of atmospheric copper and cadmium deposition on the metal accumulation of camphor leaves and rings around a large smelter

The atmospheric deposition of copper (Cu) and cadmium (Cd) was monitored in eight sites around a Cu smelter with similar distance to verify whether tree leaf and ring can be used as bio-indicators to track spatial pollution record. Results showed that total atmospheric deposition of Cu (103-1215 mg/m²/year) and Cd (3.57-11.2 mg/m²/year) were 4.73-66.6 and 3.15-12.2 times higher than those in background site (164 mg/m²/year and 0.93 mg/m²/year). The frequencies of wind directions significantly influenced the atmospheric deposition of Cu and Cd, and the highest atmospheric deposition of Cu and Cd were at the prevalent northeastern wind (JN), and low frequency south (WJ) and north (SW) winds for the lowest deposition fluxes. Since the bioavailability of Cd was higher than that of Cu, the atmospheric deposition of Cd was more easily adsorbed by tree leaf and ring, resulting in only significant relation between atmospheric Cd deposition and Cinnamomum camphora leaves and tree ring Cd. Although tree rings cannot correctly record the atmospheric Cu and Cd deposition, higher concentrations in the indigenous tree rings than the transplanted tree rings suggested that tree rings can reflect to some extent the variations of atmospheric deposition. Generally, spatial pollution of atmospheric deposition of heavy metals cannot reflect the distribution of soil total and available metals around the smelter, and only camphor leaf and tree ring can bio-indicate Cd deposition. A major implication of these findings is that leaf and tree ring can serve for biomonitoring purposes to assess the spatial distribution of atmospheric deposition metal with high bioavailability around a pollution source with similar distance.

Physiological and molecular mechanisms of medicinal plants in response to cadmium stress: Current status and future perspective

Medicinal plants have a wide range of uses worldwide. However, the quality of medicinal plants is affected by severe cadmium pollution. Cadmium can reduce photosynthetic capacity, lead to plant growth retardation and oxidative stress, and affect secondary metabolism. Medicinal plants have complex mechanisms to cope with cadmium stress. On the one hand, an antioxidant system can effectively scavenge excess reactive oxygen species produced by cadmium stress. On the other hand, cadmium chelates are formed by chelating peptides and then sequestered through vacuolar compartmentalization. Cadmium has no specific transporter in plants and is generally transferred to plant tissues through competition for the transporters of divalent metal ions, such as zinc, iron, and manganese. In recent years, progress has been achieved in exploring the physiological mechanisms by which medicinal plants responding to cadmium stress. The exogenous regulation of cadmium accumulation in medicinal plants has been studied, and the aim is reducing the toxicity of cadmium. However, research into molecular mechanisms is still lagging. In this paper, we review the physiological and molecular mechanisms and regulatory networks of medicinal plants exposed to cadmium, providing a reference for the study on the responses of medicinal plants to cadmium stress.

Transfer and transformation characteristics of Zn and Cd in soil-rotation plant (Brassica napus L and Oryza sativa L) system and its influencing factors

Rice-rape rotation is a widely practiced cropping system in China. However, changes in soil properties and management could change the bioavailability of Cd, In order to explore the occurrence state, transportation and transformation characteristics of heavy metals Cd and Zn in rice-rape rotation system in Guizhou karst area with high background value of Cd. In the karst rice-rape rotation area, the physical and chemical properties of soil, chemical specifications and activities of Cd and Zn at different soil depths and during various crop growth stages, and the bioaccumulation of Cd and Zn in different tissues of rice and rape were studied by field experiment and laboratory analysis. The bioaccumulation of Cd and Zn and the effects of physical and chemical soil properties on the activities and bioavailabilities of Cd and Zn during rice-rape rotation were explored. The findings revealed that soil particle size, composition, pH, redox potential, soil organic matter, and Cd and Zn contents varied dramatically, especially in deep soils. The physical and chemical properties of the deep and surface soils were significantly related to the bioaccumulation of Cd and Zn. Cd and Zn are activated during crop rotation. Cd was easier to be enriched in rice, while Zn was easier to be enriched in rape. The correlation between Cd and Zn contents in Brassica campestris L and their enrichment abilities were not significant, but that in Oryza sativa L were significant. During rice-rape rotation, the chemical speciations and activities of Cd and Zn changed with the changes of soil properties and waterlogging environment. This study had important basic guiding significance for the evaluation, prevention and control of heavy metal pollution, and improving soil quality in different rotation systems in karst areas, and was conducive to promoting the safe production of rape and rice.

The Potential of CRISPR/Cas Technology to Enhance Crop Performance on Adverse Soil Conditions

Worldwide food security is under threat in the actual scenery of global climate change because the major staple food crops are not adapted to hostile climatic and soil conditions. Significant efforts have been performed to maintain the actual yield of crops, using traditional breeding and innovative molecular techniques to assist them. However, additional strategies are necessary to achieve the future food demand. Clustered regularly interspaced short palindromic repeat/CRISPR-associated protein (CRISPR/Cas) technology, as well as its variants, have emerged as alternatives to transgenic plant breeding. This novelty has helped to accelerate the necessary modifications in major crops to confront the impact of abiotic stress on agriculture systems. This review summarizes the current advances in CRISPR/Cas applications in crops to deal with the main hostile soil conditions, such as drought, flooding and waterlogging, salinity, heavy metals, and nutrient deficiencies. In addition, the potential of extremophytes as a reservoir of new molecular mechanisms for abiotic stress tolerance, as well as their orthologue identification and edition in crops, is shown. Moreover, the future challenges and prospects related to CRISPR/Cas technology issues, legal regulations, and customer acceptance will be discussed.

Overexpression of Sedum SpHMA2, SpHMA3 and SpNramp6 in Brassica napus increases multiple heavy metals accumulation for phytoextraction

Phytoextraction is an environmentally friendly phytoremediation technology that can reduce the total amount of heavy metals (HMs) in the soil. Hyperaccumulators or hyperaccumulating transgenic plants with biomass are important biomaterials for phytoextraction. In this study, we show that three different HM transporters from the hyperaccumulator Sedum pumbizincicola, SpHMA2, SpHMA3, and SpNramp6, possess Cd transport. These three transporters are located at the plasma membrane, tonoplast, and plasma membrane, respectively. Their transcripts could be strongly stimulated by multiple HMs treatments. To create potential biomaterials for phytoextraction, we overexpressed the three single genes and two combining genes, SpHMA2&SpHMA3 and SpHMA2&SpNramp6, in rapes having high biomass and environmental adaptability, and found that the aerial parts of the SpHMA2-OE3 and SpHMA2&SpNramp6-OE4 lines accumulated more Cd from single Cd-contaminated soil because SpNramp6 transports Cd from root cells to the xylem and SpHMA2 from the stems to the leaves. However, the accumulation of each HM in the aerial parts of all selected transgenic rapes was strengthened in multiple HMs-contaminated soils, probably due to the synergistic transport. The HMs residuals in the soil after the transgenic plant phytoremediation were also greatly reduced. These results provide effective solutions for phytoextraction in both Cd and multiple HMs-contaminated soils.

Mercury accumulation potential of aquatic plant species in West Dongting Lake, China

West Dongting Lake is a protected wetland with the potential for high levels of mercury release via wastewater and deposition from industry and agriculture during the last decade. To find out the ability of various plant species to accumulate mercury pollutants from soil and water, nine sites were studied in the downstream direction of the flow of the Yuan and Li Rivers, which are tributaries of the Yellow River flowing into West Dongting Lake, where mercury levels arere high in soil and plant tissues. The total mercury (THg) concentration in wetland soil was 0.078-1.659 mg/kg, which varied along the gradient of water flow along the river. According to canonical correspondence analysis and correlation analysis, there was a positive correlation between the soil THg concentration and the soil moisture in West Dongting Lake. There is high heterogeneity in the spatial distribution of soil THg concentration in West Dongting Lake, which may be related to the spatial heterogeneity of the soil moisture. Some plant species had higher THg concentrations in aboveground tissues (translocation factor >1), but none of these plant species fit the criteria as hyperaccumulators of mercury. And some species of the same ecological type (e.g., emergent, submergent, floating-leaved) exhibited very different strategies for mercury uptake. The concentrations of mercury in these species were lower than in other studies but these had relatively higher translocation factors. To phytoremediate soil mercury in West Dongting Lake, the regular harvest of plants could help remove mercury from soil and plant tissue.

Exogenous ATP triggers antioxidant defense system and alleviates Cd toxicity in maize seedlings

The role of exogenous adenosine 5'-triphosphate (ATP) in the regulation of antioxidant response in plants under heavy metal stress is unclear. Here, we investigated the effects of exogenous ATP application on plant growth, antioxidant response, and Cd accumulation in maize seedlings. Treatment with 0.1 mM CdCl₂ moderately reduced dry weight, decreased chlorophyll content, impaired photosynthesis, and increased lipid peroxidation in maize seedlings compared with controls. However, toxicity due to Cd was alleviated after 10-200 µM ATP treatment. Subsequently, the activity of Cd-regulated antioxidant enzymes, antioxidant metabolite accumulation, and total antioxidant capacity were drastically enhanced after 50 µM ATP treatment. Similar patterns were observed in the ADP-treated group but not in the AMP-treated group under Cd stress. However, the ATP-induced elevation in antioxidant defense ability was decreased by the inhibition of NADPH oxidase (NOX). ATP-induced elevation in NOX activity and H₂O₂ production was partly reversed by the inhibition of NOX in maize seedlings under Cd stress. Furthermore, ATP promoted Cd accumulation in the roots and shoots of maize seedlings. However, the ATP-induced increase in Cd accumulation was partly abolished by the inhibition of NOX. To our knowledge, this is the first report on the role and mechanism of exogenous ATP in regulating plant growth, antioxidant response, and heavy metal phytoextraction. The study provides a new method based on exogenous ATP for enhancing heavy metal tolerance in plants.

Regulatory module WRKY33-ATL31-IRT1 mediates cadmium tolerance in Arabidopsis

Cadmium (Cd) is one of the most dangerous environmental pollutants among heavy metals, and threatens food safety and human health by accumulating in plant sink tissues. Here, we report a novel regulatory cascade that profoundly influences Cd tolerance in Arabidopsis. Phenotypic analysis showed that an insertional knockdown mutation at the Arabidopsis Tóxicos en Levadura 31 (ATL31) locus resulted in hypersensitivity to Cd stress, most likely due to a significant increase in Cd accumulation. Consistently, ATL31-overexpressing lines exhibited enhanced Cd stress tolerance and reduced Cd accumulation. Further, IRON-REGULATED TRANSPORTER 1 (IRT1) was identified, and yeast two-hybrid, co-immunoprecipitation and bimolecular fluorescence complementation assays demonstrated its interaction with ATL31. Biochemical, molecular, and genetic analyses showed that IRT1 is targeted by ATL31 for ubiquitin-conjugated degradation in response to Cd stress. Intriguingly, transcription of ATL31 was strongly induced by Cd stress. In addition, transgenic and molecular analyses showed that WRKY33 directly activated the transcription of ATL31 in response to Cd stress and positively regulated Cd tolerance. Genetic analysis indicated that ATL31 acts upstream of IRT1 and downstream of WRKY33 to regulate Cd tolerance. Our study revealed that the WRKY33-ATL31-IRT1 module plays a crucial role in timely blocking Cd absorption to prevent metal toxicity in Arabidopsis.

Cadmium, Lead, Chronic Physiological Stress and Endometrial Cancer: How Environmental Policy Can Alter the Exposure of At-Risk Women in the United States

The health and life outcomes of individuals are intertwined with the context in which they grow and live. The totality of exposures one experiences affects health in the short term and throughout the life course. Environmental exposure to multiple contaminants can increase stress levels in individuals and neighborhoods with psychosocial stressors such as crime, drug and alcohol misuse, and violence also taking a toll on individual and neighborhood wellbeing. In addition, the availability, organization, and quality of local institutions and infrastructure all affect health in the short and long term. The role of these factors in endometrial cancer will be explored in this paper. In addition, policy implications regarding lead, chronic physiological stress, and endometrial cancer will be explored to ascertain the impact of these factors on at-risk women.

Effects of α-Fe2O3 nanoparticles and biochar on plant growth and fruit quality of muskmelon under cadmium stress

Cadmium pollution in farmland has become a global environmental problem, threatening ecological security and human health. Biochar is effective in remediation of soil pollution. However, high concentrations of biochar can inhibit plant growth, and low concentrations of biochar have limited mitigation effect on cadmium toxicity. Therefore, the combination of low-concentration biochar and other amendments is a promising approach to alleviate cadmium toxicity in plants and improve the safety of edible parts. In this study, muskmelon was selected as the research object, and different concentrations of α-Fe₂O₃ nanoparticles were used alone or combined with biochar to explore the effects of different treatments on muskmelon plants in cadmium-contaminated soil. The results showed that the combined application of 250 mg/kg α-Fe₂O₃ nanoparticles and biochar had a good effect on the repair of cadmium toxicity in muskmelon plants. Compared with cadmium treatment, its application increased plant height by 32.53%, cadmium transport factor from root to stem decreased by 32.95%, chlorophyll content of muskmelon plants increased by 14.27%, and cadmium content in muskmelon flesh decreased by 18.83%. Moreover, after plant harvest, soil available cadmium content in 250 mg/kg α-Fe₂O₃ nanoparticles and biochar combined treatment decreased by 31.18% compared with cadmium treatment. The results of this study provide an effective reference for the composite application of different exogenous amendments and a feasible idea for soil heavy metal remediation and mitigation of cadmium pollution in farmland.

Reduction in the cadmium (Cd) accumulation and toxicity in pearl millet (Pennisetum glaucum L.) by regulating physio-biochemical and antioxidant defense system via soil and foliar application of melatonin

Cadmium (Cd) is among the toxic pollutants that harms the both animals and plants. The natural antioxidant, melatonin can improve Cd-stress tolerance but its potential role in reducing Cd stress and resilience mechanisms in pearl millet (Pennisetum glaucum L.) is remain unclear. The present study suggests that Cd causes severe oxidative damage by decreasing photosynthesis, and increasing reactive oxygen species (ROS), malondialdehyde content (MDA), and Cd content in different parts of pearl millet. However, exogenous melatonin (soil application and foliar treatment) mitigated the Cd toxicity and enhanced the growth, antioxidant defense system, and differentially regulated the expression of antioxidant-responsive genes i. e superoxide dismutase SOD-[Fe] 2, Fe-superoxide dismutase, Peroxiredoxin 2C, and L-ascorbate peroxidase-6. The results showed that foliar melatonin at F-200/50 significantly increased the plant height, chlorophyll a, b, a+b and carotenoids by 128%, 121%, 150%, 122%, and 69% over the Cd treatment, respectively. The soil and foliar melatonin at S-100/50 and F-100/50 reduced the ROS by 36%, and 44%, and MDA by 42% and 51% over the Cd treatment, respectively. Moreover, F200/50 significantly boosted the activities of antioxidant enzymes i. e SOD by 141%, CAT 298%, POD 117%, and APX 155% over the Cd treatment. Similarly, a significant reduction in Cd content in root, stem, and leaf was found on exposure to higher concentrations of exogenous melatonin. These findings suggest that exogenous melatonin may significantly and differentially improve the tolerance to Cd stress in crop plants. However, field applications, type of plant species, concentration of dose, and type of stress may vary with the degree of tolerance in crop plants.

Heavy metal(loid)s in agriculture soils, rice, and wheat across China: Status assessment and spatiotemporal analysis

Heavy metal(loid)s (HMs) accumulation in agricultural soils, rice, and wheat is of particular concern in China, while the status and spatio-temporal distribution of HMs in the soil-crops system have been rarely reported at the national scale. This study aimed to summarize the overall pollution status, spatiotemporal patterns, and drivers of HMs in agricultural soil, rice, and wheat nationwide. The metal-polluted data from 1030 agricultural soils, rice, and wheat in China were collected from the literature published from 2000 to 2022. The results showed that Cd was the most prevailing contaminant in soils based on its spatiotemporal distribution and accumulation. The pollution cases and severe pollution percentage of Cd (103 %) and Hg (128 %) show an increasing trend pattern. Mining activities are the main anthropogenic sources of agricultural soil HMs in China. Cd and Pb had the highest exceedance rate in rice (33.5 and 32.2 %) and wheat (25.8 and 30.3 %). The rice from Hunan, Fujian, and Guangxi showed the highest average concentration of Cd and Pb, respectively, while wheat samples from Hubei had the greatest exceedance rate of Pb. Besides, HMs in crops was not usually corresponding to soil HMs but increased gradually from north to south areas. Several mitigation strategies and accurate health risk assessments model of HMs based on bioavailability were also proposed and recommended. Collectively, this review provides valuable information to improve the management of farmland nationwide, optimize the accurate risk assessment, and reduce HMs pollution.

Effects of cadmium on transcription, physiology, and ultrastructure of two tobacco cultivars

Cadmium (Cd) is one of the most toxic heavy metal pollutants worldwide. Tobacco is an important cash crop; however, the accumulation of Cd in its biomass is very high. Cadmium may enter the body of smokers with contaminated tobacco and the surrounding environment via smoke. Therefore, it is important to understand the mechanisms of Cd accumulation and tolerance in tobacco plants, especially in the leaves. In this study, the effects of Cd on the growth, accumulation, and biochemical indices of two tobacco varieties, K326 (Cd resistant) and NC55 (Cd sensitive), were studied through transcriptomic and physiological experiments. Transcriptome and physiological analyses showed differences in the expression of Cd transport and Cd resistance related genes between NC55 and K326 under Cd stress. The root meristem cells of NC55 were more severely damaged. The antioxidant enzyme activity, ABA and ZT content, chlorophyll content, photosynthetic rate, and nitrogen metabolism enzyme activity in K326 leaves were higher than in NC55. These data elucidate the mechanisms of low Cd accumulation and high Cd tolerance in K326 leaves and provide a theoretical basis for cultivating tobacco varieties with low Cd accumulation and high Cd resistance.

Effect of selenium and soil pH on cadmium phytoextraction by Urochloa decumbens grown in Oxisol

It has been speculated that selenium (Se) supply can affect cadmium (Cd) 'availability' and increase the Cd tolerance of plants used for phytoextraction, in a pH-dependent process. Thus, we evaluated the interaction Cd-Se and the effects of soil pH in this interaction on plant availability of Cd and phytoextraction efficiency of Urochloa decumbens cv. Basilisk grown in Oxisol. Two soil concentrations of Cd (0.93 and 3.6 mg kg^-1) and Se (<0.2 and 1 mg kg^-1) and two soil pH (0.01 mol L^-1 CaCl₂) conditions (4.1 and 5.7) were considered. At both pH, Se supply increased the exchangeable fraction of Cd and decreased the residual Cd fraction. At pH 4.1, the growth of U. decumbens was impaired by Se addition, regardless of Cd exposure. The lower root growth and tillering of U. decumbens exposed to Cd disappeared at pH 5.7 due to uptake of low Se concentrations. Thus, the toxic or beneficial effects of Se on growth of U. decumbens used for Cd phytoextraction depend on the amount of Se assimilated. The Cd phytoextraction efficiency of U. decumbens was not improved by Se supply, regardless of soil pH. Therefore, we cannot recommend the application of Se to increase Cd phytoextraction by this grass.

Trade-offs between fertilizer-N availability and Cd pollution potential under crop straw incorporation by 15 N stable isotopes in rice

Application of crop residues and chemical nitrogen (N) fertilizer is a conventional practice for achieving high yield in a rice system. However, the fallacious combination of N fertilizers with crop straw not only significantly reduces the N use efficiencies (NUEs) but also leads to serious environmental problems. The present study employed five treatments including no N fertilization and no straw incorporation (ck), N fertilization incorporation only (S0), N fertilization with 40% straw (S₄₀), N fertilization with 60% straw (S₆₀), and N fertilization with 100% straw (S₁₀₀) to improve N use efficiency as well as reduced Cd distribution in rice. The crop yields were largely enhanced by fertilization ranging from 13 to 52% over the straw addition treatments. Compared with ck, N fertilizer input significantly decreased soil pH, while DOC contents were raised in response to straw amendment, reaching the highest in S₆₀ and S₁₀₀ treatments, respectively. Moreover, straw addition substantially impacted the Cd accumulation and altered the bacterial community structure. The soil NH₄⁺-N concentration under S₀ performed the maximum in yellow soil, while the minimum in black soil compared to straw-incorporated pots. In addition, the soil NO₃^--N concentration in straw-incorporated plots tended to be higher than that in straw-removed plots in both soils, indicating that crop straw triggering the N mineralization was associated with native soil N condition. Furthermore, the NUE increased with ¹⁵ N uptake in the plant, and the residual ¹⁵ N in soil was increased by 26.8% with straw addition across four straw application rates. Overall, our study highlights the trade-offs between straw incorporation with N fertilizer in eliminating potential Cd toxicity, increasing fertilizer-N use efficiencies and help to provide a feasible agricultural management.

Critical review on biogeochemical dynamics of mercury (Hg) and its abatement strategies

Mercury (Hg) is among the naturally occurring heavy metal with elemental, organic, and inorganic distributions in the environment. Being considered a global pollutant, high pools of Hg-emissions ranging from >6000 to 8000 Mg Hg/year get accumulated by the natural and anthropogenic activities in the atmosphere. These toxicants have high persistence, toxicity, and widespread contamination in the soil, water, and air resources. Hg accumulation inside the plant parts amplifies the traces of toxic elements in the linking food chains, leads to Hg exposure to humans, and acts as a potential genotoxic, neurotoxic and carcinogenic entity. However, excessive Hg levels are equally toxic to the plant system and severely disrupt the physiological and metabolic processes in plants. Thus, a plausible link between Hg-concentration and its biogeochemical behavior is highly imperative to analyze the plant-soil interactions. Therefore, it is requisite to bring these toxic contaminants in between the acceptable limits to safeguard the environment. Plants efficiently incorporate or absorb the bioavailable Hg from the soil thus a constructive understanding of Hg uptake, translocation/sequestration involving specific heavy metal transporters, and detoxification mechanisms are drawn. Whereas recent investigations in biological remediation of Hg provide insights into the potential associations between the plants and microbes. Furthermore, intense research on Hg-induced antioxidants, protein networks, metabolic mechanisms, and signaling pathways is required to understand these bioremediations techniques. This review sheds light on the mercury (Hg) sources, pollution, biogeochemical cycles, its uptake, translocation, and detoxification methods with respect to its molecular approaches in plants.

Phytoremediation of cadmium from soil, air and water

Potentially toxic elements (PTEs) pose a great threat to ecosystems and long-term exposure causes adverse effects to wildlife and humans. Cadmium induces a variety of diseases including cancer, kidney dysfunction, bone lesions, anemia and hypertension. Here we review the ability of plants to accumulate cadmium from soil, air and water under different environmental conditions, focusing on absorption mechanisms and factors affecting these. Cadmium possess various transport mechanisms and pathways roughly divided into symplast and apoplast pathway. Excessive cadmium concentrations in the environment affects soil properties, pH and microorganism composition and function and thereby plant uptake. At the same time, plants resist cadmium toxicity by antioxidant reaction. The differences in cadmium absorption capacity of plants need more exploration to determine whether it is beneficial for crop breeding or genetic modification. Identify whether plants have the potential to become hyperaccumulator and avoid excessive cadmium uptake by edible plants. The use of activators such as wood vinegar, GLDA (Glutamic acid diacetic acid), or the placement of earthworms and fungi can speed up phytoremediation of plants, thereby reducing uptake of crop varieties and reducing human exposure, thus accelerating food safety and the health of the planet.

The endo-beta mannase MAN7 contributes to cadmium tolerance by modulating root cell wall binding capacity in Arabidopsis thaliana

The heavy metal cadmium (Cd) is detrimental to crop growth and threatens human health through the food chain. To cope with Cd toxicity, plants employ multiple strategies to decrease Cd uptake and its root-to-shoot translocation. However, genes that participate in the Cd-induced transcriptional regulatory network, including those encoding transcription factors, remain largely unidentified. In this study, we demonstrate that ENDO-BETA-MANNASE 7 (MAN7) is necessary for the response of Arabidopsis thaliana to toxic Cd levels. We show that MAN7 is responsible for mannase activity and modulates mannose content in the cell wall, which plays a role in Cd compartmentalization in the cell wall under Cd toxicity conditions. Additionally, the repression of root growth by Cd was partially reversed via exogenous application of mannose, suggesting that MAN7-mediated cell wall Cd redistribution depends on the mannose pathway. Notably, we identified a basic leucine zipper (bZIP) transcription factor, bZIP44, that acts upstream of MAN7 in response to Cd toxicity. Transient dual-luciferase assays indicated that bZIP44 directly binds to the MAN7 promoter region and activates its transcription. Loss of bZIP44 function was associated with greater sensitivity to Cd treatment and higher accumulation of the heavy metal in roots and shoots. Moreover, MAN7 overexpression relieved the inhibition of root elongation seen in the bzip44 mutant under Cd toxicity conditions. This study thus reveals a pathway showing that MAN7-associated Cd tolerance in Arabidopsis is controlled by bZIP44 upon Cd exposure.

Integrated transcriptome and metabonomic analysis of key metabolic pathways in response to cadmium stress in novel buckwheat and cultivated species

INTRODUCTION

Buckwheat (Fagopyrum tataricum), an important food crop, also has medicinal uses. It is widely planted in Southwest China, overlapping with planting areas remarkably polluted by cadmium (Cd). Therefore, it is of great significance to study the response mechanism of buckwheat under Cd stress and further develop varieties with excellent Cd tolerance.

METHODS

In this study, two critical periods of Cd stress treatment (days 7 and 14 after Cd treatment) of cultivated buckwheat (Pinku-1, named K33) and perennial species (F. tatari-cymosum Q.F. Chen) (duoku, named DK19) were analyzed using transcriptome and metabolomics.

RESULTS

The results showed that Cd stress led to changes in reactive oxygen species (ROS) and the chlorophyll system. Moreover, Cd-response genes related to stress response, amino acid metabolism, and ROS scavenging were enriched or activated in DK19. Transcriptome and metabolomic analyses highlighted the important role of galactose, lipid (glycerophosphatide metabolism and glycerophosphatide metabolism), and glutathione metabolism in response to Cd stress in buckwheat, which are significantly enriched at the gene and metabolic levels in DK19.

DISCUSSION

The results of the present study provide valuable information for a better understanding of the molecular mechanisms underlying Cd tolerance in buckwheat and useful clues for the genetic improvement of drought tolerance in buckwheat.

Contrasting Cd accumulation of Arabidopsis halleri populations: a role for (1→4)-β-galactan in pectin

Cadmium (Cd) accumulation is highly variable among Arabidopsis halleri populations. To identify cell wall (CW) components that contribute to the contrasting Cd accumulation between PL22-H (Cd-hyperaccumulator) and I16-E (Cd-excluder), Cd absorption capacity of CW polysaccharides, CW mono- and poly- saccharides contents and CW glycan profiles were compared between these two populations. PL22-H pectin contained 3-fold higher Cd concentration than I16-E pectin in roots, and (1→4)-β-galactan pectic epitope showed the biggest difference between PL22-H and I16-E. CW-related differentially expressed genes (DEGs) between PL22-H and I16-E were identified and corresponding A. thaliana mutants were phenotyped for Cd tolerance and accumulation. A higher Cd translocation was observed in GALACTAN SYNTHASE1 A. thaliana knockout and overexpressor mutants, which both showed a lengthening of the RG-I sidechains after Cd treatment, contrary to the wild-type. Overall, our results support an indirect role for (1→4)-β-galactan in Cd translocation, possibly by a joint effect of regulating the length of RG-I sidechains, the pectin structure and interactions between polysaccharides in the CW. The characterization of other CW-related DEGs between I16-E and PL22-H selected allowed to identify a possible role in Zn translocation for BIIDXI and LEUNIG-HOMOLOG genes, which are both involved in pectin modification.

A state-of-the-art review on cadmium uptake, toxicity, and tolerance in rice: From physiological response to remediation process

Cadmium (Cd), a major contaminant of concern, has been extensively reviewed and debated for its anthropogenic global shifts. Cadmium levels in rice grains raise wide food safety concerns. The aim of this review is therefore to capture the dynamics of Cd in paddy soil, translocation pathways of Cd from soil to consumption rice, and assess its bio-accessibility in human consumption. In crop plants, Cd reduces absorption of nutrients and water, triggers oxidative stress, and inhibits plant metabolism. Understanding the mechanisms and behaviour of Cd in paddy soil and rice allows to explain, predict and intervene in Cd transferability from soil to grains and human exposure. Factors affecting Cd movement in soil, and further to rice grain, are elucidated. Recently, physiological and molecular understanding of Cd transport in rice plants have been advanced. Morphological-biochemical characteristics and Cd transporters of plants in such a movement were also highlighted. Ecologically viable remediation approaches, including low input cost agronomic methods, phytoremediation and microbial bioremediation methods, are emerging.

Copper, zinc, and chromium accumulation in aquatic macrophytes from a highly polluted river of Argentina

The aims of this study were to assess Cu, Zn, and Cr pollution in a highly polluted river in Argentina (Matanza-Riachuelo) and to evaluate tolerance strategies and toxic effects in aquatic macrophytes. Chemical techniques were used to assess the bioavailability of these metals and to evaluate their uptake and translocation by plants. The ultrastructure of the roots of a free-floating plant (Eichhornia crassipes) and the leaves of an emergent macrophyte (Sagittaria montevidensis) was examined using transmission electron microscopy. In the lower basin of the river, the highest concentrations of total heavy metals were detected in water (179 µgZn/g; 54 µgCu/g; 240 µgCr/g) and sediments (1499 µgZn/g; 393 µgCu/g; 4886 µgCr/g). In the upper basin of the river, low percentages of Zn and Cu (8 to 25%) were extracted with DTPA and EDTA, probably due to the lithogenic origin of these metals. Higher extraction percentages (24 to 66%) were obtained in the lower basin, in accordance with anthropogenic pollution. For Cr, extraction percentages were low in the upper basin of the river (< 4.5%) and extremely low in the lower basin (< 0.03%). In S. montevidensis, the BCF (bioconcentration factor) and TF (translocation factor) indexes were compatible with heavy metal exclusion mechanisms in sediments, whereas in the E. crassipes, root compartmentalization could be the main tolerance strategy. The leaves of S. montevidensis showed no evidence of damage, whereas ultrastructural alterations (plasmolyzed cells, disorganized membranes) were observed in E. crassipes.

Polyaspartic acid assisted-phytoremediation of cadmium-contaminated farmland: Phytoextraction efficiency, soil quality, and rhizosphere microbial community

Cadmium is highly toxic and one of the most dangerous metal pollutants in soil, and poses a serious threat to human health through soil-crop-food chain transmission. Polyaspartic acid (PASP) is a biodegradable additive that is environment-friendly compared to traditional chelating agents. Current studies have explored its effect on auxiliary phytoextraction at a laboratory scale; however, the method is still rarely reported at the field scale. Therefore, this study used two ecotypes of Pennisetum sinese in a field experiment for 3 years in Jiaoxi Township, Liuyang City, Hunan Province, China, to understand the effect of PASP on the phytoremediation of Cd-contaminated soil and soil quality through long-term field studies. Moreover, because the soil microbial community responds well to the phytoremediation effect of heavy metal (including Cd)-contaminated soil, the changes in rhizosphere soil microbial community diversity and composition were analyzed. After 2 years of PASP-enhanced phytoremediation, the PASP application increased the total Cd reduction in soil by 237 % and 255 %, and the soil DTPA-extractable Cd content decreased to 0.092 and 0.087 mg kg^-1. When the application of PASP ceased in the third year, the two ecotypes of P. sinese obtained after harvest could achieve feed safety. Our study showed that the application of PASP could significantly increase the Cd extraction capacity and shoot biomass of P. sinese, and maintain soil health by optimizing the composition and structure of rhizosphere bacterial communities. The rhizosphere bacterial community structure was improved and dominated by Acidobacteriota, Proteobacteria, and Chloroflexi at the phylum level, and the increased abundance of Acetobacter, Enterobacter, Pseudomonas, and Stenotrophomonas at the genus level may promote heavy metal detoxification in soil, plant growth, and phytoremediation. Long-term field monitoring demonstrated that the low-cost and eco-friendly features of PASP made it a good candidate for enhancing phytoextraction efficiency and regulating soil microbial communities for remediation.

Glutathione primed seed improved lead-stress tolerance in Brassica rapa L. through modulation of physio-biochemical attributes and nutrient uptake

Heavy metal toxicity is a major environmental issue that affects all life forms, including plants. The accumulation of lead (Pb) in agricultural soils is a significant contributor to reduced crop yields, and it poses serious health risks to people who consume lead-contaminated agricultural products. The current study was undertaken to investigate the beneficial effects of glutathione (GSH) on the amelioration of stress induced by Pb (300 mg kg-1 Pb) in Brassica rapa L. (turnip). For this purpose, B. rapa seeds primed with 25, 50, and 75 µmol L-1. The root and shoot length, seedling biomass, and leaf area, was reduced under Pb stress. Lead toxicity inhibited the net photosynthetic rate (31.36%), total chlorophyll content (74.54%) of B. rapa plants in comparison to control. Lead-stressed plants additionally exhibited changes in proline levels, as well as lower levels of total soluble protein and phenolic content. Nevertheless, seed priming with GSH resulted in higher concentrations of the nutritional content (Mg+2, Zn+2, Na+, K+) that increased Pb stress tolerance. The GSH2 treated seed enhanced the photosynthetic rate (46.34%), stomatal conductance (80.55%), and transpiration rate (53.125%) over Pb stress. Furthermore, GSH2 enhanced total soluble proteins (37.75%), phenolic content (58.38%), and DPPH (1.5fold) of turnip plant over control seedlings. According to our research, GSH2 primed B. rapa seed demonstrated a reduction in Pb toxicity, which could be used to help seedling establishment in soils contaminated with Pb.

Cadmium Transport in Maize Root Segments Using a Classical Physiological Approach: Evidence of Influx Largely Exceeding Efflux in Subapical Regions

The bidirectional fluxes of cadmium and calcium across the plasma membrane were assessed and compared in subapical maize root segments. This homogeneous material provides a simplified system for investigating ion fluxes in whole organs. The kinetic profile of cadmium influx was characterized by a combination of a saturable rectangular hyperbola (K_m = 30.15) and a straight line (k = 0.0013 L h^-1 g^-1 fresh weight), indicating the presence of multiple transport systems. In contrast, the influx of calcium was described by a simple Michaelis-Menten function (K_m = 26.57 µM). The addition of calcium to the medium reduced cadmium influx into the root segments, suggesting a competition between the two ions for the same transport system(s). The efflux of calcium from the root segments was found to be significantly higher than that of cadmium, which was extremely low under the experimental conditions used. This was further confirmed by comparing cadmium and calcium fluxes across the plasma membrane of inside-out vesicles purified from maize root cortical cells. The inability of the root cortical cells to extrude cadmium may have driven the evolution of metal chelators for detoxifying intracellular cadmium ions.

Use of Three Different Nanoparticles to Reduce Cd Availability in Soils: Effects on Germination and Early Growth of Sinapis alba L

Globally, cadmium (Cd) is one of the metals that causes the most significant problems of contamination in agricultural soils and toxicity in living organisms. In this study, the ability of three different nanoparticles (dose 3% w/w) (hydroxyapatite (HANPs), maghemite (MNPs), or zero-valent iron (FeNPs)) to decrease the availability of Cd in artificially contaminated agricultural soil was investigated. The effect of Cd and nanoparticles on germination and early growth of Sinapis alba L. was also assessed by tolerance/toxicity bioassays. The available Cd contents in the contaminated soil decreased after treatment with the nanoparticles (available Cd decreased with HANPs: >96.9%, MNPs: >91.9%, FeNPs: >94%), indicating that these nanoparticles are highly efficient for the fixation of available Cd. The toxicity/tolerance bioassays showed different behavior for each nanoparticle. The HANPs negatively affected germination (G(%): 20% worsening compared to control soil), early root growth (G_index: -27.7% compared to control soil), and aerial parts (Ap_index: -12%) of S. alba, but showed positive effects compared to Cd-contaminated soils (G_index: +8-11%; Ap_index: +26-47%). MNP treatment in Cd-contaminated soils had a positive effect on germination (G(%): 6-10% improvement) and early growth of roots (G_index: +16%) and aerial parts (Ap_index: +16-19%). The FeNPs had a positive influence on germination (G(%): +10%) and growth of aerial parts (Ap_index: +12-16%) but not on early growth of roots (G_index: 0%). These nanoparticles can be used to reduce highly available Cd contents in contaminated soils, but MNPs and FeNPs showed the most favorable effects on the early growth and germination of S. alba.

A Coculture of Enterobacter and Comamonas Species Reduces Cadmium Accumulation in Rice

The accumulation of cadmium (Cd) in plants is strongly impacted by soil microbes, but its mechanism remains poorly understood. Here, we report the mechanism of reduced Cd accumulation in rice by coculture of Enterobacter and Comamonas species. In pot experiments, inoculation with the coculture decreased Cd content in rice grain and increased the amount of nonbioavailable Cd in Cd-spiked soils. Fluorescence in situ hybridization and scanning electron microscopy detection showed that the coculture colonized in the rhizosphere and rice root vascular tissue and intercellular space. Soil metagenomics data showed that the coculture increased the abundance of sulfate reduction and biofilm formation genes and related bacterial species. Moreover, the coculture increased the content of organic matter, available nitrogen, and potassium and increased the activities of arylsulfatase, β-galactosidase, phenoloxidase, arylamidase, urease, dehydrogenase, and peroxidase in soils. In subsequent rice transcriptomics assays, we found that the inoculation with coculture activated a hypersensitive response, defense-related induction, and mitogen-activated protein kinase signaling pathway in rice. Heterologous protein expression in yeast confirmed the function of four Cd-binding proteins (HIP28-1, HIP28-4, BCP2, and CID8), a Cd efflux protein (BCP1), and three Cd uptake proteins (COPT4, NRAM5, and HKT6) in rice. Succinic acid and phenylalanine were subsequently proved to inhibit rice divalent Cd [Cd(II)] uptake and activate Cd(II) efflux in rice roots. Thus, we propose a model that the coculture protects rice against Cd stress via Cd immobilization in soils and reducing Cd uptake in rice. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Simultaneous alleviation of Cd availability in contaminated soil and accumulation in rice (Oryza sativa L.) by Fe-Mn oxide-modified biochar

Fe-Mn oxide-modified biochar (BC-FM) was used to remediate Cd-contaminated soil and mitigate Cd accumulation in rice. The roles of Fe and Mn in soil Cd immobilization and in controlling Cd uptake by rice were investigated via X-ray photoelectron spectroscopy (XPS) characterization and chemical analysis. Fe and Mn loaded on BC-FM increased the removal efficiencies of CaCl₂ extractable Cd in soil and Cd in pore water compared to those in only biochar (BC)-treated soil, with maximum removal rates at 67.9 % and 77.8 %, respectively. The XPS results indicated that the redox reactions of the Fe-Mn oxides on BC-FM surface affected Cd immobilization in the soil. The Fe (II/III) components on BC-FM were primarily converted to Fe₃O₄ in the soil system, which may form stable complexes with Cd²⁺ (Fe-O-Cd) during the entire rice growth period, and Cd may be bound to MnO or Mn₂O₃ in the form of CdMn₂O₄. The excellent adsorption performance of BC-FM enhanced by Fe-Mn oxides reduced the available Cd in the soil and stimulated Fe and Mn transport in rice, thereby inhibiting Cd accumulation in the aerial parts of rice. Cd concentrations in brown rice under BC-FM treatments reached the national safety standard (0.2 mg/kg, GB2762-2017). And BC-FM significantly increased the biomass of brown rice with a maximum rate of 26.8 %. These findings suggest that BC-FM could be used as an efficient material for Cd-contaminated soil remediation, and Fe-Mn plays important role in immobilizing Cd in soil and reducing Cd transport in rice.

Chronic exposure to yttrium induced cell apoptosis in the testis by mediating Ca2+/IP3R1/CaMKII signaling

Introduction

Environmental pollutants, such as rare earth elements, affect human health and particularly induce reproductive system injury. Yttrium (Y), one of the most widely used heavy rare earth elements, has been reported the cytotoxicity. However, the biological effects of Y³⁺ in the human body are largely unknown.

Methods

To further investigate the effects of Y on the reproductive system, in vivo (rat models) and in vitro studies were performed. Histopathological and immunohistochemical examination were conducted, and western blotting assays were performed to detect the protein expression. TUNEL/DAPI staining were used to detect cell apoptosis, and the intracellular calcium concentrations were also determined.

Results

Long-term exposure to YCl₃ in rats produced significant pathological changes. YCl₃ treatment could induce cell apoptosis in vivo and in vitro. In addition, YCl₃ enhanced the concentration of cytosolic Ca²⁺ and up regulated the expression of IP3R1/CaMKII axis in Leydig cells. However, inhibition of IP3R1 and CaMKII with 2-APB and KN93, respectively, could reverse these effects.

Conclusion

Long-term exposure to yttrium could induce testicular injury by stimulating cell apoptosis, which might be associated with activation of Ca²⁺/IP3R1/CaMKII axis in Leydig cells.

Oxidative Stress Response and Metal Transport in Roots of Macleaya cordata Exposed to Lead and Zinc

Heavy metal pollution possesses potential hazards to plant, animal and human health, which has become the focus of recent attention. Hence, phytoremediation has been regarded as one of the most important remediation technologies for heavy-metal-contaminated soils. In this research, a dominant mine tailing plant, Macleaya cordata, was used as the experimental material to compare the metal transport and oxidative stress response in its roots under lead (Pb) and zinc (Zn) treatments. The result showed that Pb was mainly accumulated in the roots of M. cordata under the Pb treatment; less than 1% Pb was transported to the parts above. An analysis of the Zn content demonstrated a 39% accumulation in the shoots. The production of reactive oxygen species was detected using the in situ histological staining of roots, which showed that hydrogen peroxide in the root tips was observed to increase with the increase in both Pb and Zn concentrations. No significant superoxide anion changes were noted in the root tips under the Pb treatment. An analysis of the root enzyme activity showed that increase in NADPH oxidase activity can be responsible for the production of superoxide anions, subsequent the inhibition of root growth and decrease in antioxidant enzyme activities in the roots of M. cordata exposed to excess Zn. In total, this research provides evidence that the root of M. cordata has a high antioxidant capacity for Pb stress, so it can accumulate more Pb without oxidative damage. On the other hand, the Zn accumulated in the roots of M. cordata causes oxidative damage to the root tips, which can stimulate more Zn transport to the shoots to reduce the damage to the roots. This result will provide a basis for the application of M. cordata in the phytoremediation of soil polluted by Pb-Zn compounds.

Do we know the cellular location of heavy metals in seaweed? An up-to-date review of the techniques

Seaweeds are dominant organisms in coastal environments. However, in the context of global change, the integrity of these organisms is threatened by metal pollution. It is therefore important to understand how seaweeds are affected by metal concentrations in the water. Measuring the concentrations of metals in seaweed provides information about the effects of metal pollution on the seaweeds themselves and their ecosystems. Nonetheless, correct interpretation of this type of analysis requires knowledge of the cellular location of the pollutants, as the effects will differ depending on whether the metals are present in particles adhered to the surface, attached to external polysaccharides or dissolved in the cytoplasm. Thus, the objectives of this study were to compile the available information on the subcellular distribution of metals in seaweeds and to conduct a critical review of the information. We found that the existing studies provide contrasting, sometimes contradictory, results. Thus, metals have been detected entirely intracellularly and also mainly outside of the cells. In all of the studies reviewed, which used different techniques (mainly extracellular elution, X-ray microanalysis and centrifugation), methodological and/or conceptual problems were identified that raise questions about the effectiveness of each approach. To obtain reliable information about the distribution of metals in algal cells, further studies must be conducted that take into consideration the differences between elements and algal species and the limits of the methods used to measure the elements.

Cadmium tolerance and accumulation from the perspective of metal ion absorption and root exudates in broomcorn millet

Cadmium (Cd) is a persistent heavy metal that poses environmental and public health concerns. This study aimed to identify the potential biomarkers responsible for Cd tolerance and accumulation by investigating the response of the content of essential metal elements, transporter gene expression, and root exudates to Cd stress in broomcorn millet (Panicum miliaceum). A hydroponics experiment was conducted using two broomcorn millet cultivars with distinct Cd tolerance levels and accumulation phenotypes (Cd-tolerant and Cd-sensitive cultivars). Cd stress inhibited lateral root growth, especially in the Cd-sensitive cultivar. Furthermore, Cd accumulation was significantly greater in the Cd-tolerant cultivar than in the Cd-sensitive cultivar. Cd stress significantly inhibited the absorption of essential metal elements and significantly increased the calcium concentration. Differentially expressed genes involved in metal ion transport were identified via transcriptome analysis. Cd stress altered the composition of root exudates, thus increasing lipid species and decreasing alkaloid, lignan, sugar, and alcohol species. Moreover, Cd stress significantly reduced most alkaloid, organic acid, and phenolic acid exudates in the Cd-tolerant cultivar, while it increased most lipid and phenolic acid exudates in the Cd-sensitive cultivar. Some significantly changed root exudates (ferulic acid, O-coumaric acid, and spermine) are involved in the phenylalanine biosynthesis, and arginine and proline metabolic pathways, thus, may be potential biomarkers of Cd stress response. Overall, metal ion absorption and root exudates are critical for Cd tolerance and accumulation in broomcorn millet. These findings provide valuable insights into improving Cd phytoremediation by applying mineral elements or metabolites.

Nitric oxide (NO) involved in Cd tolerance in NHX1 transgenic duckweed during Cd stress

Anthropogenic activities cause heavy metal pollution, such as cadmium (Cd). Na⁺/H⁺ antiporter (NHX1) transgenic duckweed showed Cd tolerance in our previous study, and the signal mechanism needs to be explored. As an important signal molecule, nitric oxide (NO) is involved in a number of functions under abiotic stress response. This study analyzed the levels of endogenous NO in wild-type (WT) duckweed and NHX1 duckweed under Cd treatment. The results showed that after 24 h Cd treatment, the endogenous NO level of WT duckweed decreased, which was significantly lower than that in NHX1 duckweed. Studies have proved that NHX1 influences pH. The level of NO in this study has been investigated at different pH. The NO level was the highest in the duckweed cultured with pH 5.3. Nitrate reductase gene expression was down-regulated and NO synthesis was decreased under Cd stress in WT duckweed. This study showed that NO level has been modified in NHX1 duckweed, which could be influcened by pH.

Phytoremediation of CdS/Te quantum dots by Ocimum basilicum in the presence of EDTA

Purpose

The use of nanomaterials like quantum dots (QDs) with optical properties has increased in the last decade because of their electronics, medicine, and environmental applications. The lack of recycling and appropriate disposal causes these materials to be considered new emerging contaminants. In this research, the extraction and translocation (phytoextraction) of cadmium as QDs by Ocimum basilicum "basil" in the presence of EDTA (chelating agent) was studied. For edible plants are essential to know where the contaminants are located to minimize human consumption.

Methods

In this work, the phytoextraction, distribution, and translocation of cadmium (under ionic solution-CdIS and CdS/Te QDs) at 25 and 50 mg/kg-soil and in the presence of 1,000 mg/kg-soil EDTA was studied in O. basilicum (a commercialized culinary herb) for three and six weeks. Basil seedlings were grown in an environmentally controlled chamber at 24-28o C and 12/12 hours periods of light and darkness.

Results

The highest cadmium concentration was found in the roots from where it is translocated to stems and leaves. CdS/Te QDs at low concentration (25 mg/kg and 3 weeks of exposure) had the highest translocation factor, indicating that cadmium's nanocrystal (QDs) forms can affect the phytoextraction mechanism. The highest bioconcentration of cadmium was reached at a high contaminant concentration.

Conclusion

The bioconcentration factors confirm that O. basilicum phytoextracts cadmium from soils contaminated with CdS/Te QDs and CdIS. The bioconcentration factors of cadmium (under both species CdS/Te QDs and CdIS) increase in the presence of EDTA. The bioconcentration and translocation factors suggest that consuming "basil" from contaminated soils with CdS/Te QDs at low concentrations increases the exposition to this metal.

Mercury contamination in the riparian ecosystem during the reservoir discharging regulated by a mega dam

Mercury (Hg) is extremely poisonous and can be absorbed through touch, inhalation, or consumption. In the living environment, Hg in contaminated sediment can be transferred into grass by the direct absorption through the roots or shoots. The intake of Hg due to Hg emissions may pose a threat to living bodies especially to human beings. The present study aims to provide a novel insight about total mercury (THg) and methyl mercury (MeHg) in a riparian grass (Cynodon dactylon (L).Pers) and sediments during the discharging phase (summertime at 145 m water level) in Three Gorges Reservoir (TGR-China); where C. dactylon is a dominant perennial herb in the riparian zone. Yet, the potential risk of Hg contamination in the riparian ecosystem is not thoroughly assessed in the dam regulated reservoir. This study was conducted in the riparian zones of the reservoir formed by a mega dam (Three Gorge Dam) which regulates the water levels during the summer and winter period in the TGR. Our results showed that riparian sediments were acting as a sink for THg and MeHg. Insignificant correlation of THg and MeHg was found between the amphiphyte C. dactylon and its surrounding sediments in the TGR. Bioconcentration factors values for MeHg were found higher than 1 in all study locations in the riparian zones in TGR, which could be due to action of certain bacteria/purely chemical-based methylation on inorganic form of Hg. Additionally, translocation factor indices also highlighted that the amphiphyte C. dactylon was MeHg accumulator in riparian zones. These results suggested that since riparian sediment was found acting as the sink for THg and MeHg during discharging phase, MeHg contamination in the amphiphyte C. dactylon in riparian zones was not caused by the riparian sediments but by other factors, for instance, the anthropogenic activities in the TGR. Finally, this study leads to conclude that amphiphyte C. dactylon can be used as biomonitoring agent for Hg pollution in the TGR.

Glutathione improves low temperature stress tolerance in pusa sheetal cultivar of Solanum lycopersicum

To investigate the impact of Glutathione (GSH) in mitigating low-temperature stress in Pusa Sheetal cv. of Solanum lycopersicum and imparting low-temperature tolerance by evaluating the different physiological responses. The plant under research was also being studied for its growth and stress tolerance. Low temperatures (LT) stress was applied to seedlings with or without GSH application 12 h before LT stress (prophylactic dose), after 12 h-LT (preemptive dose), and post 12-h recovery (curative dose). Different concentrations of GSH [0, G1 (0.5 mM), G2 (1 mM) and G3 (2 mM)] against LT stress were used. Antioxidant activities, photosynthesis, growth, and stress tolerance indices were quantified. LT stress caused an oxidative burst in S. lycopersicum seedlings of the Pusa Sheetal cv. as indicated by increased peroxidation of lipids and H₂O₂ concentration. Glutathione reductase (GR), superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) activities were enhanced. The best concentration was G2 (1 mM), which resulted in a rise in antioxidant activity. Moreover, a decline in lipid peroxidation and H₂O₂ levels was also seen. The purpose of this study is to identify the role of GSH in reducing LT stress and to find the best dose concentration. This is the first report to assess the GSH-mediated LT stress tolerance in S. lycopersicum (Pusa Sheetal cv.). Therefore, exogenous GSH application of optimal concentration of GSH to LT stressed S. lycopersicum can be an effective approach for augmenting the plant detoxification system and promoting its growth and development.

Do Volatiles Affect Bacteria and Plants in the Same Way? Growth and Biochemical Response of Non-Stressed and Cd-Stressed Arabidopsis thaliana and Rhizobium E20-8

Plant roots are colonized by rhizobacteria, and these soil microorganisms can not only stimulate plant growth but also increase tolerance to stress through the production of volatile organic compounds. However, little is known about the effect that these plant beneficial volatiles may have on bacteria. In this study, the effects on growth and oxidative status of different concentrations of three volatiles already reported to have a positive influence on plant growth (2-butanone, 3-methyl-1-butanol, and 2,3-butanediol) were determined in A. thaliana and Rhizobium sp. strain E20-8 via airborne exposure in the presence and absence of Cd. It was expected to ascertain if the plant and the bacterium are influenced in the same way by the volatiles, and if exposure to stress (Cd) shifts the effects of volatiles on plants and bacteria. Results showed the antioxidant activity of the volatiles protecting the plant cell metabolism from Cd toxicity and increasing plant tolerance to Cd. Effects on bacteria were less positive. The two alcohols (3-methyl-1-butanol and 2,3-butanediol) increased Cd toxicity, and the ketone (2-butanone) was able to protect Rhizobium from Cd stress, constituting an alternative way to protect soil bacterial communities from stress. The application of 2-butanone thus emerges as an alternative way to increase crop production and crop resilience to stress in a more sustainable way, either directly or through the enhancement of PGPR activity.

Genetic Behavior of Tomato (Solanum lycopersicum L.) Germplasm Governing Heavy Metal Tolerance and Yield Traits under Wastewater Irrigation

Wastewater irrigation is a substitute for surface water scarcity, but traces of heavy metals (HMs) result in deleterious implications for soil, crop productivity, and in humans. Crops presenting HMs tolerance in genetic behavior are important for producing tolerant genotypes cultivated under wastewater irrigation. In the first part of this experiment, the results obtained previously are re-assessed in a hydroponic system and similar patterns and concentrations of HMs are found in different tomato organs. Following this trial, the tomato’s (Solanum lycopersicum L.) genetic basis of traits conferring HMs tolerance and yield are assessed when irrigated with waste or canal water. The North Carolina Mating II analysis illustrate the amount of gene action, nature, and inheritance pattern. Genetic components depict the involvement of non-additive, additive, and maternal genetic effects in HMs tolerance inheritance and yield. A noticeable increase in cumulative additive variance for the number of flowers (11,907.2) and the number of fruits (10,557.9) is recorded for tomato plants irrigated with wastewater, illustrating additive gene action. However, female and male (MSf/MSm) square ratios also show an association with cytoplasmic inheritance. For HMs tolerance, both additive and dominant variances appeared to be significant; cumulative dominance variance (4.83, 16.1, 4.69, 76.95, and 249.37) is higher compared to additive variance (0.18, 2.36, 0.19, −0.27, and 14.14) for nickel (Ni), chromium (Cr), lead (Pb), manganese (Mn), and zinc (Zn), respectively, indicating dominance gene action. The genotype RIOGRANDI accumulated and translocated fewer HMs to the aerial part of the plant compared to CLN-2418A and PB-017906, thus presenting a tolerant tomato genotype according to the hydroponic experiment. This also exhibited a differential pattern of gene action for HMs tolerance, suggesting that genotypes possess significant differences for HMs tolerance.

Population-level transcriptomes reveal gene expression and splicing underlying cadmium accumulation in barley

Genetic variation is an important determinant of gene transcription, which in turn contributes to functional and phenotypic diversity. Identification of the genetic variants controlling gene expression and alternative splicing in crops responding to cadmium (Cd), an important issue for food safety and human health, is of great value to improve our understanding of Cd accumulation-related genes. Here we report an in-depth survey of population-level transcriptome variation of barley (Hordeum vulgare) core accessions under Cd exposure. We reveal marked transcriptomic changes in response to Cd exposure, and these are largely independent of tissues. A genome-wide association study (GWAS) revealed 59 498 expression quantitative trait loci (eQTLs) and 23 854 splicing quantitative trait loci (sQTLs), leading to a complex network that covers 66.6% of the expressed genes, including 68 metal transporter genes. On average, 41.0% of sQTLs overlapped with eQTLs across different tissues, indicating that these two dimensions of transcript variation are largely independent. Moreover, we found that 34.5% of GWAS QTLs that underlie 10 Cd accumulation traits in barley are co-localized with eQTLs and sQTLs, which could imply a mechanistic role of different genetic variants affecting gene expression and alternative splicing in these traits. This study highlights the role of distal and proximal genetic effects on gene expression, splicing, and phenotypic plasticity. We anticipate that our results on the genetic control of expression and splicing underlying Cd accumulation provide a bridge to better understand genetic variation and phenotypic diversity to elucidate the mechanisms underlying Cd accumulation in plants.