Synergistic effect of silicon and selenium on the alleviation of cadmium toxicity in rice plants

Multifaceted role of selenium in plant physiology and stress resilience: A review

Selenium (Se) is a naturally occurring element in both seleniferous and non-seleniferous soils. Plants absorb Se in a variety of ways, mainly as selenate (SeO42-), selenite (SeO32-), and organic compounds such as selenomethionine (SeMet). Selenium significantly impacts plant growth, development, and stress responses. It is a trace element that regulates many physiological and biochemical functions in plants, acts as an antioxidant, and increases plant resistance to abiotic stresses such as heavy metal toxicity, salinity, drought, and severe temperatures. Its beneficial effects depend on the dose and vary depending on the plant species and the environmental conditions. Several functions of Se have been thoroughly discussed in this review, with special attention given to the mechanisms of Se uptake, transport, accumulation, and metabolism. Plants use Se through its assimilation into amino acids (mostly selenocysteine and selenomethionine) and integration into proteins. These processes might have different effects depending on the Se concentration. Furthermore, Se has the potential to be a useful tool in sustainable agriculture, especially in regions where environmental stress is common. This is demonstrated by its ability to increase plant tolerance to various environmental stressors. Recent research shows that Se supplementation not only boosts plant resistance but also enhances secondary metabolite accumulation. Overall, this review concludes that Se plays a dual role in plant systems, acting as both a nutrient and a stress mitigator, and provides opportunities to optimize its use in sustainable agriculture by tailoring Se supplementation to maximize plant tolerance and productivity.

Organosilicon enhances rice root suberization and antioxidant gene expression under cadmium/arsenic stress

Organosilicon exhibits unique physicochemical and biological properties with wide applicability across diverse fields, including agriculture and industry. Previous research has verified the effectiveness of organosilicon-modified fertilizers in inhibiting the uptake of cadmium (Cd) and arsenic (As) by plants. However, further investigations are necessary to elucidate the underlying mechanisms. In this study, we explored the potential of organosilicon to mitigate the toxic effects of Cd/As and lessen their uptake and accumulation during rice seed germination. Our results showed that under Cd/As stress, organosilicon treatments significantly increased suberin biosynthesis in rice roots. This was manifested as an increased level of root suberization and an enhanced apoplast barrier, as verified by observations made through fluorol yellow (FY) staining and transmission electron microscopy (TEM). Consequently, the uptake and translocation of Cd and As in rice seedlings were significantly reduced by 48.66 % and 72.19 % in shoots, and 43.23 % and 68.93 % in roots, respectively. Moreover, the application of organosilicon enhanced the activities of antioxidant enzymes in rice, This lead to an accelerated glutathione-oxidized glutathione (GSH-GSSG) cycle, up-regulated expression of the rice glutathione peroxidase gene (OsGPX), and increased GPX activity. These modifications effectively scavenged reactive oxygen species (ROS) generated by Cd/As stress and alleviated oxidative damage in rice. Overall, our study has unraveled the physiological and molecular mechanisms underlying the role of organosilicon in alleviating Cd/As toxicity in rice and has also provided new insights for the application of suberin in reducing heavy metal toxicity in plants.

Utilization of Antagonistic Interactions Between Micronutrients and Cadmium (Cd) to Alleviate Cd Toxicity and Accumulation in Crops

The presence of cadmium (Cd) in agricultural soils poses a serious risk to crop growth and food safety. Cadmium uptake and transport in plants occur through the various transporters of nutrient ions that have similar physical and chemical properties to Cd, indicating that the genetic manipulation of these transporters and agronomic improvement in the Cd-antagonistic nutrients could be a good approach for reducing Cd uptake and accumulation in crops. In this review, we discuss the interactions between Cd and some micronutrients, including zinc (Zn) and manganese (Mn), focusing on their influence on the expression of genes encoding Cd-related transporters, including ZIP7, NRAMP3, and NRAMP4. Genetic improvements in enhancing the specificity and efficiency of transporters and agronomic improvements in optimizing micronutrient nutrition can inhibit the Cd uptake and transport by these transporters. This comprehensive review provides a deep insight into genetic and agronomic improvement for fighting against Cd contamination and enhancing sustainable agricultural production.

Promoted metabolic remolding by overexpression of AspAT9 ameliorates cadmium toxicity in Arabidopsis

Cadmium (Cd) is a toxic heavy metal that poses a serious threat to crop safety and human health. Aspartate aminotransferase (AspAT) is a prime enzyme engaged in amino acid metabolism, contributing essential metabolic substances for plant growth and acclimatization to various stresses. In this study, we identified a novel AspAT9 gene with high responsiveness to Cd stress from poplar 'Nanlin895' and subsequently transformed it into Arabidopsis. The resulting transgenic AspAT9-1 plants (designated A9) and wild-type (WT) Arabidopsis were subjected to Cd treatment (T) or maintained under control conditions (CK). Phenotypic assessments showed that A9 plants displayed greater resistance to Cd stress compared to WT, as evidenced by their stay-green trait and higher biomass. Subsequent metabolism measurement revealed that A9 plants accumulated more Cd in their roots than WT. Meanwhile, the content of various proteinogenic amino acids, Cd-chelating compounds, such as lignin and phytochelatins (PCs), along with antioxidants like glutathione (GSH) and chlorophyll in A9-T exceeded WT-T. Further RNA-seq analysis uncovered significant transcriptional changes in genes implicated in aspartate-glutamate metabolism, antioxidant systems, phenylpropanoid biosynthesis, transporters, and photosynthesis activities. Our findings demonstrate the beneficial effect of overexpressing AspAT9 on Cd phytoextraction, highlights its potential as a valuable genetic resource for phytoremediation applications.

Physiological and multi-omics analysis revealed the mechanism of arbuscular mycorrhizal fungi to cadmium toxicity in green onion

Cadmium (Cd) is a highly toxic agricultural pollutant that inhibits the growth and development of plants. Arbuscular mycorrhizal fungi (AMF) can enhance plant tolerance to Cd, but the regulatory mechanisms in Allium fistulosum (green onion) are unclear. This study used a Cd treatment concentration of 1.5 mg·kg-1, which corresponds to the risk control threshold for soil pollution in Chinese agricultural land, to examine the effects and molecular mechanisms of AMF inoculation on the growth and physiology of green onion under Cd stress. AMF formed an effective symbiotic relationship with green onion roots under Cd stress, increased plant biomass, improved root structure and enhanced root vitality. AMF-colonized green onion had reduced Cd content in roots and leaves by 63.00 % and 46.50 %, respectively, with Cd content being higher in the roots than in the leaves. The ameliorative effect of AMF on Cd toxicity was mainly due to a reduction in malondialdehyde content in leaves (30.12 %) and an enhancement of antioxidant enzyme activities (peroxidase, catalase, superoxide dismutase, glutathione reductase and reduced glutathione) that mitigated damage from excessive reactive oxygen species. In addition, AMF induced secretion of easily extractable glomalin soil protein and total glomalin-related soil protein and inhibited the translocation of Cd to the shoots. Transcriptomic and metabolomic correlation analyses revealed that differentially expressed genes and metabolites in AMF-inoculated green onion under Cd stress were predominantly enriched in the "phenylpropanoid biosynthesis" and "phenylalanine metabolism" pathways, upregulated the expression of the HCT, PRDX6, HPD, MIF, and HMA3 genes, and accumulation of the phenylalanine, L-tyrosine, and 1-O-sinapoyl-β-glucose metabolites. Thus, AMF enhance Cd tolerance in green onions by sequestering Cd in roots, restricting its translocation, modulating antioxidant defenses and inducing the expression of genes involved in the phenylpropanoid biosynthesis and phenylalanine metabolism pathways. Collectedly, we for the first time revealed the mechanism of AMF alleviating the toxicity of Cd to green onion, providing a theoretical foundation for the safe production and sustainable cultivation of green onion in Cd-contaminated soils.

Cadmium translocation combined with metabolomics analysis revealed potential mechanisms of MT@MSN-CS and GSH@MSN-CS in reducing cadmium accumulation in rice (Oryza sativa L.) grains

Applying nano-delivery systems for phytohormones via foliar application has proven effective in reducing grain cadmium (Cd) levels in crops. However, the mechanisms underlying this reduction remain inadequately understood. This study integrated the determination of leaf photosynthetic parameters, Cd translocation analysis, and metabolomics to elucidate the effects of reduced glutathione (GSH) and melatonin (MT), delivered with or without chitosan-encapsulated mesoporous silica nanoparticles (MSN-CS), on grain Cd levels in rice. Our findings revealed that the foliar application of MT@MSN-CS significantly outperformed MT alone in reducing grain Cd levels and enhancing leaf photosynthesis under Cd stress. Conversely, GSH@MSN-CS showed comparable effects to GSH alone. Foliar-applied GSH@MSN-CS and MT@MSN-CS both decreased the Cd transport coefficients from panicle nodes to brown rice by 26.2-53.3%, with MT@MSN-CS demonstrating superior efficiency in reducing Cd concentrations across roots, stems, leaves, panicle nodes, and grains. Metabolomic analysis revealed substantial shifts in rice metabolite profiles following GSH@MSN-CS and MT@MSN-CS treatments. Foliar application of MT@MSN-CS or GSH@MSN-CS may rapidly and effectively activate the primary antioxidant defense system and alleviate membrane lipid peroxidation in rice grown on low-to-moderately Cd-contaminated soils by upregulating amino acid metabolism. The secondary defense mechanism, phenylpropanoid biosynthesis, was reprogrammed to reduce energy expenditure and decrease Cd translocation.

Cadmium distribution and availability in different particle-size aggregates of post-harvest paddy soil amended with bio-based materials

Research on the use of organic materials as soil amendments for the remediation of Cd-contaminated agricultural land exists. However, the mechanisms based on which organic materials affect the distribution and availability of Cd in soil aggregates remain unclear. Here, Cd-contaminated paddy soil and different bio-based materials were used for rice pot experiments. Rhizosphere soils were separated into six particle sizes. Cd fractions were analyzed with BCR sequential extraction and specific functional groups associated with Cd were characterized using XPS. We found that bio-based materials promoted the formation of large aggregates to different extents. Cd tended to be enriched in fine- and coarse-grained soil particles, which is mainly related to the soil organic matter. Bio-based materials reduced the relative content of the weak-acid extractable fraction and increased the relative content of the reducible fraction, resulting in soil Cd immobilization. Soil dissolved organic matter (DOM) was the key factor affecting the distribution and availability of Cd in soil aggregates and different organic matter and Cd-binding functional groups in aggregates altered the Cd availability in soil. The results provide insight and guidance for understanding the cadmium immobilization mechanism and screening appropriate materials in the remediation of agricultural land.

Molecular characterization of Pleiotropic Drug Resistance (PDR) genes involved in tolerance of cadmium in peanut (Arachis hypogaea L.)

Peanut (Arachis hypogaea L.) is one of the most important oil crops worldwide. Cadmium (Cd), a heavy metal that is nonessential and toxic, has the potential to significantly impacted the quality and safety of peanut. Despite the known importance of Pleiotropic Drug Resistance (PDR) genes in heavy metal accumulation and transport in plants, there is a lack of comprehensive research on the systematic identification and functional characterization of AhPDRs in peanut. In this study, a total of 38 AhPDR genes were discovered within the peanut genome. Among these, AhPDR24, AhPDR30, and AhPDR33 displayed notable variations in expression levels in response to Cd stress. Particularly noteworthy was the observation that AhPDR33, localized in the plasma membrane, exhibited a significant increase in expression (approximately 3.8-fold) and heightened promoter activity (approximately 4.1-fold) following exposure to Cd (75 μM CdCl2). Furthermore, the study found that the overexpression of AhPDR33 in Arabidopsis resulted in increased root elongation and decreased Cd accumulation (approximately 0.42-fold) compared to wild-type plants. This suggests that AhPDR33 may have a beneficial role in facilitating Cd efflux and tolerance in plants. Additionally, transient silencing of AhPDR33 in peanut demonstrated its positive regulation of Cd tolerance through the promotion of reactive oxygen species (ROS) scavenging and membrane permeability reduction. These findings contribute to the understanding of the molecular mechanisms involved in AhPDR33-mediated Cd tolerance and detoxification in peanut. Furthermore, this study provides comprehensive information to understand the AhPDR gene family, its features, and its expression, which will hold a promising utility as an excellent candidate in the genetic improvement of peanut Cd stress tolerance.

Citric acid-driven cadmium uptake and growth promotion mechanisms in Brassica napus

Citric acid (CA) is well-known for mitigating cadmium (Cd) toxicity in plants. Yet, the underlying mechanisms driving growth promotion, Cd detoxification/tolerance, and enhanced phytoremediation processes remain incompletely understood. This study investigated the effects of CA application (2.5 mM) on Brassica napus grown in Cd-contaminated (30 mg kg-1) growth medium through a controlled pot experiment. Cd exposure alone significantly impaired various plant physiological parameters in B. napus. Whereas CA application significantly (p < 0.05) enhanced physiological attributes, Cd detoxification and tolerance by modulating key genes involved in photosynthesis and Cd transport, including the metal-transporting P1B-type ATPases (Cd/zinc heavy metal-transporting ATPase 1; HMA1) and light-harvesting chlorophyll a/b-binding 3 (LHCB3). Notably, CA application increased Cd accumulation in stems and leaves by 4% and 35%, respectively, enhancing bioconcentration factors (BCF) by 12% in stems and 40% in leaves while reducing root BCF by 10%. This translocation was facilitated by the upregulation of HMA4, HMA2, and plant Cd resistance (PCR2) genes in plant leaves, improving Cd mobility within the plant. Furthermore, CA induced a 34% increase in phytochelatins and a 32% upregulation in metallothioneins, accompanied by a significant reduction in oxidative stress markers, including a 40% decrease in hydrogen peroxide and a 44% decline in malondialdehyde levels in leaves. Enhanced antioxidant enzyme activity and osmolyte accumulation further contributed to improved Cd detoxification/sequestration in leaves, reduced oxidative stress, and improved photosynthetic efficiency, resulting in enhanced plant biomass production and Cd tolerance. Transcriptomic analysis showed that CA treatment substantially influenced the expression of 12,291 differentially expressed genes (DEGs), with 750 common genes consistently downregulated in CK vs Cd treatment group but upregulated in Cd vs Cd-CA treatment group. Additionally, CA modulated 11 DEGs associated with 32 gene ontologies in the citrate pathway under Cd stress, highlighting its targeted regulatory effect on metabolic pathways involved in Cd stress response. This study offers novel insights into the synergistic role of CA in promoting plant growth and regulating Cd uptake in B. napus, highlighting its potential to enhance phytoremediation strategies.

Phytotoxicity of Prussian blue nanoparticles to rice and the related defence mechanisms: In vivo observations and physiological and biochemical analysis

While the nanotoxic effects on plants have been extensively studied, the underlying mechanisms of plant defense responses and resistance to nanostress remain insufficiently understood. Particularly, Prussian blue nanoparticles (PB NPs) have been extensively used in pigments, pharmaceuticals, electrocatalysis, biosensors and energy storage. However, the impact of PB NPs on plants' health and growth are largely unknown. Herein, the phytotoxicity of PB NPs to rice and trace the uptake, accumulation and biotransformation of PB NPs was explored, along with the underlying defence mechanisms. The results showed that PB NPs (≥50 mg L-1) significantly inhibited the growth of rice seedling up to 16.16%, 27.80%, and 29.37% in plant height, shoot biomass and root biomass, respectively. The X-ray spectroscopic studies and in vivo elemental and particle-imaging demonstrated that PB NPs were transported through the cortex via xylem from root to shoot. However, most of the PB NPs and their transformation products were retained in the root, where they were blocked owing to root cell wall (RCW) remodeling, and 81.4%-83.4% of Fe accumulated in the RCW compared to 66.6% in the control. Specifically, PB NPs stimulated pectin methylesterase activity by promoting hydrogen peroxide production to participate in RCW remodeling. More interestingly, Si was specifically regulated to covalently bind to hemicellulose to form the Si-hemicellulose complex that strongly bound with PB NPs during RCW remodeling, resulting in the strong defense against PB NPs. These findings provide new insights into the phytotoxicity of artificial NPs and the defense mechanisms of plants.

Improving peanut growth and cadmium phytoextraction capacity by inoculating Bacillus megaterium and Trichoderma harzianum

Arachis hypogaea L. (peanut) is an economic crop with abundant biomass and remarkable capacity for cadmium (Cd) uptake. In a two-year field experiment, the translocation and accumulation mechanisms of Cd in peanuts were investigated following inoculation of Bacillus megaterium (BM) and Trichoderma harzianum (TH). The results demonstrated that inoculating BM and TH enhanced both biomass and Cd concentration in peanut roots and shoots compared with those of the CK treatment. There was no statistically significant difference observed in kernel biomass between peanut plants inoculated with TH and the CK treatment. The inoculation of BM and TH increased the Cd concentration in the soluble fraction of peanut roots by 24.36% and 102.78%, thus promoting Cd translocation from roots to shoots. Additionally, inoculating BM and TH resulted in a 31.75% and 52.88% elevation in Cd concentration within the leaf cell walls, thereby facilitating the accumulation of Cd within the shoots. Simultaneously, inoculating BM and TH enhanced the concentration of highly bioavailable Cd forms in peanuts. The accumulation of Cd in shoots is the primary factor determining the phytoextraction capacity in peanut, and inoculation of TH resulted in a 16.35-54.54% increase in shoot biomass and an enhancement of 99.10-99.95% in shoot Cd concentration. Therefore, inoculating TH can enhance the phytoextraction capacity for Cd in peanuts, particularly the production of economically valuable components (kernels), without compromising production.

Selenate simultaneously alleviated cadmium and arsenic accumulation in rice (Oryza sativa L.) via regulating transport genes

Cadmium (Cd) and arsenic (As) have contrasting biogeochemical behaviors in paddy soil, which posed an obstacle for reducing their accumulation in rice (Oryza sativa L.) simultaneously. In this study, selenate exhibited a more effective ability than selenite on simultaneous alleviation of Cd and As accumulation in rice under Cd-As co-exposure, and the mechanisms need to be further investigated. The results showed that selenate significantly decreased the root Cd and As contents by 59%-83% and 43%-72% compared to Cd-As compound exposure, respectively. Correspondingly, it significantly down-regulated the expression of uptake-related genes OsNramp5 (87.1%) and OsLsi1 (95.5%) in rice roots. Decreases in Cd (64.5%) and As (16.2%) contents in shoots were also found after selenate addition. Moreover, selenate may promoted the reduction of As(V) to As(Ⅲ) and As(III) efflux to the external medium, resulting in decreased As accumulation and As(Ⅲ) proportion in rice shoots and roots. In addition, selenate could promote the binding of Cd (by 14%-24%) and As (by 9%-15%) in the cell wall, and significantly reduced the oxidative stress by elevating levels of antioxidant enzymes (by 10%-105%) and thiol compounds (by 6%-210%). Additionally, selenate significantly down-regulated the expression of OsNramp1 (49.3%) and OsLsi2 (82.1%) associated with Cd and As transport in rice. These findings suggest selenate has the potential to be an effective material for the simultaneous reduction of Cd and As accumulation in rice under Cd-As co-contamination.

Foliar application of silicon and selenium reduce the toxicity of cadmium to soybeans

Silicon (Si) and selenium (Se), two environmental protection materials, which are beneficial to plant growth and stress resistance, can also alleviate crop stress induced by heavy metals. However, the effects of Si, Se and their interactions in reducing cadmium (Cd) toxicity and the related mechanisms require further elucidation. Hence, this study implemented a foliar application of Si and Se on soybean (Glycine max L.) that subjected to Cd-induced stress with four treatments (sole/combined application of Si, Se, no fertilizer treatment). The results demonstrated that Si and Se showed effective mitigation of Cd toxicity on soybeans mainly by promoting growth, enhancing photosynthesis, maintaining root vigor, improving antioxidant capacity, alleviating oxidative damage, altering the storage form, subcellular distribution of Cd in soybeans, and was more noticeable when combined overall (Si + Se＞Se＞Si). Si + Se increased root activity by 28% and CAT activity in leaves by 130.65%. Overall, the combined application of Si and Se exhibited a pronounced synergistic effect in enhancing the healthy growth of soybean plants under Cd pollution, with a more prominent impact observed following the second fertilization.

Integrated transcriptomics, metabolomics and physiological analyses reveal differential response mechanisms of wheat to cadmium and/or salinity stress

Many soils face dual challenges of cadmium (Cd) contamination and salinization. However, the response of crops, especially wheat, to combined Cd and salinity stress is not understood. Here, wheat was grown in a hydroponic model for 14 days under single and combined Cd and NaCl stresses. Growth parameters, tissue Cd2+ and Na+ contents, and leaf chlorophyll (Chl), O2•-, and MDA levels were determined. Comparative transcriptomic and metabolomic analyses of the leaves were performed. The results showed that combined stress had a greater inhibitory effect on Chl contents and generated more O2•- and MDA, resulting in more severe wheat growth retardation than those under Cd or NaCl stress. Stress-induced decrease in Chl levels may be attributed to the inhibition of Chl biosynthesis, activation of Chl degradation, or a decline in glutamate content. Cd addition weakened the promotional effect of NaCl on SOS1 gene expression, thereby increasing the Na+ content. Contrastingly, NaCl supplementation downregulated the Nramp and ZIP gene expressions related to Cd uptake and transport, thereby impeding Cd2+ accumulation. All stresses enhanced tryptophan content via promoting tryptophan biosynthesis. Meanwhile, Cd and NaCl stresses activated phenylpropanoid biosynthesis and purine metabolism, respectively, thereby increasing the levels of caffeic acid, fumaric acid, and uric acid. Activating the TCA cycle was important in the wheat's response to combined stress. Additionally, NaCl and combined stresses affected starch and sucrose metabolism, resulting in sucrose and trehalose accumulation. Our findings provide a comprehensive understanding of the response of wheat to the combined Cd and salinity stress.

Exposure to toxic cadmium concentration induce physiological and molecular mechanisms alleviating herbivory infestation in Wedelia

Cadmium (Cd) toxicity induces significant disruptions in growth and development, plants have developed strategies to alleviate metal toxicity promoting establishment even during herbivores infestation. The study demonstrates that W. trilobata maintains growth and development under the combined stress of Cd exposure and herbivore invasion by Spodoptera litura, in contrast to W. chinensis. Cd toxicity markedly reduce shoot elongation and total fresh biomass, and a significant decrease in the dry weight of the shoot biomass and leaf count by 19%, 18%, 16%, and 19% in W. trilobata compared to controls. An even more pronounced decrease of 35%, 43%, 45% and 43% was found in W. chinensis. Compared to W. chinensis, W. trilobata showed a higher increase in phytohormone production including abscisic acid (ABA), gibberellic acid (GA3), indole-3-acetic acid (IAA) and methyl jasmonic acid (JA-me) under both Cd and herbivory stress as compared with respective controls. In addition, leaf ultra-structure also showed the highest damage to cell membranous structures by Cd-toxicity in W. chinensis. Furthermore, RNA-seq analysis revealed numerous genes viz., EMSY, MCCA, TIRI, BED-type, ABA, JAZ, CAB-6, CPSI, LHCII, CAX, HNM, ABC-Cd-trans and GBLP being differentially expressed between Cd-stress and herbivory groups in both W. trilobata and W. chinensis, with a particular emphasis on genes associated with metal transport and carbohydrate metabolism. Analyses employing the Gene Ontology (GO) system, the Clusters of Orthologous Groups (COG) categorization, and the Kyoto Encyclopedia of Genes and Genomes (KEGG) database, highlight the functional and evolutionary relationships among the genes of the Phenylpropanoid and Flavonoid biosynthesis pathways and brassinosterod metabolism, associated with plant growth and development under Cd-toxicity and herbivory. W. trilobata opposite of W. chinensis, significantly improve plant growth and mitigates Cd toxicity through modulation of metabolic processes, and regulation of responsible genes, to sustain its growth under Cd and herbivory stress, which can be used in stress improvement in plants for sustainable ecosystem biodiversity and food security.

Hydrogen Peroxide Is Involved in Methane-Alleviated Cadmium Toxicity in Alfalfa (Medicago sativa L.) Seedlings by Enhancing Cadmium Chelation onto Root Cell Walls

Although previous studies have demonstrated that methane (CH4) can mitigate the toxicity of cadmium (Cd) in alfalfa seedlings, the CH4-rich water used in these studies may create hypoxic conditions, potentially influencing the experimental outcomes. Therefore, this study aimed to investigate whether CH4 can reduce Cd toxicity in alfalfa seedlings without the interference of hypoxia and to analyze its underlying mechanisms. Here, it was observed that supplementing oxygen with saturated CH4-rich water can significantly alleviate the inhibition of 75 μM CdCl2 on the growth of alfalfa (Medicago sativa L.) seedlings. Less Cd accumulation was also observed in both root and shoot parts, which could be explained by the CH4-altered cell wall components in alfalfa seedling roots, including covalent and ionic soluble pectin, and the degree of demethylation in pectin, thus enabling a higher proportion of Cd binding to the cell walls and reducing the entry of Cd into the cells. The above actions of CH4 were accompanied by an increase in hydrogen peroxide (H2O2) content and NADPH oxidase activity, which could be blocked by the addition of the NADPH oxidase inhibitor diphenylene iodonium (DPI). Taken together, these results implied that exogenously applied CH4 could alleviate Cd toxicity in alfalfa seedlings by enhancing Cd chelation onto the root cell walls, which might be closely associated with NADPH oxidase-dependent H2O2 signals. These findings could provide insight into the mechanism through which CH4 alleviates Cd toxicity in alfalfa plants.

Exogenous selenium mitigates cadmium uptake and accumulation in two rice (Oryza sativa L.) varieties in cadmium-contaminated soil

Rice grown in cadmium (Cd)-contaminated soil, is a potential threat to human health, but exogenous selenium (Se) application on rice can mitigate Cd toxicity. However, the mechanisms underlying Se mitigation of Cd stress in ratoon rice (RR) are still poorly understood. We conducted a pot experiment with moderate Cd-contaminated yellow-brown paddy soil on two rice varieties 'Taoyouxiangzhan' (TX) and 'Liangyou 6326'(LY). For all treatments, 1.0 mg kg-1 sodium selenite solution was added to soil. Treatment T1 was sodium selenite only, and in the other treatments 100 mg L-1 Se solution was sprayed on the leaves at seedling stage (T2), at tillering stage (T3), and in early anthesis stage (T4). Se treatments decreased Cd accumulation in rice grains and herbage. Under foliar spraying 100 mg L-1 Se at the seedling + 1.0 mg kg-1 Se in soil (T2), leaf Cd content decreased 16.95% in the current season and grains content decreased 46.67% in the subsequent season. Furthermore, grain Se content increased 0.94 mg kg-1 for the TX variety combined with the analysis of Cd bio-accumulation factor in grains, and Se treatments effectively decreased Cd grain concentrations due to reduced Cd translocation from roots to grains. TX variety rice showed a more pronounced response to Se treatments than LY.

Foliar application of selenium and gibberellins reduce cadmium accumulation in soybean by regulating interplay among rhizosphere soil metabolites, bacteria community and cadmium speciation

Both selenium (Se) and gibberellins (GA3) can alleviate cadmium (Cd) toxicity in plants. However, the application of Se and GA3 as foliar spray to against Cd stress on soybean and its related mechanisms have been poorly explored. Herein, this experiment evaluated the effects of Se and GA3 alone and combined application on soybean rhizosphere microenvironment, Cd accumulation and growth of soybean seedlings. The results revealed that both Se and GA3 can effectively decrease the accumulation of Cd in soybean seedlings. Foliar application of Se, GA3 and their combination reduced Cd contents in soybean seedlings respectively by 21.70 %, 27.53 % and 45.07 % when compared with the control treatment, suggest a synergistic effect of Se and GA3 in decreasing Cd accumulation. Se and GA3 also significantly increased diversity and abundance of the metabolites in rhizosphere, which consequently played an important role in shaping rhizosphere bacteria community and improve rhizosphere soil physicochemical properties of Cd contaminated soil, as well as decreased the Cd available forms contents but enhance the immobilized form levels. Overall, this study affords a novel approach on mitigating Cd accumulation in soybean seedlings which is attributed to Se and GA3 regulated interplay among rhizosphere soil metabolites, bacteria community and cadmium speciation.

Exogenous selenium promotes cadmium reduction and selenium enrichment in rice: Evidence, mechanisms, and perspectives

Cadmium (Cd) accumulation in rice, a global environmental issue, poses a significant threat to human health due to its widespread presence and potential transfer through the food chain. Selenium (Se), an essential micronutrient for humans and plants, can reduce Cd uptake in rice and alleviate Cd-induced toxicity. However, the effects and mechanisms of Se supplementation on rice performance in Cd-contaminated soil remain largely unknown. Here, a global meta-analysis was conducted to evaluate the existing knowledge on the effects and mechanisms by which Se supplementation impacts rice growth and Cd accumulation. The result showed that Se supplementation has a significant positive impact on rice growth in Cd-contaminated soil. Specifically, Se supplementation decreased Cd accumulation in rice roots by 16.3 % (11.8-20.6 %), shoots by 24.6 % (19.9-29.1 %), and grain by 37.3 % (33.4-40.9 %), respectively. The grain Cd reduction was associated with Se dose and soil Cd contamination level but not Se type or application method. Se influences Cd accumulation in rice by regulating the expression of Cd transporter genes (OSLCT1, OSHMA2, and OSHMA3), enhancing Cd sequestration in the cell walls, and reducing Cd bioavailability in the soil. Importantly, Se treatment promoted Se enrichment in rice and alleviated oxidative damage associated with Cd exposure by stimulating photosynthesis and activating antioxidant enzymes. Overall, Se treatment mitigated the health hazard associated with Cd in rice grains, particularly in lightly contaminated soil. These findings reveal that Se supplementation is a promising strategy for simultaneous Cd reduction and Se enrichment in rice.

Interactive effect of 24-epibrassinolide and silicon on the alleviation of cadmium toxicity in rice (Oryza sativa L.) plants

Cadmium (Cd) pollution is a serious threat to food safety and human health. Minimization of Cd uptake and enhancing Cd tolerance in plants are vital to improve crop yield and reduce hazardous effects to humans. In this study, we investigate the effect of a synergistic system with phytohormone (24-Epibrassinolide, EBL) and silicon (Si) on Cd toxicity and accumulation of rice plants. The results revealed that Si, EBL and their combination rescued Cd-induced growth inhibition, as evidenced by the increased dry weight of root and shoot. The chlorophyll content and photosynthetic performance were improved. The activity of antioxidant enzymes (SOD, POD and CAT) was increased and oxidative stress was alleviated. More importantly, Cd content in root was decreased by 20.25%, 17.72% and 27.84%, while Cd content in shoot decreased by 21.17%, 16.47% and 25.88%, respectively. Moreover, Si, EBL and Si + EBL treatment enriched cell wall-bound Cd and reduced Cd toxicity to functional organelles. Meanwhile, the residual form of Cd was enriched and the highly toxic forms of Cd (inorganic and water-soluble Cd) were decreased. The joint application showed better effects than applying Si and EBL alone. Collectively, this study provides an effective way for Cd toxicity mitigation in rice plants.

Mitigation of uranium toxicity in rice by Sphingopyxis sp. YF1: Evidence from growth, ultrastructure, subcellular distribution, and physiological characteristics

Uranium (U) contamination of rice is an urgent ecological and agricultural problem whose effective alleviation is in great demand. Sphingopyxis genus has been shown to remediate heavy metal-contaminated soils. Rare research delves into the mitigation of uranium (U) toxicity to rice by Sphingopyxis genus. In this study, we exposed rice seedlings for 7 days at U concentrations of 0, 10, 20, 40, and 80 mg L-1 with or without the Sphingopyxis sp. YF1 in the rice nutrient solution. Here, we firstly found YF1 colonized on the root of rice seedlings, significantly mitigated the growth inhibition, and counteracted the chlorophyll content reduction in leaves induced by U. When treated with 1.1 × 107 CFU mL-1 YF1 with the amendment of 10 mg L-1 U, the decrease of U accumulation in rice seedling roots and shoots was the largest among all treatments; reduced by 39.3% and 32.1%, respectively. This was associated with the redistribution of the U proportions in different organelle parts, leading to the alleviation of the U damage to the morphology and structure of rice root. Interestingly, we found YF1 significantly weakens the expression of antioxidant enzymes genes (CuZnSOD,CATA,POD), promotes the up-regulation of metal-transporters genes (OsHMA3 and OsHMA2), and reduces the lipid peroxidation damage induced by U in rice seedlings. In summary, YF1 is a plant-probiotic with potential applications for U-contaminated rice, benefiting producers and consumers.

Comprehensive transcriptome, physiological and biochemical analyses reveal that key role of transcription factor WRKY and plant hormone in responding cadmium stress

Cadmium (Cd) is readily absorbed by tobacco and accumulates in the human body through smoke inhalation, posing threat to human health. While there have been many studies on the negative impact of cadmium in tobacco on human health, the specific adaptive mechanism of tobacco roots to cadmium stress is not well understood. In order to comprehensively investigate the effects of Cd stress on the root system of tobacco, the combination of transcriptomic, biochemical, and physiological methods was utilized. In this study, tobacco growth was significantly inhibited by 50 μM of Cd, which was mainly attributed to the destruction of root cellular structure. By comparing the transcriptome between CK and Cd treatment, there were 3232 up-regulated deferentially expressed genes (DEGs) and 3278 down-regulated DEGs. The obvious differential expression of genes related to the nitrogen metabolism, metal transporters and the transcription factors families. In order to mitigate the harmful effects of Cd, the root system enhances Cd accumulation in the cell wall, thereby reducing the Cd content in the cytoplasm. This result may be mediated by plant hormones and transcription factor (TF). Correlational statistical analysis revealed significant negative correlations between IAA and GA with cadmium accumulation, indicated by correlation coefficients of -0.91 and -0.93, respectively. Conversely, ABA exhibited a positive correlation with a coefficient of 0.96. In addition, it was anticipated that 3 WRKY TFs would lead to a reduction in Cd accumulation. Our research provides a theoretical basis for the systematic study of the specific physiological processes of plant roots under Cd stress.

Nanosized-Selenium-Application-Mediated Cadmium Toxicity in Aromatic Rice at Different Stages

Cadmium (Cd) pollution restricts the rice growth and poses a threat to human health. Nanosized selenium (NanoSe) is a new nano material. However, the effects of NanoSe application on aromatic rice performances under Cd pollution have not been reported. In this study, a pot experiment was conducted with two aromatic rice varieties and a soil Cd concentration of 30 mg/kg. Five NanoSe treatments were applied at distinct growth stages: (T1) at the initial panicle stage, (T2) at the heading stage, (T3) at the grain-filling stage, (T1+2) at both the panicle initial and heading stages, and (T1+3) at both the panicle initial and grain-filling stages. A control group (CK) was maintained without any application of Se. The results showed that, compared with CK, the T1+2 and T1+3 treatments significantly reduced the grain Cd content. All NanoSe treatments increased the grain Se content. The grain number per panicle, 1000-grain weight, and grain yield significantly increased due to NanoSe application under Cd pollution. The highest yield was recorded in T3 and T1+3 treatments. Compared with CK, all NanoSe treatments increased the grain 2-acetyl-1-pyrroline (2-AP) content and impacted the content of pyrroline-5-carboxylic acid and 1-pyrroline which are the precursors in 2-AP biosynthesis. In conclusion, the foliar application of NanoSe significantly reduced the Cd content, increased the Se content, and improved the grain yield and 2-AP content of aromatic rice. The best amendment was applying NanoSe at both the panicle initial and grain-filling stages.

Unveiling silicon-mediated cadmium tolerance mechanisms in mungbean (Vigna radiata (L.) Wilczek): Integrative insights from gene expression, antioxidant responses, and metabolomics

Cadmium (Cd), one of the most phytotoxic heavy metals, is a major contributor to yield losses in several crops. Silicon (Si) is recognized for its vital role in mitigating Cd toxicity, however, the specific mechanisms governing this mitigation process are still not fully understood. In the present study, the effect of Si supplementation on mungbean (Vigna radiata (L.) Wilczek) plants grown under Cd stress was investigated to unveil the intricate pathways defining Si derived stress tolerance. Non-invasive leaf imaging technique revealed improved growth, biomass, and photosynthetic efficiency in Si supplemented mungbean plants under Cd stress. Further, physiological and biochemical analysis revealed Si mediated increase in activity of glutathione reductase (GR), ascorbate peroxidase (APX), and catalase (CAT) enzymes involved in reactive oxygen species (ROS) metabolism leading to mitigation of cellular damage and oxidative stress. Untargeted metabolomic analysis using liquid chromatography coupled with mass spectrometry (LC-MS/MS) provided insights into Si mediated changes in metabolites and their respective pathways under Cd stress. Alteration in five different metabolic pathways with major changes in flavanols and flavonoids biosynthesis pathway which is essential for controlling plants antioxidant defense system and oxidative stress management were observed. The information reported here about the effects of Si on photosynthetic efficiency, antioxidant responses, and metabolic changes will be helpful in understanding the Si-mediated resistance to Cd stress in plants.

Effect of silicon spraying on rice photosynthesis and antioxidant defense system on cadmium accumulation

Cadmium (Cd) pollution is a serious threat to food safety and human health. Minimizing Cd uptake and enhancing Cd tolerance in plants are vital to improve crop yield and reduce hazardous effects to humans. In this study, we designed three Cd concentration stress treatments (Cd1: 0.20 mg·kg-1, Cd2: 0.60 mg·kg-1, and Cd3: 1.60 mg·kg-1) and two foliar silicon (Si) treatments (CK: no spraying of any material, and Si: foliar Si spraying) to conduct pot experiments on soil Cd stress. The results showed that spraying Si on the leaves reduced the Cd content in brown rice by 4.79-42.14%. Si application increased net photosynthetic rate (Pn) by 1.77-4.08%, stomatal conductance (Gs) by 5.27-23.43%, transpiration rate (Tr) by 2.99-20.50% and intercellular carbon dioxide (CO2) concentration (Ci) by 6.55-8.84%. Foliar spraying of Si significantly increased the activities of superoxide dismutase (SOD) and peroxidase (POD) in rice leaves by 9.84-14.09% and 4.69-53.09%, respectively, and reduced the content of malondialdehyde (MDA) by 7.83-48.72%. In summary, foliar Si spraying protects the photosynthesis and antioxidant system of rice canopy leaves, and is an effective method to reduce the Cd content in brown rice.

Salicylic Acid's impact on Sedum alfredii growth and cadmium tolerance: Comparative physiological, transcriptomic, and metabolomic study

With the acceleration of industrialization, Cd pollution has emerged as a major threat to soil ecosystem health and food safety. Hyperaccumulating plants like Sedum alfredii Hance are considered to be used as part of an effective strategy for the ecological remediation of Cd polluted soils. This study delved deeply into the physiological, transcriptomic, and metabolomic responses of S. alfredii under cadmium (Cd) stress when treated with exogenous salicylic acid (SA). We found that SA notably enhanced the growth of S. alfredii and thereby increased absorption and accumulation of Cd, effectively alleviating the oxidative stress caused by Cd through upregulation of the antioxidant system. Transcriptomic and metabolomic data further unveiled the influence of SA on photosynthesis, antioxidant defensive mechanisms, and metal absorption enrichment pathways. Notably, the interactions between SA and other plant hormones, especially IAA and JA, played a central role in these processes. These findings offer us a comprehensive perspective on understanding how to enhance the growth and heavy metal absorption capabilities of hyperaccumulator plants by regulating plant hormones, providing invaluable strategies for future environmental remediation efforts.

Selenium nanoparticles conferred drought tolerance in tomato plants by altering the transcription pattern of microRNA-172 (miR-172), bZIP, and CRTISO genes, upregulating the antioxidant system, and stimulating secondary metabolism

Drought stress is one of the major limiting factors for the production of tomato in Iran. In this study, the efficiency of selenate and Se nanoparticle (SeNP) foliar application on tomato plants was assessed to vestigate mitigating the risk associated with water-deficit conditions. Tomato plants were treated with SeNPs at the concentrations of 0 and 4 mg L-1; after the third sprays, the plants were exposed to water-deficit conditions. The foliar spraying with SeNPs not only improved growth, yield, and developmental switch to the flowering phase but also noticeably mitigated the detrimental risk associated with the water-deficit conditions. Gene expression experiments showed a slight increase in expression of microRNA-172 (miR-172) in the SeNP-treated plants in normal irrigation, whereas miR-172 displayed a downregulation trend in response to drought stress. The bZIP transcription factor and CRTISO genes were upregulated following the SeNP and drought treatments. Drought stress significantly increased the H2O2 accumulation that is mitigated with SeNPs. The foliar spraying with Se or SeNPs shared a similar trend to alleviate the negative effect of drought stress on the membrane integrity. The applied supplements also conferred drought tolerance through noticeable improvements in the non-enzymatic (ascorbate and glutathione) and enzymatic (catalase and peroxidase) antioxidants. The SeNP-mediated improvement in drought stress tolerance correlated significantly with increases in the activity of phenylalanine ammonia-lyase, proline, non-protein thiols, and flavonoid concentrations. SeNPs also improved the fruit quality regarding K, Mg, Fe, and Se concentrations. It was concluded that foliar spraying with SeNPs could mitigate the detrimental risk associated with the water-deficit conditions.

Silicon and selenium alleviate cadmium toxicity in Artemisia selengensis Turcz by regulating the plant-rhizosphere

Soil cadmium (Cd) pollution has emerged as a pressing concern due to its deleterious impacts on both plant physiology and human well-being. Silicon (Si) is renowned for its ability to mitigate excessive Cd accumulation within plant cells and reduce the mobility of Cd in soil, whereas Selenium (Se) augments plant antioxidant capabilities and promotes rhizosphere microbial activity. However, research focusing on the simultaneous utilization of Si and Se to ameliorate plant Cd toxicity through multiple mechanisms within the plant-rhizosphere remains comparatively limited. This study combined hydroponic and pot experiments to investigate the effects of the combined application of Si and Se on Cd absorption and accumulation, as well as the growth and rhizosphere of A. selengensis Turcz under Cd stress. The results revealed that a strong synergistic effect was observed between both Si and Se. The combination of Si and Se significantly increased the activity and content of enzymes and non-enzyme antioxidants within A. selengensis Turcz, reduced Cd accumulation and inhibiting its translocation from roots to shoots. Moreover, Si and Se application improved the levels of reducing sugar, soluble protein, and vitamin C, while reducing nitrite content and Cd bioavailability. Furthermore, the experimental results showed that the combination of Si and Se not only increased the abundance of core rhizosphere microorganisms, but also stimulated the activity of soil enzymes, which effectively limited the migration of Cd in the soil. These findings provided valuable insights into the effective mitigation of soil Cd toxicity to plants and also the potential applications in improving plant quality and safety.

Methyl jasmonate enhances the safe production ability of Cd-stressed wheat by regulating the antioxidant capacity, Cd absorption, and distribution in wheat

Identifying green and effective measures for reducing wheat Cd toxicity and grain Cd accumulation is crucial. This study used seedling sand culture and full-grown pot experiments of wheat cultivars 'Luomai23' (LM) and 'Zhongyu10' (ZY). The purpose was to determine the effects of exogenous MeJA on the phenotype, photosynthesis, antioxidant system, Cd accumulation and distribution, transporter gene expression, and cell wall properties of Cd-stressed wheat. Compared with Cd treatment alone, the plant height and maximum root length treated with 0.001 μM MeJA increased by more than 6.3% and 16.6%, respectively. Under 5 mg⋅kg-1 Cd treatment, spraying 10 μM MeJA increased the photosynthetic rate of LM and ZY by 23.5% and 35.8% at the filling stage, respectively. Methyl jasmonate significantly reduced the H2O2 and MDA contents by increasing the activities of POD, DHAR, MDHAR, and GR and the contents of AsA and GSH. Applicating MeJA increased the content of chelate substances, cell wall polysaccharides, and cell wall functional groups. Besides, MeJA regulated the expression of Cd transporter genes, with shoot and root Cd content decreasing by 46.7% and 27.9% in LM, respectively. Spraying 10 μM MeJA reduced Cd absorption and translocation from vegetative organs to grains, thus reducing the grain Cd content of LM and ZY by 36.1 and 39.9% under 5 mg⋅kg-1 Cd treatment, respectively. Overexpressing TaJMT significantly increased the MeJA content and Cd tolerance of Arabidopsis. These results have improved the understanding of the mechanism through which MeJA alleviates Cd toxicity and reduces Cd accumulation in wheat.

Efficient reduction of Cr(VI) by guava (Psidium guajava) leaf extract and its mitigation effect on Cr toxicity in rice seedlings

Hexavalent chromium (Cr(VI)) is a toxic element that has negative impacts on crop growth and yield. Using plant extracts to convert toxic Cr(VI) into less toxic Cr(III) may be a more favorable option compared to chemical reducing agents. In this study, the potential effects and mechanisms of using an aqueous extract of Psidium guajava L. leaves (AEP) in reducing Cr(VI) toxicity in rice were comprehensively studied. Firstly, the reducing power of AEP for Cr(VI) was confirmed by the cyclic voltammetry combined with X-ray photoelectron spectroscopy (XPS) assays. The highest Cr(VI) reduction efficiency reached approximately 78% under 1.5 mg gallic acid equivalent (GAE)/mL of AEP and 10 mg/L Cr(VI) condition. Additionally, Cr(VI) stress had a significant inhibitory effect on rice growth. However, the exogenous application of AEP alleviated the growth inhibition and oxidative damage of rice under Cr(VI) stress by increasing the activity and level of enzymatic and non-enzymatic antioxidants. Furthermore, the addition of AEP restored the ultrastructure of root cells, promoted Cr adsorption onto root cell walls, and limited the translocation Cr to shoots. In shoots, AEP application also triggered the expression of specific genes involved in Cr defense and detoxification response, including photosynthesis pathways, antioxidant systems, flavonoids biosynthesis, and plant hormone signal transduction. These results suggest that AEP is an efficient reduction agent for Cr(VI), and exogenous application of AEP may be a promising strategy to mitigate the harm of Cr(VI) on rice, ultimately contributing to improved crop yield in Cr-contaminated environments.

Conjoint analysis of physio-biochemical, transcriptomic, and metabolomic reveals the response characteristics of solanum nigrum L. to cadmium stress

Cadmium (Cd) is a nonessential element in plants and has adverse effects on the growth and development of plants. However, the molecular mechanisms of Cd phytotoxicity, tolerance and accumulation in hyperaccumulators Solanum nigrum L. has not been well understood. Here, physiology, transcriptome, and metabolome analyses were conducted to investigate the influence on the S. nigrum under 0, 25, 50, 75 and 100 µM Cd concentrations for 7 days. Pot experiments demonstrated that compared with the control, Cd treatment significantly inhibited the biomass, promoted the Cd accumulation and translocation, and disturbed the balance of mineral nutrient metabolism in S. nigrum, particularly at 100 µM Cd level. Moreover, the photosynthetic pigments contents were severely decreased, while the content of total protein, proline, malondialdehyde (MDA), H2O2, and antioxidant enzyme activities generally increased first and then slightly declined with increasing Cd concentrations, in both leaves and roots. Furthermore, combined with the previous transcriptomic data, numerous crucial coding-genes related to mineral nutrients and Cd ion transport, and the antioxidant enzymes biosynthesis were identified, and their expression pattern was regulated under different Cd stress. Simultaneously, metabolomic analyses revealed that Cd treatment significantly changed the expression level of many metabolites related to amino acid, lipid, carbohydrate, and nucleotide metabolism. Metabolic pathway analysis also showed that S. nigrum roots activated some differentially expressed metabolites (DEMs) involved in energy metabolism, which may enhance the energy supply for detoxification. Importantly, central common metabolism pathways of DEGs and DEMs, including the "TCA cycle", "glutathione metabolic pathway" and "glyoxylate and dicarboxylate metabolism" were screened using conjoint transcriptomics and metabolomics analysis. Our results provide some novel evidences on the physiological and molecular mechanisms of Cd tolerance in hyperaccumulator S. nigrum plants.

Associations of environmental cadmium exposure with kidney damage: Exploring mediating DNA methylation sites in Chinese adults

Environmental exposure is widely recognized as the primary sources of Cadmium (Cd) in the human body, and exposure to Cd is associated with kidney damage in adults. Nevertheless, the role of DNA methylation in Cd-induced kidney damage remains unclear. This study aimed to investigate the epigenome-wide association of environmental Cd-related DNA methylation changes with kidney damage. We included 300 non-smoking adults from the China in 2019. DNA methylation profiles were measured with Illumina Infinium MethylationEPIC BeadChip array. Linear mixed-effect model was employed to estimate the effects of urinary Cd with DNA methylation. Differentially methylated positions (DMPs) associated with urinary Cd were then tested for the association with kidney damage indicators. The mediation analysis was further applied to explore the potential DNA methylation based mediators. The prediction model was developed using a logistic regression model, and used 1000 bootstrap resampling for the internal validation. We identified 27 Cd-related DMPs mapped to 20 genes after the adjustment of false-discovery-rate for multiple testing among non-smoking adults. 17 DMPs were found to be associated with both urinary Cd and kidney damage, and 14 of these DMPs were newly identified within the Chinese. Mediation analysis revealed that DNA methylation of cg26907612 and cg16848624 mediated the Cd-related reduced kidney damage. In addition, ten variables were selected using the LASSO regression analysis and were utilized to develop the prediction model. It found that the nomogram model predicted the risk of kidney damage caused by environmental Cd with a corrected C-index of 0.779. Our findings revealed novel DMPs associated with both environmental Cd exposure and kidney damage among non-smoking adults, and developed an easy-to-use nomogram-illustrated model using these novel DMPs. These findings could provide a theoretical basis for formulating prevention and control strategies for kidney damage from the perspective of environmental pollution and epigenetic regulation.

Fertilizer application alters cadmium and selenium bioavailability in soil-rice system with high geological background levels

The co-occurrence of cadmium (Cd) pollution and selenium (Se) deficiency commonly exists in global soils, especially in China. As a result, there is great interest in developing practical agronomic strategies to simultaneously achieve Cd remediation and Se mobilization in paddy soils, thereby enhancing food quality/safety. To this end, we conducted a field-plot trial on soils having high geological background levels of Cd (0.67 mg kg-1) and Se (0.50 mg kg-1). We explored 12 contrasting fertilizers (urea, potassium sulfate (K2SO4), calcium-magnesium-phosphate (CMP)), amendments (manure and biochar) and their combinations on Cd/Se bioavailability. Soil pH, total organic carbon (TOC), soil available Cd/Se, Cd/Se fractions and Cd/Se accumulation in different rice components were determined. No significant differences existed in mean grain yield among treatments. Results showed that application of urea and K2SO4 decreased soil pH, whereas the CMP fertilizer and biochar treatments increased soil pH. There were no significant changes in TOC concentrations. Three treatments (CMP, manure, biochar) significantly decreased soil available Cd, whereas no treatment affected soil available Se at the maturity stage. Four treatments (CMP, manure, biochar and manure＋urea＋CMP＋K2SO4) achieved our dual goal of Cd reduction and Se enrichment in rice grain. Structural equation modeling (SEM) demonstrated that soil available Cd and root Cd were negatively affected by pH and organic matter (OM), whereas soil available Se was positively affected by pH. Moreover, redundancy analysis (RDA) showed strong positive correlations between soil available Cd, exchangeable Cd and reducible Cd with grain Cd concentration, as well as between pH and soil available Se with grain Se concentration. Further, there was a strong negative correlation between residual Cd/Se (non-available fraction) and grain Cd/Se concentrations. Overall, this study identified the primary factors affecting Cd/Se bioavailability, thereby providing new guidance for achieving safe production of Se-enriched rice through fertilizer/amendment management of Cd-enriched soils.

The Uptake, Transfer, and Detoxification of Cadmium in Plants and Its Exogenous Effects

Cadmium (Cd) exerts a toxic influence on numerous crucial growth and development processes in plants, notably affecting seed germination rate, transpiration rate, chlorophyll content, and biomass. While considerable advances in Cd uptake and detoxification of plants have been made, the mechanisms by which plants adapt to and tolerate Cd toxicity remain elusive. This review focuses on the relationship between Cd and plants and the prospects for phytoremediation of Cd pollution. We highlight the following issues: (1) the present state of Cd pollution and its associated hazards, encompassing the sources and distribution of Cd and the risks posed to human health; (2) the mechanisms underlying the uptake and transport of Cd, including the physiological processes associated with the uptake, translocation, and detoxification of Cd, as well as the pertinent gene families implicated in these processes; (3) the detrimental effects of Cd on plants and the mechanisms of detoxification, such as the activation of resistance genes, root chelation, vacuolar compartmentalization, the activation of antioxidant systems and the generation of non-enzymatic antioxidants; (4) the practical application of phytoremediation and the impact of incorporating exogenous substances on the Cd tolerance of plants.

Biosynthetic selenium nanoparticles (Bio-SeNPs) mitigate the toxicity of antimony (Sb) in rice (Oryza sativa L.) by limiting Sb uptake, improving antioxidant defense system and regulating stress-related gene expression

Nanotechnology offers a promising and innovative approach to mitigate biotic and abiotic stress in crop production. In this study, the beneficial role and potential detoxification mechanism of biogenic selenium nanoparticles (Bio-SeNPs) prepared from Psidium guajava extracts in alleviating antimony (Sb) toxicity in rice seedlings (Oryza sativa L.) were investigated. The results revealed that exogenous addition of Bio-SeNPs (0.05 g/L) into the hydroponic-cultured system led to a substantial enhancement in rice shoot height (73.3%), shoot fresh weight (38.7%) and dry weight (28.8%) under 50 μM Sb(III) stress conditions. Compared to Sb exposure alone, hydroponic application of Bio-SeNPs also greatly promoted rice photosynthesis, improved cell viability and membrane integrity, reduced reactive oxygen species (ROS) levels, and increased antioxidant activities. Meanwhile, exogenous Bio-SeNPs application significantly lowered the Sb accumulation in rice roots (77.1%) and shoots (35.1%), and reduced its root to shoot translocation (55.3%). Additionally, Bio-SeNPs addition were found to modulate the subcellular distribution of Sb and the expression of genes associated with Sb detoxification in rice, such as OsCuZnSOD2, OsCATA, OsGSH1, OsABCC1, and OsWAK11. Overall, our findings highlight the great potential of Bio-SeNPs as a promising alternative for reducing Sb accumulation in crop plants and boosting crop production under Sb stress conditions.

Utilizing transcriptomics and proteomics to unravel key genes and proteins of Oryza sativa seedlings mediated by selenium in response to cadmium stress

BACKGROUND

Cadmium (Cd) pollution has declined crop yields and quality. Selenium (Se) is a beneficial mineral element that protects plants from oxidative damage, thereby improving crop tolerance to heavy metals. The molecular mechanism of Se-induced Cd tolerance in rice (Oryza sativa) is not yet understood. This study aimed to elucidate the beneficial mechanism of Se (1 mg/kg) in alleviating Cd toxicity in rice seedlings.

RESULTS

Exogenous selenium addition significantly improved the toxic effect of cadmium stress on rice seedlings, increasing plant height and fresh weight by 20.53% and 34.48%, respectively, and increasing chlorophyll and carotenoid content by 16.68% and 15.26%, respectively. Moreover, the MDA, ·OH, and protein carbonyl levels induced by cadmium stress were reduced by 47.65%, 67.57%, and 56.43%, respectively. Cell wall metabolism, energy cycling, and enzymatic and non-enzymatic antioxidant systems in rice seedlings were significantly enhanced. Transcriptome analysis showed that the expressions of key functional genes psbQ, psbO, psaG, psaD, atpG, and PetH were significantly up-regulated under low-concentration Se treatment, which enhanced the energy metabolism process of photosystem I and photosystem II in rice seedlings. At the same time, the up-regulation of LHCA, LHCB family, and C4H1, PRX, and atp6 functional genes improved the ability of photon capture and heavy metal ion binding in plants. Combined with proteome analysis, the expression of functional proteins OsGSTF1, OsGSTU11, OsG6PDH4, OsDHAB1, CP29, and CabE was significantly up-regulated under Se, which enhanced photosynthesis and anti-oxidative stress mechanism in rice seedlings. At the same time, it regulates the plant hormone signal transduction pathway. It up-regulates the expression response process of IAA, ABA, and JAZ to activate the synergistic effect between each cell rapidly and jointly maintain the homeostasis balance.

CONCLUSION

Our results revealed the regulation process of Se-mediated critical metabolic pathways, functional genes, and proteins in rice under cadmium stress. They provided insights into the expression rules and dynamic response process of the Se-mediated plant resistance mechanism. This study provided the theoretical basis and technical support for crop safety in cropland ecosystems and cadmium-contaminated areas.

Integrated ultrastructural, physiological, transcriptomic, and metabolomic analysis uncovers the mechanisms by which nicotinamide alleviates cadmium toxicity in Pistia stratiotes L

Exogenous nicotinamide (NIC) is a promising solution to relieve heavy metal (HM) toxicity in plants. Nonetheless, the underlying mechanisms involved remain poorly understood. As NIC addition (200 μM) can increase the tolerance of Pistia stratiotes L. to Cd stress (10 mg L-1), this strategy was subjected to integrated ultrastructural, physiological, transcriptomic, and metabolomic analysis to reveal the mechanisms involved. Exogenous NIC initiated a series of physiological, transcriptional, and metabolic responses that alleviated Cd damage. NIC addition improved Cd transfer from roots to leaves and reduced Cd damage in roots. The transported Cd to leaves did not induce further toxicity because it was abundantly compartmentalised in cell walls, which might be mediated by lignin synthesis. Moreover, NIC addition improved the repair of photosystem II in leaves under Cd stress by inducing key genes (e.g., chlorophyll A-B binding protein and PSII repair protein encoding genes), resulting in the restoration of Fv/Fm. In addition, antioxidant enzyme activities (e.g., peroxidase and catalase) and synthesis of antioxidants (e.g., stachydrine and curculigoside) were triggered to overcome oxidative stress. Our work paves the way for a deeper understanding of the mechanisms by which NIC alleviates HM toxicity in plants, providing a basis for improving phytoremediation.

Selenium increases antimony uptake in ramie (Boehmeria nivea L.) by enhancing the physiological, antioxidative, and ionomic mechanisms

Ramie (Boehmeria nivea L.) is a promising phytoremediation candidate due to its high tolerance and enrichment capacity for antimony (Sb). However, challenges arise as Sb accumulated mainly in roots, complicating soil extraction. Under severe Sb contamination, the growth of ramie may be inhibited. Strategies are needed to enhance Sb accumulation in ramie's aboveground parts and improve tolerance to Sb stress. Considering the beneficial effects of selenium (Se) on plant growth and enhancing resistance to abiotic stresses, this study aimed to investigate the potential use of Se in enhancing Sb uptake by ramie. We investigated the effects of Se (0.5, 1, 2, 5, or 10 μM) on ramie growth, Sb uptake and speciation, antioxidant responses, and ionomic profiling in ramie under 10 mg/L of SbIII or antimonate (SbV) stresses. Results revealed that the addition of 0.5 μM Se significantly increased shoot biomass by 75.73% under SbIII stress but showed minimal effects on shoot and root length in both SbIII and SbV treatments. Under SbIII stress, 2 μM Se significantly enhanced Sb concentrations by 48.42% in roots and 62.88% in leaves. In the case of SbV exposure, 10 μM Se increased Sb content in roots by 42.57%, and 1 μM Se led to a 91.74% increase in leaves. The speciation analysis suggested that Se promoted the oxidation of SbIII to less toxic SbV to mitigate Sb toxicity. Additionally, Se addition effectively minimized the excess reactive oxygen species produced by Sb exposure, with the lowest malondialdehyde (MDA) content at 0.5 μM Se under SbIII and 2 μM Se under SbV, by activating antioxidant enzymes including superoxide dismutase, catalase, peroxidase, and glutathione peroxidase. Ionomic analysis revealed that Se helped in maintaining the homeostasis of certain nutrient elements, including magnesium, potassium (K), calcium (Ca), iron (Fe), and copper (Cu) in the SbIII-treated roots and K and manganese (Mg) in the SbV-treated roots. The results suggest that low concentrations of Se can be employed to enhance the phytoremediation of Sb-contaminated soils using ramie.

Silicon reduces toxicity and accumulation of arsenic and cadmium in cereal crops: A meta-analysis, mechanism, and perspective study

Arsenic (As) and cadmium (Cd) are two toxic metal(loid)s that pose significant risks to food security and human health. Silicon (Si) has attracted substantial attention because of its positive effects on alleviating the toxicity and accumulation of As and Cd in crops. However, our current knowledge of the comprehensive effects and detailed mechanisms of Si amendment is limited. In this study, a global meta-analysis of 248 original articles with over 7000 paired observations was conducted to evaluate Si-mediated effects on growth and As and Cd accumulation in rice (Oryza sativa L.), wheat (Triticum aestivum L.), and maize (Zea mays L.). Si application increases the biomass of these crops under As and/or Cd contamination. Si amendment also decreased shoot As and Cd accumulation by 24.1 % (20.6 to 27.5 %) and 31.9 % (29.0 to 31.9 %), respectively. Furthermore, the Si amendment reduced the human health risks posed by As (2.6 %) and Cd (12.9 %) in crop grains. Si-induced inhibition of Cd accumulation is associated with decreased Cd bioavailability and the downregulation of gene expression. The regulation of gene expression by Si addition was the driving factor limiting shoot As accumulation. Overall, our analysis demonstrated that Si amendment has great potential to reduce the toxicity and accumulation of As and/or Cd in crops, providing a scientific basis for promoting food safety globally.

Metagenomic and biochemical analyses reveal the potential of silicon to alleviate arsenic toxicity in rice (Oryza sativa L.)

Arsenic (As) pollution in agricultural systems poses a serious threat to crop productivity and food safety. Silicon (Si) has been reported to mitigate toxic effects of heavy metals in plants. However, the mechanisms behind Si-mediated alleviation of As toxicity in rice (Oryza sativa L.) remain poorly understood. Here, we performed metagenomic and biochemical analyses to investigate the potential of Si in alleviating As toxicity to rice plants. As exposure reduced plant growth, chlorophyll contents, antioxidant enzyme levels and soil enzymes activity, while increasing reactive oxygen species (ROS) activity and inducing alterations in the rhizosphere microbiome of rice seedlings. Silicon amendments enhanced rice growth (24%), chlorophyll a (25%), and chlorophyll b (26.7%), indicating enhanced photosynthetic capacity. Si amendments also led to the upregulation of antioxidant enzymes viz., superoxide dismutase (15.4%), and peroxidase (15.6%), resulting in reduced ROS activity and oxidative stress compared to the As-treated control. Furthermore, Si treatment reduced uptake and translocation of As in rice plants, as evidenced by the analysis of elemental contents. Microscopic examination of leaf and root ultrastructure showed that Si mitigated As-induced cellular damage and maintained normal morphology. Metagenomic analysis of the rice rhizosphere microbiome revealed that Si application modulated composition and diversity of microbial communities e.g., Proteobacteria, Actinobacteria, and Firmicutes. Additionally, Si amendments upregulated the relative expression levels of OsGSH, OsPCs, OsNIP1;1 and OsNIP3;3 genes, while the expression levels of the OsLis1 and OsLis2 genes were significantly downregulated compared with As-treated rice plants. Overall, these findings contribute to our understanding of Si-mediated plant resilience to As stress and offer potential strategies for sustainable agriculture in As-contaminated regions.

Effect of hesperidin on growth, photosynthesis, antioxidant systems and uptake of cadmium, copper, chromium and zinc by Celosia argentea plants

Rapid industrialization and extensive agricultural practices are the major causes of soil heavy metal contamination, which needs urgent attention to safeguard the soils from contamination. However, the phytotoxic effects of excessive metals in plants are the primary obstacle to efficient phytoextraction. The present study evaluated the effects of hesperidin (HSP) on metals (Cu, Cd, Cr, Zn) phytoextraction by hyperaccumulator (Celosia argentea L.) plants. For this purpose, HSP, a flavonoid compound with strong antioxidant potential to assist metal phytoextraction was used under metal stress in plants. Celosia argentea plants suffered significant (P ≤ 0.001) oxidative damage due to the colossal accumulation of metals (Cu, Cd, Cr, Zn). However, HSP supplementation notably (P ≤ 0.001) abated ROS generation (O2•‒, •OH, H2O2), lipoxygenase activity, methylglyoxal production, and relative membrane permeability that clearly indicated HSP-mediated decline in oxidative injury in plants. Exogenous HSP improved (P ≤ 0.001) the production of non-protein thiol, phytochelatins, osmolytes, and antioxidant compounds. Further, HSP enhanced (P ≤ 0.001) H2S and NO endogenous production, which might have improved the GSH: GSSG ratio. Consequently, HSP-treated C. argentea plants had higher biomass alongside elevated metal accumulation mirrored as profound modifications in translocation factor (TF), bioaccumulation coefficient (BAC), and bioconcentration factor (BCF). In this context, HSP significantly enhanced TF of Cr (P ≤ 0.001), Cd (P ≤ 0.001), and Zn (P ≤ 0.01), while BAC of Cr (P ≤ 0.001), Cd (P ≤ 0.001), and Zn (P ≤ 0.001). Further, BCF was significant (P ≤ 0.05) only in plants grown under Cr-spiked soil. Overall, HSP has the potential for phytoremediation of metals by C. argentea, which might be a suitable strategy for metal-polluted soils.

Soil inorganic amendments produce safe rice by reducing the transfer of Cd and increasing key amino acids in brown rice

The digestibility of cadmium (Cd) in brown rice is directly related to amino acid metabolism in rice and human health. In our field study, three kinds of alkaline calcium-rich soil inorganic amendments (SIAs) at three dosages were applied to produce safe rice and improve the quality of rice in Cd-contaminated paddy. With the increased application of SIA, Cd content in iron plaque on rice root significantly increased, the transfer of Cd from rice root to grain significantly decreased, and then Cd content in brown rice decreased synchronously. The vitro digestibility of Cd in brown rice was estimated by a physiologically based extraction test. Results showed that more than 70% of Cd in brown rice could be digested by simulated gastrointestinal juice. Based on the total and digestible Cd contents in brown rice to evaluate the health risk, the application of 2.25 ton SIA/ha could produce safe rice in acidic slightly Cd-contaminated paddy soils. The amino acids (AAs) in brown rice were determined by high-performance liquid chromatography. The contents of 5 key AAs (KAAs) that actively respond to environmental changes increased significantly with the increased application of SIA. The structural equation model indicated that KAAs could be affected by the Cd translocation capacity from rice root to grain, and consequently altered the ratio of indigestible Cd in brown rice. The formation of indigestible KAAs-Cd complexes by combining KAAs (phenylalanine, leucine, histidine, glutamine, and asparagine) with Cd in brown rice could be considered a potential mechanism for reducing the digestibility of Cd.

Transcriptome Analysis Reveals the Mechanism of Exogenous Selenium in Alleviating Cadmium Stress in Purple Flowering Stalks (Brassica campestris var. purpuraria)

In China, cadmium (Cd) stress has a significant role in limiting the development and productivity of purple flowering stalks (Brassica campestris var. purpuraria). Exogenous selenium supplementation has been demonstrated in earlier research to mitigate the effects of Cd stress in a range of plant species; nevertheless, the physiological and molecular processes by which exogenous selenium increases vegetable shoots' resistance to Cd stress remain unclear. Purple flowering stalks (Brassica campestris var. purpuraria) were chosen as the study subject to examine the effects of treatment with sodium selenite (Na2SeO3) on the physiology and transcriptome alterations of cadmium stress. Purple flowering stalk leaves treated with exogenous selenium had higher glutathione content, photosynthetic capacity, and antioxidant enzyme activities compared to the leaves treated with Cd stress alone. Conversely, the contents of proline, soluble proteins, soluble sugars, malondialdehyde, and intercellular CO2 concentration tended to decrease. Transcriptome analysis revealed that 2643 differentially expressed genes (DEGs) were implicated in the response of exogenous selenium treatment to Cd stress. The metabolic pathways associated with flavonoid production, carotenoid synthesis, glutathione metabolism, and glucosinolate biosynthesis were among those enriched in these differentially expressed genes. Furthermore, we discovered DEGs connected to the production route of glucosinolates. This work sheds fresh light on how purple flowering stalks' tolerance to cadmium stress is improved by exogenous selenium.

Effects of different phosphorus fertilizers on cadmium absorption and accumulation in rice under low-phosphorus and rich-cadmium soil

Rice is the main food crops with the higher capacity for cadmium (Cd) uptake, necessitating the urgent need for remediation measures to address Cd in paddy soil. Reasonable agronomic methods are convenient and favorable for fixing the issue. In this study, a pot experiment was employed to evaluate the effects of two foliar (NaH2PO4, SDP; KH2PO4, PDP) and two solid phosphate fertilizers (double-superphosphate, DSP; calcium-magnesium phosphate, CMP) on uptake and remobilization of Cd in rice plants under the low-P and rich-Cd soil. The results revealed that these four phosphorus fertilizer significantly down-regulated the relative expression of OsNRAMP5 involved in Cd absorption, while up-regulated OsPCS1 expression and increased distribution of Cd into the cell wall in roots. Furthermore, phosphorus fertilizer resulted in a significant decrease in the relative expression of OsLCT1 in stems and OsLCD in leaves, decreased the transfer factor of Cd from shoots to grains, and ulterior reduced the Cd accumulation in three protein components of globulin, albumin, and glutelin, making the average Cd concentration of brown rice decreased by 82.96%. These results comprehensively indicate that in situations with similar soil backgrounds, the recommended application of solid CMP and foliar PDP can alleviate the toxicity of Cd by reducing its absorption and remobilization.

Dynamic response of cadmium immobilization to a Ca-Mg-Si soil conditioner in the contaminated paddy soil

Soil conditioners are often used to immobilize soil heavy metals. Understanding the transfer of Cd in soil-plant system to different application rates and modes of soil conditioners application is essential for food safety. The stabilization persistence of soil conditioners in immobilizing Cd, to date however, is still limited. In this study, the stabilization persistence of a Ca-Mg-Si soil conditioner (SC) was assessed based on a six-year Cd-contaminated paddy field study with growth of two rice local main varieties (Yongyou17-YY and Xiushui14-XS) and four application rates (1500 kg ha-1 (low), and 3000 kg ha-1 (high) for the first year only, and 1500 kg ha-1 and 3000 kg ha-1 every year). Results showed that continuous SC application with high rate increased soil pH, simultaneously with more water soluble and exchangeable Cd was transferred to Fe-Mn oxides bound and carbonate-bound Cd in the first 3-4 years; while the low rate was only effective with growth of YY that were applied for a shorter period of time. Statistical analysis indicated that the stability effect of SC was integratedly affected by soil pH, SC application rate, and meteorological factors (precipitation and temperature). Especially, soil fractionation contributed the most changes of Cd availability in soil, while meteorological factors, SC application rate and crop varieties altogether exhibited the great effect on Cd accumulation in grain. Our finding demonstrated the potential long-term stabilization of SC in soil Cd immobilization, with the performance needed for further verification on the basis of different soil types.

Heavy Metals in Agricultural Soils: Sources, Influencing Factors, and Remediation Strategies

Soil heavy metal pollution is a global environmental challenge, posing significant threats to eco-environment, agricultural development, and human health. In recent years, advanced and effective remediation strategies for heavy metal-contaminated soils have developed rapidly, and a systematical summarization of this progress is important. In this review paper, first, the anthropogenic sources of heavy metals in agricultural soils, including atmospheric deposition, animal manure, mineral fertilizers, and pesticides, are summarized. Second, the accumulation of heavy metals in crops as influenced by the plant characteristics and soil factors is analyzed. Then, the reducing strategies, including low-metal cultivar selection/breeding, physiological blocking, water management, and soil amendment are evaluated. Finally, the phytoremediation in terms of remediation efficiency and applicability is discussed. Therefore, this review provides helpful guidance for better selection and development of the control/remediation technologies for heavy metal-contaminated agricultural soils.

Differential responses of chili varieties grown under cadmium stress

Heavy metal cadmium (Cd) naturally occurs in soil and is a hazardous trace contaminant for humans, animals, and plants. The main sources of Cd pollution in soil include overuse of phosphatic fertilizers, manure, sewage sludge, and aerial deposition. That's why an experiment was conducted to analyze the effect of Cd toxicity in Capsicum annuum L. by selecting its seven varieties: Hybrid, Desi, Sathra, G-916, BR-763, BG-912, and F1-9226. Cadmium was spiked in soil with four levels, i.e., (0, 3, 4, and 5 mg Cd kg- 1 of soil) for a week for homogeneous dispersion of heavy metal. Chili seeds were sown in compost-filled loamy soil, and 25-day-old seedlings were transplanted into Cd-spiked soil. Cadmium increasing concentration in soil decreased chili growth characteristics, total soluble sugars, total proteins, and amino acids. On the other hand, the activities of antioxidant enzymes were increased with the increasing concentration of Cd in almost all the varieties. Treatment 5 mg Cd/kg application caused - 197.39%, -138.78%, -60.77%, -17.84%, -16.34%, -11.82% and - 10.37% decrease of carotenoids level in chili V2 (Desi) followed by V4 (G-916), V1 (Hy7brid), V7 (F1-9226), V6 (BG-912), V5 (BR-763) and V3 (Sathra) as compared to their controls. The maximum flavonoids among varieties were in V5 (BR-763), followed by V6 (BG-912), V7 (F1-9226), V3 (Sathra) and V1 (Hybrid). Flavonoids content was decreased with - 37.63% (Sathra), -34.78% (Hybrid), -33.85% (G-916), -31.96% (F1-9226), -31.44% (Desi), -30.58% (BR-763), -22.88% (BG-912) as compared to their control at 5 mg Cd/kg soil stress. The maximum decrease in POD, SOD, and CAT was - 31.81%, -25.98%, -16.39% in chili variety V7 (F1-9226) at 5 mg Cd/kg stress compared to its control. At the same time, maximum APX content decrease was - 82.91%, followed by -80.16%, -65.19%, -40.31%, -30.14%, -10.34% and - 6.45% in V4 (G-916), V2 (Desi), V3 (Sathra), V6 (BG-912), V1 (Hybrid), V7 (F1-9226) and V5 (BR-763) at 5 mg Cd/kg treatment as compared to control chili plants. The highest CAT was found in 5 chili varieties except Desi and G-916. Desi and G-916 varieties. V5 (BR-763) and V6 (BG-912) were susceptible, while V1 (Hybrid), V3 (Sathra), and V7 (F1-9226) were with intermediate growth attributes against Cd stress. Our results suggest that Desi and G-916 chili varieties are Cd tolerant and can be grown on a large scale to mitigate Cd stress naturally.

Selenite reduced cadmium uptake, interfered signal transduction of endogenous phytohormones, and stimulated secretion of tartaric acid based on a combined analysis of non-invasive micro-test technique, transcriptome and metabolome

Selenium (Se) can reduce uptake and translocation of cadmium (Cd) in plants via plenty of ways, including regulation of root morphology. However, the underlying mechanisms on how Se will regulate root morphology under metal(loid) stresses are not fully illustrated. To fill up this knowledge gap, we investigated the effects of 0.5 mg L-1 selenite (Se(IV)) on root exudates, root morphology, root endogenous hormones, and Cd uptake efficiency of rice under the 1 mg L-1 Cd stress condition. The results showed that Se(IV) significantly reduced shoot and root Cd concentrations, and decreased Cd uptake efficiency via root hairs determined by a non-invasive micro-test (NMT) technology. When compared to the 1 mg L-1 Cd (Cd1) treatment, addition of 0.5 mg L-1 Se(IV) (1) significantly reduced root surface area and tip numbers, and non-significantly reduced root length, but significantly enhanced root diameter and root volume; (2) significantly enhanced concentrations of tartaric acid in the root exudate solution, root auxin (IAA) and root jasmonic acid (JA) via a UHPLC or a HPLC analysis; (3) significantly up-regulated metabolites correlated with synthesis of IAA, JA, gibberellin (GA), and salicylic acid, such as GA53, M-SA, (+/-)7-epi-JA, and derivatives of tryptophan and indole in the metabolome analysis. However, results of transcriptome analysis showed that (1) no upregulated differentially expressed genes (DEGs) were enriched in IAA synthesis; (2) some upregulated DEGs were found to be enriched in JA and GA53 synthesis pathways. In summary, although Se(IV) stimulated the synthesis of IAA, JA, and GA53, it significantly inhibited root growth mainly by 1) affecting signal transduction of IAA and GA; 2) altering IAA polar transport and homeostasis; and 3) regulating DEGs including SAUR32, SAUR36, SAUR76, OsSub33, OsEXPA8, OsEXPA18, and Os6bglu24.

Silicon-Selenium Interplay Imparts Cadmium Resistance in Wheat through an Up-Regulating Antioxidant System

Cadmium (Cd), being a highly toxic heavy metal, significantly impacts plant growth and development by altering nutrient uptake and causing oxidative and structural damage, resulting in reduced yield. To combat Cd toxicity and accumulation in wheat, it was hypothesized that co-application of Selenium (Se) and Silicon (Si) can reduce the adverse effect of Cd and regulate Cd resistance while improving Se fortification in wheat. Therefore, this study evaluated the comparative effect of Se and Si on the growth and antioxidant defense systems of wheat plants grown in a hydroponic setup. Briefly, the plants were acclimatized to the hydroponic solution for 1 week and then exposed to 10 µmol Cd. Afterwards, the treatments, including 0.2 mmol Si and 1.5 µmol Se, were applied as a root and foliar application, respectively. Plants supplemented with both Se and Si showed improved biomass and other physiological growth attributes, and this response was associated with improved activity/contents of antioxidants, including glutathione (GSH) content, glutathione reductase (GR), ascorbate peroxidase (APX), and catalase (CAT), with related lowering of hydrogen peroxide, malondialdehyde content, and structural damages. Moreover, by Se + Si supplementation, a decrease in total S levels in plant tissues was observed, whereas an increase in total protein concentration and GSH indicated a different and novel mechanism of Cd tolerance and S homeostasis in the plant. It was observed that Si was more involved in significantly reducing Cd translocation by stabilizing Cd in the root and reducing its content in the soluble fraction in both the root and shoot. Whereas Se was found to play the main role in reducing the oxidative damage caused by Cd, and the effect was more profound in the shoot. In addition, this study also observed a positive correlation between Si and Se for relative uptake, which had not been reported earlier. Our findings show that the Se and Si doses together benefit growth regulation and nutrient uptake; additionally, their combinations support the Cd resistance mechanism in wheat through upregulation of the antioxidant system and control of Cd translocation and subcellular distribution, ultimately contributing to the nutritional quality of wheat produced. Thus, it is concluded that the co-application of Se and Si has improved the nutritional quality while reducing the Cd risk in wheat and therefore needs to be employed as a potential strategy to ensure food safety in a Cd-contaminated environment.

Strontium alleviated the growth inhibition and toxicity caused by cadmium in rice seedlings

Cadmium (Cd) contamination of rice is an urgent ecological and agricultural problem. Strontium (Sr) has been shown to promote plant growth. However, the effect of Sr on rice seedlings under Cd stress is currently unclear. In this work hydroponic experiments were used to assess the impact of Sr on rice seedling growth under Cd stress. The findings demonstrated that foliar application of 0.5 mg L-1 Sr had no discernible impact on the development of rice seedlings. However, Sr significantly alleviated growth inhibition and toxicity in rice seedlings when threatened by Cd. Compared with the Cd treatment (Cd, 2.5 mg L-1), the root length, shoot height, and whole plant length of rice seedlings in the Cd + Sr treatment (Cd, 2.5 mg L-1; Sr, 0.5 mg L-1) increased by 4.96 %, 12.47 % and 9.60 %, respectively. The content of Cd in rice decreased by 23.34 % (roots) and 5.79 % (shoots). Sr lessened the degree of membrane lipid peroxidation damage (lower MDA concentration) among the seedlings of rice under Cd stress by controlling the activities of antioxidant enzymes and GSH content. By changing the expression of antioxidant enzyme-encoding genes and downregulating the heavy metal transporter gene (OsNramp5), Sr reduced accumulation and the detrimental effects of Cd on rice seedlings. Our study provides a new solution to the problem of Cd contamination in rice, which may promote the safe production of rice and benefit human health.