Co-application of biochar and microorganisms improves soybean performance and remediate cadmium-contaminated soil.

Sole biochar addition or microbial inoculation as a soil amendment helps to reduce cadmium (Cd) toxicity in polluted agricultural soils. Yet the synergistic effects of microorganisms and biochar application on Cd absorption and plant productivity remain unclear. Therefore, a pot experiment was conducted to investigate the combined effect of microorganisms (Trichoderma harzianum L. and Bacillus subtilis L.), biochar (maize straw, cow manure, and poultry manure), and Cd (0, 10, and 30 ppm) on plant physiology and growth to test how biochar influences microbial growth and plant nutrient uptake, and how biochar ameliorates under Cd-stressed soil. Results showed that in comparison to non-Cd polluted soil, the highest reduction in chlorophyll content, photosynthetic rate, transpiration rate, stomatal conductance, water use efficiency, and intercellular CO2 were observed in Cd2 (30 ppm), which were 9.34%, 22.95%, 40.45%, 29.07%, 20.67%, and 22.55% respectively less than the control Cd0 (0 ppm). Among sole inoculation of microorganisms, highest stomatal conductance, water use efficiency, and intercellular CO2 were recorded with combined inoculation of both microorganisms (M3), which were 5.92%, 7.65%, and 7.28% respectively higher than the control, and reduced the Cd concentration in soil, root, and shoot by 21.34%, 28.36%, and 20.95%, respectively, compared to the control. Similarly, co-application of microorganisms and biochar ameliorated the adverse effect of Cd in soybean as well as significantly improved plant biomass, photosynthetic activity, nutrient contents, and antioxidant enzyme activities, and minimized the production of reactive oxygen species and Cd content in plants. Soil amended with poultry manure biochar had significantly improved the soil organic carbon, total nitrogen, total phosphorous, and available potassium by 43.53%, 36.97%, 22.28%, and 4.24%, respectively, and decreased the concentration of Cd in plant root and shoot by 34.68% and 47.96%, respectively, compared to the control. These findings indicate that the combined use of microorganisms and biochar as an amendment have important synergistic effects not only on the absorption of nutrients but also on the reduction of soybean Cd intake, and improve plant physiology of soybean cultivated in Cd-polluted soils as compared to sole application of microorganisms or biochar.

Preliminary results from structural systems biology approach in Tetrahymena thermophila reveal novel perspectives for this toxicological model.

Tetrahymena is a unicellular microbial eukaryotic organism that has been used extensively in toxicology and environmental research. This work attempts to model for the first time the wiring of proteins involved in cellular mechanisms of Cd toxicity in Tetrahymena thermophila. 1975 high-confidence PPIs between 68 Cd-binding proteins and 422 partners were inferred through a novel structural systems biology approach that utilizes comparative analysis between Tetrahymena and other eukaryotes for which experimentally supported protein interactomes exist. The PPIs of the potential network were confirmed by known domain interactions in the Protein Data Bank and its topological characteristics were compared with publicly available experimental information for T. thermophila. To experimentally validate the robustness of the proposed PPI network, the interaction between the two most interconnected hub proteins was detected through GST pull-down assay. Potential effects on Tetrahymena's cellular and metabolic processes by PPIs involving Cd-binding proteins were uncovered. Furthermore, 244 PPIs in which Cd-binding proteins or/and their partners are encoded by orthologs of human disease genes in T. thermophila, but not in yeast, were identified and analyzed. The findings suggest that Tetrahymena could be possibly a useful model for an improved understanding of molecular mechanisms of Cd toxicity in human diseases.

Interactive effect of salinity and cadmium toxicity on soil microbial properties and enzyme activities.

Salinity has been proposed to increase the mobility and availability of heavy metals, with a potentially significant consequence for greater metal toxicity. However, the interactive effect of salinity and metal pollution on soil microbial properties and functions is still unknown. This investigation was performed to examine the response of several soil microbial properties and processes to the combined salinity and cadmium (Cd) toxicity in a clay loam soil amended with plant residue. The NaCl salt (0, 32.5 and 78.3 mM NaCl kg-1 soil), Cd (0 and 30 mg kg-1 soil) and alfalfa residue (0 and 1%) were added to the soil and the mixtures were incubated for 90 days under standard laboratory conditions (25 ±â€¯1 °C and 70% of water holding capacity). Similar treatments without residue addition were also included in the experimental arrangement. Salinity increased soil Cd availability and toxicity, and subsequently decreased soil microbial respiration rate, microbial biomass and enzyme activity. The negative effect of increasing salinity on soil microbial and biochemical properties was stronger in Cd-polluted than unpolluted soils and at high than low salinity levels. The declines in soil microbial attributes and enzyme activity were linearly related to the concentration of soil available Cd. Nevertheless, the negative effect of salinity was reduced with addition of alfalfa residue in Cd-polluted soils. The interactive effect of Cd and NaCl was synergistic in residue-unamended soils, but antagonistic in residue-amended soils. It is concluded that (i) the multiple stresses induced by salinity and Cd pollution may synergistically affect soil microbial processes and attributes and (ii) application of organic residues has a high potential for lowering the synergistic effect of salinity in Cd-polluted environments and improving the important microbial indicators of soil quality.

Salinity stress accelerates the effect of cadmium toxicity on soil N dynamics and cycling: Does joint effect of these stresses matter?

The objective of this study was to determine responses of soil nitrogen (N) transformation, microbial biomass N, and urease activity to the combined effect of cadmium (Cd) toxicity (0 and 30 mg kg-1) and NaCl stress (0, 7.5 and 15 dS m-1) in a clay loam soil unamended (0%) or amended with alfalfa residues (1%, w/w). Cd, NaCl, and alfalfa residues were added to the soil, and the mixtures were incubated for 90 days under standard laboratory conditions (25 ±â€¯1 °C and 70% of water holding capacity [WHC]). The results showed that salinity increased soil Cd availability and toxicity and subsequently decreased soil microbial N transformations (i.e., potential ammonification and nitrification as well as net N mineralization), arginine ammonification and nitrification rates, microbial biomass N, and urease activity. The adverse effects of salinity on soil microbial properties were greater in Cd-polluted than unpolluted soils, at high than low salinity levels, but were lower in residue-amended than unamended soils. These effects were mainly attributed to the increased Cd availability under saline conditions or the decreased Cd availability with residue addition. All the measured soil microbial attributes showed a negative correlation with the available Cd content in the soil. The interaction or combined effects of Cd and NaCl on soil microbial attributes were mostly synergistic in residue-unamended soils but antagonistic in residue-amended soils. The addition of organic residues to Cd-polluted soils may moderate salinity effect, and thus could stimulate the activity of ammonifiers and nitrifiers, as well as urease.

Effects of Ca addition on the uptake, translocation, and distribution of Cd in Arabidopsis thaliana.

Cadmium (Cd) pollution poses a risk to human health for its accumulation in soil and crops, but this can be alleviated by calcium (Ca) addition. However, its mechanism remains unclear yet. In this study, Arabidopsis thaliana was used to explore the alleviating effects of Ca on Cd toxicity and its specific function during uptake, upward-translocation, and distribution of Cd. Supplementing plants with 5mM CaCl2 alleviated the intoxication symptoms caused by 50µM CdCl2, such as smaller leaves, early bolting and root browning. Ca addition decreased uptake of Cd, possibly by reducing the physical adsorption of Cd since the root cell membrane was well maintained and lignin deposition was decreased as well, and by decreasing symplastic Cd transport. Expression of the genes involved (AtZIP2 and AtZIP4) was also decreased. In addition, Ca accumulated in the plant shoot to help facilitating the upward-translocation of Cd, with evidence of higher translocation factor and expression of genes that were involved in Ca transport (AtPCR1) and Cd xylem loading (AtHMA2 and AtHMA4). Dithizone-staining of Cd in leaves showed that in Cd+Ca-treated plants, Ca addition initially protected the leaf stomata by preventing Cd from entering guard cells, but with prolonged Cd treatment facilitated the Cd accumulation around trichomes and maybe its excretion. We conclude that Ca promotes the upward-translocation of Cd and changes its distribution in leaves. The results may have relevance for bioremediation.

Silicon-induced reversibility of cadmium toxicity in rice.

Silicon (Si) modulates tolerance to abiotic stresses, but little is known about the reversibility of stress effects by supplementing previously stressed plants with Si. This is surprising since recovery experiments might allow mechanisms of Si-mediated amelioration to be addressed. Rice was exposed to 10 µM CdCl2 for 4 d in hydroponics, followed by 0.6mM Si(OH)4 supplementation for 4 d. Si reversed the effects of Cd, as reflected in plant growth, photosynthesis, elemental composition, and some biochemical parameters. Cd-dependent deregulation of nutrient homeostasis was partially reversed by Si supply. Photosynthetic recovery within 48h following Si supply, coupled with strong stimulation of the ascorbate-glutathione system, indicates efficient activation of defense. The response was further verified by transcript analyses with emphasis on genes encoding members of the stress-associated protein (SAP) family. The transcriptional response to Cd was mostly reversed following Si supply. Reprogramming of the Cd response was obvious for Phytochelatin synthase 1, SAP1 , SAP14, and the transcription factor genes AP2/Erf020, Hsf31, and NAC6 whose transcript levels were strongly activated in roots of Cd-stressed rice, but down-regulated in the presence of Si. These findings, together with changes in biochemical parameters, highlight the significance of Si in growth recovery of Cd-stressed rice and indicate a decisive role for readjusting cell redox homeostasis.

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.

BnXTH1 regulates cadmium tolerance by modulating vacuolar compartmentalization and the cadmium binding capacity of cell walls in ramie (Boehmeria nivea).

Xyloglucan endotransglucosylase/hydrolases (XTH) are cell wall-modifying enzymes important in plant response to abiotic stress. However, the role of XTH in cadmium (Cd) tolerance in ramie remains largely unknown. Here, we identified and cloned BnXTH1, a member of the XTH family, in response to Cd stress in ramie. The BnXTH1 promoter (BnXTH1p) demonstrated that MeJA induces the response of BnXTH1p to Cd stress. Moreover, overexpressing BnXTH1 in Boehmeria nivea increased Cd tolerance by significantly increasing the Cd content in the cell wall and decreasing Cd inside ramie cells. Cadmium stress induced BnXTH1-expression and consequently increased xyloglucan endotransglucosylase (XET) activity, leading to high xyloglucan contents and increased hemicellulose contents in ramie. The elevated hemicellulose content increased Cd chelation onto the cell walls and reduced the level of intracellular Cd. Interestingly, overexpressing BnXTH1 significantly increased the content of Cd in vacuoles of ramie and vacuolar compartmentalization genes. Altogether, these results evidence that Cd stress induced MeJA accumulation in ramie, thus, activating BnXTH1 expression and increasing the content of xyloglucan to enhance the hemicellulose binding capacity and increase Cd chelation onto cell walls. BnXTH1 also enhances the vacuolar Cd compartmentalization and reduces the level of Cd entering the organelles and soluble solution.

Selenium bio-nanocomposite based on extracellular polymeric substances (EPS): Synthesis, characterization and application in alleviating cadmium toxicity in rice (Oryza sativa L.).

Selenium nanoparticles (SeNPs) have gained significant attention owing to their favorable bioavailability and low toxicity, making them widely applications in the fields of medicine, food and agriculture. In this study, bacterial extracellular polymeric substances (EPS) were used as a novel stabilizer and capping agent to prepare dispersed SeNPs. Results show that EPS-SeNPs presented negative potential (-38 mV), spherical morphologies with average particle size about 100-200 nm and kept stable at room temperature for a long time. X-ray diffraction (XRD) analysis demonstrated that the synthesized nanoparticles were pure amorphous nanoparticles, and X-ray photoelectron spectroscopy (XPS) spectrum showed a spike at 55.6 eV, indicating the presence of zero-valent nano­selenium. Fourier-transform infrared spectroscopy (FTIR) and three-dimensional excitation-emission matrix (3D-EEM) fluorescence spectroscopy analysis confirmed proteins and polysaccharides in EPS played a crucial role in the synthesis of EPS-SeNPs. Compared to EPS or sodium selenite (Na2SeO3), EPS-SeNPs showed a relatively moderate result in terms of scavenging free radicals in vitro. In contrast, EPS-SeNPs demonstrated lower toxicity to rice seeds than Na2SeO3. Notably, the exogenous application of EPS-SeNPs effectively alleviated the growth inhibition and oxidative damaged caused by cadmium (Cd), and significantly reduced Cd accumulation in rice plants.

LC-MS and GC-MS Metabolomics Analyses Revealed That Different Exogenous Substances Improved the Quality of Blueberry Fruits under Soil Cadmium Toxicity.

Exogenous substances (ESs) can regulate plant growth and respond to environmental stress, but the effects of different ESs on blueberry fruit quality under soil cadmium (Cd) toxicity and related metabolic mechanisms are still unclear. In this study, four ES treatments [salicylic acid (SA), spermidine (Spd), 2,4-epibrassinolide (EBR), and melatonin (MT)] significantly increased blueberry fruit size, single-fruit weight, sweetness, and anthocyanin content under soil Cd toxicity and effectively reduced fruit Cd content to safe consumption levels by promoting mineral uptake (Ca, Mg, Mn, Cu and Zn). Furthermore, a total of 445, 360, 429, and 554 differentially abundant metabolites (DAMs) (LC-MS) and 63, 48, 79, and 73 DAMs (GC-MS) were identified from four comparison groups (SA/CK, Spd/CK, EBR/CK and MT/CK), respectively. The analyses revealed that ESs improved blueberry fruit quality and tolerance to Cd toxicity mainly by regulating the changes in metabolites related to ABC transporters, the TCA cycle, flavonoid biosynthesis, and phenylpropanoid biosynthesis.

Enhanced Cd activation by Coprinus comatus endophyte Bacillus thuringiensis and the molecular mechanism.

Fungal endophytes not only tolerate and activate Cd in soil but also promote host growth, yet its Cd activation capacity and mechanism remain unrevealed. Our previous study isolated a robust endophyte Bacillus thuringiensis L1 from Coprinus comatus fruiting body with splendid Cd resistance and activation abilities under laboratory conditions. In this study, those peculiarities were investigated in the actual soil environment. L1 could significantly increase the soil bioavailable Cd content and effectively compensate for alkali-hydro nitrogen losses and microbial inhibition caused by Cd. Furthermore, L1 inoculation improved the soil's bacterial community structure and increased the relative abundance of Cd-resistant bacteria, such as Actinobacteria, Chloroflexi, Acidobacter, and Firmicutes, closely associated with the soil enzyme activity shift. The genome sequencing analysis revealed the presence of genes related to growth promotion, resistance to Cd stress, and Cd activation, which were significantly up-regulated under Cd stress. Notably, L1 mainly activates Cd in soil by secreting citric acid, succinic acid, siderophore, and soluble phosphorus substances to chelate with Cd or dissolve bounded Cd. Meanwhile, the metal-responsive transcription repressor (CadC) and the Cd-translocating protein P-type ATPase (CadA) can help the L1 to suppress the toxicity of Cd. Those results help to unveil the possible mechanism of L1 in Cd-contaminated soil remediation, providing a clear strategy for Cd bio-extraction from soil.

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.

Enhancing cauliflower growth under cadmium stress: synergistic effects of Cd-tolerant Klebsiella strains and jasmonic acid foliar application.

The pollution of heavy metals (HMs) is a major environmental concern for agricultural farming communities due to water scarcity, which forces farmers to use wastewater for irrigation purposes in Pakistan. Vegetables grown around the cities are irrigated with domestic and industrial wastewater from areas near mining, paint, and ceramic industries that pollute edible parts of crops with various HMs. Cadmium (Cd) is an extremely toxic metal in arable soil that enters the food chain and damages the native biota, ultimately causing a reduction in plant growth and development. However, the use of microbes and growth regulators enhances plant growth and development as well as HM immobilization into the cell wall and hinders their entry into the food chain. Thus, the integrated use of bacterial consortium along with exogenously applied jasmonic acid (JA) mitigates the adverse effect of metal stress, ultimately reducing the metal mobility into roots by soil. Therefore, the current study was conducted to check the impact of Cd-tolerant bacteria and JA on the growth, nutrient status, and uptake of Cd in the cauliflower (Brassica oleracea). Our results demonstrated that increasing concentrations of Cd negatively affect growth, physiological, and biochemical attributes, while the use of a bacterial consortium (SS7 + SS8) with JA (40 µmol L-1) significantly improved chlorophyll contents, stem fresh and dry biomass (19.7, 12.7, and 17.3%), root length and root fresh and dry weights (28.8, 15.2, and 23.0%), and curd fresh and dry weights and curd diameter (18.7, 12.6, and 15.1%). However, the maximum reduction in soil Cd, roots, and curd uptake was observed by 8, 11, and 9.3%, respectively, under integrated treatment as compared to the control. Moreover, integrating bacterial consortium and JA improves superoxide dismutase (SOD) (16.79%), peroxidase dismutase (POD) (26.96%), peroxidase (POX) (26.13%), and catalase (CAT) (26.86%). The plant nitrogen, phosphorus, and potassium contents were significantly increased in soil, roots, and curd up to 8, 11, and 9.3%, respectively. Hence, a consortium of Klebsiella strains in combination with JA is a potential phytostabilizer and it reduces the uptake of Cd from soil to roots to alleviate the adverse impact on cauliflower's growth and productivity.

Response strategies of slash pine (Pinus elliottii) to cadmium stress and the gain effects of inoculation with Herbaspirillum sp. YTG72 in alleviating phytotoxicity and enhancing accumulation of cadmium.

Phytoremediation using fast-growing woody plants assisted by plant growth-promoting bacteria (PGPB) on cadmium (Cd)-contaminated sites is considered a promising technique; however, its remediation efficiency is still affected by multiple factors. In this study, the mining areas' soil conditions were simulated with different Cd addition levels (0, 3, 6, 9 mg kg-1) in order to investigate the response strategy to Cd stress of fast-growing economic tree species, slash pine (Pinus elliottii), and the effects of inoculation with the PGPB strain Herbaspirillum sp. YTG72 on the physiological activity and Cd accumulation of plants. The main results showed that there were significant (p < 0.05) increases in contents of chlorophyll and nutrient elements (P, K, Ca, and Mg) at low Cd addition level (3 mg kg-1) compared to non-Cd addition treatment. When the additive amount of Cd increased, the growth of plants was severely inhibited and the content of proline was increased, as well as Cd in plants. Besides, the ratios of K:P, Ca:P, and Mg:P in plants were negatively correlated with the contents of Cd in plants and soils. Inoculation of P. elliottii with the PGPB strain Herbaspirillum sp. YTG72 improved the physiological functions of the plants under Cd stress and activated the antioxidant system, reduced the accumulation of proline, and decreased the ratios of K:P, Ca:P, and Mg:P in plant. More importantly, planting P. elliottii in Cd-contaminated soil could significantly (p < 0.05) reduce the Cd content in the rhizosphere soil, and furthermore, inoculation treatment could promote the reduction of soil Cd content and increased the accumulation of Cd by root. The results of the present study emphasized the Cd response mechanism of P. elliottii based on multifaceted regulation, as well as the feasibility of strain Herbaspirillum sp. YTG72 assisted P. elliottii for the remediation on Cd-contaminated sites.

Interactive effect of silicon and zinc on cadmium toxicity alleviation in wheat plants.

Silicon (Si) and Zinc (Zn) have been frequently used to alleviate cadmium (Cd) toxicity, which are feasible strategies for crop safety production. However, the mechanisms underlying the interaction of Si and Zn on alleviating Cd toxicity are not well understood. A hydroponic system was adopted to evaluate morphological, physiological-biochemical responses, and related gene expression of wheat seedlings to Si (1 mM) and Zn (50 µM) addition under Cd stress (10 µM). Cd induced obvious inhibition of wheat growth by disturbing photosynthesis and chlorophyll synthesis, provoking generation of reactive oxygen species (ROS) and interfering ion homeostasis. Cd concentration was decreased by 68.3%, 43.1% and 73.3% in shoot, and 78.9%, 44.1% and 85.8% in root by Si, Zn, and combination of Si with Zn, relative to Cd only, respectively. Si and Zn effectively ameliorated Cd toxicity and enhanced wheat growth; but single Si or combination of Si with Zn had more efficient ability on alleviating Cd stress than only Zn, indicating Si and Zn have synergistic effect on Cd toxicity; Interaction of them alleviated oxidative stress by reducing ROS content, improving AsA-GSH cycle and antioxidant enzymes activities, and regulating Cd into vacuole through PC-Cd complexes transported by HMA3 transporter. Our results suggest that fertilizers including Si and Zn should be made to reduce Cd content, which will beneficial for food production and safety.

Physiological and transcriptome analysis of response of soybean (Glycine max) to cadmium stress under elevated CO2 concentration.

The continuous accumulation of Cd has long-lasting detrimental effects on plant growth and food safety. Although elevated CO2 concentration (EC) has been reported to reduce Cd accumulation and toxicity in plants, evidence on the functions of elevated CO2 concentration and its mechanisms in the possible alleviation of Cd toxicity in soybean are limited. Here, we used physiological and biochemical methods together with transcriptomic comparison to explore the effects of EC on Cd-stressed soybean. Under Cd stress, EC significantly increased the weight of roots and leaves, promoted the accumulations of proline, soluble sugars, and flavonoid. In addition, the enhancement of GSH activity and GST gene expressions promoted Cd detoxification. These defensive mechanisms reduced the contents of Cd2+, MDA, and H2O2 in soybean leaves. The up-regulation of genes encoding phytochelatin synthase, MTPs, NRAMP, and vacuoles protein storage might play vital roles in the transportation and compartmentalization process of Cd. The MAPK and some transcription factors such as bHLH, AP2/ERF, and WRKY showed changed expressions and might be engaged in mediation of stress response. These findings provide a boarder view on the regulatory mechanism of EC on Cd stress and provide numerous potential target genes for future engineering of Cd-tolerant cultivars in soybean breeding programs under climate changes scenarios.

Toxic effects of cadmium on the physiological and biochemical attributes of plants, and phytoremediation strategies: A review.

Anthropogenic activities pose a more significant threat to the environment than natural phenomena by contaminating the environment with heavy metals. Cadmium (Cd), a highly poisonous heavy metal, has a protracted biological half-life and threatens food safety. Plant roots absorb Cd due to its high bioavailability through apoplastic and symplastic pathways and translocate it to shoots through the xylem with the help of transporters and then to the edible parts via the phloem. The uptake and accumulation of Cd in plants pose deleterious effects on plant physiological and biochemical processes, which alter the morphology of vegetative and reproductive parts. In vegetative parts, Cd stunts root and shoot growth, photosynthetic activities, stomatal conductance, and overall plant biomass. Plants' male reproductive parts are more prone to Cd toxicity than female reproductive parts, ultimately affecting their grain/fruit production and survival. To alleviate/avoid/tolerate Cd toxicity, plants activate several defense mechanisms, including enzymatic and non-enzymatic antioxidants, Cd-tolerant gene up-regulations, and phytohormonal secretion. Additionally, plants tolerate Cd through chelating and sequestering as part of the intracellular defensive mechanism with the help of phytochelatins and metallothionein proteins, which help mitigate the harmful effects of Cd. The knowledge on the impact of Cd on plant vegetative and reproductive parts and the plants' physiological and biochemical responses can help selection of the most effective Cd-mitigating/avoiding/tolerating strategy to manage Cd toxicity in plants.

In Situ Toxicity Reduction and Food Safety Assessment of Pak Choi (Brassica campestris L.) in Cadmium-Contaminated Soil by Jointly Using Alkaline Passivators and Organic Fertilizer.

An economical and effective method is still lacking for cadmium (Cd) toxicity reduction and food product safety improvement in soil-vegetable systems. Therefore, this study aimed to reduce the Cd toxicity to pak choi (Brassica campestris L.) by jointly using passivators and organic fertilizer, highlighting food products' safety based on pot experiments. The results showed that compared with the control, organic fertilizer decreased the Cd content in edible parts and the soil's available Cd by 48.4% and 20.9% on average, respectively, due to the 0.15-unit increases in soil pH. Once jointly applied with passivators, the decrements increased by 52.3-72.6% and 32.5-52.6% for the Cd content in edible parts and for the soil's available Cd, respectively, while the pH increment increased by 0.15-0.46 units. Compared with the control, the transport factor of Cd was reduced by 61.9% and 50.9-55.0% when applying organic fertilizer alone and together with the passivators, respectively. The combination treatment of biochar and organic fertilizer performed the best in decreasing the Cd content in the edible parts and the soil's available Cd. The combination treatment of fish bone meal and organic fertilizer induced the greatest increases in soil pH. The grey relational analysis results showed that the combination treatment of biochar and organic fertilizer performed the best in reducing the potential Cd pollution risk, thereby highlighting the vegetable food safety. This study provides a potential economical and effective technology for toxicity reduction and food safety in Cd-polluted soil.

Graphitic carbon nitride alleviates cadmium toxicity to microbial communities in soybean rhizosphere.

Cadmium (Cd) contamination has led to various harmful impacts on soil microbial ecosystem, agricultural crops, and thus human health. Nanomaterials are promising candidates for reducing the accumulation of heavy metals in plants. In this study, graphitic carbon nitride (g-C3N4), a two-dimensional polymeric nanomaterial, was applied for ameliorating Cd phytotoxicity to soybean (Glycine max (L.) Merr.). Its impacts on rhizosphere variables, microorganisms, and metabolism were examined. It was found that g-C3N4 increased carbon/nitrogen/phosphorus (C/N/P) content, especially when N contents were averagely 4.2 times higher in the g-C3N4-treated groups. g-C3N4 significantly induced alterations in microbial community structures (P < 0.05). The abundance of the probiotics class Nitrososphaeria was enriched (on average 70% higher in the g-C3N4-treated groups) as was Actinobacteria (226% higher in the g-C3N4 group than in the CK group). At the genus level, g-C3N4 recruited more Bradyrhizobium (122% higher) in the Cd + g-C3N4 group than in the Cd group and more Sphingomonas (on average 24% higher) in the g-C3N4-treated groups. The changes of microbial clusters demonstrated the potential of g-C3N4 to shape microbial functions, promote plant growth, and enhance Cd resistance, despite observing less pronounced modifications in microbial communities in Cd-contaminated soil compared to Cd-free soil. Moreover, abundance of functional genes related to C/N/P transformation was more significantly promoted by g-C3N4 in Cd-contaminated soil (increased by 146%) than in Cd-free one (increased by 32.8%). Therefore, g-C3N4 facilitated enhanced microbial survival and adaptation through the amplification of functional genes. These results validated the alleviation of g-C3N4 on the microbial communities in the soybean rhizosphere and shed a new light on the application of environmental-friendly nanomaterials for secure production of the crop under soil Cd exposure.

Arbuscular mycorrhizal fungus regulates cadmium accumulation, migration, transport, and tolerance in Medicago sativa.

Cadmium (Cd) pollution in croplands is a global environmental problem. Measures to improve the tolerance of sensitive crops and reduce pollutant absorption and accumulation are needed in contaminated agricultural areas, and inoculation with rhizosphere microorganisms to regulate plant resistance and heavy metal transport can provide an effective solution. A pot experiment was conducted to analyse the impact of arbuscular mycorrhizal fungi (AMF) on alfalfa oxidase activity, heavy metal resistance genes and transport proteins, metabolism, and other biochemical regulation mechanisms that lead to complexation, compartmentalisation, efflux, enrichment, and antioxidant detoxification pathways. The AMF reduced shoot and protoplasm Cd inflow, and promoted organic compound production (e.g., by upregulating HM-Res4 for 1.2 times), to complex with Cd, reducing its biological toxicity. The AMF increased the ROS scavenging efficiency and osmotic regulatory substance content of the alfalfa plants, reduced oxidative stress (ROS dereased), and maintained homeostasis. It also alleviated Cd inhibition of photosynthetic electron transport, tricarboxylic acid circulation, and nitrogen assimilation. These AMF effects improved leaf and root biomass by 43.87% and 59.71% and facilitated recovery of a conservative root economic strategy. It is speculated that AMF induces the resistance signal switch by regulating the negative feedback regulation mode of indole acetic acid upward transport and methyl jasmonate downward transmission in plants.