Cadmium Phytotoxicity, Tolerance, and Advanced Remediation Approaches in Agricultural Soils; A Comprehensive Review

Molecular mechanisms underlying abiotic stress responses in buckwheat

Plants have endured evolutionary changes for hundreds of years under the impact of increasing abiotic and biotic stress due to increasing human activities over the past centuries. Scientists have been working to understand the molecular mechanisms of plant responses to severe environmental stress, as plants have complex molecular arrangements to respond and adapt to abiotic stress, including drought, cold, and heat stress. Buckwheat (Fagopyrum spp.) is a resilient pseudocereal known for its nutritional value and adaptability to various environmental conditions, making it an essential crop in sustainable agriculture. It is particularly noted for its gluten-free nature and high-quality protein content, which benefit those with gluten sensitivities. However, recent studies revealed that buckwheat cultivation faces significant challenges from abiotic stressors such as drought, salinity, temperature extremes, and heavy metal toxicity, which can adversely affect its growth and yield. We have acknowledged key genes and factors in regulating complex responses and tolerance of plants in response to abiotic stresses. We compiled new data about diverse mechanisms by which different Fagopyrum species manage abiotic stress, encompassing physiological, biochemical, and molecular adaptations. As global food production demands rise, effective management strategies for these stress factors are increasingly critical for optimising buckwheat production and ensuring food security in a changing climate.

Glutathione's role in mitigating cadmium stress in Pogostemon cablin: Insights from combined transcriptomic and metabolomic approaches

Cadmium (Cd) pollution poses a growing threat to plant growth. Although glutathione (GSH) is recognized for its potential to mitigate Cd-induced stress, its specific effects on alleviating such stress in Pogostemon cablin (patchouli) remain unclear. This study investigated physiological parameters and enzymatic activities across four treatment groups: control (CK), cadmium stress (Cd), glutathione (GSH), and glutathione with cadmium stress (GSH+Cd). Results revealed that chlorophyll a, b, and carotenoid levels in the GSH were approximately 20 % higher than those in the other groups. In contrast, antioxidant enzyme activity in the Cd decreased by about 15 %. Integrated transcriptomic and metabolomic analyses demonstrated that GSH mitigates Cd stress by influencing glycerophospholipid metabolism and flavonoid biosynthesis, with key roles attributed to dgkA1, dgkA2, and CCoAOMT1-4. In conclusion, GSH alleviates Cd stress in P. cablin by enhancing photosynthetic pigment synthesis, reducing reactive oxygen species (ROS) through improved enzymatic activity, and regulating metabolic pathways. These findings provide valuable insights for optimizing the cultivation and management of P. cablin under Cd stress conditions.

Newly isolated bacterium and arbuscular mycorrhizal fungus effectively reduce the root cadmium concentration and increase the root biomass of Ophiopogon japonicus

Soil cadmium (Cd) contamination is one of the major challenges in food production. This has led to above-maximum threshold accumulation of Cd in O. japonicus roots. This research identifies Pseudomonas tianjinensis S2 (PL), a newly isolated bacterium, and Corymbiglomus tortuosum (Ct), an arbuscular mycorrhizal fungus (AMF), as effective agents for reducing Cd concentration in the roots of O. japonicus. Compared to the control (CK) treatment, the root Cd levels decreased by 62.27 % and 46.13 %, respectively, significantly enhancing root biomass. We also noticed the involvement of -OH, -CH, and CC functional groups in Cd chelation in both treatments, and the formation of precipitates, including C2H2CdO4, C4H6CdO4, Cd(OH)2, and Cd3(PO4)2, in both PL and Ct treatments. Moreover, the proportion of residual Cd in soil increased by 21.21 % and 10.61 % for the PL and Ct treatments, respectively, compared to the CK. The findings suggest that P. tianjinensis S2 is more effective than C. tortuosum for high Cd-contaminated fields, while the fungal inoculant is suitable for lower contamination levels, offering valuable strategies for bioremediation. Therefore, we suggest further research to focus on elucidating the effect of a P. tianjinensis S2 and C. tortuosum combination on O. japonicus root growth and Cd accumulation.

CLC gene family in Solanum lycopersicum: genome-wide identification, expression, and evolutionary analysis of tomato in response to salinity and Cd stress

Introduction

Chloride channels (CLCs) play critical roles in anion transport, stress adaptation, and ion homeostasis in plants. Whereas their genomic wide indentification and functional divergence in tomato (Solanum lycopersicum) remain largely unexplored.

Methods and results

In this study, we identified nine CLC genes in the tomato genome, classifying them into two evolutionarily distinct clades (Group I and II) based on phylogenetic analysis. Structural dissection revealed conserved transmembrane domains (9-12 TMDs) and motif patterns (e.g., motifs 3/7/9 in Group I), with SlCLC02 exhibiting the largest gene size (27,041 bp). Promoter analysis indicated the presence of key abiotic stress-responsive cis-elements (ABRE, MYB, MYC), aligning with the pronounced transcriptional dynamics of SlCLCs under salinity stress. Notably, qRT-PCR analysis demonstrated that most SlCLC genes (particularly SlCLC05, an ortholog to AtCLC-g) exhibited rapid upregulation within 1-4 hours followed by downregulation in roots under salinity treatment, suggesting early stress signaling roles. Likewise, preliminary expression profiling under cadmium stress further identified specific induction of SlCLC07, proposing gene-specific roles in heavy metal detoxification. Strikingly, SlCLC09 lacked collinearity with Arabidopsis/potato homologs, implying lineage-specific diversification.

Discussion

These findings elucidate the SlCLC family's structural diversity, evolutionary constraints, and stress-responsive regulation, providing a framework for targeting specific SlCLC genes (e.g., SlCLC05) to enhance chloride homeostasis in crops under combined salinity and cadmium stress. This study will open a new research direction for genetic crop improvement to ensure protected vegetable production.

Exploring the phytostabilization potential of ryegrass (Lolium perenne L.) upon synergistic application of Cd-tolerant Pseudomonas fluorescens and organic amendments

Soil Cd contamination limits plant productivity by affecting their key functions and reducing yields. In-situ immobilization of heavy metals (HMs) can achieve 'green' and 'sustainable' ways of HM remediation owing to its lower life cycle environmental footprints. This study explored the effects of Cd-resistant P. fluorescens and OAs such as rice straw, wheat straw and cow dung (1% w/w) on the Cd tolerance of ryegrass under Cd contamination (2.2 mg kg-1). In our findings, Cd exposure reduced plant height (22%), root length (38%), chlorophyll 'a' and 'b' (36 and 38%), and relative water content (32%) in uninoculated plants. However, combined use of P. fluorescens and OAs mitigated these effects by immobilizing Cd in soil, with a 56% increase in residual Cd and higher Cd retention in roots and shoots (77 and 87%). Co-application enhanced plant height (96%), root length (158%), chlorophyll content (90 and 98%), relative water content (168%), flavonoids and phenols (151 and 68%) and NPK uptake (104, 73 and 71%) as compared to uninoculated control. Integration of P. fluorescens and OAs not only reduced Cd uptake but also improved growth and yield. Thus, this approach mitigates Cd stress in ryegrass, improving growth and physiology by reducing Cd uptake.

Expression complementation between fundamental biological pathways in Populus hybrid contributes to heterosis in cadmium (Cd) accumulation and tolerance

To reveal the pattern of heterosis in cadmium (Cd) bio-accumulation of poplar and whether the heterosis can promote the phytoremediation efficiency of Cd-polluted soil, the poplar hybrid variety QB-5 ((Populus alba×(P. alba × P. glandulosa)) and its female parent I-101 (Populus alba) and male parent 84 K (P. alba × P. glandulosa) were employed in a hydroponic experiment and a field trial. Better-parent heterosis of leaf biomass, leaf area, free proline, catalase activity, salicylic acid and Cd bio-accumulation reached 100.30, 97.23, 57.96, 176.41, 102.94 and 164.17%, respectively, under Cd exposure. A more in-depth analysis unveiled that most traits related to Cd bio-concentration, including root parameters, Cd translocation factor and Cd bioconcentration factor in leaves, were dominant in 84 K. In contrast, traits related to stress tolerance were dominant in I-101. Weighted gene co-expression network analysis revealed that hub genes responsible for Cd translocation and bioconcentration were dominantly expressed in 84 K, resulting in superior leaf Cd concentration in males compared with females. Conversely, most genes responsible for stress tolerance were highly expressed in I-101. The hybrid exhibited a high-parent complementation pattern for critical traits and relevant hub genes, contributing to better-parent heterosis for these traits. Overexpression of PagP5CS1, a gene showing above-high-parent expression in hybrid, increased Cd tolerance and Cd bio-accumulation in poplar, providing molecular evidence for the dominance hypothesis of heterosis. The efficiency of phytoremediation for Cd-contaminated soil can be largely promoted by exploring and utilizing heterosis in Cd tolerance and Cd bio-accumulation.

Transcriptome analysis unveils the functional effects of ectomycorrhizal fungal colonization on cadmium tolerance of willow saplings

Introduction

Ectomycorrhizal fungus (ECMF) could enhance plant tolerance to heavy metal toxicity by altering metal accumulation and protecting plants from oxidative injury. However, the molecular mechanisms underlying ECMF-mediated detoxification of cadmium (Cd) in willow sapling are not well known. This study aimed to unveil the roles of Cenococcum geophilum (CG) and Suillus luteus (SL) in regulating Cd toxicity tolerance in willow (Salix psammophila 'Huangpi1') saplings.

Methods

This study systematically evaluated physiological and biochemical parameters in the leaf and root tissues of 18 willow saplings, while concurrently conducting transcriptomic analysis of the roots under Cd stress. The specific treatments were labeled as follows: NF (no ECMF inoculation and no Cd addition), CG (CG colonization only), SL (SL colonization only), NF+Cd (no ECMF inoculation with 100 μM Cd addition), CG+Cd (CG colonization with 100 μM Cd addition), and SL+Cd (SL colonization with 100 μM Cd addition).

Results

The results showed the growth, photosynthesis, antioxidant system and transcriptome of 2-month-old willow saplings responded differently to ECMFs colonization under Cd stress. S. luteus markedly increased the aerial parts biomass, while C. geophilum significantly enhanced the root property indices of willow saplings under Cd stress. The highest number of differentially expressed genes (DEGs) was observed in the comparison between CG+Cd (CG colonization with 100 μM Cd addition) and NF+Cd (no ECMF inoculation with 100 μM Cd addition). C. geophilum colonization activated plant hormone signal transduction and carbohydrate metabolism pathways, while S. luteus enhanced the synthesis of secondary metabolites.

Discussion

This study provides a molecular perspective on the mechanism of interaction between ECMFs and willow saplings under Cd stress and supports the application of ECMFs for phytoremediation of Cd-contaminated soil.

Mitigation of adverse effect of cadmium toxicity in lettuce (Lactuca sativa L.) through foliar application of chitosan and spermidine

Cadmium (Cd) stress is considered among the most harmful abiotic stresses because of its toxicity and ability to alter the ultrastructure of plants. Lettuce (Lactuca sativa L.) can readily accumulate Cd from the soil, but its elevated level posed negative effect on their development and nutritional quality. In this study, efficacy of chitosan and spermidine synergistic application was evaluated to improve Cd metal tolerance or its exclusion in lettuce. A pot experiment was conducted in a four-way completely randomized design (CRD) with 3 replicates, using two L. sativa varieties (VRIL-0205 and Green Check). Following treatments, Cd stress (10 ppm CdCl2), chitosan (200 ppm) and spermidine (145 ppm) were applied along with their respective controls. The negative effects of Cd stress on the morphological, physiological, and biochemical attributes of both L. sativa varieties were evaluated along with counter effect of chitosan and spermidine alone and synergistic application. Cd stress resulted in significant accumulation of Cd2+ ions in the shoot of both varieties (0.038 mg kg- 1 in VRIL-0205 and 0.041 mg kg- 1 in Green Check). It also impaired growth, biomass, gas exchange, water relation, antioxidant activities and nutrient uptake in both varieties. Foliar application of both chitosan and spermidine improved growth, biomass, chlorophyll content, photosynthesis rate, stomatal conductance, water content, antioxidant activities and nutrient uptake in both control and stressed plants. Their combined treatment reduced stress indicators including relative membrane permeability (VRIL-0205; 19% and Green Check; 22%), H2O2 (VRIL-0205; 27% and Green Check; 26%) and malondialdehyde content (VRIL-0205; 6% and Green Check; 7%) in stressed plants, compared with stress only plants. These findings showed that chitosan and spermidine synergistic application effectively mitigated the Cd toxicity in both L. sativa varieties and improved their growth under stress condition. This study provides insight into the potential use of chitosan and spermidine foliar spray as sustainable tools for improving Cd resilience in crop plants.

The MYB-bHLH-NRAMP module modulates the cadmium sensitivity of quinoa by regulating cadmium transport and absorption

Cadmium (Cd) is one of the most dangerous environmental pollutants and is easily absorbed by food crops. Quinoa is a kind of coarse grain crop with rich nutrition and strong stress resistance, which is easy to accumulate Cd. The increasingly serious soil Cd pollution poses a serious threat to the food safety of quinoa. However, there are very limited reports on Cd absorption and transport in quinoa. The identification and functional analysis of Cd absorption and transport proteins are essential for improving the food safety of quinoa. In this study, the key transporter CqNRAMP1 potentially involved in Cd uptake was identified from quinoa by expression detection. Yeast complementation test found that CqNRAMP1 has the ability to transport metal ions in yeast. Using transgenic technology, it was found that CqNRAMP1 enhanced the sensitivity of quinoa to Cd stress by promoting Cd absorption. The transcription factors CqMYB26 and CqbHLH162 that potentially regulate CqNRAMP1 were identified from the quinoa genome by bioinformatics. Physiological and biochemical, yeast two-hybrid, bimolecular fluorescence complementation and dual luciferase experiments further found that CqMYB26 and CqbHLH162 enhanced the expression of CqNRAMP1 through protein-protein interaction, thus promoting Cd absorption and further enhancing the sensitivity of quinoa to Cd exposure. This study explored the molecular mechanism of CqMYB26-CqbHLH162 promoting the expression of CqNRAMP1 and regulating Cd absorption by physiological, biochemical and molecular biological techniques. These research findings will offer a crucial theoretical foundation and practical insight for cultivating low Cd-accumulating crops and addressing food safety concerns.

Integrative study of subcellular distribution, chemical forms, and physiological responses for understanding cadmium tolerance in two garden shrubs

Urban ornamental shrubs have significant potential for restoring cadmium (Cd)-contaminated soil. The Cd enrichment characteristics and tolerance mechanisms of Buxus sinica and Ligustrum × vicaryi were investigated through a simulated pot pollution experiment. Specifically, the Cd content and accumulation in different plant tissues, the subcellular distribution and chemical forms of Cd in the roots, and the effects of Cd on the ultrastructure of root cells under various Cd concentrations (0, 25, 50, 100, and 200 mg kg⁻1) were analyzed. The results showed that: (1) As the Cd treatment levels increased, the total biomass of B. sinica gradually decreased, while L. × vicaryi exhibited a stimulation effect at low Cd concentrations but inhibition at high Cd concentrations. (2) The Cd content in different tissues of both shrubs increased with rising Cd levels. The bioconcentration factor (BCF) and translocation factor (TF) indicated that L. × vicaryi has the potential for Cd phytostabilization. (3) Cd in the roots of both shrubs was primarily present in NaCl-extractable form, and was mostly bound to the cell wall. (4) Excessive Cd caused damage to the cellular structure of B. sinica, while the cells of L. × vicaryi maintained normal morphology. (5) In both shrubs, Cd primarily bound to the cell wall through hydroxyl and amino functional groups, as well as soluble sugars. In summary, converting Cd to less active forms, immobilizing Cd in the cell wall, and providing binding sites through functional groups may be crucial resistance mechanisms for both shrubs in response to Cd stress.

Two strains of cadmium (Cd)-resistant bacteria isolated from soils and their ability to promote oilseed rape (Brassica juncea L.) to grow and absorb Cd in soils

As a highly toxic, mobile, and persistent heavy metal, cadmium (Cd) in soils is becoming a crucial environmental problem. Most of classical physical and chemical remediation measures for Cd-contaminated soils possibly cause some dangers to soil structure and characteristics and potential secondary pollution, however, Cd-resistant microbial which can sequestrate Cd by releasing extracellular polymeric substances (EPS) capable of ion exchange, coordination, and adsorption and improve plant growth should be favorable for remediation of Cd-contaminated soils due to being environmentally friendly and cost-effective. Therefore, the plant-microbe combination is becoming a priority option in the remediation of Cd-contaminated soils. Here, we isolated two strains of Cd-resistant bacteria from soils and investigated the ability of the two strains to promote growth of oilseed rape (Brassica juncea L.) and Cd uptake by the plants. Citrobacter farmeri and Cupriavidus gilardii were isolated from soils via culture media containing 30 and 50 mg/L Cd, respectively, which could release EPS including proteins, polysaccharide, and DNA. The EPS from C. gilardii was significantly higher than that from C. farmeri, and the proportion of protein in EPS was the highest for two strains. Additionally, two strains secreted indole-3-acetic acid (IAA) and could solubilize phosphorus, and the ability of C. gilardii to secret IAA was significantly higher than that of C. farmeri. The pot experiment indicated that C. farmeri and C. gilardii significantly enhanced oilseed rape biomass (by 81.99% and 76.57%, respectively), C and N contents, Cd accumulation in plants by 229.03% and 264.63%, respectively, and remediation efficiency at 40 days after emergence (flowering stage). However, the difference in promoting plant growth and Cd uptake and phytoremediation efficiency of Cd-contaminated soils between the two strains was not significant. Overall, C. farmeri and C. gilardii isolated from soils might be promising strains in enhancing phytoremediation of Cd-contaminated soils.

Salicylic acid confers cadmium tolerance in wheat by regulating photosynthesis, yield and ionic homeostasis

Wheat (Triticum aestivum L.) productivity and quality can be threatened by soil cadmium (Cd) contamination, posing a concern to food security. Salicylic acid (SA) is an endogenously produced signaling molecule that activates the defense system imparting abiotic stress tolerance in plants. Hence, an experiment was conducted to explore the roles of foliar application of SA in ameliorating Cd toxicity in two wheat varieties. The treatments comprised of, a) Cd stress: i) Cd0 = control (No Cd), Cd1 = 500 µM Cd stress at 30 days after sowing (DAS); SA applications: (i) SA0 = control (No SA) (ii) SA1 = 0.5 mM SA at 32 DAS, and c) Wheat varieties: (i) Anaj-17 and (ii) Akbar-19. The experiment was carried out with three replicates in a completely randomized design (CRD). The findings of the study have revealed that Cd stress prominently reduced the plant growth and yield, gaseous exchange attributes, and relative water content of both wheat varieties, and more reduction was observed in Anaj-17 as compared to Akbar-19. Plant height, economic yield, photosynthetic rate, and relative water content were decreased by (9.80 and 8.20%), (12.2 and 6.58%), (20 and 11.32%), and (12.5 and 10%) in Anaj-17 and Akbar-19 respectively. Further, SPAD value and chlorophyll fluorescence decreased under Cd toxicity in both wheat cultivars as compared to non-stress conditions. Contrarily, electrolyte leakage and Cd contents were increased in the plants as compared to the control. However, the foliar applications of SA in Cd-stressed plants significantly improved the plant growth and yield attributes, relative water content, gas exchange attributes, and chlorophyll content in both wheat varieties as compared to control-no SA applied. In addition, chlorophyll fluorescence and nutrient uptake were also improved under SA applications as compared to control. However, SA played an ameliorative role in reducing Cd-toxicity by reducing the electrolyte leakage and Cd uptake by the plants. Among the varieties, Akbar-19 outperformed the Anaj-17 to impart Cd toxicity under SA applications based on plant morphophysiological attributes. Hence, the outcomes of the experiment recommended that the foliar treatment of SA amended the Cd tolerance of wheat varieties by improving plant physiological and biochemical attributes.

Effects of coexisting goethite or lepidocrocite on Fe(II)-induced ferrihydrite transformation pathways and Cd speciation

The efficacy of ferrihydrite in remediating Cd-contaminated soil is tightly regulated by Fe(II)-induced mineralogical transformations. Despite the common coexistence of iron minerals such as goethite and lepidocrocite, which can act as templates for secondary mineral formation, the impact of these minerals on Fe(II)-induced ferrihydrite transformation and the associated Cd fate have yet to be elucidated. Herein, we investigated the simultaneous evolution of secondary minerals and Cd speciation during Fe(II)-induced ferrihydrite transformation in the presence of goethite versus lepidocrocite. The presence of goethite resulted in a more pronounced ferrihydrite transformation than lepidocrocite because goethite facilitates electron transfer. Coexisting goethite promoted the production of secondary goethite with different morphology by triggering template-directed nucleation and growth of labile Fe(III) derived from ferrihydrite and intermediate lepidocrocite, respectively. However, coexisting lepidocrocite impeded goethite formation from ferrihydrite and acted as the template to facilitate secondary lepidocrocite production. Furthermore, variations in the crystallinity of coexisting lepidocrocite influenced the particle size and crystallinity of the secondary lepidocrocite, reflecting different dominant mechanisms in secondary lepidocrocite formation. Despite partial Cd mobilization into the solution due to Fe(II)-induced ferrihydrite transformation, secondary goethite and lepidocrocite re-sequestered Cd through lattice Fe(III) substitution, indicated by an increased structural Cd proportion, expanded lattice spacing, and reduced hyperfine field intensity. Additionally, secondary goethite was more effective than secondary lepidocrocite in sequestering Cd. Coexisting goethite increased the structural Cd proportion by 3.5-fold compared to coexisting lepidocrocite, demonstrating the superior ability of coexisting goethite in enhancing Cd stability during Fe(II)-induced ferrihydrite transformation in natural soils. These findings highlight the impact of template-driven mineralogical transformation on Cd fate in polluted soils and provide crucial implications for toxic metal remediation using mineral amendments.

Enhanced nitrogen fixation and Cd passivation in rhizosphere soil by biochar-loaded nitrogen-fixing bacteria: Chemisorption and microbial mechanism

This study developed a biochar-loaded Ac material and clarified its chemical and microbial mechanisms for cadmium (Cd) immobilization and plant growth promotion. Results showed that biochar-loaded nitrogen-fixing bacteria (Azotobacter chroococcum; BAc) enhanced Cd adsorption by forming stable complexes with bacterial secretions and activating biochar functional groups. Compared with BC and Ac, after BAc application, Ac successfully colonized the lettuce rhizosphere, tagged with green fluorescent protein. It improved plant nitrogen by 47.39-72.47 % and increased root and shoot biomass by 50.35-107.32 % through nitrogen fixation and amino acid release. BAc reduced soil Cd bioavailability by 16.67-46.42 % and Cd accumulation in root and shoot by 14.28-69.74 %. This occurred through increasing soil pH and converting exchangeable Cd to carbonate-bound and Fe/Mn oxide-bound fractions. Importantly, BAc improved the rhizosphere nutrient environment and promoted the deterministic assembly of the rhizosphere microbial community. It also increased microbial diversity and attracted taxa like Actinomycetales (7.59 %), Solirubrobacteriales (5.17 %), Rhizobiales (5.17 %), and Sphingomonadales (5.17 %), all associated with nitrogen fixation, plant growth promotion, and Cd immobilization. Structural equation modeling (SEM) confirmed that BAc increased nitrogen utilization efficiency in lettuce and facilitated biotic immobilization of soil Cd by optimizing the microbial structure. This study provides insights into how biochar-loaded Ac improve plant growth and control soil Cd pollution.

Field-scale screening of pumpkin cultivars for cost-effectiveness of "repairing while producing" in cadmium-arsenic co-contaminated agricultural land

Soil contamination with heavy metals poses a significant health risk as these metals can be transferred to humans through agricultural products. This study aimed to identify pumpkin varieties with low cadmium and arsenic accumulation. To this end, we evaluated 25 pumpkin varieties. Results indicated that the accumulated contents of heavy metals in each organ followed the order: root (0.148 mg·kg-1) > leaf (0.100 mg·kg-1) > stem (0.076 mg·kg-1).The transfer coefficients of these 25 pumpkin varieties were greater for leaves than for stems, yet none exceeded 1. Rhizosphere pH is a critical factor influencing the uptake of Cd by pumpkins, with a less significant impact on As uptake. This study provides a foundation for identifying pumpkin varieties with low Cd and As accumulation potential.Additionally, it contributes to the exploration of pumpkin's potential as a phytoremediation resource and its safe production and utilization in heavy metal-contaminated soils.

The protective roles of Oryza glumaepatula and phytohormone in enhancing rice tolerance to cadmium stress by regulating gene expression, morphological, physiological, and antioxidant defense system

The heavy metal cadmium (Cd) is highly poisonous and has received significant attention from environmental scientists due to its harmful impacts on plants. Oryza glumaepatula is a wild rice that contains useful genes against biotic and abiotic stresses. Therefore, the current study used SG007, a single-segment substitution line (SSSL), generated by crossing O. glumaepatula with an elite rice cultivar (HJX74), to evaluate the resistance potential against Cd. Moreover, we assessed the efficacy of strigolactone GR24 (1 μM) against Cd toxicity (100 μM) by investigating physiological, biochemical, and molecular mechanisms in both cultivars (i.e., SG007 and HJX74). The findings of this study revealed that Cd toxicity declined the chlorophyll a, chlorophyll b, and carotenoids by 50%, 20%, and 44% in SG007, and 58%, 39%, and 59% in HJX74 by enhancing electrolyte leakage (EL), malondialdehyde (MDA), and hydrogen peroxide (H2O2) by 113%, 184%, and 119% in SG007 and 248%, 273% and 195% in HJX74, respectively. GR24 improved growth under Cd stress in both cultivars, and SG007 exhibited better plant growth parameters, antioxidant enzymatic activities, nitric oxide synthase (NOS), and nitric oxide (NO) levels than HJX74 under Cd toxicity. GR24 with SG007 regulated expressions of Cd transporters and reduced the cytological disruptions in cell organelles. The combined utilization of SG007 and GR24 reduced Cd accumulation and oxidative stress and improved plant growth parameters and enzymatic activities. In conclusion, our study highlights the potential of utilizing SG007 in conjunction with GR24 as a practical strategy to mitigate Cd pollution in rice. The results not only underscore the beneficial effects of strigolactone GR24 in alleviating Cd-induced stress but also emphasize the valuable genetic traits of O. glumaepatula in developing rice lines with enhanced tolerance to heavy metals, offering broader implications for sustainable agriculture and crop improvement in contaminated environments.

Comprehensive Physio-Biochemical Evaluation Reveals Promising Genotypes and Mechanisms for Cadmium Tolerance in Tibetan Hull-Less Barley

Cadmium (Cd) toxicity in agricultural soil is increasing globally and significantly impacts crop production and food safety. Tibetan hull-less barley (Hordeum vulgare L. var. nudum), an important staple food and economic crop, exhibits high genetic diversity and is uniquely adapted to the harsh conditions of the Qinghai-Tibet Plateau. This study utilized hydroponic experiments to evaluate the genotypic differences in Cd tolerance among 71 Tibetan hull-less barley genotypes. Physiological assessments revealed significant reductions in various growth parameters under Cd stress compared to normal conditions: soil-plant analysis development (SPAD) value, shoot height, root length, shoot and root fresh weight, shoot and root dry weight, of 11.74%, 39.69%, 48.09%, 52.88%, 58.39%, 40.59%, and 40.52%, respectively. Principal component analysis (PCA) revealed key traits contributing to Cd stress responses, explaining 76.81% and 46.56% of the variance in the preliminary and secondary selection. The genotypes exhibited varying degrees of Cd tolerance, with X178, X192, X215, X140, and X162 showing high tolerance, while X38 was the most sensitive based on the integrated score and PCA results. Validation experiments confirmed X178 as the most tolerant genotype and X38 as the most sensitive, with observed variations in morphological, physiological, and biochemical parameters, as well as mineral nutrient responses to Cd stress. Cd-tolerant genotypes exhibited higher chlorophyll content, net photosynthesis rates, and effective photochemical capacity of photosystem II, along with an increased Cd translocation rate and reduced oxidative stress. This was accompanied by elevated activities of antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), indicating a robust stress response mechanism. These findings could facilitate the development of high-tolerance cultivars, with X178 as a promising candidate for further research and cultivation in Cd-contaminated soils.

Ecological characteristics of tall fescue and spatially organized communities: Their contribution to mitigating cadmium damage

The threat of cadmium (Cd) stress to agricultural soil environments, as well as their productivity attracting growing global interest. Tall fescue (Festuca arundinacea Schreb.) is a strong candidate for the remediation of heavy metals in soil. However, the joint analysis of Cd tolerance, physiological responses, and multifaceted plant microbiomes in tall fescue fields has not been extensively researched. Therefore, this study employed microbial sequencing (i.e., 16S and ITS sequencing) to investigate the differences in microbial community structure among various plant compartments of Cd-resistant tall fescue (cv. 'Arid3') and Cd-sensitive tall fescue (cv. 'Barrington'). Furthermore, we examined the mechanism of resistance to Cd by introducing three different bacteria and a fungus that were isolated from the 'Arid3' rhizosheath soil. It highlighted the potential application of enriched taxa such as Delftia, Novosphingobium, Cupriavidus and Torula in enhancing the activity of antioxidant defense systems, increasing the production of osmotic regulatory substances, and stimulating the expression of Cd-resistance genes. This ultimately promoted plant growth and enhanced phytoremediation efficiency. This study shed light on the response mechanism of the tall fescue microbiome to Cd stress and underscored the potential of tall fescue-microbe co-culture in the remediation of heavy metal-contaminated areas.

Defense guard: strategies of plants in the fight against Cadmium stress

Soil Cadmium (Cd) contamination is a worldwide problem with negative impacts on human health. Cultivating the Cd-Pollution Safety Cultivar (Cd-PSC) with lower Cd accumulation in edible parts of plants is an environmentally friendly approach to ensure food security with wide application prospects. Specialized mechanisms have been addressed for Cd accumulation in crops. This review provides an extensive generality of molecular regulation mechanisms involved in Cd absorption, transport, detoxification, and tolerance in plants, highlighting key aspects of rhizosphere, apoplast barrier, Cd uptake, transfer, and cellular repair strategies under Cd stress. Additionally, we summarize the possible approaches for lowering the Cd accumulation crops, including molecular-assistant breeding, applying chemical materials, and microbial strategy to decrease Cd content in edible parts and improve Cd tolerance of crops under Cd stress. This review would provide valuable insights for cultivating low Cd accumulated crop cultivars, ultimately contributing to food safety.

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.

Unlocking plant resilience: Advanced epigenetic strategies against heavy metal and metalloid stress

The escalating threat of heavy metal and metalloid stress on plant ecosystems requires innovative strategies to strengthen plant resilience and ensure agricultural sustainability. This review provides important insights into the advanced epigenetic pathways to improve plant tolerance to toxic heavy metals and metalloid stress. Epigenetic modifications, including deoxyribonucleic acid (DNA) methylation, histone modifications, and small ribonucleic acid (RNA) engineering, offer innovative avenues for tailoring plant responses to mitigate the impact of heavy metal and metalloid stress. Technological advancements in high-throughput genome sequencing and functional genomics have unraveled the complexities of epigenetic regulation in response to heavy metal and metalloid contamination. Recent strides in this field encompass identifying specific epigenetic markers associated with stress resilience, developing tools for editing the epigenome, and integrating epigenetic data into breeding programs for stress-resistant crops. Understanding the dynamic interaction between epigenetics and stress responses holds immense potential to engineer resilient crops that thrive in environments contaminated with heavy metals and metalloids. Eventually, harnessing epigenetic strategies presents a promising trajectory toward sustainable agriculture in the face of escalating environmental challenges. Plant epigenomics expands, the potential for sustainable agriculture by implementing advanced epigenetic approaches becomes increasingly evident. These developments lay the foundation for understanding the growing significance of epigenetics in plant stress biology and its potential to mitigate the detrimental effects of heavy metal and metalloid pollution on global agriculture.

Cadmium exposure induced light/dark- and time-dependent redox changes at subcellular level in Arabidopsis plants

Cadmium (Cd) is one of the most toxic heavy metals for plants and humans. Reactive oxygen species (ROS) are some of the primary signaling molecules produced after Cd treatment in plants but the contribution of different organelles and specific cell types, together with the impact of light is unknown. We used Arabidopsis lines expressing GRX1-roGFP2 (glutaredoxin1-roGFP) targeted to different cell compartments and analysed changes in redox state over 24 h light/dark cycle in Cd-treated leaf discs. We imaged redox state changes in peroxisomes and chloroplasts in leaf tissue. Chloroplasts and peroxisomes were the most affected organelles in the dark and blocking the photosynthetic electron transport chain (pETC) by DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) promotes higher Cd-dependent oxidation in all organelles. Peroxisomes underwent the most rapid changes in redox state in response to Cd and DCMU and silencing chloroplastic NTRC (NADPH thioredoxin reductase C) considerably increases peroxisome oxidation. Total NAD(P)H and cytosolic NADH decreased during exposure to Cd, while Ca+2 content in chloroplasts and cytosol increased in the dark period. Our results demonstrate a Cd-, time- and light-dependent increase of oxidation of all organelles analysed, that could be in part triggered by disturbances in pETC and photorespiration, the decrease of NAD(P)H availability, and differential antioxidants expression at subcellular level.

The Potential of Helichsryum splendidum (Thunb.) Less. for the Restoration of Sites Polluted with Coal Fly Ash

The disposal of coal fly ash (CFA) generated from coal-fired power stations has serious impact on the ecosystem, by converting large pieces of land to barren ash dams with the potential to contaminate groundwater, surface water, air and soil. The aim of this study was to clarify the potential of phytoremediation using Helichrysum splendidum (Thunb.) Less. in areas polluted by CFA through conduction of pot trial experiments for 14 weeks. Plants of the same age were cultivated in CFA to assess their growth, photosynthetic rate and tolerance towards metal toxicity. This study revealed that the CFA was moderately polluted with heavy metals, and a lower photosynthetic rate was recorded for the CFA plants in comparison to the controls (plants grown in soil). Although the CO2 assimilation rate was lower for the CFA plants, increased growth was recorded for all the plants tested. Inductively coupled plasma mass spectrometry (ICP-MS) was used to quantify the amount of trace elements in samples and parameters including translocation factor (TF) and bioconcentration factor (BCF) were used to evaluate the phytoremediation potential of H. splendidum (Thunb.) Less. The results revealed that higher concentrations of Cd, Co, Cr, Cu, Mn and Pb were accumulated in the roots, while As, Ni and Zn were found in the shoots. Elements including As, Cr and Zn reported TF values above 1, indicating the plants' phytoextraction potential. The BCF values for As, Cu and Zn were 1.22, 1.19 and 1.03, indicating effectiveness in the phytostabilization processes. A removal rate efficiency ranging from 18.0 to 56.7% was recorded confirming that, H. splendidum (Thunb.) Less. can be employed for restoration of CFA dams.

Modulation of Cd carriers by innovative nanocomposite (Ca+Mg) and Cd-resistance microbes (Bacillus pumilus): a mechanistic approach to enhance growth and yield of rice (Oryza sativa L.)

Cadmium (Cd) is a well-known pollutant in agricultural soil, affecting human health through the food chain. To combat this issue, Ca + Mg (25 mg L-1) nanocomposite and Bacillus pumilus, either alone or combined, were applied to rice plants under Cd (5 mg kg-1, 10 mg kg-1) contamination. In our study, growth and yield traits demonstrated the beneficial influence of Ca + Mg and B. pumilus application in improving rice defense mechanism by reducing Cd stress. Combined Ca + Mg and B. pumilus application increased SPAD (15), total chlorophyll (18), chlorophyll a (11), chlorophyll b (22), and carotenoids (21%) with Cd (10 mg kg-1), compared to the application alone. Combined Ca + Mg and B. pumilus application significantly regulated MDA (15), H2O2 (13), EL (10), and O2 •- (24%) in shoots under Cd (10 mg kg-1), compared to the application alone. Cd (10 mg kg-1) increased the POD (22), SOD (21), APX (12), and CAT (13%) in shoots with combined Ca + Mg and B. pumilus application, compared to the application alone. Combined Ca + Mg and B. pumilus application significantly reduced Cd accumulation in roots (22), shoots (13), and grains (20%) under Cd (10 mg kg-1), compared to the application alone. Consequently, the combined application of Ca + Mg and B. pumilus is a sustainable solution to enhance crop production under Cd stress.

Bio-pump cadmium phytoextraction efficiency promoted by phytohormones in Festuca arundinacea

The leaves of Festuca arundinacea can excrete cadmium (Cd) out onto the leaf surface, leading to a bio-pump phytoremediation strategy based on "root uptake-root-to-leaf translocation-leaf excretion". However, the bio-bump efficiency of soil Cd is a limiting factor for the implementation of this novel technology. Bio-bump remediation involves the bioprocess of plant root uptake from soil, root-to-leaf translocation, and leaf hydathode excretion. Here we show the significant effects of phytohormones in regulating the bio-pump phytoextraction efficiency. The results showed that salicylic acid and ethylene enhanced the whole process of Cd root uptake, root-to-leaf translocation, and leaf excretion, promoting the bio-pump phytoextraction efficiency by 63.6% and 73.8%, respectively. Gibberellin also greatly promoted Cd translocation, leaf excretion, and phytoextraction, but did not significantly impact Cd root uptake. Our results indicate that salicylic acid and ethylene could be recommended to promote bio-pump phytoextraction efficiency in F. arundinacea. Gibberellin might be used for a short-term promotion of the leaf Cd excretion.

Enhancing chromium resistance and bulb quality in onion (Allium cepa L.) through copper nanoparticles and possible health risk

Chromium (Cr) is a toxic metal in soil-plant system, hence causing possible health risks prominently in the areas with forgoing industrial activities. Copper nanoparticles (Cu NPs) have been reported as an excellent adsorbent for pollutants. Therefore, this study investigates how copper nanoparticles enhance onion growth while decreasing chromium uptake in onion plants. Additionally, it examines the potential health risks of consuming onion plants with elevated chromium levels. The results demonstrated that the addition of CuNPs at 15 mg kg-1 significantly improved the plant height (48%), leaf length (37%), fresh weight of root (61%), root dry weight (70%), fresh weight of bulb (52%), bulb dry weight (59%), leaves fresh weight (52%) and dry weight of leaves (59%), leaf area (72%), number of onion leaves per plant (60%), Chl. a (42%), chl. b (36%), carotenoids (40%), total chlorophyll (40%), chlorophyll contents SPAD value (56%), relative water contents (35%), membrane stability index (16%), total sugars (25%), crude protein (21%), ascorbic acid (19%) and ash contents (64%) at 10 mg kg-1 Cr. Whereas, maximum decline of Cr by 46% in roots, 68% in leaves and 92% in bulb was found with application of 15 mg kg-1 of Cu NPs in onion plants under 10 mg kg-1 Cr toxicity. The health risk assessment parameters of onion plants showed minimum values 0.0028 for average daily intake (ADI), 0.001911 for Non-cancer risk (NCR), and 0.001433 for cancer risk (CR) in plants treated with Cu NPs at 15 mg kg-1 concentration grown in soil spiked with 10 mg kg-1 chromium. It is concluded that Cu NPs at 15 mg kg-1 concentration improved growth of plants in control as well as Cr contaminated soil. Therefore, use of Cu NPs at 15 mg kg-1 concentration is recommended for improving growth of plants under normal and metal contaminated soils.

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.

The Contribution of Trichoderma viride and Metallothioneins in Enhancing the Seed Quality of Avena sativa L. in Cd-Contaminated Soil

Pollution of arable land with heavy metals is a worldwide problem. Cadmium (Cd) is a toxic metal that poses a severe threat to humans' and animals' health and lives. Plants can easily absorb Cd from the soil, and plant-based food is the main means of exposure to this hazardous element for humans and animals. Phytoremediation is a promising plant-based approach to removing heavy metals from the soil, and plant growth-promoting micro-organisms such as the fungi Trichoderma can enhance the ability of plants to accumulate metals. Inoculation of Avena sativa L. (oat) with Trichoderma viride enhances germination and seedling growth in the presence of Cd and, in this study, the growth of 6-month-old oat plants in Cd-contaminated soil was not increased by inoculation with T. viride, but a 1.7-fold increase in yield was observed. The content of Cd in oat shoots depended on the Cd content in the soil. Still, it was unaffected by the inoculation with T. viride. A. sativa metallothioneins (AsMTs) participate in plant-fungi interaction, however, their role in this study depended on MT type and Cd concentration. The inoculation of A. sativa with T. viride could be a promising approach to obtaining a high yield in Cd-contaminated soil without increasing the Cd content in the plant.

Heavy metal stress and mitogen activated kinase transcription factors in plants: Exploring heavy metal-ROS influences on plant signalling pathways

Due to their stationary nature, plants are exposed to a diverse range of biotic and abiotic stresses, of which heavy metal (HM) stress poses one of the most detrimental abiotic stresses, targeting diverse plant processes. HMs instigate the overproduction of reactive oxygen species (ROS), and to mitigate the adverse effects of ROS, plants induce multiple defence mechanisms. Besides the negative implications of overproduction of ROS, these molecules play a multitude of signalling roles in plants, acting as a central player in the complex signalling network of cells. One of the ROS-associated signalling mechanisms is the mitogen-activated protein kinase (MAPK) cascade, a signalling pathway which transduces extracellular stimuli into intracellular responses. Plant MAPKs have been implicated in signalling involved in stress response, phytohormone regulation, and cell cycle cues. However, the influence of various HMs on MAPK activation has not been well documented. In this review, we address and summarise several aspects related to various HM-induced ROS signalling. Additionally, we touch on how these signals activate the MAPK cascade and the downstream transcription factors that influence plant responses to HMs. Moreover, we propose a workflow that could characterise genes associated with MAPKs and their roles during plant HM stress responses.

Cadmium and phthalate impacts developmental growth and mortality of Spodoptera littoralis, but not reproductive success

Our environment is increasingly polluted with various molecules, some of which are considered endocrine disruptors. Metals and phthalates, originating from industrial activities, agricultural practices, or consumer products, are prominent examples of such pollutants. We experimentally investigated the impacts of the heavy metal cadmium and the phthalate DEHP on the moth Spodoptera littoralis. More specifically, larvae were reared in laboratory conditions, where they were exposed to diets contaminated with either two doses of cadmium at concentrations of 62.5 µg/g or 125 µg/g, two doses of DEHP at 100 ng/g and 10 µg/g, or a combination of both low and high doses of the two compounds, with a control group for comparison. Our findings indicate that cadmium delays the developmental transition from larva to adult. Notably, the combination of cadmium and DEHP exacerbated this delay, highlighting a synergistic effect. In contrast, DEHP alone did not affect larval development. Additionally, we observed that cadmium exposure, both alone and in combination with DEHP, led to a lower mass at all larval stages. However, cadmium-exposed individuals that reached adulthood eventually reached a similar mass to those in other groups. Interestingly, while our results did not show any effect of the treatments on hatching success, there was a higher adult mortality rate in the cadmium-treated groups. This suggests that while moths may prioritize reproductive success, their survival at the adult stage is compromised by cadmium exposure. In conclusion, our study demonstrates the impact of cadmium on the development, mass, and adult survival of moths, and reveals synergistic effects when combined with DEHP. These results confirm cadmium as an endocrine disruptor, even at low doses. These insights underscore the importance of understanding the toxicological effects of low doses of pollutants like cadmium and DEHP, both individually and in combination.

Physiological, biochemical and transcriptomic insights into the mechanisms by which molybdenum mitigates cadmium toxicity in Triticum aestivum L

There are many heavy metal stresses in agricultural biological systems, especially cadmium (Cd) stress, which prevent the full growth of plants, lead to a serious decline in crop yield, and endanger human health. Molybdenum (Mo), an essential nutrient element for plants, regulates plant growth mainly by reducing the absorption of heavy metals and protecting plants from oxidative damage. The aim of this study was to determine the protective effect of Mo (1 μM) application on wheat plants under conditions of Cd (10 μM) toxicity. The biomass, Cd and Mo contents, photosynthesis, leaf and root ultrastructure, antioxidant system, and active oxygen content of the wheat plants were determined. Mo increased the total chlorophyll content of wheat leaves by 43.02% and the net photosynthetic rate by 38.67%, and ameliorated the inhibitory effect of cadmium on photosynthesis by up-regulating photosynthesis-related genes and light-trapping genes. In addition, Mo reduced the content of superoxide anion (O2•-) by 16.55% and 31.12%, malondialdehyde (MDA) by 20.75% and 7.17%, hydrogen peroxide (H2O2) by 24.69% and 8.17%, and electrolyte leakage (EL) by 27.59% and 16.82% in wheat leaves and roots, respectively, and enhanced the antioxidant system to reduce the burst of reactive oxygen species and alleviate the damage of Cd stress on wheat. According to the above results, Mo is considered a plant essential nutrient that enhances Cd tolerance in wheat by limiting the absorption, accumulation and transport of Cd and by regulating antioxidant defence mechanisms. ENVIRONMENTAL IMPLICATION: Cadmium (Cd)，is one of the most toxic heavy metals in the environment, and Cd pollution is a global environmental problem that threatens food security and human health. Molybdenum (Mo), as an essential plant nutrient, is often used to resist environmental stress. However, the mechanism of Mo treatment on wheat subjected to Cd stress has not been reported. In this study, we systematically analysed the effects of Mo on the phenotype, physiology, biochemistry, ultrastructure and Cd content of wheat subjected to Cd stress, and comprehensively analysed the transcriptomics. It not only reveals the mechanism of Mo tolerance to Cd stress in wheat, but also provides new insights into phytoremediation and plant growth in Cd-contaminated soil.

In vitro exploration of Acinetobacter strain (SG-5) for antioxidative potential and phytohormone biosynthesis in maize (Zea mays L.) cultivars differing in cadmium tolerance

Cadmium (Cd) poses serious threats to plant growth and development, whereas the use of plant growth-promoting rhizobacteria (PGPR) has emerged a promising approach to diminish Cd retention in crops. A pot experiment was conducted to evaluate the effect of Cd tolerant strain Acinetobacter sp. SG-5 on growth, phytohormonal response, and Cd uptake of two maize cultivars (3062 and 31P41) under various Cd stress levels (0, 5, 12, 18, 26, and 30 μM CdCl2). The results revealed that CdCl2 treatment significantly suppressed the seed germination and growth together with higher Cd retention in maize cultivars in a dose-dependent and cultivar-specific manner with pronounced negative effect in 31P41. However, SG-5 strain exerted positive impact by up-regulating seed germination traits, plant biomass, photosynthetic pigments, enzymatic and non-enzymatic antioxidants, endogenous hormone level indole-3-acetic acid (IAA), abscisic acid (ABA), and sustained optimal nutrient's levels in both cultivars but predominantly in Cd-sensitive one (31P41). Further, Cd-resistant PGPR decreased the formation of reactive oxygen species in terms of malondialdehyde (MDA) and hydrogen peroxide (H2O2) verified through 3, 3'-diaminobenzidine (DAB) and nitroblue tetrazolium (NBT) analysis in conjunction with reduced Cd uptake and translocation in maize root and shoots in comparison to controls, advocating its sufficiency for bacterial-assisted Cd bioremediation. In conclusion, both SG-5 inoculated cultivars exhibited maximum Cd tolerance but substantial Cd tolerance was acquired by Cd susceptible cultivar-31P41 than Cd-tolerant one (3062). Current work recommended SG-5 strain as a promising candidate for plant growth promotion and bacterial-assisted phytomanagement of metal-polluted agricultural soils.

The immobilization of cadmium by rape straw derived biochar in alkaline conditions: Sorption isotherm, molecular binding mechanism, and in-situ remediation of Cd-contaminated soil

The issue of cadmium (Cd) contamination in alkaline soils is escalating, necessitating the prompt implementation of effective passivation strategies. Biochar has gained significant attention for its potential in immobilizing heavy metals; however, the suitability of biochar as a remediation material and its micro-scale interaction mechanisms with Cd under alkaline conditions remain unclear. Rape straw (RS) were pyrolyzed at 400 °C (RB400) and 700 °C (RB700) to produce biochar. Adsorption and soil incubation experiments were carried out to assess the feasibility of using rape straw derived biochar pyrolyze at different temperatures and understanding their remediation mechanisms in alkaline environments. The sorption capacity for Cd immobilization was evaluated using sorption isotherms, revealing that RB700 exhibited enhanced Cd sorption performance with a maximum sorption capacity of 119.33 mg g-1 calculated from the Langmuir isotherm equation at pH 8. Cd L3-edge X-ray absorption near-edge structure (XANES) spectroscopy analysis confirmed that the dominant sorption species of Cd were organic Cd in RB400, with CdCO3 precipitation increased to 73.9% in RB700. Solid-state 13C nuclear magnetic resonance (13C-NMR) spectroscopy demonstrated that aromatic and carboxyl C functional groups are involved in the organic sorption of Cd through complexation and Cd2+-π interactions in alkaline solutions. The precipitation of CdCO3 in RB700 may resulted in a more effective passivation effect compared to RB400, leading to a significant 15.54% reduction in the DTPA-Cd content in Cd-contaminated soil. These findings highlight the effective Cd passivation Cd in alkaline environments by rape straw derived biochar, providing new molecular insights into the Cd retention mechanism of biochar. Furthermore, it presents novel ideas for improving remediation approaches for alkaline Cd-contaminated soils.

Melatonin-Regulated Chaperone Binding Protein Plays a Key Role in Cadmium Stress Tolerance in Rice, Revealed by the Functional Characterization of a Novel Serotonin N-Acetyltransferase 3 (SNAT3) in Rice

The study of the mechanisms by which melatonin protects against cadmium (Cd) toxicity in plants is still in its infancy, particularly at the molecular level. In this study, the gene encoding a novel serotonin N-acetyltransferase 3 (SNAT3) in rice, a pivotal enzyme in the melatonin biosynthetic pathway, was cloned. Rice (Oryza sativa) OsSNAT3 is the first identified plant ortholog of archaeon Thermoplasma volcanium SNAT. The purified recombinant OsSNAT3 catalyzed the conversion of serotonin and 5-methoxytryptamine to N-acetylserotonin and melatonin, respectively. The suppression of OsSNAT3 by RNAi led to a decline in endogenous melatonin levels followed by a reduction in Cd tolerance in transgenic RNAi rice lines. In addition, the expression levels of genes encoding the endoplasmic reticulum (ER) chaperones BiP3, BiP4, and BiP5 were much lower in RNAi lines than in the wild type. In transgenic rice plants overexpressing OsSNAT3 (SNAT3-OE), however, melatonin levels were higher than in wild-type plants. SNAT3-OE plants also tolerated Cd stress, as indicated by seedling growth, malondialdehyde, and chlorophyll levels. BiP4 expression was much higher in the SNAT3-OE lines than in the wild type. These results indicate that melatonin engineering could help crops withstand Cd stress, resulting in high yields in Cd-contaminated fields.

The Effect of Two Siderophore-Producing Bacillus Strains on the Growth Promotion of Perennial Ryegrass under Cadmium Stress

Cadmium (Cd) is a highly toxic and cumulative environmental pollutant. Siderophores are heavy metal chelators with high affinity to heavy metals, such as Cd. Ryegrass (Lolium perenne L.) has a potential remediation capacity for soils contaminated by heavy metals. Consequently, using ryegrass alongside beneficial soil microorganisms that produce siderophores may be an effective means to remediate soils contaminated with Cd. In this study, the Bacillus strains WL1210 and CD303, which were previously isolated from the rhizospheres of Nitraria tangutorum in Wulan and Peganum harmala L. in Dachaidan, Qinghai, China, respectively, both arid and sandy environments, were evaluated for heavy metal pollution mitigation. Our quantitative analyses have discerned that the two bacterial strains possess commendable attributes of phosphorus (P) solubilization and potassium (K) dissolution, coupled with the capacity to produce phytohormones. To assess the heavy metal stress resilience of these strains, they were subjected to a cadmium concentration gradient, revealing their incremental growth despite cadmium presence, indicative of a pronounced tolerance threshold. The subsequent phylogenetic analysis, bolstered by robust genomic data from conserved housekeeping genes, including 16S rDNA, gyr B gene sequencing, as well as dnaK and recA, delineated a species-level phylogenetic tree, thereby confirming the strains as Bacillus atrophaeus. Additionally, we identified the types of iron-carrier-producing strains as catechol (WL1210) and carboxylic acid ferrophilin (CD303). A genomic analysis uncovered functional genes in strain CD303 associated with plant growth and iron carrier biosynthesis, such as fnr and iscA. Ryegrass seed germination assays, alongside morphological and physiological evaluations under diverse heavy metal stress, underscored the strains' potential to enhance ryegrass growth under high cadmium stress when treated with bacterial suspensions. This insight probes the strains' utility in leveraging alpine microbial resources and promoting ryegrass proliferation.

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.

Foliar application protected vegetable against poisonous element cadmium and mitigated human health risks

Foliar application has been reported as an effective method to facilitate plant growth and mitigate cadmium (Cd) accumulation. However, the application of foliar fertilizers on plant production, Cd uptake and health risks of Solanaceae family remains unknown. In this study, four foliar fertilizers were applied to investigate their effects on the production, Cd accumulation and human health risk assessment of two varieties of pepper (Capsicum annuum L.) and eggplant (Solanum melongena L.), respectively. Compared with CK, the foliar application increased vegetable production to 104.16 %-123.70 % in peppers, and 100.83 %-105.17 % in eggplants, accordingly. The application of foliar fertilizers largely decreased Cd TF (transportation factor) by up to 23.32 % in JY, 18.37 % in GJ of pepper varieties, and up to 14.47 % in ZL, 15.24 % in HGR of eggplant varieties. Moreover, Cd BAF (bioaccumulation factor) also declined to different extents after the application of foliar fertilizers. As for human health risk assessments, foliar application diminished the hazard index (HI) and carcinogenic risk (CR) of both pepper and eggplant varieties. The results concluded that the application of composed foliar fertilizers was most effective, and could be a promising alternative for the improvement of vegetable production and mitigation of vegetable Cd accumulation and human health risks as well. The results further highlighted the understanding of foliar fertilizer application on vegetable production and health risks, which benefited better vegetable safe production and further guaranteed human health.

Effect of Auxin on Cadmium Toxicity-Induced Growth Inhibition in Solanum lycopersicum

Auxins play crucial regulatory roles in plants coping with cadmium (Cd) stress. However, the regulatory mechanism by which auxins alleviate Cd toxicity in tomato seedlings remains unclear. Here, we demonstrate that exposure to Cd stress leads to dynamic changes in the auxin response in tomato roots, characterized by an initial increase followed by a subsequent weakening. Under Cd stress, tomato seedlings show primary root- and hypocotyl-growth inhibition, accompanied by the accumulation of Cd and reactive oxygen species (ROS) in the roots. The exogenous application of 1-naphthylacetic acid (NAA) does not mitigate the inhibitory effect of Cd toxicity on primary root growth, but it does significantly enhance lateral root development under Cd stress. Auxin transport inhibitors, such as 1-N-naphthylphthalamic acid (NPA) and 2,3,5-triiodobenoic acid (TIBA), aggravate the growth inhibition of primary roots caused by Cd stress. Additionally, lateral root development was inhibited by NPA. However, applying auxin synthesis inhibitors L-kynurenine (kyn) and yucasin alleviated the tomato root growth inhibition caused by Cd stress; between them, the effect of yucasin was more pronounced. Yucasin mitigates Cd toxicity in tomato seedlings by reducing Cd2+ absorption and auxin accumulation, strengthening ROS scavenging, and reducing cell death in roots. These observations suggest that yucasin potentially mitigates Cd toxicity and improves the tolerance of tomato seedlings to Cd stress.

Environmental cadmium inhibits testicular testosterone synthesis via Parkin-dependent MFN1 degradation

Low testosterone (T) levels are associated with many common diseases, such as obesity, male infertility, depression, and cardiovascular disease. It is well known that environmental cadmium (Cd) exposure can induce T decline, but the exact mechanism remains unclear. We established a murine model in which Cd exposure induced testicular T decline. Based on the model, we found Cd caused mitochondrial fusion disorder and Parkin mitochondrial translocation in mouse testes. MFN1 overexpression confirmed that MFN1-dependent mitochondrial fusion disorder mediated the Cd-induced T synthesis suppression in Leydig cells. Further data confirmed Cd induced the decrease of MFN1 protein by increasing ubiquitin degradation. Testicular specific Parkin knockdown confirmed Cd induced the ubiquitin-dependent degradation of MFN1 protein through promoting Parkin mitochondrial translocation in mouse testes. Expectedly, testicular specific Parkin knockdown also mitigated testicular T decline. Mito-TEMPO, a targeted inhibitor for mitochondrial reactive oxygen species (mtROS), alleviated Cd-caused Parkin mitochondrial translocation and mitochondrial fusion disorder. As above, Parkin mitochondrial translocation induced mitochondrial fusion disorder and the following T synthesis repression in Cd-exposed Leydig cells. Collectively, our study elucidates a novel mechanism through which Cd induces T decline and provides a new treatment strategy for patients with androgen disorders.

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.

Foliar spraying of zinc oxide nanoparticles improves water transport and nitrogen metabolism in tomato (Solanum lycopersicum L.) seedlings mitigating the negative impacts of cadmium

The use of bio-nanotechnology in agriculture-such as the biological applications of metal oxide nanoparticles (NPs)-greatly improves crop yield and quality under different abiotic stress factors including soil metal contamination. Here, we explore the effectiveness of zinc oxide (ZnO)-NPs (0, 50 mg/L) foliar spraying to ameliorate the detrimental effects of cadmium (Cd) on the water transport and nitrogen metabolism in tomato (Solanum lycopersicum Mill. cv. Chibli F1) plants grown on a Cd-supplied (CdCl2; 0, 10, 40 μM) Hoagland nutrient solution. The results depicted that the individually studied factors (ZnO-NPs and Cd) had a significant impact on all the physiological parameters analyzed. Independently to the Cd concentration, ZnO-NPs-sprayed plants showed significantly higher dry weight (DW) in both leaves and roots compared to the non-sprayed ones, which was in consonance with higher and lower levels of Zn2+ and Cd2+ ions, respectively, in these organs. Interestingly, ZnO-NPs spraying improved water status in all Cd-treated plants as evidenced by the increase in root hydraulic conductance (L0), apoplastic water pathway percentage, and leaf and root relative water content (RWC), compared to the non-sprayed plants. This improved water balance was associated with a significant accumulation of osmoprotectant osmolytes, such as proline and soluble sugars in the plant organs, reducing electrolyte leakage (EL), and osmotic potential (ψπ). Also, ZnO-NPs spraying significantly improved NO3- and NH4+ assimilation in the leaf and root tissues of all Cd-treated plants, leading to a reduction in NH4+ toxicity. Our findings point out new insights into how ZnO-NPs affect water transport and nitrogen metabolism in Cd-stressed plants and support their use to improve crop resilience against Cd-contaminated soils.

Exploring the synergistic effects of indole acetic acid (IAA) and compost in the phytostabilization of nickel (Ni) in cauliflower rhizosphere

Heavy metals (HMs) contamination, owing to their potential links to various chronic diseases, poses a global threat to agriculture, environment, and human health. Nickel (Ni) is an essential element however, at higher concentration, it is highly phytotoxic, and affects major plant functions. Beneficial roles of plant growth regulators (PGRs) and organic amendments in mitigating the adverse impacts of HM on plant growth has gained the attention of scientific community worldwide. Here, we performed a greenhouse study to investigate the effect of indole-3-acetic acid (IAA @ 10- 5 M) and compost (1% w/w) individually and in combination in sustaining cauliflower growth and yield under Ni stress. In our results, combined application proved significantly better than individual applications in alleviating the adverse effects of Ni on cauliflower as it increased various plant attributes such as plant height (49%), root length (76%), curd height and diameter (68 and 134%), leaf area (75%), transpiration rate (36%), stomatal conductance (104%), water use efficiency (143%), flavonoid and phenolic contents (212 and 133%), soluble sugars and protein contents (202 and 199%), SPAD value (78%), chlorophyll 'a and b' (219 and 208%), carotenoid (335%), and NPK uptake (191, 79 and 92%) as compared to the control. Co-application of IAA and compost reduced Ni-induced electrolyte leakage (64%) and improved the antioxidant activities, including APX (55%), CAT (30%), SOD (43%), POD (55%), while reducing MDA and H2O2 contents (77 and 52%) compared to the control. The combined application also reduced Ni uptake in roots, shoots, and curd by 51, 78 and 72% respectively along with an increased relative production index (78%) as compared to the control. Hence, synergistic application of IAA and compost can mitigate Ni induced adverse impacts on cauliflower growth by immobilizing it in the soil.

Alleviation potential of green-synthesized selenium nanoparticles for cadmium stress in Solanum lycopersicum L: modulation of secondary metabolites and physiochemical attributes

KEY MESSAGE

Selenium nanoparticles reduce cadmium absorption in tomato roots, mitigating heavy metal effects. SeNPs can efficiently help to enhance growth, yield, and biomolecule markers in cadmium-stressed tomato plants. In the present study, the effects of selenium nanoparticles (SeNPs) were investigated on the tomato plants grown in cadmium-contaminated soil. Nanoparticles were synthesized using water extract of Nigella sativa and were characterized for their size and shape. Two application methods (foliar spray and soil drench) with nanoparticle concentrations of 0, 100, and 300 mg/L were used to observe their effects on cadmium-stressed plants. Growth, yield, biochemical, and stress parameters were studied. Results showed that SeNPs positively affected plant growth, mitigating the negative effects of cadmium stress. Shoot length (SL), root length (RL), number of branches (NB), number of leaves per plant (NL), and leaf area (LA) were significantly reduced by cadmium stress but enhanced by 45, 51, 506, 208, and 82%, respectively, by soil drench treatment of SeNPs. Similarly, SeNPs increased the fruit yield (> 100%) and fruit weight (> 100%), and decreased the days to fruit initiation in tomato plants. Pigments were also positively affected by the SeNPs, particularly in foliar treatment. Lycopene content was also enhanced by the addition of NPs (75%). Furthermore, the addition of SeNPs improved the ascorbic acid, protein, phenolic, flavonoid, and proline contents of the tomato plants under cadmium stress, whereas stress enzymes also showed enhanced activities under cadmium stress. It is concluded from the present study that the addition of selenium nanoparticles enhanced the growth and yield of Cd-stressed plants by reducing the absorption of cadmium and increasing the stress management of plants.

Synthesis and properties of nano-cadmium oxide and its size-dependent responses by barley plant

Present study included technological methods that made it possible to synthesize CdO nanoparticles and carry out their qualitative and quantitative diagnostics, confirming the as-prepared CdO nanoparticles (NPs) were spherical and had a size of 25 nm. Then, under the conditions of the model experiment the effect of CdO in macro and nanosized particles on absorption, transformation, and structural and functional changes occurring in cells and tissues of Hordeum vulgare L. (spring barley) during its ontogenesis was analyzed. Different analytical techniques were used to detect the transformation of CdO forms: Fourier-transform infrared spectroscopy (FTIR), Dynamic light scattering (DLS), X-ray fluorescence analysis (XRF), Scanning electron microscopy (SEM-EDXMA and TEM), X-ray diffraction (XRD), and X-ray absorption fine structure, consists of XANES - X-ray absorption near edge structure, and EXAFS - Extended X-ray absorption fine structure. Quantitative differences in the elemental chemical composition of barley root and leaf samples were observed. The predominant root uptake of Cd was revealed. CdO-NPs were found to penetrate deeply into barley plant tissues, where they accumulated and formed new mineral phases such as Cd5(PO4)3Cl and CdSO4 according to XRD analysis. The molecular-structural state of the local Cd environment in plant samples corresponding to Cd-O and Cd-Cd. The toxicity of CdO-NPs was found to significantly affect the morphology of intracellular structures are the main organelles of photosynthesis therefore, destructive changes in them obviously reduce the level of metabolic processes ensuring the growth of plants. This study is an attempt to show results how it is possible to combine some instrumental techniques to characterize and behavior of NPs in complex matrices of living organisms.

Factors influencing cadmium accumulation in plants after inoculation with rhizobacteria: A meta-analysis

Rhizobacteria have the potential to enhance phytoremediation by generating substances that stimulate plant development and influence the effectiveness of cadmium (Cd) remediation by adjusting Cd availability via metal solubilization. Furthermore, rhizobacterial inoculation affects plants' metal tolerance and uptake by controlling the expression of several metal transporters, channels, and metal chelator genes. A meta-analysis was conducted to quantitatively assess the effects of rhizobacteria on Cd accumulation in plants using 207 individual observations from 47 articles. This meta-analysis showed an average Cd concentration increase of 8.09 % in plant cells under rhizobacteria treatment. The effects of different plant-microbial interactions on the bioaccumulation of Cd in plants varied. Selecting the proper rhizobacteria-plant association is essential to affect Cd buildup in plant roots and shoots. A more extended planting period (>30 days) and a suitable soil pH (<6, 7-8) would aid in the phytoextraction of Cd from the soil. This study comprehensively and quantitatively investigated the effects of plants, rhizobacteria, soil pH, planting period, experimental sites, and plant organs on plant Cd accumulation. According to the analysis of explanatory factors, plant species, planting period, soil pH, and rhizobacteria species have a more decisive influence on Cd accumulation than other factors. The results provide information for future research on the successful remediation of soils contaminated with Cd. More investigations are required to elucidate the intricate interactions between plant roots and microorganisms.

Exploring the synergistic effect of chromium (Cr) tolerant Pseudomonas aeruginosa and nano zero valent iron (nZVI) for suppressing Cr uptake in Aloe Vera

Chromium (Cr) contamination of soil has substantially deteriorated soil health and has interfered with sustainable agricultural production worldwide and therefore, its remediation is inevitable. Inoculation of plant growth promoting rhizobacteria (PGPR) in association with nanotechnology has exerted broad based impacts in agriculture, and there is an urgent need to exploit their synergism in contaminated soils. Here, we investigated the effect of co-application of Cr-tolerant "Pseudomonas aeruginosa CKQ9" strain and nano zerovalent iron (nZVI) in improving the phytoremediation potential of aloe vera (Aloe barbadensis L.) under Cr contamination. Soil was contaminated by using potassium dichromate (K2Cr2O7) salt and 15 mg kg-1 contamination level in soil was maintained via spiking and exposure to Cr lasted throughout the duration of the experiment (120 days). We observed that the co-application alleviated the adverse impacts of Cr on aloe vera, and improved various plant attributes such as plant height, root area, number of leaves and gel contents by 51, 137, 67 and 49% respectively as compared to control treatment under Cr contamination. Similarly, significant boost in the activities of various antioxidants including catalase (124%), superoxide dismutase (87%), ascorbate peroxidase (36%), peroxidase (89%) and proline (34%) was pragmatic under contaminated soil conditions. In terms of soil Cr concentration and its plant uptake, co-application of P. aeruginosa and nZVI also reduced available Cr concentration in soil (50%), roots (77%) and leaves (84%), while simultaneously increasing the relative production index by 225% than un-inoculated control. Hence, integrating PGPR with nZVI can be an effective strategy for enhancing the phytoremediation potential of aloe vera.

Mechanisms of low cadmium accumulation in crops: A comprehensive overview from rhizosphere soil to edible parts

Cadmium (Cd) is a toxic heavy metal often found in soil and agricultural products. Due to its high mobility, Cd poses a significant health risk when absorbed by crops, a crucial component of the human diet. This absorption primarily occurs through roots and leaves, leading to Cd accumulation in edible parts of the plant. Our research aimed to understand the mechanisms behind the reduced Cd accumulation in certain crop cultivars through an extensive review of the literature. Crops employ various strategies to limit Cd influx from the soil, including rhizosphere microbial fixation and altering root cell metabolism. Additional mechanisms include membrane efflux, specific transport, chelation, and detoxification, facilitated by metalloproteins such as the natural resistance-associated macrophage protein (Nramp) family, heavy metal P-type ATPases (HMA), zinc-iron permease (ZIP), and ATP-binding cassette (ABC) transporters. This paper synthesizes differences in Cd accumulation among plant varieties, presents methods for identifying cultivars with low Cd accumulation, and explores the unique molecular biology of Cd accumulation. Overall, this review provides a comprehensive resource for managing agricultural lands with lower contamination levels and supports the development of crops engineered to accumulate minimal amounts of Cd.

Impacts of simulated atmospheric cadmium deposition on the physiological response and cadmium accumulation of Sedum plumbizincicola

Atmospheric cadmium (Cd) deposition contributes to the accumulation of Cd in the soil-plant system. Sedum plumbizincicola is a Cd and Zn hyperaccumulator commonly used for the phytoremediation of Cd-contaminated soil. However, studies on the effects of atmospheric Cd deposition on the accumulation of Cd and physiological response in S. plumbizincicola are still limited. A Cd solution spraying pot experiment was conducted with S. plumbizincicola at three atmospheric Cd deposition concentrations (4, 8, and 12 mg/L). Each Cd concentration levels was divided into two groups, non-mulching (foliar-root uptake) and mulching (foliar uptake). The soil type used in the experiment was reddish clayey soil collected from a farmland. The results showed that compared with the non-mulching control, the fresh weight of S. plumbizincicola in non-mulching with high atmospheric Cd deposition (12 mg/L) increased by 11.35%. Compared with those in the control group, the malondialdehyde (MDA) content in the non-mulching and mulching S. plumbizincicola groups increased by 0.88-11.06 nmol/L and 0.96-1.32 nmol/L, respectively. Compared with those in the non-Cd-treated control group, the shoot Cd content in the mulching group significantly increased by 11.09-180.51 mg/kg. Under high Cd depositions, the Cd in S. plumbizincicola mainly originated from the air and was stored in the shoots (39.7-158.5%). These findings highlight that the physiological response and Cd accumulation of S. plumbizincicola were mainly affected by high Cd deposition and suggest that atmospheric Cd could directly be absorbed by S. plumbizincicola. The effect of atmospheric deposition on S. plumbizincicola cannot be ignored.

Exogenous application of sulfur-rich thiourea (STU) to alleviate the adverse effects of cobalt stress in wheat

Heavy metal stress affects crop growth and yields as wheat (Triticum aestivum L.) growth and development are negatively affected under heavy metal stress. The study examined the effect of cobalt chloride (CoCl2) stress on wheat growth and development. To alleviate this problem, a pot experiment was done to analyze the role of sulfur-rich thiourea (STU) in accelerating the defense system of wheat plants against cobalt toxicity. The experimental treatments were, i) Heavy metal stress (a) control and (b) Cobalt stress (300 µM), ii) STU foliar applications; (a) control and (b) 500 µM single dose was applied after seven days of stress, and iii) Wheat varieties (a) FSD-2008 and (b) Zincol-2016. The results revealed that cobalt stress decreased chlorophyll a by 10%, chlorophyll b by 16%, and carotenoids by 5% while foliar application of STU increased these photosynthetic pigments by 16%, 15%, and 15% respectively under stress conditions as in contrast to control. In addition, cobalt stress enhances hydrogen peroxide production by 11% and malondialdehyde (MDA) by 10%. In comparison, STU applications at 500 µM reduced the production of these reactive oxygen species by 5% and by 20% by up-regulating the activities of antioxidants. Results have revealed that the activities of SOD improved by 29%, POD by 25%, and CAT by 28% under Cobalt stress. Furthermore, the foliar application of STU significantly increased the accumulation of osmoprotectants as TSS was increased by 23% and proline was increased by 24% under cobalt stress. Among wheat varieties, FSD-2008 showed better adaptation under Cobalt stress by showing enhanced photosynthetic pigments and antioxidant activities compared to Zincol-2016. In conclusion, the foliar-applied STU can alleviate the negative impacts of Cobalt stress by improving plant physiological attributes and upregulating the antioxidant defense system in wheat.

Biological roles of soil microbial consortium on promoting safe crop production in heavy metal(loid) contaminated soil: A systematic review

Heavy metal(loid) (HM) pollution of agricultural soils is a growing global environmental concern that affects planetary health. Numerous studies have shown that soil microbial consortia can inhibit the accumulation of HMs in crops. However, our current understanding of the effects and mechanisms of inhibition is fragmented. In this review, we summarise extant studies and knowledge to provide a comprehensive view of HM toxicity on crop growth and development at the biological, cellular and the molecular levels. In a meta-analysis, we find that microbial consortia can improve crop resistance and reduce HM uptake, which in turn promotes healthy crop growth, demonstrating that microbial consortia are more effective than single microorganisms. We then review three main mechanisms by which microbial consortia reduce the toxicity of HMs to crops and inhibit HMs accumulation in crops: 1) reducing the bioavailability of HMs in soil (e.g. biosorption, bioaccumulation and biotransformation); 2) improving crop resistance to HMs (e.g. facilitating the absorption of nutrients); and 3) synergistic effects between microorganisms. Finally, we discuss the prospects of microbial consortium applications in simultaneous crop safety production and soil remediation, indicating that they play a key role in sustainable agricultural development, and conclude by identifying research challenges and future directions for the microbial consortium to promote safe crop production.