Unravelling cadmium toxicity and tolerance in plants: Insight into regulatory mechanisms

Effect of pH on growth and Cd accumulation in different rice varieties under hydroponics

Currently, applying lime to cadmium (Cd)-contaminated paddy fields to increase pH and reduce Cd availability is an effective method to control excessive Cd levels in rice grain. However, under hydroponic conditions, the impact of increased pH on Cd accumulation in different rice varieties remains unclear. This study employed three rice varieties (Yuzhenxiang, Shaoxiang 100, Xiangwanxian 12) with different Cd accumulation characteristics under different pH and long-term treatment with 1 μM CdCl2, to study the effect of pH on growth and Cd accumulation in different rice varieties. The result showed that as pH shifted from 5 to 8, the SPAD values, shoot dry weight, and plant height of the three rice varieties significantly decreased. The main root length, root volume, and root dry weight of Yuzhenxiang, and Shaoxiang100 significantly decreased. Conversely, the root architecture indicators of Xiangwanxian 12 did not change significantly. As for element accumulation, increasing the pH significantly increased the content of Mn in both the shoots and roots of all three varieties. Yuzhenxiang significantly reduced Cd content in both the shoots and roots of rice, while Shaoxiang100 significantly increased Cd content in both parts. Xiangwanxian 12 showed a significant increase in Cd content in the shoots but a decrease in the roots. In terms of subcellular distribution, Yuzhenxiang significantly reduced Cd concentrations in the cell wall and organelles of root cells, resulting in lower Cd concentrations in the root tissue. Conversely, Shaoxiang100 significantly increased Cd concentrations in the cell wall, organelles, and soluble fractions of root cells, leading to higher Cd concentrations in the root tissue. Xiangwanxian 12 also exhibited a decrease in Cd concentrations in the cell wall, organelles, and soluble fraction of root cells, resulting in lower Cd concentrations in the root tissue. Additionally, the expression of the OsNRAMP5 and OsHMA3 gene was significantly increased in Shaoxiang 100, while no significantly change in Yuzhenxiang and Xiangwanxian 12. These results provide important guidance on the impact of pH on Cd accumulation during the vegetative growth stage of different rice varieties.

Rare earth elements sequestration in phytoliths: Partitioning patterns and influencing mechanism

Rare earth elements (REEs) are integral to numerous high-tech industries, yet their biogeochemical cycling within ecosystems remains inadequately characterized. Recently, phytoliths have been identified as potentially significant sinks for REEs; however, their role in the cycling of these elements has been underestimated. In this work, we investigate the accumulation of REEs in phytoliths (PhytREEs) within the Greater Khingan Mountains region, employing an optimized wet oxidation method combined with heavy liquid flotation to quantify PhytREEs contents in surface soils. The results revealed an elevation-dependent pattern of PhytREEs concentration, with heightened levels at higher altitudes and diminishing concentrations towards the eastern plains. The enrichment coefficient of PhytREEs (ECPhytREEs) was found to be approximately 2.7 %, indicative of a moderately selective sequestration process. The multivariate analysis indicated that terrain complexity, climatic patterns, soil texture, and organic matter significantly influence the uptake and storage of REEs in plants, subsequently affecting their partitioning in phytoliths. Among these factors, the complexation of REEs with organic matter emerged as a pivotal mechanism facilitating their immobilization within phytoliths. Soil characteristics also play a non-negligible role in modulating REEs dynamics. Our findings highlight the predominant influence of climate on PhytREE storage, suggesting that climatic variables are the primary drivers modulating the bioavailability and ultimate sequestration of REEs within phytoliths. This study enhances our understanding of the biotic-abiotic interplay in the sequestration of REEs and underscores the need to incorporate phytoliths into models of terrestrial REE cycling.

OsPLDα1 mediates cadmium stress response in rice by regulating reactive oxygen species accumulation and lipid remodeling

Lipid remodeling is crucial for various cellular activities and the stress tolerance of plants; however, little is known about the lipid dynamics induced by the heavy metal cadmium (Cd). In this study, we investigated the phospholipid profiles in rice (Oryza sativa) under Cd exposure. We observed a significant decline in the total amounts of phosphatidylcholine and phosphatidylserine, contrasted with an elevation in phosphatidic acid (PA) due to Cd stress. Additionally, Cd stress prompted the activation of phospholipase D (PLD) and induced the expression of PLDα1. OsPLDα1 knockout mutants (Ospldα1) showed increased sensitivity to Cd, characterized by a heightened accumulation of hydrogen peroxide in roots and diminished PA production following Cd treatment. Conversely, PLDα1-overexpressing (OsPLDα1-OE) lines demonstrated enhanced tolerance to Cd, with suppressed transcription of the respiratory burst oxidase homolog (Rboh) genes. The transcription levels of genes associated with Cd uptake and transport were accordingly modulated in Ospldα1 and OsPLDα1-OE plants relative to the wild-type. Taken together, our findings underscore the pivotal role of OsPLDα1 in conferring tolerance to Cd by modulating reactive oxygen species homeostasis and lipid remodeling in rice.

The role of gasotransmitter hydrogen sulfide in plant cadmium stress responses

Cadmium (Cd) is a toxic heavy metal that poses a significant risk to both plant growth and human health. To mitigate or lessen Cd toxicity, plants have evolved a wide range of sensing and defense strategies. The gasotransmitter hydrogen sulfide (H2S) is involved in plant responses to Cd stress and exhibits a crucial role in modulating Cd tolerance through a well-orchestrated interaction with several signaling pathways. Here, we review potential experimental approaches to manipulate H2S signals, concluding that research on another gasotransmitter, namely nitric oxide (NO), serves as a good model for research on H2S. Additionally, we discuss potential strategies to leverage H2S-reguated Cd tolerance to improve plant performance under Cd stress.

Multivariate characterization of salicylic acid and potassium induced physio-biochemical and phytoremediation responses in quinoa exposed to lead and cadmium contamination

The levels of soils pollutants such as lead (Pb) and cadmium (Cd) have significantly increased recently resulting in ecological disturbances and threatening crop production. Various amendments have been employed to enhance the tolerance of crops to withstand Cd and Pb stresses. However, the role of combined application of potassium (K) and of salicylic acid (SA) for Cd and Pb stress mitigation and phytoremediation by quinoa (Chenopodium quinoa Willd) has not been comprehended well. In the present study, the effect of 10 mM K and 0.1 mM SA was tested on the quinoa plants subjected to 250 μM Pb and/or 100 μM Cd. The Pb and Cd treatments were applied separately or together. Phytotoxicity induced by Pb and Cd resulted in drastic decrease (>60%) in chlorophyll contents, stomatal conductance, and plant biomass. The collective treatment of Pb and Cd induced an increase in the concentration of hydrogen peroxide (13-fold) and lipid peroxidation (16-fold) that resulted in a 61% reduction in membrane stability. The application of 10 mM K and/or 0.1 mM SA was remarkable in mitigating the adverse effect of Pb and Cd. The reduction in plant biomass was 17% when 10 mM K and 0.1 mM SA were applied together under the combined treatment of both the metals. The simultaneous application of K and SA effectively mitigated oxidative stress by enhancing the activities of superoxide dismutase, peroxidase, ascorbate peroxidase, and catalase by 12, 10, 7 and 10-folds respectively. The positive effect of K and SA on these attributes resulted in a remarkable reduction in metal accumulation and translocation and lipid peroxidation. The stressed plants supplemented with K and SA exhibited a significant improvement in the membrane stability index, chlorophyll content, and stomatal conductance. This study concluded that the combined application of K and SA could be a good approach for reducing Pb and Cd phytotoxicity in quinoa and enhancing their phytostabilization potential in the contaminated soils.

ABA-regulated MAPK signaling pathway promotes hormesis in sugar beet under cadmium exposure

Sugar beet (Beta vulgaris L.) shows potential as an energy crop for cadmium (Cd) phytoremediation. To elucidate its in vivo response strategy to Cd exposure, seedlings were treated with 1, 3, and 5 mmol/L CdCl2 (Cd-1, Cd-3, and Cd-5) for 6 h, using 0 mmol/L CdCl2 (Cd-0) as the control. The results showed that Cd-3 promoted a unique "hormesis" effect, leading to superior growth performance, increased levels of chlorophyll, soluble protein, and SOD activity, and reduced MDA content in sugar beet, compared to Cd-1, Cd-5, and even Cd-0. GO and KEGG enrichments and PPI networks of transcriptomic analysis revealed that the differentially expressed genes (DEGs) were primarily involved in lipid metabolism, cellular protein catabolism, and photosynthesis. Notably, the MAPK signaling pathway was significantly enriched only under Cd-3, with the up-regulation of ABA-related core gene BvPYL9 and an increase in ABA content after 6 h of Cd exposure. Furthermore, overexpression of BvPYL9 in Arabidopsis thaliana (OE-1 and OE-2) resulted in enhanced growth (fresh weight, dry weight, and root length), as well as higher ABA and soluble protein contents under different Cd treatments. Cd-induced transcriptional responses of BvPYL9 were also evident in OE-1 and OE-2, especially at 10 µmol/L, indicated by qRT-PCR. These findings suggest that ABA-mediated MAPK signaling pathway is activated in response to Cd toxicity, with BvPYL9 being a key factor in the cascade effects for the Cd-induced hormesis in sugar beet.

The effect of cadmium on soil and plants, and the influence of Serendipita indica (Piriformospora indica) in mitigating cadmium stress

Due to environmental pollution, the risk of cadmium stress for crops is soaring, so researchers are exploring inexpensive solutions to enhance cultivated crops in contaminated soil. Using microorganisms to reduce cadmium risk has been one of the most effective strategies in recent decades. Serendipita indica (Piriformospora indica) is one of the best endophyte fungi that, in addition to reducing heavy metal stress for crops, can significantly reduce the threat of other abiotic stresses. As part of this research, cadmium in soil has been investigated, as well as its effects on plants' morphophysiological and biochemical characteristics. The present review has also attempted to identify the role of Serendipita indica in improving the growth and performance of crops, as well as its possible effect on reducing the risk of cadmium. The results showed that Serendipita indica enhance the growth and productivity of plants in contaminated environments by improving soil quality, reducing cadmium absorption, improving the activity of antioxidant enzymes and secondary metabolites, raising water and mineral absorption, and altering morphophysiological structures.

Cadmium uptake and detoxification in tomato plants: Revealing promising targets for genetic improvement

Cadmium (Cd) is a hazardous heavy metal known for its detrimental effects on plants, human health, and the environment. This review article delves into the dynamics of Cd uptake, long-distance transport, and its impact on plant performance, with a specific focus on tomato plants. The process of Cd uptake by roots and its subsequent long-distance transport in the xylem and phloem are explored to understand how Cd influences plants operation. The toxic effects of Cd on tomato plants are discussed, highlighting on the challenges it poses to plant growth and development. Furthermore, the review investigates various Cd tolerance mechanisms in plants, including avoidance or exclusion by the root cell wall, root-to-shoot translocation, detoxification pathways, and antioxidative defence systems against Cd-induced stress. In addition, the transcriptomic analyses of tomato plants under Cd stress provide insights into the molecular responses and adaptations of plants to Cd toxicity. Overall, this comprehensive review enhances our understanding of Cd-plant interactions and reveal promising genes for tomato genetic improvement to increase its tolerance to cadmium.

Protective Role of Polyethylene Glycol Towards the Damaging Effects of Cadmium

This study aimed to evaluate the role of drought-induced changes in the effects of cadmium (Cd) in plants. Cd is the most hazardous and important environmental pollutant. Water deficit is the most common environmental stress encountered by plants and affects most of the plant functions. The present study assessed the effect of Cd and water deficit on Capsicum frutescens seedlings in single and combined treatments. The seedlings of Capsicum were grown in a hydroponic solution and treated with Cd. The seedlings were subjected to water deficit with the help of polyethylene glycol (PEG). The other set of seedlings was treated with combined Cd + PEG. In the absence of PEG, maximum Cd accumulation was observed. The root and shoot growth of the seedlings were affected under all treatments with maximum inhibition in Cd. Pigment, protein and sugar contents and nitrate reductase activity decreased significantly in all treatments, while proline content increased. Induction of oxidative damage occurred through the formation of free radicals which caused alteration in electrolyte leakage, lipid peroxidation and activities of antioxidant enzymes, viz. superoxide dismutase, catalase, ascorbate peroxidase, guaiacol peroxidase and non-enzymatic non-protein thiol content and ascorbic acid in the stressed seedlings. Water deficit buttressed the toxic effect of Cd on chilli seedlings.

Integrated proteomics, transcriptomics, and metabolomics offer novel insights into Cd resistance and accumulation in Poa pratensis

Kentucky bluegrass (Poa pratensis L., KB) demonstrates superior performance in both cadmium (Cd) accumulation and tolerance; however, the regulatory mechanisms and detoxification pathways in this species remain unclear. Therefore, phenotype, root ultrastructure, cell wall components, proteomics, transcriptomics, and metabolomics were analyzed under the hydroponic system to investigate the Cd tolerance and accumulation mechanisms in the Cd-tolerant KB variety 'Midnight (M)' and the Cd-sensitive variety 'Rugby II (R)' under Cd stress. The M variety exhibited higher levels of hydroxyl and carboxyl groups as revealed by Fourier transform infrared spectroscopy spectral analysis. Additionally, a reduced abundance of polysaccharide degradation proteins was observed in the M variety. The higher abundance of glutathione S-transferase and content of L-cysteine-glutathione disulfide and oxidized glutathione in the M variety may contribute to better performance of the M variety under Cd stress. Additionally, the R variety had an enhanced content of carboxylic acids and derivatives, increasing the Cd translocation capacity. Collectively, the down-regulation of cell wall polysaccharide degradation genes coupled with the up-regulation of glutathione metabolism genes enhances the tolerance to Cd stress in KB. Additionally, lignification of the endodermis and the increase in carboxylic acids and derivatives play crucial roles in the redistribution of Cd in KB.

Efficient regulation of cadmium accumulation by carboxymethylammonium chloride in rice: Correlation analysis and expression of transporter gene OsGLR3

The mechanism of carboxymethylammonium chloride (CC) regulating cadmium (Cd) accumulation in rice was studied in field and hydroponic experiments. Field experiments showed that 0.2-1.2 mmol L-1 CC spraying effectively reduced Cd accumulation by 44 %-77 % in early rice grains and 39 %-78 % in late rice grains, significantly increased calcium (Ca) content and amino acids content in grains, as well as alleviated Cd-induced oxidative damage in leaves. Hydroponic experiments further verified the inhibition effect of CC on Cd accumulation. 1.2 mmol L-1 CC made the highest decrease of Cd content in shoots and roots of hydroponic seedlings by 45 % and 53 %, respectively. Exogenous CC significantly increased glutamate (Glu), glycine (Gly) and glutathione (GSH) content, and improved the activities of catalase (CAT) and superoxide dismutase (SOD) by 41-131 % and 11-121 % in shoots of hydroponic seedlings, respectively. Exogenous CC also increased the relative expression of OsGLR3.1-3.5 in the shoots and roots of hydroponic seedlings. The quantum computational chemistry was used to clarify that the Gly radical provided by CC could form various complexes with Cd through carboxyl oxygen atoms. These results showed that exogenous application of CC improved the tolerance to Cd by enhancing the antioxidant capacity; inhibited the absorption, transport and accumulation of Cd in rice by (1) promoting chelation, (2) increasing the GLRs activity through upregulating the content of Glu, Gly, as well as the expression of OsGLR3.1-3.5.

BrMYB116 transcription factor enhances Cd stress tolerance by activating FIT3 in yeast and Chinese cabbage

Cd (cadmium) is a highly toxic heavy metal pollutant often present in soil and detrimentally impacting the production and quality of horticultural crops. Cd affects various physiological and biochemical processes in plants, including chlorophyll synthesis, photosynthesis, mineral uptake and accumulation, and hormonal imbalance, leading to cell death. The MYB family of transcription factors plays a significant role in plant response to environmental influences. However, the role of MYB116 in abiotic stress tolerance remains unclear. In this study, we reported that Chinese cabbage transcription factor BrMYB116 enhanced Cd stress tolerance in yeast. The expression level of BrMYB116 was increased by Cd stress in Chinese cabbage. Additionally, yeast cells overexpressing BrMYB116 showed improved Cd stress tolerance and reduced Cd accumulation. Moreover, we found that BrMYB116 interacted with facilitator of iron transport (FIT3) to enhance Cd stress tolerance. ChIP-qPCR results showed that ScFIT3 was activated through specific binding to its promoter. Additionally, the overexpression of ScFIT3 induced Cd stress tolerance and reduced Cd accumulation in yeast and Chinese cabbage. These results suggest new avenues for plant genomic modification to mitigate Cd toxicity and enhance the safety of vegetable production.

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.

A novel aldo-keto reductase gene, OsAKR1, from rice confers higher tolerance to cadmium stress in rice by an in vivo reactive aldehyde detoxification

Elevated levels of cadmium (Cd) have the ability to impede plant development. Aldo-keto reductases (AKRs) have been demonstrated in a number of plant species to improve tolerance to a variety of abiotic stresses by scavenging cytotoxic aldehydes; however, only a few AKRs have been identified to improve Cd tolerance. The OsAKR1 gene was extracted and identified from rice here. After being exposed to Cd, the expression of OsAKR1 dramatically rose in both roots and shoots, although more pronounced in roots. According to a subcellular localization experiment, the nucleus and cytoplasm are where OsAKR1 is primarily found. Mutants lacking OsAKR1 exhibited Cd sensitive phenotype than that of the wild-type (WT) Nipponbare (Nip), and osakr1 mutants exhibited reduced capacity to scavenge methylglyoxal (MG). Furthermore, osakr1 mutants exhibited considerably greater hydrogen peroxide (H2O2) and malondialdehyde (MDA) levels, and increased catalase (CAT) activity in comparison to Nip. The expression of three isomeric forms of CAT was found to be considerably elevated in osakr1 mutants during Cd stress, as demonstrated by quantitative real-time PCR analysis, when compared to Nip. These results imply that OsAKR1 controlled rice's ability to withstand Cd by scavenging harmful aldehydes and turning on the reactive oxygen species (ROS) scavenging mechanism.

Combined Effect of Biological and Organic Fertilizers on Agrobiochemical Traits of Corn (Zea mays L.) under Wastewater Irrigation

Corn (Zea mays L.) is an important annual grain that is cultivated as a food staple around the world. The current study examined the effect of wastewater and a combination of biological and organic fertilizers on the morphological and phytochemical traits of corn, using a factorial experiment based on a randomized complete block design with three replications. The first factor was biological and organic fertilizers at seven levels, including the control (no fertilization), bacterial biological fertilizers (NPK) along with iron and zinc Barvar biofertilizers, fungal biofertilizers made from Mycorrhiza and Trichoderma, biochar, a combination of bacterial and fungal biofertilizers, and a combination of bacterial and fungal biofertilizers with biochar. The second factor was irrigation at two levels (conventional irrigation and irrigation with wastewater). The traits studied included the morphological yield, phenols, flavonoids, polyphenols, glomalin, cadmium content in plant parts, and translocation factor (TF). The results disclosed that the best treatment in regard to the morphological traits was related to conventional water + biochar + mycorrhiza + Trichoderma + NPK. The highest phenol and flavonoid content were observed when biochar + mycorrhiza + Trichoderma + NPK treatments were used in both water treatments. Also, the wastewater + biochar + mycorrhiza + Trichoderma + NPK treatment demonstrated the highest total glomalin and phenylalanine ammonia-lyase (PAL) activity. The obtained results demonstrate that combined biological and organic fertilizer use on corn plants can effectively alleviate the deleterious effects of cadmium present in wastewater.

Adsorption of Cadmium and Lead Capacity and Environmental Stability of Magnesium-Modified High-Sulfur Hydrochar: Greenly Utilizing Chicken Feather

Chicken feathers represent a viable material for producing biochar adsorbents. Traditional slow pyrolysis methods often result in sulfur element losses from chicken feathers, whereas hydrothermal reactions generate substantial amounts of nutrient-rich hydrothermal liquor. Magnesium-modified high-sulfur hydrochar MWF was synthesized through magnesium modification, achieving a S content of 3.68%. The maximum equilibrium adsorption amounts of MWF for Cd2+ and Pb2+ were 25.12 mg·g-1 and 70.41 mg·g-1, respectively, representing 4.00 times and 2.75 times of WF. Magnesium modification elevated the sulfur content, pH, ash content, and electronegativity of MWF. The primary mechanisms behind MWF's adsorption of Cd2+ and Pb2+ involve magnesium ion exchange and complexation with C=O/O=C-O, quaternary N, and S functional groups. MWF maintains robust stability and antioxidative properties, even with low aromaticity levels. Given the lower energy consumption during hydrochar production, MWF offers notable carbon sequestration benefits. The hydrothermal solution derived from MWF is nutrient-rich. Following supplementation with inorganic fertilizer, the hydrothermal solution of MWF significantly enhanced bok choy growth compared to the control group. In general, adopting magnesium-modified hydrothermal reactions to produce hydrochar and converting the resultant hydrothermal solution into water-soluble fertilizer proves a viable strategy for the eco-friendly utilization of chicken feathers. This approach carries substantial value for heavy metal remediation and agricultural practices.

The impact of arbuscular mycorrhizal fungi and endophytic bacteria on peanuts under the combined pollution of cadmium and microplastics

It remains unclear how symbiotic microbes impact the growth of peanuts when they are exposed to the pollutants cadmium (Cd) and microplastics (MPs) simultaneously. This study aimed to investigate the effects of endophytic bacteria Bacillus velezens SC60 and arbuscular mycorrhizal fungus Rhizophagus irregularis on peanut growth and rhizosphere microbial communities in the presence of Cd at 40 (Cd40) or 80 (Cd80) mg kg-1 combined without MP or the presence of low-density polyethylene (LDPE) and poly butyleneadipate-co-terephthalate (PBAT). This study assessed soil indicators, plant parameters, and Cd accumulation indicators. Results showed that the application of R. irregularis and B. velezens significantly enhanced soil organic carbon and increased Cd content under the conditions of Cd80 and MPs co-pollution. R. irregularis and B. velezens treatment increased peanut absorption and the enrichment coefficient for Cd, with predominate concentrations localized in the peanut roots, especially under combined pollution by Cd and MPs. Under treatments with Cd40 and Cd80 combined with PBAT pollution, soil microbes Proteobacteria exhibited a higher relative abundance, while Actinobacteria showed a higher relative abundance under treatments with Cd40 and Cd80 combined with LDPE pollution. In conclusion, under the combined pollution conditions of MPs and Cd, the co-treatment of R. irregularis and B. velezens effectively immobilized Cd in peanut roots, impeding its translocation to the shoot.

The response of physiological and xylem anatomical traits under cadmium stress in Pinus thunbergii seedlings

Studying the response of physiological and xylem anatomical traits under cadmium stress is helpful to understand plants' response to heavy metal stress. Here, seedlings of Pinus thunbergii Parl. were treated with 50, 100 and 150 mg kg-1 Cd2+ for 28 days. Cadmium and nonstructural carbohydrate content of leaves, stems and roots, root Cd2+ flux, cadmium distribution pattern in stem xylem and phloem, stem xylem hydraulic traits, cell wall component fractions of stems and roots, phytohormonal content such as abscisic acid, gibberellic acid 3, molecule -indole-3-acetic acid, and jasmonic acid from both leaves and roots, as well as xylem anatomical traits from both stems and roots were measured. Root Cd2+ flux increased from 50 to 100 mmol L-1 Cd2+ stress, however it decreased at 150 mmol L-1 Cd2+. Cellulose and hemicellulose in leaves, stems and roots did not change significantly under cadmium stress, while pectin decreased significantly. The nonstructural carbohydrate content of both leaves and stems showed significant changes under cadmium stress while the root nonstructural carbohydrate content was not affected. In both leaves and roots, the abscisic acid content significantly increased under cadmium stress, while the gibberellic acid 3, indole-3-acetic acid and jasmonic acid methylester content significantly decreased. Both xylem specific hydraulic conductivity and xylem water potential decreased with cadmium stress, however tracheid diameter and double wall thickness of the stems and roots were not affected. High cadmium intensity was found in both the stem xylem and phloem in all cadmium stressed treatments. Our study highlighted the in situ observation of cadmium distribution in both the xylem and phloem, and demonstrated the instant response of physiological traits such as xylem water potential, xylem specific hydraulic conductivity, root Cd2+ flux, nonstructural carbohydrate content, as well as phytohormonal content under cadmium stress, and the less affected traits such as xylem anatomical traits, cellulose and hemicellulose.

Significance of phosphorus deficiency for the mitigation of mercury toxicity in the Robinia pseudoacacia L.- rhizobia symbiotic association

Nitrogen (N2)-fixing legumes can be used for phytoremediation of toxic heavy metal Mercury (Hg) contaminated soil, but N2-fixation highly relies on phosphorus (P) availability for nodule formation and functioning. Here, we characterized the significance of P deficiency for Hg accumulation and toxicity in woody legume plants. Consequences for foliar and root traits of rhizobia inoculation, Hg exposure (+Hg) and low P (-P) supply, individually and in combination were characterized at both the metabolite and transcriptome levels in seedlings of two Robinia pseudoacacia L. provenances originating from contrasting climate and soil backgrounds, i.e., GS in northwest and the DB in northeast China. Our results reveal that depleted P mitigates the toxicity of Hg at the transcriptional level. In leaves of Robinia depleted P reduced oxidative stress and improved the utilization strategy of C, N and P nutrition; in roots depleted P regulated the expression of genes scavenging oxidative stress and promoting cell membrane synthesis. Rhizobia inoculation significantly improved the performance of both Robinia provenances under individual and combined +Hg and -P by promoting photosynthesis, increasing foliar N and P content and reducing H2O2 and MDA accumulation despite enhanced Hg uptake. DB plants developed more nodules, had higher biomass and accumulated higher Hg amounts than GS plants and thus are suggested as the high potential Robinia provenance for future phytoremediation of Hg contaminated soils with P deficiency.

The Effects of Heavy Metal Pollution on Soil Nitrogen Transformation and Rice Volatile Organic Compounds under Different Water Management Practices

One of the most concerning global environmental issues is the pollution of agricultural soils by heavy metals (HMs), especially cadmium, which not only affects human health through Cd-containing foods but also impacts the quality of rice. The soil's nitrification and denitrification processes, coupled with the release of volatile organic compounds by plants, raise substantial concerns. In this review, we summarize the recent literature related to the deleterious effects of Cd on both soil processes related to the N cycle and rice quality, particularly aroma, in different water management practices. Under both continuous flooding (CF) and alternate wetting and drying (AWD) conditions, cadmium has been observed to reduce both the nitrification and denitrification processes. The adverse effects are more pronounced in alternate wetting and drying (AWD) as compared to continuous flooding (CF). Similarly, the alteration in rice aroma is more significant in AWD than in CF. The precise modulation of volatile organic compounds (VOCs) by Cd remains unclear based on the available literature. Nevertheless, HM accumulation is higher in AWD conditions compared to CF, leading to a detrimental impact on volatile organic compounds (VOCs). The literature concludes that AWD practices should be avoided in Cd-contaminated fields to decrease accumulation and maintain the quality of the rice. In the future, rhizospheric engineering and plant biotechnology can be used to decrease the transport of HMs from the soil to the plant's edible parts.

Physiological responses of low- and high-cadmium accumulating Robinia pseudoacacia-rhizobium symbioses to cadmium stress

The role of rhizobia in alleviating cadmium (Cd) stress in woody legumes is still unclear. Therefore, two types of black locust (Robinia pseudoacacia L.) with high and low Cd accumulation abilities were selected from 11 genotypes in China, and the effects of rhizobium (Mesorhizobium huakuii GP1T11) inoculation on the growth, CO2 and H2O gas exchange parameters, Cd accumulation, and the absorption of mineral elements of the high (SX) and low Cd-accumulator (HB) were compared. The results showed that rhizobium-inoculation significantly increased biomass, shoot Cd contents, Cd accumulation, root-to-shoot translocation factor (TF) and the absorption and accumulation of mineral elements in both SX and HB. Rhizobium-inoculation increased chlorophyll a and carotenoid contents, and the intercellular carbon dioxide concentrations in HB plants. Under Cd exposure, the high-accumulator SX exhibited a significant decrease in photosynthetic CO2 fixation (Pn) and an enhanced accumulation of Cd in leaves, but coped with Cd exposure by increasing chlorophyll synthesis, regulating stomatal aperture (Gs), controlling transpiration (Tr), and increasing the absorption and accumulation of mineral elements. In contrast, the low-accumulator HB was more sensitive to Cd exposure despite preferential accumulation of Cd in roots, with decreased chlorophyll and carotenoid contents, but significantly increased root biomass. Compared to the low-accumulator HB, non-inoculated Cd-exposed SX plants had higher chlorophyll contents, and rhizobium-inoculated Cd-exposed SX plants had higher Pn, Tr, and Gs as well as higher levels of P, K, Fe, Ca, Zn, and Cu. In conclusion, the high- and low-Cd-accumulator exhibited different physiological responses to Cd exposure. Overall, rhizobium-inoculation of black locust promoted the growth and heavy metal absorption, providing an effective strategy for the phytoremediation of heavy metal-contaminated soils by this woody legume.

Unlocking hormesis and toxic effects induced by cadmium in Polygonatum cyrtonema Hua based on morphology, physiology and metabolomics

Traditional Chinese medicine materials (TCMMs) are widely planted and used, while cadmium (Cd) is a widespread pollutant that poses a potential risk to plant growth and human health. However, studies on the influences of Cd on TCMMs have been limited. Our study aims to reveal the antioxidation-related detoxification mechanism of Polygonatum cyrtonema Hua under Cd stress based on physiology and metabolomics. The results showed that Cd0.5 (total Cd: 0.91 mg/kg; effective Cd: 0.45 mg/kg) induced hormesis on the biomass of roots, tubers and aboveground parts with increases of 22.88%, 27.12% and 17.02%, respectively, and significantly increased the flavonoids content by 57.45%. Additionally, the metabolism of caffeine, glutamine, arginine and purine was upregulated to induce hormesis in Cd0.5, which enhanced the synthesis of resistant substances such as spermidine, choline, IAA and saponins. Under Cd2 stress, choline and IAA decreased, and fatty acid metabolites (such as peanut acid and linoleic acid) and 8-hydroxyguanosine increased in response to oxidative damage, resulting in a significant biomass decrease. Our findings further reveal the metabolic process of detoxification by antioxidants and excessive Cd damage in TCMMs, deepen the understanding of detoxification mechanisms related to antioxidation, and enrich the relevant theories of hormesis induced by Cd.

Safe utilization evaluation of two typical traditional Chinese medicinal materials in Cd-contaminated soil based on the analysis of Cd transfer and AHP model

Due to the increasing scarcity of wild resources, most traditional Chinese medicinal materials (TCMMs) in the market are produced via artificial cultivation. The widespread pollution of cadmium (Cd) in soil limits the safe cultivation and use of TCMMs. This study investigated Cd accumulation, distribution, and the medicinal component content under simulated field conditions to clarify the differences in the Cd absorption, transfer and detoxification mechanisms of Polygonatum cyrtonema Hua and Bletilla striata, and provide the preliminary safe utilization conditions of TCMMs based on the analytic hierarchy process (AHP). The results showed that the Cd content of P. cyrtonema Hua was lower than the safety threshold under a high soil Cd concentration of 0.91 mg/kg (Cd-L), while B. striata was safe only at a low Cd concentration of 0.25 mg/kg (CK). Cd at 0.91 mg/kg induced hormesis affecting the net increase in biomass and medicinal component content for both TCMMs, while P. cyrtonema Hua showed better potential for safe utilization. Additionally, P. cyrtonema Hua had stronger resistance to Cd stress, exhibiting superior characteristics for synergistic absorption of Cd with mineral elements, transfer to nonmedical part and safer fixation forms in subcellular components. In contrast, B. striata showed insufficient Cd tolerance, and Cd was easily accumulated in organelles to inhibit plant growth. Our findings may attract more attention to the safe cultivation of TCMMs and provide insight into guidance for the safe utilization of slightly Cd-contaminated soil.

Mitigating cadmium accumulation and toxicity in plants: The promising role of nanoparticles

Cadmium (Cd) is a highly toxic heavy metal that adversely affects humans, animals, and plants, even at low concentrations. It is widely distributed and has both natural and anthropogenic sources. Plants readily absorb and distribute Cd in different parts. It may subsequently enter the food chain posing a risk to human health as it is known to be carcinogenic. Cd has a long half-life, resulting in its persistence in plants and animals. Cd toxicity disrupts crucial physiological and biochemical processes in plants, including reactive oxygen species (ROS) homeostasis, enzyme activities, photosynthesis, and nutrient uptake, leading to stunted growth and reduced biomass. Although plants have developed defense mechanisms to mitigate these damages, they are often inadequate to combat high Cd concentrations, resulting in yield losses. Nanoparticles (NPs), typically smaller than 100 nm, possess unique properties such as a large surface area and small size, making them highly reactive compared to their larger counterparts. NPs from diverse sources have shown potential for various agricultural applications, including their use as fertilizers, pesticides, and stress alleviators. Recently, NPs have emerged as a promising strategy to mitigate heavy metal stress, including Cd toxicity. They offer advantages, such as efficient absorption by crop plants, the reduction of Cd uptake, and the enhancement of mineral nutrition, antioxidant defenses, photosynthetic parameters, anatomical structure, and agronomic traits in Cd-stressed plants. The complex interaction of NPs with calcium ions (Ca2+), intracellular ROS, nitric oxide (NO), and phytohormones likely plays a significant role in alleviating Cd stress. This review aims to explore the positive impacts of diverse NPs in reducing Cd accumulation and toxicity while investigating their underlying mechanisms of action. Additionally, it discusses research gaps, recent advancements, and future prospects of utilizing NPs to alleviate Cd-induced stress, ultimately promoting improved plant growth and yield.

Antagonistic effect of mercury and excess nitrogen exposure reveals provenance-specific phytoremediation potential of black locust-rhizobia symbiosis

Interaction of different environmental constrains pose severe threats to plants that cannot be predicted from individual stress exposure. In this context, mercury (Hg), as a typical toxic and hazardous heavy metal, has recently attracted particular attention. Nitrogen (N2)-fixing legumes can be used for phytoremediation of Hg accumulation, whereas N availability could greatly affect its N2-fixation efficiency. However, information on the physiological responses to combined Hg exposure and excess N supply of woody legume species is still lacking. Here, we investigated the interactive effects of rhizobia inoculation, Hg exposure (+Hg), and high N (+N) supply, individually and in combination (+N*Hg), on photosynthesis and biochemical traits in Robinia pseudoacacia L. seedlings of two provenances, one from Northeast (DB) and one from Northwest (GS) China. Our results showed antagonistic effects of combined + N*Hg exposure compared to the individual treatments that were provenance-specific. Compared to individual Hg exposure, combined + N*Hg stress significantly increased foliar photosynthesis (+50.6%) of inoculated DB seedlings and resulted in more negative (-137.4%) δ15N abundance in the roots. Furthermore, combined + N*Hg stress showed 47.7% increase in amino acid N content, 39.4% increase in NR activity, and 14.8% decrease in MDA content in roots of inoculated GS seedlings. Inoculation with rhizobia significantly promoted Hg uptake in both provenances, reduced MDA contents of leaves and roots, enhanced photosynthesis and maintained the nutrient balance of Robinia. Among the two Robinia provenances investigated, DB seedlings formed more nodules, had higher biomass and Hg accumulation than GS seedlings. For example, total Hg concentrations in leaves and roots and total biomass of inoculated DB seedlings were 1.3,1.9 and 3.4 times higher than in inoculated GS seedlings under combined + N*Hg stress, respectively. Therefore, the DB provenance is considered to possess a higher potential for phytoremediation of Hg contamination compared to the GS provenance in environments subjected to N deposition.

Functional analysis of a rice 12-oxo-phytodienoic acid reductase gene (OsOPR1) involved in Cd stress tolerance

BACKGROUND

The accumulation of cadmium (Cd) in plants may compromise the growth and development of plants, thereby endangering human health through the food chain. Understanding how plants respond to Cd is important for breeding low-Cd rice cultivars.

METHODS

In this study, the functions of 12-oxo-phytodienoic acid reductase 1 (OsOPR1) were predicted through bioinformatics analysis. The expression levels of OsOPR1 under Cd stress were analyzed by using qRT-PCR. Then, the role that OsOPR1 gene plays in Cd tolerance was studied in Cd-sensitive yeast strain (ycf1), and the Cd concentration of transgenic yeast was analyzed using inductively coupled plasma mass spectrometry (ICP-MS).

RESULTS

Bioinformatics analysis revealed that OsOPR1 was a protein with an Old yellow enzyme-like FMN (OYE_like_FMN) domain, and the cis-acting elements which regulate hormone synthesis or responding abiotic stress were abundant in the promoter region, which suggested that OsOPR1 may exhibit multifaceted biological functions. The expression pattern analysis showed that the expression levels of OsOPR1 were induced by Cd stress both in roots and roots of rice plants. However, the induced expression of OsOPR1 by Cd was more significant in the roots compared to that in roots. In addition, the overexpression of OsOPR1 improved the Cd tolerance of yeast cells by affecting the expression of antioxidant enzyme related genes and reducing Cd content in yeast cells.

CONCLUSION

Overall, these results suggested that OsOPR1 is a Cd-responsive gene and may has a potential for breeding low-Cd or Cd-tolerant rice cultivars and for phytoremediation of Cd-contaminated in farmland.

Enhanced Cd phytoextraction by rapeseed under future climate as a consequence of higher sensitivity of HMA genes and better photosynthetic performance

This study aimed to investigate the underlying physiological, biochemical, and molecular mechanisms responsible for Brassica napu's potential to remediate Cd-contaminated soil under current (CC) vs. future (FC) climate (400 vs. 800 ppm of CO2, 21/14 °C vs. 25/18 °C). B. napus exhibited good tolerance to low Cd treatments (Cd-1, Cd-10, i.e., 1, 10 mg kg-1) under both climates without visible phytotoxicity symptoms. TI sharply decreased by 47 % and 68 % (p < 0.05), respectively, in Cd-50 and Cd-100 treated shoots under CC, but to a lesser extent (-26 % and -53 %, p < 0.05) under FC. This agreed with increased photosynthetic apparatus performance under FC, primarily due to a significant decrease in the closure of active PSII RCs ((dV/dt)o, TRo/RC) and less dissipated excitation energy (DIo/RC, φDo). Calvin Benson cycle-related enzyme activity also improved under FC with 2.2-fold and 2.4-fold (p < 0.05) increases in Rubisco and TPI under Cd-50 and Cd-100, respectively. Consequentially, a 2.2-fold and 2.3-fold (p < 0.05) boosted Pr resulted in a 2.3-fold and 2.4-fold (p < 0.05) increase in the DW of Cd-50 and Cd-100 treated shoots, respectively. This also led to a decrease (26 %, p < 0.05) in shoot Cd concentration under both high Cd treatments with a slight reduction in BCF. Translocation factor (TF) decreased (on average 42 %, p < 0.05) by high Cd treatments under both climates. However, under Cd-100, FC increased TF by 1.7-fold (p < 0.05) compared to CC, which could be explained by significant increases in the expression of HMA genes, especially BnaHMA4a and BnaHMA4c. Finally, Cd TU increased under FC by 65 % and 76 % (p < 0.05) under Cd-50 and Cd-100. This led to a shorter hypothetical remediation time for reaching the Cd pollution limit by 35 (p > 0.05) and 61 (p < 0.05) years, respectively, compared to CC.

Genotypic variation in grain cadmium concentration in wheat: Insights into soil pollution, agronomic characteristics, and rhizosphere microbial communities

Soil cadmium (Cd) pollution poses a serious threat to both the productivity and quality of wheat. This study aimed to investigate the genotypic variation in grain Cd concentration in wheat through field and pot experiments. Among 273 wheat genotypes, a significant genotypic difference was found in grain Cd concentration, ranging from 0.01 to 0.14 mg kg-1. Two contrasting genotypes, X321 (a low grain Cd accumulator) and X128 (a high grain Cd accumulator), were selected for pot experiments. X321 exhibited a 17.9% greater reduction in yield and a 10.2% lower shoot-to-grain Cd translocation rate than X128 under Cd treatment. Grain Cd content showed a positive correlation with soil available Cd content and a negative correlation with Cu content. Soil catalase activity significantly decreased in X128 under Cd stress, whereas no difference was found in X321. The grains of X321 exhibited a more compact spatial distribution of starch grains and protein matrix than those of X128. Moreover, the size of A-type starch in X128 was larger than in X321. Meanwhile, X128 contained much B-type starch, with some surface pits observed on A-type granules under Cd stress. Cd treatment increased the abundance of rhizosphere microorganism communities, with Ellin6067 and Ramlibacter being enriched in X128 under Cd treatment, which might facilitate Cd uptake. The accumulation of Cd in grains demonstrated a strong positive correlation with the rhizosphere bacterial diversity (correlation coefficient = 0.78). These findings provide new insights into the basis of grain Cd accumulation in wheat and have potential implications for developing new verities with low Cd accumulation to ensure food safety and minimize human exposure.

Comparative effects of silicon and silicon nanoparticles on the antioxidant system and cadmium uptake in tomato under cadmium stress

Cadmium (Cd) pollution is an important threat to agricultural production globally. Silicon (Si) and silicon nanoparticles (Si NPs) can mitigate Cd stress in plants. However, the mechanisms underlying the impacts of Si and Si NPs on Cd resistance, particularly in low-Si accumulators, remain inadequately understood. Accordingly, we conducted a comparative investigation into the roles of Si and Si NPs in regulating the antioxidant system (enzymes and antioxidants) and Cd uptake (influx rate, symplastic and apoplastic pathways) in tomato (a typical low-Si accumulator). The results revealed that Si and Si NPs improved tomato growth under Cd stress, and principal component analysis (PCA) demonstrated that Si NPs were more effective than Si. For oxidative damage, redundancy analysis (RDA) results showed that Si NPs ameliorated oxidative damage in both shoots and roots, whereas Si predominantly alleviated oxidative damage in roots. Simultaneously, Si and Si NPs regulated antioxidant enzymes and nonenzymatic antioxidants with distinct targets and strengths. Furthermore, Si and Si NPs decreased Cd concentration in tomato shoot, root, and xylem sap, while Si NPs induced a more significant decline in shoot and xylem sap Cd. Noninvasive microtest and quantitative estimation of trisodium-8-hydroxy-1,3,6-pyrenetrisulfonic (PTS, an apoplastic tracer) showed that Si and Si NPs reduced the Cd influx rate and apoplastic Cd uptake, while Si NPs induced a more significant reduction. Moreover, Si regulated the expression of genes responsible for Cd uptake (NRAMP2 and LCT1) and compartmentalization (HMA3), while Si NPs reduced the expression of NRAMP2. In conjunction with RDA, the results showed that Si and Si NPs decreased Cd uptake mainly by regulating the symplastic and apoplastic pathways, respectively. Overall, our results indicate that Si NPs is more effective in promoting tomato growth and alleviating oxidative damage than Si in tomato under Cd stress by modulating the antioxidant system and reducing apoplastic Cd uptake.

Agronomic and Genetic Strategies to Enhance Selenium Accumulation in Crops and Their Influence on Quality

Selenium (Se) is an essential trace element that plays a crucial role in maintaining the health of humans, animals, and certain plants. It is extensively present throughout the Earth's crust and is absorbed by crops in the form of selenates and selenite, eventually entering the food chain. Se biofortification is an agricultural process that employs agronomic and genetic strategies. Its goal is to enhance the mechanisms of crop uptake and the accumulation of exogenous Se, resulting in the production of crops enriched with Se. This process ultimately contributes to promoting human health. Agronomic strategies in Se biofortification aim to enhance the availability of exogenous Se in crops. Concurrently, genetic strategies focus on improving a crop's capacity to uptake, transport, and accumulate Se. Early research primarily concentrated on optimizing Se biofortification methods, improving Se fertilizer efficiency, and enhancing Se content in crops. In recent years, there has been a growing realization that Se can effectively enhance crop growth and increase crop yield, thereby contributing to alleviating food shortages. Additionally, Se has been found to promote the accumulation of macro-nutrients, antioxidants, and beneficial mineral elements in crops. The supplementation of Se biofortified foods is gradually emerging as an effective approach for promoting human dietary health and alleviating hidden hunger. Therefore, in this paper, we provide a comprehensive summary of the Se biofortification conducted over the past decade, mainly focusing on Se accumulation in crops and its impact on crop quality. We discuss various Se biofortification strategies, with an emphasis on the impact of Se fertilizer strategies on crop Se accumulation and their underlying mechanisms. Furthermore, we highlight Se's role in enhancing crop quality and offer perspective on Se biofortification in crop improvement, guiding future mechanistic explorations and applications of Se biofortification.

Expression of OsHARBI1-1 enhances the tolerance of Arabidopsis thaliana to cadmium

BACKGROUND

As one of the major food crops in the world, rice is vulnerable to cadmium (Cd) pollution. Understanding of the molecular mechanisms of Cd uptake, transport and detoxification in rice is essential for the breeding of low-Cd rice. However, the molecular mechanisms underlying the response of rice to Cd stress remains to be further clarified.

RESULTS

In this study, a novel Cd-responsive gene OsHARBI1-1 was identified in the rice genome and its expression pattern and function were characterized. Bioinformatics analysis showed that the promoter region of OsHARBI1-1 had multiple cis-acting elements in response to phytohormones and stress, and the expression of OsHARBI1-1 was induced by phytohormones. OsHARBI1-1 protein was targeted to the nucleus. qRT-PCR analysis results showed that the expression of OsHARBI1-1 in the roots was repressed while the expression in the shoots was increased under Cd stress. Heterologous expression of OsHARBI1-1 in yeast conferred tolerance to Cd and reduced Cd content in the cells. Meanwhile, the expression of OsHARBI1-1 in Arabidopsis thaliana (A. thaliana) enhanced the tolerance of A. thaliana to Cd stress. In addition, compared with the wild type plants, the POD activity of transgenic plants was increased, while the SOD and CAT activities were decreased. Interestingly, the accumulation of Cd in the roots of A. thaliana expressing OsHARBI1-1 was significantly increased, whereas the Cd accumulation in the shoots was slightly decreased. Compared to the WT plants, the expression of genes related to Cd absorption and chelation was upregulated in transgenic A. thaliana under Cd stress, while the expression of genes responsible for the translocation of Cd from the roots to the shoots was downregulated. Moreover, the expression of phytohormone-related genes was significantly influenced by the expression of OsHARBI1-1 with and without Cd treatment.

CONCLUSIONS

Findings of this study suggest that OsHARBI1-1 might play a role in the response of plants to Cd response by affecting antioxidant enzyme activities, Cd chelation, absorption and transport, and phytohormone homeostasis and signaling.

Current progress on fluoride occurrence in the soil environment: Sources, transformation, regulations and remediation

Fluorine is a halogen element widely distributed in nature, but due to excessive emissions from industrial manufacturing and agricultural production, etc., the soil is over-enriched with fluoride and the normal growth of plants is under stress, and it also poses a great threat to human health. In this review, we summarized the sources of fluoride in soil, and then analyzed the potential mechanisms of fluoride uptake in soil-plant systems. In addition, the main influences of soil ecosystems on plant fluoride uptake were discussed, soil management options to mitigate fluoride accumulation in plants were also summarized. The bioremediation techniques were found to be a developmental direction to improve fluoride pollution. Finally, we proposed other research directions, including fluoride uptake mechanisms in soil-plant systems at the molecular expression levels, development of visualization techniques for fluoride transport in plants, interactions mechanisms between soil microhabitats and plant metabolism affecting fluoride uptake, as well as combining abiotic additives, nanotechnology and biotechnology to remediate fluoride contamination problems.

Application of two- and multiway chemometric strategies for describing elementomic changes in pepper plants exposed to cadmium stress by multielement determination

The objective of this work was to evaluate elemental changes in pepper exposed to Cd stress through different chemometric tools. For this purpose, pepper plants were grown under five different treatments with different Cd concentrations in the nutrient solution. Considering the hypothesis that pepper plants exposed to Cd stress during growth undergo changes in the macro- and microelemental distribution in leaves, stems, and roots, principal component analysis (PCA) and parallel factor (PARAFAC) analysis were applied to compare bidirectional and multivariate chemometric strategies to assess elemental changes in pepper plants. Since the number of variables and the data generated were large and complex, the application of chemometric tools was justified to facilitate the visualization and interpretation of results. The mineral composition, namely the Ca, Cd, Cu, Fe, K, Mg, Mn, N, and P contents, was assessed in 180 samples of leaves, stems, and roots of the cultivated peppers. Then, PCA and PARAFAC analysis were applied to compare bidirectional and multivariate chemometric strategies to assess elemental changes throughout pepper plants. The visualization of the trend on each sample and their intrinsic relationship with the variables were possible with the application of PCA. The use of PARAFAC analysis permitted the simultaneous study of all samples in a straightforward representation of the information that facilitated a quick and comprehensive understanding of the spatial distribution of elements in plants. Thus, macroelements (Ca, K, Mg, N, and P) that were found in higher concentrations in leaves did not present significant differences in the distribution along the plants under different treatment conditions. In contrast, a significant impact on the microelement (Cu, Fe, and Mn) distribution was produced between uncontaminated and contaminated samples. This analysis revealed a significant accumulation of Cd in roots and adverse effects on normal plant growth, demonstrating their level of phytotoxicity to pepper.

The Potential of Bioaugmentation-Assisted Phytoremediation Derived Maize Biomass for the Production of Biomethane via Anaerobic Digestion

Anthropogenic behaviors are causing the severe build-up of heavy metal (HM) pollutants in the environment, particularly in soils. Amongst a diversity of remediation technologies, phytoremediation is an environmentally friendly technology that, when coupling tolerant plants to selected rhizospheric microorganisms, can greatly stimulate HM decontamination of soils. Maize (Zea mays) is a plant with the reported capacity for HM exclusion from contaminated soil but also has energetic importance. In this study, Zea mays was coupled with Rhizophagus irregularis, an arbuscular mycorrhizal fungus (AMF), and Cupriavidus sp. strain 1C2, a plant growth-promoting rhizobacteria (PGPR), as a remediation approach to remove Cd and Zn from an industrial contaminated soil (1.2 mg Cd kg-1 and 599 mg Zn kg-1) and generate plant biomass, by contrast to the conservative development of the plant in an agricultural (with no metal pollution) soil. Biomass production and metal accumulation by Z. mays were monitored, and an increase in plant yield of ca. 9% was observed after development in the contaminated soil compared to the soil without metal contamination, while the plants removed ca. 0.77% and 0.13% of the Cd and Zn initially present in the soil. The resulting biomass (roots, stems, and cobs) was used for biogas generation in several biomethane (BMP) assays to evaluate the potential end purpose of the phytoremediation-resulting biomass. It was perceptible that the HMs existent in the industrial soil did not hinder the anaerobic biodegradation of the biomass, being registered biomethane production yields of ca. 183 and 178 mL of CH4 g-1 VS of the complete plant grown in non-contaminated and contaminated soils, respectively. The generation of biomethane from HM-polluted soils' phytoremediation-derived maize biomass represents thus a promising possibility to be a counterpart to biogas production in an increasingly challenging status of renewable energy necessities.

Endophytic Fungus Talaromyces sp. MR1 Promotes the Growth and Cadmium Uptake of Arabidopsis thaliana L. Under Cadmium Stress

Endophytes play essential roles in plant growth under metal(loid)s stress. An endophytic fungus strain MR1 was isolated from the roots of Miscanthus floridulus collected from a lead-zinc mining area (Huayuan, China), which could produce indole-3-acetic acid and have Cadmium (Cd) tolerance. Further 18S rRNA sequencing analysis showed that it was highly similar (99.83%) to Talaromyces pinophilus. In pot experiments, we explored the effects of strain MR1 on the growth and Cd uptake of a wide-type Arabidopsis thaliana under low (LC) and high (HC) Cd concentrations. The results showed that MR1 effectively increased the dry weight of aboveground and underground tissues by 25.95-107.21% in both LC and HC groups. Due to MR1 inoculation, the Cd content in the underground tissues was significantly (p < 0.05) decreased by 39.28% under low Cd concentration, while it was significantly (p < 0.05) increased by 28.28% under high Cd concentration. Besides, MR1 inoculations significantly (p < 0.05) increased the total content of removed Cd (17.080 μg) and BCF (0.064) by 129.77% and 153.95% under high Cd concentration. Therefore, we speculated that MR1 might be selected as the effective microbial agent to increase crop yield and control Cd content in the crop in light Cd-contaminated soil. Besides, MR1 could potentially enhance the phytoremediation efficiency of extremely Cd-contaminated soil.

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.

Multiple insights into lignin-mediated cadmium detoxification in rice (Oryza sativa)

Cadmium (Cd) is readily absorbed by rice and enters the food chain, posing a health risk to humans. A better understanding of the mechanisms of Cd-induced responses in rice will help in developing solutions to reduce Cd uptake in rice. Therefore, this research attempted to reveal the detoxification mechanisms of rice in response to Cd through physiological, transcriptomic and molecular approaches. The results showed that Cd stress restricted rice growth, led to Cd accumulation and H2O2 production, and resulted cell death. Transcriptomic sequencing revealed glutathione and phenylpropanoid were the major metabolic pathways under Cd stress. Physiological studies showed that antioxidant enzyme activities, glutathione and lignin contents were significantly increased under Cd stress. In response to Cd stress, q-PCR results showed that genes related to lignin and glutathione biosynthesis were upregulated, whereas metal transporter genes were downregulated. Further pot experiment with rice cultivars with increased and decreased lignin content confirmed the causal relationship between increased lignin and reduced Cd in rice. This study provides a comprehensive understanding of lignin-mediated detoxification mechanism in rice under Cd stress and explains the function of lignin in production of low-Cd rice to ensure human health and food safety.

Zinc Foliar Application Mitigates Cadmium-Induced Growth Inhibition and Enhances Wheat Growth, Chlorophyll Contents, and Yield

Cadmium (Cd) is a toxic heavy metal that significantly threatens plants and the environment. Its toxicity in plants can result in various adverse effects, including reduced growth, altered metabolism, and cell damage. Cadmium can also interfere with nutrient uptake, particularly zinc (Zn), leading to Zn deficiency and further exacerbating Cd toxicity. On the other hand, foliar application of zinc might be a useful strategy to mitigate cadmium (Cd) toxicity in plants. Hence, a pot experiment was conducted with three replications. The wheat plants were treated with various concentrations of Zn as a foliar spray (control, 0.1, 0.2, 0.4, and 0.5%) in Cd-spiked soil in pots. The results showed that foliar use of Zn at 0.4 or 0.5% resulted in higher plant height, grain yield, and dry matter yield than the control group. Using Zn as foliar spray enriched shoot and grain Zn content while reducing Cd content in the shoot and grain. The leaf's electrolyte leakage (EL) decreased by 15.4, 29.8, 40.7, and 45.9% in the Zn 0.1%, Zn 0.2%, Zn 0.4%, and Zn 0.5% treatments, respectively, compared to the control treatment. Regarding superoxide dismutase (SOD) activity, Zn 0.5% treatment showed a decrease of 42.9% over control. Specifically, the Zn 0.1% showed a 27.2%, Zn 0.2% showed a 56.8%, Zn 0.4% showed a 91.1%, and Zn 0.5% showed a 133.7% increase in total chlorophyll content than control. Based on the results, it is recommended that 0.4% Zn solution may be used for foliar application for enhancing crop productivity and Zn concentration in plants under high Cd stress. Additionally, continued research on the mechanisms of cadmium uptake, transport, and detoxification in plants may lead to the identification of new targets for intervention.

Pharmaceutical-contaminated irrigation water: implications for ornamental plant production and phytoremediation using enrofloxacin-accumulating species

Enrofloxacin (Enro) has been widely encountered in natural water sources, and that water is often used for irrigation in crop production systems. Due to its phytotoxicity and accumulation in plant tissues, the presence of Enro in water used for crop irrigation may represent economical and toxicological concerns. Here, we irrigated two ornamental plant species (Zantedeschia rehmannii Engl. and Spathiphyllum wallisii Regel.) with water artificially contaminated with the antimicrobial enrofloxacin (Enro; 0, 5, 10, 100, and 1000 μg L-1) to evaluate its effects on ornamental plant production, as well as its accumulation and distribution among different plant organs (roots, leaves, bulbs, and flower stems), and examined the economic and environmental safety of commercializing plants produced under conditions of pharmaceutical contamination. The presence of Enro in irrigation water was not found to disrupt plant growth (biomass) or flower production. Both species accumulated Enro, with its internal concentrations distributed as the following: roots > leaves > bulbs > flower stems. In addition to plant tolerance, the content of Enro in plant organs indicated that both Z. rehmannii and S. wallisii could be safety produced under Enro-contaminated conditions and would not significantly contribute to contaminant transfer. The high capacity of those plants to accumulate Enro in their tissues, associated with their tolerance to it, indicates them for use in Enro-phytoremediation programs.

Unveiling Cacao Rootstock-Genotypes with Potential Use in the Mitigation of Cadmium Bioaccumulation

The accumulation of high cadmium (Cd) levels in cacao beans (Theobroma cacao) generate several commercial and health issues. We hypothesized that cacao phenotypic and genotypic diversity could provide new insights to decrease Cd accumulation in cacao beans. Nine cacao rootstock genotypes were evaluated for up to 90 days under 0, 6, and 12 (mg·kg-1) of CdCl2 exposure and Cd content and plant growth dynamics were measured in leaves, stems, and roots. Data revealed that all cacao genotypes studied here were highly tolerant to Cd, since they presented tolerance index ≥ 60%. In shoots, EET61 and PA46 presented the higher (~270 mg·kg DW-1) and lower (~20 mg·kg DW-1) Cd concentration, respectively. Accordingly, only the EET61 showed an increase in the shoot cadmium translocation factor over the 90 days of exposure. However, when analyzing cadmium allocation to different organs based on total plant dry mass production, none of the genotypes maintained high Cd compartmentalization into roots, since P46, which was the genotype with the highest allocation of Cd to the roots, presented only 20% of total cadmium per plant in this plant organ and 80% allocated into the shoots, under Cd 12 (mg·kg-1) and after 90 days of exposure. Thus, genotypic/phenotypic variability in cacao rootstocks may provide valuable strategies for maximizing the reduction in Cd content in shoots. In this sense, IMC67 and PA46 were the ones that stood out in the present study.

Integrated metabolomics, transcriptomics, and proteomics analyses reveal co-exposure effects of polycyclic aromatic hydrocarbons and cadmium on ryegrass (Lolium perenne L.)

Cadmium (Cd) and polycyclic aromatic hydrocarbons (PAHs) are prominent soil contaminants found in industrial sites, and their combined effects on plants are not yet fully understood. To investigate the mechanisms underlying the co-exposure of Cd and PAHs and identify key biomarkers for their co-effects, an integrated analysis of metabolomics, transcriptomics, and proteomics was conducted on ryegrass leaves cultivated in soil. In nontarget metabolomics analysis, nine differentially expressed metabolites that were specifically induced by the compound exposure were identified. When combined with the analysis of differentially expressed genes and proteins, it was determined that the major pathways involved in the response to the co-stress of Cd and PAHs were linoleic acid metabolism and phenylpropanoid biosynthesis. The upregulation of 12,13-dihydroxy-9Z-octadecenoic acid and the downregulation of sinapyl alcohol were identified as typical biomarkers, respectively. Compared to scenarios of single exposures, the compound exposure to Cd and PAHs disrupted the oxidation of linoleic acid, leading to alterations in the profiles of linoleate metabolites. Additionally, it intensified hydroxylation, carboxylation, and methylation processes, and interfered with reactions involving coenzyme A, thus inhibiting lignin production. As a result, oxidative stress was elevated, and the cell wall defense system in ryegrass was weakened. The findings of this study highlight the ecological risks associated with unique biological responses in plants co-exposed to Cd and PAHs in polluted soils.

Isolation of cadmium-resistance and siderophore-producing endophytic bacteria and their potential use for soil cadmium remediation

Endophyte-assisted phytoremediation is an emerging technique for soil heavy metals (HMs) remediation and has become a research focus in the world because of the benefits of endophytes on plant growth and uptake of HMs. In this study, multifunctional endophytic bacteria strains were isolated and screened, and the feasibility of these strains for soil cadmium (Cd) remediation was investigated by soil incubation experiments and pot experiments. All endophytic bacteria were isolated from the roots of woody plants grown on Cd-contaminated soil. Seven endophytic bacteria strains had capacities to tolerate Cd toxicity and produce siderophores, and sequence analysis of the 16S rRNA gene classified these strains as belonging to the genera Burkholderia, Pseudomonas, Pantoea, and Herbaspirillum. All strains were able to produce hydroxamate siderophores (32.40%-91.49%) and had three or more plant growth promoting properties such as phosphorus solubilization, nitrogen fixation, indole acetic acid and 1-aminocyclopropane-1-carboxylate deaminase production. They were all strongly resistant to Cd2+ toxicity, with the minimum inhibitory concentration in LB medium ranging from 1.5 mM to 9.0 mM. Except for strain Burkholderia contaminans JLS17, other strains showed decreasing removal rates within continuously elevated Cd2+ concentration of 10-100 mg L-1. Compared with the uninoculated treatment, the inoculation of strains B.contaminans JLS17, Pseudomonas lurida JLS32, and Pantoea endophytica JLS50 effectively increased the concentration of acid-soluble Cd and decreased the concentration of reducible, oxidizable, and residual Cd in the soils of different Cd contamination levels. In pot experiments, inoculation of strains JLS17 and YTG72 significantly (p < 0.05) promoted the growth of above-ground parts and root system of slash pine (Pinus elliottii) under Cd stress. This study provides a valuable biological resource for endophyte-assisted phytoremediation and a theoretical basis for the application of endophytic bacteria for remediation of Cd-contaminated soil.

Reduction of bioavailability and phytotoxicity effect of cadmium in soil by microbial-induced carbonate precipitation using metabolites of ureolytic bacterium Ochrobactrum sp. POC9

The application of ureolytic bacteria for bioremediation of soil contaminated with heavy metals, including cadmium (Cd), allows for the efficient immobilization of heavy metals by precipitation or coprecipitation with carbonates. Microbially-induced carbonate precipitation process may be useful also in the case of the cultivation of crop plants in various agricultural soils with trace but legally permissible Cd concentrations, which may be still uptaken by plants. This study aimed to investigate the influence of soil supplementation with metabolites containing carbonates (MCC) produced by the ureolytic bacterium Ochrobactrum sp. POC9 on the Cd mobility in the soil as well as on the Cd uptake efficiency and general condition of crop plants (Petroselinum crispum). In the frame of the conducted studies (i) carbonate productivity of the POC9 strain, (ii) the efficiency of Cd immobilization in soil supplemented with MCC, (iii) crystallization of cadmium carbonate in the soil enriched with MCC, (iv) the effect of MCC on the physico-chemical and microbiological properties of soil, and (v) the effect of changes in soil properties on the morphology, growth rate, and Cd-uptake efficiency of crop plants were investigated. The experiments were conducted in soil contaminated with a low concentration of Cd to simulate the natural environmental conditions. Soil supplementation with MCC significantly reduced the bioavailability of Cd in soil with regard to control variants by about 27-65% (depending on the volume of MCC) and reduced the Cd uptake by plants by about 86% and 74% in shoots and roots, respectively. Furthermore, due to the decrease in soil toxicity and improvement of soil nutrition with other metabolites produced during the urea degradation (MCC), some microbiological properties of soil (quantity and activity of soil microorganisms), as well as the general condition of plants, were also significantly improved. Soil supplementation with MCC enabled efficient Cd stabilization and significantly reduced its toxicity for soil microbiota and plants. Thus, MCC produced by POC9 strain may be used not only as an effective Cd immobilizer in soil but also as a microbe and plant stimulators.

Remediation of Cd contaminated paddy fields by intercropping of the high- and low- Cd-accumulating rice cultivars

Intercropping cadmium (Cd) hyperaccumulators with crops have been widely applied in the remediation of contaminated farmland soils. However, most studies were done on drylands since the majority of the hyperaccumulators are susceptible to the aquatic environment, making the remediation of Cd-contaminated paddy fields particularly difficult. Our study attempts to address the issue by intercropping the high-Cd-accumulating (henceforth, "high-Cd") rice cultivars with the low-Cd-accumulating (henceforth, "low-Cd") ones, and to study the Cd removal, uptake and translocation during the remediation process. The results indicated that intercropping mode with 20-cm row spacing (intercropping-20 treatment) performed better than the that with 30-cm row spacing (intercropping-30 treatment), while intercropping had stronger impact on late rice compared to early rice. In general, the physiological condition of rice was stable under the intercropping-20 treatment, suggesting the growth of rice was not impeded. For late rice, as the intercropping-20 treatment can significantly reduce soil pH and increase the diethylenetriaminepentaacetic acid extracted Cd (DTPA-extracted Cd) from the rhizosphere soil, Cd accumulated more in the tissues of the high-Cd rice cultivars (H2), and its dry biomass increased. As a result, a drastic improvement in the total Cd removal rate by 38.55 % was noticed. Therefore, the reduction of total Cd concentration in 0-20 cm profile caused by removal, thus it could provide safer soil environment for the growth of low Cd-rice cultivars (L2), leading to a significant drop in the root Cd concentration and safer production of L2. Interestingly, intercropping had no effect on the yield per plant of low-Cd rice cultivars. For early rice, intercropping-20 treatment exerted trivial effects to all aspects. The intercropping-30 treatment has poor representativeness of all indicators because of the large intercropping distance. Our results demonstrate that intercropping of the high-Cd and the low-Cd rice cultivars is a potential mode for Cd remediation in paddy fields.

Methyl jasmonate and selenium synergistically mitigative cadmium toxicity in hot pepper (Capsicum annuum L.) plants by improving antioxidase activities and reducing Cd accumulation

Methyl jasmonate (MeJA) or selenium (Se)-mediated response to cadmium (Cd) stress in plant has been widely reported, but the combined effects both on plant growth in response to Cd stress and the underlying mechanisms remain obscure. Here, we showed the combined effects of MeJA (2.5 μM) and Se (7 μM) on hot pepper growth under Cd stress (CdCl₂, 5 μM). The results showed Cd suppressed the accumulation of total chlorophyll and carotenoid and reduced the photosynthesis, while it increased the content of endogenous signaling molecules, e.g. nitric oxide (NO) and hydrogen peroxide (H₂O₂), as well as Cd content in leaves. The combined application of MeJA and Se significantly decreased the malondialdehyde (MDA) accumulation and improved the activities of antioxidant enzymes (AOEs, e.g. SOD and CAT) and defense-related enzymes (DREs, POD and PAL). Additionally, the synergistic application of MeJA and Se also obviously improved photosynthesis in hot pepper plants under Cd stress compared with those treated with MeJA or Se respectively or not. Moreover, the treatment of MeJA associated with Se also effectively reduced the Cd accumulation in hot pepper leaves under Cd stress compared with the plants treated with MeJA or Se separately, which implied a potentially synergistic role of MeJA and Se in alleviating Cd toxicity in hot pepper plants. This study provides a theoretical reference for the further analysis of the molecular mechanism of MeJA and Se in jointly mediating the response to heavy metals in plants.

Phytoextraction and Migration Patterns of Cadmium in Contaminated Soils by Pennisetum hybridum

This study was conducted to identify soil cadmium (Cd) removal pathways and their contribution rates during phytoremediation by Pennisetum hybridum, as well as to comprehensively assess its phytoremediation potential. Multilayered soil column tests and farmland-simulating lysimeter tests were conducted to investigate the Cd phytoextraction and migration patterns in topsoil and subsoil simultaneously. The aboveground annual yield of P. hybridum grown in the lysimeter was 206 ton·ha^-1. The total amount of Cd extracted in P. hybridum shoots was 234 g·ha^-1, which was similar to that of other typical Cd-hyperaccumulating plants such as Sedum alfredii. After the test, the topsoil Cd removal rate was 21.50-35.81%, whereas the extraction efficiency in P. hybridum shoots was only 4.17-8.53%. These findings indicate that extraction by plant shoots is not the most important contributor to the decrease of Cd in the topsoil. The proportion of Cd retained by the root cell wall was approximately 50% of the total Cd in the root. Based on column test results, P. hybridum treatment led to a significant decrease in soil pH and considerably enhanced Cd migration to subsoil and groundwater. P. hybridum decreases Cd in the topsoil through multiple pathways and provides a relatively ideal material for phytoremediation of Cd-contaminated acid soils.

Cichorium intybus L. is a potential Cd-accumulator for phytoremediation of agricultural soil with strong tolerance and detoxification to Cd

Identifying suitable plants for phytoremediation of Cd (cadmium) contaminated agricultural soil is critical. In this study, whether chicory (Cichorium intybus L.) qualified as an ideal accumulator for phytoremediation was investigated. The hydroponic and pot experiments showed that Cd concentration in chicory leaves exceeded 100 mg kg-1 (BCF >1, TF >1) with 40 mg kg-1 Cd in pot; No significant effects on chicory growth, leaf protein and physiological and biochemical aspects when treated with ≤ 20 μM or 40 mg kg-1 Cd, because chicory could relieve Cd toxicity by increasing activities of photoprotection mechanisms, the reactive oxygen species scavenging system and concentrations of functional groups in plant tissues. In field experiment, 16.2 and 26.6 t ha-1 of chicory leaves was harvested in winter and summer, respectively. The highest Cd concentration in leaves was close to 25.0 mg kg-1 (BCF >1, TF >1) from the acid soil with 0.980 mg kg-1 Cd. Over 320 g ha-1 Cd was extracted from soil by harvesting chicory leaves both in winter and summer, with 9.24% and 12.9% of theoretical phytoremediation efficiency. Therefore, chicory can be as an ideal Cd-accumulator for phytoremediation of slight-to-moderate Cd-contaminated agricultural soil in any season.

Effects of exogenous calcium on cadmium accumulation in amaranth

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

Mitigating the toxicity of reactive oxygen species induced by cadmium via restoring citrate valve and improving the stability of enzyme structure in rice

The mechanism of reactive oxygen species (ROS) burst in rice cells induced by cadmium (Cd) stress remains poorly understood. The present study shows that the burst of superoxide anions (O₂^·-) and hydrogen peroxide (H₂O₂) in roots and shoots led by Cd stress was attributed to the disturbance of citrate (CA) valve and the damage of antioxidant enzyme structure in the rice seedlings. Cd accumulation in cells altered the molecular structure of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) through attacking glutamate (Glu) and other residues, leading to the significant reduction of their activities in clearing O₂^·- and decomposing H₂O₂. Citrate supplementation obviously increased the activity of antioxidant enzymes and decreased ∼20-30% of O₂^·- and H₂O₂ contents in roots and shoots. Meanwhile, the synthesis of metabolites/ligands such as CA, α-ketoglutarate (α-KG) and Glu as well as the activities of related enzymes in CA valve were remarkably improved. The activities of antioxidant enzymes were protected by CA through forming stable hydrogen-bonds between CA and antioxidant enzymes, and forming the stable chelates between ligands and Cd. These findings indicate that exogenous CA mitigated the toxicity of ROS under Cd stress by the ways of restoring CA valve function to reduce the production of ROS, and improving the stability of enzyme structure to enhance antioxidant enzymes activity.

Comprehensive Study of Si-Based Compounds in Selected Plants (Pisum sativum L., Medicago sativa L., Triticum aestivum L.)

This review describes the role of silicon (Si) in plants. Methods of silicon determination and speciation are also reported. The mechanisms of Si uptake by plants, silicon fractions in the soil, and the participation of flora and fauna in the Si cycle in terrestrial ecosystems have been overviewed. Plants of Fabaceae (especially Pisum sativum L. and Medicago sativa L.) and Poaceae (particularly Triticum aestivum L.) families with different Si accumulation capabilities were taken into consideration to describe the role of Si in the alleviation of the negative effects of biotic and abiotic stresses. The article focuses on sample preparation, which includes extraction methods and analytical techniques. The methods of isolation and the characterization of the Si-based biologically active compounds from plants have been overviewed. The antimicrobial properties and cytotoxic effects of known bioactive compounds obtained from pea, alfalfa, and wheat were also described.