The role of silicon in cadmium alleviation by rice root cell wall retention and vacuole compartmentalization under different durations of Cd exposure

De-Methyl Esterification Modification of Root Pectin Mediates Cd Accumulation of Lactuca sativa

Cadmium (Cd) contamination in agricultural soil brings severe health risks through the dietary intake of Cd-polluted crops. The comprehensive role of pectin in lowering Cd accumulation is investigated through low Cd accumulated (L) and high Cd accumulated (H) cultivars of L. sativa. The significantly different Cd contents in the edible parts of two L. sativa cultivars are accomplished by different Cd transportations. The pectin is the dominant responsive cell wall component according to significantly increased uronic acid contents and the differential Cd absorption between unmodified and modified cell wall. The chemical structure characterization revealed the decreased methyl esterification in pectin under Cd treatment compared with control. Significantly brighter LM19 relative fluorescence density and 40.82% decreased methanol in the root pectin of L cultivar under Cd treatment (p < 0.05) supported that the de-methyl esterification of root pectin is more significant in L cultivar than in H cultivar. The pectin de-methyl esterification of L cultivar is achieved by the upregulation of pectin esterases and the downregulation of pectin esterase inhibitors under Cd treatments, which has facilitated the higher Cd-binding of pectin. Our findings provide deep insight into the differential Cd accumulation of L. sativa cultivars and contribute to the understanding the pollutant behaviors in plants.

Aquaporin mediated silicon-enhanced root hydraulic conductance is benefit to cadmium dilution in tobacco seedlings

Numerous studies shown that silicon (Si) enhanced plants' resistance to cadmium (Cd). Most studies primarily focused on investigating the impact of Si on Cd accumulation. However, there is a lack of how Si enhanced Cd resistance through regulation of water balance. The study demonstrated that Si had a greater impact on increasing fresh weight compared to dry weight under Cd stress. This effect was mainly attributed to Si enhanced plant relative water content (RWC). Plant water content depends on the dynamic balance of water loss and water uptake. Our findings revealed that Si increased transpiration rate and stomatal conductance, leading to higher water loss. This, in turn, negatively impacted water content. The increased water content caused by Si could ascribe to improve root water uptake. The Si treatment significantly increased root hydraulic conductance (Lpr) by 131 % under Cd stress. This enhancement was attributed to Si upregulation genes expression of NtPIP1;1, NtPIP1;2, NtPIP1;3, and NtPIP2;1. Through meticulously designed scientific experiments, this study showed that Si enhanced AQP activity, leading to increased water content that diluted Cd concentration and ultimately improved plant Cd resistance. These findings offered fresh insights into the role of Si in bolstering plant resistance to Cd.

Insights into the antagonistic effects of calcium on cadmium accumulation in peanuts (Arachis hypogaea L.)

Peanut (Arachis hypogaea L.) plant has a high requirement for calcium (Ca) during its growth and development, and possesses the ability to accumulate cadmium (Cd) from soil. However, the precise mechanisms underlying the antagonistic effects between Ca and Cd remain unclear. This study aimed to explore the dynamic changes in Cd accumulation in peanut seedlings by varying the Ca-to-Cd concentration ratio (CRCa/Cd) from 250 to 3500. Additionally, the influence of ion channel competition and cell wall fixation in the root on Cd accumulation in peanuts was explored by analyzing Cd chemical forms, subcellular distribution, pectin content, and Cd2+ fluxes using a non-invasive micro-test technique (NMT). The findings revealed that Cd accumulation in peanut seedlings was significantly lower when the CRCa/Cd was higher than 2000. In the Ca-pretreated seedlings (cell wall fixation treatment), Cd content in the shoots and roots decreased by 18.9% and 25.0%, respectively, compared with the simultaneous exposure to Ca and Cd (ion channel competition treatment). Cd2+ influx in peanut roots decreased by 55.8% in the Ca-pretreated group. However, increasing the competitive strength of Ca2+ and Cd2+ did not affect Cd2+ influx under normal Ca conditions (>2 mM Ca). Meanwhile, Ca pretreatment significantly increased Cd distribution in the root cell wall, pectate, and protein-binding forms, while significantly reducing Cd distribution in root soluble components and inorganic Cd forms. The pectin content in the roots increased by 128% and 226% in the Ca and Cd simultaneous exposure treatment and Ca pretreatment, respectively. These results suggest that Ca pretreatment enhanced Cd retention in the root cell wall. Overall, exogenous Ca effectively mitigated Cd accumulation in peanut plants when the CRCa/Cd was below 2000, and Ca2+ channels partially facilitate the entry of Cd2+ into peanut roots. Under normal Ca supply conditions, exogenous Ca reduced Cd accumulation in peanuts primarily through root cell wall fixation rather than ion channel competition. Our findings provide insights into the mechanism by which Ca alleviates the uptake and transfer of Cd in peanuts.

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

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

How does silicon alleviate Cd-induced phytotoxicity in barley, Hordeum vulgare L.?

Toxic heavy metal accumulation in edible plants has become a problem worth worrying about for human health. Cadmium is one of the most toxic metals presenting high bioavailability in the environment. The main route of transfer of Cd to humans is the consumption of contaminated food which suggests that reducing of Cd absorption by plants could reduce this risk. In this context, it was suggested that silicon supply would be able to limit the transfer of Cd to the plants. Thus, this work evaluated the effects of 0.5 mM Si on Cd absorption and accumulation in barley (Hordeum vulgare L.). Plants were grown hydroponically for 21 days in the presence of 0 and 15 μM Cd2+ combined or not with 0.5 mM Si. Analyses were related to growth and photosynthesis parameters, Cd accumulation in organs and Cd subcellular distribution in the shoots. Results showed that, under Cd alone, plants showed severe toxicity symptoms as chlorosis and necrosis and produced significantly less biomass as compared to control. 0.5 mM Si in the medium culture significantly reduced Cd-induced toxicity by mitigating symptoms and restoring growth, photosynthesis, and nutrition. Si also induced a significant reduction of Cd concentration in plants and changed its sub-cellular compartmentalization by enhancing fixation to cell walls and reducing the Cd concentration in the cytoplasmic and organelles fractions. These data suggest that the application of Si could significantly increase Cd tolerance and reduce the risk of the Cd accumulation in edible plants.

Physiology and transcriptomic analysis revealed the mechanism of silicon promoting cadmium accumulation in Sedum alfredii Hance

Silicon (Si) effectively promote the yield of many crops, mainly due to its ability to enhance plants resistance to stress. However, how Si helps hyperaccumulators to extract Cadmium (Cd) from soil has remained unclear. In this study, Sedum alfredii Hance (S. alfredii) was used as material to study how exogenous Si affected biomass, Cd accumulation, antioxidation, cell ultrastructure, subcellular distribution and changes in gene expression after Cd exposure. The study has shown that as Si concentration increases (1, 2 mM), the shoot biomass of plants increased by 33.1%-63.6%, the Cd accumulation increased by 31.9%-96.6%, and the chlorophyll, carotenoid content, photosynthetic gas exchange parameters significantly increased. Si reduced Pro and MDA, promoted the concentrations of SOD, CAT and POD to reduce antioxidant stress damage. In addition, Si promoted GSH and PC to chelate Cd in vacuoles, repaired damaged cell ultrastructure, improved the fixation of Cd and cell wall (especially in pectin), and reduced the toxic effects of Cd. Transcriptome analysis found that genes encoding Cd detoxification, Cd absorption and transport were up-regulated by Si supplying, including photosynthetic pathways (PSB, LHCB, PSA), antioxidant defense systems (CAT, APX, CSD, RBOH), cell wall biosynthesis such as pectinesterase (PME), chelation (GST, MT, NAS, GR), Cd absorption (Nramp3, Nramp5, ZNT) and Cd transport (HMA, PCR). Our result revealed the tentative mechanism of Si promotes Cd accumulation and enhances Cd tolerance in S. alfredii, and thereby provides a solid theoretical support for the practical use of Si fertilizer in phytoextraction.

Cadmium Stress Signaling Pathways in Plants: Molecular Responses and Mechanisms

Heavy metal (HM) pollution, specifically cadmium (Cd) contamination, is a worldwide concern for its consequences for plant health and ecosystem stability. This review sheds light on the intricate mechanisms underlying Cd toxicity in plants and the various strategies employed by these organisms to mitigate its adverse effects. From molecular responses to physiological adaptations, plants have evolved sophisticated defense mechanisms to counteract Cd stress. We highlighted the role of phytochelatins (PCn) in plant detoxification, which chelate and sequester Cd ions to prevent their accumulation and minimize toxicity. Additionally, we explored the involvement of glutathione (GSH) in mitigating oxidative damage caused by Cd exposure and discussed the regulatory mechanisms governing GSH biosynthesis. We highlighted the role of transporter proteins, such as ATP-binding cassette transporters (ABCs) and heavy metal ATPases (HMAs), in mediating the uptake, sequestration, and detoxification of Cd in plants. Overall, this work offered valuable insights into the physiological, molecular, and biochemical mechanisms underlying plant responses to Cd stress, providing a basis for strategies to alleviate the unfavorable effects of HM pollution on plant health and ecosystem resilience.

Graphitic carbon nitride nanosheets mitigate cadmium toxicity in Glycine max L. by promoting cadmium retention in root and improving photosynthetic performance

Cadmium (Cd) pollution poses a serious threat to plant growth and yield. Nanomaterials have shown great application potential for alleviation of Cd toxicity to plants. In this study, we applied graphitic carbon nitride nanosheets (g-C3N4 NSs) for alleviation of Cd-toxicity to soybean (Glycine max L.). The g-C3N4 NSs supplementation significantly improved plant growth and reduced oxidative damage in the Cd-toxicated soybean seedlings through hydroponic culture. Particularly, the g-C3N4 NSs dynamically regulated the root cell wall (RCW) components by increasing pectin content and modifying its demethylation via enhancing pectin methylesterase (PME) activity, therefore greatly enhanced stronger RCW-Cd retention (up to 82.8%) and reduced Cd migration to the shoot. Additionally, the g-C3N4 NSs reversed the Cd-induced chlorosis, increased photosynthetic efficiency because of enhancement in Fv/Fm ration, Y(II) and sugars content. These results provide new insights into the alleviation of Cd toxicity to plants by g-C3N4 NSs, and shed light on the application of low-cost and environmental-friendly carbon-based NMs for alleviating heavy metal toxicity to plants.

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

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

The adsorption-diffusion model and biomimetic simulation reveal the switchable roles of silicon in regulating toxic metal uptake in rice roots

Soil contamination by heavy metals has become a serious threat to global food security. The application of silicon (Si)-based materials is a simple and economical method for producing safe crops in contaminated soil. However, the impact of silicon on the heavy-metal concentration in plant roots, which are the first line in the chain of heavy-metal entering plants and causing stress and the main site of heavy-metal deposition in plants, remains puzzling. We proposed a process-based model (adsorption-diffusion model) to explain the results of a collection of 28 experiments on alleviating toxic metal stress in plants by Si. Then we evaluated the applicability of the model in Si-mitigated trivalent chromium (Cr[III]) stress in rice, taking into account variations in experimental conditions such as Cr(III) concentration, stress duration, and Si concentration. It was found that the adsorption-diffusion model fitted the experimental data well (R2 > 0.9). We also verified the binding interaction between Si and Cr in the cell wall using SEM-EDS and XPS. In addition, we designed a simplified biomimetic device that simulated the Si in cell wall to analyze the dual-action switch of Si from increasing Cr(III) adsorption to blocking Cr(III) diffusion. We found that the adsorption of Cr(III) by Si decreased from 58% to 7% as the total amount of Cr(III) increased, and finally the diffusion blocking effect of Si dominated. This study deepens our understanding of the role of Si in mitigating toxic metal stress in plants and is instructive for the research and use of Si-based materials to improve food security.

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

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

Role of phosphorus on the biogeochemical behavior of cadmium in the contaminated soil under leaching and pot experiments

Phosphorus (P) is involved in various biochemical reactions in plant growth, so it is beneficial to plants growing in soils contaminated by metals, including cadmium (Cd). However, few studies have reported on the mechanistic roles of P in mitigating Cd toxicity to ryegrass root, and especially in alleviating the disruption of the mitochondrial function of living cells. In this study, the physiological and biochemical mechanisms associated with ryegrass growth under various Cd and P treatments were investigated using leaching and pot systems. The concentration of Cd in soil leachates showed a significantly positive relationship with redox potential (P < 0.05), but negative relationship (P < 0.05) with leachate pH values and dissolved organic carbon (DOC), indicating that exogenous P addition (as H2PO4-) may decrease Cd leaching from contaminated soil. Compared to the control (without P addition), the cumulative Cd content was reduced by 53.3% and 64.5% in the soil leachate with exogenous P application (20 mg/L and 80 mg/L), respectively. Notably, application of P decreased the Cd concentrations in the symplastic fractions and increased the Cd concentrations in the apoplastic fractions in root tips, which may help to alleviate Cd stress to the protoplast. Moreover, exogenous P was found to play a positive role in mitochondrial function and Ca2+ variation in root cells under Cd stress, which provides novel insights into the mechanisms of exogenous P in alleviating plant Cd injury.

Unveiling mechanisms of silicon-mediated resistance to chromium stress in rice using a newly-developed hierarchical system

Silicon (Si) has been well-known to enhance plant resistance to heavy-metal stress. However, the mechanisms by which silicon mitigates heavy-metal stress in plants are not clear. In particular, information regarding the role of Si in mediating resistance to heavy-metal stress at a single cell level is still lacking. Here, we developed a hierarchical system comprising the plant, protoplast, and suspension cell subsystems to investigate the mechanisms by which silicon helps to alleviate the toxic effects of trivalent chromium [Cr(III)] in rice. Our results showed that in whole-plant subsystem silicon reduced shoot Cr(III) concentration, effectively alleviating Cr(III) stress in seedlings and causing changes in antioxidant enzyme activities similar to those observed at lower Cr(III) concentrations without silicon added. However, in protoplast subsystem lacking the cell wall, no silicon deposition occurred, leading to insignificant changes in cell survival or antioxidation processes under Cr(III) stress. Conversely, in suspension cell subsystem, silicon supplementation substantially improved cell survival and changes in antioxidant enzyme activities under Cr(III) stress. This is due to the fact that >95% of silicon was on the cell wall, reducing Cr(III) concentration in cells by 7.7%-10.4%. Collectively, the results suggested that the silicon deposited on the cell wall hindered Cr(III) bio-uptake, which consequently delayed Cr(III)-induced changes in antioxidant enzyme activities. This research emphasizes the significance of cell walls in Si-alleviated heavy-metal stress and deepens our understanding of silicon functioning in plants. Furthermore, the hierarchical system has great potential for application in studying the functioning of other elements in plant cell walls.

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

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

Amino acid application inhibits root-to-shoot cadmium translocation in Chinese cabbage by modulating pectin methyl-esterification

The exogenous application of amino acids (AAs) generally alleviates cadmium (Cd) toxicity in plants by altering their subcellular distribution. However, the physiological mechanisms underlying AA-mediated cell wall (CW) sequestration of Cd in Chinese cabbage remain unclear. Using two genotypes of Chinses cabbage, Jingcui 60 (Cd-tolerant) and 16-7 (Cd-sensitive), we characterized the root structure, subcellular distribution of Cd, CW component, and related gene expression under the Cd stress. Cysteine (Cys) supplementation led to a reduction in the Cd concentration in the shoots of Jingcui 60 and 16-7 by 65.09 % and 64.03 %, respectively. Addition of Cys alleviated leaf chlorosis in both cultivars by increasing Cd chelation in the root CW and reducing its distribution in the cytoplasm and organelles. We further demonstrated that Cys supplementation mediated the downregulation of PMEI1 expression and improving the activity of pectin methyl-esterase (PME) by 17.98 % and 25.52 % in both cultivars, respectively, compared to the Cd treatment, resulting in an approximate 12.00 %-14.70 % increase in Cd retention in pectin. In contrast, threonine (Thr) application did not significantly alter Cd distribution in the shoots of either cultivar. Taken together, our results suggest that Cys application reduces Cd root-to-shoot translocation by increasing Cd sequestration in the root CW through the downregulation of pectin methyl-esterification.

BcaSOD1 enhances cadmium tolerance in transgenic Arabidopsis by regulating the expression of genes related to heavy metal detoxification and arginine synthesis

Cadmium (Cd), which is a nonessential heavy metal element for organisms, can have a severe impact on the growth and development of organisms that absorb excessive Cd. Studies have shown that Brassica carinata, a semiwild oil crop, has strong tolerance to various abiotic stresses, and RNA-seq has revealed that the B. carinata superoxide dismutase gene (BcaSOD1) likely responds to Cd stress. To elucidate the BcaSOD1 function involved in tolerance of Cd stress, we cloned the coding sequences of BcaSOD1 from a purple B. carinata accession and successfully transferred it into Arabidopsis thaliana. The subcellular localization results demonstrated that BcaSOD1 was primarily located in the plasma membrane, mitochondria and nucleus. Overexpression of BcaSOD1 in transgenic Arabidopsis (OE) effectively decreased the toxicity caused by Cd stress. Compared to the WT (wild type lines), the OE lines exhibited significantly increased activities of antioxidant enzymes (APX, CAT, POD, and SOD) after exposure to 2.5 mM CdCl2. The Cd content of underground (root) in the OE line was dominantly higher than that in the WT; however, the Cd content of aboveground (shoot) was comparable between the OE and WT types. Moreover, the qRT‒PCR results showed that several heavy metal detoxification-related genes (AtIREG2, AtMTP3, AtHMA3, and AtNAS4) were significantly upregulated in the roots of OE lines under Cd treatment, suggesting that these genes are likely involved in Cd absorption in the roots of OE lines. In addition, both comparable transcriptome and qRT-PCR analyses revealed that exogenous BcaSOD1 noticeably facilitates detoxification by stimulating the expression of two arginine (Arg) biosynthesis genes (AtGDH1 and AtGDH2) while inhibiting the expression of AtARGAH1, a negative regulator in biosynthesis of Arg. The Arg content was subsequently confirmed to be significantly enhanced in OE lines under Cd treatment, indicating that BcaSOD1 likely strengthened Cd tolerance by regulating the expression of Arg-related genes. This study demonstrates that BcaSOD1 can enhance Cd tolerance and reveals the molecular mechanism of this gene, providing valuable insights into the molecular mechanism of Cd tolerance in plants.

The impacts of exogenous phosphorus on Cd absorption in perennial ryegrass root cell: Kinetic and mechanism study

Phosphorus (P) is critical to plants in metal-contaminated soils because it participates in various biochemical reactions during plant growth. However, the mechanisms of P in mitigating the toxicity of heavy metals to ryegrass root is still veiled. In this study, the physiological and biochemical dynamics of the ryegrass root under various cadmium (Cd) and P conditions were investigated in a hydroponic system. Cd stress decreased the length of the ryegrass root, but P application enhanced the root elongation to reduce the Cd concentration in the root. Both Cd and P dosages were positively correlated with hemicellulose 1 content, pectin content, and PME activity, while having a negative effect on cellulose content. Moreover, the addition of 80 mg L-1 P increased the contents of pectin and hemicellulose 1 by 2.5 and 5.8% even with 4 mg L-1 Cd. In addition, P supply increased pectin methylesterbase activity under Cd stress, which further changed the extra-cytoplasmic structures and cell wall composition. Thus, exogenous P promoted the immobilization of Cd onto the cell wall and protected protoplast primarily through indirectly regulating the binding capacity of the root cell wall for Cd.

Cadmium accumulation in brown rice (Oryza sativa L.) depends on environmental factors and nutrient transport: A three-year field study

Cadmium (Cd) accumulation in brown rice is a complex process in agroecosystems and is influenced by multiple factors, such as climate, soil properties, and nutrient transport. However, during the Cd transport process (soil-root-straw-brown rice), it remains unclear how Cd concentration in brown rice (BCd) is causal relationship to environmental factors and nutrient transport. The differences in precipitation, soil properties, nutrient transport, and Cd transport were studied through a three-year fixed-point field trial and linked them to the standard of Cd and nutrient absorption and transport processes. The results showed that the available Cd concentration (ACd), and BCd in 2020 were lower than those in 2019 and 2021, but monthly precipitation (MP) was higher in 2020 than in 2019 and 2021. The MP and niche metrics were significantly negatively associated with ACd and BCd. However, the relationship between the form and location of different nutrient elements and Cd in roots, Cd in straws, and BCd also varied during the transport of nutrient elements and Cd from soil to root to straw to brown rice. Structural equation modelling analysis showed that nitrogen (N 15.5 %), phosphorus (P 14.1 %), silicon (Si 4.2 %), and iron (Fe 7.6 %) transport were more closely related to BCd than to potassium (K), calcium (Ca), magnesium (Mg), and manganese (Mn). The increase in MP significantly inhibited the increase in BCd, whereas the MP led to a decrease in BCd by affecting the transport of N and Fe. Among them, Si, Fe, and BCd had indirect causal relationships, whereas N, P, and BCd had direct causal relationships. Particularly, P is a crucial nutrient in reducing BCd in the Cd transport process. Our results highlight a strong causal relationship between environmental factors and nutrient transport and BCd, and provide a theoretical basis for fertiliser application in Cd-contaminated agroecosystems.

Modulation of metal transporters, oxidative stress and cell abnormalities by synergistic application of silicon and titanium oxide nanoparticles: A strategy for cadmium tolerance in rice

Heavy metals, especially cadmium (Cd), cause severe toxicity symptoms in crop plants. Applying nanoparticles (NPs) as nano-fertilizers is a novel approach to mitigating plants' Cd stress. However, knowledge about the combinational use of silicon (Si) and titanium dioxide (TiO2) NPs to mitigate Cd stress, especially in rice, must be highlighted. TiO2-NPs (15 mg L-1) and Si-NPs (2.5 mM) were applied alone and in combination to rice plants grown without (control; no Cd stress) and with (100 μM) Cd concentration. Results revealed that compared to the control plants, root length, shoot length, shoot fresh weight, and root dry weight of rice seedlings were significantly decreased by 25.43%, 26.64%, 34.13%, and 29.87% under Cd exposure. However, the synergistic effect of TiO2- and Si-NPs increased rice plants' shoot length, root length, root dry weight, and shoot fresh weight by 24.62%, 29.81%, 36.16%, and 33.07%, respectively, under the Cd-toxicity. The concentration of malondialdehyde (MDA) and H2O2 were amplified due to Cd stress, which leads to damage to the subcellular structures. Si and TiO2-NPs co-application improved the anti-oxidative enzymatic activities (catalase, peroxidase, superoxide dismutase) and an elevated concentration of non-enzymatic glutathione in Cd-exposed rice. The Cd accumulation was condensed by 21.37% and 19.7% in the shoot, while 48.31% and 45.65% in root tissues under Si-NPs + Cd and TiO2-NPs + Cd treatments compared to Cd-alone treated seedlings, respectively. The expression patterns of metal transporters, such as OsNramp1 and OsHMA3, were the highest when rice plants were cultivated under Cd stress and significantly reduced when treated with sole and combined Si- and TiO2-NPs treatments. In conclusion, combining Si- and TiO2-NPs significantly improved the antioxidant enzymatic activities, chlorophyll contents, biomass production, and reduced cellular damage. Despite limitations, our findings guide future research, addressing risks, optimizing concentrations, and assessing long-term effects that can balance agricultural progress with environmental sustainability.

Differences of cadmium uptake and accumulation in roots of two maize varieties (Zea mays L.)

Different maize varieties respond differentially to cadmium (Cd) stress. As the first organ in contact with the soil, the response of the root is particularly important. However, the physiological mechanisms that determine the response are not well defined. Here, we compared the differences in Cd-induced related gene expression, ionic homeostasis, and ultrastructural changes in roots of Cd-tolerant maize variety (XR57) and Cd-sensitive maize variety (LY296), and assessed their effects on Cd uptake and accumulation. Our findings indicate that XR57 absorbed a significantly lower Cd than LY296 did, and that the expression levels of genes related to Cd uptake (ZmNRAMP5 and ZmZIP4) and efflux (ZmABCG4) in the root were consistent with the Cd absorption at the physiological levels. Compared with LY296, the lower Cd concentration in the roots of XR57 caused less interference with the ion balance. Transmission electron microscope images revealed that the roots from XR57 exposed to Cd had developed thicker cell walls than LY296. In addition, the large increase ZmABCC1 and ZmABCC2 expression levels in XR57 mediated the appearance of numerous electron-dense granules in the vacuoles present in the roots. As a result, the high Cd tolerance of XR57 is the result of a multi-level response that involves increased resistance to Cd uptake, a stronger capacity for vacuolar regionalization, and the formation of thicker cell walls. These findings may provide a theoretical basis for maize cultivation in Cd-contaminated areas.

Detoxification mechanisms of biochar on plants in chromium contaminated soil: Chromium chemical forms and subcellular distribution

The complete pathway of chromium (Cr) transfer from soil to plant tissues and subcellular components under biochar amendment remains to be quantified, as well as the involved diverse detoxification processes in roots and stems respectively. Pot experiments and quantitative analysis were conducted to investigate Cr fixation in soil amended with Enteromorpha prolifera-derived biochar and subsequent phytoprocesses (Cr uptake, transfer, and phytotoxicity) in cultivated Secale cereale L. (rye). The results indicated that adding 5-30 g kg^-1 of biochar increased the residual form of Cr (B4) in soil by 8-21% and decreased the bioavailable form of Cr (B1) by 9-29%. For Cr transferred to rye, Cr in the rye was mainly present in the low-toxicity bound state, with the acetic acid-extracted Cr (F4) (45-54%) in roots and the NaCl-extracted Cr (F3) (37-47%) in stems. The subcellular distribution of Cr in both roots and stems was predominantly in the cell wall and residues (T1), followed by the cytoplasm (T4). Partial least squares path model (PLS-PM) was used for quantifying the effect of biochar on the form changes and subcellular detoxification of Cr from soil to roots and stems to sub-cells. In soils, biochar reduced the bioavailability of Cr and decreased the transfer of Cr to rye. In plant roots, Cr was distributed mainly as low-toxicity phosphate complexes in cell walls and vacuoles in sub-cells (with the largest path coefficients of 0.90 and -0.91, respectively). In the stems, Cr was distributed mainly as proteins integrated into the cell walls and vacuoles. This was due to the difference in subcellular compartmentalization of detoxification in the roots and stems. These PLS-PM results provide new insights into the entire process of pollutant detoxification in complex environments.

From promoting aggregation to enhancing obstruction: A negative feedback regulatory mechanism of alleviation of trivalent chromium toxicity by silicon in rice

Trivalent chromium [Cr(III)] is a threat to the environment and crop production. Silicon (Si) has been shown to be effective in mitigating Cr(III) toxicity in rice. However, the mechanisms by which Si reduces Cr(III) uptake in rice are unclear. Herein, we hypothesized that the ability of Si to obstruct Cr(III) diffusion via apoplastic bypass is related to silicic acid polymerization, which may be affected by Cr(III) in rice roots. To test this hypothesis, we employed hydroponics experiments on rice (Oryza sativa L.) and utilized apoplastic bypass tracer techniques, as well as model simulations, to investigate 1) the effect of Si on Cr(III) toxicity and its obstruction capacity via apoplastic bypass, 2) the effect of Cr(III) on silicic acid polymerization, and 3) the relationship between the degree of silicic acid polymerization and its Cr(III) obstruction capacity. We found that Si reversed the damage caused by Cr(III) stress in rice. Si exerted an obstruction effect in the apoplast, significantly decreasing the share of Cr(III) uptake via the apoplastic bypass from 18% to 11%. Moreover, Cr(III) reduced silica particles' radii and increased Si concentration in roots. Modeling revealed that a 5-fold reduction in their radii decreased the diffusion of Cr(III) in apoplast by approximately 17%. We revealed that Cr(III) promoted silicic acid polymerization, resulting in the formation of a higher number of Si particles with a smaller radius in roots, which in turn increased the ability of Si to obstruct Cr(III) diffusion. This negative feedback regulatory mechanism is novel and crucially important for maintaining homeostasis in rice, unveiling the unique role of Si under Cr(III) ion stress and providing a theoretical basis for promoting the use of Si fertilizer in the field.

Silicon facilitated the physical barrier and adsorption of cadmium of iron plaque by changing the biochemical composition to reduce cadmium absorption of rice roots

Silicon effectively inhibits cadmium (Cd) uptake in rice, iron plaque on root surface was the primary link and first interface of Cd entering into rice root. To elucidate the mechanism of iron plaque under silicon treatment on root Cd uptake, the morphological characteristics of iron plaque, mechanisms of Cd adsorption of iron plaque and effect of iron plaque on Cd uptake by rice roots of Yuzhenxiang (YZX) and Xiangwanxian (XWX) rice varieties were studied by employing energy spectrum analysis technique, non-invasive micro-test technique, and isothermal-kinetic adsorption method. Scanning electron microscopy-X-ray energy dispersive (SEM-EDX) analysis showed that denser crystal structure of iron plaque was observed at Si treatment, silicon promoted the thickening of iron plaque and strengthened the isolation of iron plaque to Cd, which reduced the Cd content of white roots of YZX and XWX varieties by 30.2% and 20.9% respectively. However, the blocking effect of iron plaque on Cd was weakened under silicon treatment with iron plaque removed, Cd content in iron plaque of YZX and XWX cultivars was significantly decreased by 36.3% and 18.4%, Cd concentrations in white root and shoot was significantly increased, and the influxes of Cd²⁺ at elongation and maturation zone of root were increased in multiples. The results of adsorption test showed that the adsorption process of iron plaque was mainly a monolayer adsorption completed by boundary diffusion. The X-ray photoelectron spectroscopy (XPS) results demonstrated that silicon changed the biochemical composition of iron plaque and increased the density of the carbon-oxygen bound groups on iron plaque, which is the most likely reasons for the higher affinity of Cd adsorption ability of iron plaque observed in the silicon treated iron plaque. This study suggested the silicon-facilitated iron plaque have played critical effects in controlling the Cd accumulation in rice roots by changing the morphology and chemical composition of iron plaque.

Modifications in Ultrastructural Characteristics and Redox Status of Plants under Environmental Stress: A Review

The rate of global environmental change is unprecedented, with climate change causing an increase in the oscillation and intensification of various abiotic stress factors that have negative impacts on crop production. This issue has become an alarming global concern, especially for countries already facing the threat of food insecurity. Abiotic stressors, such as drought, salinity, extreme temperatures, and metal (nanoparticle) toxicities, are recognized as major constraints in agriculture, and are closely associated with the crop yield penalty and losses in food supply. In order to combat abiotic stress, it is important to understand how plant organs adapt to changing conditions, as this can help produce more stress-resistant or stress-tolerant plants. The investigation of plant tissue ultrastructure and subcellular components can provide valuable insights into plant responses to abiotic stress-related stimuli. In particular, the columella cells (statocytes) of the root cap exhibit a unique architecture that is easily recognizable under a transmission electron microscope, making them a useful experimental model for ultrastructural observations. In combination with the assessment of plant oxidative/antioxidative status, both approaches can shed more light on the cellular and molecular mechanisms involved in plant adaptation to environmental cues. This review summarizes life-threatening factors of the changing environment that lead to stress-related damage to plants, with an emphasis on their subcellular components. Additionally, selected plant responses to such conditions in the context of their ability to adapt and survive in a challenging environment are also described.

The mechanism of silicon on alleviating cadmium toxicity in plants: A review

Cadmium is one of the most toxic heavy metal elements that seriously threaten food safety and agricultural production worldwide. Because of its high solubility, cadmium can easily enter plants, inhibiting plant growth and reducing crop yield. Therefore, finding a way to alleviate the inhibitory effects of cadmium on plant growth is critical. Silicon, the second most abundant element in the Earth's crust, has been widely reported to promote plant growth and alleviate cadmium toxicity. This review summarizes the recent progress made to elucidate how silicon mitigates cadmium toxicity in plants. We describe the role of silicon in reducing cadmium uptake and transport, improving plant mineral nutrient supply, regulating antioxidant systems and optimizing plant architecture. We also summarize in detail the regulation of plant water balance by silicon, and the role of this phenomenon in enhancing plant resistance to cadmium toxicity. An in-depth analysis of literature has been conducted to identify the current problems related to cadmium toxicity and to propose future research directions.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

DISCUSSION

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

Melatonin reduces cadmium accumulation via mediating the nitric oxide accumulation and increasing the cell wall fixation capacity of cadmium in rice

Melatonin (MT) is participated in plants' response to cadmium (Cd) tolerance, although its work model remains elusive. Here, the function of MT in adjusting Cd accumulation in rice was investigated. 'Nipponbare' (Nip) was cultured in the -Cd (1/2 Kimura B), -Cd + MT (1/2 Kimura B with 1 μM MT), +Cd (1/2 Kimura B plus 1 μM Cd) and +Cd + MT (1/2 Kimura B with 1 μM Cd and 1 μM MT) nutrient solutions for 7 d. Cd markedly induced the endogenous MT accumulation in rice roots and shoots, even within 1 h. MT applied exogenously elevated the hemicelluloses level, which in turn increased the cell wall's binding capacity to Cd. Furthermore, MT applied exogenously down-regulated the transcription level of Natural Resistance-Associated Macrophage Protein 1 (OsNRAMP1), OsNRAMP5, a major facilitator superfamily gene (OsCd1), and IRON-REGULATED TRANSPORTER 1 (OsIRT1), all of which were responsible for Cd intake, thus less Cd was entered into roots. Moreover, MT applied exogenously also up-regulated transcription level of Cadmium accumulation in Leaf 1 (OsCAL1) and Heavy Metal ATPase 3 (OsHMA3), two genes both attributed to the decreased Cd accumulation in shoots through expelling Cd out of cells and chelating Cd in the vacuoles, respectively. In addition, MT applied exogenously further aggravated the production of nitric oxide (NO) that induced by Cd, while application of a NO donor-SNP mimicked this alleviatory effect of the MT, indicating MT decreased rice Cd accumulation relied on the accumulation of NO.

Co-application of combined amendment (limestone and sepiolite) and Si fertilizer reduces rice Cd uptake and transport through Cd immobilization and Si-Cd antagonism

Limestone and sepiolite combined amendment (LS) and silicon (Si) fertilizers are commonly applied for the remediation of Cd-polluted paddy soil. However, it is difficult to further decrease cadmium (Cd) accumulation in rice grains by the individual application of LS or Si fertilizer to heavily Cd-polluted paddy fields. Two seasons of continuous field experiments were conducted in heavily Cd-polluted soil to study how the co-application of LS and Si fertilizer (namely soil-applied Si and foliar-sprayed Si) influences Cd and Si bioavailability in soil and Cd uptake and transport in rice. The results indicated that LS co-applied with soil-applied Si fertilizer treatments can enhance pH, cation exchange capacity (CEC), and available Si content in soil by 0.56-1.26 units, 19.3%-57.2%, and 14.7%-58.9% (p < 0.05), respectively, and reduce the toxicity characteristic leaching procedure (TCLP) extractable Cd content in soil by 26.5%-49.8% (p < 0.05) relative to the control. Furthermore, the co-application of LS and soil and foliar-sprayed Si fertilizer treatments reduced the Cd content in brown rice by 18.8%-70.6% (p < 0.05) compared with the control. Particularly, the brown rice Cd content under the co-application treatment (4500 kg/ha of soil applied LS, 90 kg/ha of Si fertilizer, and 0.4 g/L of foliar-sprayed Si fertilizer) was below 0.20 mg/kg in both seasons. Meanwhile, the Si content in rice was considerably enhanced by LS co-applied with Si fertilizer and negatively (p < 0.05) correlated with the rice Cd content. Therefore, the reduction of Cd bioavailability in soil and the antagonistic effect between Cd and Si in rice might be the key factors regulating Cd accumulation in rice via the co-application of LS and Si fertilizer.

Exogenous silicon promotes cadmium (Cd) accumulation in Sedum alfredii Hance by enhancing Cd uptake and alleviating Cd toxicity

Soil Cadmium (Cd) pollution has become a serious environmental problem. Silicon (Si) plays key roles in alleviating Cd toxicity in plants. However, the effects of Si on mitigation of Cd toxicity and accumulation of Cd by hyperaccumulators are largely unknown. This study was conducted to investigate the effect of Si on Cd accumulation and the physiological characteristics of Cd hyperaccumulator Sedum alfredii Hance under Cd stress. Results showed that, exogenous Si application promoted the biomass, Cd translocation and concentration of S. alfredii, with an increased rate of 21.74-52.17% for shoot biomass, and 412.39-621.00% for Cd accumulation. Moreover, Si alleviated Cd toxicity by: (i) increasing chlorophyll contents, (ii) improving antioxidant enzymes, (iii) enhancing cell wall components (lignin, cellulose, hemicellulose and pectin), (iv) raising the secretion of organic acids (oxalic acid, tartaric acid and L-malic acid). The RT-PCR analysis of genes that involved in Cd detoxification showed that the expression of SaNramp3, SaNramp6, SaHMA2 and SaHMA4 in roots were significantly decreased by 11.46-28.23%, 6.61-65.19%, 38.47-80.87%, 44.80-69.85% and 33.96-71.70% in the Si treatments, while Si significantly increased the expression of SaCAD. This study expanded understanding on the role of Si in phytoextraction and provided a feasible strategy for assisting phytoextraction Cd by S. alfredii. In summary, Si facilitated the Cd phytoextraction of S. alfredii by promoting plant growth and enhancing the resistance of plants to Cd.

OsGLP participates in the regulation of lignin synthesis and deposition in rice against copper and cadmium toxicity

Copper (Cu) and cadmium (Cd) are common heavy metal pollutants. When Cd and excessive Cu accumulate in plants, plant growth is reduced. Our previous study showed that Germin-like proteins (GLPs), which exist in tandem on chromosomes, are a class of soluble glycoproteins that respond to Cu stress. In this study, hydroponic cultures were carried out to investigate the effect of GLP on Cd and Cu tolerance and accumulation in rice. The results showed that knockout of a single OsGLP8-2 gene or ten OsGLP genes (OsGLP8-2 to OsGLP8-11) resulted in a similar sensitivity to Cd and Cu toxicity. When subjected to Cu and Cd stress, the glp8-2 and glp8-(2-11) mutants displayed a more sensitive phenotype based on the plant height, root length, and dry biomass of the rice seedlings. Correspondingly, Cu and Cd concentrations in the glp8-2 and glp8-(2-11) mutants were significantly higher than those in the wild-type (WT) and OsGLP8-2-overexpressing line. However, Cu and Cd accumulation in the cell wall was the opposite. Furthermore, we determined lignin accumulation. The overexpressing-OsGLP8-2 line had a higher lignin accumulation in the shoot and root cell walls than those of the WT, glp8-2, and glp8-(2-11). The expression of lignin synthesis genes in the OsGLP8-2-overexpressing line was significantly higher than that in the WT, glp8-2, and glp8-(2-11). The SOD activity of OsGLP8-2, Diaminobe-nzidine (DAB), propidium iodide (PI) staining, and Malondialdehyde (MDA) content determination suggested that OsGLP8-2 is involved in heavy metal-induced antioxidant defense in rice. Our findings clearly suggest that OsGLPs participate in responses to heavy metal stress by lignin deposition and antioxidant defense capacity in rice, and OsGLP8-2 may play a major role in the tandem repeat gene clusters of chromosome 8 under heavy metal stress conditions.

Alleviation of Cd-polluted paddy soils through Si fertilizer application and its effects on the soil microbial community

In this study, the effects of slag-based Si fertilizers on Cd-polluted paddy soils, soil microbial diversity, and functional properties were evaluated through a long-term field experiment conducted in a double-rice cropping system in southern China. The results showed that soil pH significantly increased from 5.15 to 6.13 after seven years of Si fertilization. Cd accumulation in both the soil and rice plants were significantly decreased for all the Si fertilizers treatments. Treatments using Si fertilizer in powder form exhibited the best alleviation effects, where soil available Cd decreased from 0.50 mg kg^-1 to 0.43 mg kg^-1, and Cd accumulation in rice roots, straw, and grains decreased by 32.2 %, 57.2 %, and 45.5 %, respectively, than that in the control. Following Si application, the soil microbial richness and Shannon diversity increased from 6731 to 7549 and 7.12 to 7.28, respectively. Proteobacteria, Nitrospirae, and Gemmatimonadetes, were significantly enriched in the Si-treated samples, whereas Verrucomicrobia, Chlamydiia, Ktedonobacteria and Candidatus_Saccharibacteria exhibited opposite patterns. Bioinformatics analysis using phylogenetic investigation of communities by reconstruction of unobserved states tools revealed that the varied microbial community induced functional adaption of soil microorganisms involved in metabolism, genetic information processing, cellular processes, and environmental information processing. The soil pH, NH₄-N, and available Cd and Si contents were the key factors that best explained the variations in bacterial community composition among different treatments. Slag-based Si fertilizers are effective for Cd detoxication and can benefit the growth of rice plants throng the regulation of soil microorganisms.

Silicon modification improves biochar's ability to mitigate cadmium toxicity in tomato by enhancing root colonization of plant-beneficial bacteria

Modification of biochar, such as impregnation with minerals, can improve biochar's efficacy to mitigate heavy metal toxicity in plants. Biochar amendments can alter plant rhizosphere microbiome, which has profound effects on plant growth and fitness. Here, we tested whether rhizosphere microbiome is involved in the ability of silicon (Si)-modified biochar to mitigate cadmium toxicity in tomato (Solanum lycopersicum L.). We demonstrated that Si modification altered biochar's physico-chemical properties and enhanced its ability to mitigate cadmium toxicity in tomato. Particularly, the Si-modified biochar contained higher content of Si and increased plant-available Si content in the soil. The rhizosphere microbiome transplant experiment showed that changes in rhizosphere microbiome contributed to the mitigation of cadmium toxicity by biochar amendments. The raw biochar and Si-modified biochar differently altered tomato rhizosphere bacterial community composition. Both biochars, especially the Si-modified biochar, promoted specific bacterial taxa (e.g., Sphingomonas, Lysobacter and Pseudomonas spp.). Subsequent culturing found these promoted bacteria could mitigate cadmium toxicity in tomato. Moreover, both biochars stimulated tomato to recruit plant-beneficial bacteria with Si-modified biochar having stronger stimulatory effects, indicating that the positive effects of biochar on plant-beneficial bacteria was partially mediated via the host plant. Overall, Si modification enhanced biochar's ability to mitigate cadmium toxicity, which was linked to the stimulatory effects on plant-beneficial bacteria.

Three-season rotation of chicory-tobacco-peanut with high biomass and bioconcentration factors effectively remediates cadmium-contaminated farmland

Traditional phytoremediation is one approach to remediate heavy metal pollution. In developing countries, the key factor in promoting practical application of phytoremediation in polluted soils is selecting suitable plants that are tolerant to heavy metals and also produce products with economic value. Therefore, a field experiment was conducted with a three-season chicory-tobacco-peanut rotation to determine effects on remediation of cadmium (Cd)-contaminated farmland in China. All crops had strong Cd accumulation capacity, with bioconcentration factors of 6.61 to 11.97 in chicory, 3.85 to 21.61 in tobacco, and 1.36 to 7.0 in peanut. Yield of total dry biomass reached 32.4 t ha-1, and the Cd phytoextraction efficiency was 10.3% per year. Aboveground tissues of the three crops accounted for 83.9 to 91.2% of total biomass in the rotation experiment. Cd content in peanut grain and oil met the National Food Safety Standard of China (0.5 mg kg-1, GB 2762-2017) and the Food Contaminant Limit of the European Union (0.1 mg kg-1, 18,812,006). Therefore, in addition to phytoremediation of Cd-contaminated soils, the chicory-tobacco-peanut rotation system can also produce economic benefits for local farmers.

Effects of Cadmium on Root Morpho-Physiology of Durum Wheat

Durum wheat [Triticum turgidum L. subsp. durum (Desf.) Husn.] can accumulate a high level of Cd in grains with a significant variability depending on cultivars. Understanding how this toxic element is distributed in cereal tissues and grains is essential to improve the nutritional quality of cereal-based products. The main objective of this work was to investigate roots of durum wheat plants (cv. Iride) exposed to different Cd concentrations (0.5 and 5.0 μM) to identify the mechanisms involved in Cd management. Results showed that the root morphology was altered by Cd treatment both at macroscopic (increased number of tips and primary root length) and ultrastructural levels (cell membrane system damaged, cell walls thickened and enriched in suberin). On the other side, Cd was localized in vesicles and in cell walls, and the metal colocalized with the phytosiderophore nicotianamine (NA). Overall, data suggest that Cd is chelated by NA and then compartmentalized, through vesicular trafficking, in the root thickened walls reducing Cd translocation to the aerial organs of the plant.

Exogenous proline mitigates toxic effects of cadmium via the decrease of cadmium accumulation and reestablishment of redox homeostasis in Brassica juncea

BACKGROUND

As a vital osmoticum, proline has an important role in enhancing the tolerance of plants to environmental stress. It is unclear whether the application of exogenous proline can improve the tolerance of Brassica juncea to cadmium (Cd).

RESULTS

This study investigated the effects of different concentrations of proline (20, 40, 60, 80, and 100 mg/L) under Cd stress at different times (0 d, 2 d, and 7 d) on the growth and physiology of B. juncea. Treatment with exogenous proline not only increased the content of proline in B. juncea but also alleviated Cd-induced seedling growth inhibition via the maintenance of higher photosynthetic pigment content and cell viability and a decrease in the content of Cd. Moreover, it increased the activities of antioxidant enzymes and the glutathione/glutathione disulfide ratio to reduce the accumulation of reactive oxygen species. Compared with other concentrations, 60 mg/L of exogenous proline was the most effective at mitigating Cd toxicity in B. juncea.

CONCLUSIONS

Exogenous proline treatment enhanced the tolerance to Cd via a decrease in Cd accumulation and reestablishment of the redox homeostasis in B. juncea.