A hemicellulose-bound form of silicon inhibits cadmium ion uptake in rice (Oryza sativa) cells

Rare earth elements detoxification mechanism in the hyperaccumulator Dicranopteris linearis: [silicon-pectin] matrix fixation

Dicranopteris linearis is the best-known hyperaccumulator species of rare earth elements (REEs) and silicon (Si), capable of dealing with toxic level of REEs. Hence, this study aimed to clarify how D. linearis leaves cope with excessive REE stress, and whether Si plays a role in REE detoxification. The results show that lanthanum (La - as a representative of the REEs) stress led to decreased biomass and an increase of metabolism related to leaf cell wall synthesis and modification. However, the La stress-induced responses, especially the increase of pectin-related gene expression level, pectin polysaccharides concentration, and methylesterase activity, could be mitigated by Si supply. Approximately 70% of the Si in D. linearis leaves interacted with the cell walls to form organosilicon Si-O-C linkages. The Si-modified cell walls contained more hydroxyl groups, leading to a more efficient REE retention compared to the Si-free ones. Moreover, this [Si-cell wall] matrix increased the pectin-La accumulation capacity by 64%, with no effect on hemicellulose-La and cellulose-La accumulation capacity. These results suggest that [Si-pectin] matrix fixation is key in REE detoxification in D. linearis, laying the foundation for the development of phytotechnological applications (e.g., REE phytomining) using this species in REE-contaminated sites.

Cadmium pollution leads to selectivity loss of glutamate receptor channels for permeation of Ca2+/Mn2+/Fe2+/Zn2+ over Cd2+ in rice plant

The selective permeation of glutamate receptor channels (GLRs) for essential and toxic elements in plant cells is poorly understood. The present study found that the ratios between cadmium (Cd) and 7 essential elements (i.e., K, Mg, Ca, Mn, Fe, Zn and Cu) in grains and vegetative organs increased significantly with the increase of soil Cd levels. Accumulation of Cd resulted in the significant increase of Ca, Mn, Fe and Zn content and the expression levels of Ca channel genes (OsCNGC1,2 and OsOSCA1.1,2.4), while remarkable reduction of glutamate content and expression levels of GLR3.1-3.4 in rice. When planted in the same Cd-polluted soil, mutant fc8 displayed significantly higher content of Ca, Fe, Zn and expression levels of GLR3.1-3.4 than its wild type NPB. On the contrary, the ratios between Cd and essential elements in fc8 were significantly lower than that in NPB. These results indicate that Cd pollution may damage the structural integrity of GLRs by inhibiting glutamate synthesis and expression levels of GLR3.1-3.4, which leads to the increase of ion influx but the decrease of preferential selectivity for Ca²⁺/ Mn²⁺/ Fe²⁺/ Zn²⁺ over Cd²⁺ through GLRs in rice cells.

New insight into the mechanisms of preferential encapsulation of metal(loid)s by wheat phytoliths under silicon nanoparticle amendment

Silicon nanoparticles (SiNPs) have been widely used to immobilize toxic trace metal(loid)s (TTMs) in contaminated croplands. However, the effect and mechanisms of SiNP application on TTM transportation in response to phytolith formation and phytolith-encapsulated-TTM (PhytTTM) production in plants are unclear. This study demonstrates the promotion effect of SiNP amendment on phytolith development and explores the associated mechanisms of TTM encapsulation in wheat phytoliths grown on multi-TTM contaminated soil. The bioconcentration factors between organic tissues and phytoliths of As and Cr (> 1) were significantly higher than those of Cd, Pb, Zn and Cu, and about 10 % and 40 % of the total As and Cr that bioaccumulated in wheat organic tissues were encapsulated into the corresponding phytoliths under high-level SiNP treatment. These observations demonstrate that the potential interaction of plant silica with TTMs is highly variable among elements, with As and Cr being the two most strongly concentrated TTMs in the phytoliths of wheat treated with SiNPs. The qualitative and semi-quantitative analyses of the phytoliths extracted from wheat tissues suggest that the high pore space and surface area (≈ 200 m² g^-1) of phytolith particles could have contributed to the embedding of TTMs during silica gel polymerization and concentration to form PhytTTMs. The abundant SiO functional groups and high silicate-minerals in phytoliths are dominant chemical mechanisms for the preferential encapsulation of TTMs (i.e., As and Cr) by wheat phytoliths. Notably, the organic carbon and bioavailable Si of soils and the translocation of minerals from soil to plant aerial parts can impact TTM sequestration by phytoliths. Thus, this study has implications for the distribution or detoxification of TTMs in plants via preferential PhytTTM production and biogeochemical cycling of PhytTTMs in contaminated cropland following exogenous Si supplementation.

Rare Earth Elements (REEs) Adsorption and Detoxification Mechanisms in Cell Wall Polysaccharides of Phytolacca americana L

The cell wall (CW) is critical for the accumulation of heavy metals in metal-tolerant plants. Polysaccharides, the main component of the CW, contribute significantly to the immobilization of heavy metals. However, the mechanisms of rare earth elements (REEs) adsorption and detoxification by polysaccharides in the cell walls of Phytolacca americana L. (P. americana) remain unclear. In this work, we explored the binding sites of REEs and the modifications to polysaccharides in the cell walls of roots and leaves in P. americana, in order to elucidate the adsorption and fixation mechanism of REEs by the cell wall. Our findings indicated that up to 40.7% and 48.1% of cell-wall-bound REEs were present in the root and leaf pectin, respectively. The removal of pectin led to a 39.8% and 23.6% decrease in the maximum adsorption of REEs in the CW, suggesting that pectin was the main binding site for REEs in the cell walls of P. americana. Hydroxyl (-OH) and carboxyl (-COOH) groups in the cell wall interacted mainly with REEs ions under stress conditions, which played a key role in REEs binding. An obvious REEs fractionation was found during the various fractions of the CW, and all fractions of the root cell wall were enriched with HREEs, whereas all fractions of the leaf cell wall were enriched with LREEs. Moreover, P. americana modulated cell wall composition in reaction to REEs stress. In conclusion, cell wall pectin is the main binding site of REEs, and the functional groups on the cell wall play a significant role in the binding of REEs. At the same time, plants can control the selective adsorption and fixation of REEs by adjusting the composition of cell walls. This study offers valuable insights into the mechanisms of REEs adsorption and fixation in cell walls of P. americana, contributing to a theoretical basis for the bioremediation of REEs pollution.

Manganese and copper additions differently reduced cadmium uptake and accumulation in dwarf Polish wheat (Triticum polonicum L.)

This study investigated the effects of manganese (Mn) and copper (Cu) on dwarf Polish wheat under cadmium (Cd) stress by evaluating plant growth, Cd uptake, translocation, accumulation, subcellular distribution, and chemical forms, and the expression of genes participating in cell wall synthesis, metal chelation, and metal transport. Compared with the control, Mn deficiency and Cu deficiency increased Cd uptake and accumulation in roots, and Cd levels in root cell wall and soluble fractions, but inhibited Cd translocation to shoots. Mn addition reduced Cd uptake and accumulation in roots, and Cd level in root soluble fraction. Cu addition did not affect Cd uptake and accumulation in roots, while it caused a decrease and an increase of Cd levels in root cell wall and soluble fractions, respectively. The main Cd chemical forms (water-soluble Cd, pectates and protein integrated Cd, and undissolved Cd phosphate) in roots were differently changed. Furthermore, all treatments distinctly regulated several core genes that control the main component of root cell walls. Several Cd absorber (COPT, HIPP, NRAMP, and IRT) and exporter genes (ABCB, ABCG, ZIP, CAX, OPT, and YSL) were differently regulated to mediate Cd uptake, translocation, and accumulation. Overall, Mn and Cu differently influenced Cd uptake and accumulation; Mn addition is an effective treatment for reducing Cd accumulation in wheat.

Silicon fertilization enhances the resistance of tobacco plants to combined Cd and Pb contamination: Physiological and microbial mechanisms

Remediation of soil contaminated with cadmium (Cd) and lead (Pb) is critical for tobacco production. Silicon (Si) fertilizer can relieve heavy metal stress and promote plant growth, however, it remains unknown whether fertilization with Si can mitigate the effects of Cd and Pb on tobacco growth and alter microbial community composition in polluted soils. Here we assessed the effect of two organic (OSiFA, OSiFB) and one mineral Si fertilizer (MSiF) on Cd and Pb accumulation in tobacco plants, together with responses in plant biomass, physiological parameters and soil bacterial communities in pot experiments. Results showed that Si fertilizer relieved Cd and Pb stress on tobacco, thereby promoting plant growth: Si fertilizer reduced available Cd and Pb in the soil by 37.3 % and 28.6 %, respectively, and decreased Cd and Pb contents in the plant tissue by 42.0-55.5 % and 17.2-25.6 %, resulting in increased plant biomass by 13.0-30.5 %. Fertilization with Si alleviated oxidative damage by decreasing malondialdehyde content and increasing peroxidase and ascorbate peroxidase content. In addition, Si fertilization increased photosynthesis, chlorophyll and carotenoid content. Microbial community structure was also affected by Si fertilization. Proteobacteria and Actinobacteria were the dominant phylum in the Cd and Pb contaminated soils, but Si fertilization reduced the abundance of Actinobacteria. Si fertilization also altered microbial metabolic pathways associated with heavy metal resistance. Together, our results suggest that both organic and mineral Si fertilizers can promote tobacco growth by relieving plant physiological stress and favoring a heavy metal tolerant soil microbial community.

Comparative Responses of Silicon to Reduce Cadmium and Enrich Selenium in Rice Varieties

Cadmium (Cd), a highly toxic heavy metal for crops in China, poses a significant threat to rice cultivation. It is crucial to identify the genotypes with robust resistance to heavy metals, including Cd, in rice. The experiment was conducted to examine the mitigation effect of silicon (Si) on Cd toxicity levels in Se-enriched Z3055B and non-Se-enriched G46B rice genotypes. A basal dose of Si improved the growth and the quality of rice significantly by reducing the Cd content in rice roots, stems, leaves and grains and increased the yield, biomass and selenium (Se) content of brown rice in both genotypes. Additionally, Se content in brown rice and polished rice was notably higher in Se-enriched rice than in non-Se-enriched rice, with the highest amount at 0.129 mg/kg and 0.085 mg/kg, respectively. The results demonstrated that a basal fertilizer concentration of 30 mg/kg of Si was more effective in reducing Cd transport from roots to shoots in Se-enriched rice than in non-Se-enriched rice genotypes. Therefore, it can be concluded that Se-enriched rice genotypes are a viable option for food crop production in Cd-contaminated areas.

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.

Remediation effects and mechanisms of typical minerals combined with inorganic amendment on cadmium-contaminated soil: a field study in wheat

The remediation of cadmium (Cd)-contaminated soil has gained much attention recently because Cd in soil threatens human health through the food chain. Although tremendous progress has been made in the remediation of Cd-contaminated soil in rice acid soil system, the mechanism and effects of Cd-contaminated soil remediation under these amendments in wheat weak alkaline soil are still limited. In this study, the remediation effect and related mechanism of Cd in weakly alkaline soil were carried out using zeolite, diatomite, and sodium bentonite as the main remediation components, supplemented by calcium dihydrogen phosphate and fulvic acid. The results of field experiments showed that the concentration of Cd reduced by 27.3 ~ 31.2% in rhizosphere soil and 34.3 ~ 54.2% in non-rhizosphere soil, and the maximum reduction rate of Cd concentration in wheat grain was 25.5%. The main factors affecting the concentration of Cd in wheat grains include the change in exchangeable Cd, the absorption capacity of wheat root, and the inhibitory effect on Cd transport from stem to grain in this paper. In general, this work provides a new potential management feasible pathway to alleviate the Cd toxicity of weakly alkaline soil and wheat grain.

Wheat Selenium-binding protein TaSBP-A enhances cadmium tolerance by decreasing free Cd2+ and alleviating the oxidative damage and photosynthesis impairment

Cadmium, one of the toxic heavy metals, robustly impact crop growth and development and food safety. In this study, the mechanisms of wheat (Triticum aestivum L.) selenium-binding protein-A (TaSBP-A) involved in response to Cd stress was fully investigated by overexpression in Arabidopsis and wheat. As a cytoplasm protein, TaSBP-A showed a high expression in plant roots and its expression levels were highly induced by Cd treatment. The overexpression of TaSBP-A enhanced Cd-toleration in yeast, Arabidopsis and wheat. Meanwhile, transgenic Arabidopsis under Cd stress showed a lower H2O2 and malondialdehyde content and a higher photochemical efficiency in the leaf and a reduction of free Cd2+ in the root. Transgenic wheat seedlings of TaSBP exhibited an increment of Cd content in the root, and a reduction Cd content in the leaf under Cd2+ stress. Cd2+ binding assay combined with a thermodynamics survey and secondary structure analysis indicated that the unique CXXC motif in TaSBP was a major Cd-binding site participating in the Cd detoxification. These results suggested that TaSBP-A can enhance the sequestration of free Cd2+ in root and inhibit the Cd transfer from root to leaf, ultimately conferring plant Cd-tolerance via alleviating the oxidative stress and photosynthesis impairment triggered by Cd stress.

Organosilicon and inorganic silica inhibit polystyrene nanoparticles uptake in rice

Nanoplastics (NPs) have become an emerging global environmental problem, and the toxicity of polystyrene nanoplastics (PS-NPs) in rice plants has received widespread attention. However, few studies have focused on silicon (Si)-mediated interactions between PS-NPs and rice. Thus, two forms of Si (organosilicon/inorganic silica) treated rice cells were exposure of positively or negatively charged NPs, PS-NH₂ and PS-COOH, to evaluate the effects of Si for defense against PS-NPs toxicity in rice. The result showed PS-NH₂ nanoparticles were accumulated at relatively low levels in cells compared with that of PS-COOH, but induced a higher accumulation of hydrogen peroxide (H₂O₂) and superoxide radicals (O₂^•-). However, both organosilicon and inorganic silica can generate more negative potential on the surfaces of cell wall to absorb large numbers of positively charged PS-NH₂. In addition, they can prevent the uptake of both PS-NH₂ and PS-COOH through reducing the porosity on the surface of the cell walls. These finally alleviated the toxicity of oxidative stress caused by PS-NPs and improved the viability of rice cells. Our findings demonstrated the significant contribution of Si in combating PS-NPs in rice.

The effects of salinity and pH variation on hyperaccumulator Bidens pilosa L. accumulating cadmium with dynamic and real-time uptake of Cd2+ influx around its root apexes

Bidens pilosa L. has been confirmed to be a potential Cd hyperaccumulator by some researchers, but the dynamic and real-time uptake of Cd²⁺ influx by B. pilosa root apexes was a conundrum up to now. The aim of our study was to investigate the effects of salinity and pH variations on the characteristics of Cd²⁺ influx around the root apexes of B. pilosa. The tested seedlings of B. pilosa were obtained by sand culture experiments in a greenhouse after 1 month from germination, and the Cd²⁺ influxes from the root apex of B. pilosa under Cd treatments with different salinity and pH levels were determined with application of non-invasive micro-test technology (NMT). The results showed that Cd²⁺ influxes at 300 μm from the root tips decreased under Cd treatments with 5 mM and 10 mM NaCl, as compared to Cd stress alone. However, Cd treatments with 2.5 mM NaCl had little effect on the net Cd²⁺ influxes, as compared to Cd treatments alone. Importantly, Cd treatments at pH = 4.0 markedly increased Cd²⁺ influxes in roots, and Cd treatment at pH = 7.0 had no significant effect on the net Cd²⁺ influxes compared to Cd treatments at pH = 5.5. Results also showed that Cd treatments with 10 mM NaCl significantly decreased concentrations of chlorophyll (Chl) a and b in leaves and root vigor of B. pilosa relative to Cd treatments alone, while there were no significant differences between Cd treatments with 2.5 mM NaCl and Cd treatments alone. But root vigor was inhibited significantly under Cd treatments with 5 mM and 10 mM NaCl. A significant increase of root vigor was observed in Cd treatments at pH = 4.0, as compared to pH = 5.5. The Cd treatments with high and medium concentrations of NaCl inhibited the uptake of Cd by B. pilosa roots and affected the Chl and root vigor further. But the Cd treatments at pH = 4.0 could promote the Cd uptake and root vigor. Our results revealed the uptake mechanisms of B. pilosa as a potential phytoremediator under different salinity and pH levels combined with Cd contamination and provided a new idea for screening ideal hyperaccumulator and constructing evaluation system.

Biochar application enhanced rice biomass production and lodging resistance via promoting co-deposition of silica with hemicellulose and lignin

Biochar, an environmentally friendly soil amendment, is created via a series of thermochemical processes from carbon-rich organic matter. The biochar addition enhances soil characteristics dramatically and increases crop growth and yields. However, the mechanism by which biochar improves plant lodging resistance, which is heavily influenced by cell walls, remains unknown. Three rice cultivars were grown in an experimental field provided with four concentrations of biochar (10, 20, 30, 40 t ha^-1). The biochar application enhanced biomass production and lodging resistance in all three cultivars by up to 29 % and 22 %, respectively, with the largest improvement at a biochar application rate of 30 t ha^-1. Biochar application significantly enhanced stem cell wall-related characteristics, with an increase in stem breaking force, wall thickness, and plumpness of 52 %, 32 %, and 21 %, respectively, which are suggested to be major contributors to enhanced lodging resistance and biomass yield. Notably, cell wall composition and silica content analysis indicated a significant increase in hemicellulose, lignin, and silica content in biochar-treated samples up to 36 %, 13 %, and 58 %, respectively, when compared to plants not treated with biochar. Integrative analysis suggested that silica, hemicellulose, and lignin were co-deposited in cell walls, which influenced biomass production and lodging resistance. Furthermore, the transcriptome profile revealed that biochar application increased the expression of genes involved in biomass production, cell wall formation, and silica deposition. This study suggests that biochar application might improve both biomass production and lodging resistance by promoting the co-deposition of silicon with hemicellulose and lignin in cell walls.

Differences in the response mechanism of cadmium uptake, transfer, and accumulation of different rice varieties after foliar silicon spraying under cadmium-stressed soil

Most studies have shown that foliar silicon (Si) spraying can reduce the risk of rice quality safety caused by cadmium (Cd) contamination. However, it has recently been found that different rice varieties have different responses to Si. Therefore, we selected six rice varieties (YHSM, YXY1179, YXYLS, JLK1377, MXZ2, and YLY900) to compare the differences in the effects of leaf spray on Cd accumulation among different varieties. According to the change in Cd content in brown rice after Si application, the six rice varieties were divided into two types: Si-inhibited varieties (JLY1377, MXZ2, LY900, and YXYLS) and Si-stimulated varieties (WY1179 and YHSM). For Si-inhibited varieties, the Cd content of rice was reduced by 13.5%-65.7% after Si application. At the same time, the Cd content of the root, stem, leaf, panicle, and glume decreased to different degrees, the Cd content of the cell wall component increased by 2.2%-37.6%, the extraction state of Cd with strong mobile activity (ethanol-extracted and deionized water-extracted) was changed to the extraction state of Cd with weak mobile activity (acetic acid-extracted and hydrochloric acid-extracted), and the upward transport coefficient of different parts was reduced. For Si-stimulated varieties, Si application increased the Cd content of rice by 15.7%-24.1%. At the same time, the cell soluble component Cd content significantly increased by 68.4%-252.4% and changed the weakly mobile extraction state Cd to the strong mobile extraction state, increasing the upward transport coefficient of different sites. In conclusion, different rice varieties have different responses to Si. Foliar Si spraying inhibits the upward migration of Cd of Si-inhibited varieties, thereby reducing the Cd content of rice, but it has the opposite effect on Si-stimulated varieties. This result reminds us that we need to consider the difference in the effect of varieties in the implementation of foliar Si spraying in remediation of Cd-contaminated paddy fields.

Silicon reduces zinc absorption and triggers oxidative tolerance processes without impacting growth in young plants of hemp (Cannabis sativa L.)

Hemp (Cannabis sativa L.) is a promising crop for non-food agricultural production on soils contaminated by moderate doses of heavy metals, while silicon, as a beneficial element, is frequently reported to improve stressed plant behavior. Using a hydroponic system, plants of Cannabis sativa (cv. Santhica 27) were exposed for 1 week to 100 µM Zn in the presence or absence of 2 mM Si. Zinc accumulated in all plant organs but was mainly sequestered in the roots. Additional Si reduced Zn absorption but had no impact on Zn translocation. Zn accumulation had a slight negative impact on leaf number, stem length, and chlorophyll content, and additional Si did not mitigate these symptoms. Exogenous Si reduced the Zn-induced membrane lipid peroxidation (assessed by malondialdehyde quantification) and increased the total antioxidant activities estimated by the FRAP index. In the absence of Si, leaf phytochelatin and total glutathione were the highest in Zn-treated plants and Si significantly decreased their concentrations.

Foliar application of three dithiocarbamates inhibits the absorption and accumulation of Cd in wheat

In cadmium (Cd) contaminated farmland soil, antagonism between elements can be used to control the absorption and accumulation of Cd in crops through the external application of zinc (Zn) and manganese (Mn). Dithiocarbamates (DTCs) are highly effective fungicides commonly used in farmlands, and DTCs are rich in Zn and Mn. We selected three representative DTCs (propineb, mancozeb, and zineb) for a field experiment in Henan province, China. The effects of DTC on Cd absorption and accumulation in wheat and the interaction of Zn, Mn, and Cd in wheat after spraying of DTC were studied using different application times at the heading stage. The results showed that after foliar spraying of DTCs according to pesticide application requirements, wheat yield was not affected. The Zn and Mn contents in grains increased, with the highest increases being 19.2% and 12.4%, respectively. Zn and Cd as well as Mn and Cd were antagonistic in wheat, and the transport of Cd from soil to root and from husk to grain was inhibited. The bioconcentration factor (grains/soil) decreased from 1.3 to 0.68 and the translocation factor (grains/husks) decreased from 0.76 to 0.35. The Cd content in grains decreased by 60.4%, 52.8%, and 25.6% with mancozeb, propineb, and zineb applications, respectively, and the Cd reduction effect of spraying DTCs twice was better than that of spraying DTCs once and thrice. The results show that DTCs application could reduce the Cd content in wheat grains and realize the dual effects of crop disease prevention and Cd reduction.

The Cd sequestration effects of rice roots affected by different Si management in Cd-contaminated paddy soil

The application of exogenous silicon (Si) reportedly is one of the eco-friendly practices to mitigate cadmium (Cd) phytotoxicity and regulate the chemical behaviors of Cd in the soil-rice system. But the efficiency of Si on the Cd retention by rice root varies with the Si fertilizer management. The objective of this paper was to interpret the differences in Cd immobilization by rice roots and relevant mechanisms under different ways of Si application (T-Si, supplied at transplanting stage; TJ-Si, split at transplanting and jointing stage with the ratio of 50 % to 50 %; J-Si, supplied at jointing stage and CK, none of Si application) in Cd-contaminated paddy soils. The results showed that the Cd-retention capacity of rice root was increased by 0.60 % ~ 3.06 % under different Si management when compared to CK. The concentrations of monosilicic acid in soils and in apoplast and symplast of roots were increased significantly by Si application, while Cd concentrations in apoplast and symplast of root were decreased by 28.50 % (T-Si), 40.64 % (TJ-Si) and 30.26 % (J-Si), respectively. The distribution of Cd in rice cell wall was increased significantly by TJ-Si. The Cd concentrations of inert fractions (F3, F4 and F6) in root of TJ-Si were raised obviously. Si application downregulated the expression of OsIRT2 and OsNramp5 while upregulated OsHMA3, and the expression of OsHMA3 treated by TJ-Si was obviously higher than CK and J-Si. The distributions of the passive Cd in roots bound with thiol compounds (NPT, GSH and PCs) and polysaccharide components (pectin, hemicelluloses 1 and hemicellulose 2) were raised much more by TJ-Si than by T-Si and J-Si. On the whole, compared with T-Si and J-Si, TJ-Si could more easily replenish soil available Si and enhance Cd sequestration in roots as the result of the decrease of Cd transport factor in roots. This study unravels some mechanisms about different Si management on increasing Cd retention and decreasing Cd migration in rice roots, and TJ-Si is worthy of being recommended.

Comparative physiological and soil microbial community structural analysis revealed that selenium alleviates cadmium stress in Perilla frutescens

Cadmium (Cd) toxicity not only affects plant growth and development, but also affects human health through the food chain. Several studies have demonstrated that Selenium (Se) alleviates Cd stress in plants; however, whether and how Se-alleviated Cd stress by regulating the structure of soil microbial community remain largely unclear. Here, we investigated the alleviating effects of exogenous applied Se (foliar spraying or root application) on plant growth under Cd stress in perilla (Perilla frutescens L.) by measuring the biomass, photosynthetic fluorescence parameters, root cell wall components and soil microbial community structure and diversity. Under Cd stress, perilla seedlings supplemented with Se increased chlorophyll content. Foliar spraying Se increased the levels of relative chlorophyll content (ΦII), photosynthetic system II (Φ_PSII) and electron transport rate (ETR) in perilla leaves under Cd stress; while, root application of Se increased the levels of photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), water use efficiency (WUE) and stomatal limitation value (Ls) under Cd stress. Compared with Cd toxicity alone, root application of Se increased the contents of hemicellulosic 1 and hemicellulosic 2 in the cell wall of perilla roots. Cd toxicity or root application of Se did not affect soil bacterial community diversity. Root application of Se increased the relative abundance of Proteobacteria, Bacteroidetes, Fibrobacteres, Sphingomonas and Nitrosospira in Cd-contaminated soil, and thereby improving soil microbial community structure, finally promoting the growth of perilla seedlings.

Under cadmium stress, silicon has a defensive effect on the morphology, physiology, and anatomy of pea (Pisum sativum L.) plants

Soil pollution with cadmium (Cd) is a serious threat to plant growth and development. On the other hand, silicon (Si) can support plants to cope with Cd stress. However, the Cd stress mitigating impact of Si reduction in pea (Pisum sativum L.) is not known. The objective of this study is to see if and how Si can reduce Cd toxicity. To the end, a greenhouse pot experiment was performed twice during the 2018/2019 and 2019/2020 seasons to investigate the effect of Si on the growth, anatomy, and biochemistry of Cd stressed peas plants. Cd exposure increased the contents of Cd ions in the root and shoot of pea plants. Consequentially, Cd accumulation in pea tissue significantly reduced plant growth i.e., plant height, leaf area, and shoot and root dry weights. The effect of Cd was concentration-dependent, where at low concentration (50 mg/kg soil), the plant height was 94.33 and 97.33cm and at high concentration (100 mg/kg soil), it was 89.0 and 91.0 cm in the two seasons, respectively. This growth reduction can be explained by the decrease in plants' photosynthesis, whereas plants exposed to Cd toxicity had lower chlorophyll levels. At the anatomy level, high Cd concentrations resulted in anatomical abnormalities such as an unusual vascular system, abnormal lignification in the pith parenchyma, and enlarged cortical cells. Moreover, all Cd concentrations resulted in a highly significant decrease in stomatal area and stomatal density (the number of stomata per mm²). In addition to growth inhibition, Cd-induced oxidative damage to pea plants as indicated by increased hydrogen peroxide (H₂O₂) and Malondialdehyde (MDA) levels. To reduce stress toxicity, plants treated with Cd at 50 and 100 (mg/kg) showed a significant increase in antioxidant capacity. Peroxidase (POD) enzyme activity was significantly increased by 41.26%, 28.64%, 77.05%, and 60.77% in both seasons, respectively. Si at 300 ppm under Cd (100 mg/kg) stress conductions considerably reduced (MDA) contents by 29.02% and 29.12%, in the two seasons, respectively. The findings pointed out that Si's ability to protect pea against the oxidative stress caused by Cd toxicity.

Gibberellic acid alleviates cadmium toxicity in rice by regulating NO accumulation and cell wall fixation capacity of cadmium

Gibberellic acid (GA) has been implicated in the response of plants to cadmium (Cd) stress, but the underlying mechanism remains unclear. In the present study, our aim was to confirm the role of GA in regulating the accumulation of Cd in rice. We found that Cd stress elevated the endogenous GA level in the rice roots. Exogenous GA application not only decreased the fixation of Cd in the root cell wall through reducing the hemicelluloses content, but also decreased the expression of OsNRAMP5 (Natural Resistance-Associated Macrophage Protein 5) and OsCd1 (a major facilitator superfamily gene). Both OsNRAMP5 and OsCd1 are related to Cd absorption, therefore, less Cd was accumulated in the roots. Furthermore, GA increased the expression of OsHMA3 (Heavy Metal ATPase 3) and OsCAL1 (Cadmium accumulation in Leaf 1), which are responsible for sequestering the Cd to the vacuoles and effluxing the Cd outside the cell, respectively, as a result, less Cd was accumulated in the shoots. In contrast, more Cd was accumulated in GA deficient lines. Furthermore, GA decreased the endogenous NO levels and the activity of antioxidant enzymes, while application of a NO scavenger-cPTIO diminished the alleviatory role of GA. In summary, the GA accelerated cell wall Cd exclusion mechanism probably improved rice tolerance to Cd toxicity via regulating the accumulation of NO.

Soil applied silicon and manganese combined with foliar application of 5-aminolevulinic acid mediate photosynthetic recovery in Cd-stressed Salvia miltiorrhiza by regulating Cd-transporter genes

Salvia miltiorrhiza is an important medicinal plant that experiences significant growth and biomass losses when cultivated on cadmium (Cd) contaminated soils. High Cd accumulation in plant tissues also increases the risk of metal entry into the food chain. In this study, we proposed that Cd accumulation in S. miltiorrhiza can be restricted through plant growth regulators and nutrient management. Therefore, S. miltiorrhiza seedlings were transplanted into mixed nutrient soil for two weeks, then treated with 30 mg kg^-1 CdCl₂, 200 mg kg^-1 Na₂SiO₃·9H₂O, and 100 mg kg^-1 MnSO₄, and simultaneously sprayed with 10 mg L^-1 ALA on the leaves one week later. This study showed that elevated Cd accumulation significantly reduced plant growth and biomass. This growth inhibition damaged photosynthetic machinery and impaired carbon assimilation. In contrast, 5-aminolevulinic acid (ALA) significantly promoted the biomass of S. miltiorrhiza, and the dry weight of plants treated with ALA combined with manganese (Mn)/silicon (Si) increased by 42% and 55% as compared with Cd+Mn and Cd+Si treatments. Exogenously applied ALA and Si/Mn significantly activated antioxidant enzymes and promoted the growth recovery of S. miltiorrhiza. Further, exogenous ALA also reduced the Cd concentration in S. miltiorrhiza, especially when combined with Si. Compared with the Cd+Si treatment, the Cd+Si+ALA treatment reduced the Cd concentration in roots and leaves by 59% and 60%, respectively. Gene expression analysis suggested that ALA and Si significantly up-regulated genes associated with Cd transport. Other genes related to heavy metal tolerance mechanisms are also regulated to cope with heavy metal stress. These results indicated that the combined action of ALA and Si/Mn could reduce Cd-toxicity by increasing chlorophyll content and changing oxidative stress and can also affect Cd accumulation by regulating gene expression.

Solution chemistry mechanisms of exogenous silicon influencing the speciation and bioavailability of cadmium in alkaline paddy soil

The mechanism of silicon (Si) influencing cadmium (Cd) speciation and bioavailability in alkaline paddy soil solution remains unclear. Therefore, this study sought to elucidate the effect of Si on Cd by combining chemical analysis and rice pot experiments. In this work, the effects of Na₂SiO₃ alkalinity and the differences in Na⁺ were eliminated in all treatments, and the Cd speciation in soil solutions was determined in-situ using a Field-Donnan membrane technology (DMT) cell. Additionally, rice yields and the Cd content in various parts of the rice plant were studied. The results showed that Si application significantly increased rice biomass by 32% (P < 0.05) while significantly reduced the Cd content in brown rice by 52% (P < 0.01) and the free Cd²⁺ concentration in the soil solution. Further analysis of the interaction of Si and Cd using Fourier transform-infrared spectroscopy (FT-IR), Raman, and X-ray photoelectron spectroscopy (XPS) indicated that a Si-Cd complex was formed by Cd and Si-O groups. In summary, Si changed the chemical speciation of Cd in the alkaline soil solution and formed a water-soluble Si-Cd complex that the rice could not absorb, consequently reducing Cd bioavailability.

Transcription factor ANAC004 enhances Cd tolerance in Arabidopsis thaliana by regulating cell wall fixation, translocation and vacuolar detoxification of Cd, ABA accumulation and antioxidant capacity

Cadmium (Cd) is toxic to plants, which have evolved multiple strategies to cope with Cd stress. In this study, we identified a nucleus-localized NAC-type transcription factor, ANAC004, which is induced by Cd and involved in regulating Cd resistance in Arabidopsis. First, anac004 mutants exhibited Cd sensitive phenotype and accumulated more Cd (12-23% higher than wild type in roots and shoots); plants overexpressing ANAC004 showed the opposite phenotype and with lower Cd accumulation. Second, ANAC004 enhanced Cd fixation in cell wall hemicellulose, thus reducing Cd²⁺ influx into root cells. Third, ANAC004 was involved in the process of vacuolar Cd compartmentalization by regulating the genes associated with Cd detoxification (PCS1/2, NAS4, ABCC1/2/3, MTP1/3, IREG2 and NRAMP3/4). Fourth, ANAC004 reduced root-to-shoot Cd translocation through down-regulated Cd translocation-related genes (HMA2 and HMA4). Finally, the expression of genes related to ABA synthesis (AAO3, MCSU, and NCED3) and the activities of antioxidant enzymes (SOD, POD and CAT) were all reduced in anac004 mutants, leading to reduced levels of endogenous ABA and increased accumulation of reactive oxygen species (O₂^.- and H₂O₂) and MDA, which ultimately weakened resistance to Cd. Our results suggest that ANAC004 decreases Cd accumulation in Arabidopsis through enhancing cell wall Cd immobilization, increasing vacuolar Cd detoxification, and inhibiting Cd translocation, thus improving Cd resistance, processes that might be mediated by ABA signaling and antioxidant defense systems.

Transcriptomic and metabolomic reveals silicon enhances adaptation of rice under dry cultivation by improving flavonoid biosynthesis, osmoregulation, and photosynthesis

Dry cultivation is a new rice crop mode used to alleviate water shortage and develop water-saving agriculture. There is obvious genetic difference compared with drought-tolerant rice. Silicon (Si) plays an important role in plant adaptation to adverse environmental conditions and can significantly improve the drought tolerance and yield of rice. However, the regulatory mechanism via which Si provides plant tolerance or adaptation under dry cultivation is not well understood. The present study investigated the changes in plant growth, photosynthetic gas exchange, and oxidative stress of the rice cultivar "Suijing 18" under dry cultivation. Si improved photosynthetic performance and antioxidant enzyme activity and subsequently reduced lipid peroxidation of rice seedlings, promoted LAI and promoted leaf growth under dry cultivation. Further, transcriptomics combined with quasi-targeted metabolomics detected 1416 and 520 differentially expressed genes (DEGs), 38 and 41 differentially accumulated metabolites (DAMs) in the rice leaves and roots, respectively. Among them, 13 DEGs were involved in flavonoid biosynthesis, promoting the accumulation of flavonoids, anthocyanins, and flavonols in the roots and leaves of rice under dry cultivation. Meanwhile, 14 DEGs were involved in photosynthesis, promoting photosystem I and photosystem II responses, increasing the abundance of metabolites in leaves. On the other hand, 24 DAMs were identified involved in osmoregulatory processes, significantly increasing amino acids and carbohydrates and their derivatives in roots. These results provide new insight into the role of Si in alleviating to adverse environmental, Si enhanced the accumulation of flavonoids and osmoregulatory metabolites, thereby alleviating drought effect on the roots. On the other hand, improving dehydration resistance of leaves, guaranteeing normal photosynthesis and downward transport of organic matter. In conclusion, Si promoted the coordinated action between the above-ground and below-ground plant parts, improved the root/shoot ratio (R/S) of rice and increased the sugar content and enhancing rice adaptability under dry cultivation conditions. The establishment of the system for increasing the yield of rice under dry cultivation provides theoretical and technical support thereby promoting the rapid development of rice in Northeast China, and ensuring national food security.

Silicon-enhanced tolerance to cadmium toxicity in soybean by enhancing antioxidant defense capacity and changing cadmium distribution and transport

Cadmium (Cd) is a widely distributed heavy metal that is toxic to plants and humans. Although silicon (Si) has been reported to reduce Cd accumulation and toxicity in plants, evidence on the functions of Si and its mechanisms in the possible alleviation of soybean are limited. Therefore, a controlled experiment was conducted to investigate the impacts and mechanisms of Si on Cd retention in soybean. Here, we determined the growth index, Cd distribution, and antioxidant activity systems of Si, as well as expression levels of differentially expressed genes (DEGs) in Si under Cd stress, and conducted RNA-seq analysis. We not only found that Si can significantly promote soybean plant growth, increase plant antioxidant activities, and reduce the Cd translocation factor, but also revealed that a total of 636 DEGs were shared between CK and Cd, CK and Cd + Si, and Cd and Cd + Si. Moreover, several genes were significantly enriched in antioxidant systems and Cd distribution and transport systems. Therefore, the expression status of Si-mediated Cd stress response genes is likely involved in improving oxidative stress and changing Cd uptake and transport, as well as improving plant growth that contributes to Si alleviating Cd toxicity in plants. Moreover, numerous potential target genes were identified for the engineering of Cd-tolerant cultivars in soybean breeding programs.

Plant Nutrition: An Effective Way to Alleviate Abiotic Stress in Agricultural Crops

By the year 2050, the world's population is predicted to have grown to around 9-10 billion people. The food demand in many countries continues to increase with population growth. Various abiotic stresses such as temperature, soil salinity and moisture all have an impact on plant growth and development at all levels of plant growth, including the overall plant, tissue cell, and even sub-cellular level. These abiotic stresses directly harm plants by causing protein denaturation and aggregation as well as increased fluidity of membrane lipids. In addition to direct effects, indirect damage also includes protein synthesis inhibition, protein breakdown, and membranous loss in chloroplasts and mitochondria. Abiotic stress during the reproductive stage results in flower drop, pollen sterility, pollen tube deformation, ovule abortion, and reduced yield. Plant nutrition is one of the most effective ways of reducing abiotic stress in agricultural crops. In this paper, we have discussed the effectiveness of different nutrients for alleviating abiotic stress. The roles of primary nutrients (nitrogen, phosphorous and potassium), secondary nutrients (calcium, magnesium and sulphur), micronutrients (zinc, boron, iron and copper), and beneficial nutrients (cobalt, selenium and silicon) in alleviating abiotic stress in crop plants are discussed.

Jasmonic acid alleviates cadmium toxicity through regulating the antioxidant response and enhancing the chelation of cadmium in rice (Oryza sativa L.)

Cadmium (Cd) is a potentially hazardous element with substantial biological toxicity, adversely affecting plant growth and physiological metabolism. Therefore, it is necessary to explore practical and environment-friendly approaches to reduce toxicity. Jasmonic acid (JA) is an endogenous growth regulator which helps plants defend against biological and abiotic stresses. To determine how JA help relieve Cd toxicity in rice, both laboratory and field experiments were implemented. In the seedling stage, the role of JA in mediating rice Cd tolerance was investigated via a fluorescent probe in vivo localization, Fourier Transform Infrared Spectroscopy (FTIR), and colorimetry. At the mature growth stage of rice, field experiments were implemented to research the effects of JA on the Cd uptake and translocation in rice. In the seedling stage of rice, we found that JA application increased the cell wall compartmentalization of Cd by promoting the Cd combination on chelated-soluble pectin of rice roots and inhibited Cd movement into protoplasts, thereby reducing the Cd content in the roots by 30.5% and in the shoots by 53.3%, respectively. Application of JA reduced H2O2 content and helped relieve Cd-induced peroxidation damage of membrane lipid by increasing the level of catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), and glutathione (GSH), but had no significant effect on the superoxide dismutase (SOD) activity. Additionally, field experiments showed that foliar spraying of JA inhibited rice Cd transport from the stalk and root to the grain and reduced Cd concentration in grain by 29.7% in the high-Cd fields and 28.0% in the low-Cd fields. These results improve our understanding of how JA contributes to resistance against Cd toxicity in rice plants and reduces the accumulation of Cd in rice kernels.

Silicon fertilizers, humic acid and their impact on physicochemical properties, availability and distribution of heavy metals in soil and soil aggregates

It has been confirmed that silicon (Si) fertilizer and humic acid (HA) could effectively decrease the heavy metals in soil. Nonetheless, the impact of these additives on soil aggregate characteristics was ignored. Therefore, the effects of Si fertilizer, HA, and their combinations on the physicochemical characteristics, availability of heavy metals (Cu, Cd, Pb, Zn), and fraction changes in soils and soil aggregates were investigated in this research. The results showed that Si fertilizer and HA significantly modified soil properties such as soil pH, electrical conductivity total organic carbon, water-soluble organic carbon, and nitrate‑nitrogen. HA and Si-HA (SHA) supplementation significantly decreased the availability of Cu, Cd, Pd, and Zn. Besides, there was no significant difference in physicochemical properties between soil and soil aggregates. The availability of Cu, Cd, Pd, and Zn in soil aggregates could be significantly inhibited by the addition of HA and SHA, and the content in microaggregates was greater than that in macroaggregates. After the addition of the three additives, the main fractions of heavy metals in different particle sizes were changed and eventually transformed to the residue state. These results indicated that Si fertilizer, HA, and SHA were influential in physicochemical properties and metal availability in soil aggregates. Therefore, it is of great scientific significance to study the impact of heavy metal pollution on the ecological environment in different aggregates, which will provide reference data for future sustainable management of heavy-metal polluted soils.

Comparative transcriptomics provide new insights into the mechanisms by which foliar silicon alleviates the effects of cadmium exposure in rice

Silicon (Si) has been shown to alleviate Cd stress in rice. Here, we investigated the beneficial effects of foliar Si in an indica rice Huanghuazhan (HHZ). Our results showed that foliar Si increases the dry weight and decreases Cd translocation in Cd-exposed rice at the grain-filling stage only, implying that the filling stage is critical for foliar Si to reduce Cd accumulation. We also investigated the transcriptomics in flag leaves (FLs), spikelets (SPs), and node Is (NIs) of Cd-exposed HHZ after foliar Si application at the filling stage. Importantly, the gene expression profiles associated with the Si-mediated alleviation of Cd stress were tissue specific, while shared pathways were mediated by Si in Cd-exposed rice tissues. Furthermore, after the Si treatment of Cd-exposed rice, the ATP-binding cassette (ABC)-transporters were mostly upregulated in FL and SP, while the bivalent cation transporters were mostly downregulated in FL and NI, possibly helping to reduce Cd accumulation. The genes associated with essential nutrient transporters, carbohydrate and secondary metabolite biosynthesis, and cytochrome oxidase activity were mostly upregulated in Cd-exposed FL and SP, which may help to alleviate oxidative stress and improve plant growth under Cd exposure. Interestingly, genes responsible for signal transduction were negatively regulated in FL, but positively regulated in SP, by foliar Si. Our results provide transcriptomic evidence that foliar Si plays an active role in alleviating the effects of Cd exposure in rice. In particular, foliar Si may alter the expression pattern of genes associated with transport, biosynthesis and metabolism, and oxidation reduction.

Metabolomic and antioxidant enzyme activity changes in response to cadmium stress under boron application of wheat (Triticum aestivum)

Boron (B) has previously been shown to inhibit cadmium (Cd) uptake in wheat. Here, we investigated the physiological response of external B application (C for no B added, B for B added, B+Cd for B and Cd added, B/Cd for B 24 h pretreatment before Cd added, B and Cd were 46.2 μM and 5 μM, respectively) on wheat growth under Cd stress. The results showed that the wheat growth was significantly weaker under Cd treatment, while B application did not significantly improve the wheat growth under Cd stress. However, B application decreased Cd concentrations and malondialdehyde (MDA) concentrations of shoot and root. The key enzyme activities including superoxide dismutase (SOD) and peroxidase (POD) significantly increased under Cd treatments while decreased under B treatments. Further, a total of 198, 680 and 204 of the differential metabolites were isolated between B and C treatment, Cd and C treatment and B+Cd and Cd treatment, respectively. The metabolites with up-accumulation in B application (B+Cd) roots were mainly galactaric acid, citric acid, N6-galacturonyl-L-lysine, D-glucose, while the metabolites with down-accumulation were mainly threoninyl-tryptophan and C16 sphinganine. The differential metabolic pathways were mainly concentrated in linoleic acid metabolism, galactose metabolism, sphingolipid metabolism, glycolysis/gluconeogenesis, propanoate metabolism in diabetic complications between B+Cd treatment and B treatment. The results indicate that B alleviates Cd toxicity in winter wheat by inhibiting Cd uptake, increasing antioxidant enzyme activity and changing metabolites.

Co-application of water management and foliar spraying silicon to reduce cadmium and arsenic uptake in rice: A two-year field experiment

Water management is an effective measure for the control of cadmium (Cd) and arsenic (As) in situ uptake and transport in rice. In this study, the effects of the co-application of foliar spraying silicon (Si) and water management on Cd and As uptake and transport in rice were studied under paddy soils that were seriously co-contaminated with Cd and As with a two-year field experiment. The results showed that the co-application of water management and foliar spraying Si could effectively decrease the bioavailability of Cd and As in soil and reduce the uptake and transport of Cd and As in rice. The co-application of water management and foliar spraying Si treatments decreased the exchangeable and TCLP extractable Cd and As contents in the soil. Especially for moisture at the maturing stage combined with foliar spraying Si treatment (MMS), the exchangeable and TCLP extractable Cd and As contents were significantly decreased by 48.49%-55.14% and 45.50%-54.67%, and 41.95%-56.73% and 37.80%-46.76% in the two seasons, respectively. The moisture at the maturing stage treatment significantly decreased the Cd and As contents in brown rice by 44.26%-48.59% and 23.90%-38.16% in the two seasons relative to the control, respectively. Furthermore, MMS treatment simultaneously inhibited Cd and As transport and accumulation in rice among all co-application treatments. The translocation factor (TF)_{stem-brown rice} of Cd, TF_stem-leaf of As, and TF_{stem-brown rice} of As values in the MMS treatment were significantly decreased as compared with the MM treatment. Furthermore, both the Cd and As contents in brown rice under the MMS treatment significantly decreased by 15.33%-30.74% and 33.84%-40.80%, respectively, in the two seasons. The results suggested that foliar spraying Si combined with moisture at the maturing stage might be a promising measure to synchronously inhibit the transport and accumulation of Cd and As in rice.

Liming and tillering application of manganese alleviates iron manganese plaque reduction and cadmium accumulation in rice (Oryza sativa L.)

The application time and soil pH are key to manganese (Mn) bioavailability, which may influence Mn effects on cadmium (Cd) accumulation in rice. Accordingly, this study investigated the effects of Mn application at different stages, alone or with basal liming, on Cd accumulation in rice through pot and field experiments. The results showed that basal Mn application maximally elevated soil dissolved Mn, and increasing Mn accumulation in rice by 140%-367% compared to the control. Additionally, basal or tillering applications had better effects on enhancing iron manganese plaque (IMP) and inhibiting CaCl₂-extractable Cd than later applications. Therefore, basal and tillering Mn reduced brown rice Cd by 24.6% and 18.9% compared to the control, respectively. Liming reduced CaCl₂-extractable Cd by 83.3% compared to the control but inhibited soil dissolved Mn (25.8%-76.6%) and IMP (28.9%-29.7%), resulting in only a 41.7% reduction in brown rice Cd. Liming combined with tillering Mn maximally reduced brown rice Cd by 67.4%, structural equation modeling revealed CaCl₂-extractable Cd and manganese plaque played the greatest positive and negative roles, respectively. Therefore, basal liming and tillering application of Mn is most effective at reducing rice Cd through inhibition of Cd bioavailability and alleviation of IMP reduction.

Silicon-based additive on heavy metal remediation in soils: Toxicological effects, remediation techniques, and perspectives

Chemical fertilizer is gaining increasing attention and has been the center of much research which indicating complex beneficial and harmful effects. Chemical fertilizer might cause some environmental hazards to the biosphere, especially in the agricultural ecosystem. The application of silicon (Si) fertilizer in agriculture has been proved to be able to create good economic and environmental benefits. Si is the second most abundant earth crust element. Si fertilizer improves soil quality and alleviates biotic and abiotic crop stress. It is of great significance to understand the function of Si fertilizer in agricultural utilization and environmental remediation. This paper reviews the Si-based fertilizer in farmland use and summarizes prior research relevant with characterization, soil quality improvement, and pollution remediation effects. Its use in agriculture enhances plant silicon uptake, mediates plant salt and drought stress and remediates heavy metals such as Al, As, Cd, Cu, Zn and Cr. This article also summarizes the detoxification mechanism of silicon and its effects on plant physiological activity such as photosynthesis and transpiration. Fertilizer materials and crop fertilizer management were also considered. Foliar spraying is an effective method to improve crop growth and yield and reduce biotic or abiotic stress. Silicon nanoparticle material provides potential with great potential and prospects. More investigation and research are prospected to better understand how silicon impacts the environment and whether it is a beneficial additive.

Potassium and Silicon Synergistically Increase Cadmium and Lead Tolerance and Phytostabilization by Quinoa through Modulation of Physiological and Biochemical Attributes

Cadmium (Cd) and lead (Pb) contaminated soils have increased recently, resulting in limited crop productivity. The ameliorative role of potassium (K) and silicon (Si) is well established in plants under heavy metals stress; however, their combined role under the co-contamination of Cd and Pb is not well understood. We hypothesized that the synergistic application of K and Si would be more effective than their sole treatment for increasing the Pb and Cd tolerance and phytostabilization potential of quinoa (Chenopodium quinoa Willd.). In the current study, quinoa genotype ‘Puno’ was exposed to different concentrations of Cd (0, 200 µM), Pb (0, 500 µM) and their combination with or without 10 mM K and 1.0 mM Si supplementation. The results revealed that the combined stress of Cd and Pb was more detrimental than their separate application to plant biomass (66% less than the control), chlorophyll content and stomatal conductance. Higher accumulation of Pb and Cd led to a limited uptake of K and Si in quinoa plants. The supplementation of metal-stressed plants with 10 mM K and 1.0 mM Si, particularly in combination, caused a significant increase in the growth, stomatal conductance and pigment content of plants. The combined stress of Cd and Pb resulted in an overproduction of H₂O₂ (11-fold) and TBARS (13-fold) and a decrease in membrane stability (59%). Oxidative stress induced by metals was lessened by 8-fold, 9-fold, 7-fold and 11-fold increases in SOD, CAT, APX and POD activities, respectively, under the combined application of K and Si. It is concluded that the exogenous supply of K and Si in combination is very promising for increasing Cd and Pb tolerance and the phytostabilization potential of quinoa.

Radial transport difference mediated by root endodermal barriers contributes to differential cadmium accumulation between japonica and indica subspecies of rice (Oryza sativa L.)

Although Cd concentration of grains is generally lower in japonica than in indica subspecies, the effects of root endodermal barriers on the subspecific differences in Cd accumulation in rice (Oryza sativa L.) are poorly understood. Here, we characterized the differences in endodermal differentiation between japonica and indica subspecies and their effects on Cd radial transport. Casparian strips (CSs) and suberin lamellae (SL) in japonica subspecies were initiated at the 6%- 7% and 21%- 27% position from the root tip, respectively, which were 65% and 26% earlier than in indica subspecies, respectively. The lignin/suberin content in japonica subspecies was 47%/42% greater than that in indica subspecies because of the higher expression of lignin/suberin biosynthesis-related genes (OsCASP1, OsPAL, OsCYP86A1 and OsKCS20). Cd exposure induced endodermal plasticity in both subspecies, but the changes in japonica were greater than in indica subspecies. The earlier formation of CSs/SL in japonica subspecies significantly restricted the flow of radial transport tracer to reach the xylem and decreased Cd influx into roots, that is, endodermal barriers inhibited Cd radial transport via both apoplastic and cell-to-cell pathways, thus decreasing the root-to-shoot transport of Cd in japonica subspecies. Our findings are beneficial for the genetic modification of rice with low-Cd-accumulating ability.

The role and its transcriptome mechanisms of cell wall polysaccharides in vanadium detoxication of rice

Cell wall-polysaccharides play a crucial role in heavy metals binding, and hence, contribute to heavy metal detoxication in plants. However, there is no data regarding the molecular mechanisms of vanadium (V) binding to root cell walls in plants, especially in rice (Oryza sativa L.). Taking two rice cultivars with various V tolerance as the research material, the present study investigated the effect of various V concentrations on subcellular distribution of V and revealed the regulatory mechanism of cell wall polysaccharides to V exposure. The results showed that rice roots inhibited the upward movement of V, and root cell walls accumulated 69.85-82.71% of V in roots. Furthermore, hemicellulose-1 (HC-1) in cell walls shared up to 67.72% and 66.95% of the cell-wall-bound V in tolerant and sensitive cultivars, respectively. FTIR spectroscopy demonstrated that V stress induced the remolding of cell wall polysaccharides. Under V stress, V-tolerant rice generated up to 19.3% pectin, 40.9% HC-1, and 49.34% HC-2, which were higher than V-sensitive cultivar. The genes encoding UGDH, UGE, and AXS for polysaccharide biosynthesis were higher expressed in V-tolerant rice than V-sensitive rice when exposed to V. The results could provide novel insight for phytoremediation and food security guarantees.

Influence of silicon on polymerization process during lignin synthesis. Implications for cell wall properties

Silicon (Si) is considered a beneficial element for plants, mostly accumulating in cell walls, where its location and content are primed by the chemistry and structure of lignin. It is unrevealed how Si interacts with the process of lignin formation in the CWs. We studied, in an in vitro system, the interaction of SiO2 with the peroxidase-catalyzed polymerization of a lignin monomer into the lignin model compound, imitating conditions of the last step of lignin formation. FTIR and fluorescence spectroscopy and microscopy showed that Si is bound to the final polymer, and the structure of the Si-DHP differs from pure DHP. Fluorescence spectroscopy showed that Si does not bind to the monomers, so Si probably inhibits the formation of the larger lignin fragments, as evidenced by HPLC-DAD, by binding to dimmers formed during DHP synthesis. The structural changes of the polymer are related to the changed proportion of the fractions of various MW. The enzyme catalyzing DHP synthesis was not inhibited by Si. HRP activity was increased in presence of Si except for 6 mM Si. This may indicate that the complex formed with Si and short oligomers activates the enzyme, and prevents the formation of the large fragments.

Accumulation and partitioning of toxic trace metal(loid)s in phytoliths of wheat grown in a multi-element contaminated soil

Cropland contamination by toxic trace metal (loid)s (TTMs) has attracted increasing attention due to the serious consequential threat to crop quality and human health. Mitigation of plant TTM stress by silica amendment has been proposed recently. However, the relationship between the siliceous structure of phytoliths and TTMs in plants, and the environmental implications of phytolith-occluded trace metal (loid)s (PhytTMs) remain unclear. This study assessed the accumulation of five metal (loid)s, including lead (Pb), zinc (Zn), cadmium (Cd), copper (Cu) and arsenic (As), in the organic tissues and phytoliths of wheat grown in a mixed-TTM contaminated soil under both lightly and heavily contaminated conditions. The results show that the concentrations of plant TTMs and PhytTMs were significantly (p < 0.05) positively correlated, and higher in heavily contaminated wheats than those in lightly contaminated ones. The bio-enrichment factors between phytoliths and organic tissues were higher for As (1.83), Pb (0.27) and Zn (0.30) than for Cd (0.03) and Cu (0.14), implying that As, Pb and Zn were more readily co-precipitated with silicon (Si) in phytolith structures than Cd and Cu. Network analysis of the relationship between soil and plant elements with PhytTMs showed that severe contamination could impact the homeostasis of elements in plants by altering the translocation of TTMs between soils, plants, and phytoliths. The accumulation of TTMs in phytoliths was affected by the capacity of Si deposition in tissues and chelation of TTMs with silica, which could impact the role of PhytTMs in global biogeochemical TTM cycles.

Characterization of cadmium accumulation in the cell walls of leaves in a low-cadmium rice line and strengthening by foliar silicon application

Cadmium (Cd) remobilization in leaves is affected by whether Cd is stored in nonlabile subcellular compartments, which might be regulated by silicon (Si) application. However, the underlying mechanism is still far from being completely understood. In this research, the Cd distribution pattern in leaves and a Cd-binding characterization in the cell wall of the low-Cd rice line YaHui2816 were investigated through one hydroponic experiment with 10 μM Cd in solutions. Foliar Si application was further adopted to explore its influence on the Cd accumulation in the cell walls of leaves in YaHui2816. Most of the Cd (69.4%) was distributed in the cell walls of YaHui2816 leaves, whereas the isolated cell walls of leaves from YaHui2816 exhibited a lower capacity for Cd chemisorption than the contrasting line C268A, which was resulted from its fewer relative peak areas of functional groups in the cell wall, such as carboxyl CO and OH stretching. Foliar Si application significantly increased the Cd concentration in leaves and various cell wall fractions (pectin, hemicellulose 1 and residue) by 191% and 137-160%, respectively. RNA-seq analysis revealed that foliar Si application depressed the expression of the metal transporters OsZIP7 and OsZIP8, up-regulated the expression of genes participating in the glutathione metabolism and the cellulose synthesis. Overall, the influence of foliar Si application on Cd-accumulation in the cell wall of leaves in a low-Cd rice line was demonstrated in this research, which inspires further avenues to ensure the food safety of rice grains.

The role of polysaccharides functional groups in cadmium binding in root cell wall of a cadmium-safe rice line

Exploring the mechanism of cadmium (Cd) accumulation in Cd-safe rice lines is beneficial for ensuring rice safety. D62B, a Cd-safe rice line, accumulates less than 0.2 mg Cd kg^-1 in the brown rice due to strong capacity of Cd retention in the roots, and the root cell wall (RCW) polysaccharides play important roles. However, specific underlying mechanism of Cd binding on the polysaccharides is little known. In this study, the role of polysaccharides, especially pectin and hemicellulose 1 (HC1), in RCW of D62B was investigated by adsorption experiments and Fourier Transform Infrared Spectroscopy (FTIR) analysis compared with a common rice line (Luhui17). Cadmium was adsorbed on RCW of two rice lines by a multilayer and inhomogeneous chemisorption way with the force of ion transfer or exchange. Cadmium was adsorbed on RCW rapidly at first stage with the limit of internal and external diffusion, and gradually reached saturation. With the removal of pectin, the Cd adsorption rate, maximum Cd adsorption amount and the shift degree of carboxyl groups in the RCW of D62B sharply decreased, which showed advantages compared with Luhui17. Sequential removal of HC1 further decreased the maximum Cd adsorption amount and the shift degree of hydroxyl groups. The results showed that more available functional groups, especially carboxyl groups in pectin and hydroxyl groups in HC1, contributed to Cd immobilization within the RCW of Cd-safe rice line, thus limiting Cd translocation to the shoot and reducing Cd accumulation in the brown rice.

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

Silicon (Si) plays a pivotal role in mitigating phytotoxicity caused by cadmium (Cd). However, few former reports focused on the internal mechanism how Si assisted in alleviating Cd stress in rice under different durations of Cd exposure. Herein, the effects of Si on subcellular distribution of Cd in rice roots under short-term (12 h) and long-term (20 d) Cd exposure were explored. Results showed that Si decreased shoot Cd concentration but had little impact on root Cd levels. Under short-term Cd exposure, subcellular distribution analysis showed that Si increased the ratio of Cd in root cell wall by 23.2~24.0%, and decreased the ratio of Cd in root soluble fraction by 20.6~21.5%. This suggested that Si supply improved root retention of Cd by fixing it on the cell wall and thus restricted intracellular transportation of Cd. Further analysis unraveled that pectin (especially ionic-soluble pectin) of the cell wall was the main binding component, and Si supply induced more Cd accumulation in covalent-soluble pectin and hemicellulose. Moreover, the overexpression of germin-like proteins (GLPs) proved the role of cell wall in moderating Cd toxicity. Under long-term Cd exposure, Si promoted phytochelatin 2 (PC2) and phytochelatin 3 (PC3) synthesis in cytosol, at the same time, Si down-regulated the expression of the Cd efflux-related protein multidrug resistance-associated protein-like ATP-binding cassette transporters (MRP-like ABC transporters) and limited Cd transportation from vacuole to cytosol. Taken together, Si rather predominates in limiting Cd translocation by the cell wall of root under short-term Cd exposure and promoting vacuole compartmentalization to mitigate the Cd toxicity under long-term exposure, instead of reducing the absorption of Cd in rice roots, thereby decreasing Cd delivery into shoots.

Silicon Fertilization: A Step towards Cadmium-Free Fragrant Rice

Soil contamination with toxic cadmium (Cd) is becoming a serious global problem and poses a key hazard to environments and the health of human beings worldwide. The present study investigated the effects of foliar applications of three forms of silicate chemicals (calcium silicate, sodium silicate, and potassium silicate) at four rates (0.25%, 0.5%, 0.75%, and 1.0%) at tillering stage on rice growth and the accumulation of Cd under Cd stress (30 mg kg^-1). The results showed that Cd stress reduced the yield-related traits and enlarged Cd contents in different rice organs. The leaf gas exchange attributes and yield traits were enhanced, and the Cd accumulation and bioaccumulation factor in rice organs were reduced, especially in grains, through silicon application. In shoots, roots, and grains, foliar spray of Si reduced Cd contents by 40.3%, 50.7%, and 47.9%, respectively. The effectiveness of silicate compounds in reducing Cd toxicity varied with the kind of chemicals and doses of foliar applications. Foliar application of potassium silicate, at a rate of 0.5%, at tillering stage, showed the best effectiveness in improving grain yield, while mitigating Cd accumulation in rice grains. The outcome of this study provides a promising practicable approach in alleviating Cd toxicity in rice and preventing the entrance of Cd into the food chain.

The mechanisms of silicon on maintaining water balance under water deficit stress

Water deficit stress severely threatens crop yield and numerous reports have shown silicon could enhance plants resistance to water deficit. One of the most important mechanisms is that silicon maintains the water balance. In this review, we summarized advanced research to elucidate the effect of silicon on plant water transport processes, including leaf water loss, vessel water transport, and root water uptake. In leaves, the deposition of silica phytolith on cuticle and stomata decreases transpirational water loss under water deficit stress. However, accumulating evidence suggest that silicon maintaining leaf water content is not through reducing water loss, but through osmotic adjustments, enhancing water transport and uptake. Enhancement of stem water transport efficiency by silicon is due to silica phytolith depositing in the cell wall of vessel tubes and pits, which support it avoiding to collapse and embolism, respectively. The improvement of root water uptake capacity by silicon acts as a key role in maintaining water balance. The underlying mechanisms include (i) enlargement of the root water uptake area, (ii) improvement of the water driving force, (iii) the prevention of water loss from root to soil, and (iv) the up-regulation of aquaporin activity. This review provides three simple models to understand the mechanism of silicon on water balance and highlights the future research area.

Effects of silicon on heavy metal uptake at the soil-plant interphase: A review

Silicon (Si) is the second richest element in the soil and surface of earth crust with a variety of positive roles in soils and plants. Different soil factors influence the Si bioavailability in soil-plant system. The Si involves in the mitigation of various biotic (insect pests and pathogenic diseases) and abiotic stresses (salt, drought, heat, and heavy metals etc.) in plants by improving plant tolerance mechanism at various levels. However, Si-mediated restrictions in heavy metals uptake and translocation from soil to plants and within plants require deep understandings. Recently, Si-based improvements in plant defense system, cell damage repair, cell homeostasis, and regulation of metabolism under heavy metal stress are getting more attention. However, limited knowledge is available on the molecular mechanisms by which Si can reduce the toxicity of heavy metals, their uptake and transfer from soil to plant roots. Thus, this review is focused the following facets in greater detail to provide better understandings about the role of Si at molecular level; (i) how Si improves tolerance in plants to variable environmental conditions, (ii) how biological factors affect Si pools in the soil (iii) how soil properties impact the release and capability of Si to decrease the bioavailability of heavy metals in soil and their accumulation in plant roots; (iv) how Si influences the plant root system with respect to heavy metals uptake or sequestration, root Fe/Mn plaque, root cell wall and compartment; (v) how Si makes complexes with heavy metals and restricts their translocation/transfer in root cell and influences the plant hormonal regulation; (vi) the competition of uptake between Si and heavy metals such as arsenic, aluminum, and cadmium due to similar membrane transporters, and (vii) how Si-mediated regulation of gene expression involves in the uptake, transportation and accumulation of heavy metals by plants and their possible detoxification mechanisms. Furthermore, future research work with respect to mitigation of heavy metal toxicity in plants is also discussed.

Effect of exogenous silicon and methyl jasmonate on the alleviation of cadmium-induced phytotoxicity in tomato plants

In the present study, a hydroponic experiment was performed to evaluate the effect of exogenous silicon (Si) and methyl jasmonate (MeJA) on the mitigation of Cd toxicity in tomato seedlings. The results revealed that Cd-stressed plants exhibited growth inhibition, increased lipid peroxidation, and impaired photosynthetic pigment accumulation. However, Si and MeJA applied alone or in combination significantly ameliorated the above-mentioned adverse effects induced by Cd. Among all treatments, Cd+Si+MeJA treatment elevated the dry mass of roots, stems, and leaves by 317.39%, 110.85%, and 119.71%, respectively. The chlorophyll a, chlorophyll b, and carotenoid contents in Cd+Si+MeJA-treated group were dramatically elevated (p < 0.05). Meanwhile, the malondialdehyde content in roots and shoots were reduced by 32.24% and 69.94%, respectively. The Si and MeJA applied separately or in combination also resulted in a prominent decrease of Cd influxes in tomato roots; therefore, a reduction of Cd content in tomato tissues were detected, and the Cd concentration in tomato roots were decreased by 27.19%, 25.18%, and 17.51% in Cd+Si, Cd+MeJA and Cd+Si+MeJA-treated plants, respectively. Moreover, in Cd+Si+MeJA-treated group, the percentage of Cd in cell wall fraction was enhanced while that in organelle fraction was decreased as compared with Cd-stressed plants. Collectively, our findings indicated that Si and MeJA application provide a beneficial role in enhancing Cd tolerance and reducing Cd uptake in tomato plants.

Sustainable management of cadmium-contaminated soils as affected by exogenous application of nutrients: A review

Cadmium (Cd) pollution in arable land is of great concern as it impairs plant growth and further threats human health via food-chain. Exogenous supplementation of nutrients is an environmentally-friendly, cost-effective, convenient and feasible strategy for regulating Cd uptake, transport and accumulation in plants. To sustain Cd-contaminated soils management, on the one hand, a low level of the Cd-contaminated soil is expected to cultivate crops with decreased Cd accumulation as affected by exogenous nutrients application, on another hand, a high level of the Cd-contaminated soil is suggested to cultivate phytoextraction plants with increased Cd accumulation as affected by exogenous nutrients application. Nevertheless, effects of nutrients on Cd accumulation in plants are still ambiguous. Thus, data of Cd accumulation in shoots of plants as affected by exogenous application of nutrients were collected from previously published articles between 2005 and 2021 in the present study. According to the data, exogenous supply of calcium (Ca), magnesium (Mg), iron (Fe), manganese (Mn) and silicon (Si) to a larger extent decrease Cd amounts in shoots of plants. By contrast, exogenous nitrogen (N), and deficient Ca, Mg and Fe supply have a great possibility to increase Cd amounts in shoots of plants. Although exogenous application of phosphorus (P), sulfur (S), potassium (K), zinc (Zn) and selenium (Se) have a great opportunity to increase biomass, they show different effects on Cd concentrations. As a result, the odds are even for increasing and decreasing Cd amounts in shoots of plants. Taken together, exogenous application of Ca, Mg, Fe, Mn and Si might decrease Cd accumulation in plants that are recommended for crops production. Exogenous N and deficient Ca, Mg and Fe supply might increase Cd accumulation in plants that are recommended for phytoextraction plants. Exogenous application of P, S, K, Zn and Se have half a chance to increase or decrease Cd accumulation in plants. Therefore, dosages, forms and species should be taken into account when exogenous P, S, K, Zn and Se are added.

Molecular and Biochemical Insights Into Early Responses of Hemp to Cd and Zn Exposure and the Potential Effect of Si on Stress Response

With the intensification of human activities, plants are more frequently exposed to heavy metals (HM). Zinc (Zn) and cadmium (Cd) are frequently and simultaneously found in contaminated soils, including agronomic soils contaminated by the atmospheric fallout near smelters. The fiber crop Cannabis sativa L. is a suitable alternative to food crops for crop cultivation on these soils. In this study, Cd (20 μM) and Zn (100 μM) were shown to induce comparable growth inhibition in C. sativa. To devise agricultural strategies aimed at improving crop yield, the effect of silicon (Si; 2 mM) on the stress tolerance of plants was considered. Targeted gene expression and proteomic analysis were performed on leaves and roots after 1 week of treatment. Both Cd- and Zn-stimulated genes involved in proline biosynthesis [pyrroline-5-carboxylate reductase (P5CR)] and phenylpropanoid pathway [phenylalanine ammonia-lyase (PAL)] but Cd also specifically increased the expression of PCS1-1 involved in phytochelatin (PC) synthesis. Si exposure influences the expression of numerous genes in a contrasting way in Cd- and Zn-exposed plants. At the leaf level, the accumulation of 122 proteins was affected by Cd, whereas 47 proteins were affected by Zn: only 16 proteins were affected by both Cd and Zn. The number of proteins affected due to Si exposure (27) alone was by far lower, and 12 were not modified by heavy metal treatment while no common protein seemed to be modified by both CdSi and ZnSi treatment. It is concluded that Cd and Zn had a clear different impact on plant metabolism and that Si confers a specific physiological status to stressed plants, with quite distinct impacts on hemp proteome depending on the considered heavy metal.

Fascinating regulatory mechanism of silicon for alleviating drought stress in plants

Plants confront several environmental stresses that are crucial in defining plant productivity. Among these environmental stresses, drought stress is recognized as the foremost abiotic factor which affects the food security around the globe due to its negative impact on the plant development, and quality of plant products. Because of this, drought stress has gained an imperative appearance in the field of plant sciences in recent years. Silicon (Si), an agronomically essential mineral nutrient, is recognized highly advantageous in enhancing plant growth at various phases of plant life cycle under water deficit circumstances. Si has been considered extensively useful in mitigating harmful consequences of drought stress by enhancing root H₂O absorption, regulating uptake of nutrients, reducing transpiration rate, improving photosynthetic activity, increment in the production of compatible solutes and by elevating plant antioxidant defense functioning. Si also known to improve plant endurance to limited water availability by inducing the functioning of various stress associated genes. To maximize the potential benefits and sustainable efficiency of Si in agriculture, it is of crucial importance to gain knowledge about the underlying mechanisms of how Si counteract stress conditions. Various findings suggested that Si increases the plant's immune system against drought stress, and application of Si is an important approach to shield plants from adverse stress conditions and soil nutrient depletion. This paper shows that Si has imperative and noteworthy impacts on improving plant tolerance to drought stress via maintaining cellular homeostasis. Present review mainly provides an insight into silicon role as beneficial element to alleviate drought stress in plants by regulating their morphological, physicochemical and molecular characteristics.

Silicon distribution in leaves and roots of rice and maize in response to cadmium and zinc toxicity and the associated histological variations

At present, the levels of cadmium (Cd) and zinc (Zn) in arable land are high and affect the growth and development of important food crops, including rice and maize. However, the application of silicon (Si) in contaminated areas increases the metal tolerance potential of these plants. This work aimed to study the variations in the distribution pattern of endogenous Si in various tissue regions in roots and leaves of rice and maize exposed to cadmium (Cd) and zinc (Zn) stresses. For these experiments, 45 day-old rice (var. Varsha) and maize (var. CoHM6) seedlings were treated with 1.95 g Zn and 0.45 g Cd kg^-1 soil. Under Cd stress, the distribution of Si was high in the cortical region of the root, but under Zn stress, the highest Si deposition was found in the endodermis. In leaves, Si deposition was high in both the mesodermis and stelar regions of Cd-treated plants but more Si was deposited in the mesodermis tissue of Zn-treated plants. Heavy metal (Cd and Zn) accumulation and Si deposition showed a strong negative correlation in the roots of rice and maize plants. Complexation with metal ions and redistribution of Si were considered the major mechanisms in Si-mediated mitigation of Cd and Zn stress. Cd- and Zn-induced anatomical changes, such as endodermal thickening, deposits in the xylary elements and aerenchyma formation in the roots of rice and maize, were also associated with the Si distribution.

Cell Walls Are Remodeled to Alleviate nY2O3 Cytotoxicity by Elaborate Regulation of de Novo Synthesis and Vesicular Transport

Yttrium oxide nanoparticles (nY2O3), one of the broadly used rare earth nanoparticles, can interact with plants and possibly cause plant health and environmental impacts, but the plant defense response particularly at the nanoparticle-cell interface is largely unknown. To elucidate this, Bright Yellow 2 (BY-2) tobacco (Nicotiana tabacum L.) suspension-cultured cells were exposed to 50 mg L-1 nY2O3 (30 nm) for 12 h. Although 42.2% of the nY2O3 remained outside of protoplasts, nY2O3 could still traverse the cell wall and was partially deposited inside the vacuole. In addition to growth inhibition, morphological and compositional changes in cell walls occurred. Together with a locally thickened (7-13-fold) cell wall, increased content (up to 58%) of pectin and reduction in (up to 29%) hemicellulose were observed. Transcriptome analysis revealed that genes involved in cell wall metabolism and remodeling were highly regulated in response to nY2O3 stress. Expression of genes for pectin synthesis and degradation was up- and down-regulated by 31-78% and 13-42%, respectively, and genes for xyloglucan and pectin modifications were up- and down-regulated by 82% and 81-92%, respectively. Interestingly, vesicle trafficking seemed to be activated, enabling the repair and defense against nY2O3 disturbance. Our findings indicate that, although nY2O3 generated toxicity on BY-2 cells, it is very likely that during the recovery process cell wall remodeling was initiated to gain resistance to nY2O3 stress, demonstrating the plant's cellular regulatory machinery regarding repair and adaptation to nanoparticles like nY2O3.