Silicon regulates the expression of vacuolar H+-pyrophosphatase 1 and decreases cadmium accumulation in rice (Oryza sativa L.)

BnVP1, a novel vacuolar H+ pyrophosphatase gene from Boehmeria nivea confers cadmium tolerance in transgenic Arabidopsis

Plants have developed precise defense mechanisms against cadmium (Cd) stress, with vacuolar compartmentalization of Cd2+ being a crucial process in Cd detoxification. The transport of Cd into vacuoles by these cation / H+ antiporters is powered by the pH gradient created by proton pumps. In this study, the full-length cDNA of a vacuolar H+-pyrophosphatase (V-PPase) gene from Boehmeria nivea (ramie), BnVP1, was isolated using the rapid amplification of cDNA ends (RACE) method. The open reading frame (ORF) of BnVP1 is 2292 bp, encoding a 763 amino acid V-PPase protein with 15 predicted transmembrane domains. Sequence alignment and phylogenetic analysis revealed that BnVP1 belongs to the Type I V-PPase family. Quantitative RT-PCR assays demonstrated that BnVP1 expression was significantly higher in ramie roots than in shoots. Cd treatments markedly induced BnVP1 expression in both roots and leaves of ramie seedlings, with a more pronounced effect in roots. Additionally, BnVP1 expression was significantly upregulated by the plant hormone methyl jasmonate (MeJA). Heterologous expression of BnVP1 in transgenic Arabidopsis significantly enhanced V-PPase activity in the roots. The growth performance, root elongation, and total chlorophyll content of transgenic plants with high tonoplast H+-PPase (V-PPase) activity were superior to those of wild-type plants. Overexpression of BnVP1 reduced membrane lipid peroxidation and ion leakage, and significantly increased Cd accumulation in the roots of transgenic Arabidopsis seedlings. This study provides new genetic resources for the phytoremediation of Cd-contaminated farmland.

Effects of environmental metal and metalloid pollutants on plants and human health: exploring nano-remediation approach

Metal and metalloid pollutants severely threatens environmental ecosystems and human health, necessitating effective remediation strategies. Nanoparticle (NPs)-based approaches have gained significant attention as promising solutions for efficient removing heavy metals from various environmental matrices. The present review is focused on green synthesized NPs-mediated remediation such as the implementation of iron, carbon-based nanomaterials, metal oxides, and bio-based NPs. The review also explores the mechanisms of NPs interactions with heavy metals, including adsorption, precipitation, and redox reactions. Critical factors influencing the remediation efficiency, such as NPs size, surface charge, and composition, are systematically examined. Furthermore, the environmental fate, transport, and potential risks associated with the application of NPs are critically evaluated. The review also highlights various sources of metal and metalloid pollutants and their impact on human health and translocation in plant tissues. Prospects and challenges in translating NPs-based remediation from laboratory research to real-world applications are proposed. The current work will be helpful to direct future research endeavors and promote the sustainable implementation of metal and metalloid elimination.

Silicon nanoparticles vs trace elements toxicity: Modus operandi and its omics bases

Phytotoxicity of trace elements (commonly misunderstood as 'heavy metals') includes impairment of functional groups of enzymes, photo-assembly, redox homeostasis, and nutrient status in higher plants. Silicon nanoparticles (SiNPs) can ameliorate trace element toxicity. We discuss SiNPs response against several essential (such as Cu, Ni, Mn, Mo, and Zn) and non-essential (including Cd, Pb, Hg, Al, Cr, Sb, Se, and As) trace elements. SiNPs hinder root uptake and transport of trace elements as the first line of defence. SiNPs charge plant antioxidant defence against trace elements-induced oxidative stress. The enrolment of SiNPs in gene expressions was also noticed on many occasions. These genes are associated with several anatomical and physiological phenomena, such as cell wall composition, photosynthesis, and metal uptake and transport. On this note, we dedicate the later sections of this review to support an enhanced understanding of SiNPs influence on the metabolomic, proteomic, and genomic profile of plants under trace elements toxicity.

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.

Exogenous titanium dioxide nanoparticles alleviate cadmium toxicity by enhancing the antioxidative capacity of Tetrastigma hemsleyanum

Nanotechnology is one of the most recent approaches employed to defend plants against both biotic and abiotic stress including heavy metals such as Cadmium (Cd). In this study, we evaluated the effects of titanium dioxide (TiO2) nanoparticles (TiO2 NPs) in alleviating Cd stress in Tetrastigma hemsleyanum Diels et Gilg. Compared with Cd treatment, TiO2 NPs decreased leaf Cd concentration, restored Cd exposure-related reduction in the biomass to about 69% of control and decreased activities of antioxidative enzymes. Integrative analysis of transcriptome and metabolome revealed 325 differentially expressed genes associated with TiO2 NP treatment, most of which were enriched in biosynthesis of secondary metabolites. Among them, the flavonoid and phenylpropanoid biosynthetic pathways were significantly regulated to improve the growth of T. hemsleyanum when treated with Cd. In the KEGG Markup Language (KGML) network analysis, we found some commonly regulated pathways between Cd and Cd+TiO2 NP treatment, including phenylpropanoid biosynthesis, ABC transporters, and isoflavonoid biosynthesis, indicating their potential core network positions in controlling T. hemsleyanum response to Cd stress. Overall, our findings revealed a complex response system for tolerating Cd, encompassing the transportation, reactive oxygen species scavenging, regulation of gene expression, and metabolite accumulation in T. hemsleyanum. Our results indicate that TiO2 NP can be used to reduce Cd toxicity in T. hemsleyanum.

Multifaceted roles of silicon nano particles in heavy metals-stressed plants

Heavy metal (HM) contamination has emerged as one of the most damaging abiotic stress factors due to their prominent release into the environment through industrialization and urbanization worldwide. The increase in HMs concentration in soil and the environment has invited attention of researchers/environmentalists to minimize its' impact by practicing different techniques such as application of phytohormones, gaseous molecules, metalloids, and essential nutrients etc. Silicon (Si) although not considered as the essential nutrient, has received more attention in the last few decades due to its involvement in the amelioration of wide range of abiotic stress factors. Silicon is the second most abundant element after oxygen on earth, but is relatively lesser available for plants as it is taken up in the form of mono-silicic acid, Si(OH)4. The scattered information on the influence of Si on plant development and abiotic stress adaptation has been published. Moreover, the use of nanoparticles for maintenance of plant functions under limited environmental conditions has gained momentum. The current review, therefore, summarizes the updated information on Si nanoparticles (SiNPs) synthesis, characterization, uptake and transport mechanism, and their effect on plant growth and development, physiological and biochemical processes and molecular mechanisms. The regulatory connect between SiNPs and phytohormones signaling in counteracting the negative impacts of HMs stress has also been discussed.

New insights into the environmental application of hybrid nanoparticles in metal contaminated agroecosystem: A review

Heavy metals (HMs) contamination in agricultural soils is a major constraint to provide safe food to society. Cultivation of food crops on these soils, channels the HMs into the food chain and causes serious human health and socioeconomic problems. Multiple conventional and non-conventional remedial options are already in practice with variable success rates, but nanotechnology has proved its success due to higher efficiency. It also led the hypothesis to use hybrid nanoparticles (HNPs) with extended benefits to remediate the HMs and supplement nutrients to enhance the crop yield in the contaminated environments. Hybrid nanoparticles are defined as exclusive chemical conjugates of inorganic and/or organic nanomaterials that are combinations of two or more organic components, two or more inorganic components, or at least one of both types of components. HNPs of different elements like essential nutrients, beneficial nutrients and carbon-based nanoparticles are used for the remediation of metals contaminated soil and the production of metal free crops. Characterizing features of HNPs including particle size, surface area, reactivity, and solubility affect the efficacy of these HNPs in the contaminated environment. Hybrid nanoparticles have great potential to remove the HMs ions from soil solution and restrict their ingress into the root tissues. Furthermore, HNPs of essential nutrients not only compete with heavy metal uptake by plants but also fulfill the need of nutrients. This review provides a comprehensive overview of the challenges associated with application of HNPs in contaminated soils, environmental implications, their remediation ability, and factors affecting their dynamics in environmental matrices.

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

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

Zinc and nano zinc mediated alleviation of heavy metals and metalloids in plants: an overview

Heavy metals and metalloids (HMs) contamination in the environment has heightened recently due to increasing global concern for food safety and human livability. Zinc (Zn2+ ) is an important nutrient required for the normal development of plants. It is an essential cofactor for the vital enzymes involved in various biological mechanisms of plants. Interestingly, Zn2+ has an additional role in the detoxification of HMs in plants due to its unique biochemical-mediating role in several soil and plant processes. During any exposure to high levels of HMs, the application of Zn2+ would confer greater plant resilience by decreasing oxidative stress, maintaining uptake of nutrients, photosynthesis productivity and optimising osmolytes concentration. Zn2+ also has an important role in ameliorating HMs toxicity by regulating metal uptake through the expression of certain metal transporter genes, targeted chelation and translocation from roots to shoots. This review examined the vital roles of Zn2+ and nano Zn in plants and described their involvement in alleviating HMs toxicity in plants. Moving forward, a broad understanding of uptake, transport, signalling and tolerance mechanisms of Zn2+ /zinc and its nanoparticles in alleviating HMs toxicity of plants will be the first step towards a wider incorporation of Zn2+ into agricultural practices.

The role of nickel in cadmium accumulation in rice

Rice is one of the world's staple foods. Cadmium (Cd) levels in paddy soil are still increasing, and "Cd-contaminated rice" is a frequent occurrence, posing a serious threat to human health. Therefore, Cd contamination in rice is a key issue in agricultural production that needs to be addressed urgently. The Cd accumulation in rice is closely related to other elements. In this study, the impact of nickel (Ni) on the uptake and accumulation of Cd in rice was revealed, and the mechanism was discussed. Statistical analysis of field data showed that Cd concentration in rice grains decreased exponentially with increasing Ni concentration in paddy soils, which was verified by the hydroponic experiments. Under 5 μmol/L Cd exposure conditions, the addition of Ni (100 μmol/L) reduced the Cd contents in roots, stems, and leaves by 81.6 %, 60.6 %, and 65.9 %, respectively. With the presence of Ni, the amount of iron plaque decreased, and the Cd content in the iron plaque was reduced due to the competition between Ni and Cd for adsorption sites. In addition, the migration of Cd from stems to leaves was reduced. At the same time, the distribution of Cd in the cell was altered, and the concentration of Cd in the root cell walls increased with increasing Ni addition under 5 μmol/L Cd exposure. These findings highlight the critical role of Ni in inhibiting Cd accumulation in rice, and provide important information for understanding the effects of coexisting elements in Cd-contaminated soils on Cd accumulation in crops.

Phytoremediation technologies and their mechanism for removal of heavy metal from contaminated soil: An approach for a sustainable environment

The contamination of soils with heavy metals and its associated hazardous effects are a thrust area of today's research. Rapid industrialization, emissions from automobiles, agricultural inputs, improper disposal of waste, etc., are the major causes of soil contamination with heavy metals. These contaminants not only contaminate soil but also groundwater, reducing agricultural land and hence food quality. These contaminants enter the food chain and have a severe effect on human health. It is important to remove these contaminants from the soil. Various economic and ecological strategies are required to restore the soils contaminated with heavy metals. Phytoremediation is an emerging technology that is non-invasive, cost-effective, and aesthetically pleasing. Many metal-binding proteins (MBPs) of the plants are significantly involved in the phytoremediation of heavy metals; the MBPs include metallothioneins; phytochelatins; metalloenzymes; metal-activated enzymes; and many metal storage proteins, carrier proteins, and channel proteins. Plants are genetically modified to enhance their phytoremediation capacity. In Arabidopsis, the expression of the mercuric ion-binding protein in Bacillus megaterium improves the metal accumulation capacity. The phytoremediation efficiency of plants is also enhanced when assisted with microorganisms, biochar, and/or chemicals. Removing heavy metals from agricultural land without challenging food security is almost impossible. As a result, crop selections with the ability to sequester heavy metals and provide food security are in high demand. This paper summarizes the role of plant proteins and plant-microbe interaction in remediating soils contaminated with heavy metals. Biotechnological approaches or genetic engineering can also be used to tackle the problem of heavy metal contamination.

Proteomic Changes in Paspalum fasciculatum Leaves Exposed to Cd Stress

(1) Background: Cadmium is a toxic heavy metal that is widely distributed in water, soil, and air. It is present in agrochemicals, wastewater, battery waste, and volcanic eruptions. Thus, it can be absorbed by plants and enter the trophic chain. P. fasciculatum is a plant with phytoremediation capacity that can tolerate Cd stress, but changes in its proteome related to this tolerance have not yet been identified. (2) Methods: We conducted a quantitative analysis of the proteins present in P. fasciculatum leaves cultivated under greenhouse conditions in mining soils doped with 0 mg kg−1 (control), 30 mg kg−1, or 50 mg kg−1. This was carried out using the label-free shotgun proteomics technique. In this way, we determined the changes in the proteomes of the leaves of these plants, which allowed us to propose some tolerance mechanisms involved in the response to Cd stress. (3) Results: In total, 329 variable proteins were identified between treatments, which were classified into those associated with carbohydrate and energy metabolism; photosynthesis; structure, transport, and metabolism of proteins; antioxidant stress and defense; RNA and DNA processing; and signal transduction. (4) Conclusions: Based on changes in the differences in the leaf protein profiles between treatments, we hypothesize that some proteins associated with signal transduction (Ras-related protein RABA1e), HSPs (heat shock cognate 70 kDa protein 2), growth (actin-7), and cellular development (actin-1) are part of the tolerance response to Cd stress.

State-of-the-art OMICS strategies against toxic effects of heavy metals in plants: A review

Environmental pollution of heavy metals (HMs), mainly due to anthropogenic activities, has received growing attention in recent decades. HMs, especially the non-essential carcinogenic ones, including chromium (Cr), cadmium (Cd), mercury (Hg), aluminum (Al), lead (Pb), and arsenic (As), have appeared as the most significant air, water, and soil pollutants, which adversely affect the quantity, quality, and security of plant-based food all over the world. Plants exposed to HMs could experience significant decline in growth and yield. To avoid or tolerate the toxic effects of HMs, plants have developed complicated defense mechanisms, including absorption and accumulation of HMs in cell organelles, immobilization by forming complexes with organic chelates, extraction by using numerous transporters, ion channels, signalling cascades, and transcription elements, among others. OMICS strategies have developed significantly to understand the mechanisms of plant transcriptomics, genomics, proteomics, metabolomics, and ionomics to counter HM-mediated stress stimuli. These strategies have been considered to be reliable and feasible for investigating the roles of genomics (genomes), transcriptomic (coding), mRNA transcripts (non-coding), metabolomics (metabolites), and ionomics (metal ions) to enhance stress resistance or tolerance in plants. The recent developments in the mechanistic understandings of the HMs-plant interaction in terms of their absorption, translocation, and toxicity invasions at the molecular and cellular levels, as well as plants' response and adaptation strategies against these stressors, are summarized in the present review. Transcriptomics, genomics, metabolomics, proteomics, and ionomics for plants against HMs toxicities are reviewed, while challenges and future recommendations are also discussed.

Remediation of heavy metal(loid) contaminated soil through green nanotechnology

Modern industrialization is progressively degrading soil quality due to heavy metal contamination. Heavy metal (HM) contamination of agricultural soil has gained considerable attention due to its rapidly increasing levels. Nanoparticles (NPs) have unique physicochemical properties that make them effective stress relievers. Material science has recently been emphasizing “green” synthesis as a reliable, environmentally friendly, and sustainable method of synthesizing different kinds of materials, such as alloys, metal oxides, hybrids, and bioinspired materials. Therefore, green synthesis can be viewed as an effective tool to reduce the detrimental effects of the traditional nanoparticle synthesis methods commonly used in laboratories and industries. The review briefly describes the biosynthesis of NPs, the use of nanobiotechnology to remediate heavy metal-contaminated soil, the effect that NPs have on growth and development of plants, the behavior of NPs within plants when exposed to pollutants and the mechanisms used to alleviate HM stress. In addition, a broad overview of the major types of nanomaterials used so far in bioremediation of toxic heavy materials, recent advances regarding HM stress and the possible mechanisms by which NPs and HM interact in the agricultural system are also discussed.

Identification of low grain cadmium accumulation genotypes and its physiological mechanism in maize (Zea mays L.)

Soil cadmium (Cd) contamination poses adverse impacts on crop yield and quality. Maize is a widely cultivated cereal throughout the world. In this study, field and hydroponic experiments were conducted to investigate the genotypic difference in Cd accumulation and tolerance in maize. There were significant genotypic differences in grain Cd concentrations among 95 genotypes. From these 95 genotypes, L42 which showed a higher grain Cd concentration and L63 which showed a lower grain Cd concentration was selected for further study. Under Cd stress, L63 showed much less reduction in plant growth than L42 compared with the control. Seedlings of L63 recorded higher Cd concentration in roots, but lower in shoots L42, indicating that the low grain Cd concentration in L63 is mainly due to the low rate of transportation of Cd from roots to shoots. Most Cd accumulated in epidermis and xylem vessels of L63, while the green fluorescent was found across almost the entire cross-section of root in L42. Obvious ultrastructural damage was observed in L42 under Cd stress, especially in mesophyll cells, while L63 was less affected. These findings could contribute to developing low Cd accumulation and high tolerance maize cultivars.

Recent advances in physiological and molecular mechanisms of heavy metal accumulation in plants

Among abiotic stress, the toxicity of metals impacts negatively on plants' growth and productivity. This toxicity promotes various perturbations in plants at different levels. To withstand stress, plants involve efficient mechanisms through the implication of various signaling pathways. These pathways enhance the expression of many target genes among them gene coding for metal transporters. Various metal transporters which are localized at the plasma membrane and/or at the tonoplast are crucial in metal stress response. Furthermore, metal detoxification is provided by metal-binding proteins like phytochelatins and metallothioneins. The understanding of the molecular basis of metal toxicities signaling pathways and tolerance mechanisms is crucial for genetic engineering to produce transgenic plants that enhance phytoremediation. This review presents an overview of the recent advances in our understanding of metal stress response. Firstly, we described the effect of metal stress on plants. Then, we highlight the mechanisms involved in metal detoxification and the importance of the regulation in the response to heavy metal stress. Finally, we mentioned the importance of genetic engineering for enhancing the phytoremediation technique. In the end, the response to heavy metal stress is complex and implicates various components. Thus, further studies are needed to better understand the mechanisms involved in response to this abiotic stress.

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.

Significance of vacuolar proton pumps and metal/H+ antiporters in plant heavy metal tolerance

Soil and water are among the most valuable resources on earth. Unfortunately, their contamination with heavy metals has become a global problem. Heavy metals are not biodegradable and cannot be chemically degraded; therefore, they tend to accumulate in soils or to be transported by streaming water and contaminate both surface and groundwater. Cadmium (Cd) has no known biological function but is one of the most toxic metals. It represents a serious environmental concern since its accumulation in soils is associated with health risks to plants, animals and humans. On the other hand, copper (Cu) and zinc (Zn) are heavy metals that are indispensable to plants but become toxic when their concentration in soils exceeds a certain optimal level. Plants have evolved many mechanisms to cope with heavy metal toxicity; vacuolar sequestration is one of them. Vacuolar sequestration can be achieved through either phytochelatin-dependent or phytochelatin-independent pathways. Most of the transgenic plants meant for phytoremediation described in the literature result from the manipulation of genes involved in the phytochelatin-dependent pathway. However, recent evidence has emerged to support the importance of the phytochelatin-independent pathway in heavy metal sequestration into the vacuole, with metal/H⁺ antiporters and proton pumps playing an important role. In this review, the importance of vacuolar proton pumps and metal/H⁺ antiporters transporting Cd, Cu, and Zn is discussed. In addition, the recent advances in the production of transgenic plants with potential application in phytoremediation and food safety through the manipulation of genes encoding V-PPase proton pumps is described.

Cadmium uptake and translocation: selenium and silicon roles in Cd detoxification for the production of low Cd crops: a critical review

Cadmium (Cd) is a primary contaminant in agricultural soils of the world. The ability of Cd uptake, transport, detoxification, and accumulation varies among different plant species and genotypes. Cd is translocated from soil to root by different transporters which are used for essential plant nutrient uptake. A number of strategies have been suggested for decreasing Cd toxicity in Cd contaminated soils. Recently, a lot of research have been carried out on minimizing Cd uptake through selenium (Se) and silicon (Si) applications. Both Se and Si have been reported to mitigate Cd toxicity in different crops. Vacuolar sequestration, formation of phytochelatins, and cell wall adsorption have been reported as effective mechanisms for Cd detoxification. The present review discussed past and current knowledge of literature to better understand Cd toxicity and its mitigation by adopting different feasible and practical approaches.

Application of Nanoparticles Alleviates Heavy Metals Stress and Promotes Plant Growth: An Overview

Nanotechnology is playing a significant role in addressing a vast range of environmental challenges by providing innovative and effective solutions. Heavy metal (HM) contamination has gained considerable attention in recent years due their rapidly increasing concentrations in agricultural soil. Due to their unique physiochemical properties, nanoparticles (NPs) can be effectively applied for stress alleviation. In this review, we explore the current status of the literature regarding nano-enabled agriculture retrieved from the Web of Science databases and published from January 2010 to November 2020, with most of our sources spanning the past five years. We briefly discuss uptake and transport mechanisms, application methods (soil, hydroponic and foliar), exposure concentrations, and their impact on plant growth and development. The current literature contained sufficient information about NPs behavior in plants in the presence of pollutants, highlighting the alleviation mechanism to overcome the HM stress. Furthermore, we present a broad overview of recent advances regarding HM stress and the possible mechanism of interaction between NPs and HM in the agricultural system. Additionally, this review article will be supportive for the understanding of phytoremediation and micro-remediation of contaminated soils and also highlights the future research needs for the combined application of NPs in the soil for sustainable agriculture.

Alleviation mechanisms of metal(loid) stress in plants by silicon: a review

Silicon (Si), although not considered as an essential element for plants in general, can ameliorate the phytotoxicity induced by excess metal(loid)s whether non-essential (e.g. Cd, Pb, Cr, Al, As, and Sb) or essential (e.g. Cu, Ni, and Zn). The Si-enhanced resistance allowing plants to cope with this type of abiotic stress has been developed at multiple levels in plants. Restriction of root uptake and immobilization of metal(loid)s in the rhizosphere by Si is probably one of the first defence mechanism. Further, retention of elements in the root apoplasm might enhance the resistance and vigour of plants. At the cellular level, the formation of insoluble complexes between Si and metal(loid)s and their storage within cell walls help plants to decrease available element concentration and restrict symplasmic uptake. Moreover, Si influences the oxidative status of plants by modifying the activity of various antioxidants, improves membrane stability, and acts on gene expression, although its exact role in these processes is still not well understood. This review focuses on all currently known plant-based mechanisms related to Si supply and involved in amelioration of stress caused by excess metal(loid)s.