Advances in molecular mechanisms underlying cadmium uptake and translocation in rice

Smart reprogramming of plants against cadmium toxicity using membrane transporters and modern tools

Cadmium (Cd) in soil and water streams is now recognized as a significant environmental issue that harms plants and animals. Plants damaged by Cd toxicity experience various effects, from germination to yield reduction. Plant- and animal-based goods are allowing more Cd to enter our food chain, which could harm human health. Therefore, this urgent global concern must be addressed by implementing appropriate remedial measures. Plant-based phytoremediation is one safe, economical, and environmentally acceptable way to remove hazardous metals from the environment. Hyperaccumulator plants possess specialized transport proteins, such as metal transporters located in membranes of roots, as well as they facilitate Cd uptake from soil. This review outlines the latest findings about these membrane transporters. Moreover, we also discuss how innovative modern tools such as microbiomes, omics, nanotechnology, and genome editing have revealed molecular regulators connected to Cd tolerance, which may be employed to develop Cd-tolerant future plants. We can develop effective solutions to enhance tolerance of plant to Cd toxicity by leveraging membrane transporters and modern biotechnological tools. Additionally, implementing strategies to increase tolerance of Cd and restrict its bioavailability in plants' edible parts is crucial for improving food safety. These combined efforts will lead to the cultivation of safer food crops and support sustainable agricultural practices in contaminated environments.

Metabolomic, biochemical, and cytological observations reveal β-Pinene's protective effects against cadmium toxicity in salt-tolerant rice

Sea rice (Haidao 86) is a vital cultivar that could be cultivated in saline soil but is sensitive to heavy metal stress, and cadmium (Cd) stress in eastern coastal parts of China is frequently a great hazard. Nevertheless, there is a scarcity of research on the metabolic pathways involved in the detoxification of Cd stress in sea rice. Here, we added a kind of monoterpene hormone, (1S)-(-)-β-Pinene (βP), in Cd (100 mg/kg) stressed experiment to study its interaction with sea rice. Multiple Morphological traits were significantly rescued after the application of βP. Similarly, Cd alleviation by βP was also demonstrated in physio-chemical indicators. Cd contents in roots, leaves, grains, H2O2, and MDA contents have decreased by 28.1 %, 50.9 %, 51.4 %, 18.2 %, and 18.0 %, respectively, with the presence of βP compared to Cd alone. SOD, POD, CAT, and GPX activities were elevated by 17.1 %, 40.0 %, 12.4 %, and 22.5 %, respectively, and contents of GSH and APX were also significantly modulated after the supplementation of βP. Transmission electron microscopy also indicated that the Cd+βP group had intact cellular structure compared to the Cd group. Through metabolomic analysis, 27 and 31 differentially expressed metabolites (DEMs) were identified from CKvsCd and CdvsCd+βP. According to the results, carbohydrate metabolism (e.g. I-inositol, Gluconapoleiferin), phenylpropanoid (lignan, flavonoids) biosynthesis (e.g. Cyanidin, Leucoside), terpenoids, and alkaloids biosynthesis, were all significantly regulated with the presence of βP. Our study provided a detailed understanding of the mechanism behind Cd-stress tolerance and will aid in developing Cd tolerance in sea rice.

Insight into Cd Detoxification and Accumulation in Wheat by Foliar Application of Ferulic Acid

Cadmium (Cd) contamination in agricultural soils poses a significant threat to human health through the food chain. It is of great significance to address safe wheat production in Cd-contaminated agricultural soils. This study employed foliar spraying of ferulic acid (FA) in both hydroponic and field trials to investigate its potential in alleviating Cd toxicity and reducing Cd accumulation in wheat grains. Our findings revealed that FA application at 20 and 50 μM promoted plant growth, increased photosynthetic efficiency, and enhanced root tolerance to Cd by increasing mean root diameter, surface area, and root tip number, as well as enhancing antioxidant defense in roots. Especially, 20 μM FA foliar application significantly alleviated Cd-induced growth inhibition in seedlings and reduced grain Cd content by 66.3% compared to Cd-stressed alone. Mechanistically, FA downregulated the Cd transporter gene TaHAM2 to reduce Cd translocation from roots to shoots, while upregulated the Cd cellular compartment gene TaHAM3 to increase root Cd retention, of which 82.9% was sequestered in roots. During the grain-filling period in the field trial, FA application reduced Cd transport from roots to stems and stems to rachides, but enhanced Cd retention in rachides and roots. Additionally, FA downregulated the phloem Cd loading gene LCT1, limiting Cd allocation to bracts and grains, which in turn lowered the Cd content in the grains. Collectively, FA foliar application modulated Cd transport pathways by coordinately downregulating xylem and phloem transporter genes and enhancing root Cd retention capacity. These findings established FA as a promising strategy for Cd detoxification and reduced accumulation in crop grains through integrated physiological and molecular interventions. Overall, it holds potential for the future development of safe crop production in soils polluted with Cd.

Multiple insights into differential Cd detoxification mechanisms in new germplasms of mung bean (Vigna radiata L.) and potential mitigation strategy

Long-term cadmium (Cd) exposure inhibits plant growth and development, reduces crop yield and quality, and threatens food security. Exploring the Cd tolerance mechanisms and safe production of crops in Cd-contaminated environment has become a worldwide concern. In this study, mung bean (Vigna radiata L.) cultivar Sulu (SL) and its three mutant lines (20#, 09#, and 06#) were used to compare the difference in Cd absorption, accumulation, and tolerance through pot and field experiments. 20#, 09#, and 06# are Cd-tolerant germplasms of mung bean but exist in different Cd tolerance mechanisms, 20# exhibited the lowest Cd absorption capacity, 09# possessed lower Cd translocation capacity, while 06# accumulated more Cd in protoplasts. Mung bean germplasms with higher Cd tolerance generally showed lower absorption capacity and intracellular accumulation of Cd. Besides, Cd accumulation in mung bean seeds is mainly depended on the absorption and translocation of Cd in roots and the Cd concentration in leaves, exogenous Mn supply inhibited the Cd2+ net influx of roots and Cd accumulation in seeds, this trend was more pronounced in mung bean germplasms with higher Cd accumulation and absorption. Moreover, we characterized a Cd transporter gene VrNramp5, which was differentially expressed in different mung bean lines, overexpression of VrNramp5 increased Cd accumulation and was accompanied by Cd-sensitive phenotype in transgenic mung bean seedlings, and the Cd concentration of mung bean was significantly positively correlated with the expression levels of VrNramp5. Taken together, our findings demonstrated that different Cd tolerance mechanisms exist in mung bean. 20# is the new Cd-tolerant germplasm with low Cd absorption capacity and Cd accumulation in seeds, and has great potential for the safe production of mung bean in Cd-contaminated soils and the breeding of low Cd accumulation crop cultivars.

Phosphorylation-mediated cadmium and manganese selectivity uptake of SaNRAMP5 in nightshade

Identifying the selectivity of cadmium (Cd) and manganese (Mn) in transporters has long been a challenging scientific issue. Here, we identified the gene SaNRAMP5 from Solanum americanum, an orthologue of OsNRAMP5. SaNRAMP5 is predominantly expressed in root and localizes to the plasma membrane (PM). Knockout of SaNRAMP5 significantly reduced Cd accumulation in nightshade, while its overexpression in Arabidopsis increased Cd uptake in roots. Given the close relationship between nightshade and vegetables like potatoes, tomatoes, eggplants, and peppers, we compared the Cd absorption capabilities of NRAMP5 homologs in these species. Our results indicated that SaNRAMP5 exhibited a greater Cd uptake capacity than its homologs within the Solanaceae family. Interestingly, the Mn uptake capacities of these NRAMP5s varied independently of their Cd uptake capacities. Amino acid sequence analysis revealed that the N-terminal STNP residues, which mediate phosphorylation in SaNRAMP5, are crucial for the selective uptake of Cd and Mn. Mutating these STNP residues to a non-phosphorylatable form, SaNRAMP5(AANP), resulted in reduced Cd uptake without affecting Mn uptake. Conversely, StNRAMP5 and SlNRAMP5, which naturally lack STNP residues, demonstrated enhanced Cd uptake upon the introduction of STNP but not AANP. Notably, neither the introduction of STNP nor AANP affected their Mn uptake capacities. The reduced Cd uptake of SaNRAMP5(AANP) without compromising Mn uptake was attributed to alterations in PM localization due to continuous Cd exposure, rather than Mn exposure. Our findings provide novel insights into phosphorylation-mediated selective uptake of Cd and Mn, paving the way for engineering low-Cd crops without compromising yield.

Remediating contaminated environmental systems: the role of plants in cadmium removal

Cadmium (Cd) is one of the most harmful heavy metals in the environment, negatively impacting plant growth and development. However, phytoremediation which is an environmentally friendly and cost-effective technique can be used to treat Cd contaminated environments. It effectively removes Cd from polluted soil and water through processes, such as phytoextraction, phytostabilization, phytostimulation, phytofiltration, and phytotransformation. Numerous research has shown evidences that biological, physical, chemical, agronomic, and genetic methods are being utilized to improve phytoremediation. A special group of plants known as hyperaccumulator plants further enhance Cd removal, turning polluted areas into productive land. These plants accumulate Cd in root cell vacuoles and aerial parts. Despite the morphological and genetic variations, different plant species remediate Cd at different rates using either one or multiple mechanisms. To improve the effectiveness of phytoremediation, it is essential to thoroughly understand the mechanisms that control the accumulation and persistence of Cd in plants, including absorption, translocation, and elimination processes. However, what missing in understanding is in depth of idea on how the limitations of phytoremediation can be overcome. The limitations of phytoremediation can be addressed through various strategies, including natural and chemical amendments, genetic engineering, and natural microbial stimulation, broadly categorized into soil amelioration and plant capacity enhancement approaches. This review presents a concise overview of the latest research on various plants utilized in Cd phytoremediation and the different methods employed to enhance this process. Moreover, this review also underscores the creditability of phytoremediation technique to remediate Cd pollution as it offers a promising approach for eliminating Cd from contaminated sites and restoring their productivity. Additionally, we recommend directing future research toward enhancing the biochemical capabilities of plants for remediation purposes, elucidating the molecular mechanisms underlying the damage caused by Cd in plants, and understanding the fundamental principles regulating the enrichment of Cd in plants.

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

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

Sufficient manganese supply is necessary for OsNramp5 knockout rice plants to ensure normal growth and less Cd uptake

The development of crop cultivars with less Cd uptake in roots and accumulation in shoots is a most efficient and environment-friendly approach to deal with soil Cd contamination. Recently repression of Nramp5 expression or its knockout is commonly recognized to be efficient for reducing Cd accumulation in plants, but such mutant plants suffer from manganese deficiency. In this study, we assessed the efficacy of exogenous Mn addition in mitigating Cd stress in a japonica rice cultivar Xidao 1 (Wild Type, WT) and its OsNramp5 knockout mutant. Exposure to Cd stress resulted in notable low photosynthetic rate, growth inhibition, and high Cd accumulation in rice seedlings. Although the mutant plants contained much lower Cd concentration in both roots and shoots than the WT plants, their growth was significantly inhibited relative to the WT plants under the normal condition. Exogenous application of Mn (40 μM) dramatically reduces root and shoot Cd concentrations and alleviates the toxic effect of Cd stress in both rice types, with the mutant plants demonstrating lower Cd concentration and less Cd toxicity in comparison with WT plants. The alleviation of Cd toxicity by Mn addition was more effective in higher Cd level (1.0 μM) than in lower Cd level (0.1 μM). Mn increases the expression of OsNramp5 and other genes, including OsHMA2, OsHMA3, OsIRT1, and OsIRT2, which encode ion transporters related to Mn uptake and transportation, and meanwhile reduces Cd uptake and accumulation in rice seedlings. In short, the knockout of OsNramp5 results in the significant reduction of Cd uptake, but accompanies with Mn deficiency in rice plants, which can be efficiently overcome through exogenous Mn addition.

Cadmium absorption and translocation in rice plants are influenced by lower air temperatures during grain filling stage

The increasing frequency and severity of low temperatures, and soil cadmium (Cd) pollution threaten food security. However, the interactive effects of Cd exposure and low temperatures on rice yield and quality, as well as the mechanisms of Cd absorption and translocation, remain unclear. In this study, two rice varieties were cultivated in soils with two Cd contamination levels (Cdhigh and Cdlow) and exposed to control (CT25) or lower temperatures of 20 °C (LT20) and 17 °C (LT17) during grain-filling stage. Results showed significant decreases in seed setting rate and grain weight, reduced head rice yield, and increased chalkiness due to low temperatures, particularly in Cdhigh soils. Compared to CT25, LT17 and LT20 increased Cd concentration by 37.6 % and accumulation by 14.8 % in grains grown in Cdhigh soils. Enhanced root activity and upregulation of OsNramp1 and OsNramp5 under both low-temperatures increased Cd levels in roots. Lower temperatures also decreased phytochelatins (PCs) and increased expression of OsHMA2 and OsCAL1, facilitating Cd transport and raising Cd levels in stems. Furthermore, upregulated OsHMA2, OsLCT1, and OsZIP7 in stems under low-temperatures promoted Cd transport to panicles. Overall, low temperatures during grain filling increased Cd uptake and translocation into rice grains, especially in high Cd contaminated soils, raising health risks. The study highlights the need to address climate change's impact on cadmium hazards in rice.

The Mechanisms of Cadmium Toxicity in Living Organisms

Cadmium (Cd) is a toxic metal primarily found as a by-product of zinc production. Cd was a proven carcinogen, and exposure to this metal has been linked to various adverse health effects, which were first reported in the mid-19th century and thoroughly investigated by the 20th century. The toxicokinetics and dynamics of Cd reveal its propensity for long biological retention and predominant storage in soft tissues. Until the 1950s, Cd pollution was caused by industrial activities, whereas nowadays, the main source is phosphate fertilizers, which strongly contaminate soil and water and affect human health and ecosystems. Cd enters the human body mainly through ingestion and inhalation, with food and tobacco smoke being the primary sources. It accumulates in various organs, particularly the kidney and liver, and is known to cause severe health problems, including renal dysfunction, bone diseases, cardiovascular problems, and many others. On a cellular level, Cd disrupts numerous biological processes, inducing oxidative stress generation and DNA damage. This comprehensive review explores Cd pollution, accumulation, distribution, and biological impacts on bacteria, fungi, edible mushrooms, plants, animals, and humans on a molecular level. Molecular aspects of carcinogenesis, apoptosis, autophagy, specific gene expression, stress protein synthesis, and ROS formation caused by Cd were discussed as well. This paper also summarizes how Cd is removed from contaminated environments and the human body.

Carcinogenic and non-carcinogenic risks caused by rice contamination with heavy metals and their effect on the prevalence of cardiovascular disease (Using machine learning)

INTRODUCTION

The safety and health of food products are essential in the food industry, and the risk of contamination from various contaminants must be evaluated. Exposure to HMs from the environment (especially food) causes various adverse effects on the body and increases the risk of cardiovascular disease (CVD).

MATERIAL AND METHOD

Volunteers in the study comprised both healthy individuals and those with CVD. Patients were chosen using a cohort database of CVD individuals. A random choice of samples was conducted. Medical information (individuals with CVD) related to the participants was obtained from the Hoveyzeh Cohort Study Center. CVD-HM relationships were assessed using various machine-learning techniques.

RESULT

Based on the results of the GAM statistics approach, the baseline levels (β) of As, Cd, and Cr in rice have been calculated to be 1.05, 1.19, and 1.11, respectively. Based on the investigation's results, rice acts as a mediator between high-magnitude actions and the prevalence of CVD. Eating rice increases the probability of CVD by 0.18 and raises As eating by 0.494. The results showed that rice consumption in the research area is not associated with non-carcinogenic and carcinogenic risk (CRs and ILCRs for both categories were less than 1∗10-6).

CONCLUSION

There was neither a carcinogenic nor non-carcinogenic threat to adults or children and many hazardous HMs existed at the accepted thresholds. A notable relationship was seen between rice contaminated with HM and CVD.

Exploring genotypic variation and gene expression associated to cadmium accumulation in bread wheat

Cadmium (Cd) contamination poses significant risks to agricultural productivity and human health, particularly through its accumulation in staple crops such as bread wheat (Triticum aestivum L.). This study evaluated Cd accumulation and tolerance among six bread wheat cultivars exposed to six Cd concentrations (0, 2.5, 5, 10, 15, 20, and 25 mg kg-1 soil). Phenotypic assessments and quantitative real-time PCR (qRT-PCR) were conducted to analyze the expression patterns of TaNRAMP and TaZIP genes in various tissues and developmental stages of wheat, which play crucial roles in Cd uptake and transport. Results demonstrated significant variability in Cd accumulation. The Barat cultivar exhibited the lowest accumulation in grain (ranging from 0.21 to 8.8 mg kg-1) and the highest tolerance. In contrast, Kavir and Pishtaz displayed elevated Cd levels in both grain and straw, while Parsi accumulated more Cd in straw at lower concentrations (56.9 mg kg-1 in Cd concentration of 10 mg kg-1 soil). The gene expression analysis revealed that most cultivars showed increased expression of TaNRAMP genes, particularly TaNRAMP2 in Cd concentration of 10 mg kg-1 soil, which facilitates Cd uptake from the soil, and TaZIP genes, such as TaZIP4 and TaZIP7, involved in transporting Cd within the plant. Notably, the expression of TaZIP1 was significantly lower in cultivars with high Cd accumulation, suggesting a potential regulatory mechanism for Cd tolerance. Furthermore, cultivars exhibiting higher Cd levels correlated with increased expression of stress-responsive genes, indicating a broader response to Cd stress. These findings highlight Barat's potential for bread-making applications due to its low Cd accumulation, while Morvarid and Pishtaz which show reduced Cd content in the straw even under high Cd exposure are better suited for animal feed. This research underscores the genetic variability of wheat cultivars in response to Cd stress and provides essential insights into the molecular mechanisms underlying Cd accumulation, offering valuable information for breeding programs aimed at developing Cd-tolerant varieties to ensure food security in contaminated regions.

Ionic and nano calcium to reduce cadmium and arsenic toxicity in plants: Review of mechanisms and potentials

Contamination of agricultural soils with heavy metal(loid)s like arsenic (As) and cadmium (Cd) is an ever increasing concern for crop production, quality, and global food security. Numerous in-situ and ex-situ remediation approaches have been developed to reduce As and Cd contamination in soils. However, field-scale applications of conventional remediation techniques are limited due to the associated environmental risks, low efficacy, and large capital investments. Recently, calcium (Ca) and Ca-based nano-formulations have emerged as promising solutions with the large potential to mitigate As and Cd toxicity in soil for plants. This review provides comprehensive insights into the phytotoxic effects of As and Cd stress/toxicity and discusses the applications of Ca-based ionic and nano-agrochemicals to alleviate As and Cd toxicity in important crops such as rice, wheat, maize, and barley. Further, various molecular and physiological mechanisms induced by ionic and nano Ca to mitigate As and Cd stress/toxicity in plants are discussed. This review also critically analyzes the efficiency of these emerging Ca-based approaches, both ionic and nano-formulations, in mitigating As and Cd toxicity in comparison to conventional remediation techniques. Additionally, future perspectives and ecological concerns of the remediation approaches encompassing ionic and nano Ca have been discussed. Overall, the review provides an updated and in-depth knowledge for developing sustainable and effective strategies to address the challenges posed by As and Cd contamination in agricultural crops.

Impact of compost and biochar from agricultural waste on reducing cadmium concentration and mancozeb residue in soil

The negative impact of excessive exposure to agrochemicals in shallot cultivation causes environmental pollution and human health. Biochar has the potential to absorb agrochemical contamination. This research aimed to investigate the effect of providing compost and biochar from agricultural waste on land quality, reducing the concentration of heavy metal cadmium (Cd) and mancozeb pesticide residues in soil and products in shallot. The experiment was carried out in shallot fields in Ngurensiti Village, Pati Regency, Central Java Province. Four different treatments, including combinations of biochar and compost, were applied, along with conventional controls. Data were analyzed using the F test (ANOVA) and Tukey's test using the Minitab statistical program version 16.0. The research showed that using biochar made from sugarcane bagasse, rice husk, corncob, and compost helped more soil bacteria grow and lowered Cd and mancozeb concentrations. In addition, treatment with biochar from sugarcane bagasse waste showed a decrease in Cd and mancozeb concentrations and a more significant increase in bacterial populations compared to other treatments (rice husk biochar and corncob biochar). Although there was a slight increase in Cd concentration in shallot leaves post-treatment, Cd levels in shallot bulbs remained within safe limits. This study shows that using biochar and compost from agricultural waste effectively improves soil quality, reduces heavy metal pollution, and lowers pesticide levels to support sustainable agriculture and protect people's health.

Effects of Cadmium Stress on Tartary Buckwheat Seedlings

Cadmium (Cd) is a naturally occurring toxic heavy metal that adversely affects plant germination, growth, and development. While the effects of Cd have been described on many crop species including rice, maize, wheat and barley, few studies are available on cadmium's effect on Tartary buckwheat which is a traditional grain in China. We examined nine genotypes and found that 30 µM of Cd reduced the root length in seedlings by between 4 and 44% and decreased the total biomass by 7 to 31%, compared with Cd-free controls. We identified a significant genotypic variation in sensitivity to Cd stress. Cd treatment decreased the total root length and the emergence and growth of lateral roots, and these changes were significantly greater in the Cd-sensitive genotypes than in tolerant genotypes. Cd resulted in greater wilting and discoloration in sensitive genotypes than in tolerant genotypes and caused more damage to the structure of root and leaf cells. Cd accumulated in the roots and shoots, but the concentrations in the sensitive genotypes were significantly greater than in the more tolerant genotypes. Cd treatment affected nutrient uptake, and the changes in the sensitive genotypes were greater than those in the tolerant genotypes, which could maintain their concentrations closer to the control levels. The induction of SOD, POD, and CAT activities in the roots and shoots was significantly greater in the tolerant genotypes than in the sensitive genotypes. We demonstrated that Cd stress reduced root and shoot growth, decreased plant biomass, disrupted nutrient uptake, altered cell structure, and managed Cd-induced oxidative stress differently in the sensitive and tolerant genotypes of Tartary buckwheat.

Health risk assessment for consuming rice, bread, and vegetables in Hoveyzeh city

Introduction

People are continuously exposed to contamination, which mainly consists of heavy metals (HMs) and organic compounds. Several metals can get into grains, veggies, and bread through various methods. We estimated the health risk of HM exposure from the consumption of bread, veggies, and rice, considering the per capita amounts of these foods in the Iranian food basket, especially in Hoveyzeh and Azadegan Plain.

Material and method

The food products analyzed for the assessment of HMs include different veggies, rice, and bread. The health risk assessment was done with the Hazard Quotient and cancer risk formulae. The buying of vegetables, rice, and bread was done in random order during the fall and wintertime seasons.

Result

Tarom rice has the maximum reported levels of Cd (0.55 mg/kg), but Pakistani rice has the lowest level (0.18 mg/kg). Radish shows the highest concentrations of As, Pb, Cr, and Ni among vegetation, while Cress shows the lowest level. The study findings showed that Lavash bread had the highest levels of As (1.31 mg/kg), Cd (0.2 mg/kg), and Ni (1.2 mg/kg), whereas it indicated the lowest level of Cr (0.056 mg/kg). While the non-carcinogenic risk of HMs was evaluated between two groups of adults and children, both groups' HI and HQ levels were less than 1. The maximum HQ and HI scores for children were associated with Arsenic (As), specifically 0.0127 and 0.0137 for Tarom rice, respectively. Nevertheless, the highest HQ and HI scores for adults were associated with As, namely 0.0059 and 0.0064 for Tarom rice, respectively.

Conclusion

The evaluation of the carcinogenic risk caused by HM exposure in kids and adults showed that both groups' accumulated lifetime CRs and ILCRs were lower than 1*10-6. Hence, the consumption of veggies, rice, and bread within the study's area does not show an association with the occurrence of chronic diseases resulting from hazardous HMs.

Nano-enabled agrochemicals: mitigating heavy metal toxicity and enhancing crop adaptability for sustainable crop production

The primary factors that restrict agricultural productivity and jeopardize human and food safety are heavy metals (HMs), including arsenic, cadmium, lead, and aluminum, which adversely impact crop yields and quality. Plants, in their adaptability, proactively engage in a multitude of intricate processes to counteract the impacts of HM toxicity. These processes orchestrate profound transformations at biomolecular levels, showing the plant's ability to adapt and thrive in adversity. In the past few decades, HM stress tolerance in crops has been successfully addressed through a combination of traditional breeding techniques, cutting-edge genetic engineering methods, and the strategic implementation of marker-dependent breeding approaches. Given the remarkable progress achieved in this domain, it has become imperative to adopt integrated methods that mitigate potential risks and impacts arising from environmental contamination on yields, which is crucial as we endeavor to forge ahead with the establishment of enduring agricultural systems. In this manner, nanotechnology has emerged as a viable field in agricultural sciences. The potential applications are extensive, encompassing the regulation of environmental stressors like toxic metals, improving the efficiency of nutrient consumption and alleviating climate change effects. Integrating nanotechnology and nanomaterials in agrochemicals has successfully mitigated the drawbacks associated with traditional agrochemicals, including challenges like organic solvent pollution, susceptibility to photolysis, and restricted bioavailability. Numerous studies clearly show the immense potential of nanomaterials and nanofertilizers in tackling the acute crisis of HM toxicity in crop production. This review seeks to delve into using NPs as agrochemicals to effectively mitigate HM toxicity and enhance crop resilience, thereby fostering an environmentally friendly and economically viable approach toward sustainable agricultural advancement in the foreseeable future.

miR397b-LAC2 module regulates cadmium stress response by coordinating root lignification and copper homeostasis in Arabidopsis thaliana

Non-essential heavy metal cadmium (Cd) is toxic to plants and animals. Cadmium affects plant photosynthesis, respiration, and causes water imbalance and may lead to plant death. Cadmium induces toxicity by interfering with the essential metal copper (Cu) homeostasis, which affects plant nutrition. Though root lignin biosynthesis is positively regulated by Cd stress, the underlying mechanisms promoting lignin accumulation and controlling Cd-induced Cu limitation responses are unclear. Here, we elucidated the role of Cu-responsive microRNA (miR397b) in Arabidopsis thaliana plants for Cd stress by targeting the LACCASE2 (LAC2) gene. This study demonstrated the fundamental mechanism of miR397b-mediated Cd stress response by enhancing the lignin content in root tissues. We developed miR397b over-expressing plants, which showed considerable Cd stress tolerance. Plants with knockdown function of LAC2 also showed significant tolerance to Cd stress. miR397b overexpressing and lac2 mutant plants showed root reduction, higher biomass and chlorophyll content, and significantly lower Reactive Oxygen Species (ROS). This study demonstrated the miR397b-mediated Cd stress response in Arabidopsis by enhancing the lignin content in root tissues. We conclude that modulation in miR397b can be potentially used for improving plants for Cd tolerance and Cu homeostasis.

Alfalfa MsbHLH115 confers tolerance to cadmium stress through activating the iron deficiency response in Arabidopsis thaliana

Cadmium (Cd) pollution severely affects plant growth and development, posing risks to human health throughout the food chain. Improved iron (Fe) nutrients could mitigate Cd toxicity in plants, but the regulatory network involving Cd and Fe interplay remains unresolved. Here, a transcription factor gene of alfalfa, MsbHLH115 was verified to respond to iron deficiency and Cd stress. Overexpression of MsbHLH115 enhanced tolerance to Cd stress, showing better growth and less ROS accumulation in Arabidopsis thaliana. Overexpression of MsbHLH115 significantly enhanced Fe and Zn accumulation and did not affect Cd, Mn, and Cu concentration in Arabidopsis. Further investigations revealed that MsbHLH115 up-regulated iron homeostasis regulation genes, ROS-related genes, and metal chelation and detoxification genes, contributing to attenuating Cd toxicity. Y1H, EMSA, and LUC assays confirmed the physical interaction between MsbHLH115 and E-box, which is present in the promoter regions of most of the above-mentioned iron homeostasis regulatory genes. The transient expression experiment showed that MsbHLH115 interacted with MsbHLH121pro. The results suggest that MsbHLH115 may directly regulate the iron-deficiency response system and indirectly regulate the metal detoxification response mechanism, thereby enhancing plant Cd tolerance. In summary, enhancing iron accumulation through transcription factor regulation holds promise for improving plant tolerance to Cd toxicity, and MsbHLH115 is a potential candidate for addressing Cd toxicity issues.

Cell number regulator 8 from Salix linearistipularis enhances cadmium tolerance in poplar by reducing cadmium uptake and accumulation

Trace metals have relatively high density and high toxicity at low concentrations. Willow (Salix genus) is an excellent phytoremediation species for soil contaminated by trace metal ions. This study identified a cell number regulator (CNR) gene family member in Salix linearistipularis exhibiting strong metal ion resistance: SlCNR8. SlCNR8 expression was affected by various metal ions, including cadmium (Cd), zinc (Zn), copper (Cu), iron (Fe), and manganese (Mn). SlCNR8 overexpression enhanced Cd, Zn, Cu, and Fe resistance in transgenic poplar seedlings (84K) compared with the wild-type (WT). Moreover, transgenic poplar seedlings showed lower root Cd uptake and less Cd accumulation than WT under Cd stress. SlCNR8 was primarily localized to the nucleus and the plasma membrane-like cell periphery. Furthermore, SlCNR8 had transcriptional activation activity in yeast. The transcript levels of multiple metal ion transporters were altered in the roots of transgenic poplar seedlings compared to WT roots under Cd stress. These results suggest that SlCNR8 may enhance Cd resistance in transgenic poplar by reducing Cd uptake and accumulation. This may be related to altered transcription levels of other transporters or to itself. Our study suggests that SlCNR8 can be used as a candidate gene for genetic improvement of phytostabilisation of trace metals by genetic engineering.

Integrated physiological and omics analyses reveal the mechanism of beneficial fungal Trichoderma sp. alleviating cadmium toxicity in tobacco (Nicotiana tabacum L.)

Cadmium (Cd) is a highly toxic heavy metal and readily accumulates in tobacco, which imperils public health via Cd exposure from smoking. Beneficial microbes have a pivotal role in promoting plant growth, especially under environmental stresses such as heavy metal stresses. In this study, we introduced a novel fungal strain Trichoderma nigricans T32781, and investigated its capacity to alleviate Cd-induced stress in tobacco plants through comprehensive physiological and omics analyses. Our findings revealed that T32781 inoculation in soil leads to a substantial reduction in Cd-induced growth inhibition. This was evidenced by increased plant height, enhanced biomass accumulation, and improved photosynthesis, as indicated by higher values of key photosynthetic parameters, including the maximum quantum yield of photosystem Ⅱ (Fv/Fm), stomatal conductance (Gs), photosynthetic rate (Pn) and transpiration rate (Tr). Furthermore, element analysis demonstrated that T. nigricans T32781 inoculation resulted in a remarkable reduction of Cd uptake by 62.2% and a 37.8% decrease in available soil Cd compared to Cd-stressed plants without inoculation. The protective role of T32781 extended to mitigating Cd-induced oxidative stress by improving antioxidant enzyme activities of superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX). Metabolic profiling of tobacco roots identified 43 key metabolites, with notable contributions from compounds like nicotinic acid, succinic acid, and fumaric acid in reducing Cd toxicity in T32781-inoculated plants. Additionally, rhizosphere microbiome analysis highlighted the promotion of beneficial microbes, including Gemmatimonas and Sphingomonas, by T32781 inoculation, which potentially contributed to the restoration of plant growth under Cd exposure. In summary, our study demonstrated that T. nigricans T32781 effectively alleviated Cd stress in tobacco plants by reducing Cd uptake, alleviating Cd-induced oxidative stress, influencing plant metabolite and modulating the microbial composition in the rhizosphere. These findings offer a novel perspective and a promising candidate strain for enhancing Cd tolerance and prohibiting its accumulation in plants to reduce health risks associated with exposure to Cd-contaminated plants.

NaCl-mediated strategies for the trade-off between Cd bioconcentration and translocation in Solanum nigrum L

Salt interference significantly affects the behavior of heavy metals in the environment. This study compared and analyzed the response process, migration, and transformation of cadmium (Cd) in the hyperaccumulator Solanum nigrum (S. nigrum) under different NaCl levels to reveal the interference mechanisms of salt in plant remediation of Cd-contaminated soil. The results showed that Cd and salt stress significantly inhibited the growth of plants. The stress effect had more potent growth inhibition at the root than aboveground, thus inducing changes in the spatial configuration of the plants (decreased root-to-aboveground biomass ratio). Salt could activate Cd in plants, enhancing the inhibitory effect on plant growth. Salt increased Cd bioavailability due to the rhizosphere acidification effect, increasing plants' Cd accumulation. The Cd bioconcentration factor in plant roots peaked during the high Cd-high salt treatment (117.10), but the Cd accumulation of plants peaked during the high Cd-low salt treatment (233.04 μg plant-1). Salt additions and increased Cd concentrations enhanced root compartmentalization, inhibiting Cd transport to the aboveground. Changes in Fourier-transform infrared spectroscopy (FTIR) measurements confirmed that the functional groups in plants provided binding sites for Cd. These findings can help guide the phytoremediation of Cd contamination under saline soil conditions.

Dose dependent effect of nitrogen on the phyto extractability of Cd in metal contaminated soil using Wedelia trilobata

Cadmium (Cd) is one of the toxic heavy metal that negatively affect plant growth and compromise food safety for human consumption. Nitrogen (N) is an essential macronutrient for plant growth and development. It may enhance Cd tolerance of invasive plant species by maintaining biochemical and physiological characteristics during phytoextraction of Cd. A comparative study was conducted to evaluate the phenotypical and physiological responses of invasive W. trilobata and native W. chinensis under low Cd (10 µM) and high Cd (80 µM) stress, along with different N levels (i.e., normal 91.05 mg kg-1 and low 0.9105 mg kg-1). Under low-N and Cd stress, the growth of leaves, stem and roots in W. trilobata was significantly increased by 35-23%, 25-28%, and 35-35%, respectively, compared to W. chinensis. Wedelia trilobata exhibited heightened antioxidant activities of catalase and peroxidase were significantly increased under Cd stress to alleviate oxidative stress. Similarly, flavonoid content was significantly increased by 40-50% in W. trilobata to promote Cd tolerance via activation of the secondary metabolites. An adverse effect of Cd in the leaves of W. chinensis was further verified by a novel hyperspectral imaging technology in the form of normalized differential vegetation index (NDVI) and photochemical reflectance index (PRI) compared to W. trilobata. Additionally, W. trilobata increased the Cd tolerance by regulating Cd accumulation in the shoots and roots, bolstering its potential for phytoextraction potential. This study demonstrated that W. trilobata positively responds to Cd with enhanced growth and antioxidant capabilities, providing a new platform for phytoremediation in agricultural lands to protect the environment from heavy metals pollution.

Mitigation strategies for excessive cadmium in rice

Cadmium (Cd)-contaminated rice is a human food safety problem that lacks a clear solution. A large amount of rice having an excessive Cd content is processed yearly, but it cannot be discarded and placed in landfills because it will cause secondary pollution. How do we best cope with this toxic rice? From the perspectives of food safety, food waste prevention, and human hunger eradication, the use of contemporary physical, chemical, and biological techniques to lower the Cd content in postharvest Cd-contaminated rice so that it can be used safely is the best course of action. In this review, the contamination, chemical speciation, and distribution of Cd in rice are analyzed and discussed, as are the methods of Cd removal from rice, including a comparison of the advantages and disadvantages of various techniques. Owing to the limitations of current technology, research and technological development recommendations for removing Cd from rice grain are presented. The chemical and biological methods produce higher Cd-removal rates than physical methods. However, they are limited to small-scale laboratory applications and cannot be applied on a large industrial scale. For the efficient safe removal of Cd from food, mixed fermentation with lactic acid bacteria and yeast has good application prospects. However, limited strains having high Cd-removal rates have been screened. In addition, modern biotechnology has rarely been applied to reduce rice Cd levels. Therefore, applying genetic engineering techniques to rapidly obtain microorganisms with high Cd-removal rates in rice should be the focus of future research.

Effects of cultivar, water condition and their interactions on Cd accumulation in rice grains

Using low Cd accumulation cultivars and managing field water regimes are effective measures to mitigate Cd accumulations in rice grains. However, the effect of the cultivar-water condition interaction (CWI) on grain Cd accumulations has largely been ignored. To solve this problem, pot and hydroponic experiments were conducted using 14 rice cultivars and two contrasting water conditions. The results showed that CWI significantly affected Cd concentrations in rice grains and roots, explaining 8.8% and 22.8% of the total variance, respectively. These CWI effects were derived from cultivar-dependent variations in rhizosphere soil properties [Eh, pH and available Cd associated with root radial oxygen loss (ROL)] and root Cd uptake. In this context, cultivar HH61 exhibited low, stable Cd accumulations, owing to its stably lower translocation rate, root Cd uptake ability and available Cd in its rhizosphere than the other cultivars, which was induced by its lower ROL. Root-to-grain Cd translocation rates were vital in determining Cd accumulations in grain of different cultivars but were independent from CWI. These results indicated that CWI could play an important role in Cd accumulation in rice while stable low-Cd cultivar should possess low ROL under flooding and low root-to-grain Cd translocation rate. The results will provide novel theoretical basis for cultivar selection and hence benefit the extensive use of low-accumulation cultivars and public health.

Whole-Process Risk Management of Soil Amendments for Remediation of Heavy Metals in Agricultural Soil-A Review

Reducing the mobility and bioavailability of heavy metals in soils by adding exogenous materials is a technology for remediating soils contaminated with heavy metals. Unlike industrial sites, the use of such techniques in agricultural soils requires consideration of not only reducing the mobility of heavy metals but also avoiding adverse effects on soil fertility and the growth of plants. Due to the uncertainty of the stability of amendments applied to agricultural soil, the application of amendments in farmland soil is controversial. This article reviewed the field studies in which amendments were used to immobilize heavy metals, and identified the potential environmental impacts of all aspects of soil amendment usage, including production and processing, transportation, storage, application to soil, long-term stability, and plant absorption. Results of the study indicated that after identifying the environmental risks of the whole process of the application of improvers in agricultural fields, it is necessary to classify the risks according to their characteristics, and design differentiated risk control measures for the safe application of this type of technology.

Genetic Regulation Mechanism of Cadmium Accumulation and Its Utilization in Rice Breeding

Cadmium (Cd) is a heavy metal whose pollution in rice fields leads to varying degrees of Cd accumulation in rice. Furthermore, the long-term consumption of Cd-contaminated rice is harmful to human health. Therefore, it is of great theoretical significance and application value to clarify the genetic regulation mechanism of Cd accumulation in rice and cultivate rice varieties with low Cd accumulation for the safe use of Cd-contaminated soils. This review summarizes the effects of Cd on rice growth, yield, and quality; the physiological and molecular mechanisms of Cd absorption in the roots, loading, and transport of Cd in the xylem, the distribution of Cd in nodes, redistribution of Cd in leaves, and accumulation of Cd in the grains; the regulation mechanism of the Cd stress response; and the breeding of rice with low Cd accumulation. Future directions on the genetic regulation of Cd in rice and application are also discussed. This review provides a theoretical basis for studies exploring the genetic regulation of Cd stress in rice. It also offers a basis for formulating effective strategies to reduce the Cd content in rice.