Magnetite nanoparticle (NP) uptake by wheat plants and its effect on cadmium and chromium toxicological behavior

An assessment of nanotechnology-based interventions for cleaning up toxic heavy metal/metalloid-contaminated agroecosystems: Potentials and issues

Heavy metals (HMs) are among the most dangerous environmental variables for a variety of life forms, including crops. Accumulation of HMs in consumables and their subsequent transmission to the food web are serious concerns for scientific communities and policy makers. The function of essential plant cellular macromolecules is substantially hampered by HMs, which eventually have a detrimental effect on agricultural yield. Among these HMs, three were considered, i.e., arsenic, cadmium, and chromium, in this review, from agro-ecosystem perspective. Compared with conventional plant growth regulators, the use of nanoparticles (NPs) is a relatively recent, successful, and promising method among the many methods employed to address or alleviate the toxicity of HMs. The ability of NPs to reduce HM mobility in soil, reduce HM availability, enhance the ability of the apoplastic barrier to prevent HM translocation inside the plant, strengthen the plant's antioxidant system by significantly enhancing the activities of many enzymatic and nonenzymatic antioxidants, and increase the generation of specialized metabolites together support the effectiveness of NPs as stress relievers. In this review article, to assess the efficacy of various NP types in ameliorating HM toxicity in plants, we adopted a 'fusion approach', in which a machine learning-based analysis was used to systematically highlight current research trends based on which an extensive literature survey is planned. A holistic assessment of HMs and NMs was subsequently carried out to highlight the future course of action(s).

Iron oxide nanoparticles improving multimetal phytoextraction in Helianthus annuus

This study assessed the phytotoxicity of a mixture of five different trace elements (TEs) frequently found as pollutants in soils: arsenic, cadmium, copper, lead and zinc. On the other hand, the plant response to a magnetite (Fe3O4) nanoparticle amendment on this mixture as well as nanomagnetite remediation potential has been tested. Sunflower (Helianthus annuus) plants were grown for 90 days in soil contaminated with the five mentioned TEs at the limit levels of TEs in soils likely to receive sludge established by French legislation. Depending on the conditions, experimental set-ups were amended or not with 1% dry weight nanomagnetite (NPsMagn), citric acid-coated nanomagnetite (NPsMagn@CA) or micro-sized magnetite (μPs) in order to assess the behavior of nanomagnetites in a TEs-contaminated water-soil-plant system under repeated water-deficiency stress. The mixture of TEs did not induce phytotoxicity as estimated by plant growth, pigment content, maximum quantum yield of photosynthesis, oxidative impact and antioxidant response. Furthermore, both nanomagnetites treatments in a TEs-contaminated soil significantly increased biomass production by 64 % compared to control and antioxidant enzyme activities compared to control and TEs-treated plants. NPsMagn and NPsMagn@CA particularly enhance phytoextraction of Cd and Cu, increasing the amounts of TEs in aerial parts from 1.5 to 4.5 times compared to set-ups without nanomagnetites. Based on Cd, Cu, Pb and Zn contents in soil solutions, both nanomagnetites treatments improved TEs phytoextraction without increasing groundwater contamination. On the contrary, nanomagnetites significantly reduce arsenic uptake by plants and solubilization in dissolved phase. Our results show that modifying surface physicochemical properties of NPsMagn with citric acid coating does not improve their effects compared to bare NPsMagn. NPsMagn and NPsMagn@CA also appear to mitigate the effects of drought stress. This work highlights several positive environmental aspects related to the use of nanomagnetites in phytoremediation.

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.

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

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

Influence of biochar produced from negative pressure-induced carbonization on transformation of potentially toxic metal(loid)s concerning plant physiological characteristics in industrially contaminated soil

Soil contamination and its subsequent impact on the food chain is a pressing challenge in the present day. The application of biochar has demonstrated a significant and positive effect on soil health, thereby enhancing plant growth and development. However, the application of biochar (BC) produced from negative pressure-induced carbonization to mitigate metal(loid) contamination is a new strategy that has been studied in current research. Results depicted that the application of biochar derived from the negative pressure carbonization (vacuum-assisted biochar (VBC) has a significant (p ≤ 0.05) positive impact on plant growth and physiological characteristics by influencing immobilization and speciation of metal(loid) in the soil system. Moreover, the interactive effect of VBC on physiological characteristics (photosynthesis, gas exchange, and chlorophyll contents) and antioxidant activities of maize (Zea mays L.) was significantly (p ≤ 0.05) positive by confining the translocation and movement of metal(loid)s to the aerial part of the maize plant. X-ray diffraction (XRD) provided information on the structural and chemical changes induced by the VBC-500 °C explaining metal(loid) adsorption onto mineral surfaces and complexation that can affect their mobility, availability, and toxicity in the contaminated soil. Fourier transform infrared spectroscopy (FTIR) further provided a more detailed understanding of the metal(loid)s and biochar complexation mechanisms influenced by VBC-based functional groups -OH, C-Hn, -COOH, CO, C-O-C, CC, C-O, C-H, OH, and C-C in the binding process. These results suggest that the application of biochar prepared at 500 °C under negative pressure-induced carbonization conditions to the soil is the most efficient way to reduce the uptake and transfer of metal(loid)s by influencing their mobility and availability in the soil-plant system.

Effect of stabilization time and soil chromium concentration on Sesbania virgata growth and metal tolerance

Sesbania virgata is a pioneer shrub from the Fabaceae family, native to riparian environments in northeast of Argentina, southern of Brazil and Uruguay. In peri-urban riparian soils, metal contamination is a frequent problem, being its bioavailability partly determined by the stabilization time and frequency of contamination events. The effect of time elapsed between chromium (Cr) soil enrichment and plant seeding and Cr doses on S. virgata tolerance and metal absorption were evaluated. Treatments were developed by adding Cr (80-400 ppm) to the soil and allowing two days or fifteen months to elapse before sowing, and a control treatment without Cr addition. After 150 days from seeding, bioaccumulation and translocation factors, growth parameters (dry biomass and its aerial/radical allocation pattern, stem length and its elongation rate), morphological parameters (root volume and leaf area), and physiological parameters (chlorophyll content) of the specimens were determined. The emergence of S. virgata was inhibited since 150 ppm when Cr was added to the soil two days before seeding, with Cr accumulation in roots starting at 80 ppm (17.4 ± 2.5 mg kg-1). Under 15 months of metal stabilization, S. virgata plants survived across the entire range of Cr doses tested, with accumulation in roots since 100 ppm (35.5 ± 0.2 mg kg-1) and metal translocation to aerial tissues only under 400 ppm. The results obtained showed that S. virgata did not have high BCF and TF values, suggesting that it cannot be classified as bioaccumulator of Cr under the tested conditions. However, its presence in environments contaminated with Cr can be beneficial, as it helps to stabilize the metal in the soil.

Recent Advances in Microbial-Assisted Remediation of Cadmium-Contaminated Soil

Soil contamination with cadmium (Cd) is a severe concern for the developing world due to its non-biodegradability and significant potential to damage the ecosystem and associated services. Industries such as mining, manufacturing, building, etc., rapidly produce a substantial amount of Cd, posing environmental risks. Cd toxicity in crop plants decreases nutrient and water uptake and translocation, increases oxidative damage, interferes with plant metabolism and inhibits plant morphology and physiology. However, various conventional physicochemical approaches are available to remove Cd from the soil, including chemical reduction, immobilization, stabilization and electro-remediation. Nevertheless, these processes are costly and unfriendly to the environment because they require much energy, skilled labor and hazardous chemicals. In contrasting, contaminated soils can be restored by using bioremediation techniques, which use plants alone and in association with different beneficial microbes as cutting-edge approaches. This review covers the bioremediation of soils contaminated with Cd in various new ways. The bioremediation capability of bacteria and fungi alone and in combination with plants are studied and analyzed. Microbes, including bacteria, fungi and algae, are reported to have a high tolerance for metals, having a 98% bioremediation capability. The internal structure of microorganisms, their cell surface characteristics and the surrounding environmental circumstances are all discussed concerning how microbes detoxify metals. Moreover, issues affecting the effectiveness of bioremediation are explored, along with potential difficulties, solutions and prospects.

Alleviation of chromium stress in plants using metal and metal oxide nanoparticles

Chromium (Cr), one of the hazardous pollutants, exists predominantly as Cr(VI) and Cr(III) in the environment. Cr(VI) is more toxic than Cr(III) due to its high mobility and solubility. Elevated levels of Cr in agricultural soil due to various anthropogenic activities cause Cr accumulation in plants, resulting in a significant reduction in plant yield and quality due to Cr-induced physiological, biochemical and molecular alterations. It can infiltrate the food chain through crop plants and cause harmful effects in humans via biomagnification. Cr(VI) is linked to cancer in humans. Therefore, mitigation strategies are required to remediate Cr-polluted soils and limit its accumulation in plants for safe food production. Recent research on metal and metal oxide nanoparticles (NPs) has shown that they can effectively reduce Cr accumulation and phytotoxicity. The effects of these NPs are influenced by their type and dose, exposure method, plant species and experimental settings. In this review, we present an up-to-date compilation and comprehensive analysis of the existing literature regarding the process of uptake and distribution of Cr and impact and potential mechanisms of metal and metal oxide nanoparticles led mitigation of Cr-induced stress in plants. We have also discussed recent developments, existing research gaps and future research directions in the field of Cr stress mitigation by NPs in plants. Overall, this review can provide valuable insights in reducing Cr accumulation and toxicity using metal and metal oxide nanoparticles, thereby promoting safe and sustainable cultivation of food and phytostabilization of Cr-polluted soil.

Chromium Toxicity in Plants: Signaling, Mitigation, and Future Perspectives

Plants are very often confronted by different heavy metal (HM) stressors that adversely impair their growth and productivity. Among HMs, chromium (Cr) is one of the most prevalent toxic trace metals found in agricultural soils because of anthropogenic activities, lack of efficient treatment, and unregulated disposal. It has a huge detrimental impact on the physiological, biochemical, and molecular traits of crops, in addition to being carcinogenic to humans. In soil, Cr exists in different forms, including Cr (III) "trivalent" and Cr (VI) "hexavalent", but the most pervasive and severely hazardous form to the biota is Cr (VI). Despite extensive research on the effects of Cr stress, the exact molecular mechanisms of Cr sensing, uptake, translocation, phytotoxicity, transcript processing, translation, post-translational protein modifications, as well as plant defensive responses are still largely unknown. Even though plants lack a Cr transporter system, it is efficiently accumulated and transported by other essential ion transporters, hence posing a serious challenge to the development of Cr-tolerant cultivars. In this review, we discuss Cr toxicity in plants, signaling perception, and transduction. Further, we highlight various mitigation processes for Cr toxicity in plants, such as microbial, chemical, and nano-based priming. We also discuss the biotechnological advancements in mitigating Cr toxicity in plants using plant and microbiome engineering approaches. Additionally, we also highlight the role of molecular breeding in mitigating Cr toxicity in sustainable agriculture. Finally, some conclusions are drawn along with potential directions for future research in order to better comprehend Cr signaling pathways and its mitigation in sustainable agriculture.

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.

The Status and Research Progress of Cadmium Pollution in Rice- (Oryza sativa L.) and Wheat- (Triticum aestivum L.) Cropping Systems in China: A Critical Review

The accumulation of cadmium in rice (Oryza sativa L.) and wheat (Triticum aestivum L.) is a serious threat to the safe use of farmland and to the health of the human diet that has attracted extensive attention from researchers. In this review, a bibliometric analysis was performed using a VOS viewer (1.6.18, Netherlands) to investigate the status of cadmium contamination in rice and wheat growing systems, human health risks, mechanisms of Cd uptake and transport, and the corresponding research hotspots. It has a certain reference value for the prevention and control of cadmium pollution in rice and wheat planting systems in China and abroad. The results showed that the Cd content in rice and wheat planting systems in the Yangtze River Basin was significantly higher than that in other areas of China, and the Cd content in rice and wheat grains and the hazard quotient (HQ) in Hunan Province was the highest. The average Cd concentration exceeded the recommended limit by about 62% for rice and 81% for wheat. The main reasons for the high Cd pollution in rice and wheat growing areas in Hunan are mining activities, phosphate fertilizer application, sewage irrigation, and electronic equipment manufacturing. In this review, we demonstrate that cadmium toxicity reduces the uptake and transport of essential elements in rice and wheat. Cadmium stress seriously affected the growth and morphology of plant roots. In the shoots, Cd toxicity was manifested by a series of physiological injuries, such as decreased photosynthesis, soluble protein, sugar, and antioxidant enzyme activity. Cadmium that accumulates in the shoots is transferred to grains and then passes up the food chain to people and animals. Therefore, methods for reducing cadmium content in grains of rice and wheat are urgently needed, especially in Cd-contaminated soil. Current research on Cd pollution in rice and wheat planting systems focuses on the bioavailability of Cd, soil rhizosphere changes in wheat and rice, and the role of antioxidant enzyme systems in alleviating heavy metal stress in rice and wheat.

Efficacy of metallic nanoparticles in attenuating the accumulation and toxicity of chromium in plants: Current knowledge and future perspectives

Nanoparticles have emerged as cutting-edge technology for the improvement of crops yield and safe cultivation of agricultural plants, especially in peripheral areas impaired with toxic heavy metals including chromium (Cr). The uncontrolled release of Cr mainly from anthropogenic factors is substantially polluting the surrounding environment, thereby extensively accumulated in soil-plant system. The excessive Cr-accretion in plant tissues disturbed the morph-physiological, biochemical, cellular, metabolic and molecular processes, and impaired the plants functionality. Therefore, it is obligatory to restrict the accumulation and toxic effects of Cr in plant organs. Recent studies on metallic nanoparticles (MNPs) such as iron oxide, silicon dioxide, copper oxide and zinc oxide have approved their efficacy as potent pool to curb the Cr-induced phytotoxicities and improved the plant tolerance. MNPs attenuated the bioaccumulation and phytotoxicity of Cr by utilizing key mechanisms such as improved photosynthetic machinery, regulation of cellular metabolites, greater chelation capacity to bind with Cr, release of corresponding metallic ions, upsurge in the uptake of essential nutrients, activation of antioxidants (enzymatic and non-enzymatic), reduction in oxidative stress, and cellular injuries, thus improvement in plant growth performances. We have briefly discussed the current knowledge and research gaps in existing literature along with possible recommendations for future research. Overall, Cr-detoxification by MNPs may depends upon the target plant species, Cr speciation, plant growth stages (seedling, vegetative and ripening etc.), treatment methods (foliar spray, seed priming and nutrient solution etc.), type, size, dose and coating of applied MNPs, and conditions (hydroponic and soil environment etc.). This review would help plant scientists to develop MNPs based strategies such as nano-fertilizers to alleviate the Cr-accumulation and its toxic impacts. This may leads to safe and healthy food production. The review outcomes can provide new horizons for research in the applications of MNPs for the sustainable agriculture.

Nanoparticles: The Plant Saviour under Abiotic Stresses

Climate change significantly affects plant growth and productivity by causing different biotic and abiotic stresses to plants. Among the different abiotic stresses, at the top of the list are salinity, drought, temperature extremes, heavy metals and nutrient imbalances, which contribute to large yield losses of crops in various parts of the world, thereby leading to food insecurity issues. In the quest to improve plants' abiotic stress tolerance, many promising techniques are being investigated. These include the use of nanoparticles, which have been shown to have a positive effect on plant performance under stress conditions. Nanoparticles can be used to deliver nutrients to plants, overcome plant diseases and pathogens, and sense and monitor trace elements that are present in soil by absorbing their signals. A better understanding of the mechanisms of nanoparticles that assist plants to cope with abiotic stresses will help towards the development of more long-term strategies against these stresses. However, the intensity of the challenge also warrants more immediate approaches to mitigate these stresses and enhance crop production in the short term. Therefore, this review provides an update of the responses (physiological, biochemical and molecular) of plants affected by nanoparticles under abiotic stress, and potentially effective strategies to enhance production. Taking into consideration all aspects, this review is intended to help researchers from different fields, such as plant science and nanoscience, to better understand possible innovative approaches to deal with abiotic stresses in agriculture.

Role of metal-nanoparticles in farming practices: an insight

Nanotechnology introduces revolutionary approaches for agriculture in the form of nano-based pesticides, fertilizers, sensors, weed-controlling agents, enhanced seed germination materials, etc. Even though metal-nanoparticles (NPs) have shown their potential to improve crop yield, the mode of action at the cellular level and fate in the human body and the environment are not well understood yet. Several metal-nanoparticles have been studied extensively by researchers for their active role in enhancing the rate of seed germination and crop quality augmentation which may happen due to several mechanisms such as increased porosity in nano-primed seeds inducing up-regulation of the expression of aquaporin and Reactive Oxygen Species (ROS) genes involved in water uptake, improving the root dehydrogenase activity to enhance the water absorption capability, etc. However, researchers have also demonstrated and reported the possible toxicity of NPs in the environment due to their agricultural practices. But the fate of NPs and their environmental impact are still unclear and largely vary based on several factors such as the size of NPs, coating material, mode of discharge and locations, etc. This review thoroughly focuses on the mode of action of various NPs in seed germination and accumulation, translocation through cells, and potential environmental and health risks.

The impact of chromium ion stress on plant growth, developmental physiology, and molecular regulation

In recent years, heavy metals-induced soil pollution has increased due to the widespread usage of chromium (Cr) in chemical industries. The release of Cr into the environment has reached its peak causing hazardous environmental pollution. Heavy metal-induced soil pollution is one of the most important abiotic stress affecting the dynamic stages of plant growth and development. In severe cases, it can kill the plants and their derivatives and thereby pose a potential threat to human food safety. The chromium ion effect on plants varies and depends upon its severity range. It mainly impacts the numerous regular activities of the plant's life cycle, by hindering the germination of plant seeds, inhibiting the growth of hypocotyl and epicotyl parts of the plants, as well as damaging the chloroplast cell structures. In this review article, we tried to summarize the possible effects of chromium-induced stress on plant growth, developmental physiology, biochemistry, and molecular regulation and provided the important theoretical basis for selecting remedial plants in chromium-induced contaminated soils, breeding of low toxicity tolerant varieties, and analyzing the mechanism of plant resistance mechanisms in response to heavy metal stress.

A review of the influence of nanoparticles on the physiological and biochemical attributes of plants with a focus on the absorption and translocation of toxic trace elements

Trace elements (TEs) from various natural and anthropogenic activities contaminate the agricultural water and soil environments. The use of nanoparticles (NPs) as nano-fertilizers or nano-pesticides is gaining popularity worldwide. The NPs-mediated fertilizers encourage the balanced availability of essential nutrients to plants compared to traditional fertilizers, especially in the presence of excessive amounts of TEs. Moreover, NPs could reduce and/or restrict the bioavailability of TEs to plants due to their high sorption ability. In this review, we summarize the potential influence of NPs on plant physiological attributes, mineral absorption, and TEs sorption, accumulation, and translocation. It also unveils the NPs-mediated TE scavenging-mechanisms at plant and soil interface. NPs immobilized TEs in soil solution effectively by altering the speciation of TEs and modifying the physiological, biochemical, and biological properties of soil. In plants, NPs inhibit the transfer of TEs from roots to shoots by inducing structural modifications, altering gene transcription, and strengthening antioxidant defense mechanisms. On the other hand, the mechanisms underpinning NPs-mediated TEs absorption and cytotoxicity mitigation differ depending on the NPs type, distribution strategy, duration of NP exposure, and plants (e.g., types, varieties, and growth rate). The review highlights that NPs may bring new possibilities for resolving the issue of TE cytotoxicity in crops, which may also assist in reducing the threats to the human dietary system. Although the potential ability of NPs in decontaminating soils is just beginning to be understood, further research is needed to uncover the sub-cellular-based mechanisms of NPs-induced TE scavenging in soils and absorption in plants.

Cadmium in Cereal Crops: Uptake and Transport Mechanisms and Minimizing Strategies

Cadmium (Cd) contamination in soils and accumulation in cereal grains have posed food security risks and serious health concerns worldwide. Understanding the Cd transport process and its management for minimizing Cd accumulation in cereals may help to improve crop growth and grain quality. In this review, we summarize Cd uptake, translocation, and accumulation mechanisms in cereal crops and discuss efficient measures to reduce Cd uptake as well as potential remediation strategies, including the applications of plant growth regulators, microbes, nanoparticles, and cropping systems and developing low-Cd grain cultivars by CRISPR/Cas9. In addition, miRNAs modulate Cd translocation, and accumulation in crops through the regulation of their target genes was revealed. Combined use of multiple remediation methods may successfully decrease Cd concentrations in cereals. The findings in this review provide some insights into innovative and applicable approaches for reducing Cd accumulation in cereal grains and sustainable management of Cd-contaminated paddy fields.

New SFT2-like Vesicle Transport Protein (SFT2L) Enhances Cadmium Tolerance and Reduces Cadmium Accumulation in Common Wheat Grains

Cadmium (Cd) is one of the most toxic heavy metal elements to the environment, which seriously threatens the safe production of food crops. In this study, we identified a novel function of the cytomembrane TaSFT2L protein in wheat (Triticum aestivum). Expression of the TaSFT2L gene in yeast showed no transport activities for Cd, which could explain the role of TaSFT2L in metal tolerance. It was observed that increased autophagic activity in roots caused by silencing of TaSFT2L enhanced Cd tolerance. Transgenic wheat revealed that RNA interference (RNAi) lines enhanced the wheat growth concerning the increased shoot or root elongation, dry weight, and chlorophyll accumulation. Furthermore, RNAi lines decreased root-to-grain Cd translocation in wheat by nearly 68% and Cd accumulation in wheat grains by 53%. Meanwhile, the overexpression lines displayed a compromised growth response and increased Cd accumulation in wheat tissues, compared to wild type. These findings show that TaSFT2L is a key gene involved in regulation of Cd translocation in wheat, and its silencing to form transgenic wheat can inhibit Cd accumulation. This has the ability to alleviate the food chain-associated impact of environmental pollution on human health.

The dichotomy of nanotechnology as the cutting edge of agriculture: Nano-farming as an asset versus nanotoxicity

The unprecedented setbacks and environmental complications, faced by global agro-farming industry, have led to the advent of nanotechnology in agriculture, which has been recognized as a novel and innovative approach in development of sustainable farming practices. The agricultural regimen is the "head honcho" of the world, however presently certain approaches have been imposing grave danger to the environment and human civilization. The nano-farming paradigm has successfully elevated the growth and development of plants, parallel to the production, quality, germination/transpiration index, photosynthetic machinery, genetic progression, and so on. This has optimized the traditional farming into precision farming, utilising nano-based sensors and nanobionics, smart delivery tools, nanotech facets in plant disease management, nanofertilizers, enhancement of plant adaptive potential to external stress, role in bioenergy conservation and so on. These applications portray nanorevolution as "the big cheese" of global agriculture, mitigating the bottlenecks of conventional practices. Besides the applications of nanotechnology, the review identifies the limitations, like possible harmful impact on environment, mankind and plants, as the "Achilles heel" in agro-industry, aiming to establish its defined role in agriculture, while simultaneously considering the risks, in order to resolve them, thus abiding by "technology-yes, but safety-must". The authors aim to provide a significant opportunity to the nanotech researchers, Botanists and environmentalists, to promote judicial use of nanoparticles and establish a secure and safe environment.

Recent Advancements and Development in Nano-Enabled Agriculture for Improving Abiotic Stress Tolerance in Plants

Abiotic stresses, such as heavy metals (HMs), drought, salinity and water logging, are the foremost limiting factors that adversely affect the plant growth and crop productivity worldwide. The plants respond to such stresses by activating a series of intricate mechanisms that subsequently alter the morpho-physiological and biochemical processes. Over the past few decades, abiotic stresses in plants have been managed through marker-assisted breeding, conventional breeding, and genetic engineering approaches. With technological advancement, efficient strategies are required to cope with the harmful effects of abiotic environmental constraints to develop sustainable agriculture systems of crop production. Recently, nanotechnology has emerged as an attractive area of study with potential applications in the agricultural science, including mitigating the impacts of climate change, increasing nutrient utilization efficiency and abiotic stress management. Nanoparticles (NPs), as nanofertilizers, have gained significant attention due to their high surface area to volume ratio, eco-friendly nature, low cost, unique physicochemical properties, and improved plant productivity. Several studies have revealed the potential role of NPs in abiotic stress management. This review aims to emphasize the role of NPs in managing abiotic stresses and growth promotion to develop a cost-effective and environment friendly strategy for the future agricultural sustainability.

Explicating the cross-talks between nanoparticles, signaling pathways and nutrient homeostasis during environmental stresses and xenobiotic toxicity for sustainable cultivation of cereals

Precision farming using nanoparticles is a cutting-edge technology for safe cultivation of crop plants in marginal areas afflicted with environmental/climatic stresses like salinity, drought, extremes of temperature, ultraviolet B stress or polluted with xenobiotics like toxic heavy metals and fluoride. Major cereal crops like rice, wheat, maize, barley, sorghum and millets which provide the staple food for the entire global population are mainly glycophytes and are extremely susceptible to abiotic stress-induced oxidative injuries. Nanofertilization/exogenous spraying of beneficial nanoparticles alleviates the oxidative damages in cereals by altering the homeostasis of phytohormones like abscisic acid, gibberellins, cytokinins, auxins, salicylic acid, jasmonic acid and melatonin and by triggering the synthesis of gasotransmitter nitric oxide. Signaling cross-talks of nanoparticles with plant growth regulators enable activation of the defence machinery, comprising of antioxidants, thiol-rich compounds and glyoxalases and restrict xenobiotic mobilization by suppressing the expression of associated transporters. Accelerated nutrient uptake and grain biofortification under the influence of nanoparticles result in optimum crop productivity under sub-optimal conditions. However, over-dosing of even beneficial nanoparticles promotes severe phytotoxicity. Hence, the concentration of nanoparticles and mode of administering need to be thoroughly standardized before large-scale field applications, to ensure sustainable cereal cultivation with minimum ecological imbalance.

Current trends and future prospective in nanoremediation of heavy metals contaminated soils: A way forward towards sustainable agriculture

Heavy metals (HMs) contamination in agricultural soils is a major concern for global food safety and human health. Although, various in-situ and ex-situ remediation methods have been used for the treatment of HMs contaminated soils, however, they also have many drawbacks viz., capital investment, toxicity, and environmental health hazards. Consequently, there is an urgent need to develop a novel method to ameliorate the toxicity of HMs in agricultural soils. In recent years, nanoparticles (NPs) have gained significant attention due to their potential applications in the environment and agriculture fields. Nanoremediation employs NPs that effectively reduce the contents of toxic HMs in the soil-plant system. Several studies have reported that the application of NPs in HMs-polluted soils, which reduced plant-available HMs concentration soils. However, the long-term efficiency of NPs immobilization is still unclear. Here, we provide details about the toxicity of HMs to environmental systems and potential applications NPs to alleviate the accumulation of HMs in agricultural soils. Finally, we present the mechanistic route of HMs-toxicity alleviation in plants by NPs application as well as their long-term efficiency and future prospects.

Comparative physiological and transcriptomic analyses reveal ascorbate and glutathione coregulation of cadmium toxicity resistance in wheat genotypes

BACKGROUND

Cadmium (Cd) is a heavy metal with high toxicity that severely inhibits wheat growth and development. Cd easily accumulates in wheat kernels and enters the human food chain. Genetic variation in the resistance to Cd toxicity found in wheat genotypes emphasizes the complex response architecture. Understanding the Cd resistance mechanisms is crucial for combating Cd phytotoxicity and meeting the increasing daily food demand.

RESULTS

Using two wheat genotypes (Cd resistant and sensitive genotypes T207 and S276, respectively) with differing root growth responses to Cd, we conducted comparative physiological and transcriptomic analyses and exogenous application tests to evaluate Cd detoxification mechanisms. S276 accumulated more H₂O₂, O₂^-, and MDA than T207 under Cd toxicity. Catalase activity and levels of ascorbic acid (AsA) and glutathione (GSH) were greater, whereas superoxide dismutase (SOD) and peroxidase (POD) activities were lower in T207 than in S276. Transcriptomic analysis showed that the expression of RBOHA, RBOHC, and RBOHE was significantly increased under Cd toxicity, and two-thirds (22 genes) of the differentially expressed RBOH genes had higher expression levels in S276 than inT207. Cd toxicity reshaped the transcriptional profiling of the genes involving the AsA-GSH cycle, and a larger proportion (74.25%) of the corresponding differentially expressed genes showed higher expression in T207 than S276. The combined exogenous application of AsA and GSH alleviated Cd toxicity by scavenging excess ROS and coordinately promoting root length and branching, especially in S276.

CONCLUSIONS

The results indicated that the ROS homeostasis plays a key role in differential Cd resistance in wheat genotypes, and the AsA-GSH cycle fundamentally and vigorously influences wheat defense against Cd toxicity, providing insight into the physiological and transcriptional mechanisms underlying Cd detoxification.

Effects of nanoparticles on trace element uptake and toxicity in plants: A review

Agricultural soils are receiving higher inputs of trace elements (TEs) from anthropogenic activities. Application of nanoparticles (NPs) in agriculture as nano-pesticides and nano-fertilizers has gained rapid momentum worldwide. The NPs-based fertilizers can facilitate controlled-release of nutrients which may be absorbed by plants more efficiently than conventional fertilizers. Due to their large surface area with high sorption capacity, NPs can be used to reduce excess TEs uptake by plants. The present review summarizes the effects of NPs on plant growth, photosynthesis, mineral nutrients uptake and TEs concentrations. It also highlights the possible mechanisms underlying NPs-mediated reduction of TEs toxicity at the soil and plant interphase. Nanoparticles are effective in immobilization of TEs in soil through alteration of their speciation and improving soil physical, chemical, and biological properties. At the plant level, NPs reduce TEs translocation from roots to shoots by promoting structural alterations, modifying gene expression, and improving antioxidant defense systems. However, the mechanisms underlying NPs-mediated TEs uptake and toxicity reduction vary with NPs type, mode of application, time of NPs exposure, and plant conditions (e.g., species, cultivars, and growth rate). The review emphasizes that NPs may provide new perspectives to resolve the problem of TEs toxicity in crop plants which may also reduce the food security risks. However, the potential of NPs in metal-contaminated soils is only just starting to be realized, and additional studies are required to explore the mechanisms of NPs-mediated TEs immobilization in soil and uptake by plants. Such future knowledge gap has been highlighted and discussed.

Synergistic action of silicon nanoparticles and indole acetic acid in alleviation of chromium (CrVI) toxicity in Oryza sativa seedlings

The present study investigates ameliorative effect of silicon nanoparticles (SiNPs) and indole acetic acid (IAA) alone and in combination against hexavalent chromium (Cr^VI) toxicity in rice seedlings. The results of the study revealed protective effects of SiNPs and IAA against Cr^VI toxicity. The 100μM of Cr^VI imposed toxic effects in rice seedlings at morphological, physiological and biochemical levels which coincided with increased level of intracellular Cr^VI and declined level of endogenous nitric oxide (NO). The Cr^VI enhanced levels of superoxide radicals (SOR) (59.51% and 50.1% in shoot and root, respectively) and H₂O₂ (19.5% and 23.69% in shoot and root, respectively). However, when SiNPs and IAA were applied to plants under Cr^VI stress, they enhanced tolerance and defence mechanisms as manifested in terms of increased biomass, endogenous NO, photosynthetic pigments, and antioxidants level (ascorbate-glutathione cycle). It was also noticed that Cr^VI arrested cell cycle at G2/M phase whereas growth was restored as compared to control when SiNPs and IAA were supplemented. Thus, the hypothesis that combined application of SiNPs and IAA will be effective in alleviating Cr^VI toxicity is validated from the results of this study. Moreover, in SiNPs and IAA-mediated mitigation of Cr^VI toxicity, endogenous NO has a positive role. The importance of the study will be that the combination of SiNPs and IAA can be utilized against heavy metal stress and even when supplied alone, they will enhance the crop productivity parameters with and without stress conditions.

Combined effects of carbon nanotubes and cadmium on the photosynthetic capacity and antioxidant response of wheat seedlings

A detailed study of nanomaterials has revealed their broad application prospects. However, the presence of carbon nanotubes (CNTs) in the environment has been increasing and has aroused concerns regarding their toxicity to crops when combined with heavy metals. In the present study, the effects of Cd on the photosynthetic capacity and antioxidant activity of wheat seedlings in the presence of single-walled CNTs (SW) and multi-walled CNTs (MW) were investigated. Our results indicated that SW (5-40 mg L^-1) and MW (10-40 mg L^-1) significantly increased the oxidative stress response of wheat seedlings to Cd. Compared with Cd alone, CNTs combined with Cd decreased net photosynthetic rate, stomatal conductance, transpiration rate, primary maximum photochemical efficiency of photosystem II, actual quantum yield, photosynthetic electron transport rate, root canal protein, and ribulose-1,5-bisphosphate carboxylase/oxygenase content. Moreover, combined treatments increased the content of superoxide anion, superoxide dismutase, guaiacol peroxidase, cytochrome, and malondialdehyde in wheat seedlings. Moreover, membrane lipid peroxidation was aggravated, causing serious damage to the wheat membrane system. In addition, the toxicity of the SW treatment and the combined treatment with SW and Cd was higher than that of the MW treatment.

Combined use of different nanoparticles effectively decreased cadmium (Cd) concentration in grains of wheat grown in a field contaminated with Cd

Cadmium (Cd) accumulation in arable lands has become a serious matter for food security. Among various approaches, the application of nanoparticles (NPs) for remediation of contaminated water and soils is attaining more popularity worldwide. The current field experiment was executed to explore the impacts of single and combined use of ZnO NPs, Fe NPs and Si NPs on wheat growth and Cd intake by plants in a Cd-contaminated field. Wheat was sown in a field which was contaminated with Cd and was irrigated with the raw-city-effluent while NPs were applied as foliar spray alone and in all possible combinations. The data revealed that straw and grain yields were enhanced in the presence of NPs over control. Chlorophyll, carotenoids contents and antioxidants activities were enhanced while electrolyte leakage was reduced with all NPs over control. In comparison with control, Cd uptake in wheat straw was reduced by 84% and Cd uptake in grain was reduced by 99% in T8 where all three NPs were foliar-applied simultaneously. Zinc (Zn) and iron (Fe) contents were increased in those plants where ZnO and Fe NPs were exogenously applied which revealed that ZnO and Fe NPs enhanced the bio-fortification of Zn and Fe in wheat grains. Overall, foliar application of different NPs is beneficial for better wheat growth, yield, nutrients uptake and to lessen the Cd intake by plants grown in Cd-contaminated soil under real field conditions.

Comparison of foliar spray and soil irrigation of biogenic CuO nanoparticles (NPs) on elemental uptake and accumulation in lettuce

Nanoparticles (NPs) can be used in several ways in agriculture, including increasing production rates and improving nutritional values in plants. The present study aims to clarify how biogenic copper oxide nanoparticles (CuO NPs) applied by two routes of exposure (foliar spray and soil irrigation) affect the elemental uptake by lettuce. In vivo experiments using lettuce (n = 4) were performed with CuO NPs in comparison with copper salt (CuSO4), considering a final mass added of 20 mg of CuO per plant. The elemental composition of roots was mostly affected by the soil irrigation exposure for both Cu forms (NPs and salt). Neither Cu form added by soil irrigation was translocated to leaves. Copper concentration in leaves was mainly affected by foliar spray exposure for both Cu forms (NPs and salt). All Cu forms through foliar spray were sequestered in the leaves and no translocation to roots was observed. Foliar spray of CuO NPs caused no visual damage in leaves, resulted in less disturbance of elemental composition, and improved dry weight, number of leaves, CO2 assimilation, and the levels of K, Na, S, Ag, Cd, Cr, Cu, and Zn in leaves without causing significant changes in daily intake of most elements, except for Cu. Although Cu concentration increased in leaves by foliar spray of CuO NPs, it remained safe for consumption.

Bio-remediation approaches for alleviation of cadmium contamination in natural resources

Cadmium (Cd) is a harmful heavy metal that can cause potent environmental and health hazards at different trophic levels through food chain. Cd is relatively non-biodegradable and persists for a long time in the environment. Considering the potential toxicity and non-biodegradability of Cd in the environment as well as its health hazards, this is an urgent issue of international concern that needs to be addressed by implicating suitable remedial approaches. The current article specifically attempts to review the different biological approaches for remediation of Cd contamination in natural resources. Further, bioremediation mechanisms of Cd by microbes such as bacteria, fungi, algae are comprehensively discussed. Studies indicate that heavy metal resistant microbes can be used as suitable biosorbents for the removal of Cd (up to 90%) in the natural resources. Soil-to-plant transfer coefficient (TC) of Cd ranges from 3.9 to 3340 depending on the availability of metal to plants and also on the type of plant species. The potential phytoremediation strategies for Cd removal and the key factors influencing bioremediation process are also emphasized. Studies on molecular mechanisms of transgenic plants for Cd bioremediation show immense potential for enhancing Cd phytoremediation efficiency. Thus, it is suggested that nano-technological based integrated bioremediation approaches could be a potential futuristic path for Cd decontamination in natural resources. This review would be highly useful for the biologists, chemists, biotechnologists and environmentalists to understand the long-term impacts of Cd on ecology and human health so that potential remedial measures could be taken in advance.

Biogenic copper nanoparticles synthesized by using a copper-resistant strain Shigella flexneri SNT22 reduced the translocation of cadmium from soil to wheat plants

The mechanistic role of green copper nanoparticles (CuNPs) in cadmium (Cd) toxicity alleviation in plants is poorly understood. Here, the CuNPs, synthesized by using a bacterium Shigella flexneri SNT22, were confirmed through UV-vis spectroscopy with a characteristic peak at 334.50 nm. Moreover, FT-IR, XRD, SEM, and TEM techniques revealed that the spherical shaped crystals of CuNPs with a size range of 17.24 nm to 38.03 nm were stabilized by coating proteins. Diff ;erent levels of CuNPs (e.g., 25, 50, and 100 mg kg^-1 of soil) were examined in pots having Cd-mixed soil to evaluate their effect on wheat plants in a growth chamber under optimal environmental conditions. Treatment of soil with 100 mg kg^-1 of CuNPs increased plant length by 44.4 %, shoot dry weight by 28.26 %, nitrogen contents by 41.60 %, and phosphorus contents by 58.79 %, whereas decreased the acropetal Cd translocation by 49.62 %. An increase in the N, P, K⁺, Ca²⁺, K⁺/Na⁺, and Ca²⁺/Na⁺ contents and decrease in the Na⁺ concentration in wheat plants treated with CuNPs was also recorded. Overall, the results are valuable to establish a green CuNPs-based approach for sustainable wheat growth in metal-contaminated soils.

Uptake of iron oxide nanoparticles inhibits the photosynthesis of the wheat after foliar exposure

Iron oxide nanoparticles (nFe₂O₃)-filled materials have been widely employed in various products and their effects on plants have attracted considerable attention because of their potential release into the environment. Currently, numerous studies reporting the influences of iron-bearing nanoparticles on plants are focused on root or seed exposure. However, plants exposed to atmospheric iron-bearing nanoparticles through the leaves and their impacts on plants are still not well understood. This study focused on the uptake, translocation, and effects of foliar exposure of nFe₂O₃ on wheat seedlings. Wheat seedlings were foliar applied to various concentrations of nFe₂O₃ (0, 60 and 180 μg per plant) for 1, 7, 14 or 21 d. Our results demonstrated that after exposure for 21 d, the concentrations of Fe in leaves, stems, and roots were 1100, 280 and 160 μg kg^-1, respectively. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), as well as the backscattered electron (BSE) images, revealed the stomatal opening was likely the pathway for nFe₂O₃ uptake. Analysis of the transfer rate, translocation of Fe from leaves to stems and roots, suggested the involvement of plant Fe regulation processes. Particularly, the antioxidant enzymatic activities and malondialdehyde levels in leaves were modified, which was ascribed to the excessive hydroxyl radical (OH) generated via the Fenton-like reaction mediated by nFe₂O₃. Finally, the OH facilitated the degradation of chlorophyll, posting a negative impact on the photosynthesis, and thus inhibited the biomass production. These findings are meaningful to understand the fate and physiological effects of atmospheric nFe₂O₃ in crops.

A study on the mixture repairing effect of biochar and nano iron oxide on toxicity of Cd toward muskmelon

Soil contamination with cadmium (Cd) has become a serious problem, adversely affecting food safety and human health. Effective methods are urgently needed to alleviate toxicity of Cd in plants. In this study, a nine-week continuous pot experiments was conducted to explore the effectiveness of the different nano iron oxide (α-Fe₂O₃, γ-Fe₂O₃, Fe₃O₄) alone and combined with biochar in muskmelon grown on a Cd-contaminated soil. The antioxidant system, chlorophyll, soluble protein, other physiological indexes of muskmelon leaves and the distribution of Cd in matrix soil, leaves and fruit were detected. The results showed that Cd was readily absorbed by plants and caused oxidative stress on plants, while biochar, α-Fe₂O₃ nanoparticles (NPs) and their mixture group (BFe1 group) could significantly improve it. Specifically, the three treatments reduced the Cd content of the fruit by 19.51-78.86%, reduced the Cd content of leaves by 15.44-36.23% and 22.36-31.77% in weeks 3 and 5, respectively. For the activity of enzymes, three treatments decreased superoxide dismutase (SOD) activity and catalase (CAT) activity by 3.41-38.57% and 24.27-30.33% in week 7, respectively. So BFe1 group application immobilized Cd in soil and reduced Cd partitioning in the aboveground tissues. Overall the combination of biochar and α-Fe₂O₃ NPs can alleviate Cd toxicity in muskmelon and can protect human beings from Cd exposure.

Nanotechnology in soil remediation - applications vs. implications

Engineered nanomaterials (ENMs) and nanotechnology have shown great potential in addressing complex problems and creating innovative approaches in soil remediation due to their unique features of high reactivity, selectivity and versatility. Meanwhile, valid concerns exist with regard to their implications towards the terrestrial environment and the ecosystem. This review summarizes: (i) the applications and the corresponding mechanisms of various types of ENMs for soil remediation; (ii) the environmental behavior of ENMs in soils and their interactions with the soil content; (iii) the environmental implications of ENMs during remedial applications. The overall objective is to promote responsible innovations so as to take optimal advantage of ENMs and nanotechnology while minimizing their adverse effects to the ecological system. It is critical to establish sustainable remediation methods that ensure a healthy and safe environment without bringing additional risk.

Chromium Morpho-Phytotoxicity

Chromium (Cr) is considered as one of the chronic pollutants that cause damage to all living forms, including plants. Various industries release an excessive amount of Cr into the environment. The increasing accumulation of Cr in agricultural land causes a significant decrease in the yield and quality of economically important crops. The Cr-induced biochemical, molecule, cytotoxic, genotoxic, and hormonal impairments cause the inhibition of plant growth and development. In the current study, we reviewed Cr morpho-phytotoxicity related scientific reports published between 2009 to 2019. We mainly focused on the Cr-induced inhibition of seed germination and total biomass production. Furthermore, Cr-mediated reduction in the root, branches, and leave growth and development were separately discussed. The Cr uptake mechanism and interference with the macro and micro-nutrient uptake were also discussed and visualized via a functional model. Moreover, a comprehensive functional model has been presented for the Cr release from the industries, its accumulation in the agricultural land, and ultimate morpho-phytotoxicity. It is concluded that Cr-reduces plant growth and development via its excess accumulation in the plant different parts and/or disruption of nutrient uptake.

Green copper nanoparticles from a native Klebsiella pneumoniae strain alleviated oxidative stress impairment of wheat plants by reducing the chromium bioavailability and increasing the growth

Chromium (Cr) concentration has been increasing substantially in the environment due to industrial and anthropogenic factors. Plants can absorb Cr and undergo unrestrained oxidation cascades, resulting in cell injury. The ameliorative role of biogenic copper nanoparticles to relieve wheat plants from Cr stress by supporting their growth is still unclear. The present work aims at the biosynthesis and characterization of copper nanoparticles (CuNPs) from a native Klebsiella pneumoniae strain, followed by assessment of wheat growth and physiological responses to CuNPs mixed in Cr-rich soil. The taxonomic rank of K. pneumoniae SN35 was established by the 16 S rRNA gene sequence analysis. The properties of biogenic CuNPs were elucidated by using UV-vis spectroscopy, FTIR, XRD, SEM, and TEM. It was found that 19.01-47.47 nm spherical shaped CuNPs were stabilized by different functional groups produced extracellularly by the strain SN35. The XRD data revealed the crystalline nature of CuNPs as a face-centered cubic structure. Different concentrations of CuNPs (0, 25, 50 and 100 mg kg^-1 of soil) were added into the soil mixed with 3.5 mg kg^-1 K₂Cr₂O₇ and the pots were placed in a growth chamber for 30 days. The results revealed that the CuNPs, at 25 and 50 mg kg^-1 of soil, augmented plant growth, biomass, and cellular antioxidants contents, whereas decreased the reactive oxygen species and Cr translocation from soil to roots and shoots as compared to control plants. Overall, the results revealed that the soil amendment of CuNPs could immobilize the Cr in the soil to prevent its translocation to the upper plant parts and support wheat growth by relieving cellular oxidative stress.

Oral Co-Exposures to zinc oxide nanoparticles and CdCl2 induced maternal-fetal pollutant transfer and embryotoxicity by damaging placental barriers

Synergistic toxicity from multiple environmental pollutants poses greater threat to humans, especially to susceptible pregnant population. Here we evaluated combined toxicity from environment pollutants zinc oxide nanoparticles (ZnO NPs) and cadmium chloride (CdCl₂) using two pregnant mice models established by oral administration during peri-implantation or organogenesis period. We found that exposures to combined pollutants only at organogenesis stage induced higher fetal deformity rate compared to co-exposures at peri-implantation stage. We further discovered that surface charge of ZnO NPs were modified after Cd²⁺ adsorption and the resulting nanoadducts caused more severe damages in placental barriers by causing shed endothelial cells and decreased expressions of tight junction proteins ZO1, occludin, claudin-4 and claudin-8. These cellular and molecular events enhanced maternal-fetal transfer of both pollutants and aggravated embryotoxicity. Our findings help elucidate synergistic embryotoxicity by nanoparticle/pollutant adducts and establish proper safety criteria for pregnant population in an era that nanotechnology-based products are widely used.

Phytotoxicity and upper localization of Ag@CoFe2O4 nanoparticles in wheat plants

Environmental concern related to Ag⁺ release from conventional AgNPs is expected to be prevented once contained into a magnetic core like magnetite or CoFe₂O₄. Accordingly, we obtained CoFe₂O₄ NPs by microwave-assisted synthesis, which AgNO₃ addition rendered Ag@CoFe₂O₄ NPs. NPs were characterized, and before exploring potential applications, we carried out 7-day wheat toxicity assays. Seed germination and seedling growth were used as toxicity endpoints and photosynthetic pigments and antioxidant enzymes as oxidative stress biomarkers. Total Fe, Co, and Ag determination was initial indicative of Ag@CoFe₂O₄ NPs uptake by plants. Then NPs localization in seedling tissues was sought by scanning electron microscopy (SEM) and darkfield hyperspectral imaging (DF-HSI). Not any silver ion (Ag⁺) was detected into the ferrite structure, but results only confirmed the presence of metallic silver (Ag⁰) adsorbed on the CoFe₂O₄ NPs surface. Agglomerates of Ag@CoFe₂O₄ NPs (~10 nm) were fivefold smaller than CoFe₂O₄ NPs, and ferrimagnetic properties of the CoFe₂O₄ NPs were conserved after the formation of the Ag@CoFe₂O₄ composite NPs. Seed germination was not affected by NPs, but root and shoot lengths of seedlings diminished 50% at 54.89 mg/kg and 168.18 mg/kg NPs, respectively. Nonetheless, hormesis was observed in roots of plants exposed to lower Ag@CoFe₂O₄ NPs treatments. Photosynthetic pigments and the antioxidant enzymes catalase (CAT), superoxide dismutase (SOD), guaiacol peroxidase (GPX), and ascorbate peroxidase (APX) indicated oxidative damage by reactive oxygen species (ROS) generation. SEM suggested NPs presence in shoots and roots, whereas DF-HSI confirmed some Ag@CoFe₂O₄ NPs contained in shoots of wheat plants.

Applications of carbon quantum dots to alleviate Cd2+ phytotoxicity in Citrus maxima seedlings

Heavy metal pollution may affect plant growth. The focus of this study was to explore remediation agents that alleviate cadmium toxicity in plants. The Citrus maxima (grapefruit) seedlings were cultivated for 10 days under hydroponic conditions amended with different concentrations of Cd²⁺ (50 and 200 mg/L) and CDs (600 and 900 mg/L). Our observations on roots and leaves showed that, the plant exposed to 200 mg/L Cd²⁺ alone was damaged, supported by the changes in anthocyanin contents, activity of antioxidant enzymes and cell membrane peroxidation damage (up to 35.8-45%). However, the physiological properties of the plant were improved upon exposed to 200 mg/L Cd²⁺ plus 900 mg/L CDs; it can be ascribed to Cd²⁺ sorption to the co-exposed CDs which reduced its freely dissolved concentration by more than 22.5%, thus significantly reducing the amount of Cd²⁺ entered the plant roots by 50.7-89.4%. Due to the oxidative stress induced by Cd²⁺ exposure at 200 mg/L, expression of glutathione-producing genes was up-regulated by 30-360% relative to the control, while the genes expression upon exposure to 200 mg/L Cd²⁺ and 900 mg/L CDs was reduced by 48.4-91.5% relative to that exposed to 200 mg/L Cd²⁺ alone. However, detoxification of CDs on plant leaves at 600 mg/L was insignificant, because a portion of Cd²⁺ taken up by roots can be transported to leaves associated with the internalized CDs. Therefore, CDs can be utilized as a repair agent to mitigate toxicity of Cd²⁺ to plant especially at a high amendment level (900 mg/L).

Hazardous heavy metals contamination of vegetables and food chain: Role of sustainable remediation approaches - A review

This review emphasizes the role of toxic metal remediation approaches due to their broad sustainability and applicability. The rapid developmental processes can incorporate a large quantity of hazardous and unseen heavy metals in all the segments of the environment, including soil, water, air and plants. The released hazardous heavy metals (HHMs) entered into the food chain and biomagnified into living beings via food and vegetable consumption and originate potentially health-threatening effects. The physical and chemical remediation approaches are restricted and localized and, mainly applied to wastewater and soils and not the plant. The nanotechnological, biotechnological and genetical approaches required to more rectification and sustainability. A cellular, molecular and nano-level understanding of the pathways and reactions are responsible for potentially toxic metals (TMs) accumulation. These approaches can enable the development of crop varieties with highly reduced concentrations of TMs in their consumable foods and vegetables. As a critical analysis by authors observed that nanoparticles could provide very high adaptability for both in-situ and ex-situ remediation of hazardous heavy metals (HHMs) in the environment. These methods could be used for the improvement of the inbuilt genetic potential and phytoremediation ability of plants by developing transgenic. These biological processes involve the transfer of gene of interest, which plays a role in hazardous metal uptake, transport, stabilization, inactivation and accumulation to increased host tolerance. This review identified that use of nanoremediation and combined biotechnological and, transgenic could help to enhance phytoremediation efficiency in a sustainable way.

TiO2 nanoparticles may alleviate cadmium toxicity in co-treatment experiments on the model hydrophyte Azolla filiculoides

The hydrophyte Azolla filiculoides can be a useful model to assess if TiO₂ NPs may in some way alleviate the Cd injuries and improve the ability of the plant to cope with this metal. With this mechanistic hypothesis, after a pre-treatment with TiO₂ NPs, A. filiculoides plants were transferred to cadmium-contaminated water with or without TiO₂ nanoparticles. After 5 days of treatment, cadmium uptake, morpho-anatomical, and physiological aspects were studied in plants. The continuous presence of TiO₂ nanoparticles, though not increasing the uptake of cadmium in comparison with a priming treatment, induced a higher translocation of this heavy metal to the aerial portion. Despite the translocation factor was always well below 1, cadmium contents in the fronds, generally greater than 100 ppm, ranked A. filiculoides as a good cadmium accumulator. Higher cadmium contents in leaves did not induce damages to the photosynthetic machinery, probably thanks to a compartmentalization strategy aimed at confining most of this pollutant to less metabolically active peripheral cells. The permanence of NPs in growth medium ensured a better efficiency of the antioxidant apparatus (proline and glutathione peroxidase and catalase activities) and induced a decrease in H₂O₂ content, but did not suppress TBARS level.

Comparative effectiveness of different biochars and conventional organic materials on growth, photosynthesis and cadmium accumulation in cereals

Although biochar and conventional organic materials have been widely studied for lowering cadmium (Cd) uptake by plants but information regarding their comparative effectiveness is lacking. In this study, biochars from different feedstocks viz. rice husk biochar (RHB), cotton sticks biochar (CSB) and wheat straw biochar (WSB) were compared with conventional organic materials viz. farm manure (FM), poultry manure (PM) and press mud (PrMd) for their effectiveness to promote plant growth and to reduce Cd uptake by wheat and rice plants grown rotationally in a Cd-spiked (50 mg kg^-1) soil. Each amendment was applied at the rate of 2% (w/w) in three replicates. Results showed that the application of amendments improved the soil properties and plant growth, by retaining Cd in the soil and restricting its uptake by plants. The amendments decreased the ammonium bicarbonate diethylene penta acetic acid extractable soil Cd, and improved soil organic carbon (SOC) and cation exchange capacity (CEC) as compared to only Cd-contaminated soil. The highest SOC content of 2.68 and 1.68% and CEC of 8.77 and 9.39 cmol_c kg^-1 were found in RHB treated post-wheat and post-rice soil, respectively. Amendments treated soil showed lower concentrations of bioavailable Cd and the maximum reduction was recorded in RHB and PrMd amended soil. Similarly, bioaccumulation of Cd was decreased with the application of all amendments; the maximum decrease was recorded in RHB and PrMd treated soil. Our results suggested that RHB and PrMd could be used for reducing the bioaccumulation of Cd in cereal grains in alkaline soils.

The impacts of γ-Fe2O3 and Fe3O4 nanoparticles on the physiology and fruit quality of muskmelon (Cucumis melo) plants

Iron fertilizers are worthy to be studied due to alleviate the Fe deficiency. Different forms of iron oxide nanoparticles are selected to better understand possible particle applications as an Fe source for crop plants. In this study, we assessed the different effects of γ-Fe₂O₃ and Fe₃O₄ NPs on the physiology and fruit quality of muskmelon plants in a pot experiment for five weeks. Results showed that no increased iron content was found under NPs treatment in root, stem, leaf and fruit, except 400 mg/L Fe₃O₄ NPs had a higher iron content in muskmelon root. With the extension of NPs exposure, both γ-Fe₂O₃ and Fe₃O₄ NPs began to promote plant growth. In addition, γ-Fe₂O₃ and Fe₃O₄ NPs could increase chlorophyll content at a certain stage of exposure. Happily, 200 mg/L γ-Fe₂O₃ NPs and 100, 200 mg/L Fe₃O₄ NPs significantly increased fruit weight of muskmelon by 9.1%, 9.4% and 11.5%. It is noteworthy that both γ-Fe₂O₃ and Fe₃O₄ NPs caused positive effects on VC content, particularly 100 mg/L Fe₃O₄ NPs increased the VC content by 46.95%. To the best of our knowledge, little research has been done on the effect of nanoparticles on the whole physiological cycle and fruit quality of melon. The assessment of physiology and fruit quality of muskmelon plants in vitro upon γ-Fe₂O₃ and Fe₃O₄ NPs exposure could lay a foundation for NPs potential impact at every growth period of muskmelon plants.

Zero-valent silver nanoparticles attenuate Cd and Pb toxicities on Moringa oleifera via immobilization and induction of phytochemicals

Potentials of zero-valent extract of cocoa pod mediated silver nanoparticles (AgNPs) for heavy metals (cadmium and lead) immobilization, attenuation of induced toxicities and influence on phytochemical contents in Moringa oleifera were investigated. M. oleifera seeds were planted in soil spiked and watered with water (control), 0.2 mg AgNPs, 0.5 mg CdCl₂, 0.5 mg PbCl₂, 0.2 mg AgNPs + 0.5 mg CdCl₂, 0.2 mg AgNPs + 0.5 mg PbCl₂, 0.2 mg AgNPs + 0.75 mg CdCl₂ and 0.2 mg AgNPs + 0.75 mg PbCl₂ per g soil designated as groups A, B, C, D, E, F, G and H respectively. Significant (p < 0.05) repression in shoot and root lengths, percentage germination, number of leaves, vigour and growth tolerance indices, relative water contents with attendant inhibition of photosynthetic pigments, total carotenoid contents, total flavonoid contents and total phenolic contents were obtained for M. oleifera planted on Cd and Pb spiked soil. There were marked decrease in ferric reducing, hydrogen peroxide scavenging and free radical scavenging activities with resultant significant increase in lipid peroxidation (MDA) levels for M. oleifera grown on Cd and Pb treated soil compared to control with Pb having more deleterious effects. Conversely, AgNPs significantly enhanced both physiological and biochemical parameters in M. oleifera over control and considerably attenuated suppressions of these parameters in M. oleifera induced by Cd and Pb. Results in this study have shown AgNPs as excellent immobilizing agents and outstanding modulators of heavy metal induced toxicities.

Uptake and Translocation of Styrene Maleic Anhydride Nanoparticles in Murraya exotica Plants As Revealed by Noninvasive, Real-Time Optical Bioimaging

This work reports the in vivo uptake and translocation of PNPs in the one-year grown terrestrial plant, Murraya exotica ( M. exotica), as investigated by two-photon excitation and time-resolved (TPE-TR) optical imaging with a large field of view (FOV, 32 × 32 mm²) in a noninvasive and real-time manner. The PNPs (⟨ R_h⟩ = 12 ± 4.5 nm) synthesized from poly(styrene- co-maleic anhydride) (SMA) were Eu-luminescence labeled (λ_L ≈ 617 nm). On exposing the roots of living M. exotica plants to the colloidal suspension of SMA PNPs at different concentrations, the spatiotemporal evolution of SMA PNPs along plant stems (60 mm in length) were monitored by TPE-TR imaging, which rendered rich information on the uptake and translocation of PNPs without any interference from the autofluorescence of the plant tissues. The TPE-TR imaging combined with the high-resolution anatomy revealed an intercell-wall route in the lignified epidermis of M. exotica plants for SMA PNP uptake and translocation, as well as the similar accumulation kinetics at different positions along the plant stems. We modeled the accumulation kinetics with Gaussian distribution to account for the trapping probability of a SMA PNP by the lignified cell walls, allowing the statistical parameters, the average trapping time ( t_m) and its variance (σ), to be derived for the quantification of the PNP accumulation in individual plants. The TPE-TR imaging and the analysis protocols established herein will be helpful in exploring the mechanism of plant-PNP interaction under physiological condition.

Comparative effects of nano and bulk-Fe3O4 on the growth of cucumber (Cucumis sativus)

Cucumber (Cucumis sativus) plants were cultivated in hydroponic media with nano and bulk- iron oxide (Fe₃O₄) (50, 500 and 2000 mg/L) over a period of 21 days. At the low concentration (50 mg/L), nano-Fe₃O₄ resulted in reduction of biomass and enzyme activities compared to the control. However, at the higher concentration of nano-Fe₃O₄ dosage (2000 mg/L), there was a significant increase in biomass, antioxidant enzymes superoxide dismutase (SOD) and peroxidase (POD). In contrary, the high concentration of bulk-Fe₃O₄ caused phytotoxicity in terms of biomass and enzymes activity. The phytotoxicity was dependent on the particles property (mainly sizes and aggregation) for nano-F₃O₄ and concentration dependent for bulk-Fe₃O₄. The particle size is an important factor that can influence the bioavailability of nanomaterials, which need to be included when evaluating the exposure of nanomaterials and their deleterious effects in the environment. These promising results can help to develop the possible application of Fe₃O₄ NPs which may improve nutrient management to overcome food security.

Toxicity assessment of cobalt ferrite nanoparticles on wheat plants

Cobalt ferrite nanoparticles (NPs) have received increasing attention due to their widespread therapeutic and agricultural applicability. In the environmental field, dry powder- and ferrofluid-suspended cobalt ferrite NPs were found to be useful for removing heavy metals and metalloids from water, while diluted suspensions of cobalt ferrite NP have been promisingly applied in medicine. However, the potential toxicological implications of widespread exposure are still unknown. Since cobalt ferrite NPs are considered residual wastes of environmental or medical applications, plants may serve as a point-of-entry for engineered nanomaterials as a result of consumption of these plants. Thus, the aim of this study was to assess the effects of dry powder and fresh cobalt ferrite NP on wheat plants. Seven-day assays were conducted, using quartz sand as the plant growth substrate. The toxicity end points measured were seed germination, root and shoot lengths, total cobalt (Co) and iron (Fe) accumulation, photosynthetic pigment production, protein (PRT) production, and activities of catalase (CAT), ascorbate peroxidase (APX), and guaiacol peroxidase (GPX). Increasing total Co and Fe in plant tissues indicated that wheat plants were exposed to cobalt ferrite NP. Seed germination and shoot length were not sufficiently sensitive toxicity end points. The effective concentration (EC₅₀) that diminished root length of plants by 50% was 1963 mg/kg for fresh ferrite NPs and 5023 mg/kg for powder ferrite NP. Hence, fresh ferrite NPs were more toxic than powder NP. Plant stress was indicated by a significant decrease in photosynthetic pigments. CAT, APX, and GPX antioxidant enzymatic activity suggested the generation of reactive oxygen species and oxidative damage induced by cobalt ferrite NP. More studies are thus necessary to determine whether the benefits of using these NPs outweigh the risks.

Citric acid assisted phytoextraction of chromium by sunflower; morpho-physiological and biochemical alterations in plants

Soil and water contamination from heavy metals and metalloids is one of the most discussed and burning global issues due to its potential to cause the scarcity of healthy food and safe water. The scientific community is proposing a range of lab and field based physical, chemical and biological solutions to remedy metals and metalloids contaminated soils and water. The present study finds out a possibility of Chromium (Cr) extraction by sunflower from spiked soil under chelating role of citric acid (CA). The sunflower plants were grown under different concentrations of Cr (0, 5, 10 & 20mgkg^-1) and CA (0, 2.5 & 5mM). Growth, biomass, gas exchange, photosynthesis, electrolyte leakage (EL), reactive oxygen species (ROS; malondialdehyde (MDA), hydrogen peroxide (H₂O₂) and the activities of antioxidant enzymes such as, superoxide dismutase (SOD), guaiacole values peroxidase (POD), ascorbate peroxidase (APX), catalase (CAT) were measured. The results depicted a clear decline in plant height, root length, leaf area, number of leaves and flowers per plant along with fresh and dry biomass of all parts of plant with increasing concentration of Cr in soil. Similar reduction was observed in chlorophyll a and b, total chlorophyll, carotenoids, soluble protein, gas exchange attributes and SPAD. The increasing concentration of Cr also enhanced the Cr uptake and accumulation in plant roots, stem and leaves along with the production of ROS and EL. The activities of antioxidant enzymes increased with increasing Cr concentration from 0 to 10mg, but decreased at 20mgkg^-1 soil. The CA application significantly alleviated Cr-induced inhibition of plant growth, biomass, photosynthesis, gas exchange, soluble proteins and SPAD value. Presence of CA also enhanced the activities of all antioxidant enzymes and reduced the production of ROS and EL. The chelating potential of CA increased the concentration and accumulation of Cr in plant roots, stem and leaves. It is concluded that the sunflower can be a potential candidate for the remediation of Cr under CA treatment, while the possibility may vary with genotype, Cr level and CA concentration.

Stabilized Nanoscale Zerovalent Iron Mediated Cadmium Accumulation and Oxidative Damage of Boehmeria nivea (L.) Gaudich Cultivated in Cadmium Contaminated Sediments

Nanoparticles can be absorbed by plants, but their impacts on phytoremediation are not yet well understood. This study was carried out to determine the impacts of starch stabilized nanoscale zerovalent iron (S-nZVI) on the cadmium (Cd) accumulation and the oxidative stress in Boehmeria nivea (L.) Gaudich (ramie). Plants were cultivated in Cd-contaminated sediments amended with S-nZVI at 100, 500, and 1000 mg/kg, respectively. Results showed that S-nZVI promoted Cd accumulation in ramie seedlings. The subcellular distribution result showed that Cd content in cell wall of plants reduced, and its concentration in cell organelle and soluble fractions increased at S-nZVI treatments, indicating the promotion of Cd entering plant cells by S-nZVI. In addition, the 100 mg/kg S-nZVI alleviated the oxidative damage to ramie under Cd-stress, while 500 and 1000 mg/kg S-nZVI inhibited plant growth and aggravated the oxidative damage to plants. These findings demonstrate that nanoparticles at low concentration can improve the efficiency of phytoremediation. This study herein develops a promising novel technique by the combined use of nanotechnology and phytoremediation in the remediation of heavy metal contaminated sites.