Nanocolloids in the soil environment: Transformation, transport and ecological effects

Nanocolloids (Ncs) are ubiquitous in natural systems and play a critical role in the biogeochemical cycling of trace metals and the mobility of organic pollutants. However, the environmental behavior and ecological effects of Ncs in the soil remain largely unknown. The accumulation of Ncs may have detrimental or beneficial effects on different compartments of the soil environment. This review discusses the major transformation processes (e.g., agglomeration/aggregation, absorption, deposition, dissolution, and redox reactions), transport, bioavailability of Ncs, and their roles in element cycles in soil systems. Notably, Ncs can act as effective carriers for other pollutants and contribute to environmental pollution by spreading pathogens, nutrients, heavy metals, and organic contaminants to adjacent water bodies or groundwater. Finally, the key knowledge gaps are highlighted to better predict their potential risks, and important new directions include exploring the geochemical process and mechanism of Ncs's formation; elucidating the transformation, transport, and ultimate fate of Ncs, and their long-term effect on contaminants, organisms, and elemental cycling; and identifying the impact on the growth and quality of important crops, evaluating its dominant effect on agro-ecosystems in the soil environment.

Advancing Simultaneous Extraction and Sequential Single-Particle ICP-MS Analysis for Metallic Nanoparticle Mixtures in Plant Tissues

Engineered nanoparticles (ENPs) have been increasingly used in agricultural operations, leading to an urgent need for robust methods to analyze co-occurring ENPs in plant tissues. In response, this study advanced the simultaneous extraction of coexisting silver, cerium oxide, and copper oxide ENPs in lettuce shoots and roots using macerozyme R-10 and analyzed them by single-particle inductively coupled plasma-mass spectrometry (ICP-MS). Additionally, the standard stock suspensions of the ENPs were stabilized with citrate, and the long-term stability (up to 5 months) was examined for the first time. The method performance results displayed satisfactory accuracies and precisions and achieved low particle concentration and particle size detection limits. Significantly, the oven drying process was proved not to impact the properties of the ENPs; therefore, oven-dried lettuce tissues were used in this study, which markedly expanded the applicability of this method. This robust methodology provides a timely approach to characterize and quantify multiple coexisting ENPs in plants.

A review on toxicity of nanomaterials in agriculture: Current scenario and future prospects

Phytonanotechnology plays a crucial part in the production of good quality and high-yield food. It can also alter the plant's production systems, hence permitting the efficient, controlled and stable release of agrochemicals such as fertilizers and pesticides. An advanced understanding of nanomaterials interaction with plant responses like localization and uptake, etc. could transfigure the production of crops with high disease resistance and efficient nutrients utilization. In agriculture, the use of nanomaterials has gained acceptance due to their wide-range applications. However, their toxicity and bioavailability are the major hurdles for their massive employment. Undoubtedly, nanoparticles positively influence seeds germination, growth and development, stress management and post-harvest handling of vegetables and fruits. These nanoparticles may also cause toxicity in plants through oxidative stress by generation of excessive reactive oxygen species thus affecting the cellular biomolecules and targeting different channels. Nanoparticles have shown to exert various effects on plants that are mainly affected by various attributes such as physicochemical features of nanomaterials, coating materials for nanoparticles, type of plant, growth stages and growth medium for plants. This article discusses the interaction, accretion and toxicity of nanomaterials in plants. The factors inducing nanotoxicity and the mechanisms followed by nanomaterials causing toxicity are also instructed. At the end, detoxification mechanism of plant is also presented.

Interaction of Cerium Oxide Nanoparticles and Ionic Cerium with Duckweed (Lemna minor L.): Uptake, Distribution, and Phytotoxicity

As one of the most widely used nanomaterials, CeO2 nanoparticles (NPs) might be released into the aquatic environment. In this paper, the interaction of CeO2 NPs and Ce3+ ions (0~10 mg/L) with duckweed (Lemna minor L.) was investigated. CeO2 NPs significantly inhibited the root elongation of duckweed at concentrations higher than 0.1 mg/L, while the inhibition threshold of Ce3+ ions was 0.02 mg/L. At high doses, both reduced photosynthetic pigment contents led to cell death and induced stomatal deformation, but the toxicity of Ce3+ ions was greater than that of CeO2 NPs at the same concentration. According to the in situ distribution of Ce in plant tissues by μ-XRF, the intensity of Ce signal was in the order of root > old frond > new frond, suggesting that roots play a major role in the uptake of Ce. The result of XANES showed that 27.6% of Ce(IV) was reduced to Ce(III) in duckweed treated with CeO2 NPs. We speculated that the toxicity of CeO2 NPs to duckweed was mainly due to its high sensitivity to the released Ce3+ ions. To our knowledge, this is the first study on the toxicity of CeO2 NPs to an aquatic higher plant.

Comparative bioaccumulation, translocation, and phytotoxicity of metal oxide nanoparticles and metal ions in soil-crop system

Exposure of the soil environment to metal nanoparticles (MNPs) has been extensive because of their indiscriminate use and the disposal of MNP products in various applications. In MNP-amended soil, various crops can absorb the nanoparticles, and accumulation of the MNPs in farm products has potential risks for bioconcentration in humans and livestock. Here, we evaluated the comparative bioaccumulation, translocation, and phytotoxicity of MNPs (ZnO and CuO NPs) and metal ions (Zn(NO3)2 and Cu(NO3)2) in four different crops, namely lettuce, radish, bok choy, and tomato. We carried out pot experiments to evaluate the phytotoxicity in the crops from the presence of MNPs and metal ions. Phytotoxicity from different treatments differed depending on the plant species, and metal types. In addition, exposure to Zn and Cu showed positive dose-dependent effects on their bioaccumulation in each crop. However, there were no significant differences in metal bioaccumulation depending on whether the crops were exposed to MNPs or metal ions. By calculating the bioconcentration factor (BCF) and translocation factor (TF), we were able to estimate the biological uptake and translocation abilities of MNPs and metal ions for each crop. It was found that lettuce and radish had greater BCFs than bok choy and tomato, while bok choy and tomato had higher TFs. Also, the uptake and translocation of Zn were better than those of Cu. However, the values for BCF and TF for each crop showed no significant differences between MNP and metal ion exposure. A micro X-ray fluorescence (μ-XRF) spectrometer analysis demonstrated that only Zn elements appeared in the primary veins and edges of all leaves and the storage root of radish. Our study aims to estimate bioaccumulation, translocation, and the implied potential risks from MNPs accumulated in different plant species.

Nano-enabled agriculture: How do nanoparticles cross barriers in plants?

Nano-enabled agriculture is a topic of intense research interest. However, our knowledge of how nanoparticles enter plants, plant cells, and organelles is still insufficient. Here, we discuss the barriers that limit the efficient delivery of nanoparticles at the whole-plant and single-cell levels. Some commonly overlooked factors, such as light conditions and surface tension of applied nano-formulations, are discussed. Knowledge gaps regarding plant cell uptake of nanoparticles, such as the effect of electrochemical gradients across organelle membranes on nanoparticle delivery, are analyzed and discussed. The importance of controlling factors such as size, charge, stability, and dispersibility when properly designing nanomaterials for plants is outlined. We mainly focus on understanding how nanoparticles travel across barriers in plants and plant cells and the major factors that limit the efficient delivery of nanoparticles, promoting a better understanding of nanoparticle-plant interactions. We also provide suggestions on the design of nanomaterials for nano-enabled agriculture.

Phytotoxic effect of sub-3-nm crystalline ceria nanoparticles on the hydroponic growth of Daikon radish microgreens

Cerium oxide nanoparticles (ceria NPs) have been widely used in many industrial applications. They have been proposed as a potential remedy for reducing oxidative stress in biological systems. General concerns over the toxicity of engineered ceria NPs have led to studies of their phytotoxicity in plants. Most of these plant growth studies were conducted in soil using grain crops and commercial ceria NPs of sizes from 6 nm to 100's nm. In this paper, we report our evaluation of the phytotoxicity and uptake of sub-3-nm crystalline ceria NPs by exposing Daikon radish (Raphanus sativus var. longipinnatus) microgreens to these NPs with environmentally relevant concentrations under hydroponic growth conditions. Aqueous suspensions of different concentrations of these ceria NPs (0.1 ppm, 1 ppm, and 10 ppm) were applied to these microgreens for the last 7 days of the 12-day growth period. Our results revealed the uptake of cerium by plant roots and the translocation of cerium to the stems and the cotyledons (seed leaves). The accumulation of cerium was found to be maximum at the roots, followed by the cotyledons and the stems of the plants. Even at the lowest concentration (0.1 ppm) of the sub-3-nm ceria NPs, the accumulation of cerium at the roots significantly stunted the root growth. However, these NP treatments did not show significant changes to the distributions of macro-minerals (Mg, K, and Ca) and micro-minerals (Zn and Cu) in the microgreens at the end of the 12-day growth period. The phytotoxic effect of sub-3-nm crystalline ceria nanoparticles on the hydroponic growth of Daikon radish microgreens was studied. The cerium uptake by the plant and its effect on the bioavailability of major macro-minerals and micro-minerals within the plant were examined.

Preliminary studies of the impact of food components on nutritional properties of nanoparticles

Nowadays consumers have constantly exposed to nanoparticles (NPs) ingestion. Although the impact of NPs on the human has been studied by many authors, they did not consider the influence of food matrix components on bioaccessibility of NPs. This fact has encouraged us to investigate the influence of different food components on NPs. The investigation has been carried out to assess the influence of main food components on the MNPs (metallic nanoparticles) fate during the in vitro gastrointestinal simulation. The experiments have been carried out with the single-particle inductively coupled plasma mass spectrometry (SP-ICP-MS) as a tool for quantitative and qualitative analysis and the scanning transmission electron microscopy (STEM) as a means of qualitative analysis. The influence of various food components on NPs has been confirmed and it may be concluded that the matrix has an impact on the size and form of NPs. The presence of food components significantly changes the behaviour of NPs during simulated gastrointestinal digestion. Possible explanations of the influence of main nutrient groups, i.e. lipids, protein, salts, saccharides and vitamins on NPs have been proposed.

Cross-examination of engineered nanomaterials in crop production: Application and related implications

The review presents the current knowledge on the development and implementation of nanotechnology in crop production, giving particular attention to potential opportunities and challenges of the use of nano-sensors, nano-pesticides, and nano-fertilizers. Due to the size-dependent properties, e.g. high reactivity, targeted and controlled delivery of active ingredients, engineered nanomaterials (ENMs) are expected to be more efficient agrochemicals than conventional agents. Growing production and usage of ENMs result in the spread of ENMs in the environment. Because plants constitute an important component of the agri-ecosystem, they are subjected to the ENMs activity. A number of studies have confirmed the uptake and translocation of ENMs by plants as well as their positive/negative effects on plants. Here, these endpoints are briefly summarized to show the diversity of plant responses to ENMs. The review includes a detailed molecular analysis of ENMs-plant interactions. The transcriptomics, proteomics and metabolomics tools have been very recently employed to explore ENMs-induced effects in planta. The omics approach allows a comprehensive understanding of the specific machinery of ENMs occurring at the molecular level. The summary of data will be valuable in defining future studies on the ENMs-plant system, which is crucial for developing a suitable strategy for the ENMs usage.

Recent insights into the impact, fate and transport of cerium oxide nanoparticles in the plant-soil continuum

The advent of the nanotechnology era offers a unique opportunity for sustainable agriculture provided that the exposure and toxicity are adequately assessed and properly controlled. The global production and application of cerium oxide nanoparticles (CeO₂-NPs) in various industrial sectors have tremendously increased. Most of the nanoparticles end up in water and soil where they interact with soil microorganisms and plants. Investigating the uptake, translocation and accumulation of CeO₂-NPs is critical for its safe application in agriculture. Plant uptake of CeO₂-NPs may lead to their accumulation in different plant tissues and interference with key metabolic processes of plants. Soil microbes can also be affected by increasing CeO₂-NPs in soil, leading to changes in the physiology and enzymatic activity of soil microorganisms. The interactions between CeO₂-NPs, microbes and plants in the agricultural system need systemic research in ecologically relevant conditions. In the present review, The uptake pathways and in-planta translocation of CeO₂-NPs,and their impact on plant morphology, nutritional values, antioxidant enzymes and molecular determinants are presented. The role of CeO₂-NPs in modifying soil microbial community in plant rhizosphere is also discussed. Overall, the review aims to provide a comprehensive account on the behaviour of CeO₂-NPs in soil-plant systems and their potential impacts on the soil microbial community and plant health.

A Kinetic Approach for Assessing the Uptake of Ag from Pristine and Sulfidized Ag Nanomaterials to Plants

Nanomaterials (NMs) are thermodynamically unstable by nature, and exposure of soil organisms to NMs in the terrestrial environment cannot be assumed constant. Thus, steady-state conditions may not apply to NMs, and bioaccumulation modeling for uptake should follow a dynamic approach. The one-compartment model allows the uptake and elimination of a chemical to be determined, while also permitting changes in exposure and growth to be taken into account. The aim of the present study was to investigate the accumulation of Ag from different Ag NM types (20 nm Ag⁰ NMs, 50 nm Ag⁰ NMs, and 25 nm Ag₂ S NMs) in the crop plant wheat (Triticum aestivum). Seeds were emerged in contaminated soils (3 or 10 mg Ag/kg dry soil, nominal) and plants grown for up to 42 d postemergence. Plant roots and shoots were collected after 1, 7, 14, 21, and 42 d postemergence; and total Ag was measured. Soil porewater Ag concentrations were also measured at each sampling time. Using the plant growth rates in the different treatments and the changing porewater concentrations as parameters, the one-compartment model was used to estimate the uptake and elimination of Ag from the plant tissues. The best fit of the model to the data included growth rate and porewater concentration decline, while showing elimination of Ag to be close to zero. Uptake was highest for Ag⁰ NMs, and size did not influence their uptake rates. Accumulation of Ag from Ag₂ S NMs was lower, as reflected by the lower porewater concentrations. Environ Toxicol Chem 2021;40:1861-1872. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Screening of semi-volatile compounds in plants treated with coated cerium oxide nanoparticles by comprehensive two-dimensional gas chromatography

Literature data about semi-volatile organic compounds in plants and the effect of cerium oxide nanoparticles on them are scarce. Surface modification of nanoparticles may change nanoparticle-environment interaction, and therefore affects compounds in plants. In this research, uncoated and glucose-, levan-, and pullulan-coated cerium oxide nanoparticles were used for wheat and pea treatment during the growth. The aim was the screening of semi-volatile organic compounds from plants' shoots using comprehensive two-dimensional gas chromatography-mass spectrometry, a powerful separation technique allowing to reach unique separation resolution, and investigation of qualitative changes after the treatment with coated cerium oxide nanoparticles. The results were analyzed by the identification of individual peaks and fingerprint analysis by image processing. Wheat samples contained a higher number of semi-volatile organic compounds (108) compared to pea (77) but were less affected by the treatments with coated nanoparticles. The highest number of compounds was detected in wheat after the treatment with levan- and pullulan-coated nanoparticles, and in pea after treatment with levan-coated nanoparticles. This article reports a successful application of a semi-volatile organic compounds profile presented only as categorical variables and unique fingerprint images for the inter-cultivar recognition. This method may be useful in screening nanoparticles' effects on different plants.

Laser-induced breakdown spectroscopy as a straightforward bioimaging tool for plant biologists; the case study for assessment of photon-upconversion nanoparticles in Brassica oleracea L. plant

The main purpose of this work is to thoroughly describe the implementation protocol of laser-induced breakdown spectroscopy (LIBS) method in the plant analysis. Numerous feasibility studies and recent progress in instrumentation and trends in chemical analysis make LIBS an established method in plant bioimaging. In this work, we present an easy and straightforward phytotoxicity case study with a focus on LIBS method. We intend to demonstrate in detail how to manipulate with plants after exposures and how to prepare them for analyses. Moreover, we aim to achieve 2D maps of spatial element distribution with a good resolution without any loss of sensitivity. The benefits of rapid, low-cost bioimaging are highlighted. In this study, cabbage (Brassica oleracea L.) was treated with an aqueous dispersion of photon-upconversion nanoparticles (NaYF₄ doped with Yb³⁺ and Tm³⁺ coated with carboxylated silica shell) in a hydroponic short-term toxicity test. After a 72-hour plant exposure, several macroscopic toxicity end-points were monitored. The translocation of Y, Yb, and Tm across the whole plant was set by employing LIBS with a lateral resolution 100 µm. The LIBS maps of rare-earth elements in B.oleracea plant grown with 50 μg/mL nanoparticle-treated and ion-treated exposures showed the root as the main storage, while the transfer via stem into leaves was minimal. On the contrary, the LIBS maps of plants exposed to the 500 μg/mL nanoparticle-treated and ion-treated uncover slightly different trends, nanoparticles as well as ions were transferred through the stem into leaves. However, the main storage organ was a root as well.

Cerium uptake, translocation and toxicity in the salt marsh halophyte Halimione portulacoides (L.), Aellen

Halimione portulacoides plants were exposed to dissolved cerium (Ce) in a hydroponic medium for five days. Ce accumulation in plants followed the metal's increase in the medium although with a very low translocation factor (TF < 0.01) between roots and shoots. Ce median concentrations in roots were 586, 988 and 1103 μg/g (dry wt.), while in shoots the median values reached 1.9, 3.5 and 10.0 μg/g (dry wt.), for plants exposed to 300, 600 and 1200 μg/L of Ce, respectively. No significant differences occurred in the length of roots and shoots among treatment groups, albeit plants exposed to the highest Ce concentration showed a clear loss of turgor pressure on the fifth day. An increase of hydrogen peroxide and malondialdehyde levels were observed in the plant shoots at 1200 μg/L of Ce. The highest concentration also triggered an answer by the shoots' antioxidant enzymes with a decrease in the activity of superoxide dismutase and an increase in peroxidase. However, no significant change in catalase activity was observed, compared to the control group, which may indicate that peroxidase played a more crucial role against the oxidative stress than catalase. Combined results indicate that H. portulacoides was actively responding to a toxic effect imposed by this higher Ce concentration. Nevertheless, changes in normal environmental conditions, may increase the bioavailability of Ce, while in areas where acid mine drainage may occur, the highest Ce concentration tested in this study may be largely exceeded, placing the sustainability of halophytes and estuarine marshes at risk.

Influence of Cerium Oxide Nanoparticles on Two Terrestrial Wild Plant Species

Most current studies on the relationships between plans and engineered nanomaterials (ENMs) are focused on food crops, while the effects on spontaneous plants have been neglected so far. However, from an ecological perspective, the ENMs impacts on the wild plants could have dire consequences on food webs and ecosystem services. Therefore, they should not be considered less critical. A pot trial was carried out in greenhouse conditions to evaluate the growth of Holcus lanatus L. (monocot) and Diplotaxis tenuifolia L. DC. (dicot) exposed to cerium oxide nanoparticles (nCeO2). Plants were grown for their entire cycle in a substrate amended with 200 mg kg-1nCeO2 having the size of 25 nm and 50 nm, respectively. nCeO2 were taken up by plant roots and then translocated towards leaf tissues of both species. However, the mean size of nCeO2 found in the roots of the species was different. In D. tenuifolia, there was evidence of more significant particle aggregation compared to H. lanatus. Further, biomass variables (dry weight of plant fractions and leaf area) showed that plant species responded differently to the treatments. In the experimental conditions, there were recorded stimulating effects on plant growth. However, nutritional imbalances for macro and micronutrients were observed, as well.

Surface Properties and Environmental Transformations Controlling the Bioaccumulation and Toxicity of Cerium Oxide Nanoparticles: A Critical Review

Increasing production and utilization of cerium oxide nanoparticles (CNPs) in recent years have raised wide concerns about their toxicity. Numerous studies have been conducted to reveal the toxicity of CNPs, but the results are sometimes contradictory. In this review, the most important factors in mediating CNPs toxicity are discussed, including (1) the roles of physicochemical properties (size, morphology, agglomeration condition, surface charge, coating and surface valence state) on CNPs toxicity; (2) the phase transfer and transformation process of CNPs in various aqueous, terrestrial, and airborne environments; and (3) reductive dissolution of CNPs core and their chemical reactions with phosphate, sulfate/S^2-, and ferrous ions. The physicochemical properties play key roles in the interactions of CNPs with organisms and consequently their environmental transformations, reactivity and toxicity assessment. Also, the speciation transformations of CNPs caused by reactions with (in)organic ligands in both environmental and biological systems would further alter their fate, transport, and toxicity potential. Thus, the toxicity mechanisms are proposed based on the physical damage of direct adsorption of CNPs onto the cell membrane and chemical inhibition (including oxidative stress and interaction of CNPs with biomacromolecules). Finally, the current knowledge gaps and further research needs in identifying the toxicological risk factors of CNPs under realistic environmental conditions are highlighted, which might improve predictions about their potential environmental influences. This review aims to provide new insights into cost-effectiveness of control options and management practices to prevent environmental risks from CNPs exposure.

In vivo phytotoxicity, uptake, and translocation of PbS nanoparticles in maize (Zea mays L.) plants

PbS nanomaterials are of great concern because of their potential toxicity and unavoidable releases of multiple commercial applications of nanoparticles (NPs). Commercial NPs act as mediators of damage to plant cells and pose potential toxicity to plants and human health. The mechanisms involved in the toxicity, uptake, and biotranslocation of PbS NPs in plants are poorly understood. We synthesize 15 ± 6 nm PbS nanoparticles (NPs) and report the phytotoxicology, uptake, and translocation of PbS NPs in maize (Zea mays L.) plants under various hydroponic treatments (5 mg/L, 10 mg/L, 20 mg/L, 30 mg/L, 40 mg/L, 50 mg/L of PbS NPs, 1.5 mg/L Pb²⁺ ion and controls) for 15 days. The findings indicate that PbS NPs has phytotoxic effects on seeds germination and similar effects in root elongation. The PbS NPs significantly inhibites the biomass of shoots and roots, as well as root morphology compared with the controls. The PbS NPs can penetrate the epidermis of maize roots and bioaccumulate in shoots at higher concentrations than controls treated with Pb²⁺ ions. The observations are consistent with indices of biotranslocation factor and confirmed by STEM-EDS mapping. The results illustrate PbS NPs can enter the cell wall and exist in intercellular space and cytoplasm of the cortical cell of maize seedlings by apoplastic and symplastic pathways. This study highlights the importance of the uptake, phytotoxicity, and biotranslocation of PbS NPs in maize crops and demonstrates the possible transfer into human food as an outcome of the fate of PbS NPs in plants.

Analysis of cerium oxide and copper oxide nanoparticles bioaccessibility from radish using SP-ICP-MS

BACKGROUND

The transformation of nanoparticles (NPs) internalized in plant tissues is the human digestive system that can provide a better understanding of the impact of NPs on the human system. The presented methodology was developed to study the bioaccessibility of cerium oxide (CeO₂ ) and copper oxide (CuO) NPs from radish after the in vitro simulation of gastrointestinal digestion using single-particle inductively coupled plasma mass spectrometry (SP-ICP-MS).

RESULTS

Radish plants were cultivated hydroponically in a growth medium containing: (i) CeO₂ NPs and (ii) CuO NPs. Both cerium (Ce) and copper (Cu) were found in all organs of the radish plants after analysis by standalone ICP-MS. This confirms the bioaccumulation of CeO₂ and CuO NPs and the translocation of their Ce and Cu to the aerial parts of the plant. Less Ce (4.095 μg g^-1 ) has been detected in leaves than in roots (1.156 mg g^-1 ) while Cu content in leaves was 5.245 μg g^-1 and in roots was 10.41 μg g^-1 . Analysis of the digestive extracts obtained after the in vitro simulation of gastro (pepsin) and gastrointestinal (pancreatin) digestion showed that Ce has easy access to human system at least by 73%.

CONCLUSION

The size of CeO₂ NPs in digestive extracts showed no significant changes. However, the results obtained for CuO NPs digestion were variable and suggested that CuO NPs dissolved during the digestion process. The CuO NPs were observed in roots after the gastrointestinal digestion concluding that CuO NPs recovered after the initial dissolution. © 2020 Society of Chemical Industry.

To-Do and Not-To-Do in Model Studies of the Uptake, Fate and Metabolism of Metal-Containing Nanoparticles in Plants

Due to the increasing release of metal-containing nanoparticles into the environment, the investigation of their interactions with plants has become a hot topic for many research fields. However, the obtention of reliable data requires a careful design of experimental model studies. The behavior of nanoparticles has to be comprehensively investigated; their stability in growth media, bioaccumulation and characterization of their physicochemical forms taken-up by plants, identification of the species created following their dissolution/oxidation, and finally, their localization within plant tissues. On the basis of their strong expertise, the authors present guidelines for studies of interactions between metal-containing nanoparticles and plants.

Chitosan-Based Agronanofungicides as a Sustainable Alternative in the Basal Stem Rot Disease Management

The rise of environmental and health concerns due to the excessive use of the conventional fungicide urges the search for sustainable alternatives of agronanofungicides where the latter is aimed to enhance plant uptake and minimize the volatilization, leaching, and runoff of fungicides. With this in mind, fungicides of hexaconazole and/or dazomet were encapsulated into chitosan nanoparticles for the formulation of chitosan-based agronanofungicides. In the present study, chitosan nanoparticles (2 nm), chitosan-hexaconazole nanoparticles (18 and 168 nm), chitosan-dazomet nanoparticles (7 and 32 nm), and chitosan-hexaconazole-dazomet nanoparticles (5 and 58 nm) were synthesized and used as potent antifungal agents in combating the basal stem rot (BSR) disease caused by Ganoderma boninense in which they were evaluated via an artificial inoculation of oil palm seedlings with the rubber woodblock, which was fully colonized with the fungal Ganoderma boninense mycelium. The results revealed that chitosan nanoparticles could act as dual modes of action, which are themselves as a biocide or as a nanocarrier for the existing fungicides. In addition, the particle size of the chitosan-based agronanofungicides plays a crucial role in suppressing and controlling the disease. The synergistic effect of the double-fungicide system of 5 nm chitosan-hexaconazole-dazomet nanoparticles can be observed as the system showed the highest disease reduction with 74.5%, compared to the untreated infected seedlings.

Nutritional Status of Tomato (Solanum lycopersicum) Fruit Grown in Fusarium-Infested Soil: Impact of Cerium Oxide Nanoparticles

In this study, the impact of cerium oxide nanoparticles on the nutritional value of tomato (Solanum lycopersicum) fruit grown in soil infested with Fusarium oxysporum f. sp. lycopersici was investigated in a greenhouse pot study. Three-week old seedlings of Bonny Best tomato plants were exposed by foliar and soil routes to nanoparticle CeO₂ (NP CeO₂) and cerium acetate (CeAc) at 0, 50, and 250 mg/L and transplanted into pots containing a soil mixture infested with the Fusarium wilt pathogen. Fruit biomass, water content, diameter, and nutritional content (lycopene, reducing and total sugar) along with elemental composition, including Ce, were evaluated. Fruit Ce concentration was below the detection limit in all treatments. Foliar exposure to NP CeO₂ at 250 increased the fruit dry weight (67%) and lycopene content (9%) in infested plants, compared with the infested untreated control. Foliar exposure to CeAc at 50 mg/L reduced fruit fresh weight (46%) and water content (46%) and increased the fruit lycopene content by 11% via root exposure as compared with the untreated infested control. At 250 mg/L, CeAc increased fruit dry weight (94%), compared with the infested untreated control. Total sugar content decreased in fruits of infested plants exposed via roots to NP CeO₂ at 50 mg/kg (63%) and 250 mg/kg (54%), CeAc at 50 mg/kg (46%), and foliarly at 50 mg/L (50%) and 250 mg/L (50%), all compared with the infested untreated control. Plants grown in Fusarium-infested soil had decreased fruit dry weight (42%) and lycopene content (17%) and increased total sugar (60%) and Ca content (140%), when compared with the noninfested untreated control (p ≤ 0.05). Overall, the data suggested minimal negative effects of NP CeO₂ on the nutritional value of tomato fruit while simultaneously suppressing Fusarium wilt disease.

Advances in nanomaterials as novel elicitors of pharmacologically active plant specialized metabolites: current status and future outlooks

During the last few decades major advances have shed light on nanotechnology. Nanomaterials have been widely used in various fields such as medicine, energy, cosmetics, electronics, biotechnology and pharmaceuticals. Owing to their unique physicochemical characteristics and nanoscale structures, nanoparticles (NPs) have the capacity to enter into plant cells and interact with intracellular organelles and various metabolites. The effects of NPs on plant growth, development, physiology and biochemistry have been reported, but their impact on plant specialized metabolism (aka as secondary metabolism) still remains obscure. In reaction to environmental stress and elicitors, a common response in plants results in the production or activation of different types of specialized metabolites (e.g., alkaloids, terpenoids, phenolics and flavonoids). These plant specialized metabolites (SMs) are important for plant adaptation to an adverse environment, but also a huge number of them are biologically active and used in various commercially-valued products (pharmacy, cosmetic, agriculture, food/feed). Due to their wide array of applications, SMs have attracted much attention to explore and develop new strategies to enhance their production in plants. In this context, NPs emerged as a novel class of effective elicitors to enhance the production of various plant SMs. In recent years, many reports have been published regarding the elicitation of SMs by different types of NPs. However, in order to achieve an enhanced and sustainable production of these SMs, in-depth studies are required to figure out the most suitable NP in terms of type, size and/or effective concentration, along with a more complete understanding about their uptake, translocation, internalization and elicitation mechanisms. Herein, we are presenting a comprehensive and critical account of the plant SMs elicitation capacities of the three main classes of nanomaterials (i.e., metallic NPs (MNPs), metal oxide NPs (MONPs) and carbon related nanomaterials). Their different proposed uptake, translocation and internalization pathways as well as elicitation mechanism along with their possible deleterious effect on plant SMs and/or phytotoxic effects are summarized. We also identified and critically discussed the current research gaps existing in this field and requiring future investigation to further improve the use of these nanomaterials for an efficient production of plant SMs.

Copper oxide nanoparticles alter cellular morphology via disturbing the actin cytoskeleton dynamics in Arabidopsis roots

Copper oxide nanoparticles (CuO NPs) have severe nano-toxic effects on organisms. Limited data is available on influence of CuO NPs on plant cells. Here, the molecular mechanisms involved in the toxicity of CuO NPs are studied. Exposure to CuO NPs significantly increased copper content in roots (0.062-0.325 mg/g FW), but CuO NPs translocation rates from root to shoot were low (1.1-2.8%). Presented data were significant at p < 0.05 compared to control. CuO NPs inhibited longitudinal growth and promoted transverse growth in root tip cells. However, CuO NPs did not affect the leaf cells, implying that the transfer ability of CuO NPs was weak, and toxicity mainly affected roots. CuO NPs can conjugate with actin protein. The actin cytoskeleton experienced reorganization in the presence of CuO NPs. The longitudinal filamentous actin (F-actin) decreased, and the transverse F-actin increased. CuO NPs inhibited actin polymerization and promoted depolymerization. The behavior of individual F-actin was at steady state with time-lapse under CuO NPs treatment by time-lapse reflection fluorescence (TIRF) microscopy. The growth rate of actin filaments was weakened by CuO NPs. CuO NPs disturbed the subcellular localization of PINs and the gradient of auxin distribution in root tips in an actin-dependent manner. In conclusion, CuO NPs conjugated with actin and disturbed F-actin dynamics, triggering abnormal cell growth in the root tip, and findings provide theoretical basis for further study nano-toxicity in plants.

Uptake, translocation, size characterization and localization of cerium oxide nanoparticles in radish (Raphanus sativus L.)

Due to their unique physical and chemical properties, the production and use of cerium oxide nanoparticles (CeO₂ NPs) in different areas, especially in automotive industry, is rapidly increasing, causing their presence in the environment. Released CeO₂ NPs can undergo different transformations and interact with the soil and hence with plants, providing a potential pathway for human exposure and leading to serious concerns about their impact on the ecosystem and human organism. This study investigates the uptake, bioaccumulation, possible translocation and localization of CeO₂ NPs in a model plant (Raphanus sativus L.), whose edible part is in direct contact with the soil where contamination is more likely to happen. The stability of CeO₂ NPs in plant growth medium as well as after applying a standard enzymatic digestion procedure was tested by single particle ICP-MS (SP-ICP-MS) showing that CeO₂ NPs can remain intact after enzymatic digestion; however, an agglomeration process was observed in the growth medium already after one day of cultivation. An enzymatic digestion method was next used in order to extract intact nanoparticles from the tissues of plants cultivated from the stage of seeds, followed by size characterization by SP-ICP-MS. The results obtained by SP-ICP-MS showed a narrower size distribution in the case of roots suggesting preferential uptake of smaller nanoparticles which led to the conclusion that plants do not take up the CeO₂ NPs agglomerates present in the medium. However, nanoparticles at higher diameters were observed after analysis of leaves plus stems. Additionally, a small degree of dissolution was observed in the case of roots. Finally, after CeO₂ NPs treatment of adult plants, the spatial distribution of intact CeO₂ NPs in the radish roots was studied by laser ablation ICP-MS (LA-ICP-MS) and the ability of NPs to enter and be accumulated in root tissues was confirmed.

Impact of particle size, oxidation state and capping agent of different cerium dioxide nanoparticles on the phosphate-induced transformations at different pH and concentration

The potential hazard posed by nanomaterials can be significantly influenced by transformations which these materials undergo during their lifecycle, from manufacturing through to disposal. The transformations may depend on the nanomaterials’ own physicochemical properties as well as the environment they are exposed to. This study focuses on the mechanisms of transformation of cerium oxide nanoparticles (CeO₂ NPs) in laboratory experiments which simulate potential scenarios in which the NPs are exposed to phosphate-bearing media. We have experimented with the transformation of four different kinds of CeO₂ NPs, in order to investigate the effects of nanoparticle size, capping agent (three were uncapped and one was PVP capped) and oxidation state (two consisted mostly of Ce⁴⁺ and two were a mix of Ce^3+/Ce⁴⁺). They were exposed to a reaction solution containing KH₂PO₄, citric acid and ascorbic acid at pH values of 2.3, 5.5 and 12.3, and concentrations of 1mM and 5mM. The transformations were followed by UV-vis, zeta potential and XRD measurements, which were taken after 7 and 21 days, and by transmission electron microscopy after 21 days. X-ray photoelectron spectroscopy was measured at 5mM concentration after 21 days for some samples. Results show that for pH 5 and 5mM phosphate concentration, CePO₄ NPs were formed. Nanoparticles that were mostly Ce⁴⁺ did not dissolve at 1mM reagent concentration, and did not produce CePO₄ NPs. When PVP was present as a capping agent it proved to be an extra reducing agent, and CePO₄ was found under all conditions used. This is the first paper where the transformation of CeO₂ NPs in the presence of phosphate has been studied for particles with different size, shapes and capping agents, in a range of different conditions and using many different characterisation methods.

Influence of Surface Charge on the Phytotoxicity, Transformation, and Translocation of CeO2 Nanoparticles in Cucumber Plants

The physiochemical properties of nanoparticles (NPs), including surface charge, will affect their uptake, transformation, translocation, and final fate in the environment. In this study, we compared the phytoxoxicity and transport behaviors of nano CeO₂ (nCeO₂) functionalized with positively charged (Cs-nCeO₂) and negatively charged (PAA-nCeO₂) coatings. Cucumber seedlings were hydroponically exposed to 0-1000 mg/L of Cs-nCeO₂ and PAA-nCeO₂ for 14 days and the contents, distribution, translocation, and transformation of Ce in plants were analyzed using inductively coupled plasma mass spectrometry, micro X-ray fluorescence (μ-XRF), and X-ray absorption near-edge spectroscopy (XANES), respectively. Results showed that the seedling growth and Ce contents in plant tissues were functions of exposure concentrations and surface charge. Cs-nCeO₂ was adsorbed strongly on a negatively charged root surface, which led to significantly higher Ce contents in the roots and lower translocation factors of Ce from the roots to shoots in Cs-nCeO₂ group than in PAA-nCeO₂ group. The results of μ-XRF showed that Ce elements were mainly accumulated at the root tips and lateral roots, as well as in the veins and at the edge of leaves. XANES results revealed that the proportion of Ce(III) was comparable in the plant tissues of the two groups. We speculated that Cs-nCeO₂ and PAA-nCeO₂ were partially dissolved under the effect of root exudates, releasing Ce³⁺ ions as a result. Then, the Ce³⁺ ions were transported upward in the form of Ce(III) complexes along the vascular bundles and eventually accumulated in the veins. The other portion of Cs-nCeO₂ and PAA-nCeO₂ entered the roots through the gap of a Casparian strip at root tips/lateral roots and was transported upward as intact NPs and finally accumulated at the edge of the blade. This study will greatly advance our information on how the properties of NPs influence their phytotoxicity, uptake, and subsequent trophic transfer in terrestrial food webs.

Comparative Physiological and Transcriptomic Analyses Reveal the Toxic Effects of ZnO Nanoparticles on Plant Growth

Zinc oxide (ZnO) nanoparticles (nZnO) are among the most commonly used nanoparticles (NPs), and they have been shown to have harmful effects on plants. However, the molecular mechanisms underlying nZnO tolerance and root sensing of NP stresses have not been elucidated. Here, we compared the differential toxic effects of nZnO and Zn²⁺ toxicity on plants during exposure and recovery using a combination of transcriptomic and physiological analyses. Although both nZnO and Zn²⁺ inhibited primary root (PR) growth, nZnO had a stronger inhibitory effect on the growth of elongation zones, whereas Zn²⁺ toxicity had a stronger toxic effect on meristem cells. Timely recovery from stresses is critical for plant survival. Despite the stronger inhibitory effect of nZnO on PR growth, nZnO-exposed plants recovered from stress more rapidly than Zn²⁺-exposed plants upon transfer to normal conditions, and transcriptome data supported these results. In contrast to Zn²⁺ toxicity, nZnO induced endocytosis and caused microfilament rearrangement in the epidermal cells of elongation zones, thereby repressing PR growth. nZnO also repressed PR growth by disrupting cell wall organization and structure through both physical interactions and transcriptional regulation. The present study provides new insight into the comprehensive understanding and re-evaluation of NP toxicity in plants.

Responses of seed germination and shoot metabolic profiles of maize (Zea maysL.) to Y2O3nanoparticle stress

The potential risks of rare-earth nanoparticles (RENPs) to plants in the environment are attracting increasing attention due to their wide-spread application. In this regard, little is known about the effects of Y₂O₃ NPs as an important member of RENPs on crop plants. Seed germination is vulnerable to environmental stress, which determines the growth and yield of crops. Here, maize seeds were exposed to a Y₂O₃ NP suspension (0–500 mg L⁻¹) in the dark for 6 days. It was found that the Y₂O₃ NPs had no significant effect on the germination rates (>93%) in all treatments, but they could reduce seed vitality, delay germination, and inhibit seedling growth in a dose-dependent manner. Further, the inhibition effect of Y₂O₃ NPs on root elongation was much stronger than that on shoot elongation. Meanwhile, the activities of peroxidase (POD) and catalase (CAT) in shoots were enhanced with the increase in the Y₂O₃ NP concentration. A high-concentration (≥300 mg L⁻¹) of Y₂O₃ NPs induced a significant increase in the malondialdehyde (MDA) level in shoots compared to the control, indicating that the membrane lipid peroxidation and permeability were enhanced. ¹H NMR-based analysis showed that the polar metabolic profiles were altered significantly after treatment with 0, 10, and 500 mg L⁻¹ of Y₂O₃ NPs, but there was no marked alteration observed for the non-polar metabolic profiles. The polar metabolites (e.g., sugars, amino acids, and most organic acids) showed a dose-dependent increase to Y₂O₃ NP stress, indicating that the metabolic pathways of carbohydrate metabolism, the tricarboxylic acid cycle (TCA), and amino acid synthesis were disturbed. There were significantly positive correlations found among the metabolites related with the antioxidant response and osmotic adjustment. The simultaneous accumulation of these metabolites possibly indicated the adaptation of the seedlings to stress at the cost of retarding glycolysis, TCA, and protein synthesis. The retarded effects finally inhibited the apparent growth of the seedlings. These findings reveal the phytotoxicity of Y₂O₃ NPs and provide physiological and biochemical and molecular-scale perspectives on the response of seedlings to stress.

A hypothetic model for the adaptation of maize to Y₂O₃ NPs stress during seed germination.

Toxicity evaluation of ZnO and TiO2 nanomaterials in hydroponic red bean (Vigna angularis) plant: Physiology, biochemistry and kinetic transport

The toxicity and kinetic uptake potential of zinc oxide (ZnO) and titanium dioxide (TiO₂) nanomaterials into the red bean (Vigna angularis) plant were investigated. The results obtained revealed that ZnO, due to its high dissolution and strong binding capacity, readily accumulated in the root tissues and significantly inhibited the physiological activity of the plant. However, TiO₂ had a positive effect on plant physiology, resulting in promoted growth. The results of biochemical experiments implied that ZnO, through the generation of oxidative stress, significantly reduced the chlorophyll content, carotenoids and activity of stress-controlling enzymes. On the contrary, no negative biochemical impact was observed in plants treated with TiO₂. For the kinetic uptake and transport study, we designed two exposure systems in which ZnO and TiO₂ were exposed to red bean seedlings individually or in a mixture approach. The results showed that in single metal oxide treatments, the uptake and transport increased with increasing exposure period from one week to three weeks. However, in the metal oxide co-exposure treatment, due to complexation and competition among the particles, the uptake and transport were remarkably decreased. This suggested that the kinetic transport pattern of the metal oxide mixtures varied compared to those of its individual constituents.

Temporal Evolution of Copper Distribution and Speciation in Roots of Triticum aestivum Exposed to CuO, Cu(OH)2, and CuS Nanoparticles

Utilization of nanoparticles (NP) in agriculture as fertilizers or pesticides requires an understanding of the NP properties influencing their interactions with plant roots. To evaluate the influence of the solubility of Cu-based NP on Cu uptake and NP association with plant roots, wheat seedlings were hydroponically exposed to 1 mg/L of Cu NPs with different solubilities [CuO, CuS, and Cu(OH)₂] for 1 h then transferred to a Cu-free medium for 48 h. Fresh, hydrated roots were analyzed using micro X-ray fluorescence (μ-XRF) and imaging fluorescence X-ray absorption near edge spectroscopy (XANES imaging) to provide laterally resolved distribution and speciation of Cu in roots. Higher solubility Cu(OH)₂ NPs provided more uptake of Cu after 1 h of exposure, but the lower solubility materials (CuO and CuS) were more persistent on the roots and continued to deliver Cu to plant leaves over the 48 h depuration period. These results demonstrate that NPs, by associating to the roots, have the potential to play a role in slowly providing micronutrients to plants. Thus, tuning the solubility of NPs may provide a long-term slow delivery of micronutrients to plants and provide important information for understanding mechanisms responsible for plant uptake, transformation, and translocation of NPs.

Metallic nanoparticles influence the structure and function of the photosynthetic apparatus in plants

The applications of nanoparticles continue to expand into areas as diverse as medicine, bioremediation, cosmetics, pharmacology and various industries, including agri-food production. The widespread use of nanoparticles has generated concerns given the impact these nanoparticles - mostly metal-based such as CuO, Ag, Au, CeO₂, TiO₂, ZnO, Co, and Pt - could be having on plants. Some of the most studied variables are plant growth, development, production of biomass, and ultimately oxidative stress and photosynthesis. A systematic appraisal of information about the impact of nanoparticles on these processes is needed to enhance our understanding of the effects of metallic nanoparticles and oxides on the structure and function on the plant photosynthetic apparatus. Most nanoparticles studied, especially CuO and Ag, had a detrimental impact on the structure and function of the photosynthetic apparatus. Nanoparticles led to a decrease in concentration of photosynthetic pigments, especially chlorophyll, and disruption of grana and other malformations in chloroplasts. Regarding the functions of the photosynthetic apparatus, nanoparticles were associated with a decrease in the photosynthetic efficiency of photosystem II and decreased net photosynthesis. However, CeO₂ and TiO₂ nanoparticles may have a positive effect on photosynthetic efficiency, mainly due to an increase in electron flow between the photosystems II and I in the Hill reaction, as well as an increase in Rubisco activity in the Calvin and Benson cycle. Nevertheless, the underlying mechanisms are poorly understood. The future mechanistic work needs to be aimed at characterizing the enhancing effect of nanoparticles on the active generation of ATP and NADPH, carbon fixation and its incorporation into primary molecules such as photo-assimilates.

Toxicity assessment of metal oxide nano-pollutants on tomato (Solanum lycopersicon): A study on growth dynamics and plant cell death

The present study for the first time demonstrated the interactions of metal oxide (MO) nano-pollutants (CuO and Al₂O₃-NPs) with tissues and cellular DNA of tomato plants grown in soil sand: silt: clay (667:190:143) and Hoagland-hydroponic system and assessed the hazardous effects of NPs on cell physiology and biochemistry. Results of SEM equipped with EDX revealed attachment of variably shaped CuO-NPs (18 nm) and Al₂O₃-NPs (21 nm) on roots, and internalization followed by translocation in plants by ICP-MS and TEM. Significant variations in foliage surface area, chlorophyll, proteins, LPO, and antioxidant enzymes were recorded. Roots and shoots accumulated 225.8 ± 8.9 and 70.5 ± 4 μgAl g^-1 DW, whereas Cu accumulation was 341.6 ± 14.3 (roots) and 146.9 ± 8.1 μg g^-1 DW (shoots) which was significant (p ≤ 0.0005) as compared to control. The total soluble protein content in roots, shoots, and leaves collected from Al₂O₃-NPs treated plants increased by 120, 80, and 132%, respectively while in CuO-NPs treatments, the increase was 68 (roots), 36 (shoots), and 86% (leaves) over control. The level of antioxidant enzymes in plant tissues was significantly (p ≤ 0.05) higher at 2000 μg ml^-1 of MONPs over control. A dose-dependent increase in reactive oxygen species (ROS), biphasic change of lower and higher fluorescence in mitochondria due to dissipation of mitochondrial membrane potential (ΔΨm) and membrane defects using propidium iodide were observed. Comparatively, CuO-NPs induced higher toxicity than Al₂O₃-NPs. Perceptible changes in proteins (amide-I & II), cellulose, glucose, galactose and other carbohydrates were observed under FT-IR. The binding studies with TmDNA showed fluorescence quenching of EtBr-TmDNA and acridine orange-TmDNA complex only by CuO-NPs with -ΔG and +ΔH and +ΔS values. However, Al₂O₃-NPs induced lesser change in TmDNA conformation. Conclusively, the results are novel in better demonstrating the mechanistic basis of nano-phyto-toxicity and are important which could be used to develop strategies for safe disposal of Al₂O₃-NPs and CuO-NPs.

Cerium oxide nanoparticles transformation at the root-soil interface of barley (Hordeum vulgare L.)

The transformation of cerium oxide nanoparticles (CeO₂-NPs) in soil and its role in plant uptake is a critical knowledge gap in the literature. This study investigated the reduction and speciation of CeO₂-NPs in barley (Hordeum vulgare L.) cultivated in soil amended with 250 mg CeO₂-NPs kg^-1 soil. Synchrotron micro-X-ray fluorescence (μXRF) was employed for spatial localization and speciation of CeO₂-NPs in thin sections of intact roots at the soil-root interface. Results revealed that Ce was largely localized in soil and at the root surface in nanoparticulate form (84-89%). However, a few hot spots on root surfaces revealed highly significant reduction (55-98%) of CeO₂-NPs [Ce(IV)] to Ce(III) species. Interestingly, only roots in close proximity to hot spots showed Ce uptake which was largely CeO₂ (89-91%) with very little amount Ce(III) (9-10%). These results suggest that the reduction of CeO₂-NPs to Ce(III) is needed to facilitate uptake of Ce.

Dissolved organic matter reduces CuO nanoparticle toxicity to duckweed in simulated natural systems

With increasing demand for recycled wastewater for irrigation purposes, there is a need to evaluate the potential for manufactured nanomaterials in waste water to impact crop production and agroecosystems. Copper oxide nanoparticles (CuO NPs) have previously been shown to negatively impact the growth of duckweed (Landoltia punctata) a model aquatic plant consumed by water fowl and widely found in agricultural runoff ditches in temperate climates. However, prior studies involving CuO NP toxicity to duckweed have focused on systems without the presence of dissolved organic matter (DOM). In the current study, duckweed growth inhibition was shown to be a function of aqueous Cu²⁺ concentration. Growth inhibition was greatest from aqueous CuCl₂ and, for particles, increased with decreasing CuO particle size. The dissolution of CuO NPs in ½ Hoagland's solution was measured to increase with decreasing particle size and in the presence of Suwannee river humic and fulvic acids (HA; FA). However, the current results suggest that HA, and to a lesser extent, FA, decrease the toxicity of both CuO NPs and free ionized Cu to duckweed, likely by inhibiting Cu availability through Cu-DOM complex formation. Such results are consistent with changes to Cu speciation as predicted by speciation modeling software and suggest that DOM changes Cu speciation and therefore toxicity in natural systems.

Synthesis and biomedical applications of Cerium oxide nanoparticles - A Review

A cerium oxide nanoparticles (nanoceria) has a wide range of applications in different fields, especially biomedical division. As a matter of concern, it has a major impact on the human health and environment. The aim of this review is to address the different ways of synthesis of nanoceria using chemical and green synthesis methods and characterization and the applications of nanoceria for antioxidant, anticancer, antibacterial activities and toxicological studies including the most recent studies carried out in vivo and in vitro to study the problems. We have exclusively discussed on the toxicology of nanoceria exposed to the general public along with recent advances in the studies of antimicrobial, toxicity and anti-oxidant activity.

Chromosomal aberrations, cell suppression and oxidative stress generation induced by metal oxide nanoparticles in onion (Allium cepa) bulb

In this work, we assess the phytotoxicity of various-sized metal oxide nanoparticles on cell cycle progression and induction of oxidative stress in onions.

In Vivo Tracking of Copper-64 Radiolabeled Nanoparticles in Lactuca sativa

Engineered nanoparticles (NPs) are increasingly used in commercial products including automotive lubricants, clothing, deodorants, sunscreens, and cosmetics and can potentially accumulate in our food supply. Given their size it is difficult to detect and visualize the presence of NPs in environmental samples, including crop plants. New analytical tools are needed to fill the void for detection and visualization of NPs in complex biological and environmental matrices. We aimed to determine whether radiolabeled NPs could be used as a noninvasive, highly sensitive analytical tool to quantitatively track and visualize NP transport and accumulation in vivo in lettuce (Lactuca sativa) and to investigate the effect of NP size on transport and distribution over time using a combination of autoradiography, positron emission tomography (PET)/computed tomography (CT), scanning electron microscopy (SEM), and transition electron microscopy (TEM). Azide functionalized NPs were radiolabeled via a "click" reaction with copper-64 (64Cu)-1,4,7-triazacyclononane triacetic acid (NOTA) azadibenzocyclooctyne (ADIBO) conjugate ([64Cu]-ADIBO-NOTA) via copper-free Huisgen-1,3-dipolar cycloaddition reaction. This yielded radiolabeled [64Cu]-NPs of uniform shape and size with a high radiochemical purity (>99%), specific activity of  2.2 mCi/mg of NP, and high stability (i.e., no detectable dissolution) over 24 h across a pH range of 5-9. Both PET/CT and autoradiography showed that [64Cu]-NPs entered the lettuce seedling roots and were rapidly transported to the cotyledons with the majority of the accumulation inside the roots. Uptake and transport of intact NPs was size-dependent, and in combination with the accumulation within the roots suggests a filtering effect of the plant cell walls at various points along the water transport pathway.

Uptake, Accumulation, and in Planta Distribution of Coexisting Cerium Oxide Nanoparticles and Cadmium in Glycine max (L.) Merr.

Agricultural soils are likely to be polluted by both conventional and emerging contaminants at the same time. Understanding the interactions of coexisting engineered nanoparticles (ENPs) and trace elements (a common source of abiotic stress) is critical to gaining insights into the accumulation of these two groups of chemicals by plants. The objectives of this study were to determine the uptake and accumulation of coexisting ENPs and trace elements by soybeans and to gain insights into the physiological mechanisms resulting in different plant accumulation of these materials. The combinations of three cadmium levels (0 [control] and 0.25 and 1 milligrams per kilogram of dry soil) and two CeO2 NPs concentrations (0 [control] and 500 milligrams per kilogram of dry soil) were investigated. Measurements of the plant biomass and physiological parameters indicated that CeO2 NPs led to higher variable fluorescence to maximum fluorescence ratio, suggesting that CeO2 NPs enhanced the plant light energy use efficiency by photosystem II. In addition, the presence of CeO2 NPs did not affect Cd accumulation in soybean, but Cd significantly increased the accumulation of Ce in plant tissues, especially in roots and older leaves. The altered Ce in planta distribution was partially associated with the formation of root apoplastic barriers in the co-presence of Cd and CeO2 NPs.

Abnormal pinocytosis and valence-variable behaviors of cerium suggested a cellular mechanism for plant yield reduction induced by environmental cerium

The environmental safety of cerium (Ce) applications in many fields has been debated for almost a century because the cellular effects of environmental Ce on living organisms remain largely unclear. Here, using new, interdisciplinary methods, we surprisingly found that after Ce(III) treatment, Ce(III) was first recognized and anchored on the plasma membrane in leaf cells. Moreover, some trivalent Ce(III) was oxidized to tetravalent Ce(IV) in this organelle, which activated pinocytosis. Subsequently, more anchoring sites and stronger valence-variable behavior on the plasma membrane caused stronger pinocytosis to transport Ce(III and IV) into the leaf cells. Interestingly, a great deal of Ce was bound on the pinocytotic vesicle membrane; only a small amount of Ce was enclosed in the pinocytotic vesicles. Some pinocytic vesicles in the cytoplasm were deformed and broken. Upon breaking, pinocytic vesicles released Ce into the cytoplasm, and then these Ce particles self-assembled into nanospheres. The aforementioned special behaviors of Ce decreased the fluidity of the plasma membrane, inhibited the cellular growth of leaves, and finally, decreased plant yield. In summary, our findings directly show the special cellular behavior of Ce in plant cells, which may be the cellular basis of plant yield reduction induced by environmental Ce.

Transformation and bioavailability of metal oxide nanoparticles in aquatic and terrestrial environments. A review

Metal oxide nanoparticles (MeO-NPs) are among the most consumed NPs and also have wide applications in various areas which increased their release into the environmental system. Aquatic (water and sediments) and terrestrial compartments are predicted to be the destination of the released MeO-NPs. In these compartments, the particles are subjected to various dynamic processes such as physical, chemical and biological processes, and undergo transformations which drive them away from their pristine state. These transformation pathways can have strong implications for the fate, transport, persistence, bioavailability and toxic-effects of the NPs. In this critical review, we provide the state-of-the-knowledge on the transformation processes and bioavailability of MeO-NPs in the environment, which is the topic of interest to researchers. We also recommend future research directions in the area which will support future risk assessments by enhancing our knowledge of the transformation and bioavailability of MeO-NPs.

Melatonin Improves the Photosynthetic Carbon Assimilation and Antioxidant Capacity in Wheat Exposed to Nano-ZnO Stress

The release of nanoparticles into the environment is inevitable, which has raised global environmental concern. Melatonin is involved in various stress responses in plants. The present study investigated the effects of melatonin on photosynthetic carbon (C) assimilation and plant growth in nano-ZnO stressed plants. It was found that melatonin improved the photosynthetic C assimilation in nano-ZnO stressed wheat plants, mainly due to the enhanced photosynthetic energy transport efficiency, higher chlorophyll concentration and higher activities of Rubisco and ATPases. In addition, melatonin enhanced the activities of antioxidant enzymes to protect the photosynthetic electron transport system in wheat leaves against the oxidative burst caused by nano-ZnO stress. These results suggest that melatonin could improve the tolerance of wheat plants to nano-ZnO stress.

Cerium oxide nanoparticles alter the salt stress tolerance of Brassica napus L. by modifying the formation of root apoplastic barriers

Rapidly growing global population adds significant strains on the fresh water resources. Consequently, saline water is increasingly tapped for crop irrigation. Meanwhile, rapid advancement of nanotechnology is introducing more and more engineered nanoparticles into the environment and in agricultural soils. While some negative effects of ENPs on plant health at very high concentrations have been reported, more beneficial effects of ENPs at relatively low concentrations are increasingly noticed, opening doors for potential applications of nanotechnology in agriculture. In particular, we found that cerium oxide nanoparticles (CeO₂NPs) improved plant photosynthesis in salt stressed plants. Due to the close connections between salt stress tolerance and the root anatomical structures, we postulated that CeO₂NPs could modify plant root anatomy and improve plant salt stress tolerance. This study aimed at testing the hypothesis with Brassica napus in the presence of CeO₂NPs (0, 500 mg kg^-1 dry sand) and/or NaCl (0, 50 mM) in a growth chamber. Free hand sections of fresh roots were taken every seven days for three weeks and the suberin lamellae development was examined under a fluorescence microscope. The results confirmed the hypothesis that CeO₂NPs modified the formation of the apoplastic barriers in Brassica roots. In salt stressed plants, CeO₂NPs shortened the root apoplastic barriers which allowed more Na⁺ transport to shoots and less accumulation of Na⁺ in plant roots. The altered Na⁺ fluxes and transport led to better physiological performance of Brassica and may lead to new applications of nanotechnology in agriculture.

Evidence that Soil Properties and Organic Coating Drive the Phytoavailability of Cerium Oxide Nanoparticles

The ISO-standardized RHIZOtest is used here for the first time to decipher how plant species, soil properties, and physical-chemical properties of the nanoparticles and their transformation regulate the phytoavailability of nanoparticles. Two plants, tomato and fescue, were exposed to two soils with contrasted properties: a sandy soil poor in organic matter and a clay soil rich in organic matter, both contaminated with 1, 15, and 50 mg·kg^-1 of dissolved Ce₂(SO₄)₃, bare and citrate-coated CeO₂ nanoparticles. All the results demonstrate that two antagonistic soil properties controlled Ce uptake. The clay fraction enhanced the retention of the CeO₂ nanoparticles and hence reduced Ce uptake, whereas the organic matter content enhanced Ce uptake. Moreover, in the soil poor in organic matter, the organic citrate coating significantly enhanced the phytoavailability of the cerium by forming smaller aggregates thereby facilitating the transport of nanoparticles to the roots. By getting rid of the dissimilarities between the root systems of the different plants and the normalizing the surfaces exposed to nanoparticles, the RHIZOtest demonstrated that the species of plant did not drive the phytoavailability, and provided evidence for soil-plant transfers at concentrations lower than those usually cited in the literature and closer to predicted environmental concentrations.

Impact of Surface Charge on Cerium Oxide Nanoparticle Uptake and Translocation by Wheat (Triticum aestivum)

Nanoparticle (NP) physiochemical properties, including surface charge, affect cellular uptake, translocation, and tissue localization. To evaluate the influence of surface charge on NP uptake by plants, wheat seedlings were hydroponically exposed to 20 mg/L of ∼4 nm CeO₂ NPs functionalized with positively charged, negatively charged, and neutral dextran coatings. Fresh, hydrated roots and leaves were analyzed at various time points over 34 h using fluorescence X-ray absorption near-edge spectroscopy to provide laterally resolved spatial distribution and speciation of Ce. A 15-20% reduction from Ce(IV) to Ce(III) was observed in both roots and leaves, independent of NP surface charge. Because of its higher affinity with negatively charged cell walls, CeO₂(+) NPs adhered to the plant roots the strongest. After 34 h, CeO₂(-), and CeO₂(0) NP exposed plants had higher Ce leaf concentrations than the plants exposed to CeO₂(+) NPs. Whereas Ce was found mostly in the leaf veins of the CeO₂(-) NP exposed plant, Ce was found in clusters in the nonvascular leaf tissue of the CeO₂(0) NP exposed plant. These results provide important information for understanding mechanisms responsible for plant uptake, transformation, and translocation of NPs, and suggest that NP coatings can be designed to target NPs to specific parts of plants.

Phytotoxicity of CeO2 nanoparticles on radish plant (Raphanus sativus)

Cerium oxide nanoparticles (CeO₂ NPs) have been considered as one type of emerging contaminants that pose great potential risks to the environment and human health. The effect of CeO₂ NPs on plant-edible parts and health evaluation remains is necessary and urgently to be developed. In this study, we cultivated radish in Sigma CeO₂ NP (<25 nm)-amended soils across a series of concentration treatments, i.e., 0 mg/kg as the control and 10, 50, and 100 mg/kg CeO₂ NPs. The results showed that CeO₂ NPs accelerated the fresh biomass accumulation of radish plant; especially in the treatment of 50 mg/kg CeO₂ NPs, root expansion was increased by 2.2 times as much as the control. In addition, the relative chlorophyll content enhanced by 12.5, 12.9, and 12.2% was compared to control on 40 cultivation days. CeO₂ NPs were mainly absorbed by the root and improved the activity of antioxidant enzyme system to scavenge the damage of free radicals in radish root and leaf. In addition, this study also indicated that the nanoparticles might enter the food chain through the soil into the edible part of the plant, which will be a potential threat to human health.

Influence of phosphate on phytotoxicity of ceria nanoparticles in an agar medium

Fate and toxicity of manufactured nanoparticles (NPs) in the living organisms and the environment are highly related to their transformation. In the present study, the effect of phosphate on the phytotoxicity and transformation of CeO2 NPs was investigated in an agar medium using head lettuce plants that are sensitive to Ce3+ ions. Plants were treated by CeO2 NPs with or without phosphate for 10 days. Results suggest that the treatments of P deficiency (P(-)) and CeO2 NPs (P(+)&Ce) could separately induce significant inhibition on the growth of lettuce seedlings and cause oxidative stress, but the inhibition was the most serious when the two conditions were combined (P(-)&Ce). In the absence of phosphate, more CeO2 NPs were transformed to Ce(III) in the roots and more Ce3+ ions were translocated to the shoots, which induced higher toxicity to head lettuce. Phosphates could alleviate the phytotoxic effect of CeO2 NPs through the precipitation of dissociated Ce3+ ions. Considering the wide existence of phosphate in the environment, phosphate-related transformation may be a critical factor in evaluating the toxicity and fate of many other metal-based NPs.