Functional analyses of nanoparticle toxicity: a comparative study of the effects of TiO2 and Ag on tomatoes (Lycopersicon esculentum)

Plant response to silver nanoparticles: a critical review

Although several metal ions/metal nanoparticles (NPs) are toxic to both plants and animals, some of them are used as nutrients and growth promoters. Plants exposed to silver nanoparticles (Ag-NPs) have shown both beneficial and harmful effects. All concentrations of Ag-NPs are not effective for a given plant because any excess can block the passage of essential nutrients. Regulated treatment of plants by Ag-NPs may enhance their overall growth and development. It has been noticed that Ag-NPs decrease the mass of edible plants (Cucurbita pepo, Allium cepa, cabbage, and lettuce) and vegetables, but they also induce the germination of seeds in many cases. NPs interact with proteins, enzymes, and carbohydrates influencing the total biomass, root, and shoot growth of plants. Also, Ag-NPs act as an ethylene inhibitor and activate the antioxidants in onions. Their substantial quantity becomes deposited in onion leaves and bulbs. Size and concentration are the two major factors responsible for the increase/decrease of plant growth and biomass. Plants make adaptations to reduce the toxicity caused by Ag-NPs. In some cases, Ag-NPs induce root elongation and increase chlorophyll, carbohydrate, proteins, rate of photosynthesis and inhibit the biosynthesis of ethylene. This review article provides a comprehensive overview of both the beneficial and adverse effects of Ag-NPs on germination, growth, development, physiological, and biochemical characteristics of a wide range of edible and crop plants. We have also critically discussed: the chemistry, toxicity, uptake, translocation, and accumulation of Ag-NPs in plant systems.

Influence of Titanium Dioxide Nanoparticles on Human Health and the Environment

Nanotechnology has enabled tremendous breakthroughs in the development of materials and, nowadays, is well established in various economic fields. Among the various nanomaterials, TiO₂ nanoparticles (NPs) occupy a special position, as they are distinguished by their high availability, high photocatalytic activity, and favorable price, which make them useful in the production of paints, plastics, paper, cosmetics, food, furniture, etc. In textiles, TiO₂ NPs are widely used in chemical finishing processes to impart various protective functional properties to the fibers for the production of high-tech textile products with high added value. Such applications contribute to the overall consumption of TiO₂ NPs, which gives rise to reasonable considerations about the impact of TiO₂ NPs on human health and the environment, and debates regarding whether the extent of the benefits gained from the use of TiO₂ NPs justifies the potential risks. In this study, different TiO₂ NPs exposure modes are discussed, and their toxicity mechanisms—evaluated in various in vitro and in vivo studies—are briefly described, considering the molecular interactions with human health and the environment. In addition, in the conclusion of this study, the toxicity and biocompatibility of TiO₂ NPs are discussed, along with relevant risk management strategies.

Silver Nanoparticle's Toxicological Effects and Phytoremediation

The advancement in nanotechnology has brought numerous benefits for humans in diverse areas including industry, medicine, and agriculture. The demand in the application of nanomaterials can result in the release of these anthropogenic materials into soil and water that can potentially harm the environment by affecting water and soil properties (e.g., soil texture, pH, organic matter, and water content), plants, animals, and subsequently human health. The properties of nanoparticles including their size, surface area, and reactivity affect their fate in the environment and can potentially result in their toxicological effects in the ecosystem and on living organisms. There is extensive research on the application of nano-based materials and the consequences of their release into the environment. However, there is little information about environmentally friendly approaches for removing nanomaterials from the environment. This article provides insight into the application of silver nanoparticles (AgNPs), as one of the most commonly used nanomaterials, their toxicological effects, their impacts on plants and microorganisms, and briefly reviews the possibility of remediation of these metabolites using phytotechnology approaches. This article provides invaluable information to better understand the fate of nanomaterials in the environment and strategies in removing them from the environment.

Effect of green and chemically synthesized titanium dioxide nanoparticles on cadmium accumulation in wheat grains and potential dietary health risk: A field investigation

A field study was designed to explore the impacts of foliar-applied chemically and green synthesized titanium dioxide nanoparticles (TiO₂ NPs) on cadmium (Cd) uptake in wheat plants. The wheat was grown in field which was contaminated with Cd and plants were subjected to foliar episodes of TiO₂ NPs during plant growth period. Leaf extracts of two plant species (Trianthema portulacastrum, Chenopodium quinoa) were used for green synthesis while sol-gel method was used for chemical preparation of TiO₂ NPs. Results showed that TiO₂ NPs significantly enhanced the plant height, length of spikes photosynthesis, and straw and grain yield compared to control. TiO₂ NPs minimized the oxidative burst in leaves and improved the enzyme activities than control. Cadmium concentrations of straw, roots and grains decreased after TiO₂ NPs treatments than control. The grain Cd contents were below recommended threshold (0.2 mg Cd /kg grain DW) for cereals upon NPs exposure. The health risk index by the dietary use of grains for adults was below threshold upon NPs exposure. Overall, foliar use of TiO₂ NPs prepared from plant extracts was appropriate in minimizing Cd contents in wheat grains, thereby reducing risk of Cd to human health via food chain.

Biosynthesis of Silver Nanoparticles Mediated by Entomopathogenic Fungi: Antimicrobial Resistance, Nanopesticides, and Toxicity

Silver nanoparticles are widely used in the biomedical and agri-food fields due to their versatility. The use of biological methods for the synthesis of silver nanoparticles has increased considerably due to their feasibility and high biocompatibility. In general, microorganisms have been widely explored for the production of silver nanoparticles for several applications. The objective of this work was to evaluate the use of entomopathogenic fungi for the biological synthesis of silver nanoparticles, in comparison to the use of other filamentous fungi, and the possibility of using these nanoparticles as antimicrobial agents and for the control of insect pests. In addition, the in vitro methods commonly used to assess the toxicity of these materials are discussed. Several species of filamentous fungi are known to have the ability to form silver nanoparticles, but few studies have been conducted on the potential of entomopathogenic fungi to produce these materials. The investigation of the toxicity of silver nanoparticles is usually carried out in vitro through cytotoxicity/genotoxicity analyses, using well-established methodologies, such as MTT and comet assays, respectively. The use of silver nanoparticles obtained through entomopathogenic fungi against insects is mainly focused on mosquitoes that transmit diseases to humans, with satisfactory results regarding mortality estimates. Entomopathogenic fungi can be employed in the synthesis of silver nanoparticles for potential use in insect control, but there is a need to expand studies on toxicity so to enable their use also in insect control in agriculture.

Transfer of sulfidized silver from silver nanoparticles, in sewage sludge, to plants and primary consumers in agricultural soil environment

Consumer products containing silver nanoparticles (AgNPs) release silver (Ag) to the environment, particularly wastewater. Sewage sludge (SS), which contains numerous contaminants including Ag, is recycled by spreading on agricultural land. Although slight impacts and bioaccumulation of Ag sulfide (Ag₂S, the main species found in SS) in terrestrial organisms have been demonstrated, possible trophic transfer into plants and subsequently animal species has not been examined. Accordingly, the present study experimentally measured the transfer of Ag from AgNPs and sulfidized Ag into plants and primary consumers and compared their bioavailability. Nine plant cultivars were grown in soil mixed with SS containing Ag, which revealed that bioaccumulation of Ag by plants is species-dependent. Ryegrass (the plant species with the greatest accumulation - up to 0.2 mg kg^-1) was then cultivated on a larger scale to expose snails and locusts for several weeks. While locusts did not accumulate Ag after two weeks of exposure, snails exhibited Ag bioaccumulation after 5 weeks when soil was accessible. Sulfidized Ag derived from AgNPs were less available (bioaccumulation up to 2.5 mg kg^-1) than the Ag from the original AgNPs (bioaccumulation up to 15 mg kg^-1). This transfer potential of Ag could have consequences for food webs due to chronic exposure linked to SS spreading practices. This study shows that transformations of AgNPs in treatment plants attenuate but do not completely eliminate the risk of Ag to plant and animal species SS.

Effects of TiO2 Nanoparticles Incorporation into Cells of Tomato Roots

In this study, tomato plants were grown in vitro with and without incorporation of TiO₂ nanoparticles in Murashige and Skoog (MS) growth medium. The aim of this study was to describe the morphological (area and roundness cell) and mechanical (Young’s Modulus) change in the different tissue of tomato root, epidermis (Ep), parenchyma (Pa), and vascular bundles (Vb), when the whole plant was exposed to TiO₂ nanoparticles (TiO₂ NPs). light microscopy (LM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM), wavelength dispersive X-ray fluorescence (WDXRF) techniques were used to identify changes into the root cells when TiO₂ NPs were incorporated. TiO₂ NPs incorporation produces changes in the area, roundness, and Young’s Modulus of the tomato root. When tomato root is exposed to TiO₂ NPs, the Ep and Vb area size decreases from 260.92 µm² to 160.71 µm² and, 103.08 µm² to 52.13 µm², respectively, compared with the control area, while in Pa tissue the area size was increased considerably from 337.72 mm² to 892.96 mm². Cellular roundness was evident in tomato root that was exposed to TiO₂ NPs in the Ep (0.49 to 0.67), Pa (0.63 to 0.79), and Vb (0.76 to 0.71) area zones. Young’s Modulus in Pa zone showed a rigid mechanical behavior when tomato root is exposed to TiO₂ NPs (0.48 to 4.98 MPa control and TiO₂ NPs, respectively). Meanwhile, Ep and Vb were softer than the control sample (13.9 to 1.06 MPa and 6.37 to 4.41 MPa respectively). This means that the Pa zone was stiffer than Ep and Vb when the root is exposed to TiO₂ NPs. Furthermore, TiO₂ NPs were internalized in the root tissue of tomato, accumulating mainly in the cell wall and intercellular spaces, with a wide distribution throughout the tissue, as seen in TEM.

Effects of metal nanoparticle-mediated treatment on seed quality parameters of different crops

The increasing population of the world requires novel techniques to feed everyone, which can replace or work along with traditional methods to increase production of agricultural crops. In recent times, nanotechnology is considered as a promising and emerging approach to be incorporated in agriculture to improve productivity of different crops by the administration of nanoparticles through seed treatment, foliar spray on plants, nano-fertilizers for balanced crop nutrition, nano-herbicides for effective weed control, nanoinsecticides for plant protection, early detection of plant diseases and nutrient deficiencies using diagnostics kits, and nano-pheromones for effective monitoring of pests. Further, distinct nanoparticles with unique physicochemical and biological properties are used in agriculture to increase the percentage of seed germination, which is the initial step to increase the crop yield. In the context of agricultural crops, nanoparticles have both positive effects on seed quality parameters, such as germination percentage, seedling length, seedling dry weight and vigor indices, as well as negative impacts of causing toxicity toward the environment. Thus, the aim of this review article is to provide a comprehensive overview on the effects of super-dispersive metal powders, such as zinc, silver, and titanium nanoparticles on the seed quality parameters of different crops. In addition, the drawback of conventional seed growth enhancers, impact of metal nanoparticles toward seeds, and mechanism of nanoparticles to increase seed germination were also discussed.

Nanobiotechnology for Agriculture: Smart Technology for Combating Nutrient Deficiencies with Nanotoxicity Challenges

Nanobiotechnology in agriculture is a driver for modern-day smart, efficient agricultural practices. Nanoparticles have been shown to stimulate plant growth and disease resistance. The goal of sustainable farming can be accomplished by developing and sustainably exploiting the fruits of nanobiotechnology to balance the advantages nanotechnology provides in tackling environmental challenges. This review aims to advance our understanding of nanobiotechnology in relevant areas, encourage interactions within the research community for broader application, and benefit society through innovation to realize sustainable agricultural practices. This review critically evaluates what is and is not known in the domain of nano-enabled agriculture. It provides a holistic view of the role of nanobiotechnology in multiple facets of agriculture, from the synthesis of nanoparticles to controlled and targeted delivery, uptake, translocation, recognition, interaction with plant cells, and the toxicity potential of nanoparticle complexes when presented to plant cells.

QNAR modeling of cytotoxicity of mixing nano-TiO2 and heavy metals

The Quantitative Structure-Activity Relationship (QSAR) has been used to investigate organic mixtures but QSAR in the nanomaterial field (QNAR) is still new. Toxicity is a result of the interaction of many substances. QNAR research focuses on a single nanomaterial in the long-term. It is difficult to find an appropriate descriptor to build a model due to the complexity of the mixture. Here, we attempt to build a QNAR model to predict cell viability for HK-2 cells exposed to a mixture containing nano-TiO₂ and heavy metals. HK-2 cells were exposed to four groups of mixtures containing heavy-metals and nanomaterials and CCK8 was added to obtain the number of living cells. At the same time, ROS was investigated to study this mechanism. Each descriptor of the components and mixtures were obtained using the formula D_mix= [Formula: see text] respectively. We used the Multiple Partial Least Squares Regression (PLS) and Random Forest Regression (RF) to build a QNAR model. Both models reliably predict and assess viability of HK-2 cells exposed to the mixture. The RF model showed greater stability and higher precision in toxicity predictability and can be applied to environmental nano-toxicology.

Changes in the physiological and biochemical state of peanut plants (Arachis hypogaea L.) induced by exposure to green metallic nanoparticles

Different types of nanoparticles (NPs) are increasingly used in multiple sectors such as industry, medicine and agriculture. This application has increased the possibility of NPs accumulating and contaminating the environment. Plants are one of the essential building blocks of all ecosystems and the interaction between NPs and plants is an indispensable aspect of risk assessment. To understand the effects of NPs in agricultural systems, in the present study we investigated the effects of exposure of Ag, Cu and Cu/Ag phytonanoparticles in Arachis hypogaea L. plants at a physiological and biochemical level, for which NPs solutions were applied foliarly at concentrations of 250, 500, 750 and 1000 ppm for 48 days. Parameters such as leaf length, chlorophyll and concentration of phytohormones showed that phytonanoparticles could cause serious damage to plant growth and development. Plants exposed to phytonanoparticles showed an increase in total phenols, proline, PAL activity and antioxidant enzymes, this to mitigate the stress caused. The alteration in the composition and content of fatty acids in the peanut kernels after exposure to different NPs indicated that they could affect the yield and quality of crop. Therefore, it is necessary to investigate its potential impact on food quality. Statement of noveltyIn this manuscript, we report for the first time that green nanoparticles induced a lower degree of toxicity in plants compared to commercial nanoparticles.Our results indicate that the mechanisms by which peanut plants respond to the application of nanoparticles were an increase in the activity of phenylalanine ammonia-lyase and antioxidant enzymes. So far there are few studies on the effect of nanoparticles on plant hormones, our results revealed a significant decrease in indole-3 acetic acid and induced the synthesis of gibberellins. The modification in the composition and content of fatty acids in the peanut kernels indicated that the nanoparticles could affect the quality of the crop.

Reclaimed wastewater as a viable water source for agricultural irrigation: A review of food crop growth inhibition and promotion in the context of environmental change

The geographical and temporal distribution of precipitation has and is continuing to change with changing climate. Shifting precipitation will likely require adaptations to irrigation strategies, and because 35% of rainfed and 60% of irrigated agriculture is within 20 km of a wastewater treatment plant, we expect that the use of treated wastewater (e.g., reclaimed wastewater) for irrigation will increase. Treated wastewater contains various organic and inorganic substances that may have beneficial (e.g., nitrate) or deleterious (e.g., salt) effects on plants, which may cause a change in global food productivity should a large change to treated wastewater irrigation occur. We reviewed literature focused on food crop growth inhibition or promotion resulting from exposure to xenobiotics, engineered nanoparticles, nitrogen, and phosphorus, metals, and salts. Xenobiotics and engineered nanoparticles, in nearly all instances, were detrimental to crop growth, but only at concentrations much greater than would be currently expected in treated wastewater. However, future changes in wastewater flow and use of these compounds and particles may result in phytotoxicity, particularly for xenobiotics, as some are present in wastewater at concentrations within approximately an order of magnitude of concentrations which caused growth inhibition. The availability of nutrients present in treated wastewater provided the greatest overall benefit, but may be surpassed by the detrimental impact of salt in scenarios where either high concentrations of salt are directly deleterious to plant development (rare) or in scenarios where soils are poorly managed, resulting in soil salt accumulation.

Nanoparticles Affect the Expression Stability of Housekeeping Genes in Plant Cells

Purpose

We report on the expression stability of several housekeeping/reference genes that can be used in the normalization of target gene expression in quantitative real-time PCR (qRT-PCR) analysis of plant cells challenged with metal nanoparticles (NPs).

Materials and Methods

Uniform cell suspension cultures of Hypericum perforatum were treated with 25 mg/l silver and gold NPs (14-15 nm in diameter). Cells were collected after 0.5, 4.0, and 12 h. The total RNA isolated from the cells was analyzed for the stability of ACT2, ACT3, ACT7, EF1-α, GAPDH, H2A, TUB-α, TUB-β, and 18S rRNA genes using qRT-PCR. The cycle threshold (Ct) values of the genes were analyzed using the geNorm, NormFinder, BestKeeper, and RefFinder statistical algorithms to rank gene stability. The stability of the top-ranked genes was validated by normalizing the expression of HYP1.

Results

The expression of the tested housekeeping genes varied with treatment duration and NP types. EF1-α in gold NP treatment and TUB-α and EF1-α in silver NP treatment ranked among the top three positions. However, none of the genes retained their top ranking with time and across NP types.

Conclusion

EF1-α can be used as a reference for treatment involving both silver and gold NPs in H. perforatum cells. TUB-α can be used only for silver NP-treated cells. The expression instability of most of the housekeeping genes highlights the importance of systematic standardization of reference genes for NP treatment conditions to draw proper conclusions on the target gene expression.

Transformation of Nanomaterials and Its Implications in Gut Nanotoxicology

Ingestion of engineered nanomaterials (ENMs) is inevitable due to their widespread utilization in the agrifood industry. Safety evaluation has become pivotal to identify the consequences on human health of exposure to these ingested ENMs. Much of the current understanding of nanotoxicology in the gastrointestinal tract (GIT) is derived from studies utilizing pristine ENMs. In reality, agrifood ENMs interact with their microenvironment, and undergo multiple physicochemical transformations, such as aggregation/agglomeration, dissolution, speciation change, and surface characteristics alteration, across their life cycle from synthesis to consumption. This work sieves out the implications of ENM transformations on their behavior, stability, and reactivity in food and product matrices and through the GIT, in relation to measured toxicological profiles. In particular, a strong emphasis is given to understand the mechanisms through which these transformations can affect ENM induced gut nanotoxicity.

Effects of silver(I) toxicity on microstructure, biochemical activities, and genic material of Lemna minor L. with special reference to application of bioindicator

In this research, several biochemical variations in plant of Lemna minor L. were investigated to reflect Ag⁺ toxicity. Lemna minor L. changed colorless AgNO₃ to colloidal brown at doses equal to and greater than 1 mg L^-1. Optical and fluorescence microscopy revealed the presence of bright spots in roots of tested plant related to Ag/Ag₂O-NPs. Photosynthetic pigment contents of Lemna minor L. declined upon exposure to Ag⁺ with an evidently higher decrease in chlorophyll a than in chlorophyll b. Similarly, Ag⁺ treatment caused an evident reduction in the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). The reduction in antioxidase activity was significantly higher in POD than in SOD and CAT. Ag⁺ treatment resulted in a significant increment in the level of malondialdehyde (MDA) content as the judging criteria of cellular injury which showed sign of dose-related. The alterations occurred in RAPD profiles of treated samples following Ag⁺ toxicity containing loss of normal bands, appearance of new bands, and variation in band intensities compared with the normal plants. In addition, morphological character and biomass of Lemna minor L. subjected to increasing Ag⁺ concentrations were evaluated to reveal Ag⁺ toxicity. Our study demonstrated that Lemna minor L. have a high sensitivity to indicate fluctuation of water quality. It would be beneficial that modulating the genotype of Lemna minor L. to bear high proportion of contaminates.

Effect of Low-Dose Nano Titanium Dioxide Intervention on Cd Uptake and Stress Enzymes Activity in Cd-Stressed Cowpea [Vigna unguiculata (L.) Walp] Plants

Cadmium contamination of agricultural soils is a serious problem due to its toxic effects on health and yield of crop plants. This study investigates the potential of low-dose nano-TiO₂ as soil nanoremediation on Cd toxicity in cowpea plants. To achieve this goal, cowpea seeds were germinated on Cd-spiked soils at 10 mg/kg for 14 days and later augmented with 100 mg nTiO₂/kg (nTiO₂-50 nm and bTiO₂-68 nm, respectively). The results showed that chlorophylls were not altered by nano-TiO₂ intervention. Cadmium partitioning in roots and leaves was reduced by the applied nano-TiO₂ but significantly higher than control. Ascorbate peroxidase and catalase activities in roots and leaves were promoted by nano-TiO₂ intervention compared to control and sole Cd, respectively. However, magnitudes of activity of enzyme activities were higher in nTiO₂ compared to bTiO₂ treatments. The enhanced enzymes activity led to reduced malonaldehyde content in plant tissues. The study concludes that soil application of nano-TiO₂ could be a green alternative to ameliorate soil Cd toxicity in cowpea plants.

Uptake, translocation and ligand of silver in Lactuca sativa exposed to silver nanoparticles of different size, coatings and concentration

The broad use of silver nanoparticles (AgNPs) in daily life products enhances their possibilities to reach the environment. Therefore, it is important to understand the uptake, translocation and biotransformation in plants and the toxicological impacts derived from these biological processes. In this work, Lactuca sativa (lettuce) was exposed during 9 days to different coated (citrate, polyvinylpyrrolidone, polyethylene glycol) and sized (60, 75, 100 nm) AgNPs at different concentrations (1, 3, 5, 7, 10, 15 mg L-1). Total silver measurements in lettuce roots indicated that accumulation of AgNPs is influenced by size and concentration, but not by nanoparticle coating. On the other hand, nanosilver translocation to shoots was more pronounced for neutral charged and large sized NPs at higher NP concentrations. Single particle inductively coupled plasma mass spectrometry analysis, after an enzymatic digestion of lettuce tissues indicated the dissolution of some NPs. Ag K-edge X-ray absorption spectroscopy analysis corroborated the AgNPs dissolution due to the presence of less Ag-Ag bonds and appearance of Ag-O and/or Ag-S bonds in lettuce roots. Toxicological effects on lettuces were observed after exposure to nanosilver, especially for transpiration and stomatal conductance. These findings indicated that AgNPs can enter to edible plants, exerting toxicological effects on them.

Effects of silver-graphene oxide on seed germination and early growth of crop species

Due to its excellent material properties, silver-graphene oxide (Ag-GO) is being studied for diverse applications, such as antimicrobial agents, catalysts and absorbents. Such use of Ag-GO may lead to its release into terrestrial ecosystems, but little is known about the impact of Ag-GO on plants. In the present study, we determined the effects of Ag-GO on seed germination and early growth of crop species by analyzing the germination rate, growth of roots and shoots, hydrogen peroxide (H₂O₂) accumulation, and the uptake of Ag in alfalfa, radish and cucumber treated with 0.2–1.6 mg mL⁻¹ of Ag-GO. Ag-GO treatment increased the shoot growth of radish at 0.2–1.6 mg mL⁻¹ but decreased that of cucumber at 0.8 mg mL⁻¹. In addition, Ag-GO enhanced the root elongation of radish at 0.2 mg mL⁻¹ but inhibited that of alfalfa at 0.2, 0.8 and 1.6 mg mL⁻¹. Ag-GO treatment induced H₂O₂ production in alfalfa, radish and cucumber in a concentration-dependent manner. Larger amounts of Ag accumulated in the seedlings as the concentration of Ag-GO increased, and such accumulation suggests that Ag may be transferred to higher trophic levels when plants are exposed to Ag-GO in ecosystems. Our study can, thus, serve as an important basis for setting guidelines for the release of nanomaterials into the environment.

Foliar spray of TiO2 nanoparticles prevails over root application in reducing Cd accumulation and mitigating Cd-induced phytotoxicity in maize (Zea mays L.)

Cadmium (Cd) pollution is considered one of the global environmental issues due to its adverse effects on plant and human health. With the rapid development of nanotechnology and the practical application of engineered nanoparticles (ENPs) in agriculture, the mechanisms underlying the interactions between NPs and heavy metal on their uptake, accumulation, and phytotoxicity in crops are still not fully understood. Therefore, the impact of TiO₂ NPs (0, 100, 250 mg/L) and Cd (0, 50 μM) co-exposure on hydroponic maize (Zea mays L.) was determined under two exposure modes. Results showed that root co-exposure to TiO₂ NPs and 100 mg/L Cd significantly enhanced Cd uptake and produced greater phytotoxicity in maize than foliar exposure to TiO₂ NPs. Meanwhile, plant dry weight and chlorophyll content showed a reduction of 45.3% and 50.5%, respectively, when compared with single Cd treatment. In addition, the accumulation of Ti in shoots and roots increased by 1.61 and 4.29 times, respectively when root exposure to 250 mg/L TiO₂ NPs. By contrast, foliar exposure of TiO₂ NPs could markedly decrease shoot Cd contents from 15.2% to 17.8% and had a stronger influence on alleviating Cd-induced toxicity via increasing superoxide dismutase (SOD) and glutathione S-transferase (GST) activities and upregulating several metabolic pathways, including galactose metabolism and citrate cycle, alanine, aspartate and glutamate metabolism, as well as glycine, serine and threonine metabolism. This study provides a new strategy for the application of TiO₂ NPs in crop safety production in Cd contaminated soils.

Chemically synthesized silver nanoparticles induced physio-chemical and chloroplast ultrastructural changes in broad bean seedlings

This study was conducted to explore the effects of priming of seven-year-old aged seeds with different concentrations of silver nanoparticles (AgNPs) on growth of broad bean (Vicia faba L.). Seeds were primed with different concentrations of AgNPs for 6 h before growing in the plastic trays. Different growth parameters like growth attributes, photosynthetic pigments, carbohydrates, antioxidant enzymes and chloroplast ultrastructure were estimated after 14 days of germination. Priming with AgNPs affected the root and shoot growth attributes as compared with control depending upon concentrations of AgNPs. In all treatments, photosynthetic pigments increased significantly above control levels, but total soluble sugars decreased in 10 and 50 ppm AgNPs and slightly increased in 100 ppm AgNPs as compared with control. Starch accumulation was apparent in all treated seedlings above that of control levels. Mesophyll cells of all treated seedlings were altered with electron dense particles than control. Priming with AgNPs affected the chloroplast structure which appeared in the form of less stacking of Greene, formation of protrusions and extensions, irregular shape of chloroplasts as compared with spindle shaped regular chloroplasts of control. In all treatments, total phenols were slightly affected as compared with control. The antioxidant enzyme activities in seedlings varied with the dose and type of antioxidants. Overall, AgNPs adversely affected the chloroplast ultrastructure, but increased growth of seedlings and starch accumulation. Further studies are required to explore the effects of AgNPs on the long-term on crop productivity of aged seeds.

Ecotoxicology of silver nanoparticles and their derivatives introduced in soil with or without sewage sludge: A review of effects on microorganisms, plants and animals

Silver nanoparticles (AgNPs) are widely incorporated in many products, partly due to their antimicrobial properties. The subsequent discharge of this form of silver into wastewater leads to an accumulation of silver species (AgNPs and derivatives resulting from their chemical transformation), in sewage sludge. As a result of the land application of sewage sludge for agricultural or remediation purposes, soils are the primary receiver media of silver contamination. Research on the long-term impact of AgNPs on the environment is ongoing, and this paper is the first review that summarizes the existing state of scientific knowledge on the potential impact of silver species introduced into the soil via sewage sludge, from microorganisms to earthworms and plants. Silver species can easily enter cells through biological membranes and affect the physiology of organisms, resulting in toxic effects. In soils, exposure to AgNPs may change microbial biomass and diversity, decrease plant growth and inhibit soil invertebrate reproduction. Physiological, biochemical and molecular effects have been documented in various soil organisms and microorganisms. Negative effects on organisms of the dominant form of silver in sewage sludge, silver sulfide (Ag₂S), have been observed, although these effects are attenuated compared to the effects of metallic AgNPs. However, silver toxicity is complex to evaluate and much remains unknown about the ecotoxicology of silver species in soils, especially with respect to the possibility of transfer along the trophic chain via accumulation in plant and animal tissues. Critical points related to the hazards associated with the presence of silver species in the environment are described, and important issues concerning the ecotoxicity of sewage sludge applied to soil are discussed to highlight gaps in existing scientific knowledge and essential research directions for improving risk assessment.

Uptake and toxicity studies of magnetic TiO2-Based nanophotocatalyst in Arabidopsis thaliana

Information on the environmental impact of magnetic TiO₂-based nanophotocatalysts is scarce. This study evaluated the potential effects of an innovative magnetic nanophotocatalyst N-TiO₂/Fe₃O₄@SiO₂ (NTFS) on plants using Arabidopsis thaliana grown in a hydroponic system. NTFS was detected in the vascular tissues and mesophyll of plants, thus confirming the uptake and upwards transport of NTFS from roots to leaves. Fourier transform infrared spectroscopy was applied to determine compositional and structural alterations in plant tissues exposed to NTFS, or its two main components (N-TiO₂ and Fe₃O₄@SiO₂), at concentrations ranging from 0 to 1000 mg/L, but no changes were detected in the lipids, pectins, proteins, cellulose, hemicellulose, and carbohydrates. The morphology and biomass of the plants were not affected by the NTFS or its components either. Biosensors for inorganic phosphate (Pi) and MgATP^2- were used to monitor the in vivo Pi and MgATP^2- levels in the plant cells. The results showed that NTFS and its components did not induce any adverse effects on the cytosolic Pi level or ATP synthesis, indicating the energy physiology of Arabidopsis was unaffected. In general, NTFS has inconsequential toxic effects on Arabidopsis, but can be taken up by plants, enter the food chain, and cause potential exposure and bioaccumulation in animals and human beings.

Nanotechnology in Plant Science: To Make a Long Story Short

This mini-review aims at gaining knowledge on basic aspects of plant nanotechnology. While in recent years the enormous progress of nanotechnology in biomedical sciences has revolutionized therapeutic and diagnostic approaches, the comprehension of nanoparticle-plant interactions, including uptake, mobilization and accumulation, is still in its infancy. Deeper studies are needed to establish the impact of nanomaterials (NMs) on plant growth and agro-ecosystems and to develop smart nanotechnology applications in crop improvement. Herein we provide a short overview of NMs employed in plant science and concisely describe key NM-plant interactions in terms of uptake, mobilization mechanisms, and biological effects. The major current applications in plants are reviewed also discussing the potential use of polymeric soft NMs which may open new and safer opportunities for smart delivery of biomolecules and for new strategies in plant genetic engineering, with the final aim to enhance plant defense and/or stimulate plant growth and development and, ultimately, crop production. Finally, we envisage that multidisciplinary collaborative approaches will be central to fill the knowledge gap in plant nanotechnology and push toward the use of NMs in agriculture and, more in general, in plant science research.

TiO2 nanoparticles in irrigation water mitigate impacts of aged Ag nanoparticles on soil microorganisms, Arabidopsis thaliana plants, and Eisenia fetida earthworms

Treated wastewater is reclaimed to irrigate crops in a growing number of arid and semi-arid areas. In order to study the impacts of metallic nanoparticles (NPs) present in treated wastewater on soil ecosystems, a soil micro-ecosystem containing Arabidopsis thaliana plants, soil microorganisms, and Eisenia fetida earthworms was developed. The soil was irrigated with deionized water containing environmentally relevant concentrations of 70 µg/L of TiO₂ NPs; or 20 µg/L of an Ag mixture, which included 90% (w/w) Ag₂S NPs, 7.5% (w/w) Ag⁰ NPs, and 2.5% (w/w) Ag⁺ to represent speciation of aged Ag NPs in treated wastewater; or a combination of the TiO₂ NPs and the Ag mixture to reflect the frequent presence of both types of materials in treated wastewater. It was found that TiO₂ NPs alone were not toxic to the soil micro-ecosystem. Irrigation water containing 20 µg/L of the Ag mixture significantly reduced the soil microbial biomass, and inhibited the growth of plants and earthworms; however, a combination of 70 µg/L of TiO₂ and 20 µg/L of Ag did not show toxic impact on organism growth compared to the Control of deionized water irrigation. Taken together, these results indicate the importance of investigating the effects of different nanomaterials in combination as they are introduced to the environment-with environmentally relevant concentrations and speciation-instead of only selecting a single NP type or residual ion. Moreover, the results of this study support the safe application of reclaimed water from wastewater treatment plants for use in agricultural lands in regard to limited concentrations of aged NPs (i.e., TiO₂ and Ag) if present in combination.

Prospects, challenges and need for regulation of nanotechnology with special reference to India

To meet the challenges of food security in a sustainable way, technological intervention in agriculture is of prime importance. With the existing conventional technologies supporting high yield, better crop production and protection, the emphasis is now on use of nanotechnology. Exploring new applications of nanotechnology has gained momentum in recent years and has shown acceptance in sectors like food, medicine, chemistry etc. As compared to other sectors, the accepted role in agriculture can still be considered on the marginal side in terms of nanotechnology application. Nanotechnology offers a potential to open large scope of novel application in the fields of biotechnology and agricultural industries due to unique physicochemical properties. Nanoparticles can be used in herbicides, nano-pesticide, nano-fertilizers, or genes, which target specific cellular organelles in plant to release their content. It can potentially play an instrumental role in minimizing the application losses of agrochemicals due to their more stable emulsion, higher coverage on leaf surface, precision application, etc. Understanding that the conventional and macro-technologies in agriculture do not ensure sustainable food security and environmentally safe methods; the researchers are now inclined for more précised nanotechnology based applications. There is still a huge untapped potential of nanomaterials to be used a future technology in agriculture which remains to be explored. Besides offering potential benefits, there are high concerns about the potential challenges associated with nanoparticles. To address the safety concerns about nanoparticles, it is important that a strong regulation system should be developed. Presently, very few countries have started focusing on keeping nanoregulation on their agenda. It is very important for agricultural and biodiverse country like India to set up norms of use nanoregulation and bring nanotechnology on the safe technology net.

A potential involvement of plant systemic response in initiating genotoxicity of Ag-nanoparticles in Arabidopsis thaliana

The extensive availability of engineered nanomaterials in global markets has led to the release of substantial amounts of nanoparticles (NP) into atmosphere, water body and soil, yielding both beneficial and harmful effects in plant systems. The NP are mainly aggregated onto the surface of plant roots and leaves exposed and only slightly transported into other tissues with a low rate of internalization. This raises a question of whether plant systemic response is involved in the induction of biological effects of NP. To address this, model plant Arabidopsis thaliana were root exposed to low concentrations of Ag-NP of two particle sizes (10-nm and 60-nm), and expressions of homologous recombination (HR)-related genes and the alleviation of transcriptional gene silencing (TGS) in aerial leafy tissues were examined as genotoxic endpoints. Results showed that exposure of roots to two sizes of Ag-NP up-regulated expressions of HR genes, and reactivated TGS-silenced repetitive elements in aerial tissues. These effects were blocked by the impairment in the salicylic acid signal pathway, indicating a potential involvement of plant systemic response in the induction of Ag-NP genotoxicity. This is further supported by ICP-MS analysis, in which the Ag content in aerial tissues was not significantly changed by root exposure to 10-nm Ag-NP. Although a significant increase in the Ag content in aerial tissues was observed after root exposure to 60-nm Ag-NP, its genotoxic effects had no obvious difference from that by 10-nm Ag-NP exposure, also suggesting that the genotoxicity might be mainly induced via plant systemic response, at least in the experiments of root exposure to Ag-NP.

Impacts of Silver Nanoparticles on Plants: A Focus on the Phytotoxicity and Underlying Mechanism

Nanotechnology was well developed during past decades and implemented in a broad range of industrial applications, which led to an inevitable release of nanomaterials into the environment and ecosystem. Silver nanoparticles (AgNPs) are one of the most commonly used nanomaterials in various fields, especially in the agricultural sector. Plants are the basic component of the ecosystem and the most important source of food for mankind; therefore, understanding the impacts of AgNPs on plant growth and development is crucial for the evaluation of potential environmental risks on food safety and human health imposed by AgNPs. The present review summarizes uptake, translocation, and accumulation of AgNPs in plants, and exemplifies the phytotoxicity of AgNPs on plants at morphological, physiological, cellular, and molecular levels. It also focuses on the current understanding of phytotoxicity mechanisms via which AgNPs exert their toxicity on plants. In addition, the tolerance mechanisms underlying survival strategy that plants adopt to cope with adverse effects of AgNPs are discussed.

Proteomic Analysis of the Effect of Inorganic and Organic Chemicals on Silver Nanoparticles in Wheat

Production and utilization of nanoparticles (NPs) are increasing due to their positive and stimulating effects on biological systems. Silver (Ag) NPs improve seed germination, photosynthetic efficiency, plant growth, and antimicrobial activities. In this study, the effects of chemo-blended Ag NPs on wheat were investigated using the gel-free/label-free proteomic technique. Morphological analysis revealed that chemo-blended Ag NPs resulted in the increase of shoot length, shoot fresh weight, root length, and root fresh weight. Proteomic analysis indicated that proteins related to photosynthesis and protein synthesis were increased, while glycolysis, signaling, and cell wall related proteins were decreased. Proteins related to redox and mitochondrial electron transport chain were also decreased. Glycolysis associated proteins such as glyceraldehyde-3-phosphate dehydrogenase increased as well as decreased, while phosphoenol pyruvate carboxylase was decreased. Antioxidant enzyme activities such as superoxide dismutase, catalase, and peroxidase were promoted in response to the chemo-blended Ag NPs. These results suggested that chemo-blended Ag NPs promoted plant growth and development through regulation of energy metabolism by suppression of glycolysis. Number of grains/spike, 100-grains weight, and yield of wheat were stimulated with chemo-blended Ag NPs. Morphological study of next generational wheat plants depicted normal growth, and no toxic effects were observed. Therefore, morphological, proteomic, yield, and next generation results revealed that chemo-blended Ag NPs may promote plant growth and development through alteration in plant metabolism.

Uptake and Transformation of Silver Nanoparticles and Ions by Rice Plants Revealed by Dual Stable Isotope Tracing

Knowledge on the uptake and transformation of silver nanoparticles (AgNPs) and Ag⁺ ions by organisms is critical for understanding their toxicity. Herein, the differential uptake, transformation, and translocation of AgNPs and Ag⁺ ions in hydroponic rice ( Oryza sativa L.) is assessed in modified Hewitt (with Cl^- ions, HS(Cl)) and Hogland solutions (without Cl^- ions, HS) using dual stable isotope tracing (¹⁰⁷AgNO₃ and ¹⁰⁹AgNPs). After coexposure to ¹⁰⁷Ag⁺ ions and ¹⁰⁹AgNPs at 50 μg L^-1 (as Ag for both) for 14 days, a stimulatory effect was observed on root elongation (increased by 68.8 and 71.9% for HS(Cl) and HS, respectively). Most of the Ag⁺ ions (from ¹⁰⁷Ag⁺ ions and ¹⁰⁹AgNPs) were retained on the root surface, while the occurrence of AgNPs (from ¹⁰⁹AgNPs and ¹⁰⁷Ag⁺ ions) was observed in the root, suggesting the direct uptake of AgNPs and/or reduction of Ag⁺ ions. Higher fractions of Ag⁺ ions in the shoot suggest an in vivo oxidation of AgNPs. These results demonstrated the intertransformation between Ag⁺ ions and AgNPs and the role of AgNPs as carriers and sources of Ag⁺ ions in organisms, which is helpful for understanding the fate and toxicology of Ag.

Understanding the phyto-interaction of heavy metal oxide bulk and nanoparticles: evaluation of seed germination, growth, bioaccumulation, and metallothionein production

The fast-growing use of nano-based products without proper care has led to a major public health concern. Nanomaterials contaminating the environment pose serious threat to the productivity of plants and via food chain to human health. Realizing these, four vegetable crops, radish, cucumber, tomato, and alfalfa, were exposed to varying concentrations of heavy metal oxide (TiO₂, ZnO, Al₂O₃ and CuO) submicron or bulk (BPs) and nanoparticles (NPs) to assess their impact on relative seed germination (RSG), seed surface adsorption, root/shoot tolerance index (RTI/STI), bioaccumulation, and metallothioneins (MTs) production. The results revealed a clear inhibition of RSG, RTI, and STI, which, however, varied between species of metal-specific nanoparticles and plants. SEM and EDX analyses showed significant adsorption of MONP agglomerates on seed surfaces. The concentration of metals detected by EDX differed among vegetables. Among the metals, Al, Cu, Ti, and Zn were found maximum in alfalfa (12.46%), tomato (23.2%), cucumber (6.32%) and radish (21.74%). Of the four metal oxides, ZnO was found most inhibitory to all vegetables and was followed by CuO. The absorption/accumulation of undesirable levels of MONPs in seeds and seedlings differed with variation in dose rates, and was found to be maximum (1748–2254 μg g⁻¹ dry weight) in ZnO-NPs application. Among MONPs, the uptake of TiO₂ was minimum (2 to 140 μg g⁻¹) in radish seedlings. The concentration of MTs induced by ZnO-NPs, ZnO-BPs, and CuO-NPs ranged between 52 and 136 μ mol MTs g⁻¹ FW in vegetal organs. Conclusively, the present findings indicated that both the nanosize and chemical composition of MONPs are equally dangerous for vegetable production. Hence, the accumulation of MONPs, specifically ZnO and CuO, in edible plant organs in reasonable amounts poses a potential environmental risk which, however, requires urgent attention to circumvent such toxic problems.

Phyto-interaction of heavy metal oxide nano and bulk particles with agriculturally important crops.

Different toxicities of nanoscale titanium dioxide particles in the roots and leaves of wheat seedlings

Despite previous studies on exploring the environmental effects of titanium dioxide nanoparticles particle (nTiO₂) on plants, the detailed impacts of nTiO₂on the antioxidant system and photosynthesis of plants is still not well understood.

Titanium dioxide nanoparticles impaired both photochemical and non-photochemical phases of photosynthesis in wheat

Titanium dioxide nanoparticles (TiO₂-NP) are increasingly being proposed for nanoagriculture but their effect on photosynthesis is limited and contradictory, mostly regarding putative chronical effects associated to the exposure to the commercial P25 formulation (anatase:rutile). This research aims at evaluating how chronical exposure to P25-NP affect photosynthetic processes in Triticum aestivum. Wheat plants were exposed (from the germination stage) to 0, 5, 50, and 150 mg L^-1 P25-NP for 20 days. P25-NP impaired both light-dependent and -independent phases of photosynthesis, decreased chlorophyll a content, maximal and effective efficiency of PSII, net photosynthetic rate, transpiration rate, stomatal conductance, intercellular CO₂ concentration, and starch content. On the other hand, no effects were observed in photochemical and in non-photochemical quenching values, on total soluble sugar (TSS) content or in RuBisCO activity. Our results support that the induced decay in chlorophyll a content compromised the electron transport through PSII and that stomatal limitations impaired CO₂ assimilation. The decline of starch content seems to be a consequence of its degradation as a mechanism to maintain the TSS levels. Consequently, we propose that photosynthetic related endpoints are sensitive and valuable biomarkers to assess TiO₂-NP toxicity.

Phytostimulatory effect of silver nanoparticles (AgNPs) on rice seedling growth: An insight from antioxidative enzyme activities and gene expression patterns

The knowledge on the mode of action, biocompatibility and ecological tolerance of silver nanoparticles (AgNPs) is gradually accumulating over the years with contradictory findings. Most of the studies indicated the toxic impact of AgNPs on plant growth and development, where induction of oxidative stress was considered to be one of the causal factors. The present study demonstrates the phytostimulatory effect of bio-synthesized silver nanoparticles (AgNPs) during seed germination and seedling growth of rice (Oryza sativa L., cv. Swarna) under in vitro condition. All the tested concentrations of AgNPs (10, 20, 40 ppm) promote both the shoot and root growth which was evident from the increased length and biomass of the seedlings. Exposure to AgNPs also significantly increased the chlorophyll a and carotenoid contents. The content and the pattern of distribution of phenolic metabolites among the different treatments are indicative of non-toxic impact of AgNP mimicking mild or no stress to the seedlings. Growth stimulation of rice seedlings by AgNPs was further supported by a low level of reactive oxygen species (ROS) concomitant with decreased amount of lipid peroxidation and H₂O₂ content, compared to control. In order to unravel the stimulatory impact of AgNPs on rice seedling growth, the present study also describes the AgNPs induced changes in antioxidative enzyme activity and related gene expression levels. Elevated levels of catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) activities were recorded in all the AgNPs treated seedlings with improved growth. The activity of superoxide dismutase (SOD) was not significantly altered at low concentration of AgNPs. It appears that enzymes of ascorbate cycle, APX and GR are more active in ensuring protection against oxidative damage than SOD. There was significant up-regulation of CAT and APX gene expressions in seedlings exposed to AgNPs, whereas the expression level of CuZnSOD gene was decreased gradually with an increase in the concentration of AgNPs. The antioxidant enzyme activities and gene expression patterns coupled with the levels of H₂O₂ and lipid peroxidation indicates that the efficiency of redox reactions was increased in the presence of AgNPs and that accelerates the seedling growth.

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.

Sex-related responses of European aspen (Populus tremula L.) to combined stress: TiO2 nanoparticles, elevated temperature and CO2 concentration

The combined effects of climate change and chemical contaminants on plant performance are still not well understood. Especially, whether different sexes of dioecious plants respond differently to combined stresses is unknown. In order to study the sex-related responses of European aspen to soil nTiO₂ contamination (0, 50, 300 mg kg^-1) under elevated temperature (+1.6 °C) and CO₂ (730 ppm), we conducted a study in greenhouses. Ti accumulated in roots exposed to nTiO₂ (1.1-3.3 and 2.7-21.1 mg kg^-1 in 50 and 300 mg kg^-1 treatments, respectively). Elevated CO₂ had no effects on Ti uptake, while elevated temperature increased it in the 300 mg kg^-1 treatment. Males grew taller than females under ambient conditions, but females had greater height and biomass increment under elevated temperature. In all climate treatments, nTiO₂ increased leaf phenolics in females by 12-19% and 15-26% at 50 and 300 mg kg^-1, respectively. Leaf phenolics decreased under elevated temperature, but increased under elevated CO₂ in both sexes. Results suggest that females have better chemical defense against nTiO₂ than males under future climate conditions. In the longer run, this may cause changes in the competitive abilities of both sexes, which again may affect sex ratios and genetic variation in nature.

Alteration of Crop Yield and Quality of Wheat upon Exposure to Silver Nanoparticles in a Life Cycle Study

As a result of the rapid development of nanotechnology, metal-based nanoparticles (NPs) are inadvertently released into the environment and may pose a potential threat to the ecosystem. However, information for food quality and safety in NP-treated crops is limited. In the present study, wheat ( Triticum aestivum L.) was grown in different concentrations of Ag-NP-amended soil (20, 200, and 2000 mg kg^-1) for 4 months. At harvest, physiological parameters, Ag and micronutrient (Fe, Cu, and Zn) contents, and amino acid and total protein contents were measured. Results showed that, with increasing the exposure doses, Ag NPs exhibited severe phytotoxicity, including lower biomass, shorter plant height, and lower grain weight. Ag accumulation in roots was significantly higher than that in shoots and grains. Decreases in the content of micronutrients (Fe, Cu, and Zn) in Ag-NP-treated grains suggested low crop quality. The results of amino acid and protein contents in Ag-NP-treated wheat grains indicated that Ag NPs indeed altered the nutrient contents in the edible portion. In the amino acid profile, the presence of Ag NPs significantly decreased the contents of arginine and histidine by 13.0 and 11.8%, respectively. In summary, the effects of metal-based NPs on the edible portion of crops should be taken into account in the evaluation of nanotoxicity to terrestrial plants. Moreover, investigation of the potential impacts of NP-caused nutrient alterations on human health could further our understandings on NP-induced phytotoxicity.

Phytotoxicity of silver nanoparticles to Lemna minor: Surface coating and exposure period-related effects

Silver nanoparticles (Ag NPs) exponential production raises concern about their environmental impact. The effects of Ag NPs to aquatic plants remain scarcely studied, especially in extended exposures. This paper aims to evaluate Ag NPs effects in Lemna minor at individual and sub-individual levels, focusing on three variables: Ag form (NPs versus ions - Ag⁺), NPs surface coating (citrate vs polyvinylpyrrolidone - PVP) and exposure period (7 vs 14days). Endpoints were assessed at individual level (specific growth rate, chlorosis incidence and number of fronds per colony) and sub-individual level (enzymatic activities of catalase (CAT), guaiacol peroxidase (GPx) and glutathione-S-transferase (GST)). Generally, plants exposed to all Ag forms underwent decays on growth rate and fronds per colony, and increases on chlorosis, GPX and GST, but no effects on CAT. The most sensitive endpoints were specific growth rate and GPx activity, showing significant effects down to 0.05mg/L for Ag NPs and 3μg/L for Ag⁺, after 14days. Ag⁺ showed higher toxicity with a 14d-EC₅₀ of 0.0037mg Ag/L. Concerning surface coating, PVP-Ag NPs were more deleterious on growth rate and fronds per colony, whereas citrate-Ag NPs affected more the chlorosis incidence and GPx and GST activities. The exposure period significantly affected chlorosis: 14days triggered a chlorosis increase in Ag⁺-exposed plants and a decrease in Ag NPs-exposed plants when compared to 7days. Ag NPs induced an oxidative stress status in cells, thus ensuing upregulated enzymatic activity as a self-defense mechanism. Since Ag NPs dissolution might occur on a steady and continuous mode along time, and the average longevity of fronds, we propose longer exposures periods than the recommended by the OECD guideline. This approach would provide more relevant and holistic evidences on the overall response of freshwater plants to Ag NPs in an ecological relevant scenario.

Plant Response to Metal-Containing Engineered Nanomaterials: An Omics-Based Perspective

The increasing use of engineered nanomaterials (ENMs) raises questions regarding their environmental impact. Improving the level of understanding of the genetic and molecular basis of the response to ENM exposure in biota is necessary to accurately assess the true risk to sensitive receptors. The aim of this Review is to compare the plant response to several metal-based ENMs widely used, such as quantum dots, metal oxides, and silver nanoparticles (NPs), integrating available "omics" data (transcriptomics, miRNAs, and proteomics). Although there is evidence that ENMs can release their metal components into the environment, the mechanistic basis of both ENM toxicity and tolerance is often distinct from that of metal ions and bulk materials. We show that the mechanisms of plant defense against ENM stress include the modification of root architecture, involvement of specific phytohormone signaling pathways, and activation of antioxidant mechanisms. A critical meta-analysis allowed us to identify relevant genes, miRNAs, and proteins involved in the response to ENMs and will further allow a mechanistic understanding of plant-ENM interactions.

Morphological, proteomic and metabolomic insight into the effect of cerium dioxide nanoparticles to Phaseolus vulgaris L. under soil or foliar application

Chemically synthesized nanoparticles (NPs) are widely used in industry and concern over their impact on the environment is rising. In this study, greenhouse grown bean (Phaseolus vulgaris L.) plants were treated with CeO₂ NPs suspensions at 0, 250, 500, 1000, and 2000mgL^-1 either aerially by spraying or via soil application. At 15days after treatment, plants were analyzed for Ce uptake, morphological and biochemical assays, as well as high-resolution mass spectrometry based metabolomics and proteomics. The results from ICP-MS assays showed a dose dependent absorption, uptake and translocation of Ce through both roots and leaves; Ce content increased from 0.68 up to 1894mgkg^-1 following spray application, while concentrations were three orders lower following soil application (0.59 to 2.19mgkg^-1). Electrolyte leakage increased with NPs rate, from 25.2% to 70.3% and from 24.8% to 32.9% following spray and soil application, respectively. Spraying lowered stomatal density (from 337 to 113 per mm²) and increased stomatal length (from 12.8 to 19.4μm), and altered photosynthesis and electron transport chain biochemical machinery. The increase in Ce content induced accumulation of osmolites (proline increased from 0.54 to 0.65mg/g under spray application), phytosiderophores (muconate and mugineate compounds showed increase fold-changes >16) and proteins involved in folding or turnover. NPs application induced membrane damage, as evidenced by the increase in membrane lipids degradates and by the increase in electrolyte leakage, and caused oxidative stress. Most of the responses were not linear but dose-dependent, whereas metabolic disruption is expected at the highest NPs dosage. Both proteomics and metabolomics highlighted a stronger effect of CeO₂ NPs spraying, as compared to soil application. High concentrations of NPs in the environment have been confirmed to pose toxicity concern towards plants, although important differences could be highlighted between aerial deposition and soil contamination.

Co-exposure to titanium dioxide nanoparticles does not affect cadmium toxicity in radish seeds (Raphanus sativus)

Recent developments on environmental fate models indicate that as nano waste, engineered nanomaterials (ENMs) could reach terrestrial ecosystems thus potentially affecting environmental and human health. Plants can be therefore exposed to ENMs but controversial data in terms of fate and toxicity are currently available. Furthermore, there is a current lack of information on complex interactions/transformations to which ENMs undergo in the natural environment as for instance interacting with existing toxic compounds. The aim of the present study was to assess the behavior and biological effects of titanium dioxide nanoparticles (n-TiO₂) (Aeroxide P25, Degussa Evonik) and its interaction with cadmium (CdCl₂) in plants using radish seeds (Raphanus sativus L. Parvus) as model species. Radish seeds were exposed to n-TiO₂ (1-1000mg/L) and CdCl₂ (1-250mg/L) alone and in combination using a seed germination and seedling growth toxicity test OECD 208. Percentage of seed germination, germination index (GI) and root elongation were calculated. Cell morphology and oxidative stress parameters as glutathione-S-transferase (GST) and catalase activities (CAT) were measured in radish seeds after 5 days of exposure. Z-Average, PdI and Z-potential of n-TiO₂ in Milli-Q water as exposure medium were also determined. DLS analysis showed small aggregates of n-TiO₂, negative Z-potential and stable PdI in seed's exposure media. Germination percentage, GI and root length resulted affected by n-TiO₂ exposure compared to controls. In particular, n-TiO₂ at 1mg/L and 100mg/L did not affect radish seeds germination (100%) while at concentration of 10mg/L, 200mg/L, 500mg/L, and 1000mg/L a slight but not significant decrease of germination % was observed. Similarly root length and GI resulted significantly higher in seeds exposed to 10mg/L and 200mg/L compared to 1mg/L, 100mg/L, 500mg/L, 1000mg/L and control (p < 0.05). On the opposite, CdCl₂ significantly abolished germination % and GI compared to control seeds and a concentration dependent decrease on root elongation was observed against controls (p < 0.05). As well, significant decrease of germination %, GI and root elongation was observed in seeds co-exposed to n-TiO₂ and CdCl₂ at the highest concentrations (1000mg/L n-TiO₂ and 250mg/L CdCl₂) compared to co-exposed seeds at low concentration (1mg/L n-TiO₂ and 1mg/L CdCl₂) and controls (p < 0.05). Root elongation significantly increase compared to control at the lowest co-exposure concentration (p < 0.05). Similarly at intermediate concentrations of 10 and 100mg/L in co-exposure conditions, n-TiO₂ did not affect CdCl₂ toxicity. Concerning antioxidant enzymes, a significant increase of CAT activity in seeds exposed to single high n-TiO₂ concentration (1000mg/L) was observed while n-TiO₂ (1mg/L), CdCl₂ (1 and 250mg/L) and co-exposure resulted significantly decreased compared to controls (p < 0.05). Regarding GST activity, a slight increase in seeds exposed to 1000mg/L n-TiO₂ but no significantly was observed, however both n-TiO₂ and CdCl₂ alone (1 and 250mg/L, respectively) or in combinations caused a significant decrease in GST activity (p < 0.05). Therefore, overall data support the hypothesis that the presence of n-TiO₂ do not affect the toxicity of CdCl₂ at least at the highest concentration (100 and 250mg/L) in radish seeds. Morphological alterations in nuclei, vacuoles and shape of radish root cells were observed upon single Cd exposure and not abolished in the presence of n-TiO₂. Nevertheless, although n-TiO₂ seems not to reduce Cd toxicity at high concentration (up to 250mg/L), interactions cannot be excluded based on obtained results.

Mechanisms of Action of Nanoparticles in Living Systems

Nanoparticles are being formed continuously in processes like mineralization, natural calamities, and geological recycling of matter and present naturally in the environment. In the recent past, nanoparticles and their applications have become an extensive topic of research. Application of nanomaterials in different industries will surely enhance the chances of discharge of nanoparticles into the environment. So, a number of studies have been performed to explore the mode of action of nanoparticles on living organisms and their surroundings. The most reported modes of action of nanoparticles are antimicrobial activity, ROS-induced cytotoxicity, genotoxicity, plant growth promotion, etc. It has been successfully demonstrated that actions of nanoparticles are governed by their size, shape, dose, and concentration. However, a complete mechanism of action of nanoparticles has not been known. The present chapter focuses on the highlights of the mechanisms behind the mode of action of nanoparticles in plants and microorganisms.

Investigating long-term effect of nanoparticles on growth of Raphanus sativus plants: a trans-generational study

In the past decade, there has been an unprecedented growth in the application of nanoparticles (NPs) worldwide. Even though the acute toxicity of CuO and ZnO NPs to plants has been investigated in past, the trans-generational effects of these NPs in the environment are still unknown. In this study, we investigated whether the treatment of radish plants with CuO and ZnO NPs as single compound and as a binary mixture (10, 100 and 1000 mg/Kg soil) through their lifecycle would affect the seed quality and the development of second-generation seedlings or not. Results showed reduced root length, shoot length and biomass in F1 seedlings of NPs treated plants. The treated F1 seeds had smaller seed weight with accumulated Cu and Zn. The effect of toxic interaction between CuO and ZnO on plant growth was antagonistic in nature. Evaluation of the trans-generational impact is important to understand the long-term effect of NPs on the environment.