Environmental Stresses Increase Photosynthetic Disruption by Metal Oxide Nanomaterials in a Soil-Grown Plant

Photosynthesis governed by nanoparticulate titanium dioxide. The Pisum sativum L. case study

Wide availability of anthropogenic TiO2 nanoparticles facilitates their penetration into environment and prompts interactions with plants. They alter plants growth and change their nutritional status. In particular, metabolic processes are affected. In this work the effect of nanometric TiO2 on photosynthesis efficiency in green pea (Pisum sativum L.) was studied. Hydroponic cultivations with three Ti levels (10; 50 and 100 mg L-1) were applied. At all concentrations nanoparticles penetrated into plant tissues and were detected by the single particle ICP-MS/MS method. Nanoparticles altered the CO2 assimilation rate and gas exchange parameters (i.e. transpiration, stomatal conductance, sub-stomatal CO2 concentration). The most pronounced effects were observed for Ti 50 mg L-1 cultivation where photosynthesis efficiency, transpiration and stomatal conductance were increased by 14.69%, 4.58% and 8.92%, respectively. They were further confirmed by high maximum ribulose 1,5-bisphosphate carboxylation rate (27.40% increase), maximum electron transport rate (21.51% increase) and the lowest CO2 compensation point (45.19% decrease). Furthermore, concentrations of Cu, Mn, Zn, Fe, Mg, Ca, K and P were examined with the most pronounced changes observed for elements directly involved in photosynthesis (Cu, Zn, Mn, and Fe). The Cu concentrations in roots, stems and leaves for Ti 50 mg L-1 cultivation were below the control by 33.15%, 38.28% and 10.76%, respectively. The Zn content in analogous treatment and organs decreased by 30.24%, 26.69% and 13.35%. The Mn and Fe levels in leaves were increased by 72.22% and 50.32%, respectively. Our results indicated that plant defence mechanisms which restrain the water uptake have been overcome in pea by photocatalytic activity of nanoparticulate TiO2 which stimulated photosynthesis. On the contrary to the substantial stomatal conductance, the transpiration has been reduced because exceptional part of water flow was already consumed in chloroplasts and could not have been freed to the atmosphere.

Cd2+ Sorption Alterations in Ultisol Soils Triggered by Different Engineered Nanoparticles and Incubation Times

The progressive influx of engineered nanoparticles (ENPs) into the soil matrix catalyses a fundamental transformation in the equilibrium dynamics between the soil and the edaphic solution. This all-encompassing investigation is geared towards unravelling the implications of an array of ENP types, diverse dosages and varying incubation durations on the kinetics governing Cd2+ sorption within Ultisol soils. These soils have been subjected to detailed characterizations probing their textural and physicochemical attributes in conjunction with an exhaustive exploration of ENP composition, structure and morphology. To decipher the intricate nuances of kinetics, discrete segments of Ultisol soils were subjected to isolated systems involving ENP dosages of 20 and 500 mg ENPs·kg-1 (AgNPs, CuNPs and FeNPs) across intervals of 1, 3 and 6 months. The comprehensive kinetic parameters were unveiled by applying the pseudo-first-order and pseudo-second-order models. At the same time, the underlying sorption mechanisms were studied via the intra-particle diffusion model. This study underscores the substantial impact of this substrate on the kinetic behaviours of contaminants such as Cd, emphasizing the need for its consideration in soil-linked economic activities and regulatory frameworks to optimize resource management.

Panorama of biogenic nano-fertilizers: A road to sustainable agriculture

The ever-increasing demand for food from the growing population has augmented the consumption of fertilizers in global agricultural practices. However, the excessive usage of chemical fertilizers with poor efficacy is drastically deteriorating ecosystem health through the degradation of soil fertility by diminishing soil microflora, environment contamination, and human health by inducing chemical remnants to the food chain. These challenges have been addressed by the integration of nanotechnological and biotechnological approaches resulting in nano-enabled biogenic fertilizers (NBF), which have revolutionized agriculture sector and food production. This review critically details the state-of-the-art NBF production, types, and mechanism involved in cultivating crop productivity/quality with insights into genetic, physiological, morphological, microbiological, and physiochemical attributes. Besides, it explores the associated challenges and future routes to promote the adoption of NBF for intelligent and sustainable agriculture. Furthermore, diverse applications of nanotechnology in precision agriculture including plant biosensors and its impact on agribusiness and environmental management are discussed.

Advancing sustainable agriculture: a critical review of smart and eco-friendly nanomaterial applications

Undoubtedly, nanoparticles are one of the ideal choices for achieving challenges related to bio sensing, drug delivery, and biotechnological tools. After gaining success in biomedical research, scientists are exploring various types of nanoparticles for achieving sustainable agriculture. The active nanoparticles can be used as a direct source of micronutrients or as a delivery platform for delivering the bioactive agrochemicals to improve crop growth, crop yield, and crop quality. Till date, several reports have been published showing applications of nanotechnology in agriculture. For instance, several methods have been employed for application of nanoparticles; especially metal nanoparticles to improve agriculture. The physicochemical properties of nanoparticles such as core metal used to synthesize the nanoparticles, their size, shape, surface chemistry, and surface coatings affect crops, soil health, and crop-associated ecosystem. Therefore, selecting nanoparticles with appropriate physicochemical properties and applying them to agriculture via suitable method stands as smart option to achieve sustainable agriculture and improved plant performance. In presented review, we have compared various methods of nanoparticle application in plants and critically interpreted the significant differences to find out relatively safe and specific method for sustainable agricultural practice. Further, we have critically analyzed and discussed the different physicochemical properties of nanoparticles that have direct influence on plants in terms of nano safety and nanotoxicity. From literature review, we would like to point out that the implementation of smaller sized metal nanoparticles in low concentration via seed priming and foliar spray methods could be safer method for minimizing nanotoxicity, and for exhibiting better plant performance during stress and non-stressed conditions. Moreover, using nanomaterials for delivery of bioactive agrochemicals could pose as a smart alternative for conventional chemical fertilizers for achieving the safer and cleaner technology in sustainable agriculture. While reviewing all the available literature, we came across some serious drawbacks such as the lack of proper regulatory bodies to control the usage of nanomaterials and poor knowledge of the long-term impact on the ecosystem which need to be addressed in near future for comprehensive knowledge of applicability of green nanotechnology in agriculture.

Nanotoxicity assessment in plants: an updated overview

Nanotechnology is rapidly emerging and innovative interdisciplinary field of science. The application of nanomaterials in agricultural biotechnology has been exponentially increased over the years that could be attributed to their uniqueness, versatility, and flexibility. The overuse of nanomaterials makes it crucial to determine their fate and distribution in the in vitro (in cell and tissue cultures) and in vivo (in living species) biological environments by investigating the nano-biointerface. The literature states that the beneficial effects of nanoparticles come along with their adverse effects, subsequently leading to an array of short-term and long-term toxicities. It has been evident that the interplay of nanoparticles with abiotic and biotic communities produces several eco-toxicological effects, and the physiology and biochemistry of crops are greatly influenced by the metabolic alterations taking place at cellular, sub-cellular, and molecular levels. Numerous risk factors affect nanoparticle's accumulation, translocation, and associated cytogenotoxicity. This review article summarizes the contributing factors, possible mechanisms, and risk assessment of hazardous effects of various types of nanoparticles to plant health. The methods for evaluating the plant nanotoxicity parameters have been elaborated. Conclusively, few recommendations are put forward for designing safer, high-quality nanomaterials to protect and maintain environmental safety for smarter agriculture demanded by researchers and industrialists.

Soybean rhizosphere microorganisms alleviate Mo nanomaterials induced stress by improving soil microbial community structure

With the wide application of nanomaterials (NMs) in agriculture, it is particularly important to assess the impact of these NMs on soil microorganisms. In this study, different varieties of soybean rhizosphere microorganisms (RM) were employed to simulate the alleviate effect of molybdenum nanoparticles (Mo NPs) induced stress in presence of soybean plants. Mo NPs caused serious toxic effects on soybean growth and nitrogen fixation at a concentration of 100 mg kg^-1: plant height and biomass were reduced by 56.4% and 82.8%, respectively, and the ability to fix nitrogen was almostly lost. However, after adding different varieties of soybean RM (RM-Williams 82, RM-Youchun 1204, and RM-Zhongdou 41), the stress caused by high concentrations of Mo NPs on soybean plants was significantly reduced. The plant height, root length, biomass, and nitrogen fixation ability were improved by 70.8%, 80.7%, 145.8%, and 349.8%, respectively, following the addition of soybean RM-Williams 82. High-throughput sequencing revealed that Mo NPs treatment affected the microbial community structure. Among them, Flavisolibacter and Caulobacter genera abundance increased significantly, which might be the key factor in relieving Mo NPs-induced stress on soybean growth. These findings suggest a novel mode of RM as a promising strategy to prevent deleterious effects of stress with NPs on plants in the future.

Effect of CeO2 nanoparticles on plant growth and soil microcosm in a soil-plant interactive system

The impact of CeO₂ nanoparticles (NPs) on plant physiology and soil microcosm and the underlying mechanism remains unclear to date. This study investigates the effect of CeO₂ NPs on plant growth and soil microbial communities in both the rhizosphere of cucumber seedlings and the surrounding bulk soil, with CeCl₃ as a comparison to identify the contribution of the particulate and ionic form to the phytotoxicity of CeO₂ NPs. The results show that Ce was significantly accumulated in the cucumber tissue after CeO₂ NPs exposure. In the roots, 5.3% of the accumulated Ce has transformed to Ce³⁺. This transformation might take place prior to uptake by the roots since 2.5% of CeO₂ NPs was found transformed in the rhizosphere soil. However, the transformation of CeO₂ NPs in the bulk soil was negligible, indicating the critical role of rhizosphere chemistry in the transformation. CeO₂ NPs treatment induced oxidative stress in the roots, but the biomass of the roots was significantly increased, although the Vitamin C (Vc) content and soluble sugar content were decreased and mineral nutrient contents were altered. The soil enzymatic activity and the microbial community in both rhizosphere and bulk soil samples were altered, with rhizosphere soil showing more prominent changes. CeCl₃ treatment induced similar effects although less than CeO₂ NPs, suggesting that Ce³⁺ released from CeO₂ NPs contributed to the CeO₂ NPs induced impacts on soil health and plant physiology.

Interactions of Coated-Gold Engineered Nanoparticles with Aquatic Higher Plant Salvinia minima Baker

The study investigated the interactions of coated-gold engineered nanoparticles (nAu) with the aquatic higher plant Salvinia minima Baker in 2,7, and 14 d. Herein, the nAu concentration of 1000 µg/L was used; as in lower concentrations, analytical limitations persisted but >1000 µg/L were deemed too high and unlikely to be present in the environment. Exposure of S. minima to 1000 µg/L of citrate (cit)- and branched polyethyleneimine (BPEI)-coated nAu (5, 20, and 40 nm) in 10% Hoagland’s medium (10 HM) had marginal effect on biomass and growth rate irrespective of nAu size, coating type, or exposure duration. Further, results demonstrated that nAu were adsorbed on the plants’ roots irrespective of their size or coating variant; however, no evidence of internalization was apparent, and this was attributed to high agglomeration of nAu in 10 HM. Hence, adsorption was concluded as the basic mechanism of nAu accumulation by S. minima. Overall, the long-term exposure of S. minima to nAu did not inhibit plant biomass and growth rate but agglomerates on plant roots may block cell wall pores, and, in turn, alter uptake of essential macronutrients in plants, thus potentially affecting the overall ecological function.

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.

Biochar-mediated transformation of titanium dioxide nanoparticles concerning TiO2NPs-biochar interactions, plant traits and tissue accumulation to cell translocation

Titanium dioxide nanoparticles (TiO₂NPs) application in variety of commercial products would likely release these NPs into the environment. The interaction of TiO₂NPs with terrestrial plants upon uptake can disturb plants functional traits and can also transfer to the food chain members. In this study, we investigated the impact of TiO₂NPs on wheat (Triticum aestivum L.) plants functional traits, primary macronutrients assimilation, and change in the profile of bio-macromolecule. Moreover, the mechanism of biochar-TiO₂NPs interaction, immobilization, and tissue accumulation to cell translocation of NPs in plants was also explored. The results indicated that the contents of Ti in wheat tissues was reduced about 3-fold and the Ti transfer rate (per day) was reduced about 2 fold at the 1000 mg L^-1 exposure level of TiO₂NPs in biochar amended exposure medium. Transmission electron microscopy (TEM) with elemental mapping confirmed that Ti concentrated in plant tissues in nano-form. The interactive effect of TiO₂NPs + biochar amendment on photosynthesis related and gas exchange traits was observed at relatively low TiO₂NPs exposure level (200 mg L^-1), which induced the positive impact on wheat plants proliferation. TiO₂NPs alone exposure to wheat also modified the plant's bio-macromolecules profile with the reduction in the assimilation of primary macronutrients, which could affect the food crop nutritional value and quality. X-ray photoelectron spectroscopy (XPS) chemical analysis of biochar + TiO₂NPs showed an additional peak, which indicated the binding interaction of NPs with biochar. Moreover, Fourier-transform infrared (FTIR) spectroscopy confirmed that the biochar carboxyl group is the main functionality involved in the bonding process with TiO₂NPs. These findings will help for a mechanistic understanding of the role of biochar in the reduction of NPs bioavailability to primary producers of the terrestrial environment.

Abiotic mediation of common ions on the co-exposure of CeO2 NPs with Sb (III) or Sb (V) to Glycine max (Linn.) Merrill. (Soybean): Impacts on uptake, accumulation and physiochemical characters

With the most active Sb mines, the "dominance" on Sb production of China lead to increasingly release and omnipresence of Sb in environment through mining activities as well as the life cycle of Sb-containing productions. The introduction of engineered nanoparticles (ENPs) accidentally or intentionally (such as NP-containing sludge as fertilizer) might increase the probability of co-exposed with Sb to plants. In this study, CeO2 NPs, one of the most widely used nanomaterials in industries with potential oxidizing or reducing properties, was selected and co-exposed with Sb (III) or Sb (V) to investigate their mutual effects on uptake, accumulation and physiological effects in soybeans. The results showed that CeO2 NPs increased the Sb (III) and Sb (V) concentrations in roots by 36.7% and 14.0% respectively, while Sb (III) and Sb (V) inhibited the concentration of Ce in roots by 97.1% and 86.9% respectively. In addition, the impacts of extra common ions (Mn2+, Cu2+, Fe3+ and Zn2+) on the fate of Ce and Sb in soybeans in co-exposure of CeO2 NPs with Sb were investigated as well. Mn2+ and Fe3+ increased the accumulations of Ce and Sb (III) in the co-exposure of CeO2 NPs with Sb (III), but reduced that in the co-exposure of CeO2 NPs with Sb (V). Notably, the addition of Cu2+ and Zn2+ consistently increased the uptake and accumulation of Ce and Sb in the co-exposure treatments. Moreover, the effects of Sb on the dissolved portion of CeO2 NPs in soybean roots were also investigated. This study provided a perspective that extra ingredient (mineral elements, organic element or other nutrients) might regulated the interactions in ENPs-heavy metals-plants system which need further explorations.

Metal Homeostasis and Gas Exchange Dynamics in Pisum sativum L. Exposed to Cerium Oxide Nanoparticles

Cerium dioxide nanoparticles are pollutants of emerging concern. They are rarely immobilized in the environment. This study extends our work on Pisum sativum L. as a model plant, cultivated worldwide, and is well suited for investigating additive interactions induced by nanoceria. Hydroponic cultivation, which prompts accurate plant growth control and three levels of CeO2 supplementation, were applied, namely, 100, 200, and 500 mg (Ce)/L. Phytotoxicity was estimated by fresh weights and photosynthesis parameters. Additionally, Ce, Cu, Zn, Mn, Fe, Ca, and Mg contents were analyzed by high-resolution continuum source atomic absorption and inductively coupled plasma optical emission techniques. Analysis of variance has proved that CeO2 nanoparticles affected metals uptake. In the roots, it decreased for Cu, Zn, Mn, Fe, and Mg, while a reversed process was observed for Ca. The latter is absorbed more intensively, but translocation to above-ground parts is hampered. At the same time, nanoparticulate CeO2 reduced Cu, Zn, Mn, Fe, and Ca accumulation in pea shoots. The lowest Ce concentration boosted the photosynthesis rate, while the remaining treatments did not induce significant changes. Plant growth stimulation was observed only for the 100 mg/L. To our knowledge, this is the first study that demonstrates the effect of nanoceria on photosynthesis-related parameters in peas.

Effect of copper oxide nanoparticles on two varieties of sweetpotato plants

Little information is available on the interaction of CuO nanoparticles (nCuO) with tuberous roots. In this study, Beauregard-14 (B-14, low lignin) and Covington (COV, high lignin) sweetpotato varieties were cultivated until maturity in soil amended with nCuO, bulk copper oxide (bCuO) and CuCl2 at 25-125 mg/kg. The Cu treatments had no significant influence on chlorophyll content. Gas exchange parameters were not affected in B-14. In COV, however, at 125 mg/kg treatments, bCuO reduced the intercellular CO2 (11%), while CuCl2 increased it by 7%, compared with control (p ≤ 0.035). At 25 mg/kg nCuO increased the length of COV roots (20.7 ± 2.0 cm vs. 14.6 ± 0.8 cm, p ≤ 0.05). In periderm of B-14, nCuO, at 125 mg/kg, increased Mg by 232%, while the equivalent concentration of CuCl2 reduced P by 410%, compared with control (p ≤ 0.05). The data suggest the potential application of nCuO as nanofertilizer for sweetpotato storage root production.

Chlorophyll Content in Two Medicinal Plant Species Following Nano-TiO2 Exposure

Chlorophyll content in leaves is a convenient indicator of the physiological state of the plant following exposure to a stressor. In the present study, a pot experiment was carried out using two medicinal plant species - peppermint (Mentha X piperita L.) and common sage (Salvia officinalis L.) to determine the link between the chlorophyll content in the plant leaves and the exposure of the plants to nano-TiO₂ either through the leaves (in suspension) or through the root system (in soil). Following the exposure, the shoots were analysed for the contents of Ti, Al, Ca, K, Mg, Mn, Na and chlorophyll. Significant decrease in chlorophyll content was observed in all but one of the nano-TiO₂ treatments, the differences in the determined element content were mostly species-dependent: Ti exposure was found to be related to the decrease in the chlorophyll and Mn content in both species as well as to the decrease in Mg content in common sage.

Biochar-assisted transformation of engineered-cerium oxide nanoparticles: Effect on wheat growth, photosynthetic traits and cerium accumulation

The extensive use of nano-fabricated products in daily life is releasing a large volume of engineered nanoparticles (ENPs) in the environment having unknown consequences. Meanwhile, little efforts have been paid to immobilize and prevent the entry of these emerging contaminants in the food chain through plant uptake. Herein, we investigated the biochar role in cerium oxide nanoparticles (CeO₂NPs) bioaccumulation and subsequent translocation in wheat (Triticum aestivum L.) as well as impact on growth, photosynthesis and gas-exchange related physiological parameters. Results indicated that CeO₂NPs up to 500 mg L^-1 level promoted the plant growth by triggering photosynthesis, transpiration and stomatal conductance. Higher NPs concentration (2000 mg CeO₂NPs L^-1) has negatively affected the plant growth and photosynthesis related processes. Conversely, biochar amendment with CeO₂NPs considerably reduced (~9 folds) the plants accumulated contents of Ce even at 2000 mg L^-1 exposure level of CeO₂NPs through surface complexation process and alleviated the phyto-toxic effects of NPs on plant growth. XPS and FTIR analysis confirmed the role of biochar-mediated carboxylate and hydroxyl groups bonding with CeO₂NPs. These findings provides an inside mechanistic understanding about biochar interaction with nano-pollutants to inhibit their bioavailability to plant body.

Interaction of Copper-Based Nanoparticles to Soil, Terrestrial, and Aquatic Systems: Critical Review of the State of the Science and Future Perspectives

In the past two decades, increased production and usage of metallic nanoparticles (NPs) have inevitably increased their discharge into the different compartments of the environment, which ultimately paved the way for their uptake and accumulation in various trophic levels of the food chain. Due to these issues, several questions have been raised on the usage of NPs in everyday life and have become a matter of public health concern. Among the metallic NPs, Cu-based NPs have gained popularity due to their cost-effectiveness and multifarious promising uses. Several studies in the past represented the phytotoxicity of Cu-based NPs on plants. However, comprehensive knowledge is still lacking. Additionally, the impact of Cu-based NPs on soil organisms such as agriculturally important microbes, fungi, mycorrhiza, nematode, and earthworms is poorly studied. This review article critically analyses the literature data to achieve a more comprehensive knowledge on the toxicological profile of Cu-based NPs and increase our understanding of the effects of Cu-based NPs on aquatic and terrestrial plants as well as on soil microbial communities. The underlying mechanism of biotransformation of Cu-based NPs and the process of their penetration into plants have also been discussed herein. Overall, this review could provide valuable information to design rules and regulations for the safe disposal of Cu-based NPs into a sustainable environment.

Effects of nanoTiO2 on tomato plants under different irradiances

In this study, we investigated the physiological and photochemical influences of nanoTiO₂ exposure on tomato plants (Lycopersicum esculentum Mill.). Tomato plants were exposed to 100 mg L^-1 of nanoTiO₂ for 90 days in a hydroponic system. Light irradiances of 135 and 550 μmol_photon m^-2 s^-1 were applied as environmental stressors that could affect uptake of nanoTiO₂. To quantify nanoTiO₂ accumulation in plant bodies and roots, we used transmission electron microscopy, energy-dispersive X-ray spectroscopy, inductively coupled plasma mass spectrometry, and X-ray powder diffraction. Phenotypic and physiological influences such as color change, growth rate, fruit productivity, pigment concentration, and enzyme activity (SOD, CAT, APX) were monitored. We observed numerous effects caused by high irradiance and nanoTiO₂ exposure, such as rapid chlorophyll decrease, increased anthocyanin and carotenoid concentrations, high enzymatic activity, and an approximately eight-fold increase in fruit production. Moreover, light absorption in the nanoTiO₂-treated tomato plants, as measured by a ultraviolet-visible light spectrometer, increased by a factor of approximately 19, likely due to natural pigments that worked as sensitizers, and this resulted in an ∼120% increase in photochemical activities on A, ФPSII, ФCO₂, g_sw, and E.

Effects of Zerovalent Iron Nanoparticles on Photosynthesis and Biochemical Adaptation of Soil-Grown Arabidopsis thaliana

Nanoscale zerovalent iron (nZVI) is the most widely used nanomaterial for environmental remediation. The impacts of nZVI on terrestrial organisms have been recently reported, and in particular, plant growth was promoted by nZVI treatment in various concentrations. Therefore, it is necessary to investigate the detailed physiological and biochemical responses of plants toward nZVI treatment for agricultural application. Here, the effects of nZVI on photosynthesis and related biochemical adaptation of soil-grown Arabidopsis thaliana were examined. After treatment with 500 mg nZVI/kg soil, the plant biomass increased by 38% through enhanced photosynthesis, which was confirmed by the gas-exchange system, carbon isotope ratio and chlorophyll content analysis. Besides, the iron uptake of the plant increased in roots and leaves. The magnetic property measurements and transmission electron microscopy showed that the transformed particles were accumulated in parts of the plant tissues. The accumulation of carbohydrates such as glucose, sucrose and starch increased by the enhanced photosynthesis, and photosynthetic-related inorganic nutrients such as phosphorus, manganese and zinc maintained homeostasis, according to the increased iron uptake. These findings suggest that nZVI has additional or alternative benefits as a nano-fertilizer and a promoter of CO2 uptake in plants.

Transcriptome Reveals the Rice Response to Elevated Free Air CO2 Concentration and TiO2 Nanoparticles

Increasing CO₂ levels are speculated to change the effects of engineered nanomaterials in soil and on plant growth. How plants will respond to a combination of elevated CO₂ and nanomaterials stress has rarely been investigated, and the underlying mechanism remains largely unknown. Here, we conducted a field experiment to investigate the rice (Oryza sativa L. cv. IIyou) response to TiO₂ nanoparticles (nano-TiO₂, 0 and 200 mg kg^-1) using a free-air CO₂ enrichment system with different CO₂ levels (ambient ∼370 μmol mol^-1 and elevated ∼570 μmol mol^-1). The results showed that elevated CO₂ or nano-TiO₂ alone did not significantly affect rice chlorophyll content and antioxidant enzyme activities. However, in the presence of nano-TiO₂, elevated CO₂ significantly enhanced the rice height, shoot biomass, and panicle biomass (by 9.4%, 12.8%, and 15.8%, respectively). Furthermore, the Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis revealed that genes involved in photosynthesis were up-regulated while most genes associated with secondary metabolite biosynthesis were down-regulated in combination-treated rice. This indicated that elevated CO₂ and nano-TiO₂ might stimulate rice growth by adjusting resource allocation between photosynthesis and metabolism. This study provides novel insights into rice responses to increasing contamination under climate change.

Effects of biochar on uptake, acquisition and translocation of silver nanoparticles in rice (Oryza sativa L.) in relation to growth, photosynthetic traits and nutrients displacement

Rapid development in nanotechnology and incorporation of silver nanoparticles (AgNPs) in wide range of consumer products causing the considerable release of these NPs in the environment, leading concerns for ecosystem safety and plant health. In this study, rice (Oryza sativa) was exposed to AgNPs (0, 100, 200, 500 and 1000 mg L^-1) in biochar amended (2 %w/v) and un-amended systems. Exposure of plants to AgNPs alone reduced the root and shoot length, biomass production, chlorophyll contents, photosynthesis related physiological parameters as well as macro-and micronutrients in a dose dependent manner. However, in case of biochar amendment, physiological parameters i.e., net photosynthesis rate, maximum photosynthesis rate, CO₂ assimilation, dark respiration and stomatal conductance reduced only 16, 6, 7, 3 and 8%, respectively under AgNPs exposure at 1000 mg L^-1 dose. Meanwhile, biochar at all exposure level of AgNPs decreased the bioaccumulation of Ag in rice root and shoot tissues, thus alleviated the phyto-toxic effects of NPs on plant growth. Moreover, results showed that biochar reduced the bioavailability of AgNPs by surface complexation, suppressing dissolution and release of toxic Ag⁺ ions in the growth medium. The presence of biochar at least decreased 2-fold tissue contents of Ag even at highest AgNPs (1000 mg L^-1) concentration. These finding suggested that biochar derived from waste biomass resources can be used effectively to prevent the bioaccumulation and subsequent trophic level transfer of emerging Ag nano-pollutant in the environment.

Effects of carbonaceous nanomaterials on soil-grown soybeans under combined heat and insect stresses

Because carbonaceous nanomaterials (CNMs) are expected to enter soils, the exposure implications to crop plants and plant-microbe interactions should be understood. Most investigations have been under ideal growth conditions, yet crops commonly experience abiotic and biotic stresses. Little is known how co-exposure to these environmental stresses and CNMs would cause combined effects on plants. We investigated the effects of 1000 mg kg^-1 multiwalled carbon nanotubes (CNTs), graphene nanoplatelets (GNPs) and industrial carbon black (CB) on soybeans grown to the bean production stage in soil. Following seed sowing, plants became stressed by heat and infested with an insect (thrips). Consequently, all plants had similarly stunted growth, leaf damage, reduced final biomasses and fewer root nodules compared with healthy control soybeans previously grown without heat and thrips stresses. Thus, CNMs did not significantly influence the growth and yield of stressed soybeans, and the previously reported nodulation inhibition by CNMs was not specifically observed here. However, CNMs did significantly alter two leaf health indicators: the leaf chlorophyll a/b ratio, which was higher in the GNP treatment than in either the control (by 15 %) or CB treatment (by 14 %), and leaf lipid peroxidation, which was elevated in the CNT treatment compared with either the control (by 47 %) or GNP treatment (by 66 %). Overall, these results show that, while severe environmental stresses may impair plant production, CNMs (including CNTs and GNPs) in soil could additionally affect foliar health of an agriculturally important legume.

Ti and Zn Content in Moss Shoots After Exposure to TiO2 and ZnO Nanoparticles: Biomonitoring Possibilities

To assess the uptake of nanoparticles by moss shoots and the possibility of biomonitoring the moss of nanoparticle pollution, two moss species frequently used in biomonitoring surveys [Hylocomium splendens (Hedw.) Schimp. and Pleurozium schreberi (Brid.) Mitt.] were repeatedly exposed to known concentrations of either nano-TiO₂ or nano-ZnO suspensions. The interspecies differences were assessed by exposing both the species to 1 g L^-1 nano-ZnO suspension, H. splendens samples were also exposed to either 0.1 g L^-1 or 1 g L^-1 suspension of nano TiO₂. The exposed samples were analysed for Zn or Ti content using Inductively Coupled Plasma-Atomic Emission Spectroscopy. Both species showed a similar accumulation pattern, H. splendens being a slightly better accumulator. The washing suggests that Ti successfully penetrated the interior of the gametophyte. Since the relationship between the exposure and accumulation is linear, moss biomonitoring is, hereby, considered to be a viable, novel technique in nanoparticle pollution assessment.

Nano-based smart pesticide formulations: Emerging opportunities for agriculture

The incorporation of nanotechnology as a means for nanopesticides is in the early stage of development. The main idea behind this incorporation is to lower the indiscriminate use of conventional pesticides to be in line with safe environmental applications. Nanoencapsulated pesticides can provide controlled release kinetics, while efficiently enhancing permeability, stability, and solubility. Nanoencapsulation can enhance the pest-control efficiency over extended durations by preventing the premature degradation of active ingredients (AIs) under harsh environmental conditions. This review is thus organized to critically assess the significant role of nanotechnology for encapsulation of AIs for pesticides. The smart delivery of pesticides is essential to reduce the dosage of AIs with enhanced efficacy and to overcome pesticide loss (e.g., due to leaching and evaporation). The future trends of pesticide nanoformulations including nanomaterials as AIs and nanoemulsions of biopesticides are also explored. This review should thus offer a valuable guide for establishing regulatory frameworks related to field applications of these nano-based pesticides in the near future.

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.

Effects of the exposure of TiO2 nanoparticles on basil (Ocimum basilicum) for two generations

There is a lack of information about the transgenerational effects of titanium dioxide nanoparticles (nano-TiO₂) in plants. This study aimed to evaluate the impacts of successive exposure of nano-TiO₂ with different surface properties to basil (Ocimum basilicum). Seeds from plants exposed or re-exposed to pristine, hydrophobic, or hydrophilic nano-TiO₂ were cultivated for 65 days in soil unamended or amended with 750 mg·kg^-1 of the respective particles. Plant growth, concentration of titanium and essential elements, as well as content of carbohydrates and chlorophyll were evaluated. There were no differences on Ti concentration in roots of plants sequentially exposed to pristine or hydrophobic nano-TiO₂, or in roots of plants exposed to the corresponding particle, only in the second cycle. However, sequential exposure to hydrophilic particles resulted in 65.2% less Ti in roots, compared to roots of plants exposed the same particles, only in the second cycle. The Ti concentrations in shoots were similar in all treatments. On the other hand, pristine and hydrophilic particles reduced Mg in root by 115% and 81%, respectively, while pristine and hydrophobic particles reduced Ni in shoot by 84% and 75%, respectively, compared to unexposed plants in both cycles. Sequential exposure to pristine nano-TiO₂ increased stomatal conductance (214%, p ≤ 0.10), compared to plants that were never exposed. Hydrophobic and hydrophilic nano-TiO₂ reduced chlorophyll b (52%) and total chlorophyll (30%) but increased total sugar (186%) and reducing sugar (145%), compared to unexposed plants in both cycles. Sequential exposure to hydrophobic or hydrophilic nano-TiO₂ resulted in more adverse effects on photosynthesis but in positive effects on plant growth, compared to pristine nano-TiO₂.

Plant and Microbial Responses to Repeated Cu(OH)2 Nanopesticide Exposures Under Different Fertilization Levels in an Agro-Ecosystem

The environmental fate and potential impacts of nanopesticides on agroecosystems under realistic agricultural conditions are poorly understood. As a result, the benefits and risks of these novel formulations compared to the conventional products are currently unclear. Here, we examined the effects of repeated realistic exposures of the Cu(OH)2 nanopesticide, Kocide 3000, on simulated agricultural pastureland in an outdoor mesocosm experiment over 1 year. The Kocide applications were performed alongside three different mineral fertilization levels (Ambient, Low, and High) to assess the environmental impacts of this nanopesticide under low-input or conventional farming scenarios. The effects of Kocide over time were monitored on forage biomass, plant mineral nutrient content, plant-associated non-target microorganisms (i.e., N-fixing bacteria or mycorrhizal fungi) and six soil microbial enzyme activities. We observed that three sequential Kocide applications had no negative effects on forage biomass, root mycorrhizal colonization or soil nitrogen fixation rates. In the Low and High fertilization treatments, we observed a significant increase in aboveground plant biomass after the second Kocide exposure (+14% and +27%, respectively). Soil microbial enzyme activities were significantly reduced in the short-term after the first exposure (day 15) in the Ambient (-28% to -82%) and Low fertilization (-25% to -47%) but not in the High fertilization treatment. However, 2 months later, enzyme activities were similar across treatments and were either unresponsive or responded positively to subsequent Kocide additions. There appeared to be some long-term effects of Kocide exposure, as 6 months after the last Kocide exposure (day 365), both beta-glucosidase (-57% in Ambient and -40% in High fertilization) and phosphatase activities (-47% in Ambient fertilization) were significantly reduced in the mesocosms exposed to the nanopesticide. These results suggest that when used in conventional farming with high fertilization rates, Kocide applications did not lead to marked adverse effects on forage biomass production and key plant-microorganism interactions over a growing season. However, in the context of low-input organic farming for which this nanopesticide is approved, Kocide applications may have some unintended detrimental effects on microbially mediated soil processes involved in carbon and phosphorus cycling.

Quantitative mapping of elements in basil leaves (Ocimum basilicum) based on cesium concentration and growth period using laser ablation ICP-MS

Quantitative elemental mapping of metallic pollutants in sweet basil was studied by laser ablation (LA)-ICP-MS. For this, the sweet basil was cultivated in Hoagland nutrient solution spiked with 100 and 1000 ng mL^-1 of Cs for 10-60 days. Then, the Cs distribution in collected leaves was determined by LA-ICP-MS using lab-synthesized standard pellets based on NIST 1573a tomato leaves. For comparison, S, Ca, and K were also simultaneously determined in this measurement with a¹³C⁺ signal from the leaves as an internal standard. The obtained calibration curves showed linear coefficient of determination (R²) of 0.991 for K and 0.999 for Cs. The concentration of Cs measured in the basil leaves increased with growth period and pollutant concentration, and accumulation followed the order of leaf margin, petiole, midrib, and veins. Although no visible symptom was detected, significant suppression of the growth rate was observed due to the presence of high-concentration Cs. The experimental model demonstrated herein showed potential for studying the influence of radioactive pollutants on plants and other organisms in the food chain.

Anionic Cerium Oxide Nanoparticles Protect Plant Photosynthesis from Abiotic Stress by Scavenging Reactive Oxygen Species

Plant abiotic stress leads to accumulation of reactive oxygen species (ROS) and a consequent decrease in photosynthetic performance. We demonstrate that a plant nanobionics approach of localizing negatively charged, sub-11 nm, spherical cerium oxide nanoparticles (nanoceria) inside chloroplasts in vivo augments ROS scavenging and photosynthesis of Arabidopsis thaliana plants under excess light (2000 μmol m^-2 s^-1, 1.5 h), heat (35 °C, 2.5 h), and dark chilling (4 °C, 5 days). Poly(acrylic acid) nanoceria (PNC) with a hydrodynamic diameter (10.3 nm)-lower than the maximum plant cell wall porosity-and negative ζ-potential (-16.9 mV) exhibit significantly higher colocalization (46%) with chloroplasts in leaf mesophyll cells than aminated nanoceria (ANC) (27%) of similar size (12.6 nm) but positive charge (9.7 mV). Nanoceria are transported into chloroplasts via nonendocytic pathways, influenced by the electrochemical gradient of the plasma membrane potential. PNC with a low Ce³⁺/Ce⁴⁺ ratio (35.0%) reduce leaf ROS levels by 52%, including hydrogen peroxide, superoxide anion, and hydroxyl radicals. For the latter ROS, there is no known plant enzyme scavenger. Plants embedded with these PNC that were exposed to abiotic stress exhibit an increase up to 19% in quantum yield of photosystem II, 67% in carbon assimilation rates, and 61% in Rubisco carboxylation rates relative to plants without nanoparticles. In contrast, PNC with high Ce³⁺/Ce⁴⁺ ratio (60.8%) increase overall leaf ROS levels and do not protect photosynthesis from oxidative damage during abiotic stress. This study demonstrates that anionic, spherical, sub-11 nm PNC with low Ce³⁺/Ce⁴⁺ ratio can act as a tool to study the impact of oxidative stress on plant photosynthesis and to protect plants from abiotic stress.

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.

Interactions, Transformations, and Bioavailability of Nano-Copper Exposed to Root Exudates

Due to the potential for interactions between crop plants and engineered nanomaterials (ENMs), there is increasing interest in understanding the bioavailability and effects of ENMs released into soil systems. Here, we investigate the influence of root exudates on the fate of ENMs from a thermodynamic perspective. Nano isothermal titration calorimetry was applied to determine thermodynamic parameters for the interaction between nanocopper (nCu) and synthetic root exudate (SRE) and its components (including sugars, organic acids, amino acids, and phenolic acids), as well as Cu²⁺ and SRE. The measured binding constant (K_d = 5.645 × 10³ M^-1) indicated strong interactions between nCu particles and SRE, as well as with individual organic acids. The interaction between Cu²⁺ and SRE was stronger (K_d = 7.181 × 10⁴ M^-1) but varies for the individual SRE components. nCu dissolution in the presence of SRE was the predominant interaction. In addition, SRE resulted in a complex transformation of nCu, where Cu²⁺, Cu⁺, and Cu⁰ were formed via oxidation and reduction. Plant-nCu exposure experiments indicate that the binding of SRE with nCu and dissolved Cu ions can significantly decrease Cu uptake and bioaccumulation in plants. nITC provides a fundamental thermodynamic understanding of interactions between nCu and plant root exudates, providing an important tool for understanding plant NP-interactions.

Damage assessment for soybean cultivated in soil with either CeO2 or ZnO manufactured nanomaterials

With increasing use, manufactured nanomaterials (MNMs) may enter soils and impact agriculture. Herein, soybean (Glycine max) was grown in soil amended with either nano-CeO2 (0.1, 0.5, or 1.0gkg-1 soil) or nano-ZnO (0.05, 0.1, or 0.5gkg-1 soil). Leaf chlorosis, necrosis, and photosystem II (PSII) quantum efficiency were monitored during plant growth. Seed protein and protein carbonyl, plus leaf chlorophyll, reactive oxygen species (ROS), lipid peroxidation, and genotoxicity were measured for plants at harvest. Neither PSII quantum efficiency, seed protein, nor protein carbonyl indicated negative MNM effects. However, increased ROS, lipid peroxidation, and visible damage, along with decreased total chlorophyll concentrations, were observed for soybean leaves in the nano-CeO2 treatments. These effects correlated to aboveground leaf, pod, and stem production, and to root nodule N2 fixation potential. Soybeans grown in soil amended with nano-ZnO maintained growth, yield, and N2 fixation potential similarly to the controls, without increased leaf ROS or lipid peroxidation. Leaf damage was observed for the nano-ZnO treatments, and genotoxicity appeared for the highest nano-ZnO treatment, but only for one plant. Total chlorophyll concentrations decreased with increasing leaf Zn concentration, which was attributable to zinc complexes-not nano-ZnO-in the leaves. Overall, nano-ZnO and nano-CeO2 amended to soils differentially triggered aboveground soybean leaf stress and damage. However, the consequences of leaf stress and damage to N2 fixation, plant growth, and yield were only observed for nano-CeO2.

Silver nanoparticles induced reactive oxygen species via photosynthetic energy transport imbalance in an aquatic plant

The rapid growth in silver nanoparticles (AgNPs) commercialization has increased environmental exposure, including aquatic ecosystem. It has been reported that the AgNPs have damaging effects on photosynthesis and induce oxidative stress, but the toxic mechanism of AgNPs is still a matter of debate. In the present study, on the model aquatic higher plant Spirodela polyrhiza, we found that AgNPs affect photosynthesis and significantly inhibit Photosystem II (PSII) maximum quantum yield (F_v/F_m) and effective quantum yield (Φ_PSII). The changes of non-photochemical fluorescence quenching (NPQ), light-induced non-photochemical fluorescence quenching [Y(NPQ)] and non-light-induced non-photochemical fluorescence quenching [Y(NO)] showed that AgNPs inhibit the photo-protective capacity of PSII. AgNPs induce reactive oxygen species (ROS) that are mainly produced in the chloroplast. The activity of ribulose-1, 5-bisphosphate carboxylase-oxygenase (Rubisco) was also very sensitive to AgNPs. The internalized Ag, regardless of whether the exposure was Ag⁺or AgNPs had the same capacity to generate ROS. Our results support the hypothesis that intra-cellular AgNP dissociate into high toxic Ag⁺. Rubisco inhibition leads to slowing down of CO₂ assimilation. Consequently, the solar energy consumption decreases and then the excess excitation energy promotes ROS generation in chloroplast.

Phytotoxicity, uptake and transformation of nano-CeO2 in sand cultured romaine lettuce

Toxicity and uptake of nano-CeO2 (nCeO2) in edible vegetables are not yet fully understood. In the present study, we grew romaine lettuce in sand amended with nCeO2. At high concentrations (1000 and 2000 mg/kg), nCeO2 diminished the chlorophyll content by 16.5% and 25.8%, respectively, and significantly inhibited the biomass production. nCeO2 (≥100 mg/kg) altered antioxidant enzymatic activities and malondialdehyde levels in the plants. nCeO2 (≥500 mg/kg) triggered a remarkable increase of nitrate-N level in the shoots, which can be converted to toxic nitrite in humans thereby posed risk to human health. Concentration dependent accumulation of Ce in the plant tissues was observed. X ray absorption near edge spectroscopy (XANES) results indicate that Ce presented as nCeO2 and CePO4 in the roots while as nCeO2 and Ce carboxylates in the shoots. Chelation of Ce3+ by citric acid or precipitation of Ce3+ by PO43- reduced the translocation and toxicity of nCeO2, indicating that release of Ce3+ played a critical role in the toxicity nCeO2.

Physiological effects of cerium oxide nanoparticles on the photosynthesis and water use efficiency of soybean (Glycine max (L.) Merr.)

CeO₂NPs displayed concentration and coating property dependent effects on soybean photosynthesis and water use efficiency.

Exposure of engineered nanomaterials to plants: Insights into the physiological and biochemical responses-A review

Recent investigations show that carbon-based and metal-based engineered nanomaterials (ENMs), components of consumer goods and agricultural products, have the potential to build up in sediments and biosolid-amended agricultural soils. In addition, reports indicate that both carbon-based and metal-based ENMs affect plants differently at the physiological, biochemical, nutritional, and genetic levels. The toxicity threshold is species-dependent and responses to ENMs are driven by a series of factors including the nanomaterial characteristics and environmental conditions. Effects on the growth, physiological and biochemical traits, production and food quality, among others, have been reported. However, a complete understanding of the dynamics of interactions between plants and ENMs is not clear enough yet. This review presents recent publications on the physiological and biochemical effects that commercial carbon-based and metal-based ENMs have in terrestrial plants. This document focuses on crop plants because of their relevance in human nutrition and health. We have summarized the mechanisms of interaction between plants and ENMs as well as identified gaps in knowledge for future investigations.

Reprint of: Silver and titanium dioxide nanoparticle toxicity in plants: A review of current research

Nanoparticles (NPs) have become widely used in recent years for many manufacturing and medical processes. Recent literature suggests that many metallic nanomaterials including those of silver (Ag) and titanium dioxide (TiO₂) cause significant toxic effects in animal cell culture and animal models, however, toxicity studies using plant species are limited. This review examines current progress in the understanding of the effect of silver and titanium dioxide nanoparticles on plant species. There are many facets to this ongoing environmental problem. This review addresses the effects of NPs on oxidative stress-related gene expression, genotoxicity, seed germination, and root elongation. It is largely accepted that NP exposure results in the cellular generation of reactive oxygen species (ROS), leading to both positive and negative effects on plant growth. However, factors such as NP size, shape, surface coating and concentration vary greatly among studies resulting in conflicting reports of the effect at times. In addition, plant species tend to differ in their reaction to NP exposure, with some showing positive effects of NP augmentation while many others showing detrimental effects. Seed germination studies have shown to be less effective in gauging phytotoxicity, while root elongation studies have shown more promise. Given the large increase in nanomaterial applications in consumer products, agriculture and energy sectors, it is critical to understand their role in the environment and their effects on plant life. A closer look at nanomaterial-driven ecotoxicity is needed. Ecosystem-level studies are required to indicate how these nanomaterials transfer at the critical trophic levels affecting human health and biota.

Interaction of metal oxide nanoparticles with higher terrestrial plants: Physiological and biochemical aspects

Multiple applications of metal oxide nanoparticles (MONPs) could result in their accumulation in soil, threatening higher terrestrial plants. Several reports have shown the effects of MONPs on plants. In this review, we analyze the most recent reports about the physiological and biochemical responses of plants to stress imposed by MONPs. Findings demonstrate that MONPs may be taken up and accumulated in plant tissues causing adverse or beneficial effects on seed germination, seedling elongation, photosynthesis, antioxidative stress response, agronomic, and yield characteristics. Given the importance of determining the potential risks of MONPs on crops and other terrestrial higher plants, research questions about field long-term conditions, transgenernational phytotoxicity, genotype specific sensitivity, and combined pollution problems should be considered.

Engineered nanomaterial-mediated changes in the metabolism of terrestrial plants

Engineered nanomaterials (ENMs) possess remarkable physicochemical characteristics suitable for different applications in medicine, pharmaceuticals, biotechnology, energy, cosmetics and electronics. Because of their ultrafine size and high surface reactivity, ENMs can enter plant cells and interact with intracellular structures and metabolic pathways which may produce toxicity or promote plant growth and development by diverse mechanisms. Depending on their type and concentration, ENMs can have positive or negative effects on photosynthesis, photochemical fluorescence and quantum yield as well as photosynthetic pigments status of the plants. Some studies have shown that ENMs can improve photosynthetic efficiency via increasing chlorophyll content and light absorption and also broadening the spectrum of captured light, suggesting that photosynthesis can be nano-engineered for harnessing more solar energy. Both up- and down-regulation of primary metabolites such as proteins and carbohydrates have been observed following exposure of plants to various ENMs. The potential capacity of ENMs for changing the rate of primary metabolites lies in their close relationship with activation and biosynthesis of the key enzymes. Several classes of secondary metabolites such as phenolics, flavonoids, and alkaloids have been shown to be induced (mostly accompanied by stress-related factors) in plants exposed to different ENMs, highlighting their great potential as elicitors to enhance both quantity and quality of biologically active secondary metabolites. Considering reports on both positive and negative effects of ENMs on plant metabolism, in-depth studies are warranted to figure out the most appropriate ENMs (type, size and optimal concentration) in order to achieve the desirable effect on specific metabolites in a given plant species. In this review, we summarize the studies performed on the impacts of ENMs on biosynthesis of plant primary and secondary metabolites and mention the research gaps that currently exist in this field.

Soil organic matter influences cerium translocation and physiological processes in kidney bean plants exposed to cerium oxide nanoparticles

Soil organic matter plays a major role in determining the fate of the engineered nanomaterials (ENMs) in the soil matrix and effects on the residing plants. In this study, kidney bean plants were grown in soils varying in organic matter content and amended with 0-500mg/kg cerium oxide nanoparticles (nano-CeO2) under greenhouse condition. After 52days of exposure, cerium accumulation in tissues, plant growth and physiological parameters including photosynthetic pigments (chlorophylls and carotenoids), net photosynthesis rate, transpiration rate, and stomatal conductance were recorded. Additionally, catalase and ascorbate peroxidase activities were measured to evaluate oxidative stress in the tissues. The translocation factor of cerium in the nano-CeO2 exposed plants grown in organic matter enriched soil (OMES) was twice as the plants grown in low organic matter soil (LOMS). Although the leaf cover area increased by 65-111% with increasing nano-CeO2 concentration in LOMS, the effect on the physiological processes were inconsequential. In OMES leaves, exposure to 62.5-250mg/kg nano-CeO2 led to an enhancement in the transpiration rate and stomatal conductance, but to a simultaneous decrease in carotenoid contents by 25-28%. Chlorophyll a in the OMES leaves also decreased by 27 and 18% on exposure to 125 and 250mg/kg nano-CeO2. In addition, catalase activity increased in LOMS stems, and ascorbate peroxidase increased in OMES leaves of nano-CeO2 exposed plants, with respect to control. Thus, this study provides clear evidence that the properties of the complex soil matrix play decisive roles in determining the fate, bioavailability, and biological transport of ENMs in the environment.

Changes of primary and secondary metabolites in barley plants exposed to CdO nanoparticles

The environmental fate of airborne nanoparticles and their toxicity to plants is not yet fully understood. Pot-grown barley plants with second leaves developed were therefore exposed to CdO nanoparticles (CdONPs) of ecologically relevant size (7-60 nm) and concentration (2.03 ± 0.45 × 10⁵ particles cm^-3) in air for 3 weeks. An experiment was designed to test the effects of different treatments when only leaves (T1); leaves and soil substrate (T2); and leaves, soil, and water supply were exposed to nanoparticles (T3). A fourth, control group of plants was left without treatment (T0). Although CdONPs were directly absorbed by leaves from the air, a part of leaf-allocated Cd was also transported from roots by transpiration flow. Chromatographic assays revealed that CdONPs had a significant effect on total content of primary metabolites (amino acids and saccharides) but no significant effect on total content of secondary metabolites (phenolic compounds, Krebs cycle acids, and fatty acids). In addition, the compositions of individual metabolite classes were affected by CdONP treatment. For example, tryptophan and phenylalanine were the most affected amino acids in both analysed organs, while ferulic acid and isovitexin constituted the polyphenols most affected in leaves. Even though CdONP treatment had no effect on total fatty acids content, there were significant changes in the composition of saturated and unsaturated fatty acids in both the roots and leaves of treated plants. Although the results indicate the most pronounced effect in T3 plants as compared to T1 and T2 plants, even just leaf exposure to CdONPs has the potential to induce changes in plant metabolism.

Silver and titanium dioxide nanoparticle toxicity in plants: A review of current research

Nanoparticles (NPs) have become widely used in recent years for many manufacturing and medical processes. Recent literature suggests that many metallic nanomaterials including those of silver (Ag) and titanium dioxide (TiO2) cause significant toxic effects in animal cell culture and animal models, however, toxicity studies using plant species are limited. This review examines current progress in the understanding of the effect of silver and titanium dioxide nanoparticles on plant species. There are many facets to this ongoing environmental problem. This review addresses the effects of NPs on oxidative stress-related gene expression, genotoxicity, seed germination, and root elongation. It is largely accepted that NP exposure results in the cellular generation of reactive oxygen species (ROS), leading to both positive and negative effects on plant growth. However, factors such as NP size, shape, surface coating and concentration vary greatly among studies resulting in conflicting reports of the effect at times. In addition, plant species tend to differ in their reaction to NP exposure, with some showing positive effects of NP augmentation while many others showing detrimental effects. Seed germination studies have shown to be less effective in gauging phytotoxicity, while root elongation studies have shown more promise. Given the large increase in nanomaterial applications in consumer products, agriculture and energy sectors, it is critical to understand their role in the environment and their effects on plant life. A closer look at nanomaterial-driven ecotoxicity is needed. Ecosystem-level studies are required to indicate how these nanomaterials transfer at the critical trophic levels affecting human health and biota.

Gel-free/label-free proteomic analysis of wheat shoot in stress tolerant varieties under iron nanoparticles exposure

Iron nanoparticles (Fe NPs) have stimulatory effects on the germination ratio and plant growth of wheat. To elucidate the effects of Fe NPs on shoot of drought tolerant Pakistan-13 and salt tolerant NARC-11, a gel-free/label-free proteomic technique was used. The weights/lengths of seedling, shoot, and root of wheat varieties were increased on 5ppm Fe NPs exposure. The number of proteins related to photosynthesis and protein metabolism was decreased and increased in drought tolerant variety and salt tolerant variety, respectively, treated with Fe NPs compared to untreated plants. Differentially changed proteins in drought tolerant variety and salt tolerant variety were mainly related to photosynthesis. Out of photosynthesis related proteins, light reaction was enhanced in salt tolerant variety compared to drought tolerant variety on Fe NPs exposure. The abundance of ribulose bisphosphate carboxylase/oxygenase small chain in drought tolerant variety was higher than that in salt tolerant variety; however, in salt tolerant variety, it was increased 3 fold by Fe NPs exposure compared to untreated plant. These results suggest that Fe NPs improve the growth of wheat seedling, which might be associated with the increase of protein abundance in photosynthesis in salt tolerant variety.

Where does the toxicity of metal oxide nanoparticles come from: The nanoparticles, the ions, or a combination of both?

The toxicity of metal oxide nanoparticles (NPs) has aroused great concern over the past few years. However, there still remains the question whether the toxicity of the metal oxide NPs originates from the released ions or the NPs themselves. In this study, the metal ion release of CuO, Fe2O3, ZnO, Co3O4, Cr2O3, and NiO NPs in aqueous media was investigated, and their contributions to the metal oxide NPs' inhibition on the bioluminescence of Photobacterium phosphoreum were studied. It was found that the ions release of the metal oxide NPs in aqueous media was complex, depending on both the dissolution and adsorption processes of the metal oxide NPs. The relationships between the metal oxide NPs' antibacterial effects and their released metal ions could be divided into three categories: (1) the ZnO NPs' antibacterial effect was due solely to the released Zn(2+); (2) the CuO NPs' antibacterial effect originated from both the released Cu(2+),and the CuO particles; and (3) the antibacterial effects of Fe2O3, Co3O4, Cr2O3, and NiO NPs were caused by the NPs themselves. Our findings suggest that the ions release and their contributions to the NPs' toxicity should be considered in the toxicity evaluations of the metal oxide NPs.