Phenotypic and genomic responses to titanium dioxide and cerium oxide nanoparticles in Arabidopsis germinants

Unveiling key mechanisms: Transcriptomic meta-analysis of diverse nanomaterial applications addressing biotic and abiotic stresses in Arabidopsis Thaliana

The potential applications of nanomaterials in agriculture for alleviating diverse biotic and abiotic stresses have garnered significant attention. The reported mechanisms encompass promoting plant growth and development, alleviating oxidative stress, inducing defense responses, modulating plant-microbe interactions, and more. However, individual studies may not fully uncover the common pathways or distinguish the effects of different nanostructures. We examined Arabidopsis thaliana transcriptomes exposed to biotic, abiotic, and metal or carbon-based nanomaterials, utilizing 24 microarray chipsets and 17 RNA-seq sets. The results showed that: 1) from the perspective of different nanostructures, all metal nanomaterials relieved biotic/abiotic stresses via boosting metal homeostasis, particularly zinc and iron. Carbon nanomaterials induce hormone-related immune responses in the presence of both biotic and abiotic stressors. 2) Considering the distinct features of various nanostructures, metal nanomaterials displayed unique characteristics in seed priming for combating abiotic stresses. In contrast, carbon nanomaterials exhibited attractive features in alleviating water deprivation and acting as signaling amplifiers during biotic stress. 3) For shared pathway analysis, response to hypoxia emerges as the predominant and widely shared regulatory mechanism governing diverse stress responses, including those induced by nanomaterials. By deciphering shared and specific pathways and responses, this research opens new avenues for precision nano-agriculture, offering innovative strategies to optimize plant resilience, improve stress management, and advance sustainable crop production practices.

Strategies for Enhancing Plant Immunity and Resilience Using Nanomaterials for Sustainable Agriculture

Research on plant-nanomaterial interactions has greatly advanced over the past decade. One particularly fascinating discovery encompasses the immunomodulatory effects in plants. Due to the low doses needed and the comparatively low toxicity of many nanomaterials, nanoenabled immunomodulation is environmentally and economically promising for agriculture. It may reduce environmental costs associated with excessive use of chemical pesticides and fertilizers, which can lead to soil and water pollution. Furthermore, nanoenabled strategies can enhance plant resilience against various biotic and abiotic stresses, contributing to the sustainability of agricultural ecosystems and the reduction of crop losses due to environmental factors. While nanoparticle immunomodulatory effects are relatively well-known in animals, they are still to be understood in plants. Here, we provide our perspective on the general components of the plant's immune system, including the signaling pathways, networks, and molecules of relevance for plant nanomodulation. We discuss the recent scientific progress in nanoenabled immunomodulation and nanopriming and lay out key avenues to use plant immunomodulation for agriculture. Reactive oxygen species (ROS), the mitogen-activated protein kinase (MAPK) cascade, and the calcium-dependent protein kinase (CDPK or CPK) pathway are of particular interest due to their interconnected function and significance in the response to biotic and abiotic stress. Additionally, we underscore that understanding the plant hormone salicylic acid is vital for nanoenabled applications to induce systemic acquired resistance. It is suggested that a multidisciplinary approach, incorporating environmental impact assessments and focusing on scalability, can expedite the realization of enhanced crop yields through nanotechnology while fostering a healthier environment.

Molecular Mechanisms in Metal Oxide Nanoparticle-Tryptophan Interactions

One of the crucial metabolic processes for both plant and animal kingdoms is the oxidation of the amino acid tryptophan (TRP) that regulates plant growth and controls hunger and sleeping patterns in animals. Here, we report revolutionary insights into how this process can be crucially affected by interactions with metal oxide nanoparticles (NPs), creating a toolbox for a plethora of important biomedical and agricultural applications. Molecular mechanisms in TRP-NP interactions were revealed by NMR and optical spectroscopy for ceria and titania and by X-ray single-crystal study and a computational study of model TRP-polyoxometalate complexes, which permitted the visualization of the oxidation mechanism at an atomic level. Nanozyme activity, involving concerted proton and electron transfer to the NP surface for oxides with a high oxidative potential, like CeO2 or WO3, converted TRP in the first step into a tricyclic organic acid belonging to the family of natural plant hormones, auxins. TiO2, a much poorer oxidant, was strongly binding TRP without concurrent oxidation in the dark but oxidized it nonspecifically via the release of reactive oxygen species (ROS) in daylight.

Nanobiostimulant action of trigolic formulated zinc sulfide nanoparticles (ZnS-T NPs) on rice seeds by triggering antioxidant defense network and plant growth specific transcription factors

Under a changing climate, nanotechnological interventions for climate resilience in crops are critical to maintaining food security. Prior research has documented the affirmative response of nano zinc sulfide (nZnS) on physiological traits of fungal-infested rice seeds. Here, we propose an application of trigolic formulated zinc sulfide nanoparticles (ZnS-T NPs) on rice seeds as nanobiostimulant to improve physiological parameters by triggering antioxidative defense system, whose mechanism was investigated at transcriptional level by differential expression of genes in germinated seedlings. Nanopriming of healthy rice seeds with ZnS-T NPs (50 μg/ml), considerably intensified the seed vitality factors, including germination percentage, seedling length, dry weight and overall vigor index. Differential activation of antioxidant enzymes, viz. SOD (35.47%), APX (33.80%) and CAT (45.94%), in ZnS-T NPs treated seedlings reduced the probability of redox imbalance and promoted the vitality of rice seedlings. In gene expression profiling by reverse transcription quantitative real time PCR (qRT-PCR), the notable up-regulation of target antioxidant genes (CuZn SOD, APX and CAT) and plant growth specific genes (CKX and GRF) in ZnS-T NPs treated rice seedlings substantiates their molecular role in stimulating both antioxidant defenses and plant growth mechanisms. The improved physiological quality parameters of ZnS-T NPs treated rice seeds under pot house conditions corresponded well with in vitro findings, which validated the beneficial boosted impact of ZnS-T NPs on rice seed development. Inclusively, the study on ZnS-T NPs offers fresh perspectives into biochemical and molecular reactions of rice, potentially positioning them as nanobiostimulant capable of eliciting broad-spectrum immune and growth-enhancing responses.

Paradoxical effects of nanomaterials on plants: Phytohormonal perspective exposes hidden risks amidst potential benefits

The rapid growth of nanotechnology has led to the production of a significant amount of engineered nanomaterials (NMs), raising concerns about their impact on various domains. This study investigates the negative interactions between NMs and phytohormones in plants, revealing the changes in signaling crosstalk, integrated responses and ecological repercussions caused by NM pollution. Phytohormones, which include auxins, cytokinins, gibberellins, abscisic acid, ethylene, jasmonic acid, salicylic acid and brassinosteroids are essential for plant growth, development, and stress responses. This review examines the intricate relationships between NMs and phytohormones, highlighting disruptions in signaling crosstalk, integrated responses, and ecological consequences in plants due to NM pollution. Various studies demonstrate that exposure to NMs can lead to alterations in gene expression, enzyme functions, and ultimately affect plant growth and stress tolerance. Exposure to NMs has the capacity to affect plant phytohormone reactions by changing their levels, biosynthesis, and signaling mechanisms, indicating a complex interrelation between NMs and phytohormone pathways. The complexity of the relationships between NMs and phytohormones necessitates further research, utilizing modern molecular techniques, to unravel the intricate molecular mechanisms and develop strategies to mitigate the ecological consequences of NM pollution. This review provides valuable insights for researchers and environmentalists concerned about the disruptive effects of NMs on regulating phytohormone networks in plants.

Proteomic insights to decipher nanoparticle uptake, translocation, and intercellular mechanisms in plants

Advent of proteomic techniques has made it possible to identify a broad spectrum of proteins in living systems. Studying the impact of nanoparticle (NP)-mediated plant protein responses is an emerging field. NPs are continuously being released into the environment and directly or indirectly affect plant's biochemistry. Exposure of plants to NPs, especially crops, poses a significant risk to the food chain, leading to changes in underlying metabolic processes. Once absorbed by plants, NPs interact with cellular proteins, thereby inducing changes in plant protein patterns. Based on the reactivity, properties, and translocation of nanoparticles, NPs can interfere with proteins involved in various cellular processes in plants such as energy regulation, redox metabolism, and cytotoxicity. Such interactions of NPs at the subcellular level enhance ROS scavenging activity, especially under stress conditions. Although higher concentrations of NPs induce ROS production and hinder oxidative mechanisms under stress conditions, NPs also mediate metabolic changes from fermentation to normal cellular processes. Although there has been lots of work conducted to understand the different effects of NPs on plants, the knowledge of proteomic responses of plants toward NPs is still very limited. This review has focused on the multi-omic analysis of NP interaction mechanisms with crop plants mainly centering on the proteomic perspective in response to both stress and non-stressed conditions. Furthermore, NP-specific interaction mechanisms with the biological pathways are discussed in detail.

Boosting plant resilience: The promise of rare earth nanomaterials in growth, physiology, and stress mitigation

Rare earth elements (REE) have been extensively used in a variety of applications such as cell phones, electric vehicles, and lasers. REEs are also used as nanomaterials (NMs), which have distinctive features that make them suitable candidates for biomedical applications. In this review, we have highlighted the role of rare earth element nanomaterials (REE-NMs) in the growth of plants and physiology, including seed sprouting rate, shoot biomass, root biomass, and photosynthetic parameters. In addition, we discuss the role of REE-NMs in the biochemical and molecular responses of plants. Crucially, REE-NMs influence the primary metabolites of plants, namely sugars, amino acids, lipids, vitamins, enzymes, polyols, sorbitol, and mannitol, and secondary metabolites, like terpenoids, alkaloids, phenolics, and sulfur-containing compounds. Despite their protective effects, elevated concentrations of NMs are reported to induce toxicity and affect plant growth when compared with lower concentrations, and they not only induce toxicity in plants but also affect soil microbes, aquatic organisms, and humans via the food chain. Overall, we are still at an early stage of understanding the role of REE in plant physiology and growth, and it is essential to examine the interaction of nanoparticles with plant metabolites and their impact on the expression of plant genes and signaling networks.

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

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

Use of metal nanoparticles in agriculture. A review on the effects on plant germination

Agricultural nanotechnology has become a powerful tool to help crops and improve agricultural production in the context of a growing world population. However, its application can have some problems with the development of harvests, especially during germination. This review evaluates nanoparticles with essential (Cu, Fe, Ni and Zn) and non-essential (Ag and Ti) elements on plant germination. In general, the effect of nanoparticles depends on several factors (dose, treatment time, application method, type of nanoparticle and plant). In addition, pH and ionic strength are relevant when applying nanoparticles to the soil. In the case of essential element nanoparticles, Fe nanoparticles show better results in improving nutrient uptake, improving germination, and the possibility of magnetic properties could favor their use in the removal of pollutants. In the case of Cu and Zn nanoparticles, they can be beneficial at low concentrations, while their excess presents toxicity and negatively affects germination. About nanoparticles of non-essential elements, both Ti and Ag nanoparticles can be helpful for nutrient uptake. However, their potential effects depend highly on the crop type, particle size and concentration. Overall, nanotechnology in agriculture is still in its early stages of development, and more research is needed to understand potential environmental and public health impacts.

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

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

Cobalt oxide nanoparticles: An effective growth promoter of Arabidopsis plants and nano-pesticide against bacterial leaf blight pathogen in rice

Recently, the application of cobalt oxide nanoparticles (Co₃O₄NPs) has gained popularity owing to its magnetic, catalytic, optical, antimicrobial, and biomedical properties. However, studies on its use as a crop protection agent and its effect on photosynthetic apparatus are yet to be reported. Here, Co₃O₄NPs were first green synthesized using Hibiscus rosa-sinensis flower extract and were characterized using UV-Vis spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction (XRD), transmission/scanning electron microscopy methods. Formation of the Co₃O₄NPs was attested based on surface plasmon resonance at 210 nm. XRD assay showed that the samples were crystalline having a mean size of 34.9 nm. The Co₃O₄NPs at 200 µg/ml inhibited the growth (OD₆₀₀ = 1.28) and biofilm formation (OD₅₇₀ = 1.37) of Xanthomonas oryzae pv. oryzae (Xoo) respectively, by 72.87% and 79.65%. Rice plants inoculated with Xoo had disease leaf area percentage (DLA %) of 57.25% which was significantly reduced to 11.09% on infected plants treated with 200 µg/ml Co₃O₄NPs. Also, plants treated with 200 µg/ml Co₃O₄NPs only had significant increment in shoot length, root length, fresh weight, and dry weight in comparison to plants treated with double distilled water. The application of 200 µg/ml Co₃O₄NPs on the Arabidopsis plant significantly increased the photochemical efficacy of PSII (ΦPSII) and photochemical quenching (qP) respectively, by 149.10% and 125.00% compared to the control while the non-photochemical energy dissipation (ΦNPQ) was significantly lowered in comparison to control. In summary, it can be inferred that Co₃O₄NPs can be a useful agent in the management of bacterial phytopathogen diseases.

Recent Advances in Metal-Based Nanoparticle-Mediated Biological Effects in Arabidopsis thaliana: A Mini Review

The widespread application of metal-based nanoparticles (MNPs) has prompted great interest in nano-biosafety. Consequently, as more and more MNPs are released into the environment and eventually sink into the soil, plants, as an essential component of the ecosystem, are at greater risk of exposure and response to these MNPs. Therefore, to understand the potential impact of nanoparticles on the environment, their effects should be thoroughly investigated. Arabidopsis (Arabidopsis thaliana L.) is an ideal model plant for studying the impact of environmental stress on plants’ growth and development because the ways in which Arabidopsis adapt to these stresses resemble those of many plants, and therefore, conclusions obtained from these scientific studies have often been used as the universal reference for other plants. This study reviewed the main findings of present-day interactions between MNPs and Arabidopsis thaliana from plant internalization to phytotoxic effects to reveal the mechanisms by which nanomaterials affect plant growth and development. We also analyzed the remaining unsolved problems in this field and provide a perspective for future research directions.

A New Look at the Effects of Engineered ZnO and TiO2 Nanoparticles: Evidence from Transcriptomics Studies

Titanium dioxide (TiO2) and zinc oxide (ZnO) nanoparticles (NPs) have attracted a great deal of attention due to their excellent electrical, optical, whitening, UV-adsorbing and bactericidal properties. The extensive production and utilization of these NPs increases their chances of being released into the environment and conferring unintended biological effects upon exposure. With the increasingly prevalent use of the omics technique, new data are burgeoning which provide a global view on the overall changes induced by exposures to NPs. In this review, we provide an account of the biological effects of ZnO and TiO2 NPs arising from transcriptomics in in vivo and in vitro studies. In addition to studies on humans and mice, we also describe findings on ecotoxicology-related species, such as Danio rerio (zebrafish), Caenorhabditis elegans (nematode) or Arabidopsis thaliana (thale cress). Based on evidence from transcriptomics studies, we discuss particle-induced biological effects, including cytotoxicity, developmental alterations and immune responses, that are dependent on both material-intrinsic and acquired/transformed properties. This review seeks to provide a holistic insight into the global changes induced by ZnO and TiO2 NPs pertinent to human and ecotoxicology.

Application of titanium regulates the functional components of photosynthetic apparatus in grafted seedlings of Carya cathayensis Sarg. under shade

Light acts as a key environmental factor for normal growth and development of plants. Carya cathayensis Sarg. (hickory) faces low light conditions, especially those caused by cloudy or rainy days during the rapid growth period, which has caused adverse effects on its growth. In the current investigation, to alleviate the adverse effects of insufficient light on the cultivation of hickory, anti-hydrolyze stabilized ionic titanium (ASIT) was sprayed on the leaves of the three kinds of grafted seedlings and the non-grafted seedlings of hickory grown under different shade conditions. Results showed that the leaf mass per area and chlorophyll content of grafted hickory seedlings were increased after ASIT application. Rubisco content and photosynthetic rate (P_n) of seedlings grown under shading conditions were positively affected by ASIT treatment, especially on the 45th day of treatment, while the interaction effects of the two parameters between ASIT application and different shade treatments were significant. Titanium accumulation was the highest in roots, followed by leaves, and then in stems, while ASIT had the most significant effects on roots and leaves under 50 ± 5% shade. Severe shading inhibited growth and lead to serious destruction of chloroplast ultrastructure. In addition, the role of ASIT was rootstock-dependent, since ASIT had the weakest mitigation effect on the C/H grafted seedlings. To sum up, the application of ASIT to the grafted seedlings of hickory could improve its ability to resist shade stress.

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.

Dose-Dependent Physiological and Transcriptomic Responses of Lettuce (Lactuca sativa L.) to Copper Oxide Nanoparticles-Insights into the Phytotoxicity Mechanisms

Understanding the complex mechanisms involved in plant response to nanoparticles (NPs) is indispensable in assessing the environmental impact of nano-pollutants. Plant leaves can directly intercept or absorb NPs deposited on their surface; however, the toxicity mechanisms of NPs to plant leaves are unclear. In this study, lettuce leaves were exposed to copper oxide nanoparticles (CuO-NPs, 0, 100, and 1000 mg/L) for 15 days, then physiological tests and transcriptomic analyses were conducted to evaluate the negative impacts of CuO-NPs. Both physiological and transcriptomic results demonstrated that CuO-NPs adversely affected plant growth, photosynthesis, and enhanced reactive oxygen species (ROS) accumulation and antioxidant system activity. The comparative transcriptome analysis showed that 2270 and 4264 genes were differentially expressed upon exposure to 100 and 1000 mg/L CuO-NPs. Gene expression analysis suggested the ATP-binding cassette (ABC) transporter family, heavy metal-associated isoprenylated plant proteins (HIPPs), endocytosis, and other metal ion binding proteins or channels play significant roles in CuO-NP accumulation by plant leaves. Furthermore, the variation in antioxidant enzyme transcript levels (POD1, MDAR4, APX2, FSDs), flavonoid content, cell wall structure and components, and hormone (auxin) could be essential in regulating CuO-NPs-induced stress. These findings could help understand the toxicity mechanisms of metal NPs on crops, especially NPs resulting from foliar exposure.

Effects of different surface-coated nTiO2 on full-grown carrot plants: Impacts on root splitting, essential elements, and Ti uptake

The production and environmental release of surface-modified titanium dioxide nanoparticles (nTiO₂) have increased. Hence, crops may be directly exposed to the nTiO₂ in soil. In this study, we grew carrots in soils amended with pristine, hydrophilic and hydrophobic surface-coated nTiO₂ at 100, 200, and 400 mg kg^-1 until full-plant maturity. The content of Ti in plant secondary roots treated with different nTiO₂ at 400 mg kg^-1 was in the order of hydrophobic > hydrophilic > pristine treatments, with values of 140.1, 100.5, and 64.3 mg kg^-1, respectively. The fresh biomass of the taproot was significantly decreased by all nTiO₂ forms at 400 mg kg^-1 by up to 56 %, compared to control. Pristine nTiO₂ at 100 mg kg^-1 enhanced the fresh weight of leaves by 51 % with respect to control. Remarkably, an abnormal increase of taproot splitting was found in plants treated with all nTiO₂ forms. In carrots treated with the surface-coated nTiO₂, the accumulation of Ca, Mg, Fe, and Zn increased in leaves; but Mg, Mn, and Zn decreased in taproots. These results suggest that future regulation of nTiO₂ release into soils should consider its surface coating properties since the phytotoxicity effects depend on nTiO₂ outer structure.

Titanium Application Increases Phosphorus Uptake Through Changes in Auxin Content and Root Architecture in Soybean (Glycine Max L.)

Phosphorus (P) is an essential macronutrient needed for plant growth, development, and production. A deficiency of P causes a severe impact on plant development and productivity. Several P-based fertilizers are being used in agriculture but limited uptake of P by the plant is still a challenge to be solved. Titanium (Ti) application increases the nutrient uptake by affecting the root growth; however, the role of Ti in plant biology, specifically its application under low light and phosphorus stress, has never been reported. Therefore, a pot study was planned with foliar application of Ti (in a different concentration ranging from 0 to 1,000 mg L^-1) under different light and P concentrations. The result indicated that under shade and low P conditions the foliar application of Ti in different concentrations significantly improves the plant growth parameters such as root length, root surface area, root dry matter, and shoot dry matters. The increase was observed to be more than 100% in shade and low P stressed soybean root parameter with 500 mg L^-1 of Ti treatment. Ti was observed to improve the plant growth both in high P and low P exposed plants, but the improvement was more obvious in Low P exposed plants. Auxin concentration in stressed and healthy plant roots was observed to be slightly increased with Ti application. Ti application was also observed to decrease rhizosphere soil pH and boosted the antioxidant enzymatic activities with an enhancement in photosynthetic efficiency of soybean plants under shade and P stress. With 500 mg L^-1 of Ti treatment, the photosynthetic rate was observed to improve by 45% under shade and P stressed soybean plants. Thus, this work for the first time indicates a good potential of Ti application in the low light and P deficient agricultural fields for the purpose to improve plant growth and development parameters.

Can the properties of engineered nanoparticles be indicative of their functions and effects in plants?

The extensive applicability of engineered nanoparticles (ENPs) in various fields such as environment, agriculture, medicine or biotechnology has mostly been attributed to their better physicochemical properties as compared with conventional bulk materials. However, functions and biological effects of ENPs change across different scenarios which impede the progress in their risk assessment and safety management. This review thus intends to figure out whether properties of ENPs can be indicators of their behavior through summarizing and analyzing the available literature and knowledge. The studies have indicated that size, shape, solubility, specific surface area, surface charge and surface reactivity constitute a more accurate measure of ENPs functions and toxic effects in addition to mass concentration. Effects of ENPs are also highly dependent on dose metrics, species and strains of organisms, environmental conditions, exposure route and duration. Searching correlations between properties and functions or biological effects may serve as an effective way in understanding positive and negative impacts of ENPs. This will ensure safe design and sustainable future use of ENPs.

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.

Astaxanthin overproduction and proteomic analysis of Phaffia rhodozyma under the oxidative stress induced by TiO2

This study analyzed the effect of TiO₂ on the growth and astaxanthin yield of P. rhodozyma PR106. Subsequently, proteomics method was used to analyze the proteins changes of the strain under TiO₂ treatment, to investigate the metabolic mechanism of the active oxygen generator TiO₂ promoting the astaxanthin synthesis in P. rhodozyma. The results showed that TiO₂ caused oxidative stress response in P. rhodozyma, and astaxanthin yield was 14.74 mg/L, which was 2 times of the control group; while, TiO₂ had no effect on biomass and apoptosis of the cells. Proteomics analysis and parallel reaction monitoring (PRM) technology initially explored that bud-site selection protein (BUD22), ubiquitin-40s ribosomal protein s31 fusion protein, cell cycle control protein, C-4 methyl sterol oxidase and glutaredoxin were associated with astaxanthin synthesis.

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.

Metabolomics of wheat grains generationally-exposed to cerium oxide nanoparticles

This study investigated changes in metabolite compositions over three generation exposure of wheat (Triticum aestivum) to cerium oxide nanoparticles (CeO₂-NPs) in low or high nitrogen soil. The goal was to determine if CeO₂-NPs affects grains/seeds quality across generational exposure. Seeds from plants exposed for two generations to 0 or 500 mg CeO₂-NPs per kg soil treatment were cultivated for third year in low or high nitrogen soil amended with 0 or 500 mg CeO₂-NPs per kg soil. Metabolomics identified 180 metabolites. Multivariate analysis showed that continuous generational exposure to CeO₂-NPs altered 18 and 11 metabolites in low N and high N grains, respectively. Interestingly, DNA/RNA metabolites such as thymidine, uracil, guanosine, deoxyguanosine, adenosine monophosphate were affected; a finding that has not been observed on DNA/RNA metabolites of plants exposed to nanoparticles. Nicotianamine, a metabolite playing crucial role in Fe storage in grains, decreased by 33% in grains continuously exposed for three generations to CeO₂-NPs at high N soil. Notably, these grains also exhibited a concomitant decrease of 13-16% in Fe concentration. Together these changes suggest alterations in grain quality or implications in ecosystem processes (i.e., productivity, nutrient cycling, ecosystem stability) of progeny plants generationally-exposed to CeO₂-NPs.

Impact of synthesized metal oxide nanomaterials on seedlings production of three Solanaceae crops

Prospective involvement of metal oxide nanomaterials as a prominent agriculture practice for improving existing crop production directed the present investigation for synthesizing of ZnO and TiO₂ nanomaterials as an attempt to enhance the transplants production of some Solanaceae crops. The morphological characterizations of the prepared nanomaterials indicated that the hydrothermal synthesized ZnO was produced in nanorod structure with an average aspect ratio of 7. However, SEM and TEM micrographs of microwave prepared TiO₂ evident that it has a nanoparticle structure with an average diameter of 43 nm. The BET results confirmed the high specific areas of the two prepared metal oxide nanomaterials. The two synthesized metal oxide nanomaterials were coated in gel and mixed with the seeds of eggplant, pepper and tomato crops at four concentrations 0, 50, 100 and 150 mg/L, whilst the control seeds were germinated in distilled water without gel-coating. The results pointed to the outstanding effect of TiO₂ and ZnO nanoparticles on germination characters and seedlings growth. The maximum transplants lengths, fresh and dry weight were recorded at the level 100 mg/L whatever the crop plant used. Hastening germination operation of nanomaterials-gel coated seedlings compared to control plants may be ascribed to the reduction of mean germination time and coefficient variation of the germination process besides increasing the mean germination rate and the synchrony of germination traits. Overall, better performance of growing transplants has been accredited for nanoparticles-gel coated seedlings more than the control treatments which could be efficient for the safer production of transplants in an innovative way.

Antioxidant mechanisms to counteract TiO2-nanoparticles toxicity in wheat leaves and roots are organ dependent

Nanoparticles (NP) bioactivity is under deep scrutiny. In this work, the antioxidant response to TiO₂-NP in wheat (Triticum aestivum) was determined. For that, enzymatic and the non-enzymatic antioxidants were evaluated in plants exposed to the P25 anatase:rutile material composed of TiO₂-NP and under environmentally realistic doses (0; 5; 50; 150 mg/L for 20 days). Shoot but not root growth was reduced. In leaves, thiol metabolism and ascorbate accumulation were the preferred route whereas in roots the pre-existing antioxidant capacity was preferentially utilized. Both leaves and roots showed increased glutathione reductase and dehydroascorbate reductase activities and decreased ascorbate peroxidase activity. Roots, nevertheless, presented higher enzymatic basal levels than leaves. On the other hand, when examining non-enzymatic antioxidants, the ratio of reduced-to-oxidized glutathione (GSH/GSSG) increased in leaves and decreased in roots. Exposed leaves also presented higher total ascorbate accumulation compared to roots. TiO₂-NP exposure down regulated, with more prominence in roots, antioxidant enzyme genes encoding catalase, ascorbate peroxidase, monodehydroascorbate reductase and dehydroascorbate reductase. In leaves, superoxide dismutase gene expression was increased. All data pinpoint to TiO₂-NP toxicity above 5 mg/L, with aerial parts being more susceptible, which draws concerns on the safety doses for the use of these NPs in agricultural practices.

Toxicity assessment of anatase (TiO2) nanoparticles: A pilot study on stress response alterations and DNA damage studies in Lens culinaris Medik

The research was targeted to investigate the effect of nano-TiO₂ (anatase) on germination, vigour index, stress enzymes and mitotic cell cycle profile in lentils (Lens culinaris Medik.). Seed germination results indicated that TiO₂ NP (Nanoparticle) at lowest concentration promotes seed germination, vigour index and biomass; however, at higher concentrations, they showed significant reduction in growth parameters and photosynthetic pigments in concentration-dependent manner. NP treatments triggered an excessive formation of reactive oxygen species (ROS) which was evident from increased production of stress enzymes, lipid peroxidation, augmented DNA damage and aberrant mitotic cell division. The results exhibit a dose-dependent modification of NP- mediated oxidative stress and genotoxicity in lentil.

Assessing the impacts of sewage sludge amendment containing nano-TiO2 on tomato plants: A life cycle study

Increasing evidence indicates the presence of engineered nanoparticles (ENPs) in sewage sludge derived from wastewater treatment. Land application of sewage sludge is, therefore, considered as an important pathway for ENP transfer to the environment. The aim of this work was to understand the effects of sewage sludge containing nano-TiO₂ on plants (tomato) when used as an amendment in agricultural soil. We assessed developmental parameters for the entire plant life cycle along with metabolic and bio-macromolecule changes and titanium accumulation in plants. The results suggest that the sewage sludge amendment containing nano-TiO₂ increased plant growth (142% leaf biomass, 102% fruit yield), without causing changes in biochemical responses, except for a 43% decrease in leaf tannin concentration. Changes in elemental concentrations (mainly Fe, B, P, Na, and Mn) of plant stem, leaves and, to a lesser extent fruits were observed. Fourier-transformed infrared analysis showed maximum changes in plant leaves (decrease in tannins and lignins and increase in carbohydrates) but no change in fruits. No significant Ti enrichment was detected in tomato fruits. In conclusion, we evidenced no acute toxicity to plants and no major implication for food safety after one plant life cycle exposure.

Changes in morphology, chlorophyll fluorescence performance and Rubisco activity of soybean in response to foliar application of ionic titanium under normal light and shade environment

Titanium (Ti) is considered an essential element for plant growth; however, its role in crop performance through stimulating the activities of certain enzymes, enhancing chlorophyll content and photosynthesis, and improving crop morphology and growth requires more study. We therefore conducted a laboratory experiments to study the effects of ionic Ti application on morphology, growth, biomass distribution, chlorophyll fluorescence performance and Rubisco activity of soybean (Glycine max L.) under normal light (NL) and shade conditions (SC). In this study, we sprayed soybean plants with five different levels of ionic Ti (T1 = 0, T2 = 1.25, T3 = 2.5, T4 = 5 and T5 = 10 mg Ti Plant-1) through foliar application method. Our results show that with increasing moderate (2.5 mg Ti Plant-1) Ti concentration, the chlorophyll pigments (chlorophyll [Chl] a, b, carotenoid [Car]), plant biomass, photochemical efficiency of photosystem II (Fv/Fm), and electron transport rate (ETR) of soybean increased, but higher levels (5-10 mg Ti Plant-1), resulted in leaf anatomical and chloroplast structural disruptions under both NL and SC. Soybean plants showed maximum biomass, leaf area, leaf thickness, Chl a, b, Car, Rubisco activity, Fv/Fm and ETR for T3 at 2.5 mg Ti Plant-1; however, declined significantly for T5 at high concentration of 10 mg Plant-1. In NL, the application of 2.5 mg Ti Plant-1 (T3) increased the Chl a, b, and total Chl contents 40, 20, and 27% as compared to control treatment (T1). In SC, the application of 1.25 mg Ti mg Plant-1 (T2) increased the Chl a, b, and total Chl contents 38, 19, and 14% as compared to control treatment. In NL, the Fv/Fm, qP, PSII, and ETR were higher in the T3 treatment over the T1 (control) by 7, 0.3, 16, and 16%, respectively. In SC, the Fv/Fm, qP, PSII, and ETR were higher in the T3 treatment over the T1 (control) by 5, 5, 19, and 19%, respectively. Moreover, Rubisco activity was at peak (55 and 6% increase under NL and SC) at 2.5 mg Ti Plant-1and decreased with increasing Ti concentration, reaching the lowest at 10 mg Ti Plant-1, which indicates that leaf cells were damaged as observed in the leaf anatomy. We concluded that ionic Ti expresses a hormesis effect: at lower concentrations, promoting soybean growth, however, at higher concentrations, suppressing soybean growth both under NL and SC. We therefore suggest that under different light stress conditions, Ti application could serve to mitigate abiotic stresses, especially in intercropping systems.

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.

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.

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.

Uptake and transformations of engineered nanomaterials: Critical responses observed in terrestrial plants and the model plant Arabidopsis thaliana

With the applications of engineered nanomaterials (ENMs) continually expanding and production quickly growing, residues of ENMs will end up in the environment at levels that may be harmful to non-target organisms. Many of the tunable properties that have made them desirable, such as type, size, charge, or coating, also contribute to the current difficulties in understanding the fate of ENMs in the environment. This review article focuses on studies that investigate plant-ENM interactions, including techniques used to study these interactions and documented plant responses due to the phytotoxic effects of ENMs. The many variables which can be altered for an experiment, such as type, size, and concentration of ENMs, make it difficult to formulate generalizations about the uptake mechanism involved, or to make an inference on the subcellular localization and distribution of the internalized ENMs in plant tissue. In order to avoid these challenges, studies can utilize a model organism such as Arabidopsis thaliana, and a combination of analytical techniques that can reveal complementary information in order to assess how the different experimental conditions influence the uptake and phytotoxicity of ENMs. This review presents recent studies regarding plant-ENM interactions employing Arabidopsis to demonstrate how the use of this model plant can advance our understanding of plant-ENM interactions and guide additional studies using other plant species. Overarching results suggest that more sensitive tests and consistency in experimental designs are needed to fully assess and understand the phytotoxic effects of ENMs in the environment.

Wheat chronic exposure to TiO2-nanoparticles: Cyto- and genotoxic approach

This study investigates the phytotoxicity of chronic exposure (up to 20 d) of different TiO₂ nanoparticles (TiO₂-NP) concentrations (5, 50, 150 mg L^-1) in Triticum aestivum. Germination was not affected by TiO₂-NP exposure and seedling shoot length (3 d) was enhanced. Contrarily, plants' shoot growth (20 d) was impaired. Effects on membrane permeability and total antioxidant capacity in TiO₂-NP chronic exposure were organ dependent: increased in leaves and decreased in roots. Roots also showed lower levels of lipid peroxidation. Flow cytometry revealed no changes in ploidy levels as well as in the cell cycle dynamics for both organs. However, TiO₂-NP induced clastogenic effects in roots with increases in micronucleated cells in root tips in a dose dependent manner. Also, increases of DNA single/double strand breaks were found in leaves, and effects were similar to all doses. Ti uptake and translocation to leaves were confirmed by ICP-MS, which was dependent on NP concentration. Overall, these data indicate that TiO₂-NP phytotoxicity is more severe after longer exposure periods, higher doses and more severe for shoots than roots. The observed effects are a result of both direct and indirect (oxidative stress and/or water imbalances) action of TiO₂-NP. Additionally, results highlight the negative impact that TiO₂-NP may have on crop growth and production and to the risk of trophic transfer.

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

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

The effects of metallic engineered nanoparticles upon plant systems: An analytic examination of scientific evidence

Recent evidence for the effects of metallic engineered nanoparticles (ENPs) on plants and plant systems was examined together with its implications for other constituents of the Society-Environment-Economy (SEE) system. In this study, we were particularly interested to determine whether or not metallic ENPs have both stimulatory and inhibitory effects upon plant performance. An emphasis was made to analyze the scientific evidence on investigations examining both types of effects in the same studies. Analysis of evidence demonstrated that metallic ENPs have both stimulatory and inhibitory effects mostly in well-controlled environments and soilless media. Nano zero-valent iron (nZVI) and Cu ENPs have potential for use as micronutrients for plant systems, keeping in mind the proper formulation at the right dose for each type of ENP. The concentration levels for the stimulatory effects of Cu ENPs are lower than for those for nZVI. Newer findings showed that extremely smaller concentrations of Au ENPs (smaller than those for nZVI and Cu ENPs) induce positive effects for plant growth, which is attributed to effects on secondary metabolites. Ag ENPs have demonstrated their usage as antimicrobial/pesticidal agents for plant protection; however, precautions should be taken to avoid higher concentrations not only for plant systems, but also, other constituents in the SEE. Further research is warranted to investigate the stimulatory and inhibitory effects of metallic ENPs in soil media in order to broaden the horizon of sustainable agriculture production in terms of higher and safer yields so as to meet the food requirements of human population.

Effect of metal and metal oxide nanoparticles on growth and physiology of globally important food crops: A critical review

The concentrations of engineered metal and metal oxide nanoparticles (NPs) have increased in the environment due to increasing demand of NPs based products. This is causing a major concern for sustainable agriculture. This review presents the effects of NPs on agricultural crops at biochemical, physiological and molecular levels. Numerous studies showed that metal and metal oxide NPs affected the growth, yield and quality of important agricultural crops. The NPs altered mineral nutrition, photosynthesis and caused oxidative stress and induced genotoxicity in crops. The activities of antioxidant enzymes increased at low NPs toxicity while decreased at higher NPs toxicity in crops. Due to exposure of crop plants to NPs, the concentration of NPs increased in different plant parts including fruits and grains which could transfer to the food chain and pose a threat to human health. In conclusion, most of the NPs have both positive and negative effects on crops at physiological, morphological, biochemical and molecular levels. The effects of NPs on crop plants vary greatly with plant species, growth stages, growth conditions, method, dose, and duration of NPs exposure along with other factors. Further research orientation is also discussed in this review article.

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.

Titanium as a Beneficial Element for Crop Production

Titanium (Ti) is considered a beneficial element for plant growth. Ti applied via roots or leaves at low concentrations has been documented to improve crop performance through stimulating the activity of certain enzymes, enhancing chlorophyll content and photosynthesis, promoting nutrient uptake, strengthening stress tolerance, and improving crop yield and quality. Commercial fertilizers containing Ti, such as Tytanit and Mg-Titanit, have been used as biostimulants for improving crop production; however, mechanisms underlying the beneficial effects still remain unclear. In this article, we propose that the beneficial roles Ti plays in plants lie in its interaction with other nutrient elements primarily iron (Fe). Fe and Ti have synergistic and antagonistic relationships. When plants experience Fe deficiency, Ti helps induce the expression of genes related to Fe acquisition, thereby enhancing Fe uptake and utilization and subsequently improving plant growth. Plants may have proteins that either specifically or nonspecifically bind with Ti. When Ti concentration is high in plants, Ti competes with Fe for ligands or proteins. The competition could be severe, resulting in Ti phytotoxicity. As a result, the beneficial effects of Ti become more pronounced during the time when plants experience low or deficient Fe supply.

Molecular and physiological responses to titanium dioxide and cerium oxide nanoparticles in Arabidopsis

Changes in tissue transcriptomes and productivity of Arabidopsis thaliana were investigated during exposure of plants to 2 widely used engineered metal oxide nanoparticles, titanium dioxide (nano-titania) and cerium dioxide (nano-ceria). Microarray analyses confirmed that exposure to either nanoparticle altered the transcriptomes of rosette leaves and roots, with comparatively larger numbers of differentially expressed genes found under nano-titania exposure. Nano-titania induced more differentially expressed genes in rosette leaves, whereas roots had more differentially expressed genes under nano-ceria exposure. MapMan analyses indicated that although nano-titania up-regulated overall metabolism in both tissues, metabolic processes under nano-ceria remained mostly unchanged. Gene enrichment analysis indicated that both nanoparticles mainly enriched ontology groups such as responses to stress (abiotic and biotic), and defense responses (pathogens), and responses to endogenous stimuli (hormones). Nano-titania specifically induced genes associated with photosynthesis, whereas nano-ceria induced expression of genes related to activating transcription factors, most notably those belonging to the ethylene responsive element binding protein family. Interestingly, there were also increased numbers of rosette leaves and plant biomass under nano-ceria exposure, but not under nano-titania. Other transcriptomic responses did not clearly relate to responses observed at the organism level, possibly because of functional and genomic redundancy in Arabidopsis, which may mask expression of morphological changes, despite discernable responses at the transcriptome level. In addition, transcriptomic changes often relate to transgenerational phenotypic development, and hence it may be productive to direct further experimental work to integrate high-throughput genomic results with longer term changes in subsequent generations. Environ Toxicol Chem 2017;36:71-82. Published 2016 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

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.

Germination and early plant development of ten plant species exposed to titanium dioxide and cerium oxide nanoparticles

Ten agronomic plant species were exposed to different concentrations of nano-titanium dioxide (nTiO2 ) or nano-cerium oxide (nCeO2 ) (0 μg/mL, 250 μg/mL, 500 μg/mL, and 1000 μg/mL) to examine potential effects on germination and early seedling development. The authors modified a standard test protocol developed for soluble chemicals (OPPTS 850.4200) to determine if such an approach might be useful for screening engineered nanomaterials (ENMs) and whether there were differences in response across a range of commercially important plant species to 2 common metal oxide ENMs. Eight of 10 species responded to nTiO2 , and 5 species responded to nCeO2 . Overall, it appeared that early root growth may be a more sensitive indicator of potential effects from ENM exposure than germination. The observed effects did not always relate to the exposure concentration, indicating that mass-based concentration may not fully explain the developmental effects of these 2 ENMs. The results suggest that nTiO2 and nCeO2 have different effects on early plant growth of agronomic species, with unknown effects at later stages of the life cycle. In addition, standard germination tests, which are commonly used for toxicity screening of new materials, may not detect the subtle but potentially more important changes associated with early growth and development in terrestrial plants. Environ Toxicol Chem 2016;35:2223-2229. Published 2016 Wiley Periodicals Inc. on behalf of SETAC. This article is a US Government work and, as such, is in the public domain in the United States of America.

Developmental and Reproductive Effects of Iron Oxide Nanoparticles in Arabidopsis thaliana

Increasing use of iron oxide nanoparticles in medicine and environmental remediation has led to concerns regarding exposure of these nanoparticles to the public. However, limited studies are available to evaluate their effects on the environment, in particular on plants and food crops. Here, we investigated the effects of positive (PC) and negative (NC) charged iron oxide (Fe₂O₃) nanoparticles (IONPs) on the physiology and reproductive capacity of Arabidopsis thaliana at concentrations of 3 and 25 mg/L. The 3 mg/L treated plants did not show evident effects on seeding and root length. However, the 25 mg/L treatment resulted in reduced seedling (positive-20% and negative-3.6%) and root (positive-48% and negative-negligible) length. Interestingly, treatment with polyethylenimine (PEI; IONP-PC coating) also resulted in reduced root length (39%) but no change was observed with polyacrylic acid (PAA; IONP-NC coating) treatment alone. However, treatment with IONPs at 3 mg/L did lead to an almost 5% increase in aborted pollen, a 2%–6% reduction in pollen viability and up to an 11% reduction in seed yield depending on the number of treatments. Interestingly, the treated plants did not show any observable phenotypic changes in overall size or general plant structure, indicating that environmental nanoparticle contamination could go dangerously unnoticed.