Offspring toxicity of silver nanoparticles to Arabidopsis thaliana flowering and floral development

Synergy of plant growth promoting rhizobacteria and silicon in regulation of AgNPs induced stress of rice seedlings

Silver Nanoparticles (AgNPs), as an emerging pollutant, have been receiving significant attention as they deepen the concern regarding the issue of food security. Silicon (Si) and plant growth-promoting rhizobacteria (PGPR) are likely to serve as a sustainable approach to ameliorating abiotic stress and improving plant growth through various mechanisms. The present study aims to evaluate the synergistic effect of Si and PGPRs on growth, physiological, and molecular response in rice seedlings (Oryza sativa) under AgNPs stress. Data suggested that under AgNPs exposure, the root and shoot growth, photosynthetic pigments, antioxidant enzymes (CAT and APX), expression of antioxidant genes (OsAPX and OsGR), silicon transporter (OsLsi2), and auxin hormone-related genes (OsPIN10 and OsYUCCA1) were significantly decreased which accompanied with the overproduction of reactive oxygen species (ROS), nitric oxide (NO) and might be due to higher accumulation of Ag in plant cells. Interestingly, the addition of Si along with the AgNPs enhances the level of ROS generation, thus oxidative stress, which causes severe damage in all the above-tested parameters. On the other hand, application of PGPR alone and along with Si reduced the toxic effect of AgNPs through the improvement of growth, biochemical, and gene regulation (OsAPX and OsGR, OsPIN10 and OsYUCCA1). However, the addition of L-NAME along with PGPR and silicon drastically lowered the AgNPs induced toxicity through lowering the oxidative stress and maintained the overall growth of rice seedlings, which suggests the role of endogenous NO in Si and PGPRs mediated management of AgNPs toxicity in rice seedlings.

Toxicological effects of nanoparticles in plants: Mechanisms involved at morphological, physiological, biochemical and molecular levels

The rapid advancement of nanotechnology has led to unprecedented innovations across diverse industries, including pharmaceuticals, agriculture, cosmetics, electronics, textiles, and food, owing to the unique properties of nanoparticles. The extensive production and unregulated release of synthetic nanoparticles may contribute to nanopollution within the ecosystem. In the agricultural sector, nanotechnology is increasingly utilized to improve plant productivity, enhance resistance to stressors, and reduce the usage of chemicals. However, the uncontrolled discharge of nanoparticles into the natural environment raises concerns regarding possible plant toxicological impacts. The review focuses on the translocation of these particles within the plants, emphasizing their phytotoxicological effects at morphological, physiological, biochemical, and molecular levels. Eventhough the beneficial aspects of these nanoparticles are evident, excessive usage of nanoparticles at higher concentrations may lead to potential adverse effects. The phytotoxicity resulting from excessive amounts of nanoparticles affects seed germination and biomass production, disrupts the photosynthesis system, induces oxidative stress, impacts cell membrane integrity, alters gene expression, causes DNA damage, and leads to epigenetic variations in plants. Nanoparticles are found to directly associate with the cell membrane and cell organelles, leading to the dissolution and release of toxic ions, generation of reactive oxygen species (ROS) and subsequent oxidative stress. The present study signifies and accumulates knowledge regarding the application of nanoparticles in agriculture and illustrates a clear picture of their possible impacts on plants and soil microbes, thereby paving the way for future developments in nano-agrotechnology. The review concludes by addressing current challenges and proposing future directions to comprehend and mitigate the possible biological risks associated with nanoparticles in agriculture.

Plant-nano interactions: A new insight of nano-phytotoxicity

Whether nanoparticles (NPs) are boon or bane for society has been a centre of in-depth debate and key consideration in recent times. Exclusive physicochemical properties like small size, large surface area-to-volume ratio, robust catalytic activity, immense surface energy, magnetism and superior biocompatibility make NPs obligatory in many scientific, biomedical and industrial ventures. Nano-enabled products are newer entrants in the present era. To attenuate environmental stress and maximize crop yields, scientists are tempted to introduce NPs as augmented supplements in agriculture. The feasible approaches for NPs delivery are irrigation, foliar spraying or seed priming. Internalization of excessive NPs to plants endorses negative implications at higher trophic levels via biomagnification. The characteristics of NPs (dimensions, type, solubility, surface charge), applied concentration and duration of exposure are prime factors conferring nanotoxicity in plants. Several reports approved NPs persuaded toxicity can precisely mimic abiotic stress effects. The signature effects of nanotoxicity include poor root outgrowth, biomass reduction, oxidative stress evolution, lipid peroxidation, biomolecular damage, perturbed antioxidants, genotoxicity and nutrient imbalance in plants. NPs stress impels mitogen-activated protein kinase signaling cascade and urges stress responsive defence gene expression to counteract stress in plants. Exogenous supplementation of nitric oxide (NO), arbuscular mycorrhizal fungus (AMF), phytohormones, and melatonin (ME) is novel strategy to circumvent nanotoxicity. Briefly, this review appraises plants' physio-biochemical responses and adaptation scenarios to endure NPs stress. As NPs stress represents large-scale contaminants, advanced research is indispensable to avert indiscriminate NPs usage for synchronizing nano-security in multinational markets.

Silver nanoparticle ecotoxicity and phytoremediation: a critical review of current research and future prospects

Silver nanoparticles (AgNPs) are widely used in various industries, including textiles, electronics, and biomedical fields, due to their unique optical, electronic, and antimicrobial properties. However, the extensive use of AgNPs has raised concerns about their potential ecotoxicity and adverse effects on the environment. AgNPs can enter the environment through different pathways, such as wastewater, surface runoff, and soil application and can interact with living organisms through adsorption, ingestion, and accumulation, causing toxicity and harm. The small size, high surface area-to-volume ratio, and ability to generate reactive oxygen species (ROS) make AgNPs particularly toxic. Various bioremediation strategies, such as phytoremediation, have been proposed to mitigate the toxic effects of AgNPs and minimize their impact on the environment. Further research is needed to improve these strategies and ensure their safety and efficacy in different environmental settings.

Noteworthy biocompatibility of effective microorganisms (EM) like microbial beneficial culture formulation with metal and metal oxide nanoparticles

The present study evaluates the biocompatibility of silver and zinc oxide nanoparticles with various effective microorganisms (EM), like beneficial microbial formulations. The respective nanoparticle was synthesised by chemical reduction of metal precursor with reducer via simple route green technology principles. The synthesised nanoparticles were characterised by UV visible spectroscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) studies, revealing highly stable, nanoscale particles with marked crystallinity. EM-like beneficial cultures composed of viable cells of Lactobacillus lactis, Streptomyces sp, Candida lipolytica, and Aspergillus oryzae were formulated with rice bran, sugarcane syrup, and groundnut cake. The respective formulation was inoculated into the nanoparticles amalgamated pots raised with green gram seedlings. Biocompatibility was determined by measuring plant growth parameters of a green gram at pre-determined periods associated with enzymatic antioxidants like catalase (CAT), superoxide dismutase (SOD), and glutathione S transferase (GST) levels. Most significantly, the expression level of these enzymatic antioxidants level was also investigated by quantitative real-time polymerase chain reaction (qRT-PCR). The impact of the soil conditioning effect on soil nutrients like nitrogen, phosphorous, potassium, organic carbon, soil enzymes glucosidases, and β-xylosidases activity was also studied. Among the formulation, rice bran-groundnut cake-sugar syrup formulation recorded the best biocompatibility. This formulation showed high growth promotion, soil conditioning effect and no impact on the oxidative stress enzymes genes that revealed the best compatibility of nanoparticles. This study concluded that biocompatible, eco-friendly formulations of microbial inoculants could be used for the desirable agro active properties that show extreme tolerance or biocompatibility to the nanoparticles. This present study also suggests the utilisation of the above said beneficial microbial formulation and metal-based nanoparticles with desirable agro active properties in a synergistic manner due to their high tolerance or compatibility towards the metal or metal oxide nanoparticles.

Engineered nanoparticles in plant growth: Phytotoxicity concerns and the strategies for their attenuation

In the agricultural sector, the use of engineered nanoparticles (ENPs) has been acclaimed as the next big thing for sustaining and increasing crop productivity. A vast amount of literature is available regarding the growth-promoting attributes of different ENPs. In this context, it has been emphasized that the ENPs can bolster vegetative growth, leaf development, and seed setting and also help in mitigating the effects of abiotic and biotic stresses. At the same time, there have been a lot of speculations and concerns regarding the phytotoxicity of ENPs off-late. In this connection, many research articles have presented the negative effects of ENPs on plant systems. These studies have highlighted that almost all the ENPs impart a certain degree of phytotoxicity in terms of reduction in growth, biomass, impairment of photosynthesis, oxidative status of plant cells, etc. Mostly, the ENPs based on metal or metal oxides (Cd, Cr, Pb, Ag, Ce, etc.) and nonmetals (C) that are introduced into the environment are known to incite inhibitory effects. However, the phytotoxicity of ENPs are known to be determined mostly by the chemical nature of the element, size, surface charge, coating molecules, and abiotic factors like pH and light. This review article, therefore, elucidates the phytotoxic properties of different ENPs and the plant responses induced at the molecular level subjected to nanoparticle exposure. Moreover, the article highlights the probable strategies that may be adopted for the suppression of the phytotoxicity of ENPs to ensure the safe and sustainable application of ENPs in crop fields.

Negative effects of abamectin on soil microbial communities in the short term

With the widespread use of abamectin in agriculture, there is increasing urgency to assess the effects of abamectin on soil microorganisms. Here, we treated plant-soil microcosms with abamectin at concentrations of 0.1 and 1.0 mg/kg and quantified the impacts of abamectin on bulk and rhizosphere soil microbial communities by shotgun metagenomics after 7 and 21 days of exposure. Although abamectin was reported to be easily degradable, it altered the composition of the soil microbial communities, disrupted microbial interactions, and decreased community complexity and stability after 7 days of exposure. After treatment with abamectin at a concentration of 1.0 mg/kg, some opportunistic human diseases, and soil-borne pathogens like Ralstonia were enriched in the soil. However, most ecological functions in soil, particularly the metabolic capacities of microorganisms, recovered within 21 days after abamectin treatment. The horizontal and vertical gene transfer under abamectin treatments increased the levels of antibiotic resistance genes dissemination. Overall, our findings demonstrated the negative effects of abamectin on soil ecosystems in the short-term and highlight a possible long-term risk to public and soil ecosystem health associated with antibiotic resistance genes dissemination.

Effects of ecotoxicity of penoxsulam single and co-exposure with AgNPs on Eisenia fetida

Penoxsulam (PNX) and silver nanoparticles (AgNPs) are likely to coexist in soils due to continuous use. However, the ecotoxicity of PNX in earthworms and the effect of AgNPs on PNX toxicity are unknown. Therefore, the toxicity of PNX (0.05, 0.5, and 2.5 mg/kg) single and co-exposure with AgNPs (10 mg/kg) after 28 and 56 days on Eisenia fetida (E. fetida) was investigated from biochemical, genetic, histopathological, and transcriptomic aspects. The results showed that the low concentration of PNX (0.05PNX) had almost no effect on the biochemical level of E. fetida. However, the addition of AgNPs resulted in 0.05PNX causing E. fetida to produce excessive reactive oxygen species, and the activity of antioxidant and detoxification enzymes were interfered, resulting in lipid peroxidation and DNA damage. From the genetic level, even the lowest concentration of PNX can significantly interfere with the expression of functional genes, thus inducing oxidative stress and apoptosis and inhibited reproductive behavior in E. fetida. The integrated biomarker response results at the biochemical and genetic levels showed that the comprehensive toxicity of PNX and PNX + AgNPs on E. fetida was PNX dose-dependent. And the toxicity of all co-exposure groups was greater than that of the PNX only exposure groups. Furthermore, the addition of AgNPs significantly increased the damage of PNX on E. fetida intestinal tissue. Meanwhile, transcriptomic analysis showed that PNX + AgNPs had a greater effect on E. fetida than PNX single, and multiple pathways related to oxidative stress, inflammation, and cellular process regulation were disturbed. These results provide a basis for comprehensive evaluation of the ecotoxicity of PNX and confirm that the AgNPs does increase the ecotoxicity of PNX in soil environment.

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.

Bacillus mojavensis, a Metal-Tolerant Plant Growth-Promoting Bacterium, Improves Growth, Photosynthetic Attributes, Gas Exchange Parameters, and Alkalo-Polyphenol Contents in Silver Nanoparticle (Ag-NP)-Treated Withania somnifera L. (Ashwagandha)

Discharge of nanoparticles (NPs) into aquatic and terrestrial ecosystems during manufacturing processes and from various commercial goods has become a significant ecotoxicological concern. After reaching soil systems, NPs cause deleterious effects on soil fertility, microbial activity, and crop productivity. Taking into consideration the medicinal importance of Withania somnifera (L.) (ashwagandha), the present study assessed the potential hazards of silver nanoparticles (Ag-NPs) and the toxicity amelioration by a metal-tolerant plant growth-promoting rhizobacterium (PGPR). Bacillus mojavensis BZ-13 (NCBI accession number MZ950923) recovered from metal-polluted rhizosphere soil, tolerated an exceptionally high level of Ag-NPs. The growth-regulating substances synthesized by B. mojavensis were increased with increasing concentrations (0-1000 μg mL^-1) of Ag-NPs. Also, strain BZ-13 had the ability to form biofilm, produce alginate and exopolysaccharides (EPSs), as well maintain swimming and swarming motilities in the presence of Ag-NPs. Soil application of varying concentrations of Ag-NPs resulted in a dose-related reduction in growth and biochemical features of ashwagandha. In contrast, following soil inoculation, B. mojavensis relieved the Ag-NPs-induced phytotoxicity and improved plant productivity. Root, shoot length, dry biomass, and leaf area increased by 13, 17, 37, 25%, respectively, when B. mojavensis was applied with 25 mg/kg Ag-NPs when compared to noninoculated controls. Furthermore, the soil plant analysis development (SPAD) index, photosystem efficiency (Fv/Fm), PS II quantum yield (FPS II), photochemical quenching (qP), non-photochemical quenching (NpQ), and total chlorophyll and carotenoid content of BZ-13-inoculated plants in the presence of 25 mg Ag-NPs/kg increased by 33, 29, 41, 47, 35, 26, and 25%, respectively, when compared to noninoculated controls that were exposed to the same amounts of NPs. In addition, a significant (p ≤ 0.05) increase in 48, 18, 21, and 19% in withaferin-A (alkaloids), flavonoids, phenols, and tannin content, respectively, was recorded when plants were detached from bacterized and Ag-NP-treated plants. Leaf gas exchange parameters were also modulated in the case of inoculated plants. Furthermore, bacterial inoculation significantly decreased proline, lipid peroxidation, antioxidant enzymes, and Ag-NP's absorption and build-up in phyto-organs. In conclusion, soil inoculation with B. mojavensis may possibly be used as an alternative to protect W. somnifera plants in soil contaminated with nanoparticles. Therefore, phytohormone and other biomolecule-synthesizing and NP-tolerant PGPR strains like B. mojavensis might serve as an agronomically significant and cost-effective remediation agent for augmenting the yield and productivity of medicinally important plants like ashwagandha raised in soil contaminated with nanoparticles in general and Ag-NPs in particular.

Evaluating impacts of biogenic silver nanoparticles and ethylenediurea on wheat (Triticum aestivum L.) against ozone-induced damages

Tropospheric ozone (O₃) is a phytotoxic pollutant that leads to a reduction in crop yield. Nanotechnology offers promising solutions to stem such yield losses against abiotic stresses. Silver nanoparticles are major nanomaterials used in consumer products however, their impact on crops under abiotic stress is limited. In this study, we evaluated the anti-ozonant efficacy of biogenic silver nanoparticles (B-AgNPs) and compared them with a model anti-ozonant ethylenediurea (EDU) against ozone phyto-toxicity. Growth, physiology, antioxidant defense, and yield parameters in two wheat cultivars (HD-2967 & DBW-17), treated with B-AgNPs (25 mg/L and 50 mg/L) and EDU (150 mg/L and 300 mg/L), were studied at both vegetative and reproductive stages. During the experimental period, the average ambient ozone concentration and accumulated dose of ozone over a threshold of 40 ppb (AOT40) (8 h day^-1) were found to be 60 ppb and 6 ppm h, respectively, which were sufficient to cause ozone-induced phyto-toxicity in wheat. Growth and yield for B-AgNPs as well as EDU-treated plants were significantly higher in both the tested cultivars over control ones. However, 25 mg/L B-AgNPs treatment showed a more pronounced effect in terms of yield attributes and its lower accumulation in grains for both cultivars. DBW-17 cultivar responded better with B-AgNPs and EDU treatments as compared to HD-2967. Meanwhile, foliar exposure of B-AgNPs (dose; 25 mg/L) significantly enhanced grain weight plant^-1, thousand-grain weight, and harvest index by 54.22 %, 29.46 %, and 14.21 %, respectively in DBW-17, when compared to control. B-AgNPs could enhance ozone tolerance in wheat by increasing biochemical and physiological responses. It is concluded that B-AgNPs at optimum concentrations were as effective as EDU, hence could be a promising ozone protectant for wheat.

Synthesis approach-dependent antiviral properties of silver nanoparticles and nanocomposites

Numerous viral infections are common among humans, and some can lead to death. Even though conventional antiviral agents are beneficial in eliminating viral infections, they may lead to side effects or physiological toxicity. Silver nanoparticles and nanocomposites have been demonstrated to possess inhibitory properties against several pathogenic microbes, including archaea, bacteria, fungi, algae, and viruses. Its pronounced antimicrobial activity against various microbe-mediated diseases potentiates its use in combating viral infections. Notably, the appropriated selection of the synthesis method to fabricate silver nanoparticles is a major factor for consideration as it directly impacts antiviral efficacy, level of toxicity, scalability, and environmental sustainability. Thus, this article presents and discusses various synthesis approaches to produce silver nanoparticles and nanocomposites, providing technological insights into selecting approaches to generate antiviral silver-based nanoparticles. The antiviral mechanism of various formulations of silver nanoparticles and the evaluation of its propensity to combat specific viral infections as a potential antiviral agent are also discussed.

Phytonanotechnology applications in modern agriculture

With the rapidly changing global climate, the agricultural systems are confronted with more unpredictable and harsh environmental conditions than before which lead to compromised food production. Thus, to ensure safer and sustainable crop production, the use of advanced nanotechnological approaches in plants (phytonanotechnology) is of great significance. In this review, we summarize recent advances in phytonanotechnology in agricultural systems that can assist to meet ever-growing demands of food sustainability. The application of phytonanotechnology can change traditional agricultural systems, allowing the target-specific delivery of biomolecules (such as nucleotides and proteins) and cater the organized release of agrochemicals (such as pesticides and fertilizers). An amended comprehension of the communications between crops and nanoparticles (NPs) can improve the production of crops by enhancing tolerance towards environmental stresses and optimizing the utilization of nutrients. Besides, approaches like nanoliposomes, nanoemulsions, edible coatings, and other kinds of NPs offer numerous selections in the postharvest preservation of crops for minimizing food spoilage and thus establishing phtonanotechnology as a sustainable tool to architect modern agricultural practices.

Synergetic toxicity of silver nanoparticle and glyphosate on wheat (Triticum aestivum L.)

Silver nanoparticles (AgNPs) are one of the most commonly used nanomaterials in industrial and agricultural production. Glyphosate is a broad-spectrum systemic herbicide, which mainly acts in the phloem of weeds that compete with crop growth and is widely used in agriculture. This study investigated the interactive effects of AgNPs and glyphosate on the physiological morphology, gene transcription, and rhizosphere microorganisms of wheat. Our results demonstrated that wheat growth, and the structure and diversity of rhizosphere microorganisms were slightly influenced by AgNPs and glyphosate single treatment at the test concentration. However, AgNPs and glyphosate (Gly) combined treatment (AgNPs + Gly) strongly inhibited wheat growth and influenced gene transcription. In total, 955, 601, and 1336 genes were determined to be differentially expressed in AgNPs, glyphosate, and combined treatment, respectively. According to KEGG analysis, the combined groups induced an antioxidant response by upregulating the transcription of phenylpropanoid biosynthesis-related genes. In addition, more energy was needed, and disrupted cell membrane was shown in the combined treatment, which displayed in the upregulation of sucrose, starch, and lipid synthesis. Moreover, the relative abundance of Bradyrhizobium, Devosia, Kribbella, Sphingopyxis (nitrogen-fixing bacteria), and Streptomyces (plant growth-promoting bacteria) in soil microbiota were decreased, implicated that nitrogen fixation and some beneficial substance secretions were inhibited by the combined treatment. This study emphasized that the synergetic effects of AgNPs and glyphosate exerted a negative impact on wheat growth.

Nano-Sized Polystyrene at 1 mg/L Concentrations Does Not Show Strong Disturbance on the Freshwater Microbial Community

In recent years, microplastics and nanoplastics have gained public attention, but their impacts on the freshwater microbial communities is rarely evaluated. In this study, the effects of 1 mg/L nano-sized polystyrene (nPS) and its modified forms (carboxyl-modified and amino-modified nPS) on the structures and functions of freshwater microbial community were determined. The nPS were found to slightly reduce the chlorophyll-a and increase the phycocyanin contents of freshwater microbial communities. Moreover, the richness of the microbial communities temporarily decreased during this process, while their diversity remained uninfluenced by treatment with nPS. Although the three tested nPS types were found to disturb the compositions of both the prokaryotic and eukaryotic communities to some degree, they did not affect the functions of freshwater bacterial communities significantly due to functional redundancy. Our study demonstrated that the ecotoxicities of the nPS itself were found to be lower than what is generally expected.

Plant response to silver nanoparticles: a critical review

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

Silver Nanoparticle's Toxicological Effects and Phytoremediation

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

Effects of S-metolachlor on wheat (Triticum aestivum L.) seedling root exudates and the rhizosphere microbiome

S-metolachlor (S-ME) is a common chloroacetanilide herbicide. Here, we investigated the effects of S-ME on wheat seedling growth and explored via metabolomics the driver through which S-ME changes the rhizosphere microbiome. The results indicated that 4 mg/kg S-ME had a strong inhibitory effect on plant growth by inducing hydrogen peroxide (H₂O₂) levels. The richness of the rhizosphere microbiome markedly decreased after S-ME treatment, although the abundance of some potential beneficial rhizobacteria, such as Rhizobiaceae and Burkholderiaceae, increased suggesting that plants recruited potential beneficial microorganisms to resist S-ME-induced stress. Spearman correlation analysis revealed that Rhizobiaceae and Burkholderiaceae were positively correlated with organic acids secreted by plants after S-ME treatment, implying that potential beneficial microorganisms may be attracted mainly by organic acids. Our results demonstrated the phytotoxicity of S-ME on crop growth and indicated both that S-ME could influence rhizosphere microorganism abundance and that recruitment of potential beneficial microorganisms could be the result of root exudate regulation.

Type-specific impacts of silver on the protein profile of tomato (Lycopersicon esculentum L.)

Silver nanoparticles (AgNPs) are particularly among the widely used nanomaterials in medicine, industry, and agriculture. The small size and large surface area of AgNPs and other nanomaterials result in their high reactivity in biological systems. To better understand the effects of AgNPs on plants at the molecular level, tomato (Lycopersicon esculentum L.) seedlings were exposed to 30 mg/L silver in the form of nanoparticle (AgNPs), ionic (AgNO₃), or bulk (Ag⁰) in 50% Hoagland media for 7 days. The effects of silver on the expression of plant membrane transporters H⁺-ATPase, vacuolar type H⁺-ATPase (V-ATPase), and enzymes isocitrate dehydrogenase (IDH), and catalase in roots was assessed using RT-qPCR and immunofluorescence-confocal microscopy. We observed significantly higher expression of catalase in plants exposed to AgNPs (Fold of expression 1.1) and AgNO₃ (Fold of expression 1.2) than the control group. The immunofluorescence imaging of the proteins confirmed the gene expression data; the expression of the enzyme catalase was upregulated 41, 216, and 770% higher than the control group in plants exposed to AgNPs, Ag⁰, and AgNO₃, respectively. Exposure to AgnO₃ resulted in the upregulation (fold of expression 1.2) of H⁺-ATPase and downregulation (fold of expression 0.7) of V-ATPase. A significant reduction in the expression of the redox-sensitive tricarboxylic cycle (TCA) enzyme mitochondrial IDH was observed in plants exposed to AgNPs (38%), AgNO₃ (48%), or Ag⁰ (77%) compared to the control. This study shows that exposure to silver affects the expression of genes and protein involved in membrane transportation and oxidative response. The ionic form of silver had the most significant effect on the expression of genes and proteins compared to other forms of silver. The results from this study improve our understanding about the molecular effects of different forms of silver on important crop species. Novelty statementSilver nanoparticles released into the environment can be oxidized and be transformed into ionic form. Both the particulate and ionic forms of silver can be taken by plants and affect plants physiological and molecular responses. Despite the extensive research in this area, there is a scarce of information about the effects of silver nanoparticles on the expression of membrane transporters especially H⁺-ATPase involved in regulating cells' electrochemical charge, and the activity of enzymes involved in oxidative stress responses. This is a unique study that evaluates the expression of cellular proton transporters and enzymes of redox balance and energy metabolisms such as membrane transporters, H⁺-ATPase, and V-ATPases, and enzymes catalase and IDH. The results provide us valuable information about the impact of silver on plants at the molecular level by evaluating the expression of genes and proteins. Key MessageThe exposure of plants to silver as an environmental stressor affects the expression of genes and proteins involved in maintaining cell's electrochemical gradient (H⁺-ATPase, V-ATPase) and redox potential (IDH, catalase).

Synergistic effects of glyphosate and multiwall carbon nanotubes on Arabidopsis thaliana physiology and metabolism

Agricultural chemicals have the potential to become pollutants that adversely affect plant growth. Interactions between these compounds are likely, but potential synergies are under-researched. Multiwall carbon nanotubes are increasingly finding novel uses in agriculture, as delivery mechanisms and as slow-release fertilizers. There is potential for nanotubes to interact with other agricultural chemicals in unpredictable ways. To investigate this possibility, we examined interactions with glyphosate, a widely used herbicide that is also attracting increasing concern over its potential for non-target effects. Here we examined potential synergistic effects on hydroponically grown Arabidopsis thaliana. Single treatments did not affect plant growth significantly, or did only mildly. However, combined treatment significantly affected both plant root and shoot growth. High-level content of malondialdehyde and up-regulated of metabolic antioxidant molecules in plant indicated that combined group caused the strong oxidative damage, while the decreased of antioxidant enzyme activities indicated an imbalance between reactive oxygen species (ROS)and the antioxidant defense system due to the continuously generated ROS. Besides, several intermediate metabolites of unsaturated fatty acids synthesis pathways were up-regulated in combined treatment, which clarified that combined group changed membrane components. The increase of intermediate metabolites in combined group also reflected more energy consumption in the repairment of the disrupt of combined treatment. The synergistic effect observed was attributed to the accumulation of glyphosate resulting from permeability and transportability of the carbon nanotubes. Overall, the risk of nanotube-herbicide interaction suggests a caution use of nanotubes in agricultural applications.

The effects of solubility of silver nanoparticles, accumulation, and toxicity to the aquatic plant Lemna minor

The use of silver nanoparticles (AgNPs) in commercial products has increased due to their antibacterial properties and their impacts on the environment must be investigated. This scenario has motivated the conduction of this study, which relates different factors that affect the toxicity of AgNPs to the aquatic plant Lemna minor such as size, accumulation, concentration, and dissolution of AgNPs. To this end, synthesized AgNPs measuring 30, 85, and 110 nm were added into the culture medium to observe toxicity for 30 days. The mapping by SEM showed that the smallest AgNPs can translocate from roots to leaves due to its mobility and internalization. As predicted by the Ostwald equation, the solubility for 30-nm AgNPs increased almost 3 times at the end of 30 days, while for 85 and 110 nm size nanoparticles, after 7 days, the solubility decreased due to "Ostwald ripening" process. Plant mortality was assessed and, after 1 month, the size of 30 nm was the most toxic with negative growth in all studied concentrations, with 60% mortality in the worst case. The concentration of 50 μg mL^-1 was toxic in all sizes with negative growth in the period. Therefore, the investigation of AgNPs' toxicity needs to consider a different factor to better understand their effects on aquatic plants and the environment.

Phyllosphere bacterial assemblage is affected by plant genotypes and growth stages

The interaction between plants and microorganisms directly affects plant health and sustainable agricultural development. Leaves represent a wide-area habitat populated by a variety of microorganisms, whose impact on host environmental adaptability could influence plant growth and function. The driving factors for phyllosphere microbiota assemblage are the focus of current research. Here, we investigated the effect of growth stage (i.e., bolting, flowering, and maturation) and genotype of Arabidopsis thaliana (wild-type and the two photosynthetic mutants ndf4 and pgr5) on the composition of phyllosphere microbiota. Our results show that species abundance varied significantly between the three genotypes at different growth stages, whereas species richness and evenness varied only for ndf4. The leaf surface shared a core microbiota dominated by Proteobacteria, Actinobacteria, Bacteroidetes, and Firmicutes in all tested growth stages and genotypes. Phyllosphere specificity varied more with respect to growth stage than to genotype. In summary, both the growth stage and genotype of A. thaliana are crucial in shaping phyllosphere bacterial composition, with the former being a stronger driver. Our findings provide a novel for investigating whether the host properties influence the phyllosphere community and favor healthy development of plants.

The long-term effects of using nitrite and urea on the enrichment of comammox bacteria

The discovery of complete ammonia oxidizer (comammox) was a breakthrough in the study of nitrification. However, slow growth of comammox bacteria makes it challenging to distinguish them from traditional ammonia oxidizing microorganisms. Genomic data indicated that comammox bacteria encoded genes that can metabolize urea and had higher nitrite tolerance, which could only be found in several ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB). This implies that using nitrite and urea as nitrogen sources may accelerate comammox bacteria's enrichment efficiency. In this study, two reactors using nitrite and urea as substrates, respectively, were operated for 390 days. At the end of cultivation, the reactor fed with urea exhibited higher nitrification potential than the reactor fed with nitrite. Comammox bacteria outcompeted AOA and AOB, regardless of whether they were cultured with nitrite or urea. Using nitrite can improve the proportion of comammox amoA to total amoA of 92%, while using urea may increase the proportion of comammox bacteria among total bacteria to 14.2%. Metagenomic results implied that nitrite was converted to ammonia by nitrate reduction and absorbed by comammox bacteria. On the other hand, urea may be directly utilized as substrate. These results demonstrated that using different nitrogen sources caused niche differentiation of comammox bacteria, AOA, and AOB. Using nitrite can increase the relative abundance of comammox amoA to total amoA, while using urea can increase the quantity of comammox amoA. Comammox bacteria were dominant among ammonia oxidizing microorganisms for both nitrite and urea cultures.

Impact of metal-oxide nanoparticles on growth, physiology and yield of tomato (Solanum lycopersicum L.) modulated by Azotobacter salinestris strain ASM

The current study for the first time demonstrates the interference of a free-living, N₂-fixing, and nanoparticle (NP) tolerant Azotobacter salinestris strain ASM recovered from metal-polluted soil with tomato plant-metal oxide NPs (ZnO, CuO, Al₂O_3, and TiO₂) interactions in a sandy clay loam soil system with bulk materials as control. Tomato plants were grown till full maturity in soils amended with 20-2000 mg kg^-1 of each metal-oxide NP with and without seed biopriming and root-inoculation of A. salinestris. A. salinestris was found metabolically active, producing considerably high amounts of bioactive indole-3-acetic-acid, morphologically unaffected, and with low alteration of cell membrane permeability under 125-1500 μgml^-1 of NPs. However, ZnO-NPs slightly alter bacterial membrane permeability. Besides, A. salinestris secreted significantly higher amounts of extracellular polymeric substance (EPS) even under NP exposure, which could entrap the NPs and form metal-EPS complex as revealed and quantified by SEM-EDX. NPs were also found adsorbed on bacterial biomass. EPS stabilized the NPs and provided negative zeta potential to NPs. Following soil application, A. salinestris improved the plant performance and augmented the yield of tomato fruits and lycopene content even in NPs stressed soils. Interestingly, A. salinestris inoculation enhanced photosynthetic pigment formation, flower attributes, plant and fruit biomass, and reduced proline level. Bacterial inoculation also reduced the NP's uptake and accumulation significantly in vegetative organs and fruits. The organ wise order of NP's internalization was roots > shoots > fruits. Conclusively, A. salinestris inoculation could be an alternative to increase the production of tomato in metal-oxide NPs contaminated soils.

Pollutant toxicology with respect to microalgae and cyanobacteria

Microalgae and cyanobacteria are fundamental components of aquatic ecosystems. Pollution in aquatic environment is a worldwide problem. Toxicological research on microalgae and cyanobacteria can help to establish a solid foundation for aquatic ecotoxicological assessments. Algae and cyanobacteria occupy a large proportion of the biomass in aquatic environments; thus, their toxicological responses have been investigated extensively. However, the depth of toxic mechanisms and breadth of toxicological investigations need to be improved. While existing pollutants are being discharged into the environment daily, new ones are also being produced continuously. As a result, the phenomenon of water pollution has become unprecedentedly complex. In this review, we summarize the latest findings on five kinds of aquatic pollutants, namely, metals, nanomaterials, pesticides, pharmaceutical and personal care products (PPCPs), and persistent organic pollutants (POPs). Further, we present information on emerging pollutants such as graphene, microplastics, and ionic liquids. Efforts in studying the toxicological effects of pollutants on microalgae and cyanobacteria must be increased in order to better predict the potential risks posed by these materials to aquatic ecosystems as well as human health.

Alteration of dominant cyanobacteria in different bloom periods caused by abiotic factors and species interactions

Freshwater cyanobacterial blooms have drawn public attention because they threaten the safety of water resources and human health worldwide. Heavy cyanobacterial blooms outbreak in Lake Taihu in summer annually and vanish in other months. To find out the factors impacting the cyanobacterial blooms, the present study measured the physicochemical parameters of water and investigated the composition of microbial community using the 16S rRNA gene and internal transcribed spacer amplicon sequencing in the months with or without bloom. The most interesting finding is that two major cyanobacteria, Planktothrix and Microcystis, dramatically alternated during a cyanobacterial bloom in 2016, which is less mentioned in previous studies. When the temperature of the water began increasing in July, Planktothrix appeared first and showed as a superior competitor for M. aeruginosa in NO₃^--rich conditions. Microcystis became the dominant genus when the water temperature increased further in August. Laboratory experiments confirmed the influence of temperature and the total dissolved nitrogen (TDN) form on the growth of Planktothrix and Microcystis in a co-culture system. Besides, species interactions between cyanobacteria and non-cyanobacterial microorganisms, especially the prokaryotes, also played a key role in the alteration of Planktothrix and Microcystis. The present study exhibited the alteration of two dominant cyanobacteria in the different bloom periods caused by the temperature, TDN forms as well as the species interactions. These results helped the better understanding of cyanobacterial blooms and the factors which contribute to them.

Effects of residual S-metolachlor in soil on the phyllosphere microbial communities of wheat (Triticum aestivum L.)

S-metolachlor (S-ME) is a widely used chiral herbicide that can cause potential ecological risks via long-term usage. In this work, we chose a model plant, wheat, as the test material to determine the effects of applying 10 mg/kg S-ME to soil on its fresh weight, chlorophyll and malondialdehyde (MDA) content, and superoxide dismutase (SOD) activity and the diversity and structural composition of the phyllosphere microorganisms after 7 and 14 days of exposure. Our work showed that this concentration of residual S-ME in soil only slightly decreased plant biomass and had little effect on lipid peroxidation, the antioxidant enzyme system and chlorophyll content. Interestingly, although the test concentration of S-ME did not exert strong inhibitory effects on the physiological activities of wheat, it decreased the diversity of phyllosphere microbial communities and changed their structure, indicating that microorganisms were more sensitive stress indicators. S-ME reduced the colonization by some beneficial bacteria related to plant nitrogen fixation among the phyllosphere microorganisms, which influenced the growth and yield of wheat because these bacteria contribute to plant fitness. In addition, S-ME affected the association between the host and the composition of the phyllosphere microbial communities under different growth conditions. Our work provides insights into the ecological implications of the effects of herbicides on the phyllosphere microbiome.

Enantioselective effects of imazethapyr residues on Arabidopsis thaliana metabolic profile and phyllosphere microbial communities

Imazethapyr (IM) is a widely used acetolactate synthase-inhibiting chiral herbicide. It has long-term residuals that may be absorbed by the human body through the edible parts of plants, such as vegetable leaves or fruits. Here, we selected a model plant, Arabidopsis thaliana, to determine the effects of R-IM and S-IM on its leaf structure, photosynthetic efficiency, and metabolites, as well as the structures of microorganisms in the phyllosphere, after 7 days of exposure. Our results indicated enantiomeric differences in plant growth between R-IM and S-IM; 133 µg/kg R-IM showed heavier inhibition of photosynthetic efficiency and greater changes to subcellular structure than S-IM. R-IM and S-IM also had different effects on metabolism and leaf microorganisms. S-IM mainly increased lipid compounds and decreased amino acids, while R-IM increased sugar accumulation. The relative abundance of Moraxellaceae human pathogenic bacteria was increased by R-IM treatment, indicating that R-IM treatment may increase leaf surface pathogenic bacteria. Our research provides a new perspective for evaluating the harmfulness of pesticide residues in soil, phyllosphere microbiome changes via the regulation of plant metabolism, and induced pathogenic bacterial accumulation risks.

Lability-specific enrichment of typical engineered metal (oxide) nanoparticles by surface-functionalized microbubbles from waters

Enrichment of metallic engineered nanoparticles (MENPs) from environmental waters is a prerequisite for their removal, reliable analyses, and environmental process interpretations. This work investigated the enrichment of typical MENPs with different degrees of lability using surface-functionalized microbbubles. During the process, the transformation/dissolution characteristics of MENPs were considered, and the impact of surfactant or coagulant dose, pH of MENP suspensions, and water matrix was systematically investigated. Results show that the colloidal gas aphrons (CGAs) were capable of enriching over 90.0% of ionic Ag(I) which ended up as AgBr and Ag₂CO₃ in floats when the pH of suspension was 6.0. The polyaluminum chloride-modified CGAs with positive surface charges were good at capturing the particulate ZnO-NPs (~84.8%) but failed to collect the ionic species. It should be noted that the total MENP enrichment efficiency closely related to the content proportions of different species. In the river water, both of the dissolved natural organic matter (fulvic acids) and the electrolytes might influence the enrichment process by affecting the species transformation of Ag-NPs and ZnO-NPs. For the stable TiO₂-NPs, 97.1% of the nanoparticles were captured by CGAs. FAs apparently reinforced the enrichment performance since the molecules acted as bridge and facilitated the attachment between TiO₂-NP and CGAs. This work contributes to establishing the robust microbubble-induced enrichment method considering the characteristics of MENP contaminants.

Enantioselective effects of imazethapyr on Arabidopsis thaliana root exudates and rhizosphere microbes

Imazethapyr (IM) is a chiral herbicide with two enantiomers (R-IM and S-IM). Here, we determined the enantioselective effects of IM on Arabidopsis thaliana biomass and chlorophyll content, root exudates and rhizosphere microbes after 7 days of exposure. The results suggested that 133 μg/kg R-IM enantiomer in soil slightly inhibited plant biomass but S-IM did not exert significant inhibitory effects. The rhizosphere microorganism composition was also found to have enantiomeric differences between R- and S-IM. The relative abundance of beneficial rhizosphere microbes such as Bacillus and Ramlibacter increased much more with R-IM treatment than with S-IM treatment, indicating that the rhizosphere recruited some beneficial microbes to resist the herbicide stress. The IM enantiomers exerted a significant influence on root exudates with enantioselectivity. R-IM resulted in higher levels of most amino acids, organic acids, sugars and other metabolites after 7 days of exposure; few metabolites were increased by only the S-IM treatment. The correlation analyses between compounds (sugars, amino acids and organic acid) and microbes at the genus level revealed that the number of microbes was more positively correlated with organic acids than other compounds, indicating that organic acids can attract more microbes than amino acids and sugars. Some organic acids, such as 3-hydroxybutyric acid, may be a carbon source for the beneficial microbe Ramlibacter. This study increases the understanding of the differences in IM enantiomer toxicity with respect to plant physiological activity and soil microorganisms.

Rhizosphere Microbiome Assembly and Its Impact on Plant Growth

Microorganisms colonizing the plant rhizosphere provide a number of beneficial functions for their host. Although an increasing number of investigations clarified the great functional capabilities of rhizosphere microbial communities, the understanding of the precise mechanisms underlying the impact of rhizosphere microbiome assemblies is still limited. Also, not much is known about the various beneficial functions of the rhizosphere microbiome. In this review, we summarize the current knowledge of biotic and abiotic factors that shape the rhizosphere microbiome as well as the rhizosphere microbiome traits that are beneficial to plants growth and disease-resistance. We give particular emphasis on the impact of plant root metabolites on rhizosphere microbiome assemblies and on how the microbiome contributes to plant growth, yield, and disease-resistance. Finally, we introduce a new perspective and a novel method showing how a synthetic microbial community construction provides an effective approach to unravel the plant-microbes and microbes-microbes interplays.

Understanding the influence of glyphosate on the structure and function of freshwater microbial community in a microcosm

Glyphosate, one of the most popular herbicides, has become a prominent aquatic contaminant because of its huge usage. The eco-safety of glyphosate is still in controversy, and it is inconclusive how glyphosate influences aquatic microbial communities. In the present study, the effects of glyphosate on the structure and function of microbial communities in a freshwater microcosm were investigated. 16S/18S rRNA gene sequencing results showed that glyphosate treatment (2.5 mg L-1, 15 days) did not significantly alter the physical and chemical condition of the microcosm or the composition of the main species in the community, but metatranscriptomic analyses indicated that the transcriptions of some cyanobacteria were significantly influenced by glyphosate. The microbial community enhanced the gene expression in pathways related to translation, secondary metabolites biosynthesis, transport and catabolism to potentially withstand glyphosate contamination. In the low phosphorus (P) environment, a common cyanobacterium, Synechococcus, plays a special role by utilizing glyphosate as P source and thus reducing its toxicity to other microbes, such as Pseudanabaena. In general, addition of glyphosate in our artificial microcosms did not strongly affect the aquatic microbial community composition but did alter the community's transcription levels, which might be potentially explained by that some microbes could alleviate glyphosate's toxicity by utilizing glyphosate as a P source.