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.

Defining the Surface Oxygen Threshold That Switches the Interaction Mode of Graphene Oxide with Bacteria.

As antimicrobials, graphene materials (GMs) may have advantages over traditional antibiotics due to their physical mechanisms of action which ensure less chance of development of microbial resistance. However, the fundamental question as to whether the antibacterial mechanism of GMs originates from parallel interaction or perpendicular interaction, or from a combination of these, remains poorly understood. Here, we show both experimentally and theoretically that GMs with high surface oxygen content (SOC) predominantly attach in parallel to the bacterial cell surface when in the suspension phase. The interaction mode shifts to perpendicular interaction when the SOC reaches a threshold of ∼0.3 (the atomic percent of O in the total atoms). Such distinct interaction modes are highly related to the rigidity of GMs. Graphene oxide (GO) with high SOC is very flexible and thus can wrap bacteria while reduced GO (rGO) with lower SOC has higher rigidity and tends to contact bacteria with their edges. Neither mode necessarily kills bacteria. Rather, bactericidal activity depends on the interaction of GMs with surrounding biomolecules. These findings suggest that variation of SOC of GMs is a key factor driving the interaction mode with bacteria, thus helping to understand the different possible physical mechanisms leading to their antibacterial activity.

Impact of nanoplastic debris on the stability and transport of metal oxide nanoparticles: role of varying soil solution chemistry.

The release of metal-based nanoparticles (MNPs) and nanoplastic debris (NPDs) has become ubiquitous in the natural ecosystem. Interaction between MNPs and NPDs may alter their fate and transport in the sub-surface environment and have not been addressed so far. Therefore, the present study has explored the role of NPDs on the stability and mobility of extensively used MNPs, i.e., CuO nanoparticles (NPs) under varying soil solutions (SS) chemistry. In the absence of NPDs, a very high aggregation of CuO NPs observed in SS extracted from black, lateritic, and red soils, which can be correlated with ionic strength (IS) and type of ionic species. The sedimentation rate (ksed(1/h)) for CuO NPs was >0.5 h-1 in the case of these SS. Interestingly, the stability and sedimentation behavior of CuO NPs varied significantly in the presence of NPDs. The ksed for CuO NPs decreased to half and found <0.25 h-1 in the presence of NPDs in all SS. C/C0 values in breakthrough curves increased drastically (black < alluvial < laterite < red) in presence of NPDs. Results suggest that the release of NPDs in the terrestrial ecosystem is a potential threat leading to increased mobility of MNPs in the environment.

Trophic transfer of Cu nanoparticles in a simulated aquatic food chain.

The goal of the current study was to quantify the trophic transfer of copper nanoparticles (CuNPs) in a food chain consisting of the microalga Pseudokirchneriella subcapitata as the representative of primary producer, the grazer Daphnia magna, and the omnivorous mysid Limnomysis benedeni. To quantify the size and number concentration of CuNPs in the biota, tissue extraction with tetramethylammonium hydroxide (TMAH) was performed and quantification was done by single particle inductively coupled plasma mass spectrometry (sp-ICP-MS). The bioconcentration factor (BCF) of the test species for CuNPs varied between 102 - 103 L/kg dry weight when expressing the internal concentration on a mass basis, which was lower than BCF values reported for Cu2+ (103 - 104 L/kg dry weight). The particle size of CuNPs determined by sp-ICP-MS ranged from 22 to 40 nm in the species. No significant changes in the particle size were measured throughout the food chain. Moreover, the measured number of CuNPs in each trophic level was in the order of 1013 particles/kg wet weight. The calculated trophic transfer factor (mass concentration basis) was > 1. This indicates biomagnification of particulate Cu from P. subcapitata to L. benedeni. It was also found that the uptake of particulate Cu (based on the particle number concentration) was mainly from the dietary route rather than from direct aqueous exposure. Furthermore, dietary exposure to CuNPs had a significant effect on the feeding rate of mysid during their transfer from daphnia to mysid and from alga through daphnia to mysid. This work emphasizes the importance of tracing the particulate fraction of metal-based engineered nanoparticles when studying their uptake and trophic transfer.

Gold nanoparticles decorated with ovalbumin-derived epitopes: effect of shape and size on T-cell immune responses.

Gold nanoparticles (GNPs) can be manufactured in various shapes, and their size is programmable, which permits the study of the effects imposed by these parameters on biological processes. However, there is currently no clear evidence that a certain shape or size is beneficial. To address this issue, we have utilised GNPs and gold nanorods (GNRs) functionalised with model epitopes derived from chicken ovalbumin (OVA257-264 and OVA323-339). By using two distinct epitopes, it was possible to draw conclusions regarding the impact of nanoparticle shape and size on different aspects of the immune response. Our findings indicate that the peptide amphiphile-coated GNPs and GNRs are a safe and versatile epitope-presenting system. Smaller GNPs (∼15 nm in diameter) induce significantly less intense T-cell responses. Furthermore, effective antigen presentation via MHC-I was observed for larger spherical particles (∼40 nm in diameter), and to a lesser extent for rod-like particles (40 by 15 nm). At the same time, antigen presentation via MHC-II strongly correlated with the cellular uptake, with smaller GNPs being the least efficient. We believe these findings will have implications for vaccine development, and lead to a better understanding of cellular uptake and antigen egress from lysosomes into the cytosol.

Chemical composition and particle size influence the toxicity of nanoscale plastic debris and their co-occurring benzo(α)pyrene in the model aquatic organisms Daphnia magna and Danio rerio.

Little is known about how particle chemical composition and size might influence the toxicity of nanoscale plastic debris (NPD) and their co-occurring chemicals. Herein, we investigate the toxicity of 3 × 1010 particles/L polyethylene (PE, 50 nm), polypropylene (PP, 50 nm), polystyrene (PS, 200 and 600 nm), and polyvinyl chloride (PVC, 200 nm) NPD and their co-occurring benzo(a)pyrene (BaP) to Daphnia magna and Danio rerio. During the 21 days of exposure to PE 50 nm and PS 200 nm, the number of broods produced by D. magna decreased compared to other treatments. Exposure to BaP alone did not produce any effects on the reproduction of the daphnids, however, the mixture of BaP with PS (200 or 600 nm) or with PE (50 nm) reduced the number of broods. Exposure of D. rerio embryos to PE 50 nm, PS 200 nm, and PS 600 nm led to a delay in the hatching. The presence of PS 200 nm and PVC 200 nm eliminated the effects of BaP on the hatching rate of zebrafish. Our findings suggest that data generated for the toxicity of one type of NPD, e.g. PVC or PS may not be extrapolated to other types of NPD.

The Differences between the Effects of a Nanoformulation and a Conventional Form of Atrazine to Lettuce: Physiological Responses, Defense Mechanisms, and Nutrient Displacement.

The rapid development of nanotechnology influences the developments within the agro-sector. An example is provided by the production of nanoenabled pesticides with the intention to optimize the efficiency of the pesticides. At the same time, it is important to collect information on the unintended and unwanted adverse effects of emerging nanopesticides on nontarget plants. Currently, this information is limited. In the present study, we compared the effects of a nanoformulation of atrazine (NPATZ) and the nonencapsulated atrazine formulation (ATZ) on physiological responses, defense mechanisms, and nutrient displacement in lettuce over time with the applied concentrations ranging from 0.3 to 3 mg atrazine per kg soil. Our results revealed that both NPATZ and ATZ induced significant decreases in plant biomass, chlorophyll content, and protein content. Additionally, exposure to NPATZ and ATZ caused oxidative stress to the lettuce plant and significantly elevated the activities of the tested ROS scavenger enzymes in plant tissues. These results indicate that NPATZ and ATZ cause distinct adverse impacts on lettuce plants. When comparing the adverse effects in plants after exposure to NPATZ and ATZ, no obvious differences in plant biomass and chlorophyll content were observed between NPATZ and ATZ treatments at the same exposure concentration regardless of exposure duration. An enhanced efficiency of the active ingredient of the nanopesticide as compared to the conventional formulation was observed after long-term exposure to the high concentration of NPATZ, as it induced higher impacts on plants in terms of the end points of the contents of protein, superoxide anion (O2̇-), and MDA, and the activities of stress-related enzymes as compared to the same concentration of ATZ. Furthermore, exposure to both NPATZ and ATZ disrupted the uptake of mineral nutrients in plants, and the differences in the displacement of nutrients between the NPATZ and ATZ treatments depended on the element type, plant organ, exposure concentration, and time. Overall, the application dose of a nanopesticide should balance their increased herbicidal efficiency with the long-term adverse effects in order to maximize the desired impact while minimizing adverse impacts; only then will we be able to understand the potential impact of nanopesticides on the environment.

Surface Functionalization of Graphene-Based Materials: Biological Behavior, Toxicology, and Safe-By-Design Aspects.

The increasing exploitation of graphene-based materials (GBMs) is driven by their unique properties and structures, which ignite the imagination of scientists and engineers. At the same time, the very properties that make them so useful for applications lead to growing concerns regarding their potential impacts on human health and the environment. Since GBMs are inert to reaction, various attempts of surface functionalization are made to make them reactive. Herein, surface functionalization of GBMs, including those intentionally designed for specific applications, as well as those unintentionally acquired (e.g., protein corona formation) from the environment and biota, are reviewed through the lenses of nanotoxicity and design of safe materials (safe-by-design). Uptake and toxicity of functionalized GBMs and the underlying mechanisms are discussed and linked with the surface functionalization. Computational tools that can predict the interaction of GBMs behavior with their toxicity are discussed. A concise framing of current knowledge and key features of GBMs to be controlled for safe and sustainable applications are provided for the community.

Growing Rice (Oryza sativa) Aerobically Reduces Phytotoxicity, Uptake, and Transformation of CeO2 Nanoparticles.

This study compared the impact and uptake of root-administered CeO2 nanoparticles (NPs) in rice growing under flooded and aerobic soil conditions, which are two water regimes commonly used for rice cultivation. CeO2 NPs at 100 mg/kg improved photosynthesis and plant growth by reducing the oxidative damage and enhancing plant tolerance to stress, while a higher concentration (500 mg/kg) of CeO2 NPs negatively affected plant growth. More significant effects were observed under the flooded condition than under the aerobic condition. CeO2 NPs of 100 and 500 mg/kg resulted in 78% and 70% higher accumulation of Ce in shoots under the flooded condition compared to the aerobic condition. CeO2 NPs partially transformed to Ce(III) species in soils and plants under both conditions. A higher extent of transformation under the flooded condition, which was partly attributed to the lower soil pH and redox potential under the flooded condition, leads to higher plant uptake of Ce. A higher extent of transformation in rhizosphere soil was observed. A higher plant transpiration rate (TR) under flooded conditions resulted in a higher accumulation of CeO2 species in shoots. This study, for the first time, reported that water regimes influenced the biotransformation of CeO2 NPs and their uptake and impact in rice plants.

Characteristics and spatial distribution of microplastics in the lower Ganga River water and sediment.

Although India is one of the major plastic-waste-generating countries, few studies have been conducted on microplastics (MPs) in freshwater systems that are key contributors to oceans. The current study explores MPs in sediments and water that were collected at five major cities across the Ganga River. MPs number and mass density range in sediment were found to be 17 to 36 items/kg dry weight (d.w.) and 10 to 45 mg/kg d.w. of sediments, respectively, while in the water sample, they were 380 to 684 items/1000 m3 and 143 to 340 mg/1000 m3, respectively. Overall, white color and film-shaped MPs were the major contributors in all samples. MPs of 2.5-5 mm size contributed to a greater number and mass as compared to other fractions. Polyethylene was found to be a widely distributed plastic-type reflecting its high usability.

Impact of long-term storage of various redox-sensitive supported nanocomposites on their application in removal of dyes from wastewater: Mechanisms delineation through spectroscopic investigations.

For the prevention of freshwater reservoirs from contamination through industrial effluents, eco-friendly adsorbents with minimal aging impact are required. Here, redox-sensitive nanoscale zero-valent iron(nZVI) particles were supported on four different surfaces with varying bentonite(B)/charcoal(C) ratio to mimic layered and porous surfaces. Different dyes, i.e. rhodamine-B(RB) and methylene blue(MB) were reacted with redox-sensitive supported nZVI composites, and degradation mechanisms were delineated using FT-IR spectroscopic analysis of reaction precipitates. A 300-day exposure to open-air was provided to the composites to comparatively evaluate the impact of aging on their reactivity for dyes in wastewater. Results interpret that dyes removal was a combination of different interfacial chemical processes, i.e., reduction or organic degradation probably through Fenton like processes, along with sorption. These mechanisms were found to be surface dependent, i.e., nZVI on charcoal enriched porous surfaces, degrade dyes through organic degradation while on layered clay surfaces, MB gets removed through reduction with limited and slower RB removal. Nanocomposites show a minimal impact of aging with removal capacities >100 mg/g for BC-1/3-nZVI and C-nZVI for MB and 50-75 mg/g for RB with significant removal in wastewater. Overall, the study concludes C-nZVI and novel BC-1/3-nZVI as two efficient dye adsorbents with minimal aging impact.

Application of Zn/Al layered double hydroxides for the removal of nano-scale plastic debris from aqueous systems.

Nano-scale plastic debris (NPDs) are emerging as potential contaminants as they can be easily ingested by aquatic organisms and carry many pollutants in the environment. This study is aimed to remove NPDs from aqueous environment for the first time by using eco-friendly adsorption techniques. Initially, the interaction between NPDs and synthesized Zn-Al layered double hydroxide (LDH) was confirmed by pH titration of Zn-Al LDH against NPDs at varying mass ratio (50:1 to 50:7) and FTIR analysis for both before and after 2 h of contact time. Fast removal was observed in deionized water and synthetic freshwater with maximum sorption capacity (Qmax) of 164.49 mg/g,162.62 mg/g, respectively, according to Sips isotherm. Whereas, removal was least in synthetic hard water having a Qmax value of 53 mg/g. For 2 mM concentration of SO42- and PO43-, the adsorption capacity significantly decreased to 2%. The removal efficiency was found 100 % at pH 4, while at pH 9, it reached 37 % due to increased competitive binding and destabilization of LDH under alkaline conditions. The process of sorption was spontaneous in different types of water studied. The study reveals that Zn-Al LDH can be used as potential adsorbent for the removal of NPDs from freshwater systems.

Accurate quantification of TiO2 nanoparticles in commercial sunscreens using standard materials and orthogonal particle sizing methods for verification.

The implementation and enforcement of product labeling obligation as required, for example, by the cosmetic product regulation, needs simple and precise validated analytical methods. This also applies to the analysis of nanoparticles in products such as cosmetics. However, the provision of such methods is often hampered by inaccurate sizing due to unwanted nanoparticle changes, interference of matrix components with sizing and interactions between nanoparticles and analytical instrumentation. It is, therefore, necessary to develop appropriate sample preparation methods that preserve NP properties and reduce or remove matrix compounds that interfere with sizing. Further, accurate particle size analysis of samples containing unknown and possibly multiple nanoparticulate constituents is needed. In this study, we evaluated three sample preparation methods to identify and quantify TiO2 nanoparticles in sunscreens. Specifically, we used a combination of ultracentrifugation and hexane washing, thermal destruction of the matrix, and surfactant assisted particle extraction. The method accuracy was assessed by two internal reference samples: pristine TiO2 nanoparticles (NM104) and similar TiO2 nanoparticles dispersed in a sunscreen matrix. The PSDs were determined using an asymmetrical flow field-flow fractionation hyphenated with multi-angle light scattering and inductively coupled plasma-mass spectroscopy. Particle sizing was based on size calibration of the particle retention time in the AF4. Computation of radius of gyration from MALS data was used as an orthogonal particle sizing approach to verify ideal elution and particle size data from the AF4 calibration. Among the three tested sample preparation methods surfactant assisted particle extraction revealed TiO2 nanoparticle recoveries of above 90% and no increase in particle size due to sample preparation was observed. Finally, the sample preparation methods were applied to two commercial sunscreen samples revealing the existence of TiO2-NP < 100 nm. Conclusively, the surfactant assisted particle extraction method can provide valid data for TiO2-NPs in sunscreen and possibly for cosmetic samples of similar matrix.

Graphene Oxide-Induced pH Alteration, Iron Overload, and Subsequent Oxidative Damage in Rice (Oryza sativa L.): A New Mechanism of Nanomaterial Phytotoxicity.

The mechanism of graphene-based nanomaterial (GBM)-induced phytotoxicity and its association with the GBM physicochemical properties are not yet fully understood. The present study compared the effects of graphene oxide (GO) and reduced GO (rGO) on rice seedling growth under hydroponic conditions for 3 weeks. GO at 100 and 250 mg/L reduced shoot biomass (by 25 and 34%, respectively) and shoot elongation (by 17 and 43%, respectively) and caused oxidative damage, while rGO exhibited no overt effect except for the enhancement of the antioxidant enzyme activities, suggesting that the surface oxygen content is a critical factor affecting the biological impacts of GBMs. GO treatments (100 and 250 mg/L) enhanced the iron (Fe) translocation and caused excessive Fe accumulation in shoots (2.2 and 3.6 times higher than control), which was found to be the main reason for the oxidative damage in shoots. GO-induced acidification of the nutrient solution was the main driver for the Fe overload in plants. In addition to the antioxidant regulators, the plants triggered other pathways to defend against the Fe toxicity via downregulation of the Fe transport associated metabolites (mainly coumarins and flavonoids). Plant root exudates facilitated the reduction of toxic GO to nontoxic rGO, acting as another route for plant adaption to GO-induced phytotoxicity. This study provides new insights into the mechanism of the phytotoxicity of GBMs. It also provides implications for the agricultural application of GBM that the impacts of GBMs on the uptake of multiple nutrients in plants should be assessed simultaneously and reduced forms of GBMs are preferential to avoid toxicity.

Effect of the irrigation water type and other environmental parameters on CeO2 nanopesticide-clay colloid interactions.

In this work, the stability and aggregation behaviour of CeO2 nanoparticles (NPs) was investigated to predict their fate in the agricultural environment. For this, the aggregation kinetics of CeO2 NPs was studied under varying pH, ionic strength (IS), dissolved organic matter (DOM) and carbonate concentrations in the presence of clay. Furthermore, different types of irrigation water have been used to check the fate of CeO2 nanoparticles (NPs) in complex aqueous matrices. The results show that critical coagulation concentration (CCC) values obtained for CeO2 NPs, i.e. 26.5 mM and 7.9 mM for NaCl and CaCl2 respectively, drastically decreased to 16.2 mM and 1.87 mM in the presence of bentonite clay colloids, which may lead to their deposition within the soil matrix. However, the presence of bicarbonate ions (0.1-2 mM) along with DOM (1-20 mg L-1) may result in their stabilization and co-transport of CeO2 NPs with clay in water bodies having low ionic strength. It was also observed that the negative charge of a bentonite clay suspension was completely reversed with an increase in CeO2 concentration by 37.5 times. The critical charge reversal concentration value was 284.4 mg L-1 in Milli-Q water whereas values were observed to be 680 mg L-1 in synthetic-soft water, followed by natural river water (867 mg L-1) and synthetic-hard water (910 mg L-1). The synergistic effect of temperature and ionic strength was observed on the aggregation behaviour of CeO2 NPs in environmental water samples of varying composition.

Interaction of zero valent copper nanoparticles with algal cells under simulated natural conditions: Particle dissolution kinetics, uptake and heteroaggregation.

Some metal-based engineered nanoparticles (ENPs) undergo fast dissolution and/or aggregation when they are released in the environment. The underlying processes are controlled by psychochemical/biological parameters of the environment and the properties of the particles. In this study, we investigated the interaction between algal cells and zero valent copper nanoparticles (Cu0-ENPs) to elucidate how the cells influence the dissolution and aggregation kinetics of the particles and how these kinetics influence the cellular uptake of Cu. Our finding showed that the concentration of dissolved Cu ([Cu]dissolved) in the supernatant of the culture media without algal cells was higher than the [Cu]dissolved in the media with algal cells. In the absence of the cells, dissolved organic matter (DOC) increased the dissolution of the particle due to increasing the stability of the particles against aggregation, thus increasing the available surface area. In the presence of algae, Cu0-ENPs heteroaggregated with the cells. Thus, the available surface area decreased over time and this resulted in a low dissolution rate of the particles. The DOC corona on the surface of the particles increased the heteroaggregation of the particles with the cells and decreases the uptake of the particles. Our findings showed that microorganisms influence the fate of ENPs in the environment, and they do so by modifying the dissolution and aggregation kinetics of the Cu0-ENPs.

Heavy metals' concentration in sediment, shrimp and two fish species from the northwest Persian Gulf.

The concentrations of heavy metals (cadmium (Cd), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn)) were measured in hepatopancreas and muscle of a commercial shrimp (Metapenaeus affinis), in the muscle, liver and gills of two fish species (Thryssa vitrirostris and Johnius belangerii) and in the sediment samples taken from the mouth of the Arvand river, Meleh estuary and Musa estuary in the northeast Persian Gulf. Concentration of heavy metals varied depending on different tissues, species and sampling sites. Liver of fish and hepatopancreas of shrimp exhibited higher metals' concentration than the other tissues. Generally, in the mouth of the Arvand river, the highest concentration of metals was found in benthic species; while in the mouth of Musa estuary, the highest level of the metals was found in pelagic fish species. Bioaccumulation factors were observed to follow the order: J. belangerii-liver-Cd > T. vitrirostris-liver-Pb > M. affinis-hepatopancreas-Zn >M. affinis-hepatopancreas-Cu >M. affinis- hepatopancreas-Ni. The analysed heavy metals were found in sediment samples at mean concentration in the sediment quality guideline proposed by National Oceanic and Atmospheric Administration (NOAA) and Regional Organization for the Protection of The Marine Environment (ROPME), except for Ni concentration in some cases.

The effect of primary producers of experimental aquatic food chains on mercury and PCB153 biomagnification.

The biomagnification of mercury and PCB153 was studied in experimental aquatic food chains involving three species of phytoplankton, one species of zooplankton and one species of fish. The phytoplankton species Ceratium furca, Ceratium tripos and Chaetoceros brevis were exposed to 0, 0.2, 0.5, 1.0 and 2.0 mg/l of Hg and 0, 0.5 and 2.0 mg/kg of PCB 153. Subsequently, each species was fed to the zooplankton Daphnia hyaline, which was then used as food for the fish Liza abu. The results indicated biomagnification of Hg and PCB153 in all three chains. Highest concentration of mercury was found in C. brevis and the highest concentration of PCB153 was observed in C. tripos. Accordingly, highest concentration of Hg and PCB 153 was found in D. hyaline and in the liver of L. abu belonging to food chains started from Chaetoceros brevis and Ceratium tripos respectively.