Impacts of foliar exposure to multi-walled carbon nanotubes on physiological and molecular traits of Salvia verticillata L., as a medicinal plant

Carbon-based nanomaterials as inducers of biocompounds in plants: Potential risks and perspectives

Biocompounds are metabolites synthesized by plants, with clinically proven capacity in preventing and treating degenerative diseases in humans. Carbon-based nanomaterials (CNMs) are atomic structures that assume different hybridization and shape. Due to the reactive property, CNMs can induce the synthesis of metabolites, such as biocompounds in cells and various plant species, by generating reactive oxygen species (ROS). In response, plants positively or negatively regulate the expression of various families of genes and enzymes involved in physiological and metabolomic pathways of plants, such as carbon and nitrogen metabolism, which are directly involved in plant development and growth. Likewise, ROS can modulate the expression of enzymes and genes related to the adaptation of plants to stress, such as the glutathione ascorbate cycle, the shikimic acid, and phenylpropanoid pathways, from which the largest amount of biocompounds in plants are derived. This document exposes the ability of three CNMs (fullerene, graphene, and carbon nanotubes) to positively or negatively regulate the activity of enzymes and genes involved in various plant species' primary and secondary metabolism. The mechanism of action of CNMs on the production of biocompounds and the effect of the translocation of CNMs on the growth and content of primary metabolites in plants are described. Adverse effects of CNMs on plants, prospects, and possible risks involved are also discussed. The use of CNMs as inducers of biocompounds in plants could have implications and relevance for human health, crop quality, and plant adaptation and resistance to biotic and abiotic stress.

Carbon nanotubes in plant dynamics: Unravelling multifaceted roles and phytotoxic implications

Carbon nanotubes (CNTs) have emerged as a promising frontier in plant science owing to their unique physicochemical properties and versatile applications. CNTs enhance stress tolerance by improving water dynamics and nutrient uptake and activating defence mechanisms against abiotic and biotic stresses. They can be taken up by roots and translocated within the plant, impacting water retention, nutrient assimilation, and photosynthesis. CNTs have shown promise in modulating plant-microbe interactions, influencing symbiotic relationships and mitigating the detrimental effects of phytopathogens. CNTs have demonstrated the ability to modulate gene expression in plants, offering a powerful tool for targeted genetic modifications. The integration of CNTs as sensing elements in plants has opened new avenues for real-time monitoring of environmental conditions and early detection of stress-induced changes. In the realm of agrochemicals, CNTs have been explored for their potential as carriers for targeted delivery of nutrients, pesticides, and other bioactive compounds. CNTs have the potential to demonstrate phytotoxic effects, detrimentally influencing both the growth and developmental processes of plants. Phytotoxicity is characterized by induction of oxidative stress, impairment of cellular integrity, disruption of photosynthetic processes, perturbation of nutrient homeostasis, and alterations in gene expression. This review aims to provide a comprehensive overview of the current state of knowledge regarding the multifaceted roles of CNTs in plant physiology, emphasizing their potential applications and addressing the existing challenges in translating this knowledge into sustainable agricultural practices.

Nanovehicles for melatonin: a new journey for agriculture

The important role of melatonin in plant growth and metabolism together with recent advances in the potential use of nanomaterials have opened up interesting applications in agriculture. Various nanovehicles have been explored as melatonin carriers in animals, and it is now important to explore their application in plants. Recent findings have substantiated the use of silicon and chitosan nanoparticles (NPs) in targeting melatonin to plant tissues. Although melatonin is an amphipathic molecule, nanocarriers can accelerate its uptake and transport to various plant organs, thereby relieving stress and improving plant shelf-life in the post-harvest stages. We review the scope and biosafety concerns of various nanomaterials to devise novel methods for melatonin application in crops and post-harvest products.

Integrative effects of phytohormones in the phenolic acids production in Salvia verticillata L. under multi-walled carbon nanotubes and methyl jasmonate elicitation

Salvia verticillata L. is a well-known herb rich in rosmarinic acid (RA) and with therapeutic values. To better understand the possible roles of phytohormones in the production of phenolic acids in S. verticillata, in this work, we investigated some physiological and biochemical responses of the species to methyl jasmonate (MJ) and multi-walled carbon nanotubes (MWCNTs) as two effective elicitors. The leaves were sprayed with aqueous solutions containing 100 mg L-1 MWCNTs and 100 µM MJ and then harvested during interval times of exposure up to 96 h. The level of abscisic acid, as the first effective phytohormone, was altered in the leaves in response to MJ and MWCNTs elicitation (2.26- and 3.06-fold more than the control, respectively), followed by significant increases (P ˂ 0.05) detected in jasmonic acid and salicylic acid contents up to 8 h after exposure. Obtained data revealed that simultaneously with changes in phytohormone profiles, significant (P ˂ 0.05) rises were observed in the content of H2O2 (8.85- and 9.74-folds of control), and the amount of lipid peroxidation (10.18- and 17.01-folds of control) during the initial times after exposure to MJ and MWCNTs, respectively. Later, the content of phenolic acids increased in the elicited leaves due to changes in the transcription levels of key enzymes involved in their biosynthesis pathways, so 2.71- and 11.52-fold enhances observed in the RA content of the leaves after exposure to MJ and MWCNTs, respectively. It is reasonable to conclude that putative linkages between changes in some phytohormone pools lead to the accumulation of phenolic acids in the leaves of S. verticillata under elicitation. Overall, the current findings help us improve our understanding of the signal transduction pathways of the applied stimuli that led to enhanced secondary metabolite production in medicinal plants.

Elucidating the efficacy of functionalized multi-walled carbon nanotube in the biogenesis of L-Dopa and antioxidant metabolites in cell cultures of Hybanthus enneaspermus

Hybanthus enneaspermus (L.)F.Muell. is a highly indispensable medicinal herb yielding L-Dopa, deemed the gold standard drug among the therapeutic options for Parkinson's disease. This investigation is the first attempt to evaluate the eliciting influence of carboxylic acid functionalized multi-walled carbon nanotube (MWCNT-COOH) on the biosynthesis of L-Dopa and on biomass aggregation and antioxidant metabolites in H. enneaspermus cell suspension cultures. Suspension cells were accomplished from friable calli generated from the nodal segments of H. enneaspermus in Murashige and Skoog (MS) liquid medium infused with 2 mg L-1 2, 4-Dichlorophenoxyacetic acid (2, 4-D), and 0.3 mg L-1meta-Topolin (mT). The influence of MWCNTs on L-Dopa synthesis, biomass accumulation, and biochemical parameters was examined on the basis of the exposure time and in a concentration-dependent manner of MWCNTs. The inclusion of 30 mg L-1 MWCNTs increased the biomass and the L-Dopa level by 2.00 and 16.37-folds, respectively, compared with that of the control. Furthermore, the effect of MWCNTs on physiological parameters such as catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPX), ascorbate peroxidase (APX), hydrogen peroxide (H2O2), malondialdehyde (MDA) content, 2-diphenylpicrylhydrazyl (DPPH), and ferric-reducing ability of plasma (FRAP) was examined over the elicited cells. Among the antioxidant enzymatic activities, CAT enhanced 8.0 fold compared with that of the control. MDA and DPPH content enhanced 2.60 and 1.12 folds, respectively, compared with that of the control. The current study showed that MWCNTs offer new possibilities for their usage over in vitro by acting as potential innovative plant metabolite elicitors and stress-protecting entities.

Nitro-oxidative response to internalized multi-walled carbon nanotubes in Brassica napus and Solanum lycopersicum

In addition to their beneficial effects on plant physiology, multi-walled carbon nanotubes (MWCNTs) are harmful to plants in elevated concentrations. This study compared the effects of two doses of MWCNT (10 and 80 mg/L) in Brassica napus and Solanum lycopersicum seedlings focusing on nitro-oxidative processes. The presence of MWCNTs was detectable in the root and hypocotyl of both species. Additionally, transmission electron microscopy analysis revealed that MWCNTs are heavily transformed within the root cells forming large aggregates. The uptake of MWCNTs negatively affected root viability and root cell proliferation of both species, but more intense toxicity was observed in S. lycopersicum compared to B. napus. The presence of MWCNT triggered more intense protein carbonylation in the relative sensitive S. lycopersicum, where increased hydrogen peroxide levels were observed. Moreover, MWCNT exposure increased the level of physiological protein tyrosine nitration which was more intense in S. lycopersicum where notable peroxynitrite accumulation occurred. These suggest for the first time that MWCNT triggers secondary nitro-oxidative stress which contributes to its toxicity. Moreover, the results indicate that the extent of the nitro-oxidative processes is associated with the extent of MWCNT toxicity.

Physiological and omics-based insights for underpinning the molecular regulation of secondary metabolite production in medicinal plants: UV stress resilience

Despite complex phytoconstituents, the commercial potential of medicinal plants under ultraviolet (UV) stress environment hasn't been fully comprehended. Due to sessile nature, these plants are constantly exposed to damaging radiation, which disturbs their natural physiological and biochemical processes. To combat with UV stress, plants synthesized several small organic molecules (natural products of low molecular mass like alkaloids, terpenoids, flavonoids and phenolics, etc.) known as plant secondary metabolites (PSMs) that come into play to counteract the adverse effect of stress. Plants adapted a stress response by organizing the expression of several genes, enzymes, transcription factors, and proteins involved in the synthesis of chemical substances and by making the signaling cascade (a series of chemical reactions induced by a stimulus within a biological cell) flexible to boost the defensive response. To neutralize UV exposure, secondary metabolites and their signaling network regulate cellular processes at the molecular level. Conventional breeding methods are time-consuming and difficult to reveal the molecular pattern of the stress tolerance medicinal plants. Acquiring in-depth knowledge of the molecular drivers behind the defensive mechanism of medicinal plants against UV radiation would yield advantages (economical and biological) that will bring prosperity to the burgeoning world's population. Thus, this review article emphasized the comprehensive information and clues to identify several potential genes, transcription factors (TFs), proteins, biosynthetic pathways, and biological networks which are involved in resilience mechanism under UV stress in medicinal plants of high-altitudes.

Root Exposure of Graphitic Carbon Nitride (g-C3N4) Modulates Metabolite Profile and Endophytic Bacterial Community to Alleviate Cadmium- and Arsenate-Induced Phytotoxicity to Rice (Oryza sativa L.)

To investigate the mechanisms by which g-C3N4 alleviates metal(loid)-induced phytotoxicity, rice seedlings were exposed to 100 and 250 mg/kg graphitic carbon nitride (g-C3N4) with or without coexposure to 10 mg/kg Cd and 50 mg/kg As for 30 days. Treatment with 250 mg/kg g-C3N4 significantly increased shoot and root fresh weight by 22.4-29.9%, reduced Cd and As accumulations in rice tissues by 20.6-26.6%, and elevated the content of essential nutrients (e.g., K, S, Mg, Cu, and Zn) compared to untreated controls. High-throughput sequencing showed that g-C3N4 treatment increased the proportion of plant-growth-promoting endophytic bacteria, including Streptomyces, Saccharimonadales, and Thermosporothrix, by 0.5-3.30-fold; these groups are known to be important to plant nutrient assimilation, as well as metal(loid) resistance and bioremediation. In addition, the population of Deinococcus was decreased by 72.3%; this genus is known to induce biotransformation As(V) to As(III). Metabolomics analyses highlighted differentially expressed metabolites (DEMs) involved in the metabolism of tyrosine metabolism, pyrimidines, and purines, as well as phenylpropanoid biosynthesis related to Cd/As-induced phytotoxicity. In the phenylpropanoid biosynthesis pathway, the increased expression of 4-coumarate (1.13-fold) and sinapyl alcohol (1.26-fold) triggered by g-C3N4 coexposure with Cd or As played a critical role in promoting plant growth and enhancing rice resistance against metal(loid) stresses. Our findings demonstrate the potential of g-C3N4 to enhance plant growth and minimize the Cd/As-induced toxicity in rice and provide a promising nanoenabled strategy for remediating heavy metal(loid)-contaminated soil.

Carboxylic acid-functionalized multiwalled carbon nanotubes (COOH-MWCNTs) improved production of atropine in callus of Datura inoxia by influencing metabolism, gene regulation, and DNA cytosine methylation; an in vitro biological assessment

Atropine is a well-known tropane alkaloid commonly employed in medicine class called anticholinergics. This study intends to address biochemical and molecular responses of Datura inoxia calluses to fortifying culture medium with carboxylic acid-functionalized multi-walled carbon nanotubes (COOH-MWCNTs). The application of MWCNTs influenced callogenesis performance and biomass in a dose-dependent manner. The MWCNT at 5 mgL-1 resulted in the highest biomass of calluses by 57%. While, MWCNTs at high concentrations were accompanied by cytotoxicity. On the other hand, MWCNTs at concentrations above 100 mgL-1 exhibited cytotoxicity, decreased callogenesis performance, and reduced Atropine biosynthesis. The MWCNTs increased the activity of phenylalanine ammonia-lyase (PAL) and catalase enzymes. The concentrations of proline and soluble phenols displayed upward trends in response to using MWCNTs. According to the HPLC assessment, enriching culture medium with MWCNTs at 5 mgL-1 elicited Atropine production in calluses by 64%. The quantitative PCR assessment referred to the upregulation in the transcription of the PAL gene. The expression of ornithine decarboxylase (ODC) and putrescine N-methyltransferase 1 (PMT) genes were also upregulated in calluses cultured in a medium supplemented with MWCNTs. Methylation Sensitive Amplification Polymorphism (MSAP) technique indicated that employing MWCNTs altered the DNA methylation profile, reflecting epigenetic modification. Overall, engineering plant cells with MWCNTs as a nano-elicitor can be suggested for large-scale synthesis of industrially-valuable secondary metabolites.

Use of titanium dioxide doped multi-wall carbon nanotubes as promoter for the growth, biochemical indices of Sesamum indicum L. under heat stress conditions

The behavior of multi-walled carbon nanotubes (MWCNTs) and titanium dioxide nanoparticles (TiO2 NPs) as plant growth enhancers was still unclear; however, in this study, the effects of MWCNTs, TiO2NPs, 5%TiO2@MWCNTs, 10%TiO2@MWCNTs and 15%TiO2@MWCNTs on physical and biochemical contents in Sesamum indicum L. under heat stress conditions were studied. The content of malondialdehyde (MDA) and hydrogen peroxide (H2O2) concentrations were reduced by the spraying MWCNTs and TiO2 NPs on plants. The hydrogen peroxide (H2O2) content was reduced by 49.02% in plants treated with 15%TiO2@MWCNTs while 42.14% reduction was found in plants treated with 10%TiO2@MWCNTs. The proportion of oil and the peroxidase enzyme activity in plants treated with 15%TiO2@MWCNTs were increased by 48.99%, for the oil content, and 2.39 times for POD activity respected to the stressed plants. The proportion of unsaturated fatty acids increased in plants treated with 15%TiO2@MWCNTs, 10%TiO2@MWCNTs and TiO2 NPs by 2.7, 2.52, and 2.09 times, respectively, greater than the control of the Shandweel-3 variety. Finally, plants treated with 15%TiO2@MWCNTs showed increases in seed yield and weight 1000-seeds by 4.42 and 1.67 times, respectively. These findings suggest that TiO2@MWCNTs more effective than separated MWCNTs and TiO2 NPs in improve plant growth. In addition, the cultivar Shandweel-3 showed an improvement in growth indicators more than the Giza-32 cultivar.

Effects of foliar application of single-walled carbon nanotubes on carbohydrate metabolism in crabapple plants

Carbon nanotubes (CNTs) regulate growth in many plants. Carbohydrates provide energy and carbon skeleton for cell growth. However, how CNTs influence plant carbohydrate metabolism remains largely unknown. For a comprehensive understanding the response of carbohydrate metabolism and accumulation in leaves of crabapple (Malus hupehensis Rehd) to single-walled carbon nanotubes (SWCNTs), the expression of key enzymes and genes involved in apple sugar metabolism was investigated. In this report, TEM showed that SWCNTs particles were absorbed in apple leaf. Foliar application of 10 and 20 mg/L SWCNTs promoted chlorophyll content, net photosynthetic rate, stomatal conductance and transpiration rate. SWCNTs up-regulate the activity of aldose-6-phosphate reductase (A6PR), accompanied by increased concentration of photosynthetic assimilate‒sorbitol. However, the activities of sucrose phosphate synthase (SPS) and the accumulation of sucrose did not change significantly in SWCNTs-sprayed apple leaves compared with the control. In addition, the activities of photoassimilate degradation enzyme (sorbitol dehydrogenase, SDH; sucrose synthase, SUSY; neutral invertase, NINV) and hexose degradation enzyme (fructokinase, FRK; hexokinase, HK) were higher in SWCNTs-treated apple leaves than that in the control leaves. Quantitative real-time polymerase chain reaction (qRT‒PCR) results indicated that the expression of genes associated with sugar metabolism changed significantly after SWCNTs application. Taken together, we propose that spraying apple leaves with 10 and 20 mg/L SWCNTs can improve photosynthetic activity and accelerate carbohydrate metabolism in apple leaves. Our results provide insight into understanding the biological effects of CNTs in plants and are valuable for continued use of SWCNTs in agri-nanotechnology.

The effects of multiwalled carbon nanotubes and Bacillus subtilis treatments on the salt tolerance of maize seedlings

Nanomaterials, including multiwalled carbon nanotubes (MWCNTs), have been recently applied in agriculture to improve stress resistance, leading to contradictory findings for antioxidant responses and mineral nutrient uptake. A pot experiment involving maize in low-salinity sandy loam soils was conducted with the application of different concentrations (0, 20, 50 mg/L) of MWCNTs and the growth-promoting rhizobacterium Bacillus subtilis (B. subtilis). The dose-dependent effects of MWCNTs were confirmed: 20 mg/L MWCNTs significantly promoted the accumulation of osmolytes in maize, particularly K⁺ in the leaves and roots, increased the leaf indoleacetic acid content, decreased the leaf abscisic acid content; but the above-mentioned promoting effects decreased significantly in 50 mg/L MWCNTs-treated plants. We observed a synergistic effect of the combined application of MWCNTs and B. subtilis on plant salt tolerance. The increased lipid peroxidation and antioxidant-like proline, peroxidase (POD), and catalase (CAT) activities suggested that MWCNTs induced oxidative stress in maize growing in low-salinity soils. B. subtilis reduced the oxidative stress caused by MWCNTs, as indicated by a lower content of malondialdehyde (MDA). The MWCNTs significantly increased the leaf Na⁺ content and leaf Na⁺/K⁺ ratio; however, when applied in combination with B. subtilis, the leaf Na⁺/K⁺ ratio decreased sharply to 69% and 44%, respectively, compared to those of the control (CK) group, the contents of which were partially regulated by abscisic acid and nitrate, according to the results of the structural equation model (SEM). Overall, the increased osmolytes and well-regulated Na⁺/K⁺ balance and transport in plants after the combined application of MWCNTs and B. subtilis reveal great potential for their use in combating abiotic stress.

Effect of different CO2 concentrations on biogas upgrading and nutrient removal by microalgae-fungi co-culture

Owing to the high carbon dioxide (CO₂)-fixation efficiency, microalgae-based technology has been widely used for biogas purification. The present study explored the effect of CO₂ concentration on biogas purification by an algal-fungal-bacterial symbiotic system. Two algal-fungal-bacterial symbiotic systems were cultivated to purify four simulated biogas samples with different CO₂ concentrations. The results showed that GR24, a synthetic analog of strigolactone, stimulated the growth of the algal-fungal-bacterial symbiotic system. The optimal CO₂ concentration for the purification of the simulated biogas was 45% (V/V), and the optimal symbiotic system was Chlorella vulgaris-Ganoderma lucidum-endophytic bacteria-GR24. The maximum chemical oxygen demand (COD; 82.61 ± 7.73%), total nitrogen (TN; 81.36 ± 7.97%), total phosphorus (TP; 85.69 ± 8.19), and CO₂ (69.23 ± 6.56%) removal efficiencies were detected with the addition of 10^-9 M GR24 to the C. vulgaris-G. lucidum-endophytic bacterial symbiotic system. These findings confirmed the effect of CO₂ concentration on the purification of biogas by the algal-bacterial symbiotic system. The study provides a theoretical basis for further research on the treatment of wastewater and biogas.

Preparation and application of nanostructured carbon from oil fly ash for growth promotion and improvement of agricultural crops with different doses

Application of carbon nanomaterials (CNMs) in agricultural production has piqued the interest of researchers. However, despite the enormous importance of CNMs in plant development, little is known about the effects of carbon nanoparticle (CNP) doses on plant physiological responses. Therefore, the aim of the current study was to check the effects of nanostructured carbon derived from oil fly ash (COFA), which was derived for the first time from high-energy ball-milling followed by a sonication process, on Phaseolus vulgaris L. and Cicer arietinum L. plants. We evaluated the plant physiological and biochemical parameters of the COFA-treated seedlings. Two different doses (4 mg L^-1 and 8 mg L^-1) of COFA and a control were studied. The results indicated that the germination rate (%), shoot length, root length, pod length, leaf area, fresh weight and dry weight were increased with the addition of COFA. Likewise, COFA increased the contents of chlorophyll pigments (Chla, Chlb, carotenoids), proteins, and carbohydrates in both species compared to the control. Finally, these findings showed that a COFA treatment at 4 mg L^-1 after ball milled-sonication in water (BMW4) constituted the best dose for growth and physiology. Our findings reveal that the novel strategy of COFA engineering led to a boost in the growth of Phaseolus vulgaris and Cicer arietinum. Our results have high potential for agricultural research and provide an impact on food security.

Multiwalled Carbon Nanotubes Alter the PSII Photochemistry, Photosystem-Related Gene Expressions, and Chloroplastic Antioxidant System in Zea mays under Copper Toxicity

A critical approach against copper (Cu) toxicity is the use of carbon nanomaterials (CNMs). However, the effect of CNMs on Cu toxicity-exposed chloroplasts is not clear. The photosynthetic, genetic, and biochemical effects of multiwalled carbon nanotubes (50-100-250 mg L^-1 CNT) were investigated under Cu stress (50-100 μM CuSO₄) in Zea mays chloroplasts. F_v/F_m and F_v/F_o were suppressed under stress. Stress altered the antioxidant system and the expression of psaA, psaB, psbA, and psbD. The chloroplastic activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione S-transferase (GST), and glutathione peroxidase (GPX) increased under CNT + stress, and those of hydrogen peroxide (H₂O₂) and lipid peroxidation decreased. CNTs were promoted to the maintenance of the redox state by regulating enzyme/non-enzyme activity/contents involved in the AsA-GSH cycle. Furthermore, CNTs inverted the negative effects of Cu by upregulating the transcriptions of photosystem-related genes. However, the high CNT concentration had adverse effects on the antioxidant capacity. CNT has great potential to confer tolerance by reducing Cu-induced damage and protecting the biochemical reactions of photosynthesis.

Pre-Harvest Application of Multi-Walled Carbon Nanotubes Improves the Antioxidant Capacity of ‘Flame Seedless’ Grapes during Storage

As a widely distributed fruit, grapes are susceptible to oxidative damage during storage and transportation, resulting in declining quality and commodity value. This study aimed to investigate the effects of preharvest application of different concentrations of multi-walled carbon nanotubes (MWCNTs) on the postharvest quality of ‘Flame Seedless’ grapes. The results showed that low-concentration (25 and 50 mg L−1) MWCNTs treatments maintained the comprehensive quality index, firmness, soluble sugar, titratable acid, pH value, and ascorbic acid (AsA) content of grapes. MWCNTs at 25 and 50 mg L−1 increased the activities of peroxidase (POD), catalase (CAT), superoxide dismutase (SOD), and ascorbic acid (APX). Furthermore, MWCNTs reduced the malondialdehyde (MDA) content and decreased the accumulation of excessive reactive oxygen species (ROS) in grape peel and pulp tissues. In addition, transmission electron microscopy (TEM) images demonstrated that MWCNTs were absorbed by parenchymal cells in the grape peel and pulp through the epidermal cell layer. MWCNTs with a specific concentration can be used as a new inducer for the biosynthesis of antioxidants to reduce oxidative damage in grapes during storage.

Carbon nanostructures: a comprehensive review of potential applications and toxic effects

There is no doubt that nanotechnology has revolutionized our life since the 1970s when it was first introduced. Nanomaterials have helped us to improve the current products and services we use. Among the different types of nanomaterials, the application of carbon-based nanomaterials in every aspect of our lives has rapidly grown over recent decades. This review discusses recent advances of those applications in distinct categories, including medical, industrial, and environmental applications. The first main section introduces nanomaterials, especially carbon-based nanomaterials. In the first section, we discussed medical applications, including medical biosensors, drug and gene delivery, cell and tissue labeling and imaging, tissue engineering, and the fight against bacterial and fungal infections. The next section discusses industrial applications, including agriculture, plastic, electronic, energy, and food industries. In addition, the environmental applications, including detection of air and water pollutions and removal of environmental pollutants, were vastly reviewed in the last section. In the conclusion section, we discussed challenges and future perspectives.

Engineering plants with carbon nanotubes: a sustainable agriculture approach

Sustainable agriculture is an important conception to meet the growing food demand of the global population. The increased need for adequate and safe food, as well as the ongoing ecological destruction associated with conventional agriculture practices are key global challenges. Nanomaterials are being developed in the agriculture sector to improve the growth and protection of crops. Among the various engineered nanomaterials, carbon nanotubes (CNTs) are one of the most promising carbon-based nanomaterials owing to their attractive physiochemical properties such as small size, high surface area, and superior mechanical and thermal strength, offering better opportunities for agriculture sector applications. This review provides basic information about CNTs, including their history; classification; and electrical, thermal, and mechanical properties, with a focus on their applications in the agriculture field. Furthermore, the mechanisms of the uptake and translocation of CNTs in plants and their defense mechanisms against environmental stresses are discussed. Finally, the major shortcomings, threats, and challenges of CNTs are assessed to provide a broad and clear view of the potential and future directions for CNT-based agriculture applications to achieve the goal of sustainability.

Nutrient and tetracycline removal from simulated biogas slurry and biogas upgrading by microalgae cultivation under different carbon nanotubes concentrations

The present study sought to determine the effects of multi-walled carbon nanotubes (MWCNTs) concentrations (0-10 mg L^-1) on tetracycline (TC) and biogas slurry nutrient removal by microalga Chlorella vulgaris cultivation. Treatments with 1 mg L^-1 MWCNTs yielded the maximum chlorophyll a content, dry weight, and algal density of 143.73 ± 3.11 μg L^-1, 0.81 ± 0.008 g L^-1, and 5.83×10⁷ cells L^-1, respectively, suggesting that 1 mg L^-1 MWCNTs could enhance microalgal growth performance and photosynthesis effectively. The highest removal rates of chemical oxygen demand, total phosphorus, total nitrogen, TC, and CO₂ under 1 mg L^-1 MWCNTs were 90.43 ± 5.15%, 78.12 ± 4.33%, 77.07 ± 4.12%, 89.64 ± 3.08%, and 64.26 ± 0.71%, respectively. These results elucidated that moderate MWCNTs concentrations might promote TC and nutrient removal by enhancing Chlorella vulgaris photosynthesis activity.

Multi-walled carbon nanotubes prevent high temperature-induced damage by activating the ascorbate-glutathione cycle in Paeonia ostii T. Hong et J. X. Zhang

Multi-walled carbon nanotubes (MWCNTs) are considered important nanomaterials with rapidly growing applications. They are inevitably released into the environment, which has attracted considerable attention for their potential threats to ecosystems. In this study, Paeonia ostii T. Hong et J. X. Zhang was exposed to MWCNTs at different concentrations under high temperature. The results showed that high temperature-induced P. ostii damage was prevented by MWCNTs, and 200 mg/L was the most effective concentration. First, MWCNTs prevented increases in reactive oxygen species, relative electrical conductivity and free proline content, and reduced decreases in SPAD, chlorophyll and carotenoid contents. Moreover, the ascorbate-glutathione (ASA-GSH) cycle was activated in response to the MWCNTs treatments, whereas the superoxide dismutase and catalase activities were inhibited. And the MWCNTs treatments also resulted in higher photosynthesis and more intact anatomical structures. Furthermore, the metabolome also confirmed that the ASA-GSH cycle played a critical role in P. ostii high-temperature tolerance, and other biological processes also responded to the MWCNTs treatments. Additionally, the genes involved in the P. ostii ASA-GSH cycle were highly expressed in response to the MWCNTs treatments. These results elucidated the beneficial role of MWCNTs in P. ostii growth under high temperature.

Use of Carbon Nanoparticles to Improve Soil Fertility, Crop Growth and Nutrient Uptake by Corn (Zea mays L.)

The use of carbon nanoparticles (CNPs) as a fertilizer synergist to enhance crop growth has attracted increasing interest. However, current understanding about plant growth and soil response to CNPs is limited. In the present study, we investigated the effects of CNPs at different application rates on soil properties, the plant growth and nutrient use efficiency (NUE) of corn (Zea mays L.) in two agricultural soils (Spodosol and Alfisol). The results showed that CNPs affected corn growth in a dose-dependent manner, augmenting and retarding growth at low and at high concentrations, respectively. The amendment at the optimal rate of 200 mg CNPs kg⁻¹ significantly enhanced corn growth as indicated by improved plant height, biomass yield, nutrient uptake and nutrient use efficiency, which could be explained by the higher availability of phosphorus and nitrogen in the amended soils. The application of CNPs largely stimulated soil urease activity irrespectively of soil types. However, the responses of dehydrogenase and phosphatase to CNPs were dose dependent; their activity significantly increased with the increasing application rates of CNPs up to 200 mg kg⁻¹ but declined at higher rates (>400 mg kg⁻¹). These findings have important implications in the field application of CNPs for enhancing nutrient use efficiency and crop production in tropical/subtropical regions.

Multi-Walled Carbon Nanotubes Improved Development during In Vitro Multiplication of Sugarcane (Saccharum spp.) in a Semi-Automated Bioreactor

Carbon nanotubes play an important role in plant biotechnology due to their effects on the growth and differentiation of cells, tissues, organs, and whole plants. This study aimed to evaluate the effect of multi-walled carbon nanotubes (MWCNTs) during in vitro multiplication of sugarcane (Saccharum spp.) using a temporary immersion system. Morphological characterization of MWCNTs was carried out under a transmission electron microscope. Different concentrations (0, 50, 100, 200 mg L⁻¹) of MWCNTs were added to Murashige and Skoog liquid culture medium in the multiplication stage. At 30 d of culture, number of shoots per explant, shoot length, number of leaves per shoot, total chlorophyll, dry matter percentage, carbon percentage, and macro- and micronutrient content were evaluated. Results showed an increase in the development of sugarcane shoots at concentrations of 100 and 200 mg L⁻¹ MWCNT. Total chlorophyll content increased at concentrations of 50 and 100 mg L⁻¹ MWCNT, whereas macro- and micronutrient content was variable at the different MWCNT concentrations. Results suggest a hormetic effect, characterized by stimulation at low concentrations. In conclusion, the use of low concentrations of MWCNTs had positive effects on development, total chlorophyll, carbon percentage, and macro- and micronutrient (N, Ca, S, Fe, Cu, Zn and Na) contents during in vitro multiplication of sugarcane and may have a potential use in other species of agricultural interest.

Insights into the mechanism of multi-walled carbon nanotubes phytotoxicity in Arabidopsis through transcriptome and m6A methylome analysis

With the increasing production and wide application of carbon nanotubes (CNTs), they are inevitably released into the natural environment and ecosystems, where plants are the main primary producers. Hence, it is imperative to understand the toxic effects of CNTs on plants. The molecular mechanisms underlying the toxic effects of CNTs on plants are still unclear. Therefore, in the present study, we investigated the effects of high concentrations of multi-walled CNTs (MWCNTs) on Arabidopsis. Root elongation and leaf development were severely inhibited after MWCNT exposure. Excess production of H₂O₂, O₂^-, and malondialdehyde was observed, indicating that MWCNTs induced oxidative stress. The antioxidant system was activated to counter MWCNTs-induced oxidative stress. Combinatorial transcriptome and m6A methylome analysis revealed that MWCNTs suppressed auxin signaling and photosynthesis. Reactive oxygen species metabolism, toxin metabolism, and plant responses to pathogens were enhanced to cope with the phytotoxicity of MWCNTs. Our results provide new insights into the molecular mechanisms of CNT phytotoxicity and plant defense responses to CNTs.

Protective rules of natural antioxidants against gamma-induced damage-A review

Phytochemicals accessible in food have demonstrated efficiency against impairment by gamma radiation. The review presented here is an attempt to show the pharmacological outline of the activity of the natural antioxidants and its primary action of molecular mechanism against the damage induced by gamma rays. This research focused on the results of the in vitro dosage of natural antioxidants relationship, and on the correlation of this information with the statistical variables. Moreover, it deliberated the natural compounds which could decrease the unwelcome impacts of gamma radiation and safeguard biological systems from radiation-stimulated genotoxicity. The outcomes indicated that natural compounds can be utilized as an adjunct to orthodox radiotherapy and cultivate it as an effectual drug for the clinical administration of ailments.

Small structures with big impact: Multi-walled carbon nanotubes enhanced remediation efficiency in hyperaccumulator Solanum nigrum L. under cadmium and arsenic stress

With the fast development of nanotechnology, nanomaterials are being increasingly applied for the remediation of contaminated soils. However, few researches have been reported on the complex interactions of carbon nanotubes with heavy metal (loid)s in phytoremediation. Here, we conduct a pot experiment to investigate the effects of multi-walled carbon nanotubes (MWCNTs) on the plant growth and behavior of heavy metal (loid)s in hyperaccumulator-soil system. Cd hyperaccumulator Solanum nigrum L. (S. nigrum) were cultivated in Cadmium (Cd) and Arsenic (As) contaminated soils amended with MWCNTs at 100, 500, and 1000 mg kg^-1 for 60 days, respectively. The application of MWCNTs increased the shoot length and plant dry biomass by 5.56%∼25.13% and 5.23%∼27.97%. Whereas, root and leaf growth were inhibited in 1000 mg kg^-1 MWCNTs treatments. Meanwhile, MWCNTs at 500 mg kg^-1 significantly enhanced the accumulation of heavy metal (loid)s in S. nigrum（18.29% for Cd and 32.47% for As）and alleviated co-contamination induced toxicity, by motivating plant growth, stimulating antioxidant enzymatic activities, and increasing micronutrient content (p < 0.05). The bio-concentration factor of As was decreased (15.31-28.08%) under MWCNTs application, which plays an important role in the alleviation of phytotoxicity. Besides, bioavailable Cd and As were reduced in rhizosphere soils, and the most significant reduction (16.29% for Cd and 8.19% for As) were shown in 500 mg kg^-1 MWCNTs treatment. These findings demonstrate that suitable concentration of MWCNTs can enhance remediation efficiency. Our study gives a strong evidence to promote the phytoremediation for co-contaminated soils by using nanomaterials.

Carbon Nanotubes Decrease the Negative Impact of Alternaria solani in Tomato Crop

The diseases that attack the tomato crop are a limiting factor for its production and are difficult to control or eradicate. Stem and fruit rot and leaf blight caused by Alternaria solani causes severe damage and substantial yield losses. Carbon nanotubes (CNTs) could be an alternative for the control of pathogens since they have strong antimicrobial activity, in addition to inducing the activation of the antioxidant defense system in plants. In the present study, multi-walled carbon nanotubes were evaluated on the incidence and severity of A. solani. Moreover, to the impact they have on the antioxidant defense system and the photosynthetic capacity of the tomato crop. The results show that the application of CNTs had multiple positive effects on tomato crop. CNTs decreased the incidence and severity of A. solani. Furthermore, CNTs increased the fruit yield of tomato crop and dry shoot biomass. The antioxidant system was improved, since the content of ascorbic acid, flavonoids, and the activity of the glutathione peroxidase enzyme were increased. The net photosynthesis and water use efficiency were also increased by the application of CNTs. CNTs can be an option to control A. solani in tomato crop, and diminish the negative impact of this pathogen.

Efficacy of multi-walled carbon nanotubes in regulating growth performance, total glutathione and redox state of Calendula officinalis L. cultivated on Pb and Cd polluted soil

Multi-walled carbon nanotubes (MWCNTs) have recently attracted huge attention to their impacts on the environment and plants. Therefore, this experiment was conducted to investigate the responses of lead (Pb) and cadmium (Cd) exposed pot marigold plants to various levels of MWCNT. Calendula officinalis (L.) seedlings were cultivated in Pb and Cd-polluted soils with exposure to 0, 50, 100, 250, 500 and 1000 mg L^-1 of MWCNT. The results demonstrated that foliar-applied MWCNT up to 250 mg L^-1 not only alleviated Pb and Cd-induced toxicity by reducing oxidative damage and boosting both enzymatic and non-enzymatic antioxidant defense system but also promoted the phytoremediation property of pot marigold plants by enhancing the accumulation of both Pb and Cd from the soil. Interestingly, oxidative damage exacerbation and both Pb and Cd accumulation reduction were noticed in pot marigold seedlings exposed to 500 and 1000 mg L^-1 MWCNTs. The findings of this study clearly showed that the use of appropriate concentrations of MWCNTs in increasing the phytoremediation properties of pot marigold was justified, while the use of high concentrations is toxic to the plant and intensifies the toxic effects of heavy metals (HMs) on plant physiology. This study provides a novel method to facilitate the phytoremediation of HMs polluted soils using MWCNT as well as explores the potential risks of these nanoparticles to the plants.

Responses of Medicinal and Aromatic Plants to Engineered Nanoparticles

Medicinal and aromatic plants have been used by mankind since ancient times. This is primarily due to their healing effects associated with their specific secondary metabolites (some of which are also used as drugs in modern medicine), or their structures, served as a basis for the development of new effective synthetic drugs. One way to increase the production of these secondary metabolites is to use nanoparticles that act as elicitors. However, depending on the specific particle size, composition, concentration, and route of application, nanoparticles may have several other benefits on medicinal and aromatic plants (e.g., increased plant growth, improved photosynthesis, and overall performance). On the other hand, particularly at applications of high concentrations, they are able to damage plants mechanically, adversely affect morphological and biochemical characteristics of plants, and show cytotoxic and genotoxic effects. This paper provides a comprehensive overview of the beneficial and adverse effects of metal-, metalloid-, and carbon-based nanoparticles on the germination, growth, and biochemical characteristics of a wide range of medicinal and aromatic plants, including the corresponding mechanisms of action. The positive impact of nanopriming and application of nanosized fertilizers on medicinal and aromatic plants is emphasized. Special attention is paid to the effects of various nanoparticles on the production of valuable secondary metabolites in these plants cultivated in hydroponic systems, soil, hairy root, or in vitro cultures. The beneficial impact of nanoparticles on the alleviation of abiotic stresses in medicinal and aromatic plants is also discussed.

Nano-Elicitation as an Effective and Emerging Strategy for In Vitro Production of Industrially Important Flavonoids

Flavonoids represent a popular class of industrially important bioactive compounds. They possess valuable health-benefiting and disease preventing properties, and therefore they are an important component of the pharmaceutical, nutraceutical, cosmetical and medicinal industries. Moreover, flavonoids possess significant antiallergic, antihepatotoxic, anti-inflammatory, antioxidant, antitumor, antiviral, and antibacterial as well as cardio-protective activities. Due to these properties, there is a rise in global demand for flavonoids, forming a significant part of the world market. However, obtaining flavonoids directly from plants has some limitations, such as low quantity, poor extraction, over-exploitation, time consuming process and loss of flora. Henceforth, there is a shift towards the in vitro production of flavonoids using the plant tissue culture technique to achieve better yields in less time. In order to achieve the productivity of flavonoids at an industrially competitive level, elicitation is a useful tool. The elicitation of in vitro cultures induces stressful conditions to plants, activates the plant defense system and enhances the accumulation of secondary metabolites in higher quantities. In this regard, nanoparticles (NPs) have emerged as novel and effective elicitors for enhancing the in vitro production of industrially important flavonoids. Different classes of NPs, including metallic NPs (silver and copper), metallic oxide NPs (copper oxide, iron oxide, zinc oxide, silicon dioxide) and carbon nanotubes, are widely reported as nano-elicitors of flavonoids discussed herein. Lastly, the mechanisms of NPs as well as knowledge gaps in the area of the nano-elicitation of flavonoids have been highlighted in this review.

Nanoparticles in Agroindustry: Applications, Toxicity, Challenges, and Trends

Nanotechnology is a tool that in the last decade has demonstrated multiple applications in several sectors, including agroindustry. There has been an advance in the development of nanoparticulated systems to be used as fertilizers, pesticides, herbicides, sensors, and quality stimulants, among other applications. The nanoencapsulation process not only protects the active ingredient but also can affect the diffusion, interaction, and activity. It is important to evaluate the negative aspects of the use of nanoparticles (NPs) in agriculture. Given the high impact of the nanoparticulated systems in the agro-industrial field, this review aims to address the effects of various nanomaterials on the morphology, metabolomics, and genetic modification of several crops.