Different concentrations of carbon nanotubes promote or inhibit organogenesis of Arabidopsis explants by regulating endogenous hormone homeostasis

MAIN CONCLUSION

Carbon nanotubes concentration modulates endogenous hormone balance, influencing callogenesis and organogenesis efficiency, with potential for optimizing plant transformation programs. A unique feature of plant somatic cells is their remarkable ability to regenerate new organs and even an entire plant in vitro. In this work, we investigated how an important group of environmental factors, carbon nanotubes (CNTs) (both single-walled nanotubes as SWCNTs and multi-walled nanotubes as MWCNTs), affect the regenerative capacity of plants and the underlying molecular mechanisms. Our data show that both the induction of pluripotent callus from Arabidopsis root explants and the frequency of de novo shoot regeneration were influenced by the concentration, but not the type of CNTs. Raman analyses show that CNTs can be transported and accumulate in the callus tissue and in the newly formed seedlings. The contrasting effects of CNTs at 0.1 mg L-1 and 50 mg L-1 were reflected not only in the concentrations of endogenous auxin and trans-zeatin (tZT), but also in the changes in the expression levels of positive cell cycle regulators and transcriptional regulators that control callus pluripotency and the establishment of shoot apical meristem (SAM). Since most existing plant transformation strategies involve the conversion of dedifferentiated calli into regenerated plantlets and are very time consuming and inefficient, this work suggests that CNTs could be used as an additive to optimize plant micropropagation and genetic engineering systems by modulating hormone balance and stimulating the intrinsic totipotency of plants, thus overcoming organogenic recalcitrance.

Multifunctional Roles and Ecological Implications of Nano-Enabled Technologies in Oryza sativa Production Systems: A Comprehensive Review

Micro-nanomaterials have garnered significant attention in rice (Oryza sativa L.) cultivation due to their unique physicochemical properties. This study reviews the multifunctional applications of micro-nanomaterials in enhancing rice resilience, promoting nutrient uptake, improving photosynthetic efficiency, and increasing the utilization rates of fertilizers and pesticides. Using keyword and clustering analyses, this review identifies key research hotspots and emerging trends in the field, including heavy metal stress, nanoplastic pollution, and biochar applications. While early studies predominantly focused on the synthesis and characterization of these materials, recent research has shifted towards evaluating their comprehensive ecological impacts on rice production systems. Despite the promising potential of micro-nanomaterials in improving rice yield and quality while supporting sustainable agriculture, concerns about their long-term accumulation in ecosystems and potential toxicity remain unresolved. Future research should prioritize the development of cost-effective, efficient, and environmentally friendly micro-nanomaterials and establish standardized frameworks for ecological risk assessments to facilitate their large-scale agricultural application. This study provides theoretical insights and practical references for advancing micro-nanotechnology in global food security and sustainable agriculture.

Multi-walled carbon nanotubes affect yield, antioxidant response, and rhizosphere microbial community of scented rice under combined cadmium-lead (Cd-Pb) stress

Rice production is threatened by heavy metal stress. The use of multi-walled carbon nanotubes (MWCNTs) in agriculture has been reported in previous studies. We aimed to quantify the impact of MWCNTs on the growth and physiological characteristics of scented rice under cadmium (Cd) and lead (Pb) stresses. Therefore, a pot experiment was conducted, two scented rice varieties Yuxiangyouzhan and Xiangyaxiangzhan were used as materials grown under different concentrations of MWCNTs (0, 100, and 300 mg kg-1 recorded as CK, CNPs100, and CNPs300, respectively). The yield, antioxidant response, and rhizosphere microbial community of scented rice were studied. The results showed that compared with the CK treatment, the CNPs100 and CNPs300 treatments increased leaf dry weight by 17.95%-56.22% at the heading stage, and the H2O2 content in leaves decreased significantly by 36.64%-42.27% at the maturity stage. Under CNPs100 treatment, the grain yield of two scented rice varieties increased significantly by 17.54% and 27.40%, respectively. The MWCNTs regulated the distribution of the Cd and Pb in different plant tissues. The content of Cd (0.11-0.20 mg kg-1) and Pb (0.01-0.04 mg kg-1) in grain were at a safety level (<0.2 mg kg-1). Moreover, MWCNTs increased soil microbial community abundance and altered community composition structure under Cd-Pb stress, which in turn improved agronomic traits and quality of scented rice. Overall, this study suggested that the application of MWCNTs regulates the growth, yield, physiological response, and soil microbial community, the genotypes response effect of scented rice to MWCNTs is needed further studied.

Pea Seed Priming with Pluronic P85-Grafted Single-Walled Carbon Nanotubes Affects Photosynthetic Gas Exchange but Not Photosynthetic Light Reactions

Nanotechnology is rapidly advancing towards the development of applications for sustainable plant growth and photosynthesis optimization. The nanomaterial/plant interaction has been intensively investigated; however, there is still a gap in knowledge regarding their effect on crop seed development and photosynthetic performance. In the present work, we apply a priming procedure with 10 and 50 mg/L Pluronic-P85-grafted single-walled carbon nanotubes (P85-SWCNT) on garden pea seeds and examine the germination, development, and photosynthetic activity of young seedlings grown on soil substrate. The applied treatments result in a distorted topology of the seed surface and suppressed (by 10-19%) shoot emergence. No priming-induced alterations in the structural and functional features of the photosynthetic apparatus in 14-day-old plants are found. However, photosynthetic gas exchange measurements reveal reduced stomatal conductance (by up to 15%) and increased intrinsic water use efficiency (by 12-15%), as compared to hydro-primed variants, suggesting the better ability of plants to cope with drought stress-an assumption that needs further verification. Our study prompts further research on the stomatal behavior and dark reactions of photosynthesis in order to gain new insights into the effect of carbon nanotubes on plant performance.

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

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

Graphitic carbon nitride alleviates cadmium toxicity to soybeans through nitrogen supply

Graphitic carbon nitride (g-C3N4) is a promising candidate for heavy metal remediation, primarily composed of carbon (C) and nitrogen (N). It has been demonstrated that g-C3N4 adjusts rhizosphere physicochemical conditions, especially N conditions, alleviating the absorption and accumulation of Cadmium (Cd) by soybeans. However, the mechanisms by which g-C3N4 induces N alterations to mitigates plant uptake of Cd remain unclear. This study investigated the impact of g-C3N4-mediated changes in N conditions on the accumulation of Cd by soybeans using pot experiments. It also explored the microbiological mechanisms underlying alterations in soybean rhizospheric N cycling induced by g-C3N4. It was found that g-C3N4 significantly increased N content in the soybean rhizosphere (p < 0.05), particularly in terms of available nitrogen (AN) of nitrate and ammonium. Plants absorbed more ammonium nitrogen (NH₄⁺-N), the content of which in the roots showed a significant negative correlation with Cd concentration in plant (p < 0.05). Additionally, g-C3N4 significantly affected rhizospheric functional genes associated with N cycling (p < 0.05) by increasing the ratio of the N-fixation functional gene nifH and decreasing the ratios of functional genes amoA and nxrA involved in nitrification. This enhances soybean's N-fixing potential and suppresses denitrification potential in the rhizosphere, preserving NH₄⁺-N. Niastella, Flavisolibacter, Opitutus and Pirellula may play a crucial role in the N fixation and preservation process. In summary, the utilization of g-C3N4 offers a novel approach to ensure safe crop production in Cd-contaminated soils. The results of this study provide valuable data and a theoretical foundation for the remediation of Cd polluted soils.

Nanoparticles modulate heavy-metal and arsenic stress in food crops: Hormesis for food security/safety and public health

Heavy metal and arsenic (HM-As) contamination at the soil-food crop interface is a threat to food security/safety and public health worldwide. The potential ecotoxicological effects of HM-As on food crops can perturb normal physiological, biochemical, and molecular processes. To protect food safety and human health, nanoparticles (NPs) can be applied to seed priming and soil amendment, as 'manifestation of hormesis' to modulate HM-As-induced oxidative stress in edible crops. This review provides a comprehensive overview of NPs-mediated alleviation of HM-As stress in food crops and resulting hormetic effects. The underlying biochemical and molecular mechanisms in the amelioration of HM-As-induced oxidative stress is delineated by covering the various aspects of the interaction of NPs (e.g., magnetic particles, silicon, metal oxides, selenium, and carbon nanotubes) with plant microbes, phytohormone, signaling molecules, and plant-growth bioregulators (e.g., salicylic acid and melatonin). With biotechnical advances (such as clustered regularly interspaced short palindromic repeats (CRISPR) gene editing and omics), the efficacy of NPs and associated hormesis has been augmented to produce "pollution-safe designer cultivars" in HM-As-stressed agriculture systems. Future research into nanoscale technological innovations should thus be directed toward achieving food security, sustainable development goals, and human well-being, with the aid of HM-As stress resilient food crops.

Unveiling the Effects of Carbon-Based Nanomaterials on Crop Growth: From Benefits to Detriments

To systematically assess the impact of typical CNMs on the growth effects of cereal crops, we conducted a meta-analysis of 48 independent studies worldwide. The pooled results showed that shoot weight (13.39%) and antioxidant metabolite content (SOD: 106.32%, POD: 32.29%, CAT: 22.63%) of cereal crops exposed to the presence of CNMs were significantly increased, but phytohormones secretion (17.84%) was inhibited. The results of subgroup analysis showed that there were differences in the results of different CNM types with the same exposure concentration on growth effects. Short-term exposure adversely affected the root and photosynthetic capacity of the crop, but prolonged exposure instead showed a promoting effect. Multiple linear regression analysis showed that the concentration of CNMs and cereal variety variables were significantly associated with changes in multiple growth effect values. This work could offer references and fresh perspectives for investigating how nanoparticles and crops interact.

Comparative analysis of different artificial neural networks for predicting and optimizing in vitro seed germination and sterilization of petunia

The process of optimizing in vitro seed sterilization and germination is a complicated task since this process is influenced by interactions of many factors (e.g., genotype, disinfectants, pH of the media, temperature, light, immersion time). This study investigated the role of various types and concentrations of disinfectants (i.e., NaOCl, Ca(ClO)2, HgCl2, H2O2, NWCN-Fe, MWCNT) as well as immersion time in successful in vitro seed sterilization and germination of petunia. Also, the utility of three artificial neural networks (ANNs) (e.g., multilayer perceptron (MLP), radial basis function (RBF), and generalized regression neural network (GRNN)) as modeling tools were evaluated to analyze the effect of disinfectants and immersion time on in vitro seed sterilization and germination. Moreover, non‑dominated sorting genetic algorithm‑II (NSGA‑II) was employed for optimizing the selected prediction model. The GRNN algorithm displayed superior predictive accuracy in comparison to MLP and RBF models. Also, the results showed that NSGA‑II can be considered as a reliable multi-objective optimization algorithm for finding the optimal level of disinfectants and immersion time to simultaneously minimize contamination rate and maximize germination percentage. Generally, GRNN-NSGA-II as an up-to-date and reliable computational tool can be applied in future plant in vitro culture studies.

Potential translocation process and effects of polystyrene microplastics on strawberry seedlings

A growing body of concerns focuses on microplastics as an emerging threat to terrestrial soil-plant ecosystems, but few previous studies have concentrated on asexual plants. To fill this knowledge gap, we carried out a biodistribution study of polystyrene microplastics (PS-MPs) of different particle sizes in strawberry (Fragaria × ananassa Duch. cv. "Akihime") seedlings via the hydroponic cultivation method. Confocal laser scanning microscopy (CLSM) results indicated that both 100 and 200 nm PS-MPs entered the roots and were further translocated to the vascular bundle through the apoplastic pathway. Both PS-MP sizes were detected in the vascular bundles of the petioles after 7 d of exposure, indicating a xylem-based upward translocation pathway. After 14 d, continuous upward translocation of 100 nm PS-MPs was observed above the petiole, while 200 nm PS-MPs could not be directly observed in the strawberry seedlings. This means that the uptake and translocation of PS-MPs depended on the size of PS-MPs and appropriate timing. The significant influence of strawberry seedling's antioxidant, osmoregulation, and photosynthetic systems（p < 0.05）was presented at 200 nm PS-MPs than 100 nm PS-MPs. Our findings provide scientific evidence and valuable data for the risk assessment of PS-MP exposure in asexual plant systems such as strawberry seedlings.

Multi-walled carbon nanotubes promote the accumulation, distribution, and assimilation of 15N-KNO3 in Malus hupehensis by entering the roots

INTRODUCTION

Multi-walled nanotubes (MWCNTs) consist of multiple rolled layers of graphene. Nitrogen plays an important role in apple growth. The effect of MWCNTs on nitrogen utilization in apple needs to be further investigated.

METHODS

In this study, the woody plant Malus hupehensis seedlings were used as plant materials, the distribution of MWCNTs in the roots was observed, and the effects of MWCNTs on the accumulation, distribution, and assimilation of nitrate by the seedlings were explored.

RESULTS

The results showed that MWCNTs could penetrate the roots of Malus hupehensis seedlings, and the 50, 100, and 200 µg·mL^-1 MWCNTs significantly promoted the root growth of seedlings, increased root number, root activity, fresh weight, and nitrate content of seedlings, and also increased nitrate reductase activity, free amino acid, and soluble protein content of roots and leaves. ¹⁵N tracer experiments indicated that MWCNTs decreased the distribution ratio of ¹⁵N-KNO₃ in Malus hupehensis roots but increased its distribution ratio in stems and leaves. MWCNTs improved the utilization ratio of ¹⁵N-KNO₃ in Malus hupehensis seedlings, with the values being increased by 16.19%, 53.04%, and 86.44% following the 50, 100, and 200 µg·mL^-1 MWCNTs, respectively. The RT-qPCR analysis showed that MWCNTs significantly affected the expression of genes (MhNRTs) related to nitrate uptake and transport in roots and leaves, and MhNRT1.4, MhNRT1.7, MhNRT1.8, MhNRT2.1, MhNRT2.5, and MhNRT2.7 were notably up-regulated in response to 200 µg·mL^-1 MWCNTs. Raman analysis and transmission electron microscopy images indicated that MWCNTs could enter the root tissue of Malus hupehensis and were distributed between the cell wall and cytoplasmic membrane. Pearson correlation analysis showed that root tip number, root fractal dimension, and root activity were the main factors affecting root uptake and assimilation of nitrate.

CONCLUSIONS

These findings suggest that MWCNTs promoted root growth by entering the root, stimulated the expression of MhNRTs, and increased NR activity, thereby enhancing the uptake, distribution, and assimilation of nitrate by root, and ultimately improved the utilization of ¹⁵N-KNO₃ by Malus hupehensis seedlings.

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.

Nanomaterials as an alternative to increase plant resistance to abiotic stresses

The efficient use of natural resources without negative repercussions to the environment has encouraged the incursion of nanotechnology to provide viable alternatives in diverse areas, including crop management. Agriculture faces challenges due to the combination of different abiotic stresses where nanotechnology can contribute with promising applications. In this context, several studies report that the application of nanoparticles and nanomaterials positively affects crop productivity through different strategies such as green synthesis of nanoparticles, plant targeted protection through the application of nanoherbicides and nanofungicides, precise and constant supply of nutrients through nanofertilizers, and tolerance to abiotic stress (e.g., low or high temperatures, drought, salinity, low or high light intensities, UV-B, metals in soil) by several mechanisms such as activation of the antioxidant enzyme system that alleviates oxidative stress. Thus, the present review focuses on the benefits of NPs against these type of stress and their possible action mechanisms derived from the interaction between nanoparticles and plants, and their potential application for improving agricultural practices.

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.

A comprehensive review of impacts of diverse nanoparticles on growth, development and physiological adjustments in plants under changing environment

The application of nanotechnology in agriculture includes the use of nanofertilizers, nanopesticides, and nanoherbicides that enhance plant nutrition without disturbing the soil texture and protect it against microbial infections. Thus, nanotechnology maintains the plant's health by maintaining its soil health. The use of nanoparticles (NPs) in agriculture reduces the chemical spread and nutrient loss and boosts crop yield and productivity. Effect of NPs varies with their applied concentrations, physiochemical properties, and plant species. Various NPs have an impact on the plant to increase biomass productivity, germination rate and their physiology. Also, NPs change the plant molecular mechanisms by altering gene expression. Metal and non-metal oxides of NPs (Au, Ag, ZnO, Fe₂O₃, TiO₂, SiO₂, Al₂O₃, Se, carbon nanotubes, quantum dots) exert an important role in plant growth and development and perform an essential role in stress amelioration. On the other hand, other effects of NPs have also been well investigated by observing their role in growth suppression and inhibition of chlorophyll and photosynthetic efficiency. In this review, we addressed a description of studies that have been made to understand the effects of various kind of NPs, their translocation and interaction with the plants. Also, the phytoremediation approaches of contaminated soil with combined use of NPs for sustainable agriculture is covered.

Effects of functional carbon nanodots on water hyacinth response to Cd/Pb stress: Implication for phytoremediation

Phytoremediation is one of the effective, economic and green approaches to cope with the increasing worldwide heavy metal (HM) pollution. Here, we evaluate the effects of functional carbon nanodots (FCNs) against the hyperaccumulation capacity as well as the physiological and genetic responses of water hyacinth under Pb²⁺ or/and Cd²⁺ stress. The bioaccumulation efficiency, HM content and transfer factor, biomass, root development, chlorophyll content, antioxidant system and genes expression are investigated at various concentration of HMs. Based on the excellent adsorption capacity and plant growth regulation ability, FCNs and nitrogen doped FCNs (N-FCNs) cooperate with water hyacinth to improve their HMs removal efficiencies. FCNs and N-FCNs immobilize excess HMs ions in plant, smartly regulate enzymatic levels to mitigate oxidative damage, as well as regulate the microelement uptake and related gene expression, thus improve plant tolerance against HMs stress. Although Pb and Cd have antagonistic effects on bioaccumulation of water hyacinth to the single metal, FCNs and N-FCNs can cooperate with water hyacinth to raise the removal efficiency of HMs in water, and enhance plant tolerance under Pb-Cd combined stress. The promotion effects of FCNs and N-FCNs on phytoremediation are more effective than conventional carbon nanomaterials, including carbon nanotubes and graphene oxides. These findings demonstrate that the application of FCNs or N-FCNs can improve the phytoremediation efficiency in the restoration of HMs contaminated water area. This study provides important insights into the possibility of using FCNs-based nanomaterials and water hyacinth as synergistic system for remediation of Cd-Pb contaminated water area.

Can the multi-walled carbon nanotubes be used to alleviate the phytotoxicity of herbicides in soils?

Herbicides are commonly used globally. However, residual herbicides in soils for ages often result in phytotoxicity and serious yield loss to subsequent crops. In this paper, the multi-walled carbon nanotubes (MWCNTs) were utilized to amend the herbicide polluted soil, and the adsorption performance of herbicides to MWCNTs amended soil was studied. Results indicate efficient alleviation of herbicide-induced phytotoxicity to rice and tobacco due to MWCNTs amendment. When 0.4% MWCNTs were applied, the concentration of sulfentrazone that inhibited the same rice height by 50% (IC₅₀) increased to more than 3 times that of pure soil. When the MWCNTs were used to alleviate the phytotoxicity of quinclorac to tobacco, the MWCNTs not only alleviated the phytotoxicity of quinclorac but also promoted the growth of tobacco. The MWCNTs amended soil significantly increased the adsorption of herbicide to soil than biochar. The soil microbial analysis shows that MWCNTs had no significant effect on soil microbial community diversity, but the long-term exposure to MWCNTs could change the structure of the soil microbial community. Above all, our results highlighted the potential implication of the MWCNTs to ensure crop production by promoting crop growth and reducing the residual bioavailability of herbicides.

Polymer-Modified Single-Walled Carbon Nanotubes Affect Photosystem II Photochemistry, Intersystem Electron Transport Carriers and Photosystem I End Acceptors in Pea Plants

Single-walled carbon nanotubes (SWCNT) have recently been attracting the attention of plant biologists as a prospective tool for modulation of photosynthesis in higher plants. However, the exact mode of action of SWCNT on the photosynthetic electron transport chain remains unknown. In this work, we examined the effect of foliar application of polymer-grafted SWCNT on the donor side of photosystem II, the intersystem electron transfer chain and the acceptor side of photosystem I. Analysis of the induction curves of chlorophyll fluorescence via JIP test and construction of differential curves revealed that SWCNT concentrations up to 100 mg/L did not affect the photosynthetic electron transport chain. SWCNT concentration of 300 mg/L had no effect on the photosystem II donor side but provoked inactivation of photosystem II reaction centres and slowed down the reduction of the plastoquinone pool and the photosystem I end acceptors. Changes in the modulated reflection at 820 nm, too, indicated slower re-reduction of photosystem I reaction centres in SWCNT-treated leaves. We conclude that SWCNT are likely to be able to divert electrons from the photosynthetic electron transport chain at the level of photosystem I end acceptors and plastoquinone pool in vivo. Further research is needed to unequivocally prove if the observed effects are due to specific interaction between SWCNT and the photosynthetic apparatus.

Graphitic carbon nitride (g-C3N4) alleviates cadmium-induced phytotoxicity to rice (Oryza sativa L.)

In the present study, graphitic carbon nitride (g-C3N4) was synthesized in a tube furnace and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR). Different concentrations (0-200 mg/L) of g-C3N4 were prepared in nutrient solution amended with or without 20 mg/L CdCl2 for the greenhouse study. Rice seedlings were exposed to g-C3N4 and Cd for 20 days. Our results suggest that 200 mg/L g-C3N4 significantly increased the fresh weight and root and shoot length as compared with the control, and notably alleviated Cd-induced toxicity. The addition of 200 mg/L g-C3N4 significantly reduced the root and shoot Cd content by approximately 14% and 23%, respectively. In addition, 200 mg/L g-C3N4 significantly elevated the nitrogen content and decreased C/N ration in rice shoots; most importantly, it alleviated Cd-induced nitrogen reduction. Our findings demonstrated the potential of g-C3N4 in regulating plant growth and minimizing the Cd-induced phytotoxicity, and shed light on providing a new strategy to maintain heavy metal contamination in agriculture using a low-cost and environmental friendly NMs.

Carbon nanotubes affect early growth, flowering time and phytohormones in tomato

Carbon nanotube (CNT) applications are increasing in consumer products, including agriculture devices, making them an important contaminant to study in the field of plant nanotoxicology. Several studies have observed the uptake and effects of CNTs in plants. However, in other studies differing results were observed on growth and physiology depending on the plant species and type of CNT. This study focused on the effects of CNTs on plant phenotype with growth, time to flowering, fruiting time as endpoints, and physiology, through amino acid and phytohormone content, in tomato after exposure to multiple types of CNTs. Plants grown in CNT-contaminated soil exhibited a delay in early growth and flowering (especially in treatments of 1 mg/kg multi-walled nanotubes (MWNTs), 10 mg/kg MWNTs, and 1 mg/kg MWNTs-COOH). However, CNTs did not affect plant growth or height later in the life cycle. No significant differences in abscisic acid (ABA) and citrulline content were observed between the treated and control plants. However, single-walled nanotube (SWNT) exposure significantly increased salicylic acid (SA) content in tomato. These results suggest that SWNTs may elicit a stress response in tomatoes. Results from this study offer more insight into how plants respond and acclimate to CNTs. These results will lead to a better understanding of CNT impact on plant phenotype and physiology.

Applications of carbon nanomaterials in the plant system: A perspective view on the pros and cons

With the remarkable development in the field of nanotechnology, carbon-based nanomaterials (CNMs) have been widely used for numerous applications in different areas of the plant system. The current understanding about the CNMs' accumulation, translocation, plant growth responses, and stress modulations in the plant system is far from complete. There have been relentless efforts by the researchers worldwide in order to acquire newer insights into the plant-CNMs interactions and the consequences. The present review intends to update the reader with the status of the impacts of the different CNMs on plant growth. Research reports from the plant biotechnologists have documented mixed effects (which are dependent on CNMs' concentration) of the CNMs' exposure on plants ranging from enhanced crop yield to acute cytotoxicity. The growth and yield pattern vary from species to species and are dependent on the dosage of the CNMs applied. Studies found an increase in vegetative growth and yield of fruit/seed at lower concentration of CNMs, but a decrease in these observables were also noted when higher concentrations of CNMs were used. In general, at lower concentrations, CNMs were found to be effective in enhancing (water uptake, water transport, seed germination, nitrogenase, photosystem and antioxidant activities), activating (water channels proteins) and promoting (nutrition absorption); all these change when concentrations are raised. All these aspects have been reviewed thoroughly in this article, with a focus on the recent updates on the role of the CNMs in augmenting or retarding plant growth. Sections have been devoted to the various features of the CNMs and their roles in inducing plant growth, phytotoxic responses of the plants and overall crop improvement. Concluding remarks have been added to propose future directions of research on the CNMs-plant interactions and also to sound a warning on the use of CNMs in agriculture.