Impact of carbon nanotube exposure to seeds of valuable crops

Comparative study of response of four crop species exposed to carbon nanotube contamination in soil

Crop plants are exposed to a variety of contaminants through sewage sludge spreading but very little is known about the impact of emerging contaminants such as nanomaterials. To date their impact on plants is still very controversial with many works claiming negative impacts while some authors suggest their use as plant growth regulator in agriculture. In this study, aiming to better understand where these discrepancies may come from, we investigated the influence of plant species (tomato, rapeseed, cucumber and maize) on plant response to a carbon nanotube contamination in soil condition. Our results demonstrate that the same CNT contamination can lead to different effects depending on plant species with positive impacts on cucumber and rapeseed (more than 50% increase in leaf biomass and surface area and 29% increase in chlorophyll for cucumber) but negative impact on maize (-14% for plant height), while tomato was insensitive. FTIR analysis of biomacromolecule composition suggested that these differences could be related with plant cell wall composition (in particular: pectins, xyloglucans and lignins). As a summary, no overall conclusion can be drawn about the toxicity of a specific nanomaterial for all plant species.

Role of nanoparticles in crop improvement and abiotic stress management

Nanoparticles (NPs) possess specific physical and chemical features and they are capable enough to cross cellular barriers and show their effect on living organisms. Their capability to cross cellular barriers have been noticed for their application not only in medicine, electronics, chemical and physical sciences, but also in agriculture. In agriculture, nanotechnology can help to improve the growth and crop productivity by the use of various nanoscale products such as nanofertilizers, nanoherbicides, nanofungicides, nanopesticides etc. An optimized concentration of NPs can be administered by incubation of seeds, roots, pollen, isolated cells and protoplast, foliar spraying, irrigation with NPs, direct injection, hydroponic treatment and delivery by biolistics. Once NPs come in contact with plant cells, they are uptaken by plasmodesmatal or endocytosed pathways and translocated via apoplastic and / symplastic routes. Once beneficial NPs reach different parts of plants, they boost photosynthetic rate, biomass measure, chlorophyll content, sugar level, buildup of osmolytes and antioxidants. NPs also improve nitrogen metabolism, enhance chlorophyll as well as protein content and upregulate the expression of abiotic- and biotic stress-related genes. Herein, we review the state of art of different modes of application, uptake, transport and prospective beneficial role of NPs in stress management and crop improvement.

Advantage of Nanotechnology-Based Genome Editing System and Its Application in Crop Improvement

Agriculture is an important source of human food. However, current agricultural practices need modernizing and strengthening to fulfill the increasing food requirements of the growing worldwide population. Genome editing (GE) technology has been used to produce plants with improved yields and nutritional value as well as with higher resilience to herbicides, insects, and diseases. Several GE tools have been developed recently, including clustered regularly interspaced short palindromic repeats (CRISPR) with nucleases, a customizable and successful method. The main steps of the GE process involve introducing transgenes or CRISPR into plants via specific gene delivery systems. However, GE tools have certain limitations, including time-consuming and complicated protocols, potential tissue damage, DNA incorporation in the host genome, and low transformation efficiency. To overcome these issues, nanotechnology has emerged as a groundbreaking and modern technique. Nanoparticle-mediated gene delivery is superior to conventional biomolecular approaches because it enhances the transformation efficiency for both temporal (transient) and permanent (stable) genetic modifications in various plant species. However, with the discoveries of various advanced technologies, certain challenges in developing a short-term breeding strategy in plants remain. Thus, in this review, nanobased delivery systems and plant genetic engineering challenges are discussed in detail. Moreover, we have suggested an effective method to hasten crop improvement programs by combining current technologies, such as speed breeding and CRISPR/Cas, with nanotechnology. The overall aim of this review is to provide a detailed overview of nanotechnology-based CRISPR techniques for plant transformation and suggest applications for possible crop enhancement.

Innovations in nanoscience for the sustainable development of food and agriculture with implications on health and environment

A rapid increase in world population is leading to the rise in global demand of food and agriculture (agri) products. Nanotechnology and its applications have emerged as one of the most pioneering and promising technology for transforming conventional food and agri industries, with the aim of sustainable farming, improving the food security, quality and safety which could revolutionize the food and agri industries. Current developments in nanotechnology have led to the new paths progressively and bringing the radical changes the way food is perceived throughout the farming, transportation, processing, packaging, storage, monitoring and consumption. This review brings the current updates on novel nanomaterials in food and agri industries. Emphasis is given on the importance of nanotechnological applications, offering complete food solutions from farm to fork; including nutraceutical and functional foods, improving bioavailability, efficiency, nutritional status, nano-additives, food texture, color, taste and packaging. Agricultural sector also witnessed several nano-based products, such as nano-fertilizer, nano-pesticide, nano growth promoters and many more for the development of sustainable farming and crop improvement. Despite of numerous advantages of nanotechnology, there are still toxicity challenges, safety concerns, which needs to be addressed and demands transformations in regulatory policies. Rapid development is projected to transform several foods and agri sectors, with rapid increase in market stake and investment. Government agencies, private research centers as well as academicians are also coming together to explore the benefits of nanotechnology to improve food scarcity in the coming years.

Multi-Wall Carbon Nanotubes Promote the Growth of Maize (Zea mays) by Regulating Carbon and Nitrogen Metabolism in Leaves

Previous studies have suggested that multiwalled carbon nanotubes (MWCNTs) promote plant growth; however, the mechanism is yet to be fully understood. In this study, the effects of MWCNTs (20, 100, and 500 mg/L) on the carbon (C) and nitrogen (N) metabolism in maize were studied to explore the molecular mechanism of the action of MWCNTs on plants. The results showed that 100 mg/L MWCNTs increased the shoot fresh and dry weight, root fresh weight, and seedling length while other doses showed no significant effects. Further studies showed that 100 mg/L MWCNTs increased the chlorophyll content, transpiration rate, stomatal conductance, and intercellular CO₂ concentration, by 50.6%, 60.8%, 47.2%, and 32.1%, respectively. Activities of key enzymes including sucrose synthase (SS), sucrose phosphate synthase (SPS) and phosphoenolpyruvate carboxylase (PEPC) that are involved in the carbon metabolism, and nitrate reductase (NR), glutamine synthetase (GS), and glutamate synthetase (GOGAT) that are involved in N metabolism, were all upregulated by 100 mg/L MWCNTs, which contributed to the increase of the accumulation of carbohydrates (sugar and starch), soluble protein, and N in plants. These findings suggest that MWCNTs can improve plant growth by regulating the key enzymes involved in C and N metabolism thereby enhancing the carbohydrate production and the use of N and improving plant growth. This study provides significant insights into the molecular mechanism of the positive effects of MWCNTs on plants and provide a basis for the agricultural application of MWCNTs.

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.

Nitric oxide signalling in plant nanobiology: current status and perspectives

Plant nanobiology as a novel research field provides a scientific basis for the agricultural use of nanoparticles (NPs). Plants respond to the presence of nanomaterials by synthesizing signal molecules, such as the multifunctional gaseous nitric oxide (NO). Several reports have described the effects of different nanomaterials (primarily chitosan NPs, metal oxide NPs, and carbon nanotubes) on endogenous NO synthesis and signalling in different plant species. Other works have demonstrated the ameliorating effect of exogenous NO donor (primarily sodium nitroprusside) treatments on NP-induced stress. NO-releasing NPs are preferred alternatives to chemical NO donors, and evaluating their effects on plants has recently begun. Previous studies clearly indicate that endogenous NO production in the presence of nanomaterials or NO levels increased by exogenous treatments (NO-releasing NPs or chemical NO donors) exerts growth-promoting and stress-ameliorating effects in plants. Furthermore, an NP-based nanosensor for NO detection in plants has been developed, providing a new and excellent perspective for basic research and also for the evaluation of plants' health status in agriculture.

Derivatized Carbon Nanotubes for Gene Therapy in Mammalian and Plant Cells

The concept of gene vectors for therapeutic applications has been known for several years, but it is far from revealing its actual potential. With the advent of hollow cylindrical carbon nanomaterials such as carbon nanotubes (CNTs), researchers have invented several new tools to deliver genes at the required site of action in mammalian and plant cells. The ease of diversified functionalization has allowed CNTs to be by far the most adaptable non-viral vector for gene therapy. This Minireview addresses the dexterity with which CNTs undergo surface modifications and their applications as a potent vector in gene therapy of humans and plants. Specifically, we will discuss the new tools that scientific communities have invented to achieve gene therapy using plasmid DNA, RNA silencing, suicide gene therapy, and plant genetic engineering. Additionally, we will shed some light on the mechanism of gene transportation using carbon nanotubes in cancer cells and plants.

Nanotechnology Potential in Seed Priming for Sustainable Agriculture

Our agriculture is threatened by climate change and the depletion of resources and biodiversity. A new agriculture revolution is needed in order to increase the production of crops and ensure the quality and safety of food, in a sustainable way. Nanotechnology can contribute to the sustainability of agriculture. Seed nano-priming is an efficient process that can change seed metabolism and signaling pathways, affecting not only germination and seedling establishment but also the entire plant lifecycle. Studies have shown various benefits of using seed nano-priming, such as improved plant growth and development, increased productivity, and a better nutritional quality of food. Nano-priming modulates biochemical pathways and the balance between reactive oxygen species and plant growth hormones, resulting in the promotion of stress and diseases resistance outcoming in the reduction of pesticides and fertilizers. The present review provides an overview of advances in the field, showing the challenges and possibilities concerning the use of nanotechnology in seed nano-priming, as a contribution to sustainable agricultural practices.

Efficacy of nanoparticles as nanofertilizer production: a review

Owing to the ever-increasing demand for food, the growing global population has forced farmers to increase fertilizer use. The overall use of fertilizers increased by 13 times between 1950 and 2020, from 15 to 194 million tons. Due to the resource shortages of chemical fertilizers on the market, agricultural costs are rising drastically every day because they cause an adverse impact on the environment by releasing chemical particulates and run-off agriculture. Biofertilizers have thus become a safer supplement to increase crop production without doing any harm to the environment, as they are produced industrially from a selected community of microorganisms that either develop a mutually beneficial relationship with plants or are part of their rhizosphere. They still have some drawbacks, which led to the development of a new avenue for the application of nanotechnology-mediated nanofertilizers. Nanotechnology recommends significant prospects for tailoring nanofertilizer production. They are typically coated with desired chemical composition having controlled release and targeted delivery of effective nanoscale ingredients, ability to improve plant productivity and to minimize environmental pollutants. The present review focuses primarily on the usefulness of nanofertilizers, as well as its environmental and safety concerns. The research would also include useful knowledge related to the introduction of different forms of nanoparticles within the agricultural field, contributing to the opening of a new route to nanorevolution.

Dual Effect of Nanomaterials on Germination and Seedling Growth: Stimulation vs. Phytotoxicity

Due to recent active research, a large amount of data has been accumulated regarding the effects of different nanomaterials (mainly metal oxide nanoparticles, carbon nanotubes, chitosan nanoparticles) on different plant species. Most studies have focused on seed germination and early seedling development, presumably due to the simplicity of these experimental systems. Depending mostly on size and concentration, nanomaterials can exert both positive and negative effects on germination and seedling development during normal and stress conditions, thus some research has evaluated the phytotoxic effects of nanomaterials and the physiological and molecular processes behind them, while other works have highlighted the favorable seed priming effects. This review aims to systematize and discuss research data regarding the effect of nanomaterials on germination and seedling growth in order to provide state-of-the-art knowledge about this fast developing research area.

Nanoparticle-Based Sustainable Agriculture and Food Science: Recent Advances and Future Outlook

In the current scenario, it is an urgent requirement to satisfy the nutritional demands of the rapidly growing global population. Using conventional farming, nearly one third of crops get damaged, mainly due to pest infestation, microbial attacks, natural disasters, poor soil quality, and lesser nutrient availability. More innovative technologies are immediately required to overcome these issues. In this regard, nanotechnology has contributed to the agrotechnological revolution that has imminent potential to reform the resilient agricultural system while promising food security. Therefore, nanoparticles are becoming a new-age material to transform modern agricultural practices. The variety of nanoparticle-based formulations, including nano-sized pesticides, herbicides, fungicides, fertilizers, and sensors, have been widely investigated for plant health management and soil improvement. In-depth understanding of plant and nanomaterial interactions opens new avenues toward improving crop practices through increased properties such as disease resistance, crop yield, and nutrient utilization. In this review, we highlight the critical points to address current nanotechnology-based agricultural research that could benefit productivity and food security in future.

Multi-Walled Carbon Nanotubes Can Promote Brassica napus L. and Arabidopsis thaliana L. Root Hair Development through Nitric Oxide and Ethylene Pathways

Here, we report that multi-walled carbon nanotubes (MWCNTs) can promote plant root hair growth in the species analyzed in this study; however, low and excessive concentrations of MWCNTs had no significant effect or even an inhibiting influence. Further results show that MWCNTs can enter rapeseed root cells. Meanwhile, nitrate reductase (NR)-dependent nitric oxide (NO) and ethylene syntheses, as well as root hair formation, were significantly stimulated by MWCNTs. Transcription of root hair growth-related genes were also modulated. The above responses were sensitive to the removal of endogenous NO or ethylene with a scavenger of NO or NO/ethylene synthesis inhibitors. Pharmacological and molecular evidence suggested that ethylene might act downstream of NR-dependent NO in MWCNTs-induced root hair morphogenesis. Genetic evidence in Arabidopsis further revealed that MWCNTs-triggered root hair growth was abolished in ethylene-insensitive mutants ein2-5 and ein3-1, and NR mutant nia1/2, but not in noa1 mutant. Further data placed NO synthesis linearly before ethylene production in root hair development triggered by MWCNTs. The above findings thus provide some insights into the molecular mechanism underlying MWCNTs control of root hair morphogenesis.

1H Nuclear Magnetic Resonance and Liquid Chromatography Coupled with Mass Spectrometry-Based Metabolomics Reveal Enhancement of Growth-Promoting Metabolites in Onion Seedlings Treated with Green-Synthesized Nanomaterials

Seed priming is a promising approach to improve germination, emergence, and seedling growth by triggering pre-germinative metabolism and enhancing seedling vigor. Recently, nanopriming gained importance in seed improvement as a result of the small size and unique physicochemical characteristics of nanomaterials. In the present study, silver and gold nanoparticles were synthesized using onion extracts as the reducing agent. Similarly, the agro-food industrial byproducts citrus seed oil and curcumin-removed turmeric oleoresin were used for the preparation of nanoemulsions. For seed priming, these green-synthesized nanomaterials were incubated with seeds of two onion (Allium cepa L.) cultivars (Legend and 50147) for 72 h, and then the plants were grown in a greenhouse for 3 weeks. Seed priming with these nanomaterials increased seed germination and seedling emergence. One-dimensional ¹H nuclear magnetic resonance and liquid chromatography coupled with mass spectrometry metabolomics studies showed that different nanopriming treatments distinctly altered the metabolome of onion seedlings. Seed priming treatments significantly inhibited plant hormones and growth regulators, such as abscisic acid and cis-(+)-12-oxo-phytodienoic acid, and enhanced germination stimulators, such as γ-aminobutyric acid and zeatin, in onion seeds and seedlings. Therefore, these priming treatments have positive impact on improving seed performance and plant growth.

Reclaimed wastewater as a viable water source for agricultural irrigation: A review of food crop growth inhibition and promotion in the context of environmental change

The geographical and temporal distribution of precipitation has and is continuing to change with changing climate. Shifting precipitation will likely require adaptations to irrigation strategies, and because 35% of rainfed and 60% of irrigated agriculture is within 20 km of a wastewater treatment plant, we expect that the use of treated wastewater (e.g., reclaimed wastewater) for irrigation will increase. Treated wastewater contains various organic and inorganic substances that may have beneficial (e.g., nitrate) or deleterious (e.g., salt) effects on plants, which may cause a change in global food productivity should a large change to treated wastewater irrigation occur. We reviewed literature focused on food crop growth inhibition or promotion resulting from exposure to xenobiotics, engineered nanoparticles, nitrogen, and phosphorus, metals, and salts. Xenobiotics and engineered nanoparticles, in nearly all instances, were detrimental to crop growth, but only at concentrations much greater than would be currently expected in treated wastewater. However, future changes in wastewater flow and use of these compounds and particles may result in phytotoxicity, particularly for xenobiotics, as some are present in wastewater at concentrations within approximately an order of magnitude of concentrations which caused growth inhibition. The availability of nutrients present in treated wastewater provided the greatest overall benefit, but may be surpassed by the detrimental impact of salt in scenarios where either high concentrations of salt are directly deleterious to plant development (rare) or in scenarios where soils are poorly managed, resulting in soil salt accumulation.

Multi-walled carbon nanotubes stimulate growth, redox reactions and biosynthesis of antioxidant metabolites in Thymus daenensis celak. in vitro

This research was aimed at determining the effects of multi-walled carbon nanotubes (MWCNTs) on seed germination, seedling growth parameters and secondary metabolite (SM) production of Thymus daenensis in vitro. Seeds were aseptically cultured in Murashige and Skoog medium (MS) with various concentrations of MWCNTs (0, 125, 250, 500, 1000 and 2000 μg ml^-1). Seed germination and morphological changes in seedlings were measured. The measurements were aimed at quantifying the total phenolic contents (TPC) and flavonoids (TFC), antioxidant activities and the activity of polyphenol oxidase (PPO), l-phenylalanine ammonia-lyase (PAL), dehydrogenase (DHA) and peroxidase enzyme (POD) of the seedling extract. Seedling biomass and seedling height grew significantly as the MWCNTs level increased. The biomass and height peaked at 250 μg ml^-1 (0.41 ± 0.01 gr FW, 5.99 ± 0.55 cm) and then rapidly decreased to 0.040 ± 0.1 gr FW and 1.42 ± 0.24 cm in response to 1000 μg ml^-1, 30 days after the treatment. Additionally, SM and the analyses of enzyme activity revealed that the highest amounts of TPC (6.70 ± 0.06 mg GAE g^-1 DW), TFC (8.19 ± 0.01 mg QUE g^-1 DW), antioxidant activities (73.88 ± 0.47%) and maximum PAL activity (1.25 ± 0.08 mM cm g^-1 FW) were detected in plants grown on MS media fortified with 250 μg ml^-1 MWCNTs. The results reveal that MWCNTs in low doses (250 μg ml^-1) can encourage the production of biomass, elicit more SM from seedlings and enhance the biosynthesis of antioxidants. TEM images showed that MWCNTs could cross the plant cell wall and enter the cellular cytoplasm.

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

Owing to the growing applications of the multi-walled carbon nanotubes (MWCNTs) in the communications and energy industries, they have attracted increasing attention for their effects on the environment and plants. Therefore, we investigated the impact of foliar exposure to MWCNTs on the oxidative stress responses in the Salvia verticillata as a medicinal plant. Furthermore, we evaluated the possible correlations between gene expression and activity of the key enzymes in the phenolic acids biosynthesis pathways and their accumulation in the treated leaves. The leaves of two-month-old plants were sprayed with different concentrations (0-1000 mg L^-1) of MWCNTs. Raman's data and Transmission Electron Microscopy images have confirmed the absorption of MWCNTs via epidermal cells layer into the parenchymal cells of the exposed leaves. The results showed that exposure to MWCNTs led to a decrease in the photosynthetic pigments and increases in the oxidative stress indices (enzymatic and non-enzymatic antioxidants) in the leaves with a dose-dependent manner. The content of rosmarinic acid as a main phenolic acid was increased in the MWCNTs-exposed leaves to 50 and 1000 mg L^-1, nearly four times relative to the control. Unlike with other examined enzymes, a positive correlation was deduced between the activity and gene expression patterns of the rosmarinic acid synthase with the rosmarinic acid accumulation in the treatments. Overall, MWCNTs at the low concentrations could promote the production of the pharmaceutical metabolites by the changes in the ROS generation. However, at the higher concentrations, MWCNTs were toxic and induced the oxidative damages in S. verticillata.

Multi-walled carbon nanotubes produced after forest fires improve germination and development of Eysenhardtia polystachya

Background

Multi-walled carbon nanotubes (MWCNTs) are nanoparticles with countless applications. MWCNTs are typically of synthetic origin. However, recently, the formation of MWCNTs in nature after forest fires has been documented. Previous reports have demonstrated the positive effects of synthetic MWCNTs on the germination and development of species of agronomic interest; nevertheless, there is practically no information on how synthetic or natural MWCNTs affect forest plant development. In this report, based on insights from dose-response assays, we elucidate the comparative effects of synthetic MWCNTs, amorphous carbon, and natural MWCNTs obtained after a forest fire on Eysenhardtia polystachya plant.

Methods

E. polystachya seeds were sown in peat moss-agrolite substrate and conserved in a shade house. Germination was recorded daily up to 17 days after sowing, and plant development (manifested in shoot and root length, stem diameter, foliar area, and root architecture parameters) was recorded 60 days after sowing.

Results

The treatments with natural MWCNTs accelerated the emergence and improved the germination of this plant, thus while untreated seeds achieve 100% of germination within 16th day, seeds supplemented with natural MWCNTs at doses of 20 µg/mL achieve the above percentage within the 4th day. Natural MWCNTs also promoted fresh and dry biomass in all applied treatments, specially at doses of 40 µg/mL where natural MWCNTs significantly promoted leaf number, root growth, and the dry and fresh weights of shoots and roots of seedlings. Seeds supplemented with doses between 20 and 40 µg/mL of amorphous carbon achieving 100% of germination within the 6th day; however, seeds supplemented either with doses of 60 µg/mL of the above carbon or with synthetic MWCNTs at all the tested concentrations could achieve at most 80 % and 70% of germination respectively within the 17 days. Finally, neither treatments added with amorphous carbon nor those added with synthetic MWCNTs, showed significant increases in the fresh and dry biomass of the tested plant. Likewise, the survival of seedlings was reduced between 10 and 20 % with 40 and 60 µg/mL of amorphous carbon, and with synthetic MWCNTs in all the doses applied was reduced at 30% of survival plants.

Conclusions

These findings indicate that MWCNTs produced by wildfire act as plant growth promoters, contributing to the germination and development of adapted to fire-prone conditions species such as E. polystachya.

Physiological, Metabolic, and Transcriptomic Analyses Reveal the Responses of Arabidopsis Seedlings to Carbon Nanohorns

Carbon-based nanomaterials have potential applications in nanoenabled agriculture. However, the physiological and molecular mechanisms underlying single-walled carbon nanohorn (SWCNH)-mediated plant growth remain unclear. Here, we investigated the effects of SWCNHs on Arabidopsis grown in ¹/₄-strength Murashige and Skoog medium via physiological, genetic, and molecular analyses. Treatment with 0.1 mg/L SWCNHs promoted primary root (PR) growth and lateral root (LR) formation; 50 and 100 mg/L SWCNHs inhibited PR growth. Treatment with 0.1 mg/L SWCNHs increased the lengths of the meristematic and elongation zones, and transcriptomic and genetic analyses confirmed the positive effects of SWCNHs on root tip stem cell niche activity and meristematic cell division potential. Increased expression of YUC3 and YUC5 and increased PIN2 abundance improved PR growth and LR development in 0.1 mg/L SWCNH-treated seedlings. Metabolomic analyses revealed that SWCNHs altered the levels of sugars, amino acids, and organic acids, suggesting that SWCNHs reprogrammed carbon/nitrogen metabolism in plants. SWCNHs also regulate plant growth and development by increasing the levels of several secondary metabolites; transcriptomic analyses further supported these results. The present results are valuable for continued use of SWCNHs in agri-nanotechnology, and these molecular approaches could serve as examples for studies on the effects of nanomaterials in plants.

Carbon Nanotubes-Based Nanomaterials and Their Agricultural and Biotechnological Applications

Carbon nanotubes (CNTs) are considered a promising nanomaterial for diverse applications owing to their attractive physicochemical properties such as high surface area, superior mechanical and thermal strength, electrochemical activity, and so on. Different techniques like arc discharge, laser vaporization, chemical vapor deposition (CVD), and vapor phase growth are explored for the synthesis of CNTs. Each technique has advantages and disadvantages. The physicochemical properties of the synthesized CNTs are profoundly affected by the techniques used in the synthesis process. Here, we briefly described the standard methods applied in the synthesis of CNTs and their use in the agricultural and biotechnological fields. Notably, better seed germination or plant growth was noted in the presence of CNTs than the control. However, the exact mechanism of action is still unclear. Significant improvements in the electrochemical performances have been observed in CNTs-doped electrodes than those of pure. CNTs or their derivatives are also utilized in wastewater treatment. The high surface area and the presence of different functional groups in the functionalized CNTs facilitate the better adsorption of toxic metal ions or other chemical moieties. CNTs or their derivatives can be applied for the storage of hydrogen as an energy source. It has been observed that the temperature widely influences the hydrogen storage ability of CNTs. This review paper highlighted some recent development on electrochemical platforms over single-walled CNTs (SWCNTs), multi-walled CNTs (MWCNTs), and nanocomposites as a promising biomaterial in the field of agriculture and biotechnology. It is possible to tune the properties of carbon-based nanomaterials by functionalization of their structure to use as an engineering toolkit for different applications, including agricultural and biotechnological fields.

Current trends in nano-technological interventions on plant growth and development: a review

Nanomaterials, recently have found burgeoning attention in the field of agriculture, owing to the positive correlation between nanoparticle (NP) application and the enhanced nutritional status of the applied plants. A wide range of NPs, namely carbon-based NPs, titanium dioxide NPs, silica NPs etc. has been found to influence plants in a positive way by increasing their nutrient uptake ratio, nutrient usage efficiency, among others. All these attributes have paved the way for possible improvement in plant growth, development, vigour etc. through the use of these NPs, mainly as nanofertiliser. In view of all these, it can also be concluded that in the global scenario of increased demand of food production and supply in the coming years, nanotechnology promises to play a critical role. In this review, an attempt has been made to consolidate all the positive trends with respect to application of NPs on plants, along with their probable mechanism of action, which may provide a comprehensive insight for researchers working in this field.

Nitric oxide is involved in nano-titanium dioxide-induced activation of antioxidant defense system and accumulation of osmolytes under water-deficit stress in Vicia faba L

Nano-titanium dioxide (nTiO₂) has been reported to improve tolerance of plants against different environmental stresses by modulating various physiological and biochemical processes. Nitric oxide (NO) has been shown to act as an important stress signaling molecule during plant responses to abiotic stresses. The present work was planned to investigate the involvement of endogenous NO in nTiO₂-induced activation of defense system of fava bean (Vicia faba L.) plants under water-deficit stress (WDS) conditions. Water-suffered plants showed increased concentration of hydrogen peroxide (H₂O₂) and superoxide (O₂^-) content coupled with increased electrolyte leakage and lipid peroxidation which adversely affected nitrate reductase (NR) activity, chlorophyll content and growth of the plants. However, application of 15 mg L^-1 nTiO₂ to stressed plants significantly induced NR activity and synthesis of NO which elevated enzymatic and non-enzymatic defense system of the stressed plants and suppressed the generation of H₂O₂ and O₂^- content, leakage of electrolytes, and lipid peroxidation. Application of nTiO₂, in association with NO, also enhanced the accumulation of osmolytes (proline and glycine betaine) that assisted the stressed plants in osmotic adjustment as witnessed by improved hydration level of the plants. Involvement of NO in nTiO₂-induced activation of defense system was confirmed with NO scavenger cPTIO [2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide] which caused recurrence of WDS.

The mutual effects of graphene oxide nanosheets and cadmium on the growth, cadmium uptake and accumulation in rice

The broad application and unique properties of graphene oxide (GO) nanosheets make them interact with other pollutants and subsequently alter their behaviors and toxicities. However, investigation on the effects of GO nanosheets on plant uptake of co-occurring heavy metals is scarce. We evaluated the mutual effects of cadmium (Cd) at 1 mg/L and different concentrated GO nanosheets (0, 1 and 10 mg/L) on the rice seed germination, further seedling growth, Cd uptake and accumulation in rice roots and shoots in a hydroponic system. The effects of GO were concentration dependent. GO alone at 1 mg/L showed no apparent effects, while GO alone at 10 mg/L accelerated the rice seed germination and root growth due to the improved water uptake. Cd alone showed adverse effects on the rice seed germination, which was alleviated by the presence of GO at 1 or 10 mg/L. GO at 10 mg/L also increased the membrane permeability, thus enhancing Cd uptake by rice roots and shoots. These results indicate that GO can change the effects of Cd on the rice seed germination and Cd uptake as well as accumulation in the roots and shoots of rice seedlings, which is helpful for understanding the fate and ecotoxicological impacts of both GO and Cd.

Discerning the mechanism of the multiwalled carbon nanotubes effect on root cell water and nutrient transport

Multiwalled carbon nanotubes (MWCNTs) are tubular carbon structures that are able to enter cells through holes in the plasma membrane and produce changes in gene expression. In this work, we compared the functionality of carbon nanotubes with the electroporation that perforates membranes, in Brassica oleracea var. Italica (broccoli) root protoplasts. For this, we combined those treatments with control conditions and abiotic stress (salinity) in order to elucidate if the response is related to conditions optimal for the plant. The measurement of the osmotic water permeability (Pf), mineral concentrations and expression levels of aquaporins (PIP1s and PIP2s) revealed that the physiological action of the nanotubes was similar to that achieved with electroporation for both Pf and the concentrations of nutrients in the protoplasts. On the other hand, PIP1s and PIP2s expression was increased in the protoplasts receiving the control plus MWCNTs treatment but not in those treated with electroporation. This opens new and interesting lines, as it shows that nanotubes are able to modulate the expression of aquaporins.

Single-wall carbon nanotubes improve cell survival rate and reduce oxidative injury in cryopreservation of Agapanthus praecox embryogenic callus

BACKGROUND

Cryopreservation is the best way for long-term in vitro preservation of plant germplasm resources. The preliminary studies found that reactive oxygen species (ROS) induced oxidative stress and ice-induced membrane damage are the fundamental causes of cell death in cryopreserved samples. How to improve plant cryopreservation survival rate is an important scientific issue in the cryobiology field.

RESULTS

This study found that the survival rate was significantly improved by adding single-wall carbon nanotubes (SWCNTs) to plant vitrification solution (PVS) in cryopreservation of Agapanthus praecox embryogenic callus (EC), and analyzed the oxidative response of cells during the control and SWCNTs-added cryopreservation protocol. The SWCNTs entered EC at the step of dehydration and mainly located around the cell wall and in the vesicles, and most of SWCNTs moved out of EC during the dilution step. Combination with physiological index and gene quantitative expression results, SWCNTs affect the ROS signal transduction and antioxidant system response during plant cryopreservation. The EC treated by SWCNTs had higher antioxidant levels, like POD, CAT, and GSH than the control group EC. The EC mainly depended on the AsA-GSH and GPX cycle to scavenge H₂O₂ in the control cryopreservation, but depended on CAT in the SWCNTs-added cryopreservation which lead to low levels of H₂O₂ and MDA. The elevated antioxidant level in dehydration by adding SWCNTs enhanced cells resistance to injury during cryopreservation. The ROS signals of EC were balanced and stable in the SWCNTs-added cryopreservation.

CONCLUSIONS

The SWCNTs regulated oxidative stress responses of EC during the process and controlled oxidative damages by the maintenance of ROS homeostasis to achieve a high survival rate after cryopreservation. This study is the first to systematically describe the role of carbon nanomaterial in the regulation of plant oxidative stress response, and provided a novel insight into the application of nanomaterials in the field of cryobiology.

Improvement of Commercially Valuable Traits of Industrial Crops by Application of Carbon-based Nanomaterials

Carbon-based nanomaterials (CBNs) have great potential as a powerful tool to improve plant productivity. Here, we investigated the biological effects of graphene and carbon nanotubes (CNTs) on fiber-producing species (cotton, Gossypium hirsutum) and ornamental species (vinca, Catharanthus roseus). The exposure of seeds to CNTs or graphene led to the activation of early seed germination in Catharanthus and overall higher germination in cotton and Catharanthus seeds. The application of CBNs resulted in higher root and shoot growth of young seedlings of both tested species. Cultivation of Catharanthus plants in soil supplemented with CBNs resulted in the stimulation of plant reproductive system by inducing early flower development along with higher flower production. Catharanthus plants cultivated in CNTs or graphene supplemented soil accelerated total flower production by 37 and 58%, respectively. Additionally, CBNs reduced the toxic effects caused by NaCl. Long-term application of CBNs to crops cultivated under salt stress conditions improved the desired phenotypical traits of Catharanthus (higher flower number and leaf number) and cotton (increased fiber biomass) compared to untreated plants of both species cultivated at the same stress condition. The drought stress experiments revealed that introduction of CBNs to matured Catharanthus plant increased the plant survival with no symptoms of leaf wilting as compared to untreated Catharanthus growing in water deficit conditions.

Effects of tetracycline on growth, oxidative stress response, and metabolite pattern of ryegrass

Tetracycline is an antibiotic that frequently contaminates the environment. In this study, the growth and metabolites of ryegrass seedlings treated with tetracycline (0, 1, 10 or 100 mg/L) for 5 days were investigated. The results showed that the growth of ryegrass and the concentrations of carotenoid and chlorophyll decreased as the tetracycline concentration increased. Tetracycline increased the production of reactive oxygen species (ROS) and cell permeability and triggered mitochondrial membrane potential loss in the roots of ryegrass. The metabolic profiles of ryegrass differed between the control and tetracycline-treated groups. The contents of glucose, shikimic acid, aconitic acid, serine, lactose, phenylalanine, mannitol, galactose, gluconic acid, asparagine, and glucopyranose were positively correlated with root length and had high variable importance projection values. These compounds may have crucial functions in root extension. Tetracycline also affected aminoacyl-tRNA biosynthesis, nitrogen metabolism, and alanine, aspartate and glutamate metabolism in the roots. Tetracycline may affect root extension by regulating the synthesis/degradation of these metabolites or the activity of their biosynthetic pathways. These results provide an insight into the stress response of ryegrass to tetracycline.

Multi-walled carbon nanotubes improved growth, anatomy, physiology, secondary metabolism, and callus performance in Catharanthus roseus: an in vitro study

This study was conducted to monitor the physiological and molecular responses of Catharanthus roseus (rose periwinkle) to multi-walled carbon nanotube (MWCNT) incorporation into the culture medium. The seeds were grown on hormone-free MS medium supplemented with 0, 50, 100, and 150 mgL^-1of MWCNT. The supplementations of culture medium with MWCNTs led to significant increases in plant growth indexes such as leaf width, leaf area, leaf fresh weight, root length, and total plant biomass). Slight increases were also observed in chlorophyll a (Chla), Chlb, and carotenoid contents (mean = 18.6%) in MWCNT-treated seedlings. Protein concentrations increased by an average of 34% relative to the control. The application of MWCNT resulted in twofold increases in the catalase and peroxidase activities. A similar trend was also observed in the phenylalanine ammonia lyase activities (by an average of 36.5%), soluble phenols (by 23%), and alkaloids (by 1.7-fold). Moreover, upregulations (mean = 37-fold) in the transcriptions of the DAT gene resulted from the MWCNT supplementations. Exposure to MWCNT improved cell sizes and xylem conducting tissue in treated seedlings. The applications of MWCNTs also stimulated the callus initiation and performance, implying their effects on proliferation and possible differentiation. This study has provided evidence of role MWCNT play in improving plant performance and production of pharmaceutical secondary metabolites.

Soybean Interaction with Engineered Nanomaterials: A Literature Review of Recent Data

With a continuous increase in the production and use in everyday life applications of engineered nanomaterials, concerns have appeared in the past decades related to their possible environmental toxicity and impact on edible plants (and therefore, upon human health). Soybean is one of the most commercially-important crop plants, and a perfect model for nanomaterials accumulation studies, due to its high biomass production and ease of cultivation. In this review, we aim to summarize the most recent research data concerning the impact of engineered nanomaterials on the soya bean, covering both inorganic (metal and metal-oxide nanoparticles) and organic (carbon-based) nanomaterials. The interactions between soybean plants and engineered nanomaterials are discussed in terms of positive and negative impacts on growth and production, metabolism and influences on the root-associated microbiota. Current data clearly suggests that under specific conditions, nanomaterials can negatively influence the development and metabolism of soybean plants. Moreover, in some cases, a possible risk of trophic transfer and transgenerational impact of engineered nanomaterials are suggested. Therefore, comprehensive risk-assessment studies should be carried out prior to any mass productions of potentially hazardous materials.

FePO4 nanoparticles produced by an industrially scalable continuous-flow method are an available form of P and Fe for cucumber and maize plants

Nanomaterials are widely used in medical and pharmaceutical fields, but their application in plant nutrition is at its infancy. Phosphorous (P) and iron (Fe) are essential mineral nutrients limiting in a wide range of conditions the yield of crops. Phosphate and Fe fertilizers to-date on the market display low efficiency (P fertilizers) and low persistence in soil (Fe fertilizers) and negatively affect the environment. In the tentative to overcome these problems, we developed a continuous industrially scalable method to produce FePO₄ NPs based on the rapid mixing of salt solutions in a mixing chamber. The process, that included the addition of citrate as capping agent allowed to obtain a stable suspension of NPs over the time. The NPs were tested for their effectiveness as P and Fe sources on two hydroponically grown crop species (cucumber and maize) comparing their effects to those exerted by non-nanometric FePO₄ (bulk FePO₄). The results showed that FePO₄ NPs improved the availability of P and Fe, if compared to the non-nano counterpart, as demonstrated by leaf SPAD indexes, fresh biomasses and P and Fe contents in tissues. The results open a new avenue in the application of nanosized material in the field of plant nutrition and fertilization.

Applications of Nanotechnology in Plant Growth and Crop Protection: A Review

In the era of climate change, global agricultural systems are facing numerous, unprecedented challenges. In order to achieve food security, advanced nano-engineering is a handy tool for boosting crop production and assuring sustainability. Nanotechnology helps to improve agricultural production by increasing the efficiency of inputs and minimizing relevant losses. Nanomaterials offer a wider specific surface area to fertilizers and pesticides. In addition, nanomaterials as unique carriers of agrochemicals facilitate the site-targeted controlled delivery of nutrients with increased crop protection. Due to their direct and intended applications in the precise management and control of inputs (fertilizers, pesticides, herbicides), nanotools, such as nanobiosensors, support the development of high-tech agricultural farms. The integration of biology and nanotechnology into nonosensors has greatly increased their potential to sense and identify the environmental conditions or impairments. In this review, we summarize recent attempts at innovative uses of nanotechnologies in agriculture that may help to meet the rising demand for food and environmental sustainability.

Applications of Nanotechnology in Plant Growth and Crop Protection: A Review

In the era of climate change, global agricultural systems are facing numerous, unprecedented challenges. In order to achieve food security, advanced nano-engineering is a handy tool for boosting crop production and assuring sustainability. Nanotechnology helps to improve agricultural production by increasing the efficiency of inputs and minimizing relevant losses. Nanomaterials offer a wider specific surface area to fertilizers and pesticides. In addition, nanomaterials as unique carriers of agrochemicals facilitate the site-targeted controlled delivery of nutrients with increased crop protection. Due to their direct and intended applications in the precise management and control of inputs (fertilizers, pesticides, herbicides), nanotools, such as nanobiosensors, support the development of high-tech agricultural farms. The integration of biology and nanotechnology into nonosensors has greatly increased their potential to sense and identify the environmental conditions or impairments. In this review, we summarize recent attempts at innovative uses of nanotechnologies in agriculture that may help to meet the rising demand for food and environmental sustainability.

Nanoparticles: biosynthesis, translocation and role in plant metabolism

Nanotechnology is an emerging field of science that applies particles between 1 and 100 nm in size for a range of practical uses. Nano-technological discoveries have opened novel applications in biotechnology and agriculture. Many reactions involving nanoparticles (NPs) are more efficient compared to those of their respective bulk materials. NPs obtained from plant material, denoted as biogenic or phytosynthesised NPs, are preferred over chemically synthesised NPs due to their low toxicity, rapid reactions and cost-effective production. NPs impart both positive and negative impacts on plant growth and development. NPs exhibit their unique actions as a function of their size, reactivity, surface area and concentration. An insight into NP biosynthesis and translocation within the plant system will shed some light on the roles and mechanisms of NP-mediated regulation of plant metabolism. This review is a step towards that goal.

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.

Nitrate reductase-dependent nitric oxide is crucial for multi-walled carbon nanotube-induced plant tolerance against salinity

Although there have been some studies on the plant-carbonaceous nanomaterials (CNMs) interactions, related conclusions were controversial. Here, we report that multi-walled carbon nanotubes (MWCNTs) can enter into rapeseed (Brassica napus L.) seedling root, and transport to stem. Further results showed that salinity-inhibited rapeseed seedling growth was obviously alleviated by MWCNTs. Meanwhile, NaCl-induced nitrate reductase (NR)-dependent NO production was significantly intensified by MWCNTs. The redox and ion imbalance was reestablished as well, confirmed by the reduction in reactive oxygen species (ROS) overproduction, the decrease in thiobarbituric acid reactive substance production, and the lower Na+/K+ ratio. These beneficial effects could be explained by the changes in related antioxidant defense genes, sodium hydrogen exchanger 1 (NHX1), salt overly sensitive 1 (SOS1), and K+transporter 1 (KT1) transcripts. The above responses were separately abolished after the removal of endogenous NO with its scavengers or the addition of the NR inhibitor. Genetic evidence revealed that the NaCl-triggered NO level in wild-type seedling roots was partly abolished in either the nitric reductase mutant (nia1/2) or noa1 mutant (exhibiting indirectly a reduced endogenous NO level). Treatment with MWCNTs could totally rescue the impaired NO production in the noa1 mutant rather than the nia1/2 mutant, suggesting that NR-dependent NO acts as a downstream signaling molecule in MWCNT signaling. This point was verified by phenotypic analyses, histochemical staining, and ion analysis. qPCR analysis further demonstrated that MWCNTs stimulated antioxidant genes and ion balance-related genes through NR-mediated NO. The above molecular and genetic evidence indicated that NR-dependent NO acts downstream of MWCNTs in salinity tolerance, which requires the reestablishment of redox and ion homeostasis.

The impact of tomato fruits containing multi-walled carbon nanotube residues on human intestinal epithelial cell barrier function and intestinal microbiome composition

Carbon nanomaterials (CNMs) can positively regulate seed germination and enhance plant growth. However, clarification of the impact of plant organs containing absorbed CNMs on animal and human health is a critical step of risk assessment for new nano-agro-technology. In this study, we have taken a comprehensive approach to studying the effect tomato fruits derived from plants exposed to multi-walled carbon nanotubes (CNTs) have on gastrointestinal epithelial barrier integrity and their impact on the human commensal intestinal microbiota using an in vitro cell culture and batch human fecal suspension models. The effects of CNTs on selected pure cultures of Salmonella enterica Typhimurium and Lactobacillus acidophilus were also evaluated. This study demonstrated that CNT-containing fruits or the corresponding residual level of pure CNTs (0.001 μg ml-1) was not sufficient to initiate a significant change in transepithelial resistance and on gene expression of the model T-84 human intestinal epithelial cells. However, at 10 μg ml-1 concentration CNTs were able to penetrate the cell membrane and change the gene expression profile of exposed cells. Moreover, extracts from CNT-containing fruits had minimal to no effect on human intestinal microbiota as revealed by culture-based analysis and 16S rRNA sequencing.

Zinc-Supported Multiwalled Carbon Nanotube Nanocomposite: A Synergism to Micronutrient Release and a Smart Distributor To Promote the Growth of Onion Seeds in Arid Conditions

In the current scenario, nanotechnological applications in the agriculture sector showing potential impacts on the improvement of plant growth in terms of protection and safety are at a very nascent stage. The present study deals with the synergistic role of zinc (Zn) and multiwalled carbon nanotubes (MWCNTs) synthesized as a zinc oxide (ZnO)/MWCNT nanocomposite, a prospective applicant to modulate the micronutrient supply and enhance the growth of onion seeds, thereby replacing harmful, unsafe chemical fertilizers. To the best of our knowledge, this is the first report wherein MWCNTs have been envisaged as a micronutrient distributor and a nutrient stabilizer enhancing the growth of onion plant under arid conditions. The growth trend of onion seeds was evaluated in an aqueous medium with varied concentrations of (i) MWCNTs, (ii) zinc oxide nanoparticles, and (iii) ZnO/MWCNT nanocomposites. ZnO/MWCNT nanocomposites with 15 μg/mL concentration displayed the best seedling growth with the maximum number of cells in telophase. A significant growth trend with increased concentration of ZnO/MWCNTs displayed no negative impact on plant growth in contrast to that with the use of MWCNTs. The synergistic impact of Zn nanoparticles and MWCNTs in ZnO/MWCNT nanocomposites on the rate of germination was explained via a mechanism supported by scanning transmission electron microscopy.

Effects of carbon-based nanomaterials on seed germination, biomass accumulation and salt stress response of bioenergy crops

Bioenergy crops are an attractive option for use in energy production. A good plant candidate for bioenergy applications should produce a high amount of biomass and resist harsh environmental conditions. Carbon-based nanomaterials (CBNs) have been described as promising seed germination and plant growth regulators. In this paper, we tested the impact of two CBNs: graphene and multi-walled carbon nanotubes (CNTs) on germination and biomass production of two major bioenergy crops (sorghum and switchgrass). The application of graphene and CNTs increased the germination rate of switchgrass seeds and led to an early germination of sorghum seeds. The exposure of switchgrass to graphene (200 mg/l) resulted in a 28% increase of total biomass produced compared to untreated plants. We tested the impact of CBNs on bioenergy crops under salt stress conditions and discovered that CBNs can significantly reduce symptoms of salt stress imposed by the addition of NaCl into the growth medium. Using an ion selective electrode, we demonstrated that the concentration of Na⁺ ions in NaCl solution can be significantly decreased by the addition of CNTs to the salt solution. Our data confirmed the potential of CBNs as plant growth regulators for non-food crops and demonstrated the role of CBNs in the protection of plants against salt stress by desalination of saline growth medium.

Nanofertilizer for Precision and Sustainable Agriculture: Current State and Future Perspectives

The increasing food demand as a result of the rising global population has prompted the large-scale use of fertilizers. As a result of resource constraints and low use efficiency of fertilizers, the cost to the farmer is increasing dramatically. Nanotechnology offers great potential to tailor fertilizer production with the desired chemical composition, improve the nutrient use efficiency that may reduce environmental impact, and boost the plant productivity. Furthermore, controlled release and targeted delivery of nanoscale active ingredients can realize the potential of sustainable and precision agriculture. A review of nanotechnology-based smart and precision agriculture is discussed in this paper. Scientific gaps to be overcome and fundamental questions to be answered for safe and effective development and deployment of nanotechnology are addressed.

Assessment of Effects of the Long-Term Exposure of Agricultural Crops to Carbon Nanotubes

Carbon-based nanoparticles (CBNs) are nanomaterials that have been shown to be plant growth regulators. Here, we investigated the effects of long-term exposure to multi-walled carbon nanotubes (MWCNTs) on the growth of three important crops (barley, soybean, and corn). The tested species were cultivated in hydroponics supplemented with 50 μg/mL MWCNTs. After 20 weeks of continuous exposure to the nanomaterials, no significant toxic effects on plant development were observed. Several positive phenotypical changes were recorded, in addition to the enhancement of photosynthesis in MWCNT-exposed crops. Raman spectroscopy with point-by-point mapping proved that the MWCNTs in the hydroponic solution moved into all tested species and were distributed in analyzed organs (leaves, stems, roots, and seeds). Our results confirmed the significant potential of CBN in plant agriculture. However, the documented presence of MWCNTs in different organs of all exposed crops highlighted the importance of detailed risk assessment of nanocontaminated plants moving into the food chain.

Characterization and toxicity of nanoscale fragments in wastewater treatment plant effluent

Much attention has been paid to extracting and isolating specific and well-known nanoparticles (especially for engineered nanomaterials) from complex environmental matrices. However, such research may not provide global information on actual contamination because nanoscale fragments exist as mixtures of various elements and matrices in the real environment. The present work first isolated and characterized nanoscale fragments in effluents from municipal wastewater treatment plants (WWTPs). The nanoscale fragments were found to be composed of 70-85% carbon and low amounts of oxygen, heavy metals and other elements and exhibited nanosheet topographies (approximately 0.87-1.31 nm thickness and 68-187 nm lateral length). Because the isolated nanoscale fragments were mixtures rather than one specific type of nanoparticle, they were present at high concentrations ranging from 0.07 to 0.55 mg/L. It was also found that the accumulation of nanoscale fragments in rice reached 0.59 mg/g under exposure to environmentally relevant concentrations, leading to marked phytotoxicity (e.g., ultrastructural damage to chloroplasts and mitochondria). Metabolic analysis revealed the toxicological mechanisms to be related to disorders of carbohydrate, amino acid and fatty acid metabolism. This study is the first to characterize the properties and analyze the toxicity of nanoscale fragments in the effluents of WWTPs. Given that WWTP effluents containing nanoscale fragments are continuously discharged to the soil, surface water and seas, nanoscale fragment materials deserve considerable attention in future work compared with the few widely studied engineered nanoparticles.

Multi-walled carbon nanotubes applied through seed-priming influence early germination, root hair, growth and yield of bread wheat (Triticum aestivum L.)

BACKGROUND

Reports of multi-walled carbon nanotubes (MWCNTs) incorporated into plants have indicated better yield and productivity, yet the phenomena need in-depth understanding especially when agricultural crops are tested. We primed wheat seeds with MWCNTs to understand the effects on germination, growth, anatomy, physiology and yield.

RESULT

This study, carried out in field conditions, is a step forward over the previous reports. Early germination, excessive root hair, denser stomata and larger root length result in faster growth and higher yield of wheat plants. Denser root hair facilitated the uptake of both water and essential minerals such as phosphorus (P) and potassium (K), which boosted the crop yield by significantly improving grain yield per plant from 1.53 to 2.5 g, a 63% increase. Increase in cell elongation by 80% was recorded, while xylem and phloem sizes dilated to almost 83% and 85% of control, thus enhancing their capacity to conduct water and nutrients.

CONCLUSION

Augmented growth of MWCNT-primed wheat, enhancement in grain number, biomass, stomatal density, xylem-phloem size, epidermal cells, and water uptake is observed while finding no DNA damage. This opens up an entirely new aspect to using cost-effective nanomaterials (the MWCNTs were produced in-house) for enhancing the performance of crop plants. © 2017 Society of Chemical Industry.