Enhancement of secondary metabolites in Bacopa monnieri (L.) Pennell plants treated with copper-based nanoparticles in vivo

Variations in the biochemical characteristics of Lavandula sublepidota Rech.f. in response to the foliar enrichment of green-synthesized copper nano complexes from extract of neem and jujube

Copper (Cu) is an essential micronutrient in plant physiology and biochemistry. This article synthesized copper nano complexes (Cu-NCs) based on aqueous extracts of jujube and neem leaves. The effects of foliar application of Cu-jujube and Cu-neem Cu-NCs at concentrations of 0, 10, 25, and 50 mg L-1 on the bioactive compounds, antioxidant capacity, and essential oil of the Iranian native medicinal herb Lavandula sublepidota Rech. f. was investigated. The highest levels of flavonoids and polyphenols were observed in the plants treated with Cu-NCs at 25 mg L-1. However, no superiority was observed between the two types of Cu-NCs. Furthermore, 25 mg L-1 nCu-Z and nCu-N foliar application boosted essential oil yield (48 and 52%, respectively) over control. This suggests an ideal threshold beyond which toxicity was found. Similarly, the amount of commercially significant secondary metabolites increased at 25 mg L-1 CuNCs compared to 10 and 50 mg L-1 concentrations. The maximum antioxidant activity was found in extracts of lavender that had been treated with 25 mg L-1 CuNCs. When CuNCs were applied exogenously, the extracts' antibacterial activity (MIC μg mL-1) was substantially increased against the three pathogen strains. The results suggest that CuNCs demonstrate notably greater effectiveness, particularly at an ideal concentration of 25 mg L-1, in enhancing the production of essential oil and bioactive compounds in Lavandula sublepidota Rech. f. Therefore, these findings indicate the importance of the biosynthesis of NCs using plants and measuring the phytochemical changes of lavender plants.

Emerging concern of nano-pollution in agro-ecosystem: Flip side of nanotechnology

Nanomaterials (NMs) have proven to be a game-changer in agriculture, showcasing their potential to boost plant growth and safeguarding crops. The agricultural sector has widely adopted NMs, benefiting from their small size, high surface area, and optical properties to augment crop productivity and provide protection against various stressors. This is attributed to their unique characteristics, contributing to their widespread use in agriculture. Human exposure from various components of agro-environmental sectors (soil, crops) NMs residues are likely to upsurge with exposure paths may stimulates bioaccumulation in food chain. With the aim to achieve sustainability, nanotechnology (NTs) do exhibit its potentials in various domains of agriculture also have its flip side too. In this review article we have opted a fusion approach using bibliometric based analysis of global research trend followed by a holistic assessment of pros and cons i.e. toxicological aspect too. Moreover, we have also tried to analyse the current scenario of policy associated with the application of NMs in agro-environment.

Nano-elicitation and hydroponics: a synergism to enhance plant productivity and secondary metabolism

MAIN CONCLUSION

This review has explored the importance of using a synergistic approach of nano-elicitation and hydroponics to improve plant growth and metabolite production. Furthermore, it emphasizes the significance of green nanotechnology and eco-friendly practices while utilizing this approach to promote the development of a sustainable agriculture system. Nano-elicitation stimulates metabolic processes in plants using nanoparticles (NPs) as elicitors. The stimulation of these biochemical processes can enhance plant yield and productivity, along with the production of secondary metabolites. Nanoparticles have garnered the attention of scientific community because of their unique characteristics, such as incredibly small size and large surface-to-volume ratio, which make them effective elicitors. Hydroponic systems, which optimize growing conditions to increase plant production, are typically used to study the effect of elicitors. By integrating these two approaches, the qualitative and quantitative output of plants can be increased while employing minimal resources. As the global demand for high-quality crops and bioactive compounds surges, embracing this synergistic approach alongside sustainable farming practices can pave the way for resilient agricultural systems, ensuring food security and fostering an eco-friendly environment.

Pseudomonas stutzeri improves the tolerance of Lemna minor to Cu(OH)2 nanopesticide by regulating the uptake of copper, antioxidant defense mechanisms, and the expression of metacaspase-1, chlorophyllase, and stress-responsive genes

This study investigated the effect of Pseudomonas stutzeri inoculation on Lemna minor treated with Cu(OH)2 nanopesticide (NP). The results showed that P. stutzeri inoculation increased the relative growth rate (RGR) in NP-treated plants. Although chlorophyll and carotenoid contents decreased significantly in NP-treated plants, P. stutzeri inoculation led to an increase in chlorophyll and carotenoid contents in NP-treated plants. Copper (Cu) content increased with increasing NP concentration, but it decreased significantly in the presence of P. stutzeri. NP treatment caused increased H2O2 and TBARS levels, as well as proline levels. However, P. stutzeri inoculation led to decreased H2O2 and TBARS levels and increased SOD, POX, GST, GR, GPX, and DHAR activities. The expression of genes encoding SOD, GST, metacaspase-1, and chlorophyllase was upregulated by NP treatment alone. Additionally, when plants were inoculated with P. stutzeri, the expression of these genes was further enhanced. In conclusion, P. stutzeri inoculation had a positive effect on the growth and antioxidant system of L. minor treated with NP as it enhanced RGR, increased chlorophyll and carotenoid contents, and decreased Cu content and oxidative stress. These findings suggested that P. stutzeri has the potential to promote aquatic plant growth and counteract the negative impacts of NP on these plants.

Copper boosts the biostimulant activity of a vegetal-derived protein hydrolysate in basil: morpho-physiological and metabolomics insights

In addition to be used as a plant protection agent, copper (Cu) is also an essential micronutrient for plant growth and development. The bioavailability of Cu in agricultural systems can be limited due to its specific physical-chemical characteristics, leading to imbalances in plant production. To address this issue, an experimental trial was conducted on Genovese basil (Ocimum basilicum L.) in protected conditions to comparatively evaluate the effects of a vegetable protein hydrolysate (VPH), free Cu and Cu complexed with peptides and amino acids of vegetal origin (Cu and Cu-VPH, respectively), and a combination of VPH and Cu-VPH (VPH+Cu-VPH). The study showed that the combined application of VPH+Cu-VPH led to a significant average increase of 16.3% in fresh yield compared to the untreated Control and Cu treatment. This finding was supported by an improved photosynthetic performance in ACO2 (+29%) and Fv/Fm (+7%). Furthermore, mineral analysis using ICP OES demonstrated that Cu and Cu-VPH treatments determined, on average, a 15.1-, 16.9-, and 1.9-fold increase in Cu in plant tissues compared to control, VPH, and VPH+Cu-VPH treatments, respectively. However, the VPH+Cu-VPH treatment induced the highest contents of the other analyzed ions, except for P. In particular, Mg, Mn, Ca, and Fe, which take part in the constitution of chlorophylls, water splitting system, and photosynthetic electron transport chain, increased by 23%, 21%, 25%, and 32% compared to respective controls. Indeed, this improved the photosynthetic efficiency and the carboxylation capacity of the plants, and consequently, the physiological and productive performance of Genovese basil, compared to all other treatments and control. Consistently, the untargeted metabolomics also pointed out a distinctive modulation of phytochemical signatures as a function of the treatment. An accumulation of alkaloids, terpenoids, and phenylpropanoids was observed following Cu treatment, suggesting an oxidative imbalance upon metal exposure. In contrast, a mitigation of oxidative stress was highlighted in Cu-VPH and VPH+Cu-VPH, where the treatments reduced stress-related metabolites. Overall, these results highlight an interaction between Cu and VPH, hence paving the way towards the combined use of Cu and biostimulants to optimize agronomic interventions.

Essential oil-grafted copper nanoparticles as a potential next-generation fungicide for holistic disease management in maize

Sustainable food production is necessary to meet the demand of the incessantly growing human population. Phytopathogens pose a major constraint in food production, and the use of conventional fungicides to manage them is under the purview of criticism due to their numerous setbacks. In the present study, essential oil-grafted copper nanoparticles (EGC) were generated, characterized, and evaluated against the maize fungal pathogens, viz., Bipolaris maydis, Rhizoctonia solani f. sp. sasakii, Macrophomina phaseolina, Fusarium verticillioides, and Sclerotium rolfsii. The ED₅₀ for the fungi under study ranged from 43 to 56 μg ml^-1, and a significant inhibition was observed at a low dose of 20 μg ml^-1 under in vitro conditions. Under net house conditions, seed treatment + foliar spray at 250 and 500 mg L^-1 of EGC performed remarkably against maydis leaf blight (MLB), with reduced percent disease index (PDI) by 27.116 and 25.292%, respectively, in two Kharif seasons (May-Sep, 2021, 2022). The activity of enzymatic antioxidants, viz., β-1, 3-glucanase, PAL, POX, and PPO, and a non-enzymatic antioxidant (total phenolics) was increased in treated maize plants, indicating host defense was triggered. The optimum concentrations of EGC (250 mg L^-1 and 500 mg L^-1) exhibited improved physiological characteristics such as photosynthetic activity, shoot biomass, plant height, germination percentage, vigor index, and root system traits. However, higher concentrations of 1,000 mg L^-1 rendered phytotoxicity, reducing growth, biomass, and copper bioaccumulation to high toxic levels, mainly in the foliar-sprayed maize leaves. In addition, EGC and copper nanoparticles (CuNPs) at 1,000 mg L^-1 reduced the absorption and concentration of manganese and zinc indicating a negative correlation between Cu and Mn/Zn. Our study proposes that the CuNPs combined with EO (Clove oil) exhibit astounding synergistic efficacy against maize fungal pathogens and optimized concentrations can be used as an alternative to commercial fungicides without any serious impact on environmental health.

Effect of silver nanoparticles on tropane alkaloid production of transgenic hairy root cultures of Hyoscyamus muticus L. and their antimicrobial activity

The utilization of nanotechnology and biotechnology for enhancing the synthesis of plant bioactive chemicals is becoming increasingly common. The hairy root culture technique can be used to increase secondary metabolites such as tropane alkaloids. Agrobacterium was used to induce hairy roots from various explants of Hyoscyamus muticus. The effect of nano-silver particles (AgNPs) at concentrations of 0, 25, 50, 100, and 200 mg/L on tropane alkaloids synthesis, particularly hyoscyamine and scopolamine, was studied in transgenic hairy root cultures. Different types of explants obtained from 10-day-old seedlings of H. muticus were inoculated with two strains of Agrobacterium rhizogenes (15,834 and A4). The antimicrobial activity of an ethanolic extract of AgNPs-induced hairy root cultures of H. muticus was tested. The frequency of hairy roots was higher in hypocotyl, root, leaf, and stem explants treated with A. rhizogenes strain A4 compared to those treated with strain 15,834. In transgenic hairy root cultures, AgNPs application at a concentration of 100 mg/L resulted in the highest total tropane alkaloid production, which exhibited broad-spectrum antimicrobial activity. The study demonstrated the potential of nano-silver as an elicitor for promoting the production of target alkaloids in Hyoscyamus muticus hairy root cultures, which exhibit high biological activity.

Strategic nanoparticle-mediated plant disease resistance

Nanotechnology is a promising means for development of sustainable agriculture while the study of nanoparticle-mediated plant disease resistance is still in its primary stage. Nanotechnology has shown great promise in regulating: the content of secondary metabolites, inducing disease resistance genes, delivering hormones, delivering biomolecules (such as: nucleotides, proteins, and activators), and obtaining transgenic plants to resist plant diseases. In this review, we conclude its versatility and applicability in disease management strategies and diagnostics and as molecular tools. With the advent of new biotechnologies (e.g. de novo regeneration, CRISPR/Cas9, and GRF4-GIF1 fusion protein), we discuss the potential of nanoparticles as an optimal platform to deliver biomolecules to plants for genetic engineering. In order to ensure the safe use and social acceptance of plant nanoparticle technology, its adverse effects are discussed, including the risk of transferring nanoparticles through the food chain.

Foliar-applied nanoscale zero-valent iron (nZVI) and iron oxide (Fe3O4) induce differential responses in growth, physiology, antioxidative defense and biochemical indices in Leonurus cardiaca L

The impacts of nZVI and iron oxides on growth, physiology and elicitation of bioactive antioxidant metabolites in medicinal aromatic plants must be critically assessed to ensure their safe utilization within the food chain and achieve nutritional gains. The present study investigated and compared the morpho-physiological and biochemical changes of Leonurus cardiaca L. plants as affected by various concentrations (0, 250, 500 and 1000 mg L^-1) of nZVI and Fe₃O₄. The foliar uptake of nZVI was verified through Scanning Electron Microscopy (SEM) images and Energy Dispersive X-ray (EDX) analytical spectra. Plants exposed to nZVI at low concentration showed comparatively monotonic deposition of NPs on the surface of leaves, however, the agglomerate size of nZVI was raised as their doses increased, leading to remarkable changes in anatomical and biochemical traits. 250 mg L^-1 nZVI and 500 mg L^-1 Fe₃O₄ significantly (P < 0.05) increased plant dry matter accumulation by 37.8 and 27% over the control, respectively. The treatments of nZVI and Fe₃O₄ at 250 mg L^-1 significantly (P < 0.01) improved chlorophyll a content by 22.4% and 15.3% as compared to the control, and then a rapid decrease (by 14.8% and 4.1%) followed at 1000 mg L^-1, respectively. Both nZVI and Fe₃O₄ at 250 mg L^-1 had no significant impact on malondialdehyde (MDA) formation, however, at an exposure of 500-1000 mg L^-1, the MDA levels and cellular electrolyte leakage were increased. Although nZVI particles could be utilized by plants and enhanced the synthesis of chlorophylls and secondary metabolites, they appeared to be more toxic than Fe₃O₄ at 1000 mg L^-1. Exposure to nZVI levels showed positive, negative and or neutral impacts on leaf water content compared to control, while no significant difference was observed with Fe₃O₄ treatments. Soluble sugar, total phenolics and hyperoside content were significantly increased upon optimum concentrations of employed treatments-with 250 mg L^-1 nZVI being most superior. Among the extracts, those obtained from plants treated with 250-500 mg L^-1 nZVI revealed the strong antioxidant activity in terms of scavenging free radical (DPPH) and chelating ferrous ions. These results suggest that nZVI (at lower concentration) has alternative and additional benefits both as nano-fertilizer and nano-elicitor for biosynthesis of antioxidant metabolites in plants, but at high concentrations is more toxic than Fe₃O₄.

Biotechnology for propagation and secondary metabolite production in Bacopa monnieri

Bacopa monnieri (L.) Wettst. or water hyssop commonly known as "Brahmi" is a small, creeping, succulent herb from the Plantaginaceae family. It is popularly employed in Ayurvedic medicine as a nerve tonic to improve memory and cognition. Of late, this plant has been reported extensively for its pharmacologically active phyto-constituents. The main phytochemicals are brahmine, alkaloids, herpestine, and saponins. The saponins include bacoside A, bacoside B, and betulic acid. Investigation into the pharmacological effect of this plant has thrived lately, encouraging its neuroprotective and memory supporting capacity among others. Besides, it possesses many other therapeutic activities like antimicrobial, antioxidant, anti-inflammatory, gastroprotective properties, etc. Because of its multipurpose therapeutic potential, it is overexploited owing to the prioritization of natural remedies over conventional ones, which compels us to conserve them. B. monnieri is confronting the danger of extinction from its natural habitat as it is a major cultivated medico-botanical and seed propagation is restricted due to less seed availability and viability. The ever-increasing demand for the plant can be dealt with mass propagation through plant tissue culture strategy. Micropropagation utilizing axillary meristems as well as de novo organogenesis have been widely investigated in this plant which has also been explored for its conservation and production of different types of secondary metabolites. Diverse in vitro methods such as organogenesis, cell suspension, and callus cultures have been accounted for with the aim of production and/or enhancement of bacosides. Direct shoot-organogenesis was initiated in excised leaf and internodal explants without any exogenous plant growth regulator(s) (PGRs), and the induction rate was improved when exogenous cytokinins and other supplements were used. Moreover, biotechnological toolkits like Agrobacterium-mediated transformation and the use of mutagens have been reported. Besides, the molecular marker-based studies demonstrated the clonal fidelity among the natural and in vitro generated plantlets also elucidating the inherent diversity among the natural populations. Agrobacterium-mediated transformation system was mostly employed to optimize bacoside biosynthesis and heterologous expression of other genes. The present review aims at depicting the recent research outcomes of in vitro studies performed on B. monnieri which include root and shoot organogenesis, callus induction, somatic embryogenesis, production of secondary metabolites by in vitro propagation, acclimatization of the in vitro raised plantlets, genetic transformation, and molecular marker-based studies of clonal fidelity. KEY POINTS: • Critical and up to date records on in vitro propagation of Bacopa monnieri • In vitro propagation and elicitation of secondary metabolites from B. monnieri • Molecular markers and transgenic studies in B. monnieri.

Nanoparticles as elicitors and harvesters of economically important secondary metabolites in higher plants: A review

Nanoparticles possess some unique properties which improve their biochemical reactivity. Plants, due to their stationary nature, are constantly exposed to nanoparticles present in the environment, which act as abiotic stress agents at sub-toxic concentrations and phytotoxic agents at higher concentrations. In general, nanoparticles exert their toxicological effect by the generation of reactive oxygen species to which plants respond by activating both enzymatic and non-enzymatic anti-oxidant defence mechanisms. One important manifestation of the defence response is the increased or de novo biosynthesis of secondary metabolites, many of which have commercial application. The present review extensively summarizes current knowledge about the application of different metallic, non-metallic and carbon-based nanoparticles as elicitors of economically important secondary metabolites in different plants, both in vivo and in vitro. Elicitation of secondary metabolites with nanoparticles in plant cultures, including hairy root cultures, is discussed. Another emergent technology is the ligand-harvesting of secondary metabolites using surface-functionalized nanoparticles, which is also mentioned. A brief explanation of the mechanism of action of nanoparticles on plant secondary metabolism is included. Optimum conditions and parameters to be evaluated and standardized for the successful commercial exploitation of this technology are also mentioned.

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.