Melatonin reduces nanoplastic uptake, translocation, and toxicity in wheat

Combined contamination of microplastic and antibiotic alters the composition of microbial community and metabolism in wheat and maize rhizosphere soil

The widespread application of antibiotics and plastic films in agriculture has led to new characteristics of soil pollution. The impacts of combined contamination of microplastics and antibiotics on plant growth and rhizosphere soil bacterial community and metabolisms are still unclear. We conducted a pot experiment to investigate the effects of polyethylene (0.2%) and norfloxacin/doxycycline (5 mg kg-1), as well as the combination of polyethylene and antibiotics, on the growth, rhizosphere soil bacterial community and metabolisms of wheat and maize seedlings. The results showed that combined contamination caused more serious damage to plant growth than individual contamination, and aggravated root oxidative stress responses. The diversity and structure of soil bacterial community were not markedly altered, but the composition of the bacterial community, soil metabolisms and metabolic pathways were altered. The co-occurrence network analysis indicated that combined contamination may inhibit the growth of wheat and maize seedings by simplifying the interrelationships between soil bacteria and metabolites, and altering the relative abundance of specific bacteria genera (e.g. Kosakonia and Sphingomonas) and soil metabolites (including sugars, organic acids and amino acids). The results help to elucidate the potential mechanisms of phytotoxicity of the combination of microplastic and antibiotics.

Effects of microplastics and combined pollution of polystyrene and di-n-octyl phthalate on photosynthesis of cucumber (Cucumis sativus L.)

Photosynthesis provides carbon sources and energy for crop growth and development, and the widespread presence of microplastics and plastic plasticisers in agricultural soils affects crop photosynthesis, but the mechanism of the effect is not clear. This study aims to investigate the effects of different microplastics and plasticizers on cucumber photosynthesis. Using polyvinyl chloride (PVC), polyethylene (PE), polystyrene (PS), and di-n-octyl phthalate (DOP) as representative microplastics and plasticizers, we assessed their impact on cucumber photosynthesis. Our results reveal significant alterations in key parameters: intercellular CO2 concentration (Ci) and transpiration rate (Tr) increased across all treatments, whereas stomatal limit value (Ls) and water use efficiency (WUE) decreased. Notably, PS + DOP treatment led to a significant reduction in the maximum efficiency of photosystem II (Fv/Fm) and ATP accumulation. Furthermore, PE and PS + DOP treatments decreased lycopene and ɛ-carotene synthesis rates, as well as abscisic acid (ABA) accumulation. All treatments inhibited the conversion of β-carotene into strigolactone (SL) and decreased chlorophyll synthesis rates, with PS + DOP exhibiting the most severe impact. Regarding chlorophyll degradation pathways, PVC and PE treatments reduced chlorophyll decomposition rates, whereas DOP with PS promoted degradation. PE and PS treatments also impaired light energy capture, electron transport, and the structural stability of photosystems I and II, as well as photosynthetic capacity and NADPH and ATP synthesis rates. Our findings underscore the differential impacts of microplastics and plasticizers on cucumber photosynthesis, with PS + DOP having the most detrimental effect. These results shed light on the complex interactions between microplastics and plant physiology, highlighting the urgent need for mitigation strategies in agricultural practices to safeguard crop productivity and environmental sustainability.

Unveiling the impact of microplastics and nanoplastics on vascular plants: A cellular metabolomic and transcriptomic review

With increasing plastic manufacture and consumption, microplastics/nanoplastics (MP/NP) pollution has become one of the world's pressing global environmental issues, which poses significant threats to ecosystems and human health. In recent years, sharp increasing researches have confirmed that MP/NP had direct or indirect effects on vegetative growth and sexual process of vascular plant. But the potential mechanisms remain ambiguous. MP/NP particles can be adsorbed and/or absorbed by plant roots or leaves and thus cause diverse effects on plant. This holistic review aims to discuss the direct effects of MP/NP on vascular plant, with special emphasis on the changes of metabolic and molecular levels. MP/NP can alter substance and energy metabolism, as well as shifts in gene expression patterns. Key aspects affected by MP/NP stress include carbon and nitrogen metabolism, amino acids biosynthesis and plant hormone signal transduction, expression of stress related genes, carbon and nitrogen metabolism related genes, as well as those involved in pathogen defense. Additionally, the review provides updated insights into the growth and physiological responses of plants exposed to MP/NP, encompassing phenomena such as seed/spore germination, photosynthesis, oxidative stress, cytotoxicity, and genotoxicity. By examining the direct impact of MP/NP from both physiological and molecular perspectives, this review sets the stage for future investigations into the complex interactions between plants and plastic pollutants.

Microplastics in agroecosystems: Soil-plant dynamics and effective remediation approaches

Increasing microplastic (MP) pollution, primarily from anthropogenic sources such as plastic film mulching, waste degradation, and agricultural practices, has emerged as a pressing global environmental concern. This review examines the direct and indirect effects of MPs on crops, both in isolation and in conjunction with other contaminants, to elucidate their combined toxicological impacts. Organic fertilizers predominantly contain 78.6% blue, 9.5% black, and 8.3% red MPs, while irrigation water in agroecosystems contains 66.2% white, 15.4% blue, and 8.1% black MPs, ranging from 0-1 mm to 4-5 mm in size. We elucidate five pivotal insights: Firstly, soil MPs exhibit affinity towards crop roots, seeds, and vascular systems, impeding water and nutrient uptake. Secondly, MPs induce oxidative stress in crops, disrupting vital metabolic processes. Thirdly, leachates from MPs elicit cytotoxic and genotoxic responses in crops. Fourthly, MPs disrupt soil biotic and abiotic dynamics, influencing water and nutrient availability for crops. Lastly, the cumulative effects of MPs and co-existing contaminants in agricultural soils detrimentally affect crop yield. Thus, we advocate agronomic interventions as practical remedies. These include biochar input, application of growth regulators, substitution of plastic mulch with crop residues, promotion of biological degradation, and encouragement of crop diversification. However, the efficacy of these measures varies based on MP type and dosage. As MP volumes increase, exploring alternative mitigation strategies such as bio-based plastics and environmentally friendly biotechnological solutions is imperative. Recognizing the persistence of plastics, policymakers should enact legislation favoring the mitigation and substitution of non-degradable materials with bio-derived or compostable alternatives. This review demonstrates the urgent need for collective efforts to alleviate MP pollution and emphasizes sustainable interventions for agricultural ecosystems.

Polystyrene nanoplastics in soil impair drought priming-induced low temperature tolerance in wheat

Drought priming is known to enhance plant low temperature tolerance, whereas polystyrene nanoplastic contamination exerts detrimental effects on plant growth. This study investigates the less-explored influence of nanoplastic contamination on cold stress tolerance in drought-primed plants. We compared the photosynthetic carbon assimilation, carbohydrate metabolism, reactive oxygen species metabolism, and grain yield between the non-primed and drought-primed wheat grown in both nanoplastic-contaminated and healthy soils. Our results reveal that the beneficial effects of drought priming on photosynthetic carbon assimilation and the efficiency of the "water-water" cycle were compromised in the presence of nanoplastics (nPS). Additionally, nPS exposure disturbed carbohydrate metabolism, which impeded source-to-sink transport of sugar and resulted in reduced grain yield in drought-primed plants under low temperature conditions. These findings unveil the suppression of nPS on drought-primed low-temperature tolerance (DPLT) in wheat plants, suggesting an intricate interplay between the induction of stress tolerance and responses to nPS contamination. The study raises awareness about a potential challenge for future crop production.

Strigolactones alleviate the toxicity of polystyrene nanoplastics (PS-NPs) in maize (Zea mays L.)

Nanoplastics are widely used across various fields, yet their uptake can potentially exert adverse effects on plant growth and development, ultimately reducing yields. While there is growing awareness of the phytotoxicity caused by nanoplastics, our understanding of effective strategies to prevent nanoplastic accumulation in plants remains limited. This study explores the role of strigolactones (SLs) in mitigating the toxicity of polystyrene nanoplastics (PS-NPs) in Zea mays L. (maize). SLs application markedly inhibited PS-NPs accumulation in maize roots, thus enhancing the root weight, shoot weight and shoot length of maize. Physiological analysis showed that SLs application activated the activities of antioxidant defence enzymes, superoxide dismutase and catalase, to decrease the malondialdehyde content and electrolyte leakage and alleviate the accumulation of H2O2 and O2.- induced by PS-NPs in maize plants. Transcriptomic analyses revealed that SLs application induced transcriptional reprogramming by regulating the expression of genes related to MAPK, plant hormones and plant-pathogen interaction signal pathways in maize treated with PS-NPs. Notably, the expression of genes, such as ZmAUX/IAA and ZmGID1, associated with phytohormones in maize treated with PS-NPs underwent significant changes. In addition, SLs induced metabolic dynamics changes related to amino acid biosynthesis, ABC transporters, cysteine and methionine metabolism in maize treated with PS-NPs. In summary, these results strongly reveal that SLs could serve as a strategy to mitigate the accumulation and alleviate the stress of PS-NPs in maize, which appears to be a potential approach for mitigating the phytotoxicity induced by PS-NPs in maize.

Uptake and effect of carboxyl-modified polystyrene microplastics on cotton plants

Microplastics (MPs) have emerged as a significant global environmental concern, particularly within agricultural soil systems. The extensive use of plastic film mulching in cotton cultivation has led to the alarming presence of MP pollution in cotton fields. However, the uptake and effects of MPs on the growth of cotton plants are poorly understood. In this study, we conducted a comprehensive analysis of hydroponically cultured cotton seedlings at the phenotypic, transcriptional, and metabolic levels after exposure to carboxyl-modified polystyrene microplastics (PS-COOH). Treatment with three concentrations of PS-COOH (100, 300, and 500 mg/L) resulted in notable growth inhibition of treated plants and exhibited a dose-dependent effect. And, PS-COOH can invade cotton roots and be absorbed through the intercellular spaces via apoplastic uptake, with accumulation commensurate with treatment duration. Transcriptomic analysis showed significant up-regulation of genes associated with antioxidant activity in response to 300 mg/L PS-COOH treatment, suggesting the induction of oxidative stress. In addition, the PS-COOH treatment activated the phenylpropanoid biosynthesis pathway, leading to lignin and flavonoid accumulation, and altered sucrose catabolism. These findings illustrate the absorption and effects of MPs on cotton seedlings and offer valuable insights into the potential toxicity of MPs to plants in soil mulched with plastic film.

The effects of Micro/Nano-plastics exposure on plants and their toxic mechanisms: A review from multi-omics perspectives

In recent years, plastic pollution has become a global environmental problem, posing a potential threat to agricultural ecosystems and human health, and may further exacerbate global food security problems. Studies have revealed that exposure to micro/nano-plastics (MPs/NPs) might cause various aspects of physiological toxicities, including plant biomass reduction, intracellular oxidative stress burst, photosynthesis inhibition, water and nutrient absorption reduction, cellular and genotoxicity, seed germination retardation, and that the effects were closely related to MP/NP properties (type, particle size, functional groups), exposure concentration, exposure duration and plant characteristics (species, tissue, growth stage). Based on a brief review of the physiological toxicity of MPs/NPs to plant growth, this paper comprehensively reviews the potential molecular mechanism of MPs/NPs on plant growth from perspectives of multi-omics, including transcriptome, metabolome, proteome and microbiome, thus to reveal the role of MPs/NPs in plant transcriptional regulation, metabolic pathway reprogramming, protein translational and post-translational modification, as well as rhizosphere microbial remodeling at multiple levels. Meanwhile, this paper also provides prospects for future research, and clarifies the future research directions and the technologies adopted.

Physical, chemical, and biological routes of synthetic titanium dioxide nanoparticles and their crucial role in temperature stress tolerance in plants

Nanotechnology is attracting significant attention worldwide due to its applicability across various sectors. Titanium dioxide nanoparticles (TiO2NPs) are among the key nanoparticles (NPs) that have gained extensive practical use and can be synthesized through a wide range of physical, chemical, and green approaches. However, TiO2NPs have attracted a significant deal of interest due to the increasing demand for enhancing the endurance to abiotic stresses such as temperature stress. In this article, we discuss the effects of temperature stresses such as low (4 °C) and high temperatures (35 °C) on TiO2NPs. Due to climate change, low and high temperature stress impair plant growth and development. However, there are still many aspects of how plants respond to low and high temperature stress and how they influence plant growth under TiO2NPs treatments which are poorly understood. TiO2NPs can be utilized efficiently for plant growth and development, particularly under temperature stress, however the response varies according to type, size, shape, dose, exposure time, metal species, and other variables. It has been demonstrated that TiO2NPs are effective at enhancing the photosynthetic and antioxidant systems of plants under temperature stress. This analysis also identifies key knowledge gaps and possible future perspectives for the reliable application of TiO2NPs to plants under abiotic stress.

Micro/nanoplastics: Critical review of their impacts on plants, interactions with other contaminants (antibiotics, heavy metals, and polycyclic aromatic hydrocarbons), and management strategies

Microplastic/nanoplastics (MPs/NPs) contamination is not only emerging threat to the agricultural system but also constitute global hazard to the environment worldwide. Recent review articles have addressed the environmental distribution of MPs/NPs and their single-exposure phytotoxicity in various plant species. However, the mechanisms of MPs/NPs-induced phytotoxicity in conjunction with that of other contaminants remain unknown, and there is a need for strategies to ameliorate such phytotoxicity. To address this, we comprehensively review the sources of MPs/NPs, their uptake by and effects on various plant species, and their phytotoxicity in conjunction with antibiotics, heavy metals, polycyclic aromatic hydrocarbons (PAHs), and other toxicants. We examine mechanisms to ameliorate MP/NP-induced phytotoxicity, including the use of phytohormones, biochar, and other plant-growth regulators. We discuss the effects of MPs/NPs -induced phytotoxicity in terms of its ability to inhibit plant growth and photosynthesis, disrupt nutrient metabolism, inhibit seed germination, promote oxidative stress, alter the antioxidant defense system, and induce genotoxicity. This review summarizes the novel strategies for mitigating MPs/NPs phytotoxicity, presents recent advances, and highlights research gaps, providing a foundation for future studies aimed at overcoming the emerging problem of MPs/NPs phytotoxicity in edible crops.

Bibliometric analysis and systematic review of the adherence, uptake, translocation, and reduction of micro/nanoplastics in terrestrial plants

Micro/nanoplastics are emerging agricultural pollutants globally. Micro/nanoplastics can adhere to terrestrial plant surfaces, be absorbed and transported by plants, and accumulate in the edible parts of plants, leading to the possibility of enrichment and transmission through the food chain and threatening human health. However, the underlying mechanism remains unclear. With increased studies on the internalization of micro/nanoplastics in terrestrial plants, a comprehensive and systematic review summarizing the current research trends and progress is warranted to provide a reference for further relevant research. Based on bibliometric analysis, this study focused on the mechanisms, study methods, and reduction techniques of micro/nanoplastics adherence, uptake, and translocation by terrestrial plants. The results showed that micro/nanoplastics can adhere to the surfaces of plant tissues such as seeds, roots, and leaves. Root uptake (root-to-leaf translocation) and foliar uptake (leaf-to-root translocation) are the two simultaneous internalization pathways of MNPs in plants. The observation methods included scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS), and inductively coupled plasma-mass spectrometry (ICP-MS). We highlighted the necessity and urgency of reducing the uptake and translocation of MNPs by plants and found that the application of silicon may be a promising approach for reducing internalization. This study identifies current knowledge gaps and proposes possible future needs.

Comprehensive analysis of nanoplastic effects on growth phenotype, nanoplastic accumulation, oxidative stress response, gene expression, and metabolite accumulation in multiple strawberry cultivars

Nanoplastics (NPs) have emerged as a novel environmental threat due to their potential impacts on both animals and plants. Currently, research on the ecotoxicity of NPs has mainly focused on marine aquatic organisms and freshwater algae, with very limited investigations conducted on horticultural plants. This study examined the effects of varying concentrations (0, 1, 10, 50 mg·L-1) of polystyrene NPs (PS-NPs) on strawberry growth. The findings revealed that low concentrations of PS-NPs stimulated strawberry growth, whereas high concentrations impeded it. Notably, diverse strawberry cultivars displayed considerable differences in their sensitivity to PS-NP exposure. Laser scanning confocal microscopy confirmed the absorption of PS-NPs by strawberry roots, with variations in PS-NP accumulation observed across different cultivars. Comparative transcriptomics analysis suggested that the differential expression of genes responsible for calcium ion transport played a significant role in the observed intervarietal differences in PS-NP accumulation among strawberry cultivars. Furthermore, distinct variations in endogenous oxidative responses were observed in different strawberry cultivars under PS-NP treatment. Further analysis indicated that the down-regulation of peroxidase (POD) gene expression and terpenoid compounds accumulation were responsible for heightened endogenous oxidative stress observed in certain strawberry cultivars under PS-NP treatment. Transcriptomic and metabolomic analyses were performed on six strawberry cultivars to investigate their response to PS-NPs in terms of endogenous gene expression and metabolite accumulation. The results identified one commonly up-regulated gene (wall-associated receptor kinase-like) and sixteen commonly down-regulated genes associated with lipid metabolism and carbohydrate metabolism. In addition, a significant reduction in fatty acid metabolite accumulation was observed in the six strawberry cultivars under PS-NP treatment. These findings have significant implications for understanding the effects of NPs on strawberry growth, metabolism, and antioxidant responses, as well as identifying marker genes for monitoring and evaluating the impact of NP pollution on strawberry.

Microplastic stress in plants: effects on plant growth and their remediations

Microplastic (MP) pollution is becoming a global problem due to the resilience, long-term persistence, and robustness of MPs in different ecosystems. In terrestrial ecosystems, plants are exposed to MP stress, thereby affecting overall plant growth and development. This review article has critically analyzed the effects of MP stress in plants. We found that MP stress-induced reduction in plant physical growth is accompanied by two complementary effects: (i) blockage of pores in seed coat or roots to alter water and nutrient uptake, and (ii) induction of drought due to increased soil cracking effects of MPs. Nonetheless, the reduction in physiological growth under MP stress is accompanied by four complementary effects: (i) excessive production of ROS, (ii) alteration in leaf and root ionome, (iii) impaired hormonal regulation, and (iv) decline in chlorophyll and photosynthesis. Considering that, we suggested that targeting the redox regulatory mechanisms could be beneficial in improving tolerance to MPs in plants; however, antioxidant activities are highly dependent on plant species, plant tissue, MP type, and MP dose. MP stress also indirectly reduces plant growth by altering soil productivity. However, MP-induced negative effects vary due to the presence of different surface functional groups and particle sizes. In the end, we suggested the utilization of agronomic approaches, including the application of growth regulators, biochar, and replacing plastic mulch with crop residues, crop diversification, and biological degradation, to ameliorate the effects of MP stress in plants. The efficiency of these methods is also MP-type-specific and dose-dependent.

Brassinosteroids alleviate nanoplastic toxicity in edible plants by activating antioxidant defense systems and suppressing nanoplastic uptake

As emerging pollutants of global concern, absorbed nanoplastics might have negative impacts on plant development and nutrient uptake, thereby decreasing yields. If nanoplastics are transferred to the edible parts of plants, they may pose a threat to human health when large quantities are ingested. While nanoplastic-induced phytotoxicity is attracting increasing attention, little is known about how to inhibit nanoplastic accumulation in plants and reduce the subsequent adverse effects. Here we investigated the absorption and accumulation of polystyrene nanoplastics (PS-NPs) in different plant species and the role of brassinosteroids in alleviating PS-NP toxicity. Brassinosteroids inhibited accumulation of PS-NPs in tomato fruit and reversed PS-NP-induced phytotoxicity to promote plant growth and increase fresh weight and plant height. Brassinosteroids also reversed the induction of aquaporin-related genes by PS-NPs including TIP2-1, TIP2-2, PIP2-6, PIP2-8, PIP2-9, SIP2-1, and NIP1-2, providing a potential stress mechanism by which PS-NPs accumulate in the edible parts and targets for inhibition. In transcriptomic analyses, brassinosteroids enhanced fatty acid and amino acid metabolism and synthesis. In conclusion, exogenous application of 50 nM brassinosteroids alleviated the adverse effects of PS-NPs on plants, and exogenous application of brassinosteroids might be an effective means to minimize PS-NP-induced phytotoxicity.

Reprogramming of microbial community in barley root endosphere and rhizosphere soil by polystyrene plastics with different particle sizes

Polystyrene plastics is an emerging pollutant affecting plant performance and soil functioning. However, little information is available on the effects of microplastics and nanoplastics on plant root endophytic and rhizospheric soil microbial communities. Here, barley plants were grown in microplastics/nanoplastics -treated soil and the diversity, composition and function of bacteria and fungi in the root and rhizosphere soil were examined. At the seedling stage, greater changes of root endophytes were found compared with rhizosphere microorganisms under the plastic treatments. Nanoplastics decreased the richness and diversity of the fungal community, while microplastics increased the diversity of the root endophytic bacterial community. The network of the bacterial community under nanoplastics showed higher vulnerability while lower complexity than that under the control. However, the bacterial community under microplastics had a relatively higher resistance than the control. For the rhizosphere microbial community, no significant effect of plastics was found on the α-diversity index at the seedling stage. In addition, the nanoplastics resulted in higher sensitivity in the relative abundance and function of rhizosphere soil microbes than root endophytic microbes at the mature stage. Treatments of polystyrene plastics with different particle sizes reprogramed the rhizosphere and root endophytic microbial communities. Different effects of microplastics and nanoplastics were found on the diversity, composition, network structure and function of bacteria and fungi, which might be due to the variation in particle sizes. These results lay a foundation for learning the effects of polystyrene plastics with different particle sizes on the microorganisms in rhizosphere soil and plant roots, which may have important implications for the adaptation of plant-microbial holobiont in polystyrene plastics-polluted soils.

Modulations in protein phosphorylation explain the physiological responses of barley (Hordeum vulgare) to nanoplastics and ZnO nanoparticles

To address the knowledge gap on the effects of the co-existence of nanomaterials on plant growth, barley (Hordeum vulgare L.) plants were irrigated with zinc oxide nanoparticles (0.5 g L^-1), nanoplastics (1 g L^-1), and the combination of these two nanomaterials for 10 days. The co-existence of nanoplastics and ZnO nanoparticles increased H₂O₂ concentration by 12.76% and 38.30%, compared with the ZnO nanoparticles and nanoplastics exposure. The concentration of abscisic acid (ABA) in plants under the co-existence of nanoplastics and ZnO nanoparticles was 29.53% and 10.42% higher than that in ZnO nanoparticles treated plants and nanoplastics treated plants. The global analysis of phosphoproteomics identified 132 phosphorylated proteins and 173 phosphorylation sites in barley leaves exposed to the nanomaterial combination, which were related to photosynthesis, carbon fixation, nitrogen metabolism, and arginine and proline metabolisms. Further physiological analysis indicated that the combination of ZnO nanoparticles and nanoplastics caused larger damage to the systems of antioxidant and carbohydrate metabolisms as exemplified by decreased activities of apoplastic peroxidases (25.10%-48.60%), glutathione reductase (91.07%-94.94%), and sucrose synthase (53.59%-61.19%) in roots and increased cell wall invertase activity (12.97%-17.61%) in leaves, compared with the single nanomaterial treatments. These results indicate that the modulations in protein phosphorylation were closely related to the physiological responses to nanomaterial exposure, suggesting that the co-existence of nanomaterials may lead to greater impacts than single ones.

Reactive oxygen species signaling is involved in melatonin-induced reduction of chlorothalonil residue in tomato leaves

Pesticide overuse has led to serious global concerns regarding food safety and environmental pollution. Although the reduction of pesticide residue is critical, our knowledge about induced pesticide metabolism in plants remains fragmentary. Melatonin (N-acetyl-5-methoxytryptamine) is an effective stress-relieving agent in both animals and plants, but little is known about the melatonin signaling mechanism and its effect on pesticide metabolism in plants. Here, we found that exogenous melatonin treatment significantly reduced chlorothalonil residue by 41 % but suppression of endogenous melatonin accumulation increased chlorothalonil residue in tomato leaves. Moreover, melatonin increased photosynthesis, Fv/Fm, Calvin cycle enzyme activity, antioxidant enzyme activity, glutathione pool, and RESPIRATORY BURST HOMOLOG1 (RBOH1) expression in tomato leaves. However, the upregulation of RBOH1, CYP724B2, GST1, GST2, GSH and ABC, the increased glutathione concentrations and the activity of detoxification enzymes due to melatonin treatment were all significantly attenuated by the treatment with an NADPH oxidase inhibitor and a ROS scavenger, indicating a clear relationship between the reduction of pesticide residue and induction in detoxifying enzymes and genes upon melatonin treatment in an apoplastic H₂O₂-dependent manner. These results reveal that melatonin-induced reduction in chlorothalonil residue is mediated by H₂O₂ signaling in tomato leaves.

Nanoplastics in the soil environment: Analytical methods, occurrence, fate and ecological implications

Soils play a very important role in ecosystems sustainability, either natural or agricultural ones, serving as an essential support for living organisms of different kinds. However, in the current context of extremely high plastic pollution, soils are highly threatened. Plastics can change the chemical and physical properties of the soils and may also affect the biota. Of particular importance is the fact that plastics can be fragmented into microplastics and, to a final extent into nanoplastics. Due to their extremely low size and high surface area, nanoplastics may even have a higher impact in soil ecosystems. Their transport through the edaphic environment is regulated by the physicochemical properties of the soil and plastic particles themselves, anthropic activities and biota interactions. Their degradation in soils is associated with a series of mechanical, photo-, thermo-, and bio-mediated transformations eventually conducive to their mineralisation. Their tiny size is precisely the main setback when it comes to sampling soils and subsequent processes for their identification and quantification, albeit pyrolysis coupled with gas chromatography-mass spectrometry and other spectroscopic techniques have proven to be useful for their analysis. Another issue as a consequence of their minuscule size lies in their uptake by plants roots and their ingestion by soil dwelling fauna, producing morphological deformations, damage to organs and physiological malfunctions, as well as the risks associated to their entrance in the food chain, although current conclusions are not always consistent and show the same pattern of effects. Thus, given the omnipresence and seriousness of the plastic menace, this review article pretends to provide a general overview of the most recent data available regarding nanoplastics determination, occurrence, fate and effects in soils, with special emphasis on their ecological implications.

Exogenous application of melatonin to mitigate drought stress-induced oxidative damage in Phoebe sheareri seedlings

Background

Drought stress is a major prevalent environmental factor impairing growth. Melatonin mitigates the impacts of drought stress on plants. However, melatonin's role in Phoebe sheareri (Hemsl.) Gamble (P. sheareri) is unknown. We aimed to reveal the protective effects of melatonin on P. sheareri seedlings under drought conditions.

Methods

Melatonin was sprayed under drought or normal water conditions. The parameters, including growth, physiological factors, and phytohormones of P. sheareri, were examined.

Results

Compared to the normal control group, drought stress inhibited the growth of seedlings and significantly reduced the content of carotenoids, SOD, POD, APX, PPO, CAT, GR, and soluble sugars, and increased the contents of MDA, O₂ ^•-, proline, soluble proteins, ABA, and JA-Me in P. sheareri seedlings. However, melatonin treatment significantly reversed the adverse drought-induced responses and promoted the P. sheareri seedling's growth. Moreover, the heatmap and principal component analysis suggested a high similarity in the behavior patterns of the six measured antioxidant enzymes in P. sheareri seedlings.

Conclusion

Our study reported for the first time that melatonin has a protective role in P. sheareri seedlings under drought-stress conditions. This role is related to ROS scavenging, activation of antioxidant enzymes, and crosstalk of phytohormones. This study provided a theoretical basis for improving the ability of P. sheareri adapted to arid environments.

Melatonin-mediated resistance to copper oxide nanoparticles-induced toxicity by regulating the photosynthetic apparatus, cellular damages and antioxidant defense system in maize seedlings

The pollution of nanoparticles (NPs) has linked with severe negative effects on crop productivity. Thus, effective strategies are needed to mitigate the phytotoxicity of NPs. The aim of present study was to evaluate the efficacy of exogenously applied melatonin (MT) in mitigating the toxic effects of copper oxide nanoparticles (CuO NPs) from maize seedlings. Therefore, we comprehensively investigated the inhibitory effects of MT against CuO NPs-induced toxicity on morpho-physiological, biochemical and ultrastructural levels in maize. Our results show that CuO NPs (300 mg L^-1) exposure displayed significantly reduction in all plant growth traits and induced toxicity in maize. Furthermore, 50 μM MT provided maximum plant tolerance against CuO NPs-induced phytotoxicity. It was noticed that MT improved plant growth, biomass, photochemical efficiency (Fv/Fm), chlorophyll contents (Chl a and Chl b), SPAD values and gas exchange attributes (stomatal conductance, net photosynthetic rate, intercellular CO₂ concentration and transpiration rate) under CuO NPs stress. In addition, MT enhanced the antioxidant defense system and conferred protection to ultrastructural (mainly chloroplast, thylakoids membrane and plastoglobuli) damages and stomatal closure in maize plants subjected to CuO NPs stress. Together, it can be stated that the exogenous supply of MT improves the resilience of maize plants against the CuO NPs-induced phytotoxicity. Our current findings can be useful for the enhancement of plant growth and yield attributes in CuO NPs-contaminated soils. The reported information can provide insight into the MT pathways that can be used to improve crop stress tolerance in a challenging environment.

Responses of cherry radish to different types of microplastics in the presence of oxytetracycline

Croplands have become a hotspot for antibiotic and microplastic (MP) pollution. However, little is known regarding their combined effects on crops. In this study, the individual and combined effects of oxytetracycline (OTC) and three MPs (i.e., polypropylene (PP), polyamide (PA), and polyvinylchloride (PVC)) on cherry radish were investigated using pot experiments. Individually, OTC (50 mg kg^-1), PA (2%, w/w), and PP (2%, w/w) induced negligible effects on cherry radish biomass and the root/shoot ratio. However, PVC (2%, w/w) significantly inhibited cherry radish growth; that is, its shoot and root fresh weight decreased by 46.2% and 81.1%, respectively. In the combined exposure groups, OTC alleviated the adverse effects of PVC on the cherry radish leaf number and shoot fresh weight. This was linked to that OTC increased the content of photosynthetic pigments. Superoxide dismutase activity in cherry radish roots was inhibited to different extents in all treatment groups except for the PA and PVC treatments. Malondialdehyde (MDA) content in cherry radish roots increased in all treatment groups, suggesting that both OTC and MPs caused oxidative damage to cherry radish root cells, therefore inhibiting cherry radish root growth. However, the presence of OTC non-significantly changed the effects of MPs on cherry radish roots. Irrespective of OTC presence, MPs induced a reduction in the root/shoot ratio of cherry radish, suggesting that the inhibitory effect of MPs on cherry radish roots was stronger than that on shoots. These findings contribute to the evaluation of the phytotoxicity of antibiotics and MPs in soil-vegetable systems.

Fe2O3-modified graphene oxide mitigates nanoplastic toxicity via regulating gas exchange, photosynthesis, and antioxidant system in Triticum aestivum

The ever-increasing plastic pollution in soil and water resources raises concerns about its effects on terrestrial plants and agroecosystems. Although there are many reports about the contamination with nanoplastics on plants, the presence of magneto-assisted nanomaterials enabling the removal of their adverse impacts still remains unclear. Therefore, the purpose of the current study is to evaluate the potential of nanomaterial Fe₂O₃-modified graphene oxide (FGO, 50-250 mg L^-1) to eliminate the adverse effects of nanoplastics in plants. Wheat plants exposed to polystyrene nanoplastics concentrations (PS, 10, 50 and 100 mg L^-1) showed decreased growth, water content and loss of photosynthetic efficiency. PS toxicity negatively altered gas exchange, antenna structure and electron transport in photosystems. Although the antioxidant system was partially activated (only superoxide dismutase (SOD), NADPH oxidase (NOX) and glutathione reductase (GR)) in plants treated with PS, it failed to prevent PS-triggered oxidative damage, as showing lipid peroxidation and hydrogen peroxide (H₂O₂) levels. FGOs eliminated the adverse impacts of PS pollution on growth, water status, gas exchange and oxidative stress markers. In addition, FGOs preserve the biochemical reactions of photosynthesis by actively increasing chlorophyll fluorescence parameters in the stressed-wheat leaves. The activities of all enzymatic antioxidants increased, and the H₂O₂ and TBARS contents decreased. GSH-mediated detoxifying antioxidants such as glutathione S-transferase (GST) and glutathione peroxidase (GPX) were stimulated by FGOs against PS pollution. FGOs also triggered the enzymes and non-enzymes related to the Asada-Halliwell cycle and protected the regeneration of ascorbate (AsA) and glutathione (GSH). Our findings indicated that FGO had the potential to mitigate nanoplastic-induced damage in wheat by regulating water relations, protecting photosynthesis reactions and providing efficient ROS scavenging with high antioxidant capacity. This is the first report on removing PS-induced damage by FGO applications in wheat leaves.

Microplastic/nanoplastic toxicity in plants: an imminent concern

The toxic impact of microplastics/nanoplastics (MPs/NPs) in plants and the food chain has recently become a top priority. Several research articles highlighted the impact of MPs/NPs on the aquatic food chain; however, very little has been done in the terrestrial ecosystem. A number of studies revealed that MPs/NPs uptake and subsequent translocation in plants alter plant morphological, physiological, biochemical, and genetic properties to varying degrees. However, there is a research gap regarding MPs/NPs entry into plants, associated factors influencing phytotoxicity levels, and potential remediation plans in terms of food safety and security. To address these issues, all sources of MPs/NPs intrusion in agroecosystems should be revised to avoid these hazardous materials with special consideration as preventive measures. Furthermore, this review focuses on the routes of accumulation and transmission of MPs/NPs into plant tissues, related aspects influencing the intensity of plant stress, and potential solutions to improve food quality and quantity. This paper also concludes by providing an outlook approach of applying exogenous melatonin and introducing engineered plants that would enhance stress tolerance against MPs/NPs. In addition, an overview of inoculation of beneficial microorganisms and encapsulated enzymes in soil has been addressed, which would make the degradation of MPs/NPs faster.

The impacts of nanoplastic toxicity on the accumulation, hormonal regulation and tolerance mechanisms in a potential hyperaccumulator - Lemna minor L

Plastic pollution, which is currently one of the most striking problems of our time, raises concerns about the dispersal of micro and nano-sized plastic particles in ecosystems and their toxic effects on living organisms. This study was designed to reveal the toxic effects of polystyrene nanoplastic (PS NP) exposure on the freshwater macrophyte Lemna minor. In addition, elucidating the interaction of this aquatic plant, which is used extensively in the phytoremediation of water contaminants and wastewater treatment facilities, with nanoplastics will guide the development of remediation techniques. For this purpose, we examined nanoplastic accumulation, oxidative stress markers, photosynthetic efficiency, antioxidant system activity and phytohormonal changes in L. minor leaves subjected to PS NP stress (P-1, 100 mg L^-1; P-2, 200 mg L^-1 PS NP). Our results showed no evidence of PS NP-induced oxidative damage in P-1 group plants, although PS NP accumulation reached 56 µg g^-1 in the leaves. Also, no significant changes in chlorophyll a fluorescence parameters were observed in this group, indicating unaffected photosynthetic efficiency. PS NP exposure triggered the antioxidant system in L. minor plants and resulted in a 3- and 4.6-fold increase in superoxide dismutase (SOD) activity in the P-1 and P-2 groups. On the other hand, high-dose PS NP treatment resulted in insufficient antioxidant activity in the P-2 group and increased hydrogen peroxide (H₂O₂) and lipid peroxidation (TBARS contents) by 25 % and 17 % compared to the control plants. Furthermore, PS NP exposure triggered abscisic acid biosynthesis (two-fold in the P-1 and three-fold in the P-2 group), which is also involved in regulating the stress response. In conclusion, L. minor plants tolerated NP accumulation without growth suppression, oxidative stress damage and limitations in photosynthetic capacity and have the potential to be used in remediation studies of NP-contaminated waters.

Joint effects of microplastics and ciprofloxacin on their toxicity and fates in wheat: A hydroponic study

The toxicological impacts of microplastics (MPs) and antibiotics in the soil environment have gradually drawn widespread attention, while little research has focused on the combined pollution of MPs and antibiotics on plants. In this work, a 21-day hydroponic study was conducted to test the hypothesis that polystyrene MPs (0.1, 1 and 10 μm particle sizes, 50 mg/L) and ciprofloxacin (CIP) (1.0 and 5.0 mg/L) had a joint toxicity to wheat seedlings and they could be absorbed by wheat. Plant samples were taken for analyses after 21 days of exposure. The results showed that 0.1 and 1 μm MP could enter wheat roots but only the former could translocate to aerial parts. Moreover, 0.1 μm MP showed a greater toxicity effect than 1 μm MP, whereas 10 μm MP exhibited little toxicity on wheat. The dosing of 0.1 μm MP significantly increased the toxic effects of CIP to wheat. Compared to the control treatment (without MPs and CIP), 0.1 μm MPs-5.0 mg/L CIP treatment resulted in inhibition of root length and weight by 60.1% and 44.3%, respectively, while the contents of chlorophyll a and chlorophyll b decreased by 36.3% and 44.6%, respectively. The presence of CIP (5.0 mg/L) potentially aggravated the combined toxicity. The exposure of 0.1 μm MP significantly reduced root superoxide distumase activity but increased root malondialdehyde content. The amount of CIP in wheat tissues carried by MPs was negligible compared with the uptake quantity of CIP by wheat.

Exogenous melatonin strongly affects dynamic photosynthesis and enhances water-water cycle in tobacco

Melatonin (MT), an important phytohormone synthesized naturally, was recently used to improve plant resistance against abiotic and biotic stresses. However, the effects of exogenous melatonin on photosynthetic performances have not yet been well clarified. We found that spraying of exogenous melatonin (100 μM) to leaves slightly affected the steady state values of CO₂ assimilation rate (A _N ), stomatal conductance (g _s ) and mesophyll conductance (g _m ) under high light in tobacco leaves. However, this exogenous melatonin strongly delayed the induction kinetics of g _s and g _m , leading to the slower induction speed of A _N . During photosynthetic induction, A _N is mainly limited by biochemistry in the absence of exogenous melatonin, but by CO₂ diffusion conductance in the presence of exogenous melatonin. Therefore, exogenous melatonin can aggravate photosynthetic carbon loss during photosynthetic induction and should be used with care for crop plants grown under natural fluctuating light. Within the first 10 min after transition from low to high light, photosynthetic electron transport rates (ETR) for A _N and photorespiration were suppressed in the presence of exogenous melatonin. Meanwhile, an important alternative electron sink, namely water-water cycle, was enhanced to dissipate excess light energy. These results indicate that exogenous melatonin upregulates water-water cycle to facilitate photoprotection. Taking together, this study is the first to demonstrate that exogenous melatonin inhibits dynamic photosynthesis and improves photoprotection in higher plants.

Melatonin alleviates cadmium toxicity and abiotic stress by promoting glandular trichome development and antioxidant capacity in Nicotiana tabacum

Melatonin is a well-known signaling molecule that mediates a range of physiological activities and various stress reactions in plants. We comprehensively tested the effect of melatonin on the development of root hairs and glandular trichomes and found that melatonin pretreatment of tobacco seeds significantly increased the length of root hairs. Furthermore, melatonin-treated tobacco exhibited significantly higher density of trichomes and larger glandular heads on long-stalk glandular trichomes than untreated plants, which resulted in enhanced secretion in glandular trichomes. Exogenous melatonin enhanced the aphid resistance of plants by facilitating the accumulation of cembranoids in the glandular trichomes and alleviated cadmium toxicity by increasing the Cd-exudation capacity of long glandular trichomes. Metabolic analysis indicated that the contents of 108 metabolites significantly changed upon melatonin treatment, with the contents of those that are directly/indirectly involved in melatonin metabolism changing the most. Further, KEGG pathway analysis suggested that the metabolic pathways of amino acids, reducing sugar, secondary metabolites, indole alkaloid biosynthesis, purine, pyrimidine, and ABC transporters were greatly influenced by exogenous melatonin application. Moreover, metabolisms of melatonin-related antioxidants and pyrimidine nucleoside antibiotics were enhanced after melatonin treatment. Melatonin improved tobacco resistance to high salinity, drought, and extreme temperature stresses, as indicated by improved photosynthetic and antioxidant capacities in treated vs. untreated plants. This study lays a foundation for the comprehensive application of melatonin to increase the stress tolerance of plants.

Bioanalytical approaches for the detection, characterization, and risk assessment of micro/nanoplastics in agriculture and food systems

This review discusses the most recent literature (mostly since 2019) on the presence and impact of microplastics (MPs, particle size of 1 μm to 5 mm) and nanoplastics (NPs, particle size of 1 to 1000 nm) throughout the agricultural and food supply chain, focusing on the methods and technologies for the detection and characterization of these materials at key entry points. Methods for the detection of M/NPs include electron and atomic force microscopy, vibrational spectroscopy (FTIR and Raman), hyperspectral (bright field and dark field) and fluorescence imaging, and pyrolysis-gas chromatography coupled to mass spectrometry. Microfluidic biosensors and risk assessment assays of MP/NP for in vitro, in vivo, and in silico models have also been used. Advantages and limitations of each method or approach in specific application scenarios are discussed to highlight the scientific and technological obstacles to be overcome in future research. Although progress in recent years has increased our understanding of the mechanisms and the extent to which MP/NP affects health and the environment, many challenges remain largely due to the lack of standardized and reliable detection and characterization methods. Most of the methods available today are low-throughput, which limits their practical application to food and agricultural samples. Development of rapid and high-throughput field-deployable methods for onsite screening of MP/NPs is therefore a high priority. Based on the current literature, we conclude that detecting the presence and understanding the impact of MP/NP throughout the agricultural and food supply chain require the development of novel deployable analytical methods and sensors, the combination of high-precision lab analysis with rapid onsite screening, and a data hub(s) that hosts and curates data for future analysis.

Function, Mechanism, and Application of Plant Melatonin: An Update with a Focus on the Cereal Crop, Barley (Hordeum vulgare L.)

Melatonin is a multiple-function molecule that was first identified in animals and later in plants. Plant melatonin regulates versatile processes involved in plant growth and development, including seed germination, root architecture, flowering time, leaf senescence, fruit ripening, and biomass production. Published reviews on plant melatonin have been focused on two model plants: (1) Arabidopsis and (2) rice, in which the natural melatonin contents are quite low. Efforts to integrate the function and the mechanism of plant melatonin and to determine how plant melatonin benefits human health are also lacking. Barley is a unique cereal crop used for food, feed, and malt. In this study, a bioinformatics analysis to identify the genes required for barley melatonin biosynthesis was first performed, after which the effects of exogenous melatonin on barley growth and development were reviewed. Three integrated mechanisms of melatonin on plant cells were found: (1) serving as an antioxidant, (2) modulating plant hormone crosstalk, and (3) signaling through a putative plant melatonin receptor. Reliable approaches for characterizing the function of barley melatonin biosynthetic genes and to modulate the melatonin contents in barley grains are discussed. The present paper should be helpful for the improvement of barley production under hostile environments and for the reduction of pesticide and fungicide usage in barley cultivation. This study is also beneficial for the enhancement of the nutritional values and healthcare functions of barley in the food industry.

Low temperature tolerance is impaired by polystyrene nanoplastics accumulated in cells of barley (Hordeum vulgare L.) plants

With increasing plastic consumption, the large amount of polystyrene nanoplastics (PS-NPs) in agricultural soil may not only directly affect the plant growth, but also indirectly affect the abiotic stress tolerance in crops. In this study, the barley (Hordeum vulgare L.) was irrigated with 2 g L^-1 PS-NPs (65.776 ± 0.528 nm) solution for 7 days, then subjected to low temperature (2 ℃) for 24 h. The imaging of protoplasts indicated that polymethylmethacrylate nanoplastics could across the cell wall and accumulate in plant cells. The PS-NPs significantly decreased Rubisco activities and ATP production, hence limiting the photosynthetic carbon assimilation in barley under low temperature. The PS-NPs accumulated in cells also caused the significantly decreased activities of key enzymes involved in sucrolytic, glycolysis and starch metabolism pathways, including UDP-glucose pyrophorylase, ADP-Glucose pyrophosphorylase, phosphoglucomutase, glucose-6-phosphate dehydrogenase, phosphoglucoisomerase, fructokinase and phosphofructokinase. In addition, under low temperature, the PS-NPs presence significantly reduced the activities of superoxide dismutase, ascorbate peroxidase and catalase in chloroplasts, and significantly reduced the activities of ascorbate peroxidase and catalase in mitochondria. Thus, it is suggested that the PS-NPs accumulated in plant cells impaired the low temperature tolerance in barley mainly by the negative effects on photosynthetic carbon assimilation, carbohydrate metabolism and ROS homeostasis in sub-cellular level.

Fine-tuning of pathogenesis-related protein 1 (PR1) activity by the melatonin biosynthetic enzyme ASMT2 in defense response to cassava bacterial blight

Melatonin is widely involved in plant disease resistance through modulation of immune responses. Pathogenesis-related (PR) proteins play important roles in plant immune responses. However, the direct association between melatonin biosynthetic enzyme and PR protein remains elusive in plants. In this study, we found that N-acetylserotonin O-methyltransferase 2 (MeASMT2) physically interacted with MePR1 in vitro and in vivo, thereby promoting the anti-bacterial activity of MePR1 against Xanthomonas axonopodis pv. manihotis (Xam). Consistently, MeASMT2 improved the effect of MePR1 on positively regulating cassava disease resistance. In addition, we found that type 2C protein phosphatase 1 (MePP2C1) interacted with MeASMT2 to interfere with MePR1-MeASMT2 interaction, so as to inhibiting the effect of MeASMT2 and MePR1 on positively regulating cassava disease resistance. In contrast to the increased transcripts of MeASMT2 and MePR1 in response to Xam infection, the transcript of MePP2C1 was decreased upon Xam infection. Therefore, disease activated MeASMT2 was released from disease inhibited MePP2C1, so as to improving the anti-bacterial activity of MePR1, resulting in improved immune response. In summary, this study illustrates the dynamic modulation of the MePP2C1-MeASMT2-MePR1 module on cassava defense response against cassava bacterial blight (CBB), extending the understanding of the correlation between melatonin biosynthetic enzyme and PR in plants.

Rhizosphere melatonin application reprograms nitrogen-cycling related microorganisms to modulate low temperature response in barley

Rhizospheric melatonin application has a positive effect on the tolerance of plants to low temperature; however, it remains unknown whether the rhizosphere microorganisms are involved in this process. The aim of this study was to investigate the effect of exogenous melatonin on the diversity and functioning of fungi and bacteria in rhizosphere of barley under low temperature. The results showed that rhizospheric melatonin application positively regulated the photosynthetic carbon assimilation and redox homeostasis in barley in response to low temperature. These effects might be associated with an altered diversity of microbial community in rhizosphere, especially the species and relative abundance of nitrogen cycling related microorganisms, as exemplified by the changes in rhizosphere metabolites in the pathways of amino acid synthesis and metabolism. Collectively, it was suggested that the altered rhizospheric microbial status upon melatonin application was associated with the response of barley to low temperature. This suggested that the melatonin induced microbial changes should be considered for its application in the crop cold-resistant cultivation.

Melatonin-Mediated Abiotic Stress Tolerance in Plants

Melatonin is a multi-functional molecule that is ubiquitous in all living organisms. Melatonin performs essential roles in plant stress tolerance; its application can reduce the harmful effects of abiotic stresses. Plant melatonin biosynthesis, which usually occurs within chloroplasts, and its related metabolic pathways have been extensively characterized. Melatonin regulates plant stress responses by directly inhibiting the accumulation of reactive oxygen and nitrogen species, and by indirectly affecting stress response pathways. In this review, we summarize recent research concerning melatonin biosynthesis, metabolism, and antioxidation; we focus on melatonin-mediated tolerance to abiotic stresses including drought, waterlogging, salt, heat, cold, heavy metal toxicity, light and others. We also examine exogenous melatonin treatment in plants under abiotic stress. Finally, we discuss future perspectives in melatonin research and its applications in plants.