Attenuation mechanisms of arsenic induced toxicity and its accumulation in plants by engineered nanoparticles: A review

Synergistic Mitochondrial Genotoxicity of Carbon Dots and Arsenate in Earthworms Eisenia fetida across Generations: The Critical Role of Binding

The escalating utilization of carbon dots (CDs) in agriculture raises ecological concerns. However, their combined toxicity with arsenic remains poorly understood. Herein, we investigated the combined mitochondrial genotoxicity of CDs and arsenate at environmentally relevant concentrations across successive earthworm generations. Iron-doped CDs (CDs-Fe) strongly bound to arsenate and arsenite, while nitrogen-doped CDs (CDs-N) exhibited weaker binding. Both CDs enhanced arsenate bioaccumulation without affecting its biotransformation, with most arsenate being reduced to arsenite. CDs-Fe generated significantly more reactive oxygen species than did CDs-N, causing stronger mitochondrial DNA (mtDNA) damage. Arsenate further exacerbated the oxidative mtDNA damage induced by CDs-N, as evidenced by increased reactive oxygen species, elevated 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-OHdG) levels, and a higher correlation between 8-OHdG and mtDNA damage. This was due to arsenic inhibiting the antioxidant enzyme catalase. This exacerbation was negligible with CDs-Fe because their strong binding with arsenic prevented catalase inhibition. Maternal mitochondrial DNA damage was inherited by filial earthworms, which experienced significant weight loss in coexposure groups coupled with mtDNA toxicity. This study reveals the synergistic genotoxicity of CDs and arsenate, suggesting that CDs could disrupt the arsenic biogeochemical cycle, increase arsenate risk to terrestrial animals, and influence ecosystem stability and health through multigenerational impacts.

Modulation of Cd carriers by innovative nanocomposite (Ca+Mg) and Cd-resistance microbes (Bacillus pumilus): a mechanistic approach to enhance growth and yield of rice (Oryza sativa L.)

Cadmium (Cd) is a well-known pollutant in agricultural soil, affecting human health through the food chain. To combat this issue, Ca + Mg (25 mg L-1) nanocomposite and Bacillus pumilus, either alone or combined, were applied to rice plants under Cd (5 mg kg-1, 10 mg kg-1) contamination. In our study, growth and yield traits demonstrated the beneficial influence of Ca + Mg and B. pumilus application in improving rice defense mechanism by reducing Cd stress. Combined Ca + Mg and B. pumilus application increased SPAD (15), total chlorophyll (18), chlorophyll a (11), chlorophyll b (22), and carotenoids (21%) with Cd (10 mg kg-1), compared to the application alone. Combined Ca + Mg and B. pumilus application significantly regulated MDA (15), H2O2 (13), EL (10), and O2 •- (24%) in shoots under Cd (10 mg kg-1), compared to the application alone. Cd (10 mg kg-1) increased the POD (22), SOD (21), APX (12), and CAT (13%) in shoots with combined Ca + Mg and B. pumilus application, compared to the application alone. Combined Ca + Mg and B. pumilus application significantly reduced Cd accumulation in roots (22), shoots (13), and grains (20%) under Cd (10 mg kg-1), compared to the application alone. Consequently, the combined application of Ca + Mg and B. pumilus is a sustainable solution to enhance crop production under Cd stress.

Unveiling the efficacy of Bacillus faecalis and composted biochar in alleviating arsenic toxicity in maize

Arsenic (As) contamination is a major environmental pollutant that adversely affects plant physiological processes and can hinder nutrients and water availability. Such conditions ultimately resulted in stunted growth, low yield, and poor plant health. Using rhizobacteria and composted biochar (ECB) can effectively overcome this problem. Rhizobacteria have the potential to enhance plant growth by promoting nutrient uptake, producing growth hormones, and suppressing diseases. Composted biochar can enhance plant growth by improving aeration, water retention, and nutrient cycling. Its porous structure supports beneficial microorganisms, increasing nutrient uptake and resilience to stressors, ultimately boosting yields while sequestering carbon. Therefore, the current study was conducted to investigate the combined effect of previously isolated Bacillus faecalis (B. faecalis) and ECB as amendments on maize cultivated under different As levels (0, 300, 600 mg As/kg soil). Four treatments (control, 0.5% composted biochar (0.5ECB), B. faecalis, and 0.5ECB + B. faecalis) were applied in four replications following a completely randomized design. Results showed that the 0.5ECB + B. faecalis treatment led to a significant rise in maize plant height (~ 99%), shoot length (~ 55%), root length (~ 82%), shoot fresh (~ 87%), and shoot dry weight (~ 96%), root fresh (~ 97%), and dry weight (~ 91%) over the control under 600As stress. There was a notable increase in maize chlorophyll a (~ 99%), chlorophyll b (~ 81%), total chlorophyll (~ 94%), and shoot N, P, and K concentration compared to control under As stress, also showing the potential of 0.5ECB + B. faecalis treatment. Consequently, the findings suggest that applying 0.5ECB + B. faecalis is a strategy for alleviating As stress in maize plants.

Exploring Aluminum Tolerance Mechanisms in Plants with Reference to Rice and Arabidopsis: A Comprehensive Review of Genetic, Metabolic, and Physiological Adaptations in Acidic Soils

Aluminum (Al) makes up a third of the Earth's crust and is a widespread toxic contaminant, particularly in acidic soils. It impacts crops at multiple levels, from cellular to whole plant systems. This review delves into Al's reactivity, including its cellular transport, involvement in oxidative redox reactions, and development of specific metabolites, as well as the influence of genes on the production of membrane channels and transporters, alongside its role in triggering senescence. It discusses the involvement of channel proteins in calcium influx, vacuolar proton pumping, the suppression of mitochondrial respiration, and the initiation of programmed cell death. At the cellular nucleus level, the effects of Al on gene regulation through alterations in nucleic acid modifications, such as methylation and histone acetylation, are examined. In addition, this review outlines the pathways of Al-induced metabolic disruption, specifically citric acid metabolism, the regulation of proton excretion, the induction of specific transcription factors, the modulation of Al-responsive proteins, changes in citrate and nucleotide glucose transporters, and overall metal detoxification pathways in tolerant genotypes. It also considers the expression of phenolic oxidases in response to oxidative stress, their regulatory feedback on mitochondrial cytochrome proteins, and their consequences on root development. Ultimately, this review focuses on the selective metabolic pathways that facilitate Al exclusion and tolerance, emphasizing compartmentalization, antioxidative defense mechanisms, and the control of programmed cell death to manage metal toxicity.

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

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

Exogenous curcumin mitigates As stress in spinach plants: A biochemical and metabolomics investigation

The spinach (S. oleracea L.) was used as a model plant to investigate As toxicity on physio-biochemical processes, exploring the potential mitigation effect of curcumin (Cur) applied exogenously at three concentrations (1, 10, and 20 μM Cur). The employment of Cur significantly mitigated As-induced stress in spinach photosynthetic performance (Fv/Fm, Fo/Fm, and Fv/Fo). Moreover, the co-incubation of Cur with As improved physiological processes mainly associated with plant water systems affected by As stress by recovering the leaf's relative water content (RWC) and osmotic potential (ψπ) nearly to the control level and increasing the transpiration rate (E; 39-59%), stomatal conductivity (gs; 86-116%), and carbon assimilation rate (A; 84-121%) compared to As stressed plants. The beneficial effect of Cur in coping with As-induced stress was also assessed at the plant's oxidative level by reducing oxidative stress biomarkers (H2O2 and MDA) and increasing non-enzymatic antioxidant capacity. Untargeted metabolomics analysis was adopted to investigate the main processes affected by As and Cur application. A multifactorial ANOVA discrimination model (AMOPLS-DA) and canonical correlation analysis (rCCA) were employed to identify relevant metabolic changes and biomarkers associated with Cur and As treatments. The results highlighted that Cur significantly determined the accumulation of glucosinolates, phenolic compounds, and an increase in glutathione redox cycle activities, suggesting an overall elicitation of plant secondary metabolisms. Specifically, the correlation analysis reported a strong and positive correlation between (+)-dihydrokaempferol, L-phenylalanine (precursor of phenolic compounds), and serotonin-related metabolites with antioxidant activities (ABTS and DPPH), suggesting the involvement of Cur application in promoting a cross-talk between ROS signaling and phytohormones, especially melatonin and serotonin, working coordinately to alleviate As-induced oxidative stress. The modulation of plant metabolism was also observed at the level of amino acids, fatty acids, and secondary metabolites synthesis, including N-containing compounds, terpenes, and phenylpropanoids to cooperate with As-induced stress response.

Toxicological effects of nanoparticles in plants: Mechanisms involved at morphological, physiological, biochemical and molecular levels

The rapid advancement of nanotechnology has led to unprecedented innovations across diverse industries, including pharmaceuticals, agriculture, cosmetics, electronics, textiles, and food, owing to the unique properties of nanoparticles. The extensive production and unregulated release of synthetic nanoparticles may contribute to nanopollution within the ecosystem. In the agricultural sector, nanotechnology is increasingly utilized to improve plant productivity, enhance resistance to stressors, and reduce the usage of chemicals. However, the uncontrolled discharge of nanoparticles into the natural environment raises concerns regarding possible plant toxicological impacts. The review focuses on the translocation of these particles within the plants, emphasizing their phytotoxicological effects at morphological, physiological, biochemical, and molecular levels. Eventhough the beneficial aspects of these nanoparticles are evident, excessive usage of nanoparticles at higher concentrations may lead to potential adverse effects. The phytotoxicity resulting from excessive amounts of nanoparticles affects seed germination and biomass production, disrupts the photosynthesis system, induces oxidative stress, impacts cell membrane integrity, alters gene expression, causes DNA damage, and leads to epigenetic variations in plants. Nanoparticles are found to directly associate with the cell membrane and cell organelles, leading to the dissolution and release of toxic ions, generation of reactive oxygen species (ROS) and subsequent oxidative stress. The present study signifies and accumulates knowledge regarding the application of nanoparticles in agriculture and illustrates a clear picture of their possible impacts on plants and soil microbes, thereby paving the way for future developments in nano-agrotechnology. The review concludes by addressing current challenges and proposing future directions to comprehend and mitigate the possible biological risks associated with nanoparticles in agriculture.

Zinc oxide application alleviates arsenic-mediated oxidative stress via physio-biochemical mechanism in rice

Arsenic (As) pollution in cultivated soils poses a significant risk to the sustainable growth of agriculture and jeopardizes food security. However, the mechanisms underlying how zinc (Zn) regulates the toxic effects induced by As in plants remain poorly understood. Hence, this study aimed to explore the potential of ZnO as an effective and environmentally friendly amendment to alleviate As toxicity in rice, thereby addressing the significant risk posed by As pollution in cultivated soils. Through a hydroponic experiment, the study assessed the mitigating effects of different ZnO dosages (Zn5, 5 mg L-1; Zn15, 15 mg L-1; Zn30, 30 mg L-1) on rice seedlings exposed to varying levels of As stress (As0, 0 µM L-1; As25, 25 µM L-1). The findings of the study demonstrate significant improvements in plant height and biomass (shoot and root), with a notable increase of 16-40% observed in the Zn15 treatment, and an even more substantial enhancement of 29-53% observed in the Zn30 treatment under As stress, compared to respective control treatment. Furthermore, in the Zn30 treatment, the shoot and root As contents substantially reduced by 47% and 63%, respectively, relative to the control treatment. The elevated Zn contents in shoots and roots enhanced antioxidant enzyme activities (POD, SOD, and CAT), and decreased MDA contents (13-25%) and H2O2 contents (11-27%), indicating the mitigation of oxidative stress. Moreover, the expression of antioxidant-related genes, OsSOD-Cu/Zn, OsCATA, OsCATB, and OsAPX1 was reduced when rice seedlings were exposed to As stress and significantly enhanced after Zn addition. Overall, the research suggests that ZnO application could effectively mitigate As uptake and toxicity in rice plants cultivated in As-contaminated soils, offering potential solutions for sustainable agriculture and food security.

Comparison of the arsenic protective effects of four nanomaterials on pakchoi in an alkaline soil

Accurately applying engineered nanoparticles (NPs) in farmland stress management is important for sustainable agriculture and food safety. We investigated the protective effects of four engineered NPs (SiO2, CeO2, ZnO, and S) on pakchoi under arsenic (As) stress using pot experiments. The results showed that CeO2, SiO2, and S NPs resulted in biomass reduction, while ZnO NPs (100 and 500 mg kg-1) significantly increased shoot height. Although 500 mg kg-1 S NPs rapidly dissolved to release SO42-, reducing soil pH and pore water As content and further reducing shoot As content by 21.6 %, the growth phenotype was inferior to that obtained with 100 mg kg-1 ZnO NPs, probably due to acid damage. The addition of 100 mg kg-1 ZnO NPs not only significantly reduced the total As content in pakchoi by 23.9 % compared to the As-alone treatment but also enhanced plant antioxidative activity by increasing superoxide dismutase (SOD) and peroxidase (POD) activities and decreasing malondialdehyde (MDA) content. ZnO NPs in soil might inhibit As uptake by roots by increasing the dissolved organic carbon (DOC) by 19.12 %. According to the DLVO theory, ZnO NPs were the most effective in preventing As in pore water from entering plant roots due to their smaller hydrated particle size. Redundancy analysis (RDA) further confirmed that DOC and SO42- were the primary factors controlling plant As uptake under the ZnO NP and S NP treatments, respectively. These findings provide an important basis for the safer and more sustainable application of NP-conjugated agrochemicals.

Chitosan nanoparticles encapsulating curcumin counteract salt-mediated ionic toxicity in wheat seedlings: an ecofriendly and sustainable approach

Over-accumulating salts in soil are hazardous materials that interfere with the biochemical pathways in growing plants drastically affecting their physiological attributes, growth, and productivity. Soil salinization poses severe threats to highly-demanded and important crops directly challenging food security and sustainable productivity. Recently, there has been a great demand to exploit natural sources for the development of nontoxic nanoformulations of growth enhancers and stress emulators. The chitosan (CS) has growth-stimulating properties and widespread use as nanocarriers, while curcumin (CUR) has a well-established high ROS scavenging potential. Herein, we use CS and CUR for the preparation of CSNPs encapsulating CUR as an ecofriendly nanopriming agent. The hydroprimed, nanoprimed (0.02 and 0.04%), and unprimed (control) wheat seeds were germinated under salt stress (150 mM NaCl) and normal conditions. The seedlings established from the aforementioned seeds were employed for germination studies and biochemical analyses. Priming imprints mitigated the ionic toxicity by upregulating the machinery of antioxidants (CAT, POD, APX, and SOD), photosynthetic pigments (Chl a, Chl b, total Chl, and lycopene), tannins, flavonoids, and protein contents in wheat seedlings under salt stress. It controlled ROS production and avoided structural injuries, thus reducing MDA contents and regulating osmoregulation. The nanopriming-induced readjustments in biochemical attributes counteracted the ionic toxicity and positively influenced the growth parameters including final germination, vigor, and germination index. It also reduced the mean germination time, significantly validating the growth-stimulating and stress-emulating role of the prepared nanosystem. Hence, the nanopriming conferred tolerance against salt stress during germination and seedling development, ensuring sustainable growth.

Differential responses of Brassica napus cultivars to dual effects of magnesium oxide nanoparticles

Magnesium oxide nanoparticles (MgO NPs) have great potential to enhance the crop productivity and sustainability of agriculture. Still, a thorough understanding is lacking about its essentiality or toxicity and precise dose for the safe cultivation of oilseed crops. Thus, we assessed the dual effects of MgO NPs (control, 5, 10, 20, 40, 80, and 200 mg/L) on the seed germination, growth performance, photosynthesis, total soluble protein, total carbohydrates, oxidative stress markers (hydrogen peroxide as H2O2 and superoxide anion as O2•‒), lipid peroxidation as MDA, and antioxidant defence machinery (SOD, CAT, APX, and GR activities, and GSH levels) of seven different oilseeds (Brassica napus L.) cultivars (ZY 758, ZD 649, ZD 635, ZD 619, GY 605, ZD 622, and ZD 630). Our findings revealed that low doses of MgO NPs (mainly at 10 mg/L) markedly boosted the seed germination, plant growth (shoot and root lengths) (15‒22%), and biomass (fresh and dry) (11‒19%) by improving the levels of photosynthetic pigments (14‒27%), net photosynthetic rate, stomatal conductance, photosynthetic efficiency (Fv/Fm), total soluble protein and total carbohydrates (16‒36%), antioxidant defence, and reducing the oxidative stress in B. napus tissues. Among all B. napus cultivars, these beneficial effects of MgO NPs were pronounced in ZD 635. ile, elevated levels of MgO NPs (particularly at 200 mg/L) induced oxidative stress, impaired antioxidant scavenging potential, photosynthetic inhibition, protein oxidation, and carbohydrate degradation and lead to inhibit the plant growth attributes. These inhibitory effects were more pronounced in ZD 622. Collectively, low-dose MgO NPs reinforced the Mg contents, protected the plant growth, photosynthesis, total soluble carbohydrates, enzyme activities, and minimized the oxidative stress. While, the excessive MgO NP levels impaired the above-reported traits. Overall, ZD 622 was highly susceptible to MgO NP toxicity and ZD 635 was found most tolerant to MgO NP toxicity.

Zinc-oxide nanoparticles ameliorated the phytotoxic hazards of cadmium toxicity in maize plants by regulating primary metabolites and antioxidants activity

Cadmium stress is a major threat to plant growth and survival worldwide. The current study aims to green synthesis, characterization, and application of zinc-oxide nanoparticles to alleviate cadmium stress in maize (Zea mays L.) plants. In this experiment, two cadmium levels (0, 0.6 mM) were applied to check the impact on plant growth attributes, chlorophyll contents, and concentration of various primary metabolites and antioxidants under exogenous treatment of zinc-oxide nanoparticles (25 and 50 mg L-1) in maize seedlings. Tissue sampling was made 21 days after the zinc-oxide nanoparticles application. Our results showed that applying cadmium significantly reduced total chlorophyll and carotenoid contents by 52.87% and 23.31% compared to non-stress. In comparison, it was increased by 53.23%, 68.49% and 9.73%, 37.53% with zinc-oxide nanoparticles 25, 50 mg L-1 application compared with cadmium stress conditions, respectively. At the same time, proline, superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase contents were enhanced in plants treated with cadmium compared to non-treated plants with no foliar application, while it was increased by 12.99 and 23.09%, 23.52 and 35.12%, 27.53 and 36.43%, 14.19 and 24.46%, 14.64 and 37.68% by applying 25 and 50 mg L-1 of zinc-oxide nanoparticles dosages, respectively. In addition, cadmium toxicity also enhanced stress indicators such as malondialdehyde, hydrogen peroxide, and non-enzymatic antioxidants in plant leaves. Overall, the exogenous application of zinc-oxide nanoparticles (25 and 50 mg L-1) significantly alleviated cadmium toxicity in maize. It provides the first evidence that zinc-oxide nanoparticles 25 ~ 50 mg L-1 can be a candidate agricultural strategy for mitigating cadmium stress in cadmium-polluted soils for safe agriculture practice.

Mitigating chromium toxicity in rice (Oryza sativa L.) via ABA and 6-BAP: Unveiling synergistic benefits on morphophysiological traits and ASA-GSH cycle

In recent years, the use of plant hormones, such as abscisic acid (ABA) and 6-benzylaminopurine (6-BAP), has gained significant attention for their role in mitigating abiotic stresses across various plant species. These hormones have been shown to play a vital role in enhancing the ascorbate-glutathione cycle and eliciting a wide range of plant growth and biomass, photosynthetic efficiency, oxidative stress and response of antioxidants and other physiological responses. While previous research has been conducted on the individual impact of ABA and 6-BAP in metal stress resistance among various crop species, their combined effects in the context of heavy metal-stressed conditions remain underexplored. The current investigation is to assess the beneficial effects of single and combined ABA (5 and 10 μM L-1) and 6-BAP (5 and 10 μM L-1) applications in rice (Oryza sativa L.) cultivated in chromium (Cr)-contaminated soil (100 μM). Our results showed that the Cr toxicity in the soil showed a significant declined in the growth, gas exchange attributes, sugars, AsA-GSH cycle, cellular fractionation, proline metabolism in O. sativa. However, Cr toxicity significantly increased oxidative stress biomarkers, organic acids, enzymatic and non-enzymatic antioxidants including their gene expression in O. sativa seedlings. Although, the application of ABA and 6-BAP showed a significant increase in the plant growth and biomass, gas exchange characteristics, enzymatic and non-enzymatic compounds and their gene expression and also decreased the oxidative stress, And Cr uptake. In addition, individual or combined application of ABA and 6-BAP enhanced the cellular fractionation and decreases the proline metabolism and AsA-GSH cycle in rice plants. These results open new insights for sustainable agriculture practices and hold immense promise in addressing the pressing challenges of heavy metal contamination in agricultural soils.

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

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

Seed priming with nano-silica effectively ameliorates chromium toxicity in Brassica napus

Plant yield is severely hampered by chromium (Cr) toxicity, affirming the urgent need to develop strategies to suppress its phyto-accumulation. Silicon dioxide nanoparticles (SiO2 NPs) have emerged as a provider of sustainable crop production and resistance to abiotic stress. But, the mechanisms by which seed-primed SiO2 NPs palliate Cr-accumulation and its toxic impacts in Brassica napus L. tissues remains poorly understood. To address this gap, present study examined the protective efficacy of seed priming with SiO2 NPs (400 mg/L) in relieving the Cr (200 µM) phytotoxicity mainly in B. napus seedlings. Results delineated that SiO2 NPs significantly declined the accumulation of Cr (38.7/35.9%), MDA (25.9/29.1%), H2O2 (27.04/36.9%) and O2• (30.02/34.7%) contents in leaves/roots, enhanced the nutrients acquisition, leading to improved photosynthetic performance and better plant growth. SiO2 NPs boosted the plant immunity by upregulating the transcripts of antioxidant (SOD, CAT, APX, GR) or defense-related genes (PAL, CAD, PPO, PAO and MT-1), GSH (assists Cr-vacuolar sequestration), and modifying the subcellular distribution (enhances Cr-proportion in cell wall), thereby confer tolerance to ultrastructural damages under Cr stress. Our first evidence to establish the Cr-detoxification by seed-primed SiO2 NPs in B. napus, indicated the potential of SiO2 NPs as stress-reducing agent for crops grown in Cr-contaminated areas.

New insights in to the ameliorative effects of zinc and iron oxide nanoparticles to arsenic stressed spinach (Spinacia oleracea L.)

Nanotechnology is capturing great interest worldwide due to their stirring applications in various fields and also individual application of iron oxide nanoparticle (FeO-NPs) and zinc oxide nanoparticle (ZnO-NPs) have been studied in many literatures. However, the combined application of FeO and ZnO-NPs is a novel approach and studied in only few studies. For this purpose, a pot experiment was conducted to examine the plant growth and biomass, photosynthetic pigments, gas exchange attributes, oxidative stress and response of antioxidant compounds (enzymatic and nonenzymatic), sugars, nutritional status of the plant, organic acid exudation pattern As accumulation from the different parts of the plants in spinach (Spinacia oleracea L.) under the different As concentrations i.e., 0 (no As), 60 and 120 μM] which were primed with combined application of two levels of FeO-NPs (10 and 20 mg L^-1) and ZnO-NPs (20 and 40 mg L^-1). Results from the present study showed that the increasing levels of As in the soil significantly (P < 0.05) decreased plant growth and biomass, photosynthetic pigments, gas exchange attributes, sugars, and nutritional contents from the roots and shoots of the plants. In contrast, increasing levels of As in the soil significantly (P < 0.05) increased oxidative stress indicators in term of malondialdehyde, hydrogen peroxide, and electrolyte leakage, and also increased organic acid exudation patter in the roots of S. oleracea. The negative impact of As toxicity can overcome the combined application of ZnO-NPs and FeO-NPs, which ultimately increased plant growth and biomass by capturing the reactive oxygen species, and decreased oxidative stress in S. oleracea by decreasing the As contents in the roots and shoots of the plants. Research findings, therefore, suggest that the combined application of ZnO-NPs and FeO-NPs can ameliorate As toxicity in S. oleracea, resulting in improved plant growth and composition under As stress, as depicted by balanced exudation of organic acids.

Piriformospora indica alter root-associated microbiome structure to enhance Artemisia annua L. tolerance to arsenic

Microorganisms in the rhizosphere are crucial allies for plant stress tolerance. Recent research suggests that by interacting with the rhizosphere microbiome, microorganisms can aid in the revegetation of soils contaminated with heavy metal(loid)s (HMs). However, it is unknown that how Piriformospora indica influences the rhizosphere microbiome to mitigate arsenic-toxicity in arsenic-enriched environments. Artemisia annua plants were grown in the presence or absence of P. indica and spiked with low (50) and high (150 µmol/L) concentrations of arsenic (As). After inoculation with P. indica, fresh weight increased by 37.7% and 10% in control and high concentration treated plants, respectively. Transmission electron microscopy showed that cellular organelles were severely damaged by As and even disappeared under high concentration. Furthermore, As was mostly accumulated by 5.9 and 18.1 mg/kg dry weight in the roots of inoculated plants treated with low and high concentrations of As, respectively. Additionally, 16 S and ITS rRNA gene sequencing were applied to analyze the rhizosphere microbial community structure of A. annua under different treatments. A significant difference was observed in microbial community structure under different treatments as revealed by non-metric multidimensional scaling ordination. The bacterial and fungal richness and diversity in the rhizosphere of inoculated plants were actively balanced and regulated by P. indica co-cultivation. Lysobacter and Steroidobacter were found to be the As-resistant bacterial genera. We conclude that P. indica inoculation could alter rhizosphere microecology, thereby mitigating As-toxicity without harming the environment.

Application of silicon and sodium hydrosulfide alleviates arsenic toxicity by regulating the physio-biochemical and molecular mechanisms of Zea mays

Soil contamination with toxic heavy metals (such as arsenic (As)) is becoming a serious global problem due to rapid development of social economy, although the use of silicon (Si) and sodium hydrosulfide (NaHS) has been found effective in enhancing plant tolerance against biotic and abiotic stresses including the As toxicity. For this purpose, a pot experiment was conducted using the different levels of As toxicity in the soil, i.e., (0 mM (no As), 50, and 100 µM) which were also supplied with the different exogenous levels of Si, i.e., (0 (no Si), 1.5, and 3 mM) and also with the NaHS, i.e., (0 (no NaHS), 1, and 2 mM) on growth, photosynthetic pigments, gas exchange characteristics, oxidative stress biomarkers, antioxidant machinery (enzymatic and non-enzymatic antioxidants), and their gene expression, ion uptake, organic acid exudation, and As uptake of maize (Zea mays L.). Results from the present study showed that the increasing levels of As in the soil significantly (P < 0.05) decreased plant growth and biomass, photosynthetic pigments, gas exchange attributes, sugars, and nutritional contents from the roots and shoots of the plants. In contrast, increasing levels of As in the soil significantly (P < 0.05) increased oxidative stress indicators in terms of malondialdehyde, hydrogen peroxide, and electrolyte leakage and also increased organic acid exudation patter in the roots of Z. mays, although the activities of enzymatic antioxidants and the response of their gene expressions in the roots and shoots of the plants and non-enzymatic such as phenolic, flavonoid, ascorbic acid, and anthocyanin contents were initially increased with the exposure of 50 µM As, but decreased by the increasing the As concentration 100 µM in the soil. The negative impact of As toxicity can overcome the application of Si and NaHS, which ultimately increased plant growth and biomass by capturing the reactive oxygen species and decreased oxidative stress in Z. mays by decreasing the As contents in the roots and shoots of the plants. Our results also showed that the Si was more sever and showed better results when we compared with NaHS under the same treatment of As in the soil. Research findings, therefore, suggest that the combined application of Si and NaHS can ameliorate As toxicity in Z. mays, resulting in improved plant growth and composition under metal stress, as depicted by balanced exudation of organic acids.

Indole-3-acetic acid (IAA) doping on the surface of CuO-NPs reduces the toxic effects of NPs on Lactuca sativa

CuO Nanoparticles (CuO NPs) retard the plant growth but at appropriate concentration boosts shoot growth and therefore may function as nano-carrier or nano-fertilizer. To overcome the toxic effects, NPs can be capped with plant growth regulators. In this work, CuO-NPs (30 nm) were synthesized as the carrier and capped with indole-3-acetic acid (IAA) to generate CuO-IAA NPs (30.4 nm) as toxicity mitigant molecules. Seedlings of dicots, Lactuca sativa L. (Lettuce) were exposed to 5, 10 mg Kg-1/ of NPs in the soil to analyze shoot length, fresh and dry weight of shoots, phytochemicals, and antioxidant response. Toxicity to shoot length was recorded at higher concentrations of CuO-NPs, however, a reduction in toxicity was observed for CuO-IAA nanocomposite. Concentration-dependent decrease in the biomass of plants was also observed at higher concentrations of CuO-NPs (10 mg/kg). The antioxidative phytochemicals (phenolics and flavonoids) and antioxidative response increased in plants when exposed to CuO-NPs. However, the presence of CuO-IAA NPs combats the toxic response and a significant decrease in non-enzymatic antioxidants and total antioxidative response and total reducing power potential was observed. The results demonstrate that CuO-NPs can be used as a carrier of hormones for the enhancement of plant biomass and IAA on the surface of NPs reduces the toxic effects on NPs.

Ethylene accelerates copper oxide nanoparticle-induced toxicity at physiological, biochemical, and ultrastructural levels in rice seedlings

The enormous use of metal-based nanoparticles (NPs) in different sectors may result in enhanced accumulation in agricultural soil, which could impose negative effects on crop productivity. Hence, strategies are needed to explore the mechanisms of copper oxide nanoparticle (CuO NP)-induced toxicity in crops. The present study aimed to investigate the involvement of ethylene in CuO NP-induced toxicity in rice seedlings. Here, our results indicate that 450 mg L^-1 of CuO NPs induced toxic effects in rice seedlings. Thus, it was evidenced by the reduced plant biomass accumulation, enhanced oxidative stress indicators, and cellular ultrastructural damages. More importantly, the exogenous supply of ethylene biosynthesis and signaling antagonists cobalt (Co) and silver (Ag) respectively provided tolerance and improved the defense system of rice seedlings against CuO NP toxicity. The ethylene antagonists could significantly reduce the extent of ultrastructural and stomatal damage by controlling the ROS accumulation in rice seedlings under CuO NP stress. Furthermore, Co and Ag augmented the antioxidant defense system against CuO NP-induced toxicity. Contrary to that, all oxidative damage attributes were further enhanced exogenous application of ethylene biosynthesis precursor [1-aminocyclopropane-1-carboxylic acid (ACC)] in the presence of CuO NPs. In addition, ACC could increase the CuO NP-induced stomatal and ultrastructural damages by reducing the ROS-scavenging ability in rice seedlings. Taken together, these results indicate the involvement of ethylene in CuO NP-induced toxicity in rice seedlings.

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.

Combined application of plant growth-promoting bacteria and iron oxide nanoparticles ameliorates the toxic effects of arsenic in Ajwain (Trachyspermum ammi L.)

Soil contamination with toxic heavy metals [such as arsenic (As)] is becoming a serious global problem because of the rapid development of the social economy. Although plant growth-promoting bacteria (PGPB) and nanoparticles (NPs) are the major protectants to alleviate metal toxicity, the study of these chemicals in combination to ameliorate the toxic effects of As is limited. Therefore, the present study was conducted to investigate the combined effects of different levels of Providencia vermicola (5 ppm and 10 ppm) and iron oxide nanoparticles (FeO-NPs) (50 mg/l^-1 and 100 mg/l^-1) on plant growth and biomass, photosynthetic pigments, gas exchange attributes, oxidative stress and response of antioxidant compounds (enzymatic and non-enzymatic), and their specific gene expression, sugars, nutritional status of the plant, organic acid exudation pattern As accumulation from the different parts of the plants, and electron microscopy under the soil, which was spiked with different levels of As [0 μM (i.e., no As), 50 μM, and 100 μM] in Ajwain (Trachyspermum ammi L.) seedlings. Results from the present study showed that the increasing levels of As in the soil significantly (p< 0.05) decreased plant growth and biomass, photosynthetic pigments, gas exchange attributes, sugars, and nutritional contents from the roots and shoots of the plants, and destroyed the ultra-structure of membrane-bound organelles. In contrast, increasing levels of As in the soil significantly (p< 0.05) increased oxidative stress indicators in term of malondialdehyde, hydrogen peroxide, and electrolyte leakage, and also increased organic acid exudation patter in the roots of T. ammi seedlings. The negative impact of As toxicity can overcome the application of PGPB (P. vermicola) and FeO-NPs, which ultimately increased plant growth and biomass by capturing the reactive oxygen species, and decreased oxidative stress in T. ammi seedlings by decreasing the As contents in the roots and shoots of the plants. Our results also showed that the FeO-NPs were more sever and showed better results when we compared with PGPB (P. vermicola) under the same treatment of As in the soil. Research findings, therefore, suggest that the combined application of P. vermicola and FeO-NPs can ameliorate As toxicity in T. ammi seedlings, resulting in improved plant growth and composition under metal stress, as depicted by balanced exudation of organic acids.

Efficacy of metallic nanoparticles in attenuating the accumulation and toxicity of chromium in plants: Current knowledge and future perspectives

Nanoparticles have emerged as cutting-edge technology for the improvement of crops yield and safe cultivation of agricultural plants, especially in peripheral areas impaired with toxic heavy metals including chromium (Cr). The uncontrolled release of Cr mainly from anthropogenic factors is substantially polluting the surrounding environment, thereby extensively accumulated in soil-plant system. The excessive Cr-accretion in plant tissues disturbed the morph-physiological, biochemical, cellular, metabolic and molecular processes, and impaired the plants functionality. Therefore, it is obligatory to restrict the accumulation and toxic effects of Cr in plant organs. Recent studies on metallic nanoparticles (MNPs) such as iron oxide, silicon dioxide, copper oxide and zinc oxide have approved their efficacy as potent pool to curb the Cr-induced phytotoxicities and improved the plant tolerance. MNPs attenuated the bioaccumulation and phytotoxicity of Cr by utilizing key mechanisms such as improved photosynthetic machinery, regulation of cellular metabolites, greater chelation capacity to bind with Cr, release of corresponding metallic ions, upsurge in the uptake of essential nutrients, activation of antioxidants (enzymatic and non-enzymatic), reduction in oxidative stress, and cellular injuries, thus improvement in plant growth performances. We have briefly discussed the current knowledge and research gaps in existing literature along with possible recommendations for future research. Overall, Cr-detoxification by MNPs may depends upon the target plant species, Cr speciation, plant growth stages (seedling, vegetative and ripening etc.), treatment methods (foliar spray, seed priming and nutrient solution etc.), type, size, dose and coating of applied MNPs, and conditions (hydroponic and soil environment etc.). This review would help plant scientists to develop MNPs based strategies such as nano-fertilizers to alleviate the Cr-accumulation and its toxic impacts. This may leads to safe and healthy food production. The review outcomes can provide new horizons for research in the applications of MNPs for the sustainable agriculture.

Nanopriming-mediated memory imprints reduce salt toxicity in wheat seedlings by modulating physiobiochemical attributes

BACKGROUND

Around the globe, salinity is one of the serious environmental stresses which negatively affect rapid seed germination, uniform seedling establishment and plant developments restricting sustainable agricultural productivity. In recent years, the concepts of sustainable agriculture and cleaner production strategy have emphasized the introduction of greener agrochemicals using biocompatible and natural sources to maximize crop yield with minimum ecotoxicological effects. Over the last decade, the emergence of nanotechnology as a forefront of interdisciplinary science has introduced nanomaterials as fast-acting plant growth-promoting agents.

RESULTS

Herein, we report the preparation of nanocomposite using chitosan and green tea (CS-GTE NC) as an ecofriendly nanopriming agent to elicit salt stress tolerance through priming imprints. The CS-GTE NC-primed (0.02, 0.04 and 0.06%), hydroprimed and non-primed (control) wheat seeds were germinated under normal and salt stress (150 mM NaCl) conditions. The seedlings developed from aforesaid seeds were used for physiological, biochemical and germination studies. The priming treatments increased protein contents (10-12%), photosynthetic pigments (Chl a (4-6%), Chl b (34-36%), Total Chl (7-14%) and upregulated the machinery of antioxidants (CAT (26-42%), POD (22-43%)) in wheat seedlings under stress conditions. It also reduced MDA contents (65-75%) and regulated ROS production resulting in improved membrane stability. The priming-mediated alterations in biochemical attributes resulted in improved final germination (20-22%), vigor (4-11%) and germination index (6-13%) under both conditions. It reduced mean germination time significantly, establishing the stress-insulating role of the nanocomposite. The improvement of germination parameters validated the stimulation of priming memory in composite-treated seeds.

CONCLUSION

Pre-treatment of seeds with nanocomposite enables them to counter salinity at the seedling development stage by means of priming memory warranting sustainable plant growth and high crop productivity.

Exogenous calcium oxide nanoparticles alleviate cadmium toxicity by reducing Cd uptake and enhancing antioxidative capacity in barley seedlings

Heavy metal contamination is a serious environmental issue that jeopardize global food production and safety, while cadmium (Cd) is a most widely distributed heavy metal in the earth's crust and highly toxic to organisms. The available strategies of fighting against heavy metal contamination are not commonly used due to their ineffectiveness and time- or cost-consuming. Recently, nanotechnology-based ameliorative strategies have emerged as a potential alternative to physic-chemical techniques. In the current study, we used two barley genotypes, LJZ (Cd sensitive) and Pu-9 (Cd tolerant), to study the effects of exogenous calcium oxide nanoparticles (CaO NPs) in alleviating Cd stress. Cd exposure to barley plants led to significant reduction in morph-physiological, nutrient contents, photosynthetic rate, and large accumulation of Cd in plant tissues. However, CaO NPs application significantly increased plant biomass, activities of anti-oxidative enzymes (i.e., ascorbate peroxidase, catalase, superoxide dismutase, and glutathione reductase) and the content of non-enzymatic antioxidants (ascorbate and glutathione) accompanied by great reduction of malondialdehyde (MDA) and hydrogen peroxide contents under Cd stress. Furthermore, CaO NPs increased the expression levels of genes associated with anti-oxidative enzymes. The alleviation of Cd stress by CaO NPs is more obvious in Pu-9 than LJZ. It may be suggested that CaO NPs can be used as a potential chemical to alleviate Cd uptake and toxicity of the crops planted in the Cd-contaminated soil.

Tandem application of endophytic fungus Serendipita indica and phosphorus synergistically recuperate arsenic induced stress in rice

In the context of eco-sustainable acquisition of food security, arsenic (As) acts as a deterring factor, which easily infiltrates our food chain via plant uptake. Therefore, devising climate-smart strategies becomes exigent for minimizing the imposed risks. Pertinently, Serendipita indica (S. indica) is well reputed for its post-symbiotic stress alleviatory and phyto-promotive potential. Management of phosphorus (P) is acclaimed for mitigating arsenic toxicity in plants by inhibiting the uptake of As molecules due to the competitive cationic exchange in the rhizosphere. The current study was designed to investigate the tandem effects of S. indica and P in combating As toxicity employing two rice genotypes, i.e., Guodao-6 (GD-6; As-sensitive genotype) and Zhongzhe You-1 (ZZY-1; As-tolerant genotype). After successful fungal colonization, alone and combined arsenic (10  μ M L^-1) and phosphorus (50  μ M L^-1) treatments were applied. Results displayed that the recuperating effects of combined S. indica and P treatment were indeed much profound than their alone treatments; however, most of the beneficial influences were harnessed by ZZY-1 in comparison with GD-6. Distinct genotypic differences were observed for antioxidant enzyme activities, which were induced slightly higher in S. indica-colonized ZZY-1 plants, with or without additional P, as compared to GD-6. Ultrastructure images of root and shoot exhibited ravages of As in the form of chloroplasts-, nuclei-and cell wall-damage with enlarged vacuole area, mellowed mostly by the combined treatment of S. indica and P in both genotypes. Gene expression of PHTs family transporters was regulated at different levels in almost all treatments across genotypes. Conclusively, the results of this study validated the promising role of S. indica and additional P in mitigating As stress, albeit corroborated that the extent of relevant benefit exploitation is highly genotype-dependent. Verily, unlocking the potential of nature-friendly solutions will mend the anthropogenic damage already been done to our environment.