Nanoparticles as a Tool for Alleviating Plant Stress: Mechanisms, Implications, and Challenges

Plants, being sessile, are continuously exposed to varietal environmental stressors, which consequently induce various bio-physiological changes in plants that hinder their growth and development. Oxidative stress is one of the undesirable consequences in plants triggered due to imbalance in their antioxidant defense system. Biochemical studies suggest that nanoparticles are known to affect the antioxidant system, photosynthesis, and DNA expression in plants. In addition, they are known to boost the capacity of antioxidant systems, thereby contributing to the tolerance of plants to oxidative stress. This review study attempts to present the overview of the role of nanoparticles in plant growth and development, especially emphasizing their role as antioxidants. Furthermore, the review delves into the intricate connections between nanoparticles and plant signaling pathways, highlighting their influence on gene expression and stress-responsive mechanisms. Finally, the implications of nanoparticle-assisted antioxidant strategies in sustainable agriculture, considering their potential to enhance crop yield, stress tolerance, and overall plant resilience, are discussed.

Plants 2024, 13, 1528 2 of 22 diverse environmental stressors [17].Normally, there is a balance in the production and elimination of ROS within the cell.However, external stressors hamper the productionelimination balance resulting in the excess generation and accumulation of ROS [18,19].Consequently, rapid leakage of ROS occurs, which further alters the metabolic, morphological, and physiological processes of the plant [20][21][22].To counteract the deleterious effects of ROS, plants have evolved complex enzymatic and non-enzymatic defense mechanisms collectively called the "antioxidant system" [23,24].The enzymes of antioxidant system include ascorbate peroxidase (APX), Catalase (CAT), dehydro-ascorbate reductase (DHAR), glutathione reductase (GR), glutathione peroxidase (GPX), glutathione S-transferase (GST), mono-hydro ascorbate reductase (MDAR), peroxide reduction (PRX) and superoxide dismutase (SOD).The non-enzymatic antioxidants include ascorbic acid (AA), α-tocopherol, carotenoids, flavonoids, glutathione (GSH), and plastoquinone/ubiquinone [25][26][27].Both groups of antioxidants are necessary for ROS homeostasis, and previous studies suggest that high antioxidative activity is linked to stress tolerance in plants and thus plays a pivotal role in adaptation to stress in plants [28][29][30].In recent years, the advancement in nanotechnology has been observed to be aligned with the study of nanoparticles in plants, as it can trigger the various enzymatic and nonenzymatic antioxidant capabilities of plants.Nanoparticles are natural or artificially synthesized particles, having sizes ranging from 1 to 100 nanometers.As compared to their bulk materials, nanoparticles have different properties; however, their effects vary according to their concentrations [31,32].Previous studies suggest that higher concentrations (up to 2000 mgL −1 ) in the application of nanoparticles negatively affects the biochemistry, morphology, and physiology of plants, as well as causing genotoxicity [33][34][35], while application at appropriately standardized concentrations causes positive effects [36][37][38][39].The current study presents a comprehensive review of the role of nanoparticles in stress amelioration through redox homeostasis and by improving the antioxidative system in plants.Furthermore, the use of different nanoparticles and their role in mediating biochemical, physiological, proteomic, and gene expression changes are discussed.

Abiotic Stressors
The term abiotic stressors refers to all the nonliving entities which negatively impact the metabolism and growth of plants.Heavy metal accumulation in soil, drought, salinity, erratic weather conditions, and extreme low and high temperatures, all contribute to abiotic stress in plants that greatly affect agriculture worldwide, consequently, leading to massive economic losses.In addition to natural causes such as climate change and global In recent years, the advancement in nanotechnology has been observed to be aligned with the study of nanoparticles in plants, as it can trigger the various enzymatic and non-enzymatic antioxidant capabilities of plants.Nanoparticles are natural or artificially synthesized particles, having sizes ranging from 1 to 100 nanometers.As compared to their bulk materials, nanoparticles have different properties; however, their effects vary according to their concentrations [31,32].Previous studies suggest that higher concentrations (up to 2000 mgL −1 ) in the application of nanoparticles negatively affects the biochemistry, morphology, and physiology of plants, as well as causing genotoxicity [33][34][35], while application at appropriately standardized concentrations causes positive effects [36][37][38][39].The current study presents a comprehensive review of the role of nanoparticles in stress amelioration through redox homeostasis and by improving the antioxidative system in plants.Furthermore, the use of different nanoparticles and their role in mediating biochemical, physiological, proteomic, and gene expression changes are discussed.

Abiotic Stressors
The term abiotic stressors refers to all the nonliving entities which negatively impact the metabolism and growth of plants.Heavy metal accumulation in soil, drought, salinity, erratic weather conditions, and extreme low and high temperatures, all contribute to abiotic stress in plants that greatly affect agriculture worldwide, consequently, leading to massive economic losses.In addition to natural causes such as climate change and global warming, various anthropogenic activities, such as intensive agriculture, rapid industrialization and rising population, indirectly trigger abiotic stress (Figure 2).For instance, drought and salinity can hinder water uptake, impairing plant physiological processes and reducing crop yields; extreme temperatures can cause thermal stress, which damages cellular structures and inhibits enzyme activity; heavy metal accumulation, such as cadmium, lead, and arsenic, in the soil can lead to phytotoxicity, disrupting cellular processes by generating reactive oxygen species (ROS) that damage DNA, proteins, and lipids.This metal-induced oxidative stress interferes with photosynthesis and respiration, ultimately stunting plant growth and development.Erratic weather conditions, including unseasonal rain or prolonged dry spells, can disrupt the phenological stages of plants, such as flowering and fruiting, thereby affecting reproductive success and crop yield.Additionally, flooding can lead to hypoxic conditions in the root zone, inhibiting root respiration and nutrient uptake [1][2][3]40,41].To counteract and promote tolerance, plants activate early stress signaling mechanisms [7].These include the release of secondary messengers, such as nitric oxide, reactive oxygen species, and calcium, that transmit and amplify the signals as well as activating protein kinases, like SnRk1, which changes the expression of key stress-responsive genes to restore homeostasis in plant cells [42][43][44].These intricate mechanisms consequently activate the transcription factors that eventually activate various stress responsive genes, thereby facilitating stress tolerance.Besides, releases of phytohormones, including ethylene and Abscisic acid, trigger the activation of stress response.
Plants 2024, 13, 1528 3 of 22 warming, various anthropogenic activities, such as intensive agriculture, rapid industrialization and rising population, indirectly trigger abiotic stress (Figure 2).For instance, drought and salinity can hinder water uptake, impairing plant physiological processes and reducing crop yields; extreme temperatures can cause thermal stress, which damages cellular structures and inhibits enzyme activity; heavy metal accumulation, such as cadmium, lead, and arsenic, in the soil can lead to phytotoxicity, disrupting cellular processes by generating reactive oxygen species (ROS) that damage DNA, proteins, and lipids.This metal-induced oxidative stress interferes with photosynthesis and respiration, ultimately stunting plant growth and development.Erratic weather conditions, including unseasonal rain or prolonged dry spells, can disrupt the phenological stages of plants, such as flowering and fruiting, thereby affecting reproductive success and crop yield.Additionally, flooding can lead to hypoxic conditions in the root zone, inhibiting root respiration and nutrient uptake [1][2][3]40,41].To counteract and promote tolerance, plants activate early stress signaling mechanisms [7].These include the release of secondary messengers, such as nitric oxide, reactive oxygen species, and calcium, that transmit and amplify the signals as well as activating protein kinases, like SnRk1, which changes the expression of key stress-responsive genes to restore homeostasis in plant cells [42][43][44].These intricate mechanisms consequently activate the transcription factors that eventually activate various stress responsive genes, thereby facilitating stress tolerance.Besides, releases of phytohormones, including ethylene and Abscisic acid, trigger the activation of stress response.Under drought stress, major phytohormones, including auxins (AUX), gibberellic acids (GA), cytokinin (CK), and abscisic acid (ABA), have been reported to be decisive in Under drought stress, major phytohormones, including auxins (AUX), gibberellic acids (GA), cytokinin (CK), and abscisic acid (ABA), have been reported to be decisive in Plants 2024, 13, 1528 4 of 22 plant adaptation to drought stress.For instance, the ABA signaling genes OsABI5, Oshox22, OsNAC5, DSM2 in rice have been reported to improve yield in drought stress through ABA biosynthesis.Similarly, induced expression of a CK biosynthetic gene, isopentyl transferase (IPT), is known to increase CK levels, thereby protecting the plant by delaying droughtinduced senescence.Another gene DRO1, upon higher expressions and improved drought tolerance, is negatively regulated by Auxin.In addition, decreased levels of GA aligned with decreased plant growth [45].Accumulation of late embryogenesis-abundant (LEA) mRNA was also observed upon downregulation of IAA [46].A similar study on barley observed a fivefold increase of ABA in drought tolerant varieties as compared to susceptible ones [47].Overexpression of ABA biosynthesis gene NCED3 (9-cis-epoxycarotenoid dioxygenase) in Arabidopsis resulted in improved shoot growth under drought stress [48].In maize, ABA deficiency resulted in increased ethylene production and triggered ethyleneinduced leave senescence [49].
Studies suggest that transcription factors are critical in mediating abiotic stress tolerance upon overexpression [50].Aligning with this, various transcription factors have been reported for promoting abiotic stress tolerance, including OsERF1 in rice, GmERF3 in soybean, and ERF1 in Arabidopsis [51][52][53][54].In transgenic Arabidopsis, the transcription factor SCDREB5 from screw moss regulated jasmonic acid biosynthesis, thereby promoting salinity stress [55].The upregulation of OsDREB1A in Arabidopsis has also been linked with salinity tolerance [56].Moreover, in rice, the upregulation of TF OsSTAP1 and Os-DREB1B enhanced salinity tolerance, and the upregulation of OsDREB2A and OsDREB2B improved salt tolerance in both Arabidopsis and rice [57].Change in temperature is also linked with triggering stress in plants; cold temperature results in inactivation of enzymes, halting cellular machinery and heat results in denaturation of proteins and enzymes [57,58].In cold stress, a cascade of transcription factors is activated which activates COR genes (cold responsive genes) that regulate the membrane fluidity and inward flow of calcium, e.g., a loss of function mutation at AtANN1 results in promoting freezing tolerance in Arabidopsis [59].Likewise, in heat stress, various heat shock proteins (HSP) are activated that prevent protein denaturation [60].For instance, in rice and Arabidopsis, heat stress (40 • C), HSP70 was activated in a short span of time [61].Various nanoparticles have been deployed to promote stress tolerance in plants.The use of silicon nanoparticles in different concentrations via two different methods (foliar and soil application) suggested improved plant growth by foliar application, as it contributed to an increased content of photosynthetic pigments and antioxidant enzymes in Lilium.Similar results were concluded for silicon nanoparticles in potato plants in drought stress, in wheat plants against Rhizoctonia solani infection and in blueberry plants against hypoxia-induced oxidative damage.Similarly, foliar supplementation of rice plants at 90 ppm of silicon dioxide nanoparticles showed improved growth under water regime conditions.Consistent with these findings, application of biosynthesized copper nanoparticles on seeds of Lens culnaris revealed that roots treated with 0.025 mgmL −1 of copper oxide nanoparticles had the highest activity of enzymes related to the defense system, along with increased total phenolic content.Supplementation of media with zinc oxide nanoparticles also resulted in olive plants in increased chlorophyll a and b content.Likewise, supplementation of culture media with silver nanoparticles suggested that higher concentrations (more than 110 mgdm −3 ) cause decreased activity of antioxidant enzymes (peroxidase, catalase, super oxidase dismutase, ascorbate peroxidase) in lavender.The spray application of boron nanoparticles at 12.5 ppm significantly increased the antioxidant activity of pea plants in drought stress [62][63][64][65][66][67][68][69][70][71][72].The application of silica nanoparticles in rice for enhanced growth in water regime conditions has been reported [68].
Moreover, a positive effect on plant growth was observed by application of magnetite nanoparticles [73].Consistent with this, a positive effect on leaf area and shoot length was observed by application of silica nanoparticles in drought stress [74].In addition, improved photosynthesis and antioxidants in wheat plant were observed by application of iron oxide Plants 2024, 13, 1528 5 of 22 nanoparticles [75].Similar studies on banana have been conducted suggesting improved resistance to cold stress by application of chitosan nanoparticles [76].

Biotic Stressors
In agriculture, biotic stress is a major contributor to pre-and post-harvest crop losses [77].Biotic stress is induced by living entities, more specifically by fungi, viruses, bacteria, insect pests, and herbivores, which unlike abiotic stress drastically hamper plant growth by nutritional deprivation, which potentially causes plant death [78,79] (Figures 1 and 3).With the course of evolution, plants have evolved sophisticated strategies that lead to activation of their defense systems, just as in the case of abiotic stresses.Jasmonic acid (JA) signaling has been reported to be critical in promoting biotic stress tolerance as it induces the production of protease inhibitors, phytoalexins, and key genes required in plant defense [80,81].In rice, JA-responsive genes ch11 and AP24 were observed to induce tolerance to sheath blight [82].Similarly, the JA-responsive WRKY gene in maize has been reported in defense against herbivore attack [83].Likewise, the ORA12 gene in Arabidopsis thaliana has been reported to be involved in plant defense against diverse biotic stressors [84].The role of zinc oxide nanoparticles in tomato plants has also been suggested to boost immunity [85].
Plants 2024, 13, 1528 5 of 22 iron oxide nanoparticles [75].Similar studies on banana have been conducted suggesting improved resistance to cold stress by application of chitosan nanoparticles [76].

Biotic Stressors
In agriculture, biotic stress is a major contributor to pre-and post-harvest crop losses [77].Biotic stress is induced by living entities, more specifically by fungi, viruses, bacteria, insect pests, and herbivores, which unlike abiotic stress drastically hamper plant growth by nutritional deprivation, which potentially causes plant death [78,79] (Figures 1 and 3).With the course of evolution, plants have evolved sophisticated strategies that lead to activation of their defense systems, just as in the case of abiotic stresses.Jasmonic acid (JA) signaling has been reported to be critical in promoting biotic stress tolerance as it induces the production of protease inhibitors, phytoalexins, and key genes required in plant defense [80,81].In rice, JA-responsive genes ch11 and AP24 were observed to induce tolerance to sheath blight [82].Similarly, the JA-responsive WRKY gene in maize has been reported in defense against herbivore attack [83].Likewise, the ORA12 gene in Arabidopsis thaliana has been reported to be involved in plant defense against diverse biotic stressors [84].The role of zinc oxide nanoparticles in tomato plants has also been suggested to boost immunity [85].Accumulation of ROS as response to abiotic and biotic stresses can impair various essential physiological processes of plants.In addition, long term exposure of these stressors might permanently damage plants, thereby affecting the overall yield and productivity of the plants.For mitigating impacts caused by abiotic and biotic stresses on plants, nanoparticles are suggested to be promising.In various studies, nanoparticles have been reported to mitigate varietal abiotic and biotic stresses.The use of various nanoparticles and their roles in alleviating varietal abiotic and biotic stresses have been highlighted in Tables 1 and 2 in the upcoming sections.

Oxidative Stress and Plant Physiology
The production of ROS is a normal part of photosynthesis [86].However, rapid ROS synthesis leads to its accumulation and activation of the antioxidative system, as discussed in the previous sections [87].The main consequence of excessive ROS is its oxidative Accumulation of ROS as response to abiotic and biotic stresses can impair various essential physiological processes of plants.In addition, long term exposure of these stressors might permanently damage plants, thereby affecting the overall yield and productivity of the plants.For mitigating impacts caused by abiotic and biotic stresses on plants, nanoparticles are suggested to be promising.In various studies, nanoparticles have been reported to mitigate varietal abiotic and biotic stresses.The use of various nanoparticles and their roles in alleviating varietal abiotic and biotic stresses have been highlighted in Tables 1 and 2 in the upcoming sections.

Oxidative Stress and Plant Physiology
The production of ROS is a normal part of photosynthesis [86].However, rapid ROS synthesis leads to its accumulation and activation of the antioxidative system, as discussed in the previous sections [87].The main consequence of excessive ROS is its oxidative effects on proteins, nucleic acids, lipids, and other cellular organelles leading to cell death [88].In plants, the chlorophyll content and carotenoids determine photosynthesis rate.These pigments absorb sunlight, and carotenoid helps to provide photoprotection to plants via non-photochemical quenching [89].The biotic/abiotic oxidative stress induced triggers oxidative damage and ROS leads to destruction of photosynthetic machinery [20].Preservation of chlorophyll and carotenoids in plants is suggested against numerous stressors, so that plants can continue to perform photosynthesis [90,91].A few studies have demonstrated the modulation of antioxidant systems in order to understand the physiological, biochemical, and morphological changes in citrus plants upon aging at three different stages, viz.young leaves, mature and senescent leaves.The study observed a gradual decrease in the effect of the non-enzymatic antioxidant system [92].Similarly, induction of phenolic compounds and expression of ROS detoxification genes was observed to be associated with chitosan in grapevine [93].Furthermore, in Arabidopsis, the effect of H 2 O 2 on chloro-plastic DJ-1B revealed that H 2 O 2 decreased glyoxalase activity [94].
Various nano-assisted approaches have been used to improve tolerance to oxidative stress in plants (Tables 1 and 2).Considering the importance of preservation of chlorophyll and other pigments for photosynthesis in plants, various attempts have been made towards nano-mediated improvement in plant pigments.A recent study on citrus (mandarin oranges) suggested considerable improvement in chlorophyll and carotenoid concentrations in HLB-infected (Huanglongbing) plants by foliar treatments with green synthesized AgNPs (silver nanoparticles).The same study further suggested that the varied amounts of AgNPs enhanced the performance of enzymatic and non-enzymatic antioxidants, including superoxide dismutase, peroxidase, catalase, total phenolics, and flavonoid content.Consistent with the findings, the authors suggested the use of AgNPs at 75 mgL −1 as ideal for increasing antioxidant enzymes [95].In another similar study in rice plants, the application of AgNPs alleviated the levels of catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR), along with enhancing the growth of plants.Besides, decreased H 2 O 2 , lipid peroxidation and ROS were observed in treated plants [96].Consistent with these findings, in bananas a significant increase in concentrations of SOD, POD and CAT was observed in seedlings treated with AgNPs, as well as an increased content of chlorophyll and carotenoids.Higher concentrations of AgNPs also resulted in increased H 2 O 2 and proline content [97].Likewise, increase in plant height and seed germination have been suggested in summer savory [98].Furthermore, enhanced sugar synthesis in tomato was reported by treatment of silver nanoparticles [99].
Recent attempts have suggested the role of nanoparticles in promoting stress tolerance by acting as antioxidants or boosting the antioxidative system [126] (Figure 3).Various recent studies have confirmed the use of nanoparticles in alleviating ROS-induced stress by boosting the antioxidant system.These include AuNPs in wheat, ZnO NPs in peas, tomato, and okra, CeO 2 and CuO NP in maize, corn, and soybean, Ca 3 (PO 4 ) 2 in beans, AgNP in pearl millet, biochar NP in wheat, Zeolite NPs in potato, chitosan NP in bitter melon, graphene oxide NPs in wheat and SiO 2 NPs in peas [127][128][129][130][131]. The various nanoparticles and their antioxidant roles have been highlighted in the tables below (Tables 1 and 2).These research projects have concluded that low concentration of NPs triggers detoxification of the ROS and activates antioxidant enzymes by upregulating the signaling genes [132].Fusarium andiyazi Chitosan Tomato Upregulation of PR genes, activation of SOD and related antioxidant genes [180] Alternaria solani AgNP Tomato Increased activity of antioxidant enzymes SOD, CAT, APX, PAL, POD, PPO [181] The table summarizes various nanoparticles used in the mitigation of various biotic stress in different crops.Abbreviations: Ag-silver; APX-ascorbate peroxidase; Ca 3 (PO 4 ) 2 -calcium phosphate; CAT-catalase; CuO-copper oxide; MgO-magnesium oxide; PAL-phenylalanine ammonia lyase; POD-peroxidase; PPO-polyphenol oxidase; PR genes-pathogenesis related genes; ROS-reactive oxygen species; SOD-superoxidase dismutase; Se-selenium; Si-silicon/silica; SiO 2 -silicon dioxide; TiO 2 -titanium dioxide; ZnO-zinc oxide.

Nano-Delivery
Recent attempts have been made to design nano-structured carriers, utilizing materials like nano-clays and polymeric nanoparticles for controlled-release formulations of fertilizers and pesticides [182].These nano-carriers protect active ingredients, enabling gradual release and targeted delivery to plants, reducing environmental impact, and optimizing resource utilization [183].Innovations include the use of controlled release nano-fertilizers (CRFs) [183].CRFs can deliver nutrient to plants for extended days to months, besides protection from the release of fertilizers in environment, contributing to their applicability in sustainable agricultural practices (Figure 4) [184,185].Various nanomaterials, including quantum dots, graphene, and carbon-nanotube, due to their small size and unique properties, have been adversely used in controlled release applications [186,187].Moreover, the nano-encapsulation technique has been recently used to protect seeds from pathogens, enhance nutrient uptake during germination, and to provide improved drought tolerance [188][189][190][191]. Nano-fertilizers possessing phosphorous, potassium and nitrogen have been reported to improve growth and productivity in plants [192].Likewise, nanofertilizers have been suggested to improve tolerance from biotic and abiotic stresses in plants [6].Advances have also focused on using nanomaterials for seed delivery and improved seed germination [193].Nano-encapsulation techniques employ materials like lipid-based nanoparticles and biodegradable polymers to protect seeds [194].Recent studies have explored the potential of nanomaterials, such as zinc oxide nanoparticles, in seed priming to enhance early growth and stress tolerance in crops [195,196].A study on bitter almond seedlings reported the successful germination of seeds treated with nano-urea modified hydroxyapatite nanoparticles under salinity stress [197].Similarly, for the growth of corn seedlings, a copper oxide-based tenorite nano-fertilizer demonstrated effective results [198].Moreover, for improvement of biomass in maize, a chitosan based sustained release nano-fertilizer was also developed [199].The use of zerovalent iron nano-fertilizer in aromatic rice improved germination [200].
of nanomaterials, such as zinc oxide nanoparticles, in seed priming to enhance early growth and stress tolerance in crops [195,196].A study on bitter almond seedlings reported the successful germination of seeds treated with nano-urea modified hydroxyapatite nanoparticles under salinity stress [197].Similarly, for the growth of corn seedlings, a copper oxide-based tenorite nano-fertilizer demonstrated effective results [198].Moreover, for improvement of biomass in maize, a chitosan based sustained release nano-fertilizer was also developed [199].The use of zerovalent iron nano-fertilizer in aromatic rice improved germination [200].

Nano-Monitoring
For maintaining sustainability in agriculture, development of new techniques is imperative.These advancements have led to the development of nano-based biosensors "nano-biosensors", which have the potential to sense their environments [201].In agriculture, nano-based sensors have evolved to provide real-time monitoring of crucial parameters.The use of these nano-biosensors, due to their ability to sense, process and detect changes, has contributed to the growth of "smart agriculture" and "precise farming" [202,203].Carbon nanotube-based sensors are gaining attention for their applications in soil sensing, offering high sensitivity and selectivity for detecting nutrient levels and moisture content [204][205][206].Similarly, quantum dot nano-biosensors have been used to detect mycotoxins in barley and corn.A surface plasmon resonance biosensor has

Nano-Monitoring
For maintaining sustainability in agriculture, development of new techniques is imperative.These advancements have led to the development of nano-based biosensors "nano-biosensors", which have the potential to sense their environments [201].In agriculture, nano-based sensors have evolved to provide real-time monitoring of crucial parameters.The use of these nano-biosensors, due to their ability to sense, process and detect changes, has contributed to the growth of "smart agriculture" and "precise farming" [202,203].Carbon nanotube-based sensors are gaining attention for their applications in soil sensing, offering high sensitivity and selectivity for detecting nutrient levels and moisture content [204][205][206].Similarly, quantum dot nano-biosensors have been used to detect mycotoxins in barley and corn.A surface plasmon resonance biosensor has been used to detect the Cymbidium Mosaic virus [207].Molecular imprinted polymer-based nanobiosensors have been employed to sense polyphenols in vegetables [208].Graphene-based molecular imprinted polymer nano-biosensors have been used to detect chlorothalonil and chlorpyrifos methyl pesticides [209].Likewise, an acetylcholine esterase biosensor has been used to detect parathion, parazoan and methyl-parathion pesticides.Moreover, a nano-biosensor "artificial nose" has been reported to sense released organic compounds and detect pathogens based on those compounds [210].Consistent with these studies, current attempts are ongoing on for the integration of nanoscale sensors with wireless communication systems, enabling remote and continuous monitoring of agricultural fields.Furthermore, nano-farming strategies have aimed at a holistic integration of nanotechnology into farming practices [211].These include the use of engineered nanomaterials, such as functionalized nanoparticles and nano-composites, for enhancing soil fertility, water retention, and nutrient availability [212] (Figure 5).The ongoing research is investigating the potential of nanoscale delivery systems not only for nutrients and pesticides but also for beneficial microorganisms, promoting sustainable and eco-friendly farming practices.
holistic integration of nanotechnology into farming practices [211].These include the use of engineered nanomaterials, such as functionalized nanoparticles and nano-composites, for enhancing soil fertility, water retention, and nutrient availability [212] (Figure 5).The ongoing research is investigating the potential of nanoscale delivery systems not only for nutrients and pesticides but also for beneficial microorganisms, promoting sustainable and eco-friendly farming practices.

Current Challenges and Limitations
The unique properties of nanoparticles contribute to their applicability in sustainable agricultural practices.The ultra-small particle size of NPs makes them immensely useful for deterioration of ROS at enzymatic, non-enzymatic, biochemical, and molecular levels.However, contrastingly, the same properties of NPs adversely affect the health of plants, as well as humans [213][214][215].These challenges and limitations hinder their widespread use and acceptance.One major concern is the potential ecotoxicity of nanoparticles, which poses a threat to the environment [216].The impact on soil microorganisms, aquatic ecosystems, and non-target organisms questions the overall safety and sustainability of nanoparticle applications.Addressing these concerns necessitates a thorough assessment of the ecological consequences associated with nanoparticle exposure.Moreover, the absence of standardized protocols for assessing nanoparticle toxicity complicates the

Current Challenges and Limitations
The unique properties of nanoparticles contribute to their applicability in sustainable agricultural practices.The ultra-small particle size of NPs makes them immensely useful for deterioration of ROS at enzymatic, non-enzymatic, biochemical, and molecular levels.However, contrastingly, the same properties of NPs adversely affect the health of plants, as well as humans [213][214][215].These challenges and limitations hinder their widespread use and acceptance.One major concern is the potential ecotoxicity of nanoparticles, which poses a threat to the environment [216].The impact on soil microorganisms, aquatic ecosystems, and non-target organisms questions the overall safety and sustainability of nanoparticle applications.Addressing these concerns necessitates a thorough assessment of the ecological consequences associated with nanoparticle exposure.Moreover, the absence of standardized protocols for assessing nanoparticle toxicity complicates the regulatory approval process [217].A still imperative challenge is the establishment of clear and universally accepted guidelines for nanoparticle safety testing.The lack of such regulatory frameworks hinders the industrial applicability of nanoparticles [218,219].Understanding the fate and transport of nanoparticles in the environment is another critical challenge.The long-term impacts of nanoparticles on ecosystems remain uncertain without comprehensive knowledge of their fate and transport dynamics.This knowledge gap makes it challenging to predict and mitigate potential associated adverse effects.Cost and scalability issues further contribute to the limited adoption of nanoparticles on a large scale.Some nanoparticles are highly expensive to produce, restricting their practical applicability.For overcoming these challenges, the development of cost-effective and scalable synthesis methods, aligning with safety for implementation, are necessary.Additionally, the variable responses of different plant species to different nanoparticle exposure makes it more difficult to assess environmental impact [220][221][222].An extensive understanding of these species-specific responses is crucial for predicting and managing the potential consequences accurately.Henceforth, these hurdles need to be addressed for ensuring the responsible, safe and sustainable use of nanoparticles in agriculture.

Future Directions
Future advancements in nanoparticles and plant interactions should prioritize longterm ecotoxicity studies, standardized testing protocols for regulatory approval, and the development of advanced tracking techniques to monitor nanoparticle fate and transport in real-time.Additionally, there is an urge for innovative and cost-effective synthesis methods, precision agriculture approaches that consider species-specific responses, and a deeper understanding of the nano-bio interface.Exploring nano-enabled nutrient delivery systems for plants and developing integrated risk assessment models are crucial for sustainable agriculture practices.Intense exploration of the benefits and risks of nanoparticles, along with interdisciplinary collaborations, will play a pivotal role in expanding nanoparticle applications.

Conclusions
Nanoparticles, based on their size, composition, and sensitivity, interact with plants in a number of ways.These interactions result in various anatomical, morpho-physiological and biochemical changes that are directly related to the overall efficiency of crop plants.Some of the beneficial effects of nanoparticles in plants include enhanced growth, increased fresh biomass, improved chlorophyll content, improved metabolism, increased antioxidant potential upregulation and improved expression of stress-related genes, which are crucial for stress resilience by alleviating protein and chlorophyll and promoting nitrogen metabolism.Despite the effectiveness of nanoparticles in ameliorating various stresses, most of these studies are still in the laboratory stage.The increased applicability of nanoparticles is of concern due to their unexpected effects on the environment, as well as their accumulation in edible plant organs, which pose serious risks of bioaccumulation in the food chain.Hence, more efforts to develop proper evaluation methodologies for evaluating the effects and predicting the fate of nanoparticles is required.Additionally, the standardization of the acceptable limits of nanoparticles in their wide range of applicable areas is needed.Future studies should focus on the development of non-toxic, ecologically safe, affordable, stable, and self-degradable nanoparticles for commercializing nanotechnology from laboratories to the agricultural fields.A multidisciplinary and collaborative approach involving researchers, policymakers, and industry stakeholders is essential to navigate these complexities and unlock the full potential of nanoparticles while ensuring environmental sustainability and safety.

Figure 1 .
Figure 1.Generalized overview of plant in response to stress and its mitigation by application of different nanoparticles (foliar and soil application).

Figure 1 .
Figure 1.Generalized overview of plant in response to stress and its mitigation by application of different nanoparticles (foliar and soil application).

Figure 2 .
Figure 2. Varietal abiotic stressors affecting plant metabolism, physiology and morphology resulting in poor growth and productivity of plants (lower yield).

Figure 2 .
Figure 2. Varietal abiotic stressors affecting plant metabolism, physiology and morphology resulting in poor growth and productivity of plants (lower yield).

Figure 3 .
Figure 3. Image describing improved growth of plant upon treatment with nanoparticles in oxidative stress leading to ROS-AOE homeostasis (ROS-Reactive oxygen species; AOE-Antioxidant enzymes).

Figure 3 .
Figure 3. Image describing improved growth of plant upon treatment with nanoparticles in oxidative stress leading to ROS-AOE homeostasis (ROS-Reactive oxygen species; AOE-Antioxidant enzymes).

Figure 4 .
Figure 4. Advantages of nano-based delivery of fertilizers as compared to traditional methods.

Figure 4 .
Figure 4. Advantages of nano-based delivery of fertilizers as compared to traditional methods.

Figure 5 .
Figure 5. Image describing diverse applications of nanoscience in agriculture highlights nanoparticle synthesis methods and their deployment in monitoring crop plants with enhanced techniques.

Figure 5 .
Figure 5. Image describing diverse applications of nanoscience in agriculture highlights nanoparticle synthesis methods and their deployment in monitoring crop plants with enhanced techniques.

Table 1 .
Different nanoparticles used in amelioration of varietal abiotic stresses in different plant species.

Table 2 .
Various nanoparticles used in mitigating biotic stress in different plants.