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

Comparative investigation on chemical and green synthesized titanium dioxide nanoparticles against chromium (VI) stress eliciting differential physiological, biochemical, and cellular attributes in Helianthus annuus L

Nanotechnology is a new scientific area that promotes unique concepts to comprehend the optimal mechanics of nanoparticles (NPs) in plants under heavy metal stress. The present investigation focuses on effects of synthetic and green synthesized titanium dioxide nanoparticles (TiO2 NPs and gTiO2 NPs) against Cr(VI). Green TiO2 NPs have been produced from plant leaf extract (Ricinus communis L.). Synthesis was confirmed employing an array of optical spectroscopic and electron microscopic techniques. Chromium strongly accelerated H2O2 and MDA productions by 227 % and 266 % at highest chromium concentration (60 mg/kg of soil), respectively, and also caused DNA damage, and decline in photosynthesis. Additionally, anomalies were observed in stomatal cells with gradual increment in chromium concentrations. Conversely, foliar applications of TiO2 NPs and gTiO2 NPs considerably mitigated chromium stress. Sunflower plants treated with modest amounts of green TiO2 NPs had significantly better growth index compared to chemically synthesized ones. Principal component analysis highlighted the variations among photosynthetic attributes, oxidative stress markers, and antioxidant defense systems. Notably, gTiO2 supplementation to the Cr(VI) strained plants minimized PC3 production which is a rare report so far. Conclusively, gTiO2 NPs have been identified to be promising nano-based nutrition resource for farming applications.

Iron oxide nanoparticles improving multimetal phytoextraction in Helianthus annuus

This study assessed the phytotoxicity of a mixture of five different trace elements (TEs) frequently found as pollutants in soils: arsenic, cadmium, copper, lead and zinc. On the other hand, the plant response to a magnetite (Fe3O4) nanoparticle amendment on this mixture as well as nanomagnetite remediation potential has been tested. Sunflower (Helianthus annuus) plants were grown for 90 days in soil contaminated with the five mentioned TEs at the limit levels of TEs in soils likely to receive sludge established by French legislation. Depending on the conditions, experimental set-ups were amended or not with 1% dry weight nanomagnetite (NPsMagn), citric acid-coated nanomagnetite (NPsMagn@CA) or micro-sized magnetite (μPs) in order to assess the behavior of nanomagnetites in a TEs-contaminated water-soil-plant system under repeated water-deficiency stress. The mixture of TEs did not induce phytotoxicity as estimated by plant growth, pigment content, maximum quantum yield of photosynthesis, oxidative impact and antioxidant response. Furthermore, both nanomagnetites treatments in a TEs-contaminated soil significantly increased biomass production by 64 % compared to control and antioxidant enzyme activities compared to control and TEs-treated plants. NPsMagn and NPsMagn@CA particularly enhance phytoextraction of Cd and Cu, increasing the amounts of TEs in aerial parts from 1.5 to 4.5 times compared to set-ups without nanomagnetites. Based on Cd, Cu, Pb and Zn contents in soil solutions, both nanomagnetites treatments improved TEs phytoextraction without increasing groundwater contamination. On the contrary, nanomagnetites significantly reduce arsenic uptake by plants and solubilization in dissolved phase. Our results show that modifying surface physicochemical properties of NPsMagn with citric acid coating does not improve their effects compared to bare NPsMagn. NPsMagn and NPsMagn@CA also appear to mitigate the effects of drought stress. This work highlights several positive environmental aspects related to the use of nanomagnetites in phytoremediation.

Nitric oxide and AMF-mediated regulation of soil enzymes activities, cysteine-H2S system and thiol metabolites in mitigating chromium (Cr (VI)) toxicity in pigeonpea genotypes

Cr (VI) hampers plant growth and yield by reducing essential nutrient uptake as it competes for phosphate and sulfate transporters. Nitric oxide (NO) and mycorrhization play important roles in mitigating Cr (VI) toxicity. Present study aimed to compare the potential of AMF (Arbuscular mycorrhizal fungi)-Rhizoglomus intraradices and NO (0.25 mM) in alleviating Cr (VI) stress (0, 10 and 20 mg/kg) in two differentially tolerant pigeonpea genotypes (Pusa 2001 and AL 201). Cr (VI) toxicity reduced growth, mycorrhizal colonization, nutrient uptake, and overall productivity by inducing reactive oxygen species (ROS) generation, with AL 201 more sensitive than Pusa 2001. NO and AM enhanced activities of soil enzymes, thereby increasing nutrients availability as well as their uptake, with AM more effective than NO. Both amendments reduced oxidative stress and restricted Cr (VI) uptake by increasing the activities of antioxidant and S- assimilatory enzymes, with Pusa 2001 more responsive than AL 201. NO was relatively more efficient in regulating cysteine-H2S system by increasing the activities of biosynthetic enzymes (ATP-sulfurylase (ATPS), O-acetylserine thiol lyase (OASTL), D-cysteine desulfhydrase (DCD) and L-cysteine desulfhydrase (LCD), while AM significantly increased glutathione reductase (GR), γ-glutamylcysteine synthetase (γ-ECS) enzymes activities and resultant glutathione (GSH), phytochelatins (PCs), and non-protein thiols (NP-SH) synthesis. Moreover, co-application of NO and AM proved to be highly beneficial in negating the toxic effects of Cr (VI) due to functional complementarity between them. Study suggested the combined use of NO and AM as a useful strategy in re-establishing pigeonpea plants growing in Cr (VI)-stressed environments.

Advances in the Involvement of Metals and Metalloids in Plant Defense Response to External Stress

Plants, as sessile organisms, uptake nutrients from the soil. Throughout their whole life cycle, they confront various external biotic and abiotic threats, encompassing harmful element toxicity, pathogen infection, and herbivore attack, posing risks to plant growth and production. Plants have evolved multifaceted mechanisms to cope with exogenous stress. The element defense hypothesis (EDH) theory elucidates that plants employ elements within their tissues to withstand various natural enemies. Notably, essential and non-essential trace metals and metalloids have been identified as active participants in plant defense mechanisms, especially in nanoparticle form. In this review, we compiled and synthetized recent advancements and robust evidence regarding the involvement of trace metals and metalloids in plant element defense against external stresses that include biotic stressors (such as drought, salinity, and heavy metal toxicity) and abiotic environmental stressors (such as pathogen invasion and herbivore attack). We discuss the mechanisms underlying the metals and metalloids involved in plant defense enhancement from physiological, biochemical, and molecular perspectives. By consolidating this information, this review enhances our understanding of how metals and metalloids contribute to plant element defense. Drawing on the current advances in plant elemental defense, we propose an application prospect of metals and metalloids in agricultural products to solve current issues, including soil pollution and production, for the sustainable development of agriculture. Although the studies focused on plant elemental defense have advanced, the precise mechanism under the plant defense response still needs further investigation.

Melatonin-regulated heat shock proteins and mitochondrial ATP synthase induce drought tolerance through sustaining ROS homeostasis in H2S-dependent manner

Drought is thought to be one of the major global hazards to crop production. Understanding the role of melatonin (Mel) during plant adaptive responses to drought stress (DS) was the aim of the current investigation. Involvement of hydrogen sulfide (H2S) was also explored in Mel-regulated mechanisms of plants' tolerance to DS. A perusal of the data shows that exposure of tomato plants to DS elevated the activity of mitochondrial enzymes viz. pyruvate dehydrogenase, malate dehydrogenase, and citrate synthase. Whereas the activity of ATP synthase and ATPase was downregulated under stress conditions. Under DS, an increase in the expression level of heat shock proteins (HSPs) and activation level of antioxidant defense system was observed as well. On the other hand, an increase in the activity of NADPH oxidase and glycolate oxidase was observed along with the commencement of oxidative stress and accompanying damage. Application of 30 μM Mel to drought-stressed plants enhanced H2S accumulation and further elevated the activity of mitochondrial enzymes, activation level of the defense system, and expression of HSP17.6 and HSP70. Positive effect of Mel on these attributes was reflected by reduced level of ROS and related damage. However, application of H2S biosynthesis inhibitor DL-propargylglycine reversed the effect of Mel on the said attributes and again the damaging effects of drought were observed even in presence of Mel. This observation led us to conclude that Mel-regulated defense mechanisms operate through endogenous H2S under DS conditions.

Unleashing the potential of nanoparticles on seed treatment and enhancement for sustainable farming

The foremost challenge in farming is the storage of seeds after harvest and maintaining seed quality during storage. In agriculture, studies showed positive impacts of nanotechnology on plant development, seed storage, endurance under various types of stress, detection of seed damages, and seed quality. Seed's response varies with different types of nanoparticles depending on its physical and biochemical properties and plant species. Herein, we aim to cover the impact of nanoparticles on seed coating, dormancy, germination, seedling, nutrition, plant growth, stress conditions protection, and storage. Although the seed treatment by nanopriming has been shown to improve seed germination, seedling development, stress tolerance, and seedling growth, their full potential was not realized at the field level. Sustainable nano-agrochemicals and technology could provide good seed quality with less environmental toxicity. The present review critically discusses eco-friendly strategies that can be employed for the nanomaterial seed treatment and seed enhancement process to increase seedling vigor under different conditions. Also, an integrated approach involving four innovative concepts, namely green co-priming, nano-recycling of agricultural wastes, nano-pairing, and customized nanocontainer storage, has been proposed to acclimatize nanotechnology in farming.

Deficit irrigation strategies (PRD, SDI) and titanium nanoparticles improve water use efficiency and flower quality in greenhouse-grown cut roses

This study explored the use of deficit irrigation techniques for water management in the hydroponic greenhouse cultivation of cut roses. A factorial experiment was conducted using three irrigation treatments: full irrigation (FI), partial root drying (PRD), and sustained deficit irrigation (SDI), and three doses of titanium dioxide nanoparticle foliar application (0, 15, and 30 ppm) as stress alleviation. Results showed that drought stress increased biochemical parameters such as the plants' proline and total phenol content. Compared to SDI treatment, the PRD treatments have an increase in flower number by 40%. The PRD strategy has positive effects on drought tolerance by increasing osmotic and elastic adjustment. Therefore, higher relative water content and longer root length in PRD treatments were observed. Thus, Biomass water use efficiency significantly increased in PRD treatments compared to others. In the PRD treatment, yield WUE increases by 26% and 61% compared to FI and SDI, respectively. The results showed TiO2-NPs positively affected mitigating and even improving some traits in drought stress conditions. These results suggest the superiority of the PRD strategy, which improves growth characteristics and water use efficiency, leading to increased sustainability, reduced environmental impact of greenhouse toxic wastewater, and total profitability of the greenhouse.

Titanium dioxide nanoparticles require K+ and hydrogen sulfide to regulate nitrogen and carbohydrate metabolism during adaptive response to drought and nickel stress in cucumber

Crop plants face severe yield losses worldwide owing to their exposure to multiple abiotic stresses. The study described here, was conducted to comprehend the response of cucumber seedlings to drought (induced by 15% w/v polyethylene glycol 8000; PEG) and nickel (Ni) stress in presence or absence of titanium dioxide nanoparticle (nTiO2). In addition, it was also investigated how nitrogen (N) and carbohydrate metabolism, as well as the defense system, are affected by endogenous potassium (K+) and hydrogen sulfide (H2S). Cucumber seedlings were subjected to Ni stress and drought, which led to oxidative stress and triggered the defense system. Under the stress, N and carbohydrate metabolism were differentially affected. Supplementation of the stressed seedlings with nTiO2 (15 mg L-1) enhanced the activity of antioxidant enzymes, ascorbate-glutathione (AsA-GSH) system and elevated N and carbohydrates metabolism. Application of nTiO2 also enhanced the accumulation of phytochelatins and activity of the enzymes of glyoxalase system that provided additional protection against the metal and toxic methylglyoxal. Osmotic stress brought on by PEG and Ni, was countered by the increase of proline and carbohydrates levels, which helped the seedlings keep their optimal level of hydration. Application nTiO2 improved the biosynthesis of H2S and K+ retention through regulating Cys biosynthesis and H+-ATPase activity, respectively. Observed outcomes lead to the conclusion that nTiO2 maintains redox homeostasis, and normal functioning of N and carbohydrates metabolism that resulted in the protection of cucumber seedlings against drought and Ni stress. Use of 20 mM tetraethylammonium chloride (K+- channel blocker), 500 μM sodium orthovanadate (PM H+-ATPase inhibitor), and 1 mM hypotaurine (H2S scavenger) demonstrate that endogenous K+ and H2S were crucial for the nTiO2-induced modulation of plants' adaptive responses to the imposed stress.

Titanium dioxide nanoparticles improve element uptake, antioxidant properties, and essential oil productivity of Melissa officinalis L. seedlings under in vitro drought stress

In vitro drought stress has a considerable impact on the mass production of active compounds in medicinal plants. Nevertheless, photosynthesis, nutrient uptake, and protein synthesis may be negatively affected by drought, which results in poor growth. Titanium dioxide nanoparticles (TiO2 NPs) have recently been shown to play an important role in increasing nutrient uptake, resistance to various environmental stresses, and better plant growth. Regarding the importance of pharmaceutical metabolites of Melissa officinalis L., this experiment aimed to assess the role of TiO2 NPs in improving physiological responses and phytochemical properties in M. officinalis under in vitro drought stress. For this, two-week-old seedlings were cultured on Murashige and Skoog (MS) medium supplemented with 0, 50, and 100 mg L-1 TiO2 NPs and 0, 3, and 6% (w/v) polyethylene glycol (PEG). Two weeks after treatments, a reduction of chlorophyll, protein content, essential elements, and enhancement of H2O2 and malondialdehyde (MDA) levels were seen as a result of drought stress. It was observed that M. officinalis partially responded to the drought by increasing non-enzymatic antioxidants, including phenolics, flavonoids, and anthocyanin and ascorbate peroxidase activity. Moreover, PEG-induced drought stress increased some important essential oil content such as limonene, alpha-pinene, myrcene, γ-3-carene, citral, and carvacrol; however, the results showed that TiO2 NPs not only increased the quantity of essential oils but also led to tolerance to the drought stress by increasing photosynthetic pigments, antioxidant systems, absorption of essential nutrients, and decreasing H2O2 and MDA levels.

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

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

Effect of foliar application of nano-nutrients solution on growth and biochemical attributes of tomato (Solanum lycopersicum) under drought stress

INTRODUCTION

Drought stress has drastically hampered the growth and yield of many crops. Therefore, environmentally safe agricultural techniques are needed to mitigate drought stress impact. To this end, foliar spray of nano-nutrients solution to (NNS) alleviate harmful aspects of drought stress.

METHODS

In a completely randomized design (CRD) experiment, seedlings were transplanted into pots at 2-3 leaf stage, each filled with loam-compost- organic manure soil (3:1:1). Plants were divided into two groups. (a) control group (b) applied stress group. Plants at vegetative stage were treated with 100% FC for control group and 60% FC for drought group, and these levels were maintained until harvesting. Three treatments of NNS with four levels i.e., 0%, 1%, 3% and 5% were given to all the pots after two weeks of drought stress treatment with a gap of 5 days at vegetative stage.

RESULTS AND DISCUSSION

Application of 1% of nano-nutrient solution displayed an improvement in shoot length, shoot fresh and dry weight, number of leaves and flowers. Leaf chlorophylls and carotenoids and total phenolics contents were found maximum while minimum electrolyte leakage was observed at 3% application compared to control. Further, 1% application of NNS increased the Leaf RWC%, total soluble sugars, flavonoids contents. 5% NNS application exhibited higher total free amino acids with minimum lipid peroxidation rate in leaves of tomato under drought. Antioxidant enzyme activities increased in a concentration dependent manner as gradual increase was observed at 1%, 3% and 5%, respectively. Overall, this study introduced a new insights on using nano-nutrient solutions to maintain natural resources and ensure agricultural sustainability.

Comprehensive physiological, transcriptomic, and metabolomic analyses reveal the synergistic mechanism of Bacillus pumilus G5 combined with silicon alleviate oxidative stress in drought-stressed Glycyrrhiza uralensis Fisch

Glycyrrhiza uralensis Fisch. is often cultivated in arid, semi-arid, and salt-affected regions that suffer from drought stress, which leads to the accumulation of reactive oxygen species (ROS), thus causing oxidative stress. Plant growth-promoting bacteria (PGPB) and silicon (Si) have been widely reported to be beneficial in improving the tolerance of plants to drought stress by maintaining plant ROS homeostasis. Herein, combining physiological, transcriptomic, and metabolomic analyses, we investigated the response of the antioxidant system of G. uralensis seedlings under drought stress to Bacillus pumilus (G5) and/or Si treatment. The results showed that drought stress caused the overproduction of ROS, accompanied by the low efficiency of antioxidants [i.e., superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), the ascorbate (AsA)-glutathione (GSH) pool, total carotenoids, and total flavonoids]. Inversely, supplementation with G5 and/or Si enhanced the antioxidant defense system in drought-stressed G. uralensis seedlings, and the complex regulation of the combination of G5 and Si differed from that of G5 or Si alone. The combination of G5 and Si enhanced the antioxidant enzyme system, accelerated the AsA-GSH cycle, and triggered the carotenoid and flavonoid metabolism, which acted in combination via different pathways to eliminate the excess ROS induced by drought stress, thereby alleviating oxidative stress. These findings provide new insights into the comparative and synergistic roles of PGPB and Si in the antioxidant system of plants exposed to drought and a guide for the application of PGPB combined with Si to modulate the tolerance of plants to stress.

The role of nanoparticles in plant biochemical, physiological, and molecular responses under drought stress: A review

Drought stress (DS) is a serious challenge for sustaining global crop production and food security. Nanoparticles (NPs) have emerged as an excellent tool to enhance crop production under current rapid climate change and increasing drought intensity. DS negatively affects plant growth, physiological and metabolic processes, and disturbs cellular membranes, nutrient and water uptake, photosynthetic apparatus, and antioxidant activities. The application of NPs protects the membranes, maintains water relationship, and enhances nutrient and water uptake, leading to an appreciable increase in plant growth under DS. NPs protect the photosynthetic apparatus and improve photosynthetic efficiency, accumulation of osmolytes, hormones, and phenolics, antioxidant activities, and gene expression, thus providing better resistance to plants against DS. In this review, we discuss the role of different metal-based NPs to mitigate DS in plants. We also highlighted various research gaps that should be filled in future research studies. This detailed review will be an excellent source of information for future researchers to adopt nanotechnology as an eco-friendly technique to improve drought tolerance.

Metallic and non-metallic nanoparticles from plant, animal, and fisheries wastes: potential and valorization for application in agriculture

Global agriculture is facing tremendous challenges due to climate change. The most predominant amongst these challenges are abiotic and biotic stresses caused by increased incidences of temperature extremes, drought, unseasonal flooding, and pathogens. These threats, mostly due to anthropogenic activities, resulted in severe challenges to crop and livestock production leading to substantial economic losses. It is essential to develop environmentally viable and cost-effective green processes to alleviate these stresses in the crops, livestock, and fisheries. The application of nanomaterials in farming practice to minimize nutrient losses, pest management, and enhance stress resistance capacity is of supreme importance. This paper explores innovative methods for synthesizing metallic and non-metallic nanoparticles using plants, animals, and fisheries wastes and their valorization to mitigate abiotic and biotic stresses and input use efficiency in climate-smart and stress-resilient agriculture including crop plants, livestock, and fisheries.

Dissection of Crop Metabolome Responses to Nitrogen, Phosphorus, Potassium, and Other Nutrient Deficiencies

Crop growth and yield often face sophisticated environmental stresses, especially the low availability of mineral nutrients in soils, such as deficiencies of nitrogen, phosphorus, potassium, and others. Thus, it is of great importance to understand the mechanisms of crop response to mineral nutrient deficiencies, as a basis to contribute to genetic improvement and breeding of crop varieties with high nutrient efficiency for sustainable agriculture. With the advent of large-scale omics approaches, the metabolome based on mass spectrometry has been employed as a powerful and useful technique to dissect the biochemical, molecular, and genetic bases of metabolisms in many crops. Numerous metabolites have been demonstrated to play essential roles in plant growth and cellular stress response to nutrient limitations. Therefore, the purpose of this review was to summarize the recent advances in the dissection of crop metabolism responses to deficiencies of mineral nutrients, as well as the underlying adaptive mechanisms. This review is intended to provide insights into and perspectives on developing crop varieties with high nutrient efficiency through metabolite-based crop improvement.

Exogenous Application of Green Titanium Dioxide Nanoparticles (TiO2 NPs) to Improve the Germination, Physiochemical, and Yield Parameters of Wheat Plants under Salinity Stress

Agriculture is the backbone of every developing country. Among various crops, wheat (Triticum aestivum L.) belongs to the family Poaceae and is the most important staple food crop of various countries. Different biotic (viruses, bacteria and fungi) and abiotic stresses (water logging, drought and salinity) adversely affect the qualitative and quantitative attributes of wheat. Among these stresses, salinity stress is a very important limiting factor affecting the morphological, physiological, biochemical attributes and grain yield of wheat. This research work was carried out to evaluate the influence of phytosynthesized TiO₂ NPs on the germination, physiochemical, and yield attributes of wheat varieties in response to salinity. TiO₂ NPs were synthesized using TiO₂ salt and a Buddleja asiatica plant extract as a reducing and capping agent. Various concentrations of TiO₂ nanoparticles (20, 40, 60 and 80 mg/L) and salt solutions (NaCl) (100 and 150 mM) were used. A total of 20 mg/L and 40 mg/L improve germination attributes, osmotic and water potential, carotenoid, total phenolic, and flavonoid content, soluble sugar and proteins, proline and amino acid content, superoxide dismutase activity, and reduce malondialdhehyde (MDA) content at both levels of salinity. These two concentrations also improved the yield attributes of wheat varieties at both salinity levels. The best results were observed at 40 mg/L of TiO₂ NPs at both salinity levels. However, the highest concentrations (60 and 80 mg/L) of TiO₂ NPs showed negative effects on germination, physiochemical and yield characteristics and causes stress in both wheat varieties under control irrigation conditions and salinity stress. Therefore, in conclusion, the findings of this research are that the foliar application of TiO₂ NPs can help to improve tolerance against salinity stress in plants.

Potassium deficiency stress tolerance in peanut (Arachis hypogaea) through ion homeostasis, activation of antioxidant defense, and metabolic dynamics: Alleviatory role of silicon supplementation

Potassium (K) scarcity of arable land is one of the important factors that hamper the growth of the plants and reduce yield worldwide. In the current study, we examine the physiological, biochemical, and metabolome response of Arachis hypogaea (GG7 genotype: fast-growing, tall, early maturing, and high yielding) under low K either solitary or in combination with Si to elucidate the ameliorative role of Si. The reduced fresh and dry biomass of peanut and photosynthetic pigments content was significantly alleviated by Si. Si application did not affect the leaf and stem K⁺, although it enhanced root K⁺ in K-limitation, which is probably due to up-regulated expression of genes responsible for K uptake. Si improves the potassium use efficiency in K-limitation as compared to control. K-deficiency increased MDA, O₂^•-, and H₂O₂ levels in leaf and root of peanut. Si improved/maintained the activity of antioxidative enzymes, which significantly lowered the ROS accumulation in K-limitation. The AsA/DHA and GSH/GSSG ratio was approximately unaffected in both leaf and root, suggesting the maintained cellular redox potential in K-starved peanut. Si promotes accumulation of sugars and sugar alcohols, phytohormones indicating their probable involvement in signal transduction, osmotic regulation, and improvement of stress tolerance. Down-regulation of aspartic acid and glutamic acid while up-regulation of lysine, histidine, and arginine could maintain charge balance in K-deprived peanut. The significant accumulation of polyphenols under K limitation supplemented with Si suggests the role of polyphenols for ROS scavenging. Our results demonstrated that Si as a beneficial element can mitigate K-nutrient toxicity and improve KUE of peanut under K-limitation conditions. Moreover, our results demonstrate that Si application can improve crop yield, quality, and nutrient use efficiency under nutrient limitation conditions.

Nanoparticles as potential hallmarks of drought stress tolerance in plants

Plants are inevitably exposed to drought stress limiting their growth and causing yield loss, thus inciting food crises across the world. Nanoparticles (NPs) are regarded as effective and promising tools for modulation of crop yield to overcome current and future constraints in sustainable agricultural production by upgrading the plant tolerance mechanism under abiotic stress conditions, including drought. NPs exhibit alleviating effects against drought stress via induction of physiological and biochemical readjustments accompanied by modulation of gene expression involved in drought response/tolerance. NPs ameliorate drought-induced reduction in carbon assimilation via increasing the photosynthetic activity. The improved root growth, upregulation of aquaporins, modification of intracellular water metabolism, accumulation of compatible solutes and ion homeostasis are the major mechanisms used by NPs to mitigate the osmotic stress caused by water deficit. NPs reduce water loss from leaves through stomatal closure due to fostered abscisic acid (ABA) accumulation and ameliorate oxidative stress damage by reducing reactive oxygen species and activating the antioxidant defense system. This review provides an evolutionary foundation regarding drought stress in plant life and summarizes the interactions between NPs and plants under drought. The subsequent impact of NPs on plant development and productivity and recent nanobiotechnological approaches to improve drought stress resilience are presented. On the whole, this review highlights the significance of NPs in dealing with the global problem of water scarcity faced by farmers.

The combined effect of water deficit stress and TiO2 nanoparticles on cell membrane and antioxidant enzymes in Helianthus annuus L

Nanotechnology has become one of the several approaches attempting to ameliorate the severe effect of drought on plant's production and to increase the plants tolerance against water deficit for the water economy. In this research, the effect of foliar application of TiO₂, nanoparticles or ordinary TiO₂, on Helianthus annuus subjected to different levels of water deficit was studied. Cell membrane injury increased by increasing the level of water deficit and TiO₂ concentration, and both types of TiO₂ affected the leaves in analogous manner. Ord-TiO₂ increased H₂O₂ generation by 67-240% and lipid peroxidation by 4-67% in leaves. These increases were more than that induced by Nano-TiO₂ and the effect was concentration dependent. Proline significantly increased in leaves by water deficit stress, reaching at 25% field capacity (FC) to more than fivefold compared to that in plants grown on full FC. Spraying plants with water significantly decreased the activities of enzymes in the water deficit stressed roots. The water deficit stress exerted the highest magnitude of effect on the changes of cell membrane injury, MDA, proline content, and activities of CAT and GPX. Nano-TiO₂ was having the highest effect on contents of H₂O₂ and GPX activity. In roots, the level of water deficit causes highest effect on enzyme activities, but TiO₂ influenced more on the changes of MDA and H₂O₂ contents. GPX activity increased by 283% in leaves of plants treated with 50 and 150 ppm Nano-TiO₂, while increased by 170% in those treated with Ord-TiO₂, but APX and CAT activities increased by 17-197%, in average, with Ord-TiO₂. This study concluded that Nano-TiO₂ didn't ameliorate the effects of drought stress on H. annuus but additively increased the stress, so its use in nano-phytotechnology mustn't be expanded without extensive studies.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-022-01153-z.

The phytotoxicity of microplastics to the photosynthetic performance and transcriptome profiling of Nicotiana tabacum seedlings

Microplastics (MPs), as emerging "new generation" organic contaminants, have attracted extensive attention regarding their severe toxicity to aquatic and terrestrial organisms. However, the responses of plant photosynthesis to soil MP pollution are unclear. In this study, Nicotiana tabacum seedlings were grown in soils containing 0~1000 g·kg-1 polyethylene (PE)-MPs for 48 days. PE-MPs significantly increased the superoxide anion content by 15.3~44.8% but decreased the chlorophyll content and Rubisco activity by 4.3~14.0% and 4.23~30.9%, respectively. PE-MPs also inhibited RuBP carboxylation activation and regeneration, restrained light use efficiency, and prevented dark respiration, thereby reducing the light-saturated photosynthesis rate. The changed shape of OJIP transients indicated that PE-MP toxicity inhibited not only the primary photochemistry rate but also photoelectrochemical quenching, resulting in decreased quantum yields. RNA-Seq revealed thousands of differentially expressed genes (DEGs), among which 79 highly expressed DEGs were enriched in photosynthesis-related processes. Functional annotation revealed that the reduction in environment stress was mainly due to the repressed expression of light harvesting-, electron transport- and photosystem-related genes in chloroplasts. This study regarding the physiological and molecular responses of photosynthetic performance to soil PE-MP pollution provides a new viewpoint for exploring the plant photosynthesis regulating and protective mechanisms under soil MP stresses.

Implementation of a LoRaWAN Based Smart Agriculture Decision Support System for Optimum Crop Yield

A majority of the population of developing countries is associated with agriculture directly or indirectly. The liaison of engineering technology and Sustainable Development Goals (SDGs) can build a bridge for farmers to enhance their skills regarding advancements through future generation agriculture trends. The next-generation trends include better soil preparation, intelligent irrigation systems, advanced methods of crop nutrient inspection, smart fertilizers applications, and multi-cropping practices. This work proposes a smart Decision Support System (DSS) that acquires the input parameters based on real-time monitoring to optimize the yield that realizes sustainability by improving per hectare production and lessening water seepage wastage in agribusiness. The proposed model comprises three basic units including an intelligent sensor module, smart irrigation system and controlled fertilizer module. The system has integrated sensors, cloud employing decision support layers, and networking based DSS to recommend cautions for optimum sustainable yield. The intelligent sensors module contains a temperature and humidity sensor, NPK sensor, soil moisture sensor, soil conductivity sensor, and pH sensor to transmit the statistics to the cloud over the internet via Long Range (LoRa) using Serial Peripheral Interface (SPI) communication protocol. Moreover, an android application has been developed for real-time data monitoring according to GPS location and node information (accessed remotely). Furthermore, the DSS contemplates the accessible information from sensors, past patterns, monitoring climate trends and creating cautions required for sustainable fertilizer consumption. The presented results and comparison validate the novelty of the design as it embraces smart irrigation with smart control and smart decision-making based on accurate real-time field data. It is better than existing systems as it transmits the data over the LoRa that is an open-source communication with long-range transmission ability up to several kilometres. The sensor nodes helped in advancing the yield of crops, which resulted in achieving inclusive and sustainable economic goals.

Recent Trends in Nano-Fertilizers for Sustainable Agriculture under Climate Change for Global Food Security

Nano-fertilizers (NFs) significantly improve soil quality and plant growth performance and enhance crop production with quality fruits/grains. The management of macro-micronutrients is a big task globally, as it relies predominantly on synthetic chemical fertilizers which may not be environmentally friendly for human beings and may be expensive for farmers. NFs may enhance nutrient uptake and plant production by regulating the availability of fertilizers in the rhizosphere; extend stress resistance by improving nutritional capacity; and increase plant defense mechanisms. They may also substitute for synthetic fertilizers for sustainable agriculture, being found more suitable for stimulation of plant development. They are associated with mitigating environmental stresses and enhancing tolerance abilities under adverse atmospheric eco-variables. Recent trends in NFs explored relevant agri-technology to fill the gaps and assure long-term beneficial agriculture strategies to safeguard food security globally. Accordingly, nanoparticles are emerging as a cutting-edge agri-technology for agri-improvement in the near future. Interestingly, they do confer stress resistance capabilities to crop plants. The effective and appropriate mechanisms are revealed in this article to update researchers widely.

Bacillus-Mediated Silver Nanoparticle Synthesis and Its Antagonistic Activity against Bacterial and Fungal Pathogens

In this article, the supernatant of the soil-borne pathogen Bacillus mn14 was used as the catalyst for the synthesis of AgNPs. The antibacterial and antifungal activity of Bs-AgNPs was evaluated, in which S. viridans and R. solani showed susceptibility at 70 µL and 100 µL concentrations. Enzyme properties of the isolates, according to minimal inhibitory action and a growth-enhancing hormone-indole acetic acid (IAA) study of the isolates, were expressed in TLC as a purple color with an Rf value of 0.7. UV/Vis spectroscopy revealed the presence of small-sized AgNPs, with a surface plasmon resonance (SPR) peak at 450 nm. The particle size analyzer identified the average diameter of the particles as 40.2 nm. The X-ray diffraction study confirmed the crystalline nature and face-centered cubic type of the silver nanoparticle. Scanning electron microscopy characterized the globular, small, round shape of the silver nanoparticle. AFM revealed the two-dimensional topology of the silver nanoparticle with a characteristic size ranging around 50 nm. Confocal microscopy showed the cell-wall disruption of S. viridans treated with Bs-AgNPs. High-content screening and compound microscopy revealed the destruction of mycelia of R. solani after exposure to Bs-AgNPs. Furthermore, the Bs-AgNPs cured sheath blight disease by reducing lesion length and enhancing root and shoot length in Oryza sativa seeds. This soil-borne pathogen Bacillus-mediated synthesis approach of AgNPs appears to be cost-efficient, ecofriendly, and farmer-friendly, representing an easy way of providing valuable nutritious edibles in the future.

Biosynthesis and characterization of titanium dioxide nanoparticles and its effects along with calcium phosphate on physicochemical attributes of wheat under drought stress

Drought stress is reducing the production of crops globally. This research was designed to evaluate the role of titanium dioxide (TiO₂ NPs) nanoparticles and calcium phosphate on wheat facing drought stress. TiO₂ NPs were prepared by green synthesis and their characterization (by UV-visible spectroscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX)) was also done. The results showed that TiO₂ NPs worked efficiently and improved plant growth under drought. However, the best results were obtained from combined applications of 40 ppm TiO₂ NPs and 40 ppm calcium phosphate on plants. They increased root length (33%), shoot length (53%), fresh weight (48%), and dry weight (44%) of wheat as compared to control. The physiological parameters including chlorophyll content, relative water content, membrane stability index, and osmolyte content (proline and sugar) were also improved. The increase in superoxide dismutase, peroxidase and, catalase activity by the combined application of TiO₂ NPs and calcium phosphate was 83% and 78%, 74% and 52%, 81%, and 67% in Pakistan-13 and Zincol-16 respectively, as compared to untreated drought exposed plants. They also enhanced the nutrients uptake (including potassium, phosphorus, and nitrogen) that ultimately improved plant biomass. They also maintained the level of growth hormones in plants. These hormones regulate cellular processes and are responsible for germination, development, and plant reaction in drought stress. The increase in the yield was also significant, hence it is recommended that the 40 ppm concentration of TiO₂ NPs along with calcium phosphate improves the productivity of wheat under drought stress.

Exogenous melatonin-mediated regulation of K+ /Na+ transport, H+ -ATPase activity and enzymatic antioxidative defence operate through endogenous hydrogen sulphide signalling in NaCl-stressed tomato seedling roots

Melatonin (Mel) and hydrogen sulphide (H₂ S) have emerged as potential regulators of plant metabolism during abiotic stress. Presence of excess NaCl in the soil is one of the main causes of reduced crop productivity worldwide. The present investigation examines the role of exogenous Mel and endogenous H₂ S in tomato seedlings grown under NaCl stress. Effect of 30 µm Mel on endogenous synthesis of H₂ S was examined in roots of NaCl-stressed (200 mm) tomato seedlings. Also, the impact of treatments on the oxidative stress markers, transport of K⁺ and Na⁺ , and activity of H⁺ -ATPase and antioxidant enzymes was assessed. Results show that NaCl-stressed seedlings supplemented with 30 µm Mel had increased levels of endogenous H₂ S through enhanced L-cysteine desulfhydrase activity. Mel in association with H₂ S overcame the deleterious effect of NaCl and induced retention of K⁺ that maintained a higher K⁺ /Na⁺ ratio. Use of plasma membrane inhibitors and an H₂ S scavenger revealed that Mel-induced regulation of K⁺ /Na⁺ homeostasis in NaCl-stressed seedling roots operates through endogenous H₂ S signalling. Synergistic effects of Mel and H₂ S also reduced the generation of ROS and oxidative destruction through the enhanced activity of antioxidant enzymes. Thus, it is suggested that the protective function of Mel against NaCl stress operates through an endogenous H₂ S-dependent pathway, wherein H⁺ -ATPase-energized secondary active transport regulates K⁺ /Na⁺ homeostasis.

Titanium dioxide nanoparticle is involved in mitigating NaCl-induced Calendula officinalis L. by activation of antioxidant defense system and accumulation of osmolytes

This study is aimed at evaluating the effects of TiO₂NPs on biochemical and physiological parameters of marigold (Calendula officinalis L.) under NaCl stress. Treatments included TiO₂NPs applied as foliar spraying in three levels (50, 100, and 200 mgL^-1), no foliar application as control, and different NaCl levels (0, 30, 60, and 90 mM) by adding NaCl to irrigation water. According to the results, the application of different concentrations of TiO₂ had various effects on the studied parameters. The use of 100 mgL^-1 TiO₂NPs increased flavonoid content of the leaves (at 30 mM NaCl), cell membrane injury (with no salinity), CAT and SOD activities (at 90 mM NaCl), and PPO activity (at 60 mM NaCl). On the other hand, using 100 mgL^-1 TiO₂NPs under salinity stress decreased MDA and H₂O₂ contents. Moreover, using 200 mgL^-1 TiO₂NPs increased photosynthetic pigments content, total flavonoid content of flowers, total soluble sugar, carotenoid content of flowers, and RWC (at the treatment with no salinity), aboveground and underground biomasses (at 30 mM and 60 mM NaCl, respectively), phenolic content and antioxidant activity (at 30 mM NaCl), and APX activity (at 90 mM NaCl). In conclusion, the findings of the present study indicated that TiO₂NPs could be a useful material to mitigate the harmful effects of salinity stress. Furthermore, the TiO₂NPs spraying could have beneficial effects on osmotic adjustment, biochemical compound, non-enzymatic and enzymatic antioxidant activities, and growth of marigold under NaCl stress conditions.

Hydrogen sulfide (H2S) and potassium (K+) synergistically induce drought stress tolerance through regulation of H+-ATPase activity, sugar metabolism, and antioxidative defense in tomato seedlings

Exogenous potassium (K⁺) and endogenous hydrogen sulfide (H₂S) synergistically alleviate drought stress through regulating H⁺-ATPase activity, sugar metabolism and redox homoeostasis in tomato seedlings. Present work evaluates the role of K⁺ in the regulation of endogenous H₂S signaling in modulating the tolerance of tomato (Solanum lycopersicum L. Mill.) seedlings to drought stress. The findings reveal that exposure of seedlings to 15% (w/v) polyethylene glycol 8000 (PEG) led to a substantial decrease in leaf K⁺ content which was associated with reduced H⁺-ATPase activity. Treatment with sodium orthovanadate (SOV, PM H⁺-ATPase inhibitor) and tetraethylammonium chloride (TEA, K⁺ channel blocker) suggests that exogenous K⁺ stimulated H⁺-ATPase activity that further regulated endogenous K⁺ content in tomato seedlings subjected to drought stress. Moreover, reduction in H⁺-ATPase activity by hypotaurine (HT; H₂S scavenger) substantiates the role of endogenous H₂S in the regulation of H⁺-ATPase activity. Elevation in endogenous K⁺ content enhanced the biosynthesis of H₂S through enhancing the synthesis of cysteine, the H₂S precursor. Synergistic action of H₂S and K⁺ effectively neutralized drought stress by regulating sugar metabolism and redox homoeostasis that resulted in osmotic adjustment, as witnessed by reduced water loss, and improved hydration level of the stressed seedlings. The integrative role of endogenous H₂S in K⁺ homeostasis was validated using HT and TEA which weakened the protection against drought stress induced impairments. In conclusion, exogenous K⁺ and endogenous H₂S regulate H⁺-ATPase activity which plays a decisive role in the maintenance of endogenous K⁺ homeostasis. Thus, present work reveals that K⁺ and H₂S crosstalk is essential for modulation of drought stress tolerance in tomato seedlings.

Nitric oxide, crosstalk with stress regulators and plant abiotic stress tolerance

Nitric oxide is a dynamic gaseous molecule involved in signalling, crosstalk with stress regulators, and plant abiotic-stress responses. It has great exploratory potentials for engineering abiotic stress tolerance in crops. Nitric oxide (NO), a redox-active gaseous signalling molecule, though present uniformly through the eukaryotes, maintain its specificity in plants with respect to its formation, signalling, and functions. Its cellular concentrations are decisive for its function, as a signalling molecule at lower concentrations, but triggers nitro-oxidative stress and cellular damage when produced at higher concentrations. Besides, it also acts as a potent stress alleviator. Discovered in animals as neurotransmitter, NO has come a long way to being a stress radical and growth regulator in plants. As a key redox molecule, it exhibits several key cellular and molecular interactions including with reactive chemical species, hydrogen sulphide, and calcium. Apart from being a signalling molecule, it is emerging as a key player involved in regulations of plant growth, development and plant-environment interactions. It is involved in crosstalk with stress regulators and is thus pivotal in these stress regulatory mechanisms. NO is getting an unprecedented attention from research community, being investigated and explored for its multifaceted roles in plant abiotic stress tolerance. Through this review, we intend to present the current knowledge and updates on NO biosynthesis and signalling, crosstalk with stress regulators, and how biotechnological manipulations of NO pathway are leading towards developing transgenic crop plants that can withstand environmental stresses and climate change. The targets of various stress responsive miRNA signalling have also been discussed besides giving an account of current approaches used to characterise and detect the NO.

Nitrate reductase is required for salicylic acid-induced water stress tolerance of pepper by upraising the AsA-GSH pathway and glyoxalase system

A trial was conducted to evaluate whether nitrate reductase (NR) participates in salicylic acid (SA)-improved water stress (WS) tolerance in pepper (Capsicum annuum L.) plants. Before starting WS treatment, 0.5 mM SA was applied to half of the well-watered (WW) plants as well as to WS-plants as a foliar spray once a day for a week. The soil water holding capacity was maintained at 40 and 80% of the full water storing capacity for WS and and well-watered (WW) plants, respectively. Water stress caused substantial decreases in total plant dry weight, F_v /F_m , chlorophyll a and b, relative water content, leaf water potential (ΨI) by 53, 37, 49, 21, 36 and 33%, respectively relative to control, but significant increases in malondialdehyde (MDA), hydrogen peroxide (H₂ O₂ ), electrolyte leakage (EL), methylglyoxal (MG), proline, key antioxidant enzymes' activities, NO and NR activity. The SA reduced oxidative stress, but improved antioxidant defence system, ascorbate-glutathione (AsA-GSH) cycle enzymes, glyoxalase system-related enzymes, glyoxalase I (Gly I) and glyoxalase II (Gly II), plant growth, photosynthetic traits, NO, NR and proline. SA-induced WS tolerance was further improved by supplementation of sodium nitroprusside (SNP), a donor of NO. NR inhibitor, sodium tungstate (ST) was applied in conjunction with SA and SA + SNP to the WW and WS-plants to assess whether NR contributes to SA-improved WS tolerance. ST abolished the beneficial effects of SA by reducing NO and NR activity in WS-pepper, but the application of SNP along with SA + ST reversed negative effects of ST, showing that NO and NR are jointly needed for SA-induced WS tolerance of pepper plants.

Exogenous Potassium (K+) Positively Regulates Na+/H+ Antiport System, Carbohydrate Metabolism, and Ascorbate-Glutathione Cycle in H2S-Dependent Manner in NaCl-Stressed Tomato Seedling Roots

Potassium (K⁺) is one of the vital macronutrients required by plants for proper growth and blossoming harvest. In addition, K⁺ also plays a decisive role in promoting tolerance to various stresses. Under stressful conditions, plants deploy their defense system through various signaling molecules, including hydrogen sulfide (H₂S). The present investigation was carried out to unravel the role of K⁺ and H₂S in plants under NaCl stress. The results of the study show that NaCl stress caused a reduction in K⁺ and an increase in Na⁺ content in the tomato seedling roots which coincided with a lower H⁺-ATPase activity and K⁺/Na⁺ ratio. However, application of 5 mM K⁺, in association with endogenous H₂S, positively regulated the Na⁺/H⁺ antiport system that accelerated K+ influx and Na+ efflux, resulting in the maintenance of a higher K⁺/Na⁺ ratio. The role of K⁺ and H₂S in the regulation of the Na⁺/H⁺ antiport system was validated by applying sodium orthovanadate (plasma membrane H⁺-ATPase inhibitor), tetraethylammonium chloride (K⁺ channel blocker), amiloride (Na⁺/H⁺ antiporter inhibitor), and hypotaurine (HT, H₂S scavenger). Application of 5 mM K⁺ positively regulated the ascorbate–glutathione cycle and activity of antioxidant enzymes that resulted in a reduction in reactive oxygen species generation and associated damage. Under NaCl stress, K⁺ also activated carbohydrate metabolism and proline accumulation that caused improvement in osmotic tolerance and enhanced the hydration level of the stressed seedlings. However, inclusion of the H₂S scavenger HT reversed the effect of K⁺, suggesting H₂S-dependent functioning of K⁺ under NaCl stress. Therefore, the present findings report that K⁺, in association with H₂S, alleviates NaCl-induced impairments by regulating the Na⁺/H⁺ antiport system, carbohydrate metabolism, and antioxidative defense system.

Nitric oxide signalling in plant nanobiology: current status and perspectives

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

Calcium-hydrogen sulfide crosstalk during K+-deficient NaCl stress operates through regulation of Na+/H+ antiport and antioxidative defense system in mung bean roots

Present investigation reports the role of calcium (Ca²⁺) and hydrogen sulfide (H₂S) crosstalk associated with Vigna radiata seedlings subjected to K⁺ deficient conditions under short-term (24 h) and long-term (72 h) NaCl stress. Perusal of the data reveals that under short-term NaCl stress an initial decline in K⁺ level led to the elevation in Ca²⁺ and H₂S levels along with improvement in antioxidant system and reduction in reactive oxygen species (ROS) production. Under long-term NaCl stress a further decline in K⁺ content was deleterious that led to a lower K⁺/Na⁺ ratio. This was followed by reduction in antioxidant system along with excessive accumulation of ROS and methylglyoxal content, and increased membrane damage. However, supplementation of the seedling roots with Ca²⁺ enhanced biosynthesis of H₂S through enhancing cysteine pool. The present findings suggest that synergistic action of Ca²⁺ and H₂S induced the activity of H⁺-ATPase that created H⁺ gradient which in turn induced Na⁺/H⁺ antiport system that accelerated K⁺ influx and Na⁺ efflux. All of these together contributed to a higher K⁺/Na⁺ ratio, activation of antioxidative defense system, and maintenance of redox homeostasis and membrane integrity in Ca²⁺-supplemented stressed seedlings. Role of Ca²⁺ and H₂S in the regulation of Na⁺/H⁺ antiport system was validated by the use of sodium orthovanadate (plasma membrane H⁺-ATPase inhibitor), tetraethylammonium chloride (K⁺ channel blocker), and amiloride (Na⁺/H⁺ antiporter inhibitor). Application of Ca²⁺-chelator EGTA (ethylene glycol-bis(b-aminoethylether)-N,N,N',N'-tetraacetic acid) and H₂S scavenger hypotaurine abolished the effect of Ca²⁺, suggesting the involvement of Ca²⁺ and H₂S in the alleviation of NaCl stress. Moreover, use of EGTA and HT also substantiates the downstream functioning of H₂S during Ca²⁺-mediated regulation of plant adaptive responses to NaCl stress. To sum up, present findings reveal the association of Ca²⁺ and H₂S signaling in the regulation of ion homeostasis and antioxidant defense during K⁺-deficient NaCl stress.

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

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

Crosstalk of hydrogen sulfide and nitric oxide requires calcium to mitigate impaired photosynthesis under cadmium stress by activating defense mechanisms in Vigna radiata

Hydrogen sulfide (H₂S) and nitric oxide (NO) have been known to affect vast number of processes in plants under abiotic stresses. Also, calcium (Ca) works as a second messenger in plants, which underpins the abiotic stress-induced damage. However, the sequence of action of these signaling molecules against cadmium (Cd)-induced cellular oxidative damage remains unidentified. Therefore, we studied the synergistic actions and/or relationship of signaling molecules and Ca-dependent activation of tolerance mechanisms in Vigna radiata seedlings under Cd stress. The present study shows that exogenous Ca supplemented to Cd-stressed V. radiata seedlings reduced Cd accumulation and improved the activity of nitrate reductase, and L/D-cysteine desulfhydrase (LCD/DCD) that resulted in improved synthesis of NO and H₂S content. Application of Ca also elevated the level of cysteine (Cys) by upregulating the activity of Cys-synthesizing enzymes serine acetyltransferase and O-acetylserine(thiol)lyase in Cd-stressed seedlings. Maintenance of Cys pool under Cd stress contributed to improved H₂S content which together with Ca and NO improved antioxidant enzymes and components of ascorbate-glutathione (AsA-GSH) cycle. All these collectively regulated the activity of NADPH oxidase and glycolate oxidase, resulting in the inhibition of Cd-induced generation of reactive oxygen species. The elevated level of Cys also assisted the Cd-stressed seedlings in maintaining GSH pool which retained normal functioning of AsA-GSH cycle and led to enhanced content of phytochelatins coupled with reduced Cd content. The positive effect of these events manifested in an enhanced rate of photosynthesis, carbohydrate accumulation, and growth attributes of the plants. On the contrary, addition of NO scavenger cPTIO [2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide], H₂S scavenger HT (Hypotaurine) and Ca-chelator EGTA (Ethylene glycol-bis(b-aminoethylether)-N,N,N',N'-tetraacetic acid) again developed a condition similar to stress and positive effect of the signaling molecules was abolished. The findings of the study postulate that Ca in association with NO and H₂S mitigates Cd-induced impairment and enhances the tolerance of the V. radiata plants against Cd stress. The results of the study also substantiate that Ca acts both upstream as well as downstream of NO signals whereas, H₂S acts downstream of Ca and NO during Cd-stress responses of the plants.

Exogenous nitric oxide requires endogenous hydrogen sulfide to induce the resilience through sulfur assimilation in tomato seedlings under hexavalent chromium toxicity

Nitric oxide (NO) and hydrogen sulfide (H₂S), versatile signaling molecules, play multiple roles in plant growth, physiological and biochemical processes under heavy metal stress. However, the mechanisms through which NO in association with endogenous H₂S mediated hexavalent chromium Cr(VI) toxicity mitigation are still not fully understood. Therefore, we investigated the role of NO and H₂S in sulfur (S)-assimilation and the effect of NO on endogenous H₂S, and cysteine (Cys) biosynthesis and maintenance of cellular glutathione (GSH) pool in tomato seedlings under Cr(VI) stress. Cr(VI) toxicity caused an increase in reactive oxygen species (ROS; O₂^•- and H₂O₂) formation and activity of chlorophyll (Chl) degrading enzyme [Chlorophyllase (Chlase)] and decrease in seedlings growth attributes, Chl a and b content, and activity of Chl synthesizing enzyme [δ-aminolevulinic acid dehydratase (δ-ALAD)], gas exchange parameters, S-assimilation, and Cys and H₂S metabolism. An increase in the content of glycinebetaine (GB), total soluble carbohydrates (TSCs) and total phenols (TPls), and decrease in DNA damage and ROS in NO treated seedlings conferred Cr(VI) toxicity tolerance. Under Cr(VI) toxicity conditions, the inclusion of H₂S scavenger hypotaurine (HT) in growth medium containing NO validated the role of endogenous H₂S in S-assimilation, H₂S and Cys and GSH metabolism by withdrawing activity of enzymes involved in S-assimilation [adenosine 5-phosphosulfatereductase (APS-R), ATP-sulfurylase (ATP-S)], in the biosynthesis of H₂S [L-cysteine desulfhydrase (L-CD) and D-cysteine desulfhydrase (D-CD)], Cys [O-acetylserin (thiol) lyase (OAST-L)], and GSH [glutamylcysteine synthetase (γ-GCS) and glutathione synthetase (GS)], and in antioxidant system. On the other hand, application of cPTIO [2-(4-32 carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide], a NO scavenger and HT diminished the effect of NO on internal H₂S levels, Cys and glutathione homeostasis, and S-assimilation, which resulted in poor immunity against oxidative stress induced by Cr(VI) toxicity. The obtained results postulate that NO-induced internal H₂S conferred tolerance of tomato seedlings to Cr(VI) toxicity and maintained better photosynthesis process and plant growth.