Nano-silicon dioxide mitigates the adverse effects of salt stress on Cucurbita pepo L

Influence of nanosilicon dioxide along with bioinoculants on Zea mays and its rhizospheric soil

Application of nanocompounds along with plant growth promoting rhizobacteria is gaining attention to improve agriculture productivity. In the present study, attempts have been made to observe the impact of nanosilicon dioxide (10 mg L^-1) and two plant growth promotory bacteria (PC1-MK106029) and (PC4-MK106024) on the growth of Zea mays and its rhizosphere in a pot experiment. Combined treatment of bacterial consortium and nanosilicon dioxide enhanced average plant height and number of leaves over control in maize after 30 days of sowing. Similarly, percent enhancement of total chlorophyll, carotenoid, sugar, soluble protein, phenol and flavonoid content was 106, 307, 116, 57, 159 and 132 respectively over control in maize leaves in the same treatment. Treated plants showed significant increase of 29.4 and 73.9% in catalase and peroxidase activities respectively over control. Physicochemical and biochemical parameters of soil health were also improved in the soil treated with PGPR and nanosilicon dioxide. An increase of 1.5-2 fold in the activities of fluorescein diacetate, dehydrogenase and alkaline phosphatase was observed in the treated soil as compared to control. Our results revealed that inoculation of beneficial microorganisms in combination with nanosilicon dioxide is an effective method for enhancing physicochemical and biochemical parameters of the soil which are responsible for increased plant growth and soil fertility by increasing enzyme activities of microbes. This approach presents an alternative to pesticides, fertilizers and GM crops to enhance crop productivity.

Zinc Oxide Nanoparticles Application Alleviates Arsenic (As) Toxicity in Soybean Plants by Restricting the Uptake of as and Modulating Key Biochemical Attributes, Antioxidant Enzymes, Ascorbate-Glutathione Cycle and Glyoxalase System

Accumulation of arsenic (As) in soils is increasing consistently day-by-day, which has resulted in increased toxicity of this element in various crop plants. Arsenic interferes with several plant metabolic processes at molecular, biochemical and physiological levels, which result in reduced plant productivity. Hence, the introduction of novel ameliorating agents to combat this situation is the need of the hour. The present study was designed to examine the effect of zinc oxide nanoparticles (ZnO-NPs) in As-stressed soybean plants. Various plant growth factors and enzymes were studied at varying concentrations of As and ZnO-NPs. Our results showed that with the application of ZnO-NPs, As concentration declined in both root and shoot of soybean plants. The lengths of shoot and root, net photosynthetic rate, transpiration, stomatal conductance, photochemical yield and other factors declined with an increase in external As level. However, the application of ZnO-NPs to the As-stressed soybean plants resulted in a considerable increase in these factors. Moreover, the enzymes involved in the ascorbate-glutathione cycle including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) showed a significant increase in their activity with the application of ZnO-NPs to the As-stressed plants. Hence, our study confirms the significance of ZnO-NPs in alleviating the toxicity of As in soybean plants.

Modified multiwall carbon nanotubes display either phytotoxic or growth promoting and stress protecting activity in Ocimum basilicum L. in a concentration-dependent manner

Carbon-based materials including multiwall carbon nanotubes (MWCNTs) have been recently implicated in a number of reports dealing with their potential use in agriculture, leading to contradictory findings. In this study, MWCNTs were successfully functionalized with carboxylic acid groups (MWCNTs-COOH) in order to increase water dispersion. Hydroponically cultured sweet basil (Ocimum basilicum L.) seedlings were subjected to four concentrations (0, 25, 50 and 100 mg L^-1) of MWCNTs-COOH under three salt stress levels (0, 50 and 100 mM NaCl). An array of agronomic, physiological, analytical and biochemical parameters were evaluated in an attempt to examine the potential use of MWCNTs in plants under optimal and abiotic stress conditions. Application of MWCNTs-COOH at optimum concentration (50 mg L^-1) could ameliorate the negative effects of salinity stress by increasing chlorophyll and carotenoids content and inducing non-enzymatic (i.e. phenolic content) and enzymatic antioxidant components (i.e. ascorbate peroxidase (APX), catalase (CAT) and guaiacol peroxidase (GP) activity). Furthermore, MWCNTs-COOH treatments under optimal conditions induced plant growth, while a significant increase (P ≤ 0.01) was recorded in essential oil content and compound profile. On the other hand, biochemical and epifluorescence microscopy evidence suggested that high dosage (100 mg L^-1) of MWCNTs-COOH leads to toxicity effects in plant tissue. Overall, the positive response of plants to low concentrations of MWCNTs-COOH under control and abiotic stress conditions renders them as potential novel plant growth promoting and stress protecting agents, opening up new perspectives for their use in agriculture.

Silicon induces phytochelatin and ROS scavengers facilitating cadmium detoxification in rice

Cadmium (Cd) is detrimental to crops and the environment. This work examines the natural mechanisms underlying silicon- (Si-)directed Cd detoxification in rice plants. The addition of Si to plants under Cd stress caused significant improvements in morphological parameters, chlorophyll score, F_v /F_m and total soluble protein concentration compared to controls, confirming that Si is able to ameliorate Cd-induced damage in rice plants. This morpho-physiological evidence was correlated with decreased cell death and electrolyte leakage after Si application. The results showed no critical changes in root Cd concentration, while shoot Cd decreased significantly after Si supplementation in comparison with Cd-stressed rice. Additionally, expression of Cd transporters (OsNRAMP5 and OsHMA2) was significantly down-regulated while the concentration of phytochelatin, cysteine and glutathione, together with expression of OsPCS1 (phytochelatin synthase) in roots of Cd-stressed rice was significantly induced when subjected to Si treatment. This confirms that the alleviation of Cd stress is not only limited to the down-regulation of Cd transporters but also closely related to the phytochelatin-driven vacuolar storage of Cd in rice roots. The enzymatic analysis further revealed the role of SOD and GR enzymes in protecting rice plants from Cd-induced oxidative harm. These findings suggest a mechanistic basis in rice plants for Si-mediated mitigation of Cd stress.

Current trends in nano-technological interventions on plant growth and development: a review

Nanomaterials, recently have found burgeoning attention in the field of agriculture, owing to the positive correlation between nanoparticle (NP) application and the enhanced nutritional status of the applied plants. A wide range of NPs, namely carbon-based NPs, titanium dioxide NPs, silica NPs etc. has been found to influence plants in a positive way by increasing their nutrient uptake ratio, nutrient usage efficiency, among others. All these attributes have paved the way for possible improvement in plant growth, development, vigour etc. through the use of these NPs, mainly as nanofertiliser. In view of all these, it can also be concluded that in the global scenario of increased demand of food production and supply in the coming years, nanotechnology promises to play a critical role. In this review, an attempt has been made to consolidate all the positive trends with respect to application of NPs on plants, along with their probable mechanism of action, which may provide a comprehensive insight for researchers working in this field.

Foliar application of nanoparticles mitigates the chilling effect on photosynthesis and photoprotection in sugarcane

Chilling is one of the main abiotic stresses that adversely affect the productivity of sugarcane, in marginal tropical regions where chilling incidence occurs with seasonal changes. However, nanoparticles (NPs) have been tested as a mitigation strategy against diverse abiotic stresses. In this study, NPs such as silicon dioxide (nSiO₂; 5-15 nm), zinc oxide (nZnO; <100 nm), selenium (nSe; 100 mesh), graphene (graphene nanoribbons [GNRs] alkyl functionalized; 2-15 μm × 40-250 nm) were applied as foliar sprays on sugarcane leaves to understand the amelioration effect of NPs against negative impact of chilling stress on photosynthesis and photoprotection. To this end, seedlings of moderately chilling tolerant sugarcane variety Guitang 49 was used for current study and spilt plot was used as statistical design. The changes in the level chilling tolerance after the application of NPs on Guitang 49 were compared with tolerance level of chilling tolerant variety Guitang 28. NPs treatments reduced the adverse effects of chilling by maintaining the maximum photochemical efficiency of PSII (F_v/F_m), maximum photo-oxidizable PSI (P_m), and photosynthetic gas exchange. Furthermore, application of NPs increased the content of light harvesting pigments (chlorophylls and cartinoids) in NPs treated seedlings. Higher carotenoid accumulation in leaves of NPs treated seedlings enhanced the nonphotochemical quenching (NPQ) of PSII. Among the NPs, nSiO₂ showed higher amelioration effects and it can be used alone or in combination with other NPs to mitigate chilling stress in sugarcane.

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

Nano-titanium dioxide (nTiO₂) has been reported to improve tolerance of plants against different environmental stresses by modulating various physiological and biochemical processes. Nitric oxide (NO) has been shown to act as an important stress signaling molecule during plant responses to abiotic stresses. The present work was planned to investigate the involvement of endogenous NO in nTiO₂-induced activation of defense system of fava bean (Vicia faba L.) plants under water-deficit stress (WDS) conditions. Water-suffered plants showed increased concentration of hydrogen peroxide (H₂O₂) and superoxide (O₂^-) content coupled with increased electrolyte leakage and lipid peroxidation which adversely affected nitrate reductase (NR) activity, chlorophyll content and growth of the plants. However, application of 15 mg L^-1 nTiO₂ to stressed plants significantly induced NR activity and synthesis of NO which elevated enzymatic and non-enzymatic defense system of the stressed plants and suppressed the generation of H₂O₂ and O₂^- content, leakage of electrolytes, and lipid peroxidation. Application of nTiO₂, in association with NO, also enhanced the accumulation of osmolytes (proline and glycine betaine) that assisted the stressed plants in osmotic adjustment as witnessed by improved hydration level of the plants. Involvement of NO in nTiO₂-induced activation of defense system was confirmed with NO scavenger cPTIO [2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide] which caused recurrence of WDS.

Nano-Biotechnology in Agriculture: Use of Nanomaterials to Promote Plant Growth and Stress Tolerance

Sustainable agriculture is a key component of the effort to meet the increased food demand of a rapidly increasing global population. Nano-biotechnology is a promising tool for sustainable agriculture. However, rather than acting as nanocarriers, some nanoparticles (NPs) with unique physiochemical properties inherently enhance plant growth and stress tolerance. This biological role of nanoparticles depends on their physiochemical properties, application method (foliar delivery, hydroponics, soil), and the applied concentration. Here we review the effects of the different types, properties, and concentrations of nanoparticles on plant growth and on various abiotic (salinity, drought, heat, high light, and heavy metals) and biotic (pathogens and herbivores) stresses. The ability of nanoparticles to stimulate plant growth by positive effects on seed germination, root or shoot growth, and biomass or grain yield is also considered. The information presented herein will allow researchers within and outside the nano-biotechnology field to better select the appropriate nanoparticles as starting materials in agricultural applications. Ultimately, a shift from testing/utilizing existing nanoparticles to designing specific nanoparticles based on agriculture needs will facilitate the use of nanotechnology in sustainable agriculture.

Synergetic Effects of Zinc, Boron, Silicon, and Zeolite Nanoparticles on Confer Tolerance in Potato Plants Subjected to Salinity

Salinity stress is a severe environmental stress that affects plant growth and productivity of potato, a strategic crop moderately sensitive to saline soils. Limited studies are available on the use of combined nano-micronutrients to ameliorate salinity stress in potato plants (Solanum tuberosum L.). Two open field experiments were conducted in salt-affected sandy soil to investigate plant growth, physiology, and yield of potato in response to soil salinity stress under single or combined application of Zn, B, Si, and Zeolite nanoparticles. It was hypothesized that soil application of nanoparticles enhanced plant growth and yield by alleviating the adverse impact of soil salinity. In general, all the nano-treatments applications significantly increased plant height, shoot dry weight, number of stems per plant, leaf relative water content, leaf photosynthetic rate, leaf stomatal conductance, chlorophyll content, and tuber yield, as compared to the untreated control. Furthermore, soil application of these treatments increased the concentration of nutrients (N, P, K, Ca, Zn, and B) in plant tissues, leaf proline, and leaf gibberellic acid hormone (GA3) in addition to contents of protein, carbohydrates, and antioxidant enzymes (polyphenol oxidase (PPO) and peroxidase (POD) in tubers. Compared to other treatments, the combined application of nanoparticles showed the highest plant growth, physiological parameters, endogenous elements (N, P, K, Ca, Zn, and B) and the lowest concentration of leaf abscisic acid (ABA) and transpiration rate. The present findings suggest that soil addition of the aforementioned nanoparticles can be a promising approach to improving crop productivity in salt-affected soils.

Silicon dioxide nanoparticles ameliorate the phytotoxic hazards of aluminum in maize grown on acidic soil

Aluminum (Al) toxicity is a major constraint for crop production in acid soils. Therefore, looking for sustainable solutions to increase plant tolerance to Al toxicity is needed. Although several studies addressed the potential utilization of silica or silicon dioxide nanoparticles (SNPs) to ameliorate heavy metal phytotoxicity, the exact mechanisms underlying SNPs-induced stress tolerance are still unknown. The current study investigated how SNPs could mitigate Al toxicity in maize plants grown on acidic soil. The impact of Al alone or in combination with SNPs on Al accumulation and detoxification, plant growth, photosynthetic C assimilation and redox homeostasis has been investigated. Al accumulation in stressed-maize organs reduced their growth, decreased photosynthesis related parameters and increased production of reactive oxygen species, through induced NADPH oxidase and photorespiration activities, and cell damage. These effects were more pronounced in roots than in leaves. SNPs ameliorated Al toxicity at growth, physiological and oxidative damage levels. Co-application of SNPs significantly reduced the activities of the photorespiratory enzymes and NADPH oxidase. It stimulated the antioxidant defense systems at enzymatic (superoxide dismutase, catalase, ascorbate and glutathione peroxidases) and non-enzymatic (ascorbate, glutathione, polyphenols, flavonoids, tocopherols, and FRAP) levels. Moreover, SNPs increased organic acids accumulation and metal detoxification (i.e. glutathione-S-transferase activity) in roots, as a protective mechanism against Al toxicity. The SNPs induced-protective mechanisms was dependent on the applied Al concentration and acted in organ-specific manner. Overall, the current study suggests the promising application of SNPs as an innovative approach to mitigate Al phytotoxicity in acidic soils and provides a comprehensive view of the cellular and biochemical mechanisms underlying this mitigation capacity.

Evaluation of cytotoxicity, biochemical profile and yield components of groundnut plants treated with nano-selenium

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Preparation and Characterization of selenium nanoparticles.

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Foliar application of the prepared nano-selenium on 3 different groundnut (Arachis hypogaea L.) cultivars.

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Evaluation of the effect of nanoselenium on Growth parameters, lipid peroxidation, antioxidants enzymes.

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Evaluation of prepared nano-selenium cytotoxicity.

Knowledge about the risks of the nanoparticles application on the plant development and human health is still limited. Different concentrations of nano-selenium (0, 20 and 40 ppm) were applied to three different Egyptian groundnut (Arachis hypogaea l.) cultivars; (NC, Gregory and Giza 6) under sandy soil conditions at vegetative growth stage to investigate their effects on yield components, protein profile, fatty acids composition, total antioxidant content and cytotoxicity of yielded seeds. The results indicate that the tested Nano-Selenium (Nano-Se) concentrations improved yield components and seeds oil. However, Nano-Se altered protein signatures as well as fatty acids composition by increasing unsaturated fatty acids and/or decreasing saturated fatty acids as compared with control, the cytotoxicity assessments proved safety of the yield for human health.

Mechanisms of Silicon-Mediated Amelioration of Salt Stress in Plants

Silicon (Si), the second most predominant element in the earth crust consists of numerous benefits to plant. Beneficial effect of Si has been apparently visible under both abiotic and biotic stress conditions in plants. Supplementation of Si improved physiology and yield on several important agricultural and horticultural crops. Salinity is one of the major abiotic stresses that affect growth and yield. The presence of high concentration of salt in growing medium causes oxidative, osmotic, and ionic stresses to plants. In extreme conditions salinity affects soil, ground water, and limits agricultural production. Si ameliorates salt stress in several plants. The Si mediated stress mitigation involves various regulatory mechanisms such as photosynthesis, detoxification of harmful reactive oxygen species using antioxidant and non-antioxidants, and proper nutrient management. In the present review, Si mediated alleviation of salinity stress in plants through the regulation of photosynthesis, root developmental changes, redox homeostasis equilibrium, and regulation of nutrients have been dealt in detail.

Hydroponic Solutions for Soilless Production Systems: Issues and Opportunities in a Smart Agriculture Perspective

Soilless cultivation represent a valid opportunity for the agricultural production sector, especially in areas characterized by severe soil degradation and limited water availability. Furthermore, this agronomic practice embodies a favorable response toward an environment-friendly agriculture and a promising tool in the vision of a general challenge in terms of food security. This review aims therefore at unraveling limitations and opportunities of hydroponic solutions used in soilless cropping systems focusing on the plant mineral nutrition process. In particular, this review provides information (1) on the processes and mechanisms occurring in the hydroponic solutions that ensure an adequate nutrient concentration and thus an optimal nutrient acquisition without leading to nutritional disorders influencing ultimately also crop quality (e.g., solubilization/precipitation of nutrients/elements in the hydroponic solution, substrate specificity in the nutrient uptake process, nutrient competition/antagonism and interactions among nutrients); (2) on new emerging technologies that might improve the management of soilless cropping systems such as the use of nanoparticles and beneficial microorganism like plant growth-promoting rhizobacteria (PGPRs); (3) on tools (multi-element sensors and interpretation algorithms based on machine learning logics to analyze such data) that might be exploited in a smart agriculture approach to monitor the availability of nutrients/elements in the hydroponic solution and to modify its composition in realtime. These aspects are discussed considering what has been recently demonstrated at the scientific level and applied in the industrial context.

Differential physiology and expression of phenylalanine ammonia lyase (PAL) and universal stress protein (USP) in the endangered species Astragalus fridae following seed priming with cold plasma and manipulation of culture medium with silica nanoparticles

KEY MESSAGE

Seed priming with cold plasma in combination with manipulation of culture medium with silica nanoparticle provokes anatomical, physiological and molecular changes, thereby reinforcing the plant growth and protection.

ABSTRACT

This study addressed responses of Astragalus fridae to seed priming with cold plasma (0.84 W/cm²; 0, 30, 60, and 90 s) and applications of SiO₂ nanoparticle (nSi; 0, 5, 40, and 80 mgl^-1) in culture medium (an in vitro study). FE-SEM confirmed nSi uptake and translocation. Bulk Si at high concentrations reduced biomass accumulation (mean = 45%), while nSi did not make significant differences. The growth-enhancing effects of plasma by 41.5% were promoted by the nSi supplementation and reached 71%. Plasma did not make significant changes in Chla, while led to the slightly higher (mean = 14%) Chlb. The presence of nSi at high doses caused slight reductions in Chlb (mean = 25%) which were mitigated by plasma. The plasma and/or nSi treatments modified activities of phenylalanine ammonia lyase (PAL) in both roots (mean = 32%) and leaves (mean = 44%). With a similar trend, both individual and combined treatments of plasma and nSi provoked inductions in peroxidase activities in roots and leaves. The simultaneous treatments of plasma and nSi had the highest expression rates of PAL gene. The individual treatments of plasma did not make a significant difference in the expression of universal stress protein (USP) gene, whereas the nSi-treated seedlings exhibited the higher expression rates of USP. Leaf thicknesses and development of the vascular system (xylem and phloem) were reinforced in response to plasma and nSi. The findings provide evidence on potential benefits and phytotoxicity of nSi and plasma which may be employed as a theoretical basis for possible exploitation.

Silicon nanoparticles enhanced the growth and reduced the cadmium accumulation in grains of wheat (Triticum aestivum L.)

The application of silicon (Si) under heavy metal stress is well known, but the use of Si nanoparticles (NPs) under metal stress in not well documented. Thus, the experiments were performed to investigate the impacts of soil and foliar applied Si NPs on wheat (Triticum aestivum L.) growth and cadmium (Cd) accumulation in grains under Cd toxicity. The plants were grown under natural environmental conditions and were harvested after physiological maturity (124 days after sowing). The results demonstrated that Si NPs significantly improved, relative to the control, the dry biomass of shoots, roots, spikes and grains by 24-69%, 14-59%, 34-87%, and 31-96% in foliar spray and by 10-51%, 11-49%, 25-69%, and 27-74% in soil applied Si NPs, respectively. The Si NPs enhanced the leaf gas exchange attributes and chlorophyll a and b concentrations, whereas diminished the oxidative stress in leaves which was indicated by the reduced electrolyte leakage and enhancement in superoxide dismutase and peroxidase activities in leaf under Si NPs treatments over the control. When compared with the control, the foliar spray of Si NPs reduced the Cd contents in shoots, roots, and grains by 16-58%, 19-64%, and 20-82%, respectively, whereas soil applied Si NPs reduced the Cd concentrations in shoots, roots, and grains by 11-53%, 10-59%, and 22-83%, respectively. In comparison with the control, Si concentrations significantly (p ≤ 0.05) increased in the shoots and roots in both foliar and soil supplementation of Si NPs. Our results suggested that Si NPs could improve the yield of wheat and more importantly, reduce the Cd concentrations in the grains. Thus, the use of Si NPs might be a feasible approach in controlling Cd entry into the human body via crops.

Nanoparticles: biosynthesis, translocation and role in plant metabolism

Nanotechnology is an emerging field of science that applies particles between 1 and 100 nm in size for a range of practical uses. Nano-technological discoveries have opened novel applications in biotechnology and agriculture. Many reactions involving nanoparticles (NPs) are more efficient compared to those of their respective bulk materials. NPs obtained from plant material, denoted as biogenic or phytosynthesised NPs, are preferred over chemically synthesised NPs due to their low toxicity, rapid reactions and cost-effective production. NPs impart both positive and negative impacts on plant growth and development. NPs exhibit their unique actions as a function of their size, reactivity, surface area and concentration. An insight into NP biosynthesis and translocation within the plant system will shed some light on the roles and mechanisms of NP-mediated regulation of plant metabolism. This review is a step towards that goal.

Silicon as a Vegetable Crops Modulator-A Review

Vegetables require an optimum supply of mineral elements like silicon (Si). Si is second to oxygen in its abundance in the earth crust, and its role is quite significant in tackling biotic and abiotic stresses of vegetables. Si application also improves several agronomic and quality traits of vegetables. Hence, Si application is recommended as a strategy for the improvement of vegetable crops production. Although the research about the role of Si in vegetable dicots still lags far behind than cereals. Recently, omics-based approaches were used to provide a deeper understanding of the role of Si in vegetable protection. Here, we have compiled the studies focusing on the role of Si for vegetables, thus, enabling all of the important information regarding the effect Si application to vegetables at one place.

Silicon improves salt tolerance of Glycyrrhiza uralensis Fisch. by ameliorating osmotic and oxidative stresses and improving phytohormonal balance

Si has a beneficial effect on improving plant tolerance to salt stress. Nevertheless, the mechanisms of Si in mediating the stress responses are still poorly understood. Glycyrrhiza uralensis Fisch. (G. uralensis), a well-known medicinal plant, possesses vast therapeutic potentials. In the present study, a pot experiment was conducted to investigate the long-term effects of Si on growth and physiobiochemical characteristics in 2-year-old G. uralensis subjected to different levels of salinity. Si markedly affected G. uralensis growth in a salt concentration-dependent manner and had no effect on G. uralensis growth under 6 g/kg NaCl. However, it partly reversed the reduction effect induced by 9 g/kg NaCl. In addition, Si significantly increased the contents of soluble sugar and protein but deceased proline content and thus increased water relations; Si markedly increased the activities of SOD, peroxidase, and CAT and further resulted in decreased MDA content and membrane permeability. Moreover, Si altered the levels of phytohormones and their balances. With correlation analysis and principal component analysis (PCA), root biomass had a significant negative correlation with MDA and membrane permeability while a positive correlation with indole-3-acetic acid and GA₃. The PCA partitioned the total variance into three PCs contributing maximum (88.234%) to the total diversity among the salt stress with or without Si due to the study of various traits. In conclusion, Si exerts a beneficial property on salt-induced harmful effects in G. uralensis by relieving osmotic stress, improving water relations, and alleviating oxidative stress; thus, altering the levels and balance of phytohormones results in improved growth of salt-stressed G. uralensis.

Engineered nanomaterials for plant growth and development: A perspective analysis

With the overwhelmingly rapid advancement in the field of nanotechnology, the engineered nanomaterials (ENMs) have been extensively used in various areas of the plant system, including quality improvement, growth and nutritional value enhancement, gene preservation etc. There are several recent reports on the ENMs' influence on growth enhancements, growth inhibition as well as certain toxic impacts on plant. However, translocation, growth responses and stress modulation mechanisms of ENMs in the plant systems call for better and in-depth understanding. Herein, we are presenting a comprehensive and critical account of different types of ENMs, their applications and their positive, negative and null impacts on physiological and molecular aspects of plant growth, development and stress responses. Recent reports revealed mixed effects on plants, ranging from enhanced crop yield, epi/genetic alterations, and phytotoxicity, resulting from the ENMs' exposure. Creditable research in recent years has revealed that the effects of ENMs on plants are species specific and are variable among plant species. ENM exposures are reported to trigger free radical formation, responsive scavenging, and antioxidant armories in the exposed plants. The ENMs are also reported to induce aberrant expressions of microRNAs, the key post-transcriptional regulators of plant growth, development and stress-responses of plants. However, these modulations, if judiciously done, may lead to improved plant growth and yield. A better understanding of the interactions between ENMs and plant responses, including their uptake transport, internalization, and activity, could revolutionize crop production through increased disease resistance, nutrient utilization, and crop yield. Therefore, in this review, we are presenting a critical account of the different selected ENMs, their uptake by the plants, their positive/negative impacts on plant growth and development, along with the resultant ENM-responsive post-transcriptional modifications, especially, aberrant miRNA expressions. In addition, underlying mechanisms of various ENM-plant cell interactions have been discussed.

Effects of silicon nanoparticles on molecular, chemical, structural and ultrastructural characteristics of oat (Avena sativa L.)

Nowadays, nanoparticles are extensively being utilized in medicine, industry, and agriculture thus distributed into the environment. Hence, it is essential to examine exactly the impact of these materials on a variety of organisms, including various species of plants. Therefore, in the current study, we compared the effects of sodium silicate and nano silicon (SiNP) (both at two concentrations of 5 and 10 mM) separately on lignification of the xylem cell wall, antioxidant enzyme activities, ultrastructure of leaf and root cells, expression of silicon transporter (Lsi1) and phenylalanine ammonia lyase (PAL), and also evaluated the protein content and chemical content of oat plants (Avena sativa L.) cultured hydroponically. The results indicated that SiNPs didn't have a toxic effect on the oat plants, and in many cases they enhanced plant growth. The effect of SiNPs on the chemical content of the treated plants was almost identical with silicate. The silicon transporter (Lsi1) gene was expressed in plants exposed to SiNPs, however, at lower levels (∼37% in roots) than those exposed to silicate treatments. The SiNPs increased PAL expression and lignification in leaves and roots, however, at lower levels those of silicate (˃50% in fourth leaves of 10 mM concentration). They were aggregated in the roots (268-366 nm) and deposited in nano size on the cell walls of leaves. In general, their effects in the plants were identical to silicate but differed in intensity.

Mechanisms of Action of Nanoparticles in Living Systems

Nanoparticles are being formed continuously in processes like mineralization, natural calamities, and geological recycling of matter and present naturally in the environment. In the recent past, nanoparticles and their applications have become an extensive topic of research. Application of nanomaterials in different industries will surely enhance the chances of discharge of nanoparticles into the environment. So, a number of studies have been performed to explore the mode of action of nanoparticles on living organisms and their surroundings. The most reported modes of action of nanoparticles are antimicrobial activity, ROS-induced cytotoxicity, genotoxicity, plant growth promotion, etc. It has been successfully demonstrated that actions of nanoparticles are governed by their size, shape, dose, and concentration. However, a complete mechanism of action of nanoparticles has not been known. The present chapter focuses on the highlights of the mechanisms behind the mode of action of nanoparticles in plants and microorganisms.

Toxicity assessment of multi-walled carbon nanotubes on Cucurbita pepo L. under well-watered and water-stressed conditions

The rapid increase in the production and application of various types of nanomaterials increases the possibility of their presence in total environment, which subsequently raises concerns about their potential threats to the first trophic level of organisms, specifically under varying environmental constraints. In this work, seeds of Cucurbita pepo L. were cultured in MS basal medium exposed to multi-walled carbon nanotubes (MWCNTs) at different concentrations (0, 125, 250, 500 and 1000μgmL^-1) under two levels of water potential, well-watered (0MPa) and water stress (-1.5MPa) induced by polyethylene glycol (PEG 6000) for 14 days. Seeds exposed to MWCNTs showed reduction in germination percentage, root and shoot length, biomass accumulation and vigor index in a dose-dependent manner. However, seedlings germinated in MWCNTs-fortified media had significantly lower germination and growth attributes than those of control under water stress conditions. This happened due to increased oxidative injury indices including hydrogen peroxide (H₂O₂), and malondialdehyde (MDA) contents, as well as electrolyte leakage index (ELI) of tissues. The impaired morpho-physiological and biochemical processes of seedlings exposed to different concentrations of MWCNTs under both PEG-induced stress and non-stress growing conditions were consequence of changes in the activation of various cellular antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (POD). Taken together, our findings reveal that MWCNTs played negative role on seed germination and subsequent growth of C. pepo L. seedlings under both levels of water potential.

Comparison of silicon nanoparticles and silicate treatments in fenugreek

Silicon (Si) fertilization improves crop cultivation and is commonly added in the form of soluble silicates. However, most natural plant-available Si originates from plant formed amorphous SiO₂ particles, phytoliths, similar to SiO₂-nanoparticles (SiNP). In this work we, therefore, compared the effect by sodium silicate and that of SiNP on Si accumulation, activity of antioxidative stress enzymes catalase, peroxidase, superoxide dismutase, lignification of xylem cell walls and activity of phenylalanine ammonia-lyase (PAL) as well as expression of genes for the putative silicon transporter (PST), defensive (Tfgd 1) and phosphoenolpyruvate carboxykinase (PEPCK) and protein in fenugreek (Trigonella foenum-graecum L.) grown in hydroponics. The results showed that Si was taken up from both silicate and SiNP treatments and increasing sodium silicate addition increased the translocation of Si to the shoot, while this was not shown with increasing SiNP addition. The silicon transporter PST was upregulated at a greater level when sodium silicate was added compared with SiNP addition. There were no differences in effects between sodium silicate and SiNP treatments on the other parameters measured. Both treatments increased the uptake and accumulation of Si, xylem cell wall lignification, cell wall thickness, PAL activity and protein concentration in seedlings, while there was no effect on antioxidative enzyme activity. Tfgd 1 expression was strongly downregulated in leaves at Si addition. The similarity in effects by silicate and SiNP would be due to that SiNP releases silicate, which may be taken up, shown by a decrease in SiNP particle size with time in the medium.

Mechanisms underlying toxicity and stimulatory role of single-walled carbon nanotubes in Hyoscyamus niger during drought stress simulated by polyethylene glycol

In this study, seeds of Hyoscyamus niger were exposed to different concentrations (50-800μgmL^-1) of single-walled carbon nanotubes (SWCNTs) under different levels of drought stress (0.5-1.5MPa) for 14days. Germinated seeds were subsequently allowed to grow in the same culture media for 7 more days to test the further response of the seedlings in terms of biochemical changes to the employed treatments. Seeds subjected to drought showed reduction in germination percentage, vigor and lengths of roots and shoots. However, inclusion of SWCNTs at the two lowest concentrations significantly alleviated the drought stress (up to moderate levels only)-induced reduction in germination and growth attributes. This happened due to increased water uptake, up-regulation of mechanisms involved in starch hydrolysis, and reduction in oxidative injury indices including H₂O₂, malondialdehyde contents and electrolyte leakage. The improved plant performance under PEG-induced drought stress was a consequence of changes in the expression of various antioxidant enzymes including SOD, POD, CAT, and APX, and also biosynthesis of proteins, phenolics, and specific metabolites such as proline. Results demonstrate that treatment by low concentrations of SWCNTs can induce tolerance in seedlings against low to moderate levels of drought through enhancing water uptake and activating plant defense system.

Silicon-mediated Improvement in Plant Salinity Tolerance: The Role of Aquaporins

Silicon (Si) is an abundant and differentially distributed element in soils that is believed to have important biological functions. However, the benefits of Si and its essentiality in plants are controversial due to differences among species in their ability to take up this element. Despite this, there is a consensus that the application of Si improves the water status of plants under abiotic stress conditions. Hence, plants treated with Si are able to maintain a high stomatal conductance and transpiration rate under salt stress, suggesting that a reduction in Na⁺ uptake occurs due to deposition of Si in the root. In addition, root hydraulic conductivity increases when Si is applied. As a result, a Si-mediated upregulation of aquaporin (PIP) gene expression is observed in relation to increased root hydraulic conductivity and water uptake. Aquaporins of the subclass nodulin 26-like intrinsic proteins are further involved in allowing Si entry into the cell. Therefore, on the basis of available published results and recent developments, we propose a model to explain how Si absorption alleviates stress in plants grown under saline conditions through the conjugated action of different aquaporins.

Engineered nanomaterial-mediated changes in the metabolism of terrestrial plants

Engineered nanomaterials (ENMs) possess remarkable physicochemical characteristics suitable for different applications in medicine, pharmaceuticals, biotechnology, energy, cosmetics and electronics. Because of their ultrafine size and high surface reactivity, ENMs can enter plant cells and interact with intracellular structures and metabolic pathways which may produce toxicity or promote plant growth and development by diverse mechanisms. Depending on their type and concentration, ENMs can have positive or negative effects on photosynthesis, photochemical fluorescence and quantum yield as well as photosynthetic pigments status of the plants. Some studies have shown that ENMs can improve photosynthetic efficiency via increasing chlorophyll content and light absorption and also broadening the spectrum of captured light, suggesting that photosynthesis can be nano-engineered for harnessing more solar energy. Both up- and down-regulation of primary metabolites such as proteins and carbohydrates have been observed following exposure of plants to various ENMs. The potential capacity of ENMs for changing the rate of primary metabolites lies in their close relationship with activation and biosynthesis of the key enzymes. Several classes of secondary metabolites such as phenolics, flavonoids, and alkaloids have been shown to be induced (mostly accompanied by stress-related factors) in plants exposed to different ENMs, highlighting their great potential as elicitors to enhance both quantity and quality of biologically active secondary metabolites. Considering reports on both positive and negative effects of ENMs on plant metabolism, in-depth studies are warranted to figure out the most appropriate ENMs (type, size and optimal concentration) in order to achieve the desirable effect on specific metabolites in a given plant species. In this review, we summarize the studies performed on the impacts of ENMs on biosynthesis of plant primary and secondary metabolites and mention the research gaps that currently exist in this field.

Mesoporous silica nanoparticles enhance seedling growth and photosynthesis in wheat and lupin

The application of mesoporous silica nanoparticles (MSNs) as a smart delivery system to agricultural crops is gaining attention but the release of nanoparticles into the environment may pose a potential threat to biological systems. We investigated the effects of MSNs on the growth and development of wheat and lupin plants grown under controlled conditions. We report a dramatic increase in the growth of wheat and lupin plants exposed to MSNs. We also found that, in leaves, MSNs localised to chloroplasts and that photosynthetic activity was significantly increased. In addition, absorption and cellular distribution of MSNs by the two plant species following root uptake were observed using scanning electron microscopy equipped with energy dispersive spectroscopy (SEM-EDS). Following uptake of MSNs at 500 and 1000 mg L(-1), there was enhancement of seed germination, increased plant biomass, total protein and chlorophyll content. Treatment of both species with MSNs at the highest concentration (2000 mg L(-1)) did not result in oxidative stress or cell membrane damage. These findings show that MSNs can be used as novel delivery systems in plants and that over the range of concentrations tested, MSNs do not have any negative impacts on plant growth or development.

Mechanisms of silicon-mediated alleviation of drought and salt stress in plants: a review

Drought and salinity are the main abiotic stresses limiting crop yield and quality worldwide. Improving food production in drought- and salt-prone areas is the key to meet the increasing food demands in near future. It has been widely reported that silicon (Si), a second most abundant element in soil, could reduce drought and salt stress in plants. Here, we reviewed the emerging role of Si in enhancing drought and salt tolerance in plants and highlighted the mechanisms through which Si could alleviate both drought and salt stress in plants. Silicon application increased plant growth, biomass, photosynthetic pigments, straw and grain yield, and quality under either drought or salt stress. Under both salt and drought stress, the key mechanisms evoked are nutrient elements homeostasis, modification of gas exchange attributes, osmotic adjustment, regulating the synthesis of compatible solutes, stimulation of antioxidant enzymes, and gene expression in plants. In addition, Si application decreased Na(+) uptake and translocation while increased K(+) uptake and translocation under salt stress. However, these mechanisms vary with plant species, genotype, growth conditions, duration of stress imposed, and so on. This review article highlights the potential for improving plant resistance to drought and salt stress by Si application and provides a theoretical basis for application of Si in saline soils and arid and semiarid regions worldwide. This review article also highlights the future research needs about the role of Si under drought stress and in saline soils.

Morphological and physiological characterization of different genotypes of faba bean under heat stress

Heat stress (HS) is the major constraint to crop productivity worldwide. The objective of the present experiment was to select the tolerant and sensitive genotype(s) on the basis of morpho-physiological and biochemical characteristics of ten Vicia faba genotypes. These genotypes were as follows: Zafar 1, Zafar 2, Shebam 1, Makamora, Espan, Giza Blanka, Giza 3, C4, C5 and G853. The experimental work was undertaken to study the effects of different levels of temperature (control, mild, and modest) on plant height (PH) plant⁻¹, fresh weight (FW) and dry weight (DW) plant⁻¹, area leaf⁻¹, content of leaf relative water (RWC), proline content (Pro) and total chlorophyll (Total Chl), electrolyte leakage (EL), malondialdehyde level (MDA), hydrogen peroxide (H₂O₂), and activities of catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) enzymes. HS significantly affected growth performance of all genotypes. However, the magnitude of reduction in genotypes ‘C5’ was relatively low, possibly due to its better antioxidant activities (CAT, POD and SOD), and accumulation of Pro and Total Chl, and leaf RWC. In the study, ‘C5’ was noted to be the most HS tolerant and ‘Espan’ most HS sensitive genotypes. It was concluded that the heat-tolerant genotypes may have better osmotic adjustment and protection from free radicals by increasing the accumulation of Pro content with increased activities of antioxidant enzyme.