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Lead (Pb) is among the most abundant toxic trace elements which causes direct and indirect negative effects on humans, animals, and plants. Thus, there is a need to alleviate the Pb toxicity in plants for good quality food production especially from marginal soils. In this study, the effects of silicon nanoparticles (Si NPs) were investigated on coriander ( Coriandrum sativum L.) biomass, vitamin C, flavonoid, antioxidant enzyme activities (i.e., catalase (CAT), peroxidase (POD), and super oxide dismutase (SOD)), malondialdehyde (MDA), and Pb concentration in plants subjected to different Pb concentrations. Treatments included four levels of Pb (0, 500, 1000, and 1500 mg/kg of soil), and two levels of Si NPs (0 and 1.5 mM) in all combinations. The Pb treatments alone decreased the plant biomass and vitamin C while increased the flavonoid, MDA, antioxidant enzyme activities, and Pb concentration in tissues depending upon the Pb treatments. The foliar-applied 1.5 mM Si NPs alleviated the adverse impacts of Pb on coriander plants which were due to the minimization of Pb concentration in plants and improvements in the plant defense system. Si NPs minimized accumulation of MDA in plant tissues and adjusted the activities of POD, CAT, and SOD in plants under Pb stress. Overall, Si NP foliar application might be a suitable approach in reducing the Pb concentrations in plants. However, field studies with various plant species and environmental conditions are required to highlight the role of Si NPs on the plant under toxic trace element stress.

Background Soil salinization leads to a significant decline in crop yield and quality, including licorice, an important medicinal cash crop. Studies have proofed that the application of exogenous silicon can significantly improve the ability of licorice to resist salt stress, however, few studies concentrated on the effects of foliar silicon application on the morphology, physiological characteristics, and anatomical structure of licorice leaves under salt stress. In this study, the effects of Si (K 2 SiO 3 ) on the structural and physiological characteristics of Glycyrrhiza uralensis Fisch. and G. inflata Bat. leaves under different salt concentrations (medium- and high-salt) were studied. Results Compared with the control (without salt), the plant height, total dry weight, leaf area, leaf number, relative water content, xylem area, phloem area, ratio of palisade to spongy tissue, gas exchange parameters, and photosynthetic pigment content of both licorice varieties were significantly reduced under high-salt (12S) conditions. However, the thickness of the leaf, palisade tissue, and spongy tissue increased significantly. Applying Si to the leaf surface increased the area of the vascular bundle, xylem, and parenchyma of the leaf’s main vein, promoted water transportation, enhanced the relative leaf water content, and reduced the decomposition of photosynthetic pigments. These changes extended the area of photosynthesis and promoted the production and transportation of organic matter. G. uralensis had a better response to Si application than did G. inflata . Conclusions In conclusion, foliar application of Si can improve water absorption, enhance photosynthesis, improve photosynthetic capacity and transpiration efficiency, promote growth and yield, and alleviate the adverse effects of salt stress on the leaf structure of the two kinds of licorice investigated.

To develop sustainable nano-agriculture, biogenic ZnO nanoparticles have been prepared using brown seaweed Turbinaria ornata (T. ornata) extract as a priming agent to promote rice seed quality and crop yield attributing to rice seeds. The results of various physico-chemical characterization analysis indicate the formation of ZnO nanoparticles. Rice seeds primed with seaweed-based biogenic ZnO nanoparticles at 10 mg/L showed that there has been enhancement in the seed germination (100%), shoot length (100 mm), shoot width (1.0 mm), root length (185.0 mm) root width (0.5 mm), seedling length (216 mm), leaf length 33.0 mm), leaf width (2.0 mm), seedling vigor (28,500 vigor index) and dry matter production (DMP) compared to the conventional hydropriming. Consequently, a micro-plot experiment has been conducted with foliar application of biogenic ZnO nanoparticles and the results revealed that at 10 mg/L recorded improvement in grain weight (653 g/m2), seed length (8.0 mm), seed thickness (1.71 mm) and seed width (3.23 mm) compared to hydroprimed seeds under. HR-SEM micrograph confirms the presence and assimilation of biogenic ZnO nanoparticles in treated seed/foliar applied leaf of rice plant. Further, ICP-MS analysis also confirmed the increase in Zn content in the nanoprimed rice seedlings and foliar applied rice crop in a dose-dependent manner. The experimental results thus demonstrate that the application of seaweed biogenic ZnO nanoparticles improving agronomical characteristics of rice.

Soil contamination with toxic heavy metals [such as lead (Pb)] is becoming a serious global problem due to the rapid development of the social economy. However, accumulation of Pb in plant parts is very toxic for plant growth and decreases crop yield and productivity. In the present study, we have investigated the different concentrations of Pb in the soil i.e., [0 (no Pb), 50, and 100 mg kg –1 ] to study plant growth and biomass, photosynthetic pigments and gas exchange characteristics, oxidative stress indicators and the response of various antioxidants (enzymatic and non-enzymatic), nutritional status of the plant, organic acid exudation pattern and also Pb accumulation in the roots and shoots of the plants of two varieties of tomato ( Solanum lycopersicum L.) i.e., Roma and Cchuas, grown under different levels of synergic acid [no spray (NS), water spray (WS), 0.3-0.5°μM]. Results from the present study showed that the increasing levels of Pb in the soil decreased non-significantly ( P < 0.05) shoot length, root length, shoot fresh weight, root fresh weight, shoot dry weight, root dry weight, chlorophyll-a, chlorophyll-b, total chlorophyll, carotenoid content, net photosynthesis, stomatal conductance, transpiration rate, soluble sugar, reducing sugar, non-reducing sugar contents, calcium (Ca 2+ ), magnesium (Mg 2+ ), iron (Fe 2+ ), and phosphorus (P) contents in the roots and shoots of the plants. However, Pb toxicity also induced oxidative stress in the roots and shoots of the plants by increasing malondialdehyde (MDA), hydrogen peroxide (H 2 O 2 ), and electrolyte leakage (EL) which also induced increased the compounds of various enzymatic and non-enzymatic antioxidants and also organic acids exudation pattern in the roots such as fumaric acid, acetic acid, citric acid, formic acid, malic acid, oxalic acid contents and increased the concentration of Pb in different parts of the plants. Results also show that the Cchuas showed better growth and development compared to Roma, under the same levels of Pb in the soil. The alleviation of Pb toxicity was induced by the application of synergic acid, and results showed that the application of synergic acid increased plant growth and biomass and also increased the gas exchange characteristics and antioxidant capacity in the roots and shoots of the plants. Research findings, therefore, suggested that synergic acid application can ameliorate Pb toxicity in S. lycopersicum varieties and result in improved plant growth and composition under metal stress as depicted by balanced exudation of organic acids.

Microalgae are attracting the interest of agrochemical industries and farmers, due to their biostimulant and biofertiliser properties. Microalgal biostimulants (MBS) and biofertilisers (MBF) might be used in crop production to increase agricultural sustainability. Biostimulants are products derived from organic material that, applied in small quantities, are able to stimulate the growth and development of several crops under both optimal and stressful conditions. Biofertilisers are products containing living microorganisms or natural substances that are able to improve chemical and biological soil properties, stimulating plant growth, and restoring soil fertility. This review is aimed at reporting developments in the processing of MBS and MBF, summarising the biologically-active compounds, and examining the researches supporting the use of MBS and MBF for managing productivity and abiotic stresses in crop productions. Microalgae are used in agriculture in different applications, such as amendment, foliar application, and seed priming. MBS and MBF might be applied as an alternative technique, or used in conjunction with synthetic fertilisers, crop protection products and plant growth regulators, generating multiple benefits, such as enhanced rooting, higher crop yields and quality and tolerance to drought and salt. Worldwide, MBS and MBF remain largely unexploited, such that this study highlights some of the current researches and future development priorities.

Nanotechnology now plays a revolutionary role in many applications; nanomaterials have experienced significant importance in both basic and applied sciences as well as in bio-nanotechnology. Zinc oxide nanoparticles (ZnO-NPs) have become one of the most important metal oxide NPs in biological applications due to their beneficial impacts. The purpose of this study was to explore the effects of ZnO-NPs in reducing Cd toxicity by studying the growth, photosynthesis reactions, antioxidant system, oxidative stress, and protein content in Lycopersicon esculentum (tomato). ZnO-NPs induced an upregulation of antioxidative enzymes which protect the photosynthetic apparatus in plants. Seeds of tomato were sown to create nursery. At 20 days after sowing (DAS), seedlings were transferred to soil pots. Varied concentrations (0.4, 0.6 or 0.8 mM) of Cd were applied to the soil after 24 and 25 DAS. Zinc (Zn; 50 mg/L) and ZnO-NPs (50 mg/L) treatments were given continuously for 5 days from 31 to 35 DAS and sampling took place at 45 DAS. The results indicate that a Cd-generated oxidative burst in the form of elevated hydrogen peroxide (H2O2) levels resulted in a decline in cell viability through enhanced activity of the antioxidant system and proline content; the data increased on follow-up treatment with ZnO-NPs. Foliar application of ZnO-NPs significantly enhanced plant height, fresh, and dry weight of plant, leaf area, SPAD chlorophyll, photosynthetic attributes, i.e., net photosynthetic rate (PN), transpiration rate (E), internal CO2 concentration (Ci), and stomatal conductance (gs). Application of ZnO-NPs reduced the adverse effects generated by Cd and increased protein content, activities of nitrate reductase and carbonic anhydrase over the control in both stressed and non-stressed plants. Additionally, microscopic studies showed a marked increase in stomatal aperture after ZnO-NPs treatment in the presence or absence of Cd. This was associated with decrease in malondialdehyde and superoxide radical (O2−) levels. The present study suggests that ZnO-NPs can be effectively used to reduce the toxicity of Cd in tomato plants and may also be suitable for testing on other crop species.

Background Nano-materials ameliorate the adverse effect of salinity stress on the physiological and biochemical processes in plants. The present investigation was designed to evaluate the physiological mechanisms through which a nano-chitosan-encapsulated nano-silicon fertilizer (NC-NS) can ameliorate the adverse effect of salinity stress on the wheat plants, and compare it with nano-chitosan (NC) and nano-silicon (NS) application. Nano-silicon was encapsulated with a chitosan-tripolyphosphate (TPP) nano-matrix by ionic gelation method for its slow release. The wheat plants were exposed to foliar application of distilled water, NC, NS, and NC-NS with two NaCl irrigation levels at 0 (distilled water) and 100 mM. Results The foliar application of NC, NS, and NC-NS induced a significant increase in the function of enzymatic and non-enzymatic antioxidant systems of the wheat plants to equilibrate cellular redox homeostasis by balancing H 2 O 2 content in the leaves and roots, as compared with salt-stressed plants without treatment. The plant's foliar-sprayed with NC, NS, and NC-NS solution exhibited a significant increase in the molecules with osmotic adjustment potentials such as proline, free amino acids, glycine betaine, and sugars to protect cells against osmotic stress-induced by salinity. The observed increase in the antioxidant power and osmoregulatory at NC, NS, and NC-NS application was accompanied by the protection of lipid membrane, proteins and photosynthetic apparatus against salinity stress. Conclusion In the present study, the beneficial role of NC, NS, and NC-NS application, particularly NC-NS, in alleviating the adverse effect of salinity stress on antioxidant systems and osmotic adjustment in wheat is well documented. An overview of the result of present study assists researchers in providing a potential solution for this increasing salinization threat in crops. Graphical abstract

Silicon is one of the most significant elements in plants under abiotic stress, so we investigated the role of silicon in alleviation of the detrimental effects of salinity at two concentrations (1500 and 3000 ppm sodium chloride) in sweet pepper plants in two seasons (2018 and 2019). Our results indicated that relative water content, concentrations of chlorophyll a and b, nitrogen, phosphorus and potassium contents, number of fruits plant−1, fruit fresh weight plant−1 (g) and fruit yield (ton hectare−1) significantly decreased in salt-stressed sweet pepper plants as compared to control plants. In addition, electrolyte leakage, proline, lipid peroxidation, superoxide (O2−) and hydrogen peroxide (H2O2) levels, soluble sugars, sucrose, and starch content as well as sodium content significantly increased under salinity conditions. Conversely, foliar application of silicon led to improvements in concentrations of chlorophyll a and b and mineral nutrients, water status, and fruit yield of sweet pepper plants. Furthermore, lipid peroxidation, electrolyte leakage, levels of superoxide, and hydrogen peroxide were decreased with silicon treatments.

Background γ-aminobutyric acid (GABA), as a regulator of many aspects of plant growth, has a pivotal role in improving plant stress resistance. However, few studies have focused on the use of GABA in increasing plants’ resistance to interactional stresses, such as drought-salinity. Therefore, the focus of this study was to examine the effect of foliar application of GABA (0, 10, 20, and 40 mM) on growth indices and physio-biochemical parameters in plants of two pomegranate cultivars, ‘Rabab’ and ‘Atabaki’ exposed to drought, salinity, and drought-salinity. Results Under stress conditions, the photosynthetic capacity of two pomegranate cultivars, including transpiration rate, net photosynthetic rate, intercellular carbon dioxide concentration, stomatal conductance of water vapour, and mesophyll conductance, was significantly reduced. This resulted in a decrease in root morphological traits such as fresh and dry weight, diameter, and volume, as well as the fresh and dry weight of the aerial part of the plants. However, the application of GABA reversed the negative effects caused by stress treatments on growth parameters and maintained the photosynthetic capacity. GABA application has induced the accumulation of compatible osmolytes, including total soluble carbohydrate, starch, glucose, fructose, and sucrose, in charge of providing energy for cellular defense response against abiotic stresses. Analysis of mineral nutrients has shown that GABA application increases the absorption of potassium, potassium/sodium, magnesium, phosphorus, manganese, zinc, and iron. As concentration increased up to 40 mM, GABA prevented the uptake of toxic ions, sodium and chloride. Conclusions These findings highlight the potential of GABA as a biostimulant strategy to enhance plant stress tolerance.

In horticultural practice accelerated plant development and particularly earlier flowering, has been reported with microalgae applications. Therefore, the objective of this work was to study the effects of foliar spraying with Scenedesmus sp. and Arthrospira platensis hydrolysates on Petunia x hybrida plant development and leaf nutrient status. Three treatments were tested: T1 (foliar application with water, the control), T2 (foliar application with Arthrospira), and T3 (foliar application with Scenedesmus). Foliar spraying was applied five times (0, 14, 28, 35, and 42 days after transplanting). The concentration of both microalgae was 10 g L−1. At the end of the trial biometric parameters and nutrient concentration in photosynthetic organs (the leaves) were measured. The results of this assay show that foliar application of Scenedesmus accelerated plant development in terms of higher rates of root growth, leaf and shoot development, and earliness of flowering. Arthrospira enhanced the root dry matter, the number of flowers per plant, and the water content. Nevertheless, a reduction was found in the conductive tissue (stem + petiole) dry weight with Arthrospira compared with Scenedesmus and the control. The results also show that microalgae hydrolysate supply can improve the plant nutrient status. Based on these results, it is advisable to use Scenedesmus hydrolysates in foliar applications to increase the blooming of Petunia x hybrida.