Exogenous Si Application Research Articles

Silicon and Potassium-Induced Modulations in Leaf Carbohydrate Metabolism Confer Freezing Tolerance in Satsuma Mandarin

Freezing temperatures are a severe issue in North Florida, primarily due to occasional cold snaps and frost events in winter and early spring that cause damage to citrus groves, resulting in reduced fruit yield. The apoplasm is the primary cell component that interacts with environmental stress and is essential for plant tolerance to freezing temperatures. The present study was conducted to gain insight into how the application of silicon (Si) and potassium (K) are involved in the leaf apoplasm contributes to freezing stress tolerance, and regulates carbohydrate metabolism. We used Satsuma mandarin (Citrus unshiu Marc.), the most successful commercially grown citrus cultivar in North Florida, and treated trees with two concentrations of Si and K (50 and 100 ppm) both individually and combined as foliar spray to determine their effect as they relate to improving cold hardiness. Freezing stress (-6 °C) caused a severe reduction in photosynthesis, and modulations in leaf carbohydrate metabolism resulted in inhibited plant growth. The exogenous application of Si and K both improved the photosynthesis rate, soluble sugars, and activities of enzymes of carbohydrate metabolism such as fructokinase, phosphofructokinase, hexokinase, sucrose and phosphate synthase, and acid and neutral invertase. Applying Si (100 ppm) and combined treatment (Si + K-50) showed the best response by inducing the maximum tolerance to freeze stress. Our data demonstrated the ameliorative effect of Si and K under freezing stress in citrus is associated with modification in carbohydrate metabolism in the leaf apoplasm. This study provides direction for future research to investigate the effect of Si and K on the transcriptome and metabolome in citrus plants and their tissues under freezing stress.Graphical

Silicon supplementation stabilizes the effect of copper stress, the use of copper chaperones and genes involved: a review.

Heavy metal stress is a major problem in present scenario and the consequences are well known. The agroecosystems are heavily affected by the heavy metal stress and the question arises on the sustainability of the agricultural products. Heavy metals inhibit the process to influence the reactive oxygen species production. When abundantly present copper metal ion has toxic effects which is mitigated by the exogenous application of Si. The role of silicon is to enhance physical parameters as well as gas exchange parameters. Si is likely to increase antioxidant enzymes in response to copper stress which can relocate toxic metals at subcellular level and remove heavy metals from the cell. Silicon regulates phytohormones when excess copper is present. Rate of photosynthesis and mineral absorption is increased in response to metal stress. Silicon manages enzymatic and non-enzymatic activities to balance metal stress condition. Cu transport by the plasma membrane is controlled by a family of proteins called copper transporter present at cell surface. Plants maintain balance in absorption, use and storage for proper copper ion homeostasis. Copper chaperones play vital role in copper ion movement within cells. Prior to that metallochaperones control Cu levels. The genes responsible in copper stress mitigation are discovered in various plant species and their function are decoded. However, detailed molecular mechanism is yet to be studied. This review discusses about the crucial mechanisms of Si-mediated alleviation of copper stress, the role of copper binding proteins in copper homeostasis. Moreover, it also provides a brief information on the genes, their function and regulation of their expression in relevance to Cu abundance in different plant species which will be beneficial for further understanding of the role of silicon in stabilization of copper stress.

Alleviating Cd Stress in Sunflower (Helianthus annuus) through the Sodium Silicate Application

Sunflower has substantial potential for the remediation of heavy metals in soil, but its efficiency in Cd-contaminated soil is limited, with high concentrations of Cd causing stress in plants. Exogenous Si enhances plant tolerance to heavy metals, but the mechanism for enhancing the tolerance of oil sunflower under Cd stress is not known. In potting experiments, sunflowers were grown in soil with a Cd concentration of 11.8 mg/kg soil (the maximum value in the Zhundong coal mining area of Xinjiang) and five Si treatment levels (0, 50, 250, 500, and 1500 mg/kg soil). Exogenous Si improved sunflower development, gas exchange characteristics, and antioxidant enzyme activities in sunflower compared with the Cd-only control; exogenous Si application increased Cd concentrations in sunflower roots, stems, and leaves, and Cd was mainly concentrated in sunflower roots. Sunflower biomass increased by 13.83–114.18%, and gas exchange parameters increased by 16.95–36.03%, 30.06–66.82%, and 9.77–14.71%, respectively, as compared to the control. With the increase in sodium silicate concentrations, sunflower antioxidant enzyme activities increased by 8.81–150.28%, 91.35–351.55%, and 35.11–54.69%, respectively, and MDA content decreased by 3.34–25.14% as compared to Si0. Moreover, exogenous Si increased Cd uptake and minimized Cd stress in sunflowers at the seedling and blooming stages, and it potentially facilitated the phytoremediation of Cd-contaminated soils through enriched plants such as sunflower, as well as contributing to the achievement of sustainable development of the soil environment.

Integrative application of silicon and/or proline improves Sweet corn (Zea mays L. saccharata) production and antioxidant defense system under salt stress condition

Silicon (Si) and/or proline (Pro) are natural supplements that are considered to induce plants' stress tolerance against various abiotic stresses. Sweet corn (Zea mays L. saccharata) production is severely afflicted by salinity stress. Therefore, two field tests were conducted to evaluate the potential effects of Si and/or Pro (6mM) used as seed soaking (SS) and/or foliar spray (FS) on Sweet corn plant growth and yield, physio-biochemical attributes, and antioxidant defense systems grown in a saline (EC = 7.14dS m−1) soil. The Si and/or Pro significantly increased growth and yield, photosynthetic pigments, free proline, total soluble sugars (TSS), K+/Na+ratios, relative water content (RWC), membrane stability index (MSI), α-Tocopherol (α-TOC), Ascorbate (AsA), glutathione (GSH), enzymatic antioxidants activities and other anatomical features as compared to controls. In contrast, electrolytes, such as SS and/or FS under salt stress compared to controls (SS and FS using tap water) were significantly decreased. The best results were obtained when SS was combined with FS via Si or Pro. These alterations are brought about by the exogenous application of Si and/or Pro rendering these elements potentially useful in aiding sweet corn plants to acclimate successfully to saline soil.

Enhancing cabbage resilience against heavy metal stress through silicon amendments and melatonin: A depth investigation

This study investigated the phytotoxic toxic effects of heavy metals and evaluated the ameliorative effects of exogenously applied silicon (Si) in cabbage. Three experiments were conducted to assess the morphological, physiological, and biochemical changes associated with heavy metal toxicity and the potential mitigation by Si. The threshold level of cabbage plants was determined in the first experiment using nickel (Ni), cadmium (Cd), and arsenic (As) as selected heavy metals. Significant reductions in growth attributes, such as plant biomass, leaf area, and root weight, were observed at all heavy metal concentrations. Physiological parameters, including photosynthetic rate, transpiration rate and stomatal conductance were also significantly reduced due to heavy metal toxicity. In the second experiment, foliar application of Si at different concentrations mitigated the negative impacts of heavy metals on plant growth and physiological attributes. Maximum mitigation was observed at Si concentrations of 2 mM and 3 mM. The third experiment confirmed the efficacy of Si at 2 mM in reducing heavy metal toxicity and improving physiological attributes. Si application significantly decreased the uptake of Cd, Ni, and As in cabbage plants. Chlorophyll contents and antioxidant enzyme activities indicated the positive impact of Si on growth and development under heavy metal stress. Heavy metals exhibited toxic effects on cabbage plants, but exogenous application of Si, particularly at 2 mM, effectively mitigated these effects and enhanced plant growth. Si application at 3mM exhibited the maximum reduction in Cd toxicity, leading to a 79% increase in fresh biomass. When Ni and Cd-stressed plants were treated with silicon at 2mM, there was maximum reduction in toxicity, resulting in a 75% and 71% increase in the photosynthetic rate. Maximum mitigation of Cd toxicity was achieved by applying silicon at 2mM, resulting in a 94% increase in stomatal conductance. Furthermore, under a-biotic stress cabbage increased the concentration of melatonin that help the plant to cope from stress. These findings demonstrate the potential of Si application as a strategy to alleviate heavy metal toxicity and improve the growth of cabbage plants

Creeping Bentgrass Nutritional, Morphological, and Putting Green Performance Response to Ca/Mg-Silicate Slag Liming Agent

While not classified as an essential plant nutrient, silicon (Si) assimilation following exogenous Si application has enhanced the wear resistance of cool-season turfgrass. Given this beneficial supplementation of lignin by Si reported in epidermal tissue of monocotyledonous plants, our research objective was to quantify root morphology, vegetative nutrition and vigor, soil chemistry, and putting green performance in response to split applications of pelletized liming agents rich in Si and/or Ca and Mg. Field evaluation of granular liming agent treatment, 2441 kg (ha year)−1, was conducted on creeping bentgrass (Agrostis stolonifera L. cv. Penn G-2) putting green maintained in the Mid-Atlantic US. Pelletized Ca/Mg-SiO3 slag or dolomitic limestone treatments were conducted in frequent split applications and incorporated into the upper 5 cm of the rootzone. Measurements of canopy color and density, shoot growth as clipping yield, soil pH, Si and nutrient content of clippings, and soil extractable Si were performed each season. Cumulative Ca/Mg-SiO3 application (kg ha−1) increased mean acetic acid (HOAc) extractable Si by 35 to 60 mg kg−1 and leaf Si content by 1.0 to 1.5 mg g−1. However, neither putting green canopy quality, shoot nutrient concentration, 5 to 15 cm depth root length density nor ball roll distance was improved by liming agent treatment. Liming agent-treated or untreated plots showed statistical, yet inconsistent, differences in clipping yield 4, 14, 15, 16, and 17 months from initiation (MFI). This thorough shuffling of treatment rank, resulting in identical experiment-wide means precludes the expectation of dependably superior vigor by any.

Silicon Accumulation in Leaves Reduces the Herbivory by Invasive Fall Armyworm Spodoptera frugiperda and Enhances the Yield of Maize

Fall armyworm (FAW) Spodoptera frugiperda is currently being considered as a serious insect pest in maize that causes significant yield losses worldwide. Silicon (Si) and plant growth regulators (PGRs) are known to induce resistance against biotic and abiotic stresses thereby enhancing the yield. This study was conducted to determine the influence of Si and PGRs on the incidence and damage of FAW on maize (Zea mays L.) under field condition. The experiment was conducted in both Kharif and Rabi seasons using a randomized complete block design with three replications and treatments. Various combinations of foliar silicic acid (FSA) and two PGRs such as gibberelic acid (GA3) and jasmonic acid (JA) were tested to study their effects on FAW incidence and maize yield. The application of FSA at 2mL/plant + GA3 at 0.5 mg/plant recorded the lowest number of larvae per plant (0.39 larva/plant) with the lowest damage score of 2.55 (Davis scale). The percent infestation was also low for the same treatment, i.e., 34.14 percent infestation with the highest percent reduction over control (56.43%). The highest yield (58.39 q/ha) and cost–benefit ratio (1:2.34) was recorded for FSA at 2 mL/plant + GA3 at 0.5 mg/plant, which was considered as the best treatment. This study demonstrated that exogenous application of Si along with PGRs has significant negative effect on field incidence of FAW and enhanced the yield of maize.

Physiological and Molecular Analysis Revealed the Role of Silicon in Modulating Salinity Stress in Mung Bean

Salinity stress acts as a significant deterrent in the course of optimal plant growth and productivity, and mung bean, being a relay crop in the cereal cropping system, is severely affected by salinity. Silicon (Si), on the other hand, has exhibited promising outcomes with regards to alleviating salinity stress. In order to understand the critical mechanisms underlying mung bean (Vigna radiata L.) tolerance towards salt stress, this study examined the effects of different salinity concentrations on antioxidant capacity, proteome level alterations, and influence on Si-transporter and salt-responsive genes. Salinity stress was seen to effect the gaseous exchange machinery, decrease the soluble protein and phenolic content and NR activity, and increase the accumulation of reactive oxygen species. An efficient regulation of stomatal opening upon Si application hints towards proficient stomatal conductance and CO2 fixation, resulting in efficient photosynthesis leading to proficient plant growth. The soluble protein and phenolic content showed improved levels upon Si supplementation, which indicates an optimal solute transport system from source to sink. The content of superoxide radicals showed a surge under salinity stress treatment, but efficient scavenging of superoxide radicles was noted under Si supplementation. Salinity stress exhibited more damaging effects on root NR activity, which was notably enhanced upon Si supplementation. Moreover, the beneficial role of Si was further substantiated as there was notable Si accumulation in the leaves and roots of salinity-stressed mung bean plants. Furthermore, Si stimulated competent ROS scavenging by reinforcing the antioxidant enzyme activity, as well coordinating with their isozyme activity, as expressed by the varying band intensities. Similarly, the Si-mediated increase in peroxidase activity may reveal changes in the mechanical characteristics of the cell wall, which are in turn associated with salinity stress adaptation. Proteomic investigations revealed the upregulation or downregulation of several proteins, which were thereafter identified by LC−MS/MS. About 45 proteins were identified and were functionally classified into photosynthesis (24%), metabolic process (19%), redox homeostasis (12%), transmembrane transport (10%), stress response (7%), and transcription regulation (4%). The gene expression analysis of the silicon transporter genes (Lsi1, Lsi2, and Lsi3) and SOS pathway genes (SOS1, SOS2, and SOS3) indicated the role of silicon in mitigating salinity stress. Hence, the findings of this study can facilitate a profound understanding of the potential mechanisms adopted by mung bean due to exogenous Si application during salinity stress.

Evaluating the Effectiveness of Calcium Silicate in Enhancing Soybean Growth and Yield.

The application of silicon (Si) fertilizer positively impacts crop health, yield, and seed quality worldwide. Si is a "quasi-essential" element that is crucial for plant nutrition and stress response but is less associated with growth. This study aimed to investigate the effect of Si on the yield of cultivated soybean (Glycine max L). Two locations, Gyeongsan and Gunwi, in the Republic of Korea were selected, and a land suitability analysis was performed using QGIS version 3.28.1. The experiments at both locations consisted of three treatments: the control, Si fertilizer application at 2.3 kg per plot (9 m × 9 m) (T1), and Si fertilizer application at 4.6 kg per plot (9 m × 9 m) (T2). The agronomic, root, and yield traits, as well as vegetative indices, were analyzed to evaluate the overall impact of Si. The results demonstrated that Si had consistently significant effects on most root and shoot parameters in the two experimental fields, which led to significantly increased crop yield when compared with the control, with T2 (22.8% and 25.6%, representing an output of 2.19 and 2.24 t ha-1 at Gyeongsan and Gunwi, respectively) showing a higher yield than T1 (11% and 14.2%, representing 1.98 and 2.04 t ha-1 at Gyeongsan and Gunwi, respectively). These results demonstrate the positive impact of exogenous Si application on the overall growth, morphological and physiological traits, and yield output of soybeans. However, the application of the optimal concentration of Si according to the crop requirement, soil status, and environmental conditions requires further studies.

Dose optimization of silicon for boosting arbuscular mycorrhizal fungi colonization and cadmium stress mitigation in maize (Zea mays L.)

The foliar applied silicon (Si) has the potential to ameliorate heavy metals, especially cadmium (Cd) toxicity; however, Si dose optimization is strategically important for boosting the growth of soil microbes and Cd stress mitigation. Thus, the current research was performed to assess the Si-induced physiochemical and antioxidant trait alterations along with Vesicular Arbuscular Mycorrhiza (VAM) status in maize roots under Cd stress. The trial included foliar Si application at the rate of 0, 5, 10, 15, and 20ppm while Cd stress (at the rate of 20ppm) was induced after full germination of maize seed. The response variables included various physiochemical traits such as leaf pigments, protein, and sugar contents along with VAM alterations under induced Cd stress. The results revealed that exogenous application of Si in higher doses remained effective in improving the leaf pigments, proline, soluble sugar, total proteins, and all free amino acids. Additionally, the same treatment remained unmatched in terms of antioxidant activity compared to lower doses of foliar-applied Si. Moreover, VAM was recorded to be at peak under 20ppm Si treatment. Thus, these encouraging findings may serve as a baseline to develop Si foliar application as a biologically viable mitigation strategy for maize grown in Cd toxicity soils. Overall, the exogenous application of Si helpful for reducing the uptake of Cd in maize and also improving the mycorrhizal association as well as the philological mechanism and antioxidant activities in plant under cadmium stress conditions. Also, future studies must test more doses concerning to varying Cd stress levels along with determining the most responsive crop stage for Si foliar application.

Gibberellic Acid and Silicon Ameliorate NaCl Toxicity in Brassica juncea: Possible Involvement of Antioxidant System and Ascorbate-Glutathione Cycle.

This work was carried out to observe the combined impact of exogenous applications of Gibberellic acid (GA3) and Silicon (Si) on Brassica juncea under salt (NaCl) stress. Application of GA3 and Si enhanced the antioxidant enzyme activities of (APX, CAT, GR, SOD) in B. juncea seedlings under NaCl toxicity. The exogenous Si application decreased Na+ uptake and enhanced the K+ and Ca2+ in salt stressed B. juncea. Moreover, chlorophyll-a (Chl-a), Chlorophyll-b (Chl-b), total chlorophyll (T-Chl), carotenoids and relative water content (RWC) in the leaves declined under salt stress, which were ameorialated after GA3 and Si supplementation individually and in combination. Further, the introduction of Si to NaCl treated B. juncea help in alleviating the negative effects of NaCl toxicity on biomass and biochemical activities. The levels of hydrogen peroxide (H2O2) increase significantly with NaCl treatments, subsequently resulting in enhanced peroxidation of membrane lipids (MDA) and electrolyte leakage (EL). The reduced levels of H2O2 and enhanced antioxidantactivities in Si and GA3 supplemented plants demonstrated the stress mitigating efficiency. In conclusion, it was observed that Si and GA3 application alleviated NaCl toxicity in B. juncea plants through enhanced production of different osmolytes and an antioxidant defence mechanism.

Exogenous silicon promotes cadmium (Cd) accumulation in Sedum alfredii Hance by enhancing Cd uptake and alleviating Cd toxicity.

Soil Cadmium (Cd) pollution has become a serious environmental problem. Silicon (Si) plays key roles in alleviating Cd toxicity in plants. However, the effects of Si on mitigation of Cd toxicity and accumulation of Cd by hyperaccumulators are largely unknown. This study was conducted to investigate the effect of Si on Cd accumulation and the physiological characteristics of Cd hyperaccumulator Sedum alfredii Hance under Cd stress. Results showed that, exogenous Si application promoted the biomass, Cd translocation and concentration of S. alfredii, with an increased rate of 21.74-52.17% for shoot biomass, and 412.39-621.00% for Cd accumulation. Moreover, Si alleviated Cd toxicity by: (i) increasing chlorophyll contents, (ii) improving antioxidant enzymes, (iii) enhancing cell wall components (lignin, cellulose, hemicellulose and pectin), (iv) raising the secretion of organic acids (oxalic acid, tartaric acid and L-malic acid). The RT-PCR analysis of genes that involved in Cd detoxification showed that the expression of SaNramp3, SaNramp6, SaHMA2 and SaHMA4 in roots were significantly decreased by 11.46-28.23%, 6.61-65.19%, 38.47-80.87%, 44.80-69.85% and 33.96-71.70% in the Si treatments, while Si significantly increased the expression of SaCAD. This study expanded understanding on the role of Si in phytoextraction and provided a feasible strategy for assisting phytoextraction Cd by S. alfredii. In summary, Si facilitated the Cd phytoextraction of S. alfredii by promoting plant growth and enhancing the resistance of plants to Cd.

Silicon-Induced Tolerance against Arsenic Toxicity by Activating Physiological, Anatomical and Biochemical Regulation in Phoenix dactylifera (Date Palm).

Arsenic is a toxic metal abundantly present in agricultural, industrial, and pesticide effluents. To overcome arsenic toxicity and ensure safety for plant growth, silicon (Si) can play a significant role in its mitigation. Here, we aim to investigate the influence of silicon on date palm under arsenic toxicity by screening antioxidants accumulation, hormonal modulation, and the expression profile of abiotic stress-related genes. The results showed that arsenic exposure (As: 1.0 mM) significantly retarded growth attributes (shoot length, root length, fresh weight), reduced photosynthetic pigments, and raised reactive species levels. Contrarily, exogenous application of Si (Na2SiO3) to date palm roots strongly influenced stress mitigation by limiting the translocation of arsenic into roots and shoots as compared with the arsenic sole application. Furthermore, an enhanced accumulation of polyphenols (48%) and increased antioxidant activities (POD: 50%, PPO: 75%, GSH: 26.1%, CAT: 51%) resulted in a significant decrease in superoxide anion (O2•−: 58%) and lipid peroxidation (MDA: 1.7-fold), in silicon-treated plants, compared with control and arsenic-treated plants. The Si application also reduced the endogenous abscisic acid (ABA: 38%) under normal conditions, and salicylic acid (SA: 52%) and jasmonic acid levels (JA: 62%) under stress conditions as compared with control and arsenic. Interestingly, the genes; zeaxanthin epoxidase (ZEP) and 9-cis-epoxycarotenoid dioxygenase (NCED-1) involved in ABA biosynthesis were upregulated by silicon under arsenic stress. Likewise, Si application also upregulated gene expression of plant plasma membrane ATPase (PMMA-4), aluminum-activated malate transporter (ALMT) responsible for maintaining cellular physiology, stomatal conductance, and short-chain dehydrogenases/reductases (SDR) involved in nutrients translocation. Hence, the study demonstrates the remarkable role of silicon in supporting growth and inducing arsenic tolerance by increasing antioxidant activities and endogenous hormones in date palm. The outcomes of our study can be employed in further studies to better understand arsenic tolerance and decode mechanism.

Physiological and Epigenetic Reaction of Barley (Hordeum vulgare L.) to the Foliar Application of Silicon under Soil Salinity Conditions.

Soil salinity is an important environmental factor affecting physiological processes in plants. It is possible to limit the negative effects of salt through the exogenous application of microelements. Silicon (Si) is widely recognized as an element improving plant resistance to abiotic and biotic stresses. The aim of the research was to determine the impact of foliar application of Si on the photosynthetic apparatus, gas exchange and DNA methylation of barley (Hordeum vulgare L.) grown under salt stress. Plants grown under controlled pot experiment were exposed to sodium chloride (NaCl) in the soil at a concentration of 200 mM, and two foliar applications of Si were made at three concentrations (0.05%, 0.1% and 0.2%). Measurements were made of relative chlorophyll content in leaves (CCl), gas exchange parameters (Ci, E, gs, and PN), and selected chlorophyll fluorescence parameters (Fv/Fm, Fv/F0, PI and RC/ABS). Additionally, DNA methylation level based on cytosine methylation within the 3′CCGG 5′ sequence was analyzed. Salinity had a negative effect on the values of the parameters examined. Exogenous application of Si by spraying leaves increased the values of the measured parameters in plants. Plants treated with NaCl in combination with the moderate (0.1%) and highest (0.2%) dose of Si indicated the lowest methylation level. Decrease of methylation implicated with activation of gene expression resulted in better physiological parameters observed in this group of barley plants.

Silicon-mediated improvement of biomass yield and physio-biochemical attributes in heat-stressed spinach (

Context Defensive action of plants against biotic and abiotic stresses has been augmented by silicon (Si). Spinach (Spinacia oleracea L.) is a nutritious leafy vegetable that is a cold-tolerant but heat-sensitive crop. Aims and methods The ability of exogenous application of Si (0, 2, 4 and 6 mmol L−1 in the form of K2SiO3) to alleviate heat stress in spinach cv. Desi Palak was investigated. After an acclimatisation period, plants were grown with or without heat stress for 15 days, followed by Si treatment for 25 days. Plant growth and physiology were assessed at 65 days after sowing. Key results Heat stress significantly inhibited plant growth, water status and photosynthesis, soluble sugar and protein contents, and osmolyte status in spinach leaves, but increased electrolyte leakage, activities of antioxidant enzymes, and proline content. Application of Si alleviated heat stress by enhancing water status, photosynthetic pigments, soluble proteins and essential minerals, and by reducing damage of the plasma membrane. The accumulation of osmolytes counterbalance the osmotic stress imposed by heat. Conclusions Silicon plays a vital role in alleviating effects of heat stress by improving water status and photosynthetic rate, and accruing osmoprotectants other than proline. Implications Exogenous application of Si is an efficient strategy to boost tolerance of spinach plants to heat stress, having significant impact on growth and productivity of spinach at higher temperatures.

Application of silicon nanoparticles enhances oxidative stress tolerance in salt stressed ‘Valencia’ sweet orange plants

Silicon (Si) can have several beneficial effects when exogenously applied to plants, including increased tolerance against several abiotic and biotic stressors. The current study investigated the role of nanosized, monodisperse silicon particles in alleviating the harmful impact of excess sodium chloride (NaCl) on ‘Valencia’ sweet orange. One-year-old ‘Valencia’ (Citrus x sinensis L. Osbeck) plants budded onto Kuharske (Citrus sinensis L. Osbeck x Poncirus trifoliata L. Raf.) rootstock were irrigated with 0, 60 or 120 mM sodium chloride (NaCl) solution for six months. We observed an incremental reduction in plant growth with increased NaCl application. Severe foliar drop and damage were observed following 60 and 120 mM NaCl application. Silicon nanoparticles applied by direct foliar application at four concentrations (0, 200, 400 and 600 mM) to these stressed plants reduced the damage in the greenhouse. Additionally, SiO2-NP application improved root growth, increased chlorophyll content, and alleviated the osmotic effect on all NaCl-treated plants compared to the control stressed plants. Furthermore, expression of Na+ cotransporter (CsSOS1, CsSOS2, CsSOS3 and CsNHX1) and aquaporin (CsPIP1;1, CsPIP2;3, and CsTIP4;1) transcripts was enhanced in the root tissues following SiO2-NP application. These results support the positive effect of exogenous Si application at 400 mM on salt-stressed citrus plants by improving photosynthesis, water status and regulating ion content. Consequently, SiO2-NPs can be applied as part of an integrated management program to improve overall citrus plant health, especially under stressful saline conditions.

Silicon-induced mitigation of drought stress in peanut genotypes (Arachis hypogaea L.) through ion homeostasis, modulations of antioxidative defense system, and metabolic regulations

Drought stress considered as a major environmental constraint that frequently limits crop production globally. In the current investigation, drought stress-induced alterations in growth, ion homeostasis, photosynthetic pigments, organic osmolytes, reactive oxygen species (ROS) generation, antioxidative components, and metabolic profile were examined in order to assess the role of silicon (Si) in mitigation of drought effects and to understand the drought adaptive mechanism in two contrasting peanut genotypes (GG7: fast growing and tall, TG26: slow growing and semi-dwarf). Si application significantly improved the leaf chlorophyll content, relative water content % (RWC %), growth and biomass in GG7 compared with TG26 genotype under water stress. Si supplementation considerably promotes the uptake and transport of mineral nutrients under drought condition in both the genotypes, which eventually promote plant growth. Exogenous application of Si protects the photosynthetic pigments from oxidative damage by reducing membrane lipid peroxidation and either maintained or reduced H2O2 accumulation in both the genotypes. The activity of enzymatic antioxidants like superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX), and glutathione reductase (GR) and non-enzymatic antioxidants like ascorbate (AsA) and glutathione (GSH) were either maintained or increased in both the genotypes in response to Si under drought as compared to those without Si. Silicon-induced higher accumulation of metabolites mainly sugars and sugar alcohols (talose, mannose, fructose, sucrose, cellobiose, trehalose, pinitol, and myo-inositol), amino acids (glutamic acid, serine, histidine, threonine, tyrosine, valine, isoleucine, and leucine) in GG7 genotype as compared to TG26, provides osmo-protection. Moreover, Si application increased phytohormones levels such as indole-3-acetic acid (IAA), gibberellic acid (GA3), jasmonic acid (JA), and zeatin in GG7 genotype under drought stress compared to non-Si treated seedlings suggesting its involvement in signaling pathways for drought adaptation and tolerance. Noteworthy increment in polyphenols (chlorogenic acid, caffeic acid, ellagic acid, rosmarinic acid, quercetin, coumarin, naringenin, and kaempferol) in the Si treated seedlings of GG7 genotype as compared to TG26 under drought stress suggests an efficient mechanism of ROS sequestration in GG7 genotype. Our findings provide comprehensive information on physiological, biochemical, and metabolic dynamics associated with Si-mediated water stress tolerance in peanut. This study indicates that the drought tolerance efficacy of peanut genotypes can be improved by Si application.

Effect of soil sulfamethoxazole on strawberry (Fragaria ananassa): Growth, health risks and silicon mitigation

The negative impact of antibiotic pollution on the agricultural system and human health is a hot issue in the world. However, little information is available on the antibiotics toxicity mechanism and the role of silicon (Si) to alleviate the antibiotics toxicity. In this study, strawberry (Fragaria ananassa) showed excitatory response to low-dose SMZ (1 mg L−1), but strawberry root and photosynthetic efficiency were damaged under high level. When SMZ level exceeded 10 mg L−1, H202, O2−, MDA and relative conductivity increased, while SOD and CAT activities first increased and then decreased. SMZ accumulated more in roots and fruits, but less in stems, and the accumulation increased with the increase of SMZ-dose. Under 1 mg L−1 SMZ, the SMZ accumulation in fruits was 110.54 μg kg−1, which exceeded the maximum residue limit. SMZ can induce the expression of sul1, sul2 and intI1, and intI1 had the highest abundance. Exogenous application of Si alleviated the toxicity of SMZ, which is mainly related to the degradation of SMZ in soil and the reduction of SMZ absorption by strawberry. In addition, Si relieved root damage, promoted the increase of photosynthetic efficiency, and improved the antioxidant system to resist SMZ toxicity.

Silicon Mitigates the Adverse Effect of Drought in Canola (Brassica napus l.) Through Promoting the Physiological and Antioxidants Activity

Drought is the major limiting factor for crops which reduces the growth and ultimately yield. However, silicon (Si) is considered one of the important elements for ameliorating adverse effect of abiotic stresses including drought also. To re-establish the previous evidence of Si, an experiment was carried out in a wire-house under pot-culture, where canola plants were grown under normal conditions (100% field capacity) and water deficit condition (40% field capacity). To know the ameliorative effect of silicon on drought-induced canola plants through promoting the physiological, growth, biochemical, and yield attributes of canola (Brassica napus L.); exogenous application of Si was done by two different methods i.e., through seed treatment (priming) before sowing and foliar spray at vegetative stage. For priming, seeds of canola were dipped for six hours in a 5 mM Si solution, whereas for foliar spray, three different levels of Si i.e., 2, 4 and 6 mM Si solution were applied at vegetative stage (after 40 days of seed emergence). Drought stress caused a substantial decrease in the parameters of water relations, and the uptake of various nutrients in canola plants. However, the application of Si significantly improved plants’ ability to withstand the drought stress through enhancing the uptake of Si in plants and also enhanced the activity of ascorbate peroxidase (APX), peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT). Data on, water potential, leaf water contents ratio and leaf pigments, (for example, chlorophyll a, chlorophyll b, total chlorophyll, carotenoids), was positively influenced by applying Si under water deficit stress. Similarly, agronomic parameters such as seeds pod−1, seed weight and seed yield were also enhanced as a result of the Si application under drought condition. Among these application methods of Si, the foliar spray has been found more effective for alleviating the adverse effects of water deficit stress on canola plants. Therefore, the results of the present study revealed that foliar application of Si at the vegetative stage may be useful for ameliorating the adverse effect of drought; since Si promoted to maintain turgor pressure, antioxidants activity in plants and also improved the nutrient accumulation both under water stress and control condition.

Silicon Defensive Role in Maize (Zea mays L.) against Drought Stress and Metals-Contaminated Irrigation Water

Irrigation water rarity and its contamination with toxic metals are increasing gradually and have become imperious issues for the environment at personal and governmental levels. Silicon (Si) can increase plant tolerance to abiotic stressors and beneficially affect plant growth and productivity. The main purpose of the current study was to investigate the effect of Si as a foliar application on growth, photosynthetic efficiency, plant-water status, metals accumulation, water-use efficiency (WUE) and yield of maize grown under drought and metals-contaminated irrigation water stresses. We conducted two-season field experiments in 2017 and 2018 summer seasons on maize grown under two irrigation regimes (Full irrigation (FI = 100%) and deficit irrigation (DI20% = 80%) of crop evapotranspiration) combined with 0 (Si0), 2 (Si2), and 4 (Si4) mM of Si in form of Na2SiO3 applied at 40 and 60 days after planting as a foliar application. In both seasons, maize plants were irrigated with metals-contaminated redundant water (Ni2+; 5.5 ppm, Cd2+; 0.27 ppm, and Cr3+; 5 ppm). Exogenous application of Si increased drought stress tolerance in maize by enhancing photosynthetic efficiency, stomatal conductance (gs) and cell membrane integrity as evaluated by membrane stability index. These results were positively reflected in improving plant growth, WUE, and productivity along with decreasing accumulation of Ni+2, Cd+2, and Cr+3 in leaves and grains under drought stress by metals-contaminated irrigation water. Deficit irrigation and metal-contaminated irrigation water conditions reduced growth and productivity of maize plants. However, foliar application of Si was effective in enhancing the physiological performance, water use efficiency, and productivity of maize under drought and/or contaminated irrigation water conditions. Therefore, Si may, in future, find value as a potential plant growth stimulant under different abiotic stresses.