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

Aquaporin mediated silicon-enhanced root hydraulic conductance is benefit to cadmium dilution in tobacco seedlings

Numerous studies shown that silicon (Si) enhanced plants' resistance to cadmium (Cd). Most studies primarily focused on investigating the impact of Si on Cd accumulation. However, there is a lack of how Si enhanced Cd resistance through regulation of water balance. The study demonstrated that Si had a greater impact on increasing fresh weight compared to dry weight under Cd stress. This effect was mainly attributed to Si enhanced plant relative water content (RWC). Plant water content depends on the dynamic balance of water loss and water uptake. Our findings revealed that Si increased transpiration rate and stomatal conductance, leading to higher water loss. This, in turn, negatively impacted water content. The increased water content caused by Si could ascribe to improve root water uptake. The Si treatment significantly increased root hydraulic conductance (Lpr) by 131 % under Cd stress. This enhancement was attributed to Si upregulation genes expression of NtPIP1;1, NtPIP1;2, NtPIP1;3, and NtPIP2;1. Through meticulously designed scientific experiments, this study showed that Si enhanced AQP activity, leading to increased water content that diluted Cd concentration and ultimately improved plant Cd resistance. These findings offered fresh insights into the role of Si in bolstering plant resistance to Cd.

Effect of silicon spraying on rice photosynthesis and antioxidant defense system on cadmium accumulation

Cadmium (Cd) pollution is a serious threat to food safety and human health. Minimizing Cd uptake and enhancing Cd tolerance in plants are vital to improve crop yield and reduce hazardous effects to humans. In this study, we designed three Cd concentration stress treatments (Cd1: 0.20 mg·kg-1, Cd2: 0.60 mg·kg-1, and Cd3: 1.60 mg·kg-1) and two foliar silicon (Si) treatments (CK: no spraying of any material, and Si: foliar Si spraying) to conduct pot experiments on soil Cd stress. The results showed that spraying Si on the leaves reduced the Cd content in brown rice by 4.79-42.14%. Si application increased net photosynthetic rate (Pn) by 1.77-4.08%, stomatal conductance (Gs) by 5.27-23.43%, transpiration rate (Tr) by 2.99-20.50% and intercellular carbon dioxide (CO2) concentration (Ci) by 6.55-8.84%. Foliar spraying of Si significantly increased the activities of superoxide dismutase (SOD) and peroxidase (POD) in rice leaves by 9.84-14.09% and 4.69-53.09%, respectively, and reduced the content of malondialdehyde (MDA) by 7.83-48.72%. In summary, foliar Si spraying protects the photosynthesis and antioxidant system of rice canopy leaves, and is an effective method to reduce the Cd content in brown rice.

Silicon derived benefits to combat biotic and abiotic stresses in fruit crops: Current research and future challenges

Fruit crops are frequently subjected to biotic and abiotic stresses that can significantly reduce the absorption and translocation of essential elements, ultimately leading to a decrease in crop yield. It is imperative to grow fruits and vegetables in areas prone to drought, salinity, and extreme high, and low temperatures to meet the world's minimum nutrient demand. The use of integrated approaches, including supplementation of beneficial elements like silicon (Si), can enhance plant resilience under various stresses. Silicon is the second most abundant element on the earth crust, following oxygen, which plays a significant role in development and promote plant growth. Extensive efforts have been made to explore the advantages of Si supplementation in fruit crops. The application of Si to plants reinforces the cell wall, providing additional support through enhancing a mechanical and biochemical processes, thereby improving the stress tolerance capacity of crops. In this review, the molecular and physiological mechanisms that explain the beneficial effects of Si supplementation in horticultural crop species have been discussed. The review describes the role of Si and its transporters in mitigation of abiotic stress conditions in horticultural plants.

Zinc oxide nanoparticles influence on plant tolerance to salinity stress: insights into physiological, biochemical, and molecular responses

A slight variation in ecological milieu of plants, like drought, heavy metal toxicity, abrupt changes in temperature, flood, and salt stress disturbs the usual homeostasis or metabolism in plants. Among these stresses, salinity stress is particularly detrimental to the plants, leading to toxic effects and reduce crop productivity. In a saline environment, the accumulation of sodium and chloride ions up to toxic levels significantly correlates with intracellular osmotic pressure, and can result in morphological, physiological, and molecular alterations in plants. Increased soil salinity triggers salt stress signals that activate various cellular-subcellular mechanisms in plants to enable their survival in saline conditions. Plants can adapt saline conditions by maintaining ion homeostasis, activating osmotic stress pathways, modulating phytohormone signaling, regulating cytoskeleton dynamics, and maintaining cell wall integrity. To address ionic toxicity, researchers from diverse disciplines have explored novel approaches to support plant growth and enhance their resilience. One such approach is the application of nanoparticles as a foliar spray or seed priming agents positively improve the crop quality and yield by activating germination enzymes, maintaining reactive oxygen species homeostasis, promoting synthesis of compatible solutes, stimulating antioxidant defense mechanisms, and facilitating the formation of aquaporins in seeds and root cells for efficient water absorption under various abiotic stresses. Thus, the assessment mainly targets to provide an outline of the impact of salinity stress on plant metabolism and the resistance strategies employed by plants. Additionally, the review also summarized recent research efforts exploring the innovative applications of zinc oxide nanoparticles for reducing salt stress at biochemical, physiological, and molecular levels.

Exogenous application of nano-silicon, potassium sulfate, or proline enhances physiological parameters, antioxidant enzyme activities, and agronomic traits of diverse rice genotypes under water deficit conditions

Water deficit is a critical obstacle that devastatingly impacts rice production, particularly in arid regions under current climatic fluctuations. Accordingly, it is decisive to reinforce the drought tolerance of rice by employing sustainable approaches to enhance global food security. The present study aimed at exploring the effect of exogenous application using different biostimulants on physiological, morphological, and yield attributes of diverse rice genotypes under water deficit and well-watered conditions in 2-year field trial. Three diverse rice genotypes (IRAT-112, Giza-178, and IR-64) were evaluated under well-watered (14400 m3/ha in total for the entire season) and water deficit (9170 m3/ha) conditions and were exogenously sprayed by nano-silicon, potassium sulfate, or proline. The results showed that drought stress substantially decreased all studied photosynthetic pigments, growth traits, and yield attributes compared to well-watered conditions. In contrast, antioxidant enzyme activities and osmoprotectants were considerably increased compared with those under well-watered conditions. However, the foliar application of nano-silicon, potassium sulfate, and proline substantially mitigated the deleterious effects of drought stress and markedly enhanced photosynthetic pigments, antioxidant enzyme activities, growth parameters, and yield contributing traits compared to untreated stressed control. Among the assessed treatments, foliar spray with nano-silicon or proline was more effective in promoting drought tolerance. The exogenous application of proline improved chlorophyll a, chlorophyll b, and carotenoids by 21.4, 19.6 and 21.0% followed by nano-silicon treatment, which enhanced chlorophyll a, chlorophyll b, and carotenoids by 21.1, 17.6 and 9.5% compared to untreated control. Besides, the application of proline demonstrated a superior improvement in the content of proline by 52.5% compared with the untreated control. Moreover, nano-silicon exhibited the maximum enhancement of catalase and peroxidase activity compared to the other treatments. The positive impacts of applied exogenously nano-silicon or proline significantly increased panicle length, number of panicles/plant, number of grains/panicle, fertility percentage, 1000-grain weight, panicle weight, and grain yield, compared to untreated plants under water deficit conditions. In addition, the physiological and agronomic performance of evaluated rice genotypes significantly contrasted under drought conditions. The genotype Giza-178 displayed the best performance under water deficit conditions compared with the other genotypes. Consequently, the integration of applied exogenously nano-silicon or proline with tolerant rice genotype as Giza-178 is an efficient approach to ameliorating drought tolerance and achieving agricultural sustainability under water-scarce conditions in arid environments.

The differential expressions of aquaporins underline the diverse strategies of cucumber and tomato against salinity and zinc stress

Salinity and excess zinc are two main problems that have limited agriculture in recent years. Aquaporins are crucial in regulating the passage of water and solutes through cells and may be essential for mitigating abiotic stresses. In the present study, the adaptive response to moderate salinity (60 mM NaCl) and excess Zn (1 mM ZnSO4 ) were compared alone and in combination in Cucumis sativus L. and Solanum lycopersicum L. Water relations, gas exchange and the differential expression of all aquaporins were analysed. The results showed that cucumber plants under salinity maintained the internal movement of water through osmotic adjustment and the overexpression of specific PIPs aquaporins, following a "conservation strategy". As tomato has a high tolerance to salinity, the physiological parameters and the expression of most aquaporins remained unchanged. ZnSO4 was shown to be stressful for both plant species. While cucumber upregulated 7 aquaporin isoforms, the expression of aquaporins increased in a generalized manner in tomato. Despite the differences, water relations and transpiration were adjusted in both plants, allowing the RWC in the shoot to be maintained. The aquaporin regulation in cucumber plants facing NaCl+ZnSO4 stress was similar in the two treatments containing NaCl, evidencing the predominance of salt in stress. However, in tomato, the induced expression of specific isoforms to deal with the combined stress differed from independent stresses. The results clarify the key role of aquaporin regulation in facing abiotic stresses and their possible use as markers of tolerance to salinity and heavy metals in plants.

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.

Physiochemical response of Cicer arietinum to zinc-containing mesoporous silica nanoparticles under water stress

Chickpea is an important food legume cultivated in semiarid regions, where water scarcity and nutrient deficiencies negatively affect crop production. This study aimed to investigate the effect of zinc and silicon from different sources, including bulk and nanostructures, on various biochemical traits of chickpea plants grown under field conditions in Maragheh, Northwest Iran. The main experimental factor consisted of three soil moisture levels: irrigation to 90% of field capacity (FC), 60% FC, and 30% FC. The subplots were assigned for foliar application of different fertilizers: control (distilled water), zinc sulfate (ZnSO), silicon dioxide nanoparticles (SiO2 NPs), ZnSO + SiO2 NPs, and zinc-containing mesoporous silica nanoparticles (MSNPs -Zn). The results showed that although decreased soil moisture had a negative impact on several biochemical processes, foliar application of Zn and Si in both conventional bulk and nanostructure significantly affected plant antioxidant system, plasma membrane integrity, and the concentrations of photosynthetic pigments and compatible solutes. However, the most inducing effects on catalase, ascorbate peroxidase, guaiacol peroxidase, superoxide dismutase, and anthocyanin were observed with the foliar spray of MSNPs-Zn and ZnSO + SiO2 under 60% FC. Moreover, foliar spray of MSNPs-Zn alleviated the negative effects of water deficit stress on photosynthetic pigments (chlorophyll a /b and carotenoid content). Water stress significantly induced the accumulation of free proline in the leaves. Overall, the results indicated that foliar spray of MSNPs -Zn, especially under 60% FC, improved the plant's defense system, scavenged reactive oxygen species, and enhanced the accumulation and stability of pigments, thereby mitigating the effects of drought stress.

Mitigating Cd and bacterial wilt stress in tomato plants through trico-synthesized silicon nanoparticles and Trichoderma metabolites

There has been a growing apprehension in recent years about the harmful effects of environmental pollutants on agricultural output, encompassing both living organisms and non-living factors that cause stress. In this study, the soil application of bulk silicon (Si), silicon nanoparticles (SiNPs) and Trichoderma metabolites (TM) were investigated alone or in combination for the management of an important abiotic stress i.e. Cd toxicity and biotic stress i.e. bacterial wilt (BW) in tomato plants. SiNPs were synthesized by Trichoderma and confirmed through XRD, FTIR, and Ranman spectrum analysis. Results showed that Si, SiNPs and TM were all effective treatments. The combine treatment of SiNPs and TM followed by SiNPs alone were superior over other treatments in mitigating Cd toxicity and reducing BW disease on tomato plants. The soil application of these treatments reduced the Cd toxicity by enhancing Cd-tolerance index, decreasing bioavailability of soil Cd, reducing Cd contents and translocation in plants, improving gaseous exchange, photosynthesis, and increasing the antioxidant enzyme activities and their transcriptions. These treatments significantly suppressed BW pathogen leading to the significant decrease in disease index and severity on plants. In vitro evaluation and scanning electron microscopic (SEM) analysis revealed that SiNPs and TM significantly disrupted the cellular morphology of BW pathogen Ralstonia solanacearum. Findings of this study proposes the possible use of SiNPs and TM in mitigating the Cd and BW stress in tomato plants and possibly in other crops.

The nutritional composition of six plant species after irrigation with treated wastewater and possible hazards by heavy metal accumulation

A field experiment was conducted investigating the possibility of using treated wastewater (TWW) on sites affected by water scarcity in summer, waterlogging during the wet season, and salinity. A corresponding pot experiment was conducted comparable to the field experiment in Kalaât Landelous. The same plant species (Atriplex nummularia Lindl., Eucalyptus gomphocephala DC., Acacia cyanophylla Lindl., Casuarina glauca Sieber ex Spreng., Cupressus sempervirens L., and Pinus halepensis Mill.) were grown with the same treatments. While, in the field the plants, elemental composition cannot be linked to inputs by TWW, this was studied under controlled conditions. Additionally, a control was established lower in salinity receiving tap water. The effect of TWW irrigation on macro- and microelement uptake by the six plant species was studied. The treatments were high soil salinity under drained saline (DS) conditions, high salinity under waterlogged saline (WS), and a drained non-saline control (DNS: EC = 3.0 dS/m, pH = 8.4). TWW application under DS treatment increased Na, Cl, Ca, Mg, N, P, and K in most plant tissues compared to the control. TWW application in WS treatment resulted in an increase in heavy metals. Cu and Zn showed the highest bioaccumulation factor (BAF). The BAF in different plant tissues followed the order: Cu > Zn > Mn > Cd > Ni > Co > Pb. The plants accumulated significant amounts of metals in their roots.

Rice straw based silicon nanoparticles improve morphological and nutrient profile of rice plants under salinity stress by triggering physiological and genetic repair mechanisms

The agricultural sector is facing numerous challenges worldwide, owing to global climate change and limited resources. Crop production is limited by numerous abiotic constraints. Among them, salinity stress as a combination of osmotic and ionic stress adversely influences the physiological and biochemical processes of the plant. Nanotechnology facilitates the production of crops either directly by eradicating the losses due to challenging environmental conditions or indirectly by improving tolerance against salinity stress. In this study, the protective role of silicon nanoparticles (SiNPs) was determined in two rice genotypes, N-22 and Super-Bas, differing in salinity tolerance. The SiNPs were confirmed through standard material characterization techniques, which showed the production of spherical-shaped crystalline SiNPs with a size in the range of 14.98-23.74 nm, respectively. Salinity stress adversely affected the morphological and physiological parameters of both varieties, with Super-Bas being more affected. Salt stress disturbed the ionic balance by minimizing the uptake of K+ and Ca2+ contents and increased the uptake of Na+ in plants. Exogenous SiNPs alleviated the toxic effects of salt stress and promoted the growth of both N-22 and Super-Bas, chlorophyll contents (16% and 13%), carotenoids (15% and 11%), total soluble protein contents (21% and 18%), and the activities of antioxidant enzymes. Expression analysis from quantitative real-time PCR showed that SiNPs relieved plants from oxidative bursts by triggering the expression of HKT genes. Overall, these findings demonstrate that SiNPs significantly alleviated salinity stress by triggering physiological and genetic repair mechanisms, offering a potential solution for food security.

Spirulina platensis extract improves the production and defenses of the common bean grown in a heavy metals-contaminated saline soil

Plants have to cope with several abiotic stresses, including salinity and heavy metals (HMs). Under these stresses, several extracts have been used as effective natural biostimulants, however, the use of Spirulina platensis (SP) extract (SPE) remains elusive. The effects of SPE were evaluated as soil addition (SA) and/or foliar spraying (FS) on antioxidant defenses and HMs content of common bean grown in saline soil contaminated with HMs. Individual (40 or 80 mg SPE/hill added as SA or 20 or 40 mg SPE/plant added as FS) or integrative (SA+FS) applications of SPE showed significant improvements in the following order: SA-80+FS-40 > SA-80+FS-20 > SA-40+FS-40 > SA-40+FS-20 > SA-80 > SA-40 > FS-40 > FS-20 > control. Therefore, the integrative SA+FS with 40 mg SP/plant was the most effective treatment in increasing plant growth and production, overcoming stress effects and minimizing contamination of the edible part. It significantly increased plant growth (74%-185%) and yield (107%-227%) by enhancing net photosynthetic rate (78.5%), stomatal conductance (104%), transpiration rate (124%), and contents of carotenoids (60.0%), chlorophylls (49%-51%), and NPK (271%-366%). These results were concurrent with the marked reductions in malondialdehyde (61.6%), hydrogen peroxide (42.2%), nickel (91%-94%), lead (80%-9%), and cadmium (74%-91%) contents due to the improved contents of glutathione (87.1%), ascorbate (37.0%), and α-tocopherol (77.2%), and the activities of catalase (18.1%), ascorbate peroxidase (18.3%), superoxide dismutase (192%), and glutathione reductase (52.2%) as reinforcing mechanisms. Therefore, this most effective treatment is recommended to mitigate the stress effects of salinity and HMs on common bean production while minimizing HMs in the edible part.

Silicon mitigates the negative impacts of salt stress in soybean plants

BACKGROUND

Soybean is widely cultivated around the world, including regions with salinity conditions. Salt stress impairs plant physiology and growth, but recent evidence suggests that silicon (Si) is able to mitigate this stressful condition. Therefore, the purpose of this study was to evaluate how different strategies of Si application impact on salt stress tolerance of an intermediate Si accumulator species (soybean). Therefore, we applied four treatments: Si-untreated plants (Si 0); foliar spraying at 20 mmol L^-1 (Si F); nutritive solution addition at 2.0 mol L^-1 (Si R), and combined foliar spraying at 20 mmol L^-1 plus nutritive solution at 2.0 mmol L^-1 (Si F + R). We investigated how Si application modified growth, leaf gas exchange, photosynthetic pigments, chlorophyll fluorescence, relative water content (RWC), nutrient accumulation, and ion homeostasis of soybean plants submitted to different levels of salt stress (50 and 100 mmol L^-1 NaCl).

RESULTS

Salinity induced an expressive reduction in ion accumulation, plant water status, and growth of soybean, while Si application promoted contrary effects and increased potassium (K⁺ ) accumulation, water status, photosynthetic pigment content, chlorophyll fluorescence parameters, and gas exchange attributes. Additionally, Si application enhanced Si accumulation associated with decreased Na⁺ uptake and improved morpho-physiological growth.

CONCLUSION

The use of exogenous Si can be an efficient strategy to attenuate the harmful effects of salt stress in soybean plants. The best application strategy was observed with combined foliar spraying with Si included in the nutritive solution (Si F + R). © 2023 Society of Chemical Industry.

The mechanism of silicon on alleviating cadmium toxicity in plants: A review

Cadmium is one of the most toxic heavy metal elements that seriously threaten food safety and agricultural production worldwide. Because of its high solubility, cadmium can easily enter plants, inhibiting plant growth and reducing crop yield. Therefore, finding a way to alleviate the inhibitory effects of cadmium on plant growth is critical. Silicon, the second most abundant element in the Earth's crust, has been widely reported to promote plant growth and alleviate cadmium toxicity. This review summarizes the recent progress made to elucidate how silicon mitigates cadmium toxicity in plants. We describe the role of silicon in reducing cadmium uptake and transport, improving plant mineral nutrient supply, regulating antioxidant systems and optimizing plant architecture. We also summarize in detail the regulation of plant water balance by silicon, and the role of this phenomenon in enhancing plant resistance to cadmium toxicity. An in-depth analysis of literature has been conducted to identify the current problems related to cadmium toxicity and to propose future research directions.

Enhancing Wheat Growth and Yield through Salicylic Acid-Mediated Regulation of Gas Exchange, Antioxidant Defense, and Osmoprotection under Salt Stress

Salinity is a major challenge for agricultural productivity, adversely affecting crop growth and yield. In recent years, various techniques have been developed to increase crop tolerance to salinity, including seed priming. This study was carried out to assess the effects of salicylic acid (SA) priming (0-, 10- and 20-mM) in comparison with hydropriming on growth, physio-biochemical activities, and yield of two wheat varieties (AARI-11 and Ujala-15) under 0- and 170-mM sodium chloride (NaCl) toxicity. The exposure of wheat plants to NaCl led to a significant reduction in various growth factors, including fresh weight (40%), total chlorophyll (39%), stomatal conductance (42%), shoot Ca2+ (39%), and 1000-grain weight (34%). In contrast, salt stress triggered the activities of POD, SOD, CAT, glycine-betaine, phenolics, and proline. The application of 20 mM SA through seed priming was found to greatly improve the fresh root weight, chlorophyll b, POD activities, shoot Ca2+, and overall yield (up to 71, 66, 35, 57, and 44%, respectively) under salt stress. While hydropriming also enhanced wheat tolerance to salinity.

Anatomical and physiological responses of Aechmea blanchetiana (Bromeliaceae) induced by silicon and sodium chloride stress during in vitro culture

Salt stress is one of the most severe abiotic stresses affecting plant growth and development. The application of silicon (Si) is an alternative that can increase the tolerance of plants to various types of biotic and abiotic stresses. The objective was to evaluate salt stress's effect in vitro and Si's mitigation potential on Aechmea blanchetiana plants. For this purpose, plants already established in vitro were transferred to a culture medium with 0 or 14 µM of Si (CaSiO₃). After growth for 30 days, a stationary liquid medium containing different concentrations of NaCl (0, 100, 200, or 300 µM) was added to the flasks. Anatomical and physiological analyses were performed after growth for 45 days. The plants cultivated with excess NaCl presented reduced root diameter and effective photochemical quantum yield of photosystem II (PSII) (ΦPSII) and increased non-photochemical dissipation of fluorescence (qN). Plants that grew with the presence of Si also had greater content of photosynthetic pigments and activity of the enzymes of the antioxidant system, as well as higher values of maximum quantum yield of PSII (F_V/F_M), photochemical dissipation coefficient of fluorescence (qP) and fresh weight bioaccumulation of roots and shoots. The anatomical, physiological and biochemical responses, and growth induced by Si mitigated the effect of salt stress on the A. blanchetiana plants cultivated in vitro, which can be partly explained by the tolerance of this species to grow in sandbank (Restinga) areas.

Physiological, Biochemical, and Epigenetic Reaction of Maize (Zea mays L.) to Cultivation in Conditions of Varying Soil Salinity and Foliar Application of Silicon

Soil salinity is one of the basic factors causing physiological, biochemical and epigenetic changes in plants. The negative effects of salt in the soil environment can be reduced by foliar application of silicon (Si). The study showed some positive effects of Si on maize plants (Zea mays L.) grown in various salinity conditions. At high soil salinity (300 and 400 mM NaCl), higher CCI content was demonstrated following the application of 0.2 and 0.3% Si. Chlorophyll fluorescence parameters (PI, F_V/F₀, F_v/F_m and RC/ABS) were higher after spraying at 0.3 and 0.4% Si, and plant gas exchange (C_i, P_N, g_s, E) was higher after spraying from 0.1 to 0.4% Si. Soil salinity determined by the level of chlorophyll a and b, and carotenoid pigments caused the accumulation of free proline in plant leaves. To detect changes in DNA methylation under salt stress and in combination with Si treatment of maize plants, the methylation-sensitive amplified polymorphism (MSAP) technique was used. The overall DNA methylation level within the 3'CCGG 5' sequence varied among groups of plants differentially treated. Results obtained indicated alterations of DNA methylation in plants as a response to salt stress, and the effects of NaCl + Si were dose-dependent. These changes may suggest mechanisms for plant adaptation under salt stress.

Alleviating Drought Stress in Brassica juncea (L.) Czern & Coss. by Foliar Application of Biostimulants-Orthosilicic Acid and Seaweed Extract

Agricultural productivity is negatively impacted by drought stress. Brassica is an important oilseed crop, and its productivity is often limited by drought. Biostimulants are known for their role in plant growth promotion, increased yields, and tolerance to environmental stresses. Silicon in its soluble form of orthosilicic acid (OSA) has been established to alleviate deteriorative effects of drought. Seaweed extract (SWE) also positively influence plant survival and provide dehydration tolerance under stressed environments. The present study was conducted to evaluate the efficacy of OSA and SWE on mitigating adverse effects of drought stress on Brassica genotype RH-725. Foliar application of OSA (2 ml/L and 4 ml/L) and SWE of Ascophyllum nodosum (3 ml/L and 4 ml/L) in vegetative stages in Brassica variety RH 725 under irrigated and rainfed condition revealed an increase in photosynthetic rate, stomatal conductance, transpirational rate, relative water content, water potential, osmotic potential, chlorophyll fluorescence, chlorophyll stability index, total soluble sugars, total protein content, and antioxidant enzyme activity; and a decrease in canopy temperature depression, proline, glycine-betaine, H₂O₂, and MDA content. Application of 2 ml/L OSA and 3 ml/L SWE at vegetative stage presented superior morpho-physiological and biochemical characteristics and higher yields. The findings of the present study will contribute to developing a sustainable cropping system by harnessing the benefits of OSA and seaweed extract as stress mitigators.

Interaction between selenium and essential micronutrient elements in plants: A systematic review

Nutrient imbalance (i.e., deficiency and toxicity) of microelements is an outstanding environmental issue that influences each aspect of ecosystems. Although the crucial roles of microelements in entire lifecycle of plants have been widely acknowledged, the effective control of microelements is still neglected due to the narrow safe margins. Selenium (Se) is an essential element for humans and animals. Although it is not believed to be indispensable for plants, many literatures have reported the significance of Se in terms of the uptake, accumulation, and detoxification of essential microelements in plants. However, most papers only concerned on the antagonistic effect of Se on metal elements in plants and ignored the underlying mechanisms. There is still a lack of systematic review articles to summarize the comprehensive knowledge on the connections between Se and microelements in plants. In this review, we conclude the bidirectional effects of Se on micronutrients in plants, including iron, zinc, copper, manganese, nickel, molybdenum, sodium, chlorine, and boron. The regulatory mechanisms of Se on these micronutrients are also analyzed. Moreover, we further emphasize the role of Se in alleviating element toxicity and adjusting the concentration of micronutrients in plants by altering the soil conditions (e.g., adsorption, pH, and organic matter), promoting microbial activity, participating in vital physiological and metabolic processes, generating element competition, stimulating metal chelation, organelle compartmentalization, and sequestration, improving the antioxidant defense system, and controlling related genes involved in transportation and tolerance. Based on the current understanding of the interaction between Se and these essential elements, future directions for research are suggested.

Identification of a Saltol-Independent Salinity Tolerance Polymorphism in Rice Mekong Delta Landraces and Characterization of a Promising Line, Doc Phung

The Mekong Delta River in Vietnam is facing salinity intrusion caused by climate change and sea-level rise that is severely affecting rice cultivation. Here, we evaluated salinity responses of 97 rice accessions (79 landraces and 18 improved accessions) from the Mekong Delta population by adding 100 mM NaCl to the nutrient solution for up to 20 days. We observed a wide distribution in salinity tolerance/sensitivity, with two major peaks across the 97 accessions when using the standard evaluation system (SES) developed by the International Rice Research Institute. SES scores revealed strong negative correlations (ranging from - 0.68 to - 0.83) with other phenotypic indices, such as shoot elongation length, root elongation length, shoot dry weight, and root dry weight. Mineral concentrations of Na⁺ in roots, stems, and leaves and Ca²⁺ in roots and stems were positively correlated with SES scores, suggesting that tolerant accessions lower their cation exchange capacity in the root cell wall. The salinity tolerance of Mekong Delta accessions was independent from the previously described salinity tolerance-related locus Saltol, which encodes an HKT1-type transporter in the salinity-tolerant cultivars Nona Bokra and Pokkali. Indeed, genome-wide association studies using SES scores and shoot dry weight ratios of the 79 accessions as traits identified a single common peak located on chromosome 1. This SNP did not form a linkage group with other nearby SNPs and mapped to the 3' untranslated region of gene LOC_Os01g32830, over 6.5 Mb away from the Saltol locus. LOC_Os01g32830 encodes chloroplast glycolate/glycerate translocator 1 (OsPLGG1), which is responsible for photorespiration and growth. SES and shoot dry weight ratios differed significantly between the two possible haplotypes at the causal SNP. Through these analyses, we characterize Doc Phung, one of the most salinity-tolerant varieties in the Mekong Delta population and a promising new genetic resource.

Alleviation of Cadmium Stress by Silicon Supplementation in Peas by the Modulation of Morpho-Physio-Biochemical Variables and Health Risk Assessment

Agricultural soil quality degradation by potentially toxic elements, specifically cadmium (Cd), poses a significant threat to plant growth and the health of humans. However, the supplementation of various salts of silicon (Si) to mitigate the adverse effect of Cd on the productivity of peas (Pisum sativum L.) is less known. Therefore, the present investigation was designed to evaluate the exogenous application at various levels (0, 0.50, 1.00 and 1.50 mM) of silicate compounds (sodium and potassium silicates) on pea growth, gaseous exchange, antioxidant enzyme activities and the potential health risk of Cd stress (20 mg kg-1 of soil) using CdCl2. The findings of the study showed that Cd stress significantly reduced growth, the fresh and dry biomass of roots and shoots and chlorophyll content. In addition, electrolyte leakage, antioxidant enzymes and the content of Cd in plant tissues were enhanced in Cd-induced stressed plants. An application of Si enhanced the development of stressed plants by modulating the growth of fresh and dry biomass, improving the chlorophyll contents and decreasing leakage from the plasma membrane. Furthermore, Si addition performed a vital function in relieving the effects of Cd stress by stimulating antioxidant potential. Hence, a significant level of metal protection was achieved by 1.00 mM of potassium silicate application under the Cd levels related to stress conditions, pointing to the fact that the Si concentration required for plant growth under Cd stress surpassed that which was required for general growth, enzymatic antioxidants regulation and limiting toxic metal uptake in plant tissues under normal conditions. The findings of this research work provide a feasible approach to reduce Cd toxicity in peas and to manage the entry and accumulation of Cd in food crops.

Nanotechnological Interventions in Agriculture

Agriculture is an important sector that plays an important role in providing food to both humans and animals. In addition, this sector plays an important role in the world economy. Changes in climatic conditions and biotic and abiotic stresses cause significant damage to agricultural production around the world. Therefore, the development of sustainable agricultural techniques is becoming increasingly important keeping in view the growing population and its demands. Nanotechnology provides important tools to different industrial sectors, and nowadays, the use of nanotechnology is focused on achieving a sustainable agricultural system. Great attention has been given to the development and optimization of nanomaterials and their application in the agriculture sector to improve plant growth and development, plant health and protection and overall performance in terms of morphological and physiological activities. The present communication provides up-to-date information on nanotechnological interventions in the agriculture sector. The present review deals with nanoparticles, their types and the role of nanotechnology in plant growth, development, pathogen detection and crop protection, its role in the delivery of genetic material, plant growth regulators and agrochemicals and its role in genetic engineering. Moreover, the role of nanotechnology in stress management is also discussed. Our aim in this review is to aid researchers to learn quickly how to use plant nanotechnology for improving agricultural production.

Integrative Seed and Leaf Treatment with Ascorbic Acid Extends the Planting Period by Improving Tolerance to Late Sowing Influences in Parsley

Abnormal production of reactive oxygen species (ROS) is an undesirable event which occurs in plants due to stress. To meet this event, plants synthesize ROS-neutralizing compounds, including the non-enzymatic oxidant scavenger known as vitamin C: ascorbic acid (AsA). In addition to scavenging ROS, AsA modulates many vital functions in stressed or non-stressed plants. Thus, two-season (2018/2019 and 2019/2020) trials were conducted to study the effect of integrative treatment (seed soaking + foliar spray) using 1.0 or 2.0 mM AsA vs. distilled water (control) on the growth, seed yield, and oil yield of parsley plants under three sowing dates (SDs; November, December, and January, which represent adverse conditions of late sowing) vs. October as the optimal SD (control). The ion balance, osmotic-modifying compounds, and different antioxidants were also studied. The experimental layout was a split plot in a completely randomized block design. Late sowing (December and January) noticeably reduced growth traits, seed and oil yield components, and chlorophyll and nutrient contents. However, soluble sugar, proline, and AsA contents were significantly increased along with the activities of catalase (CAT) and superoxide dismutase (SOD). Under late sowing conditions, the use of AsA significantly increased growth, different yields, essential oil fractions, CAT and SOD activities, and contents of chlorophylls, nutrients, soluble sugars, free proline, and AsA. The interaction treatments of SDs and AsA concentrations indicated that AsA at a concentration of 2 mM was more efficient in conferring greater tolerance to adverse conditions of late sowing in parsley plants. Therefore, this study recommends 2.0 mM AsA for integrative (seed soaking + foliar spraying) treatment to prolong the sowing period of parsley seeds (from October up to December) and avoid damage caused by adverse conditions of late sowing.

Advances in Understanding Silicon Transporters and the Benefits to Silicon-Associated Disease Resistance in Plants

Silicon (Si) is the second most abundant element after oxygen in the earth’s crust and soil. It is available for plant growth and development, and it is considered as quasi-essential for plant growth. The uptake and transport of Si is mediated by Si transporters. With the study of the molecular mechanism of Si uptake and transport in higher plants, different proteins and coding genes with different characteristics have been identified in numerous plants. Therefore, the accumulation, uptake and transport mechanisms of Si in various plants appear to be quite different. Many studies have reported that Si is beneficial for plant survival when challenged by disease, and it can also enhance plant resistance to pathogens, even at low Si accumulation levels. In this review, we discuss the distribution of Si in plants, as well as Si uptake, transport and accumulation, with a focus on recent advances in the study of Si transporters in different plants and the beneficial roles of Si in disease resistance. Finally, the application prospects are reviewed, leading to an exploration of the benefits of Si uptake for plant resistance against pathogens.

Silicon-induced alterations in the expression of aquaporins and antioxidant system activity in well-watered and drought-stressed oilseed rape

Progressing climate change necessitates the search for solutions of plant protection against the effects of water deficit. One of these solutions could be silicon supplementation. The aim of the study was to verify the hypothesis that silicon changes aquaporin expression and antioxidant system activity in a direction which may alleviate the effects of drought stress in oilseed rape. The accumulation of BnPIP1, BnPIP2-1-7 and BnTIP1;1 aquaporins and the expression of their genes, the level of catalase, superoxide dismutase activities and hydrogen peroxide content as well as total non-enzymatic antioxidant activity were analyzed in leaf tissue from control and silicon-treated oilseed rape plants growing under well-watered and drought conditions. Silicon was applied in two forms - pure silicon and a silicon complex. It was shown that under drought conditions, both pure silicon and the silicon complex (with Fe) significantly increased the accumulation of aquaporins and improved the activity of enzymatic and non-enzymatic components of the antioxidant system, while under well-watered conditions, these effects were observed only in the case of the silicon complex. The presented study proves that silicon supplementation in oilseed rape improves the regulation of water management and contributes to the protection against oxidative stress caused by drought.

Revegetation of coal mine degraded arid areas: The role of a native woody species under optimum water and nutrient resources

Ecological restoration of coal mine degraded soils across arid and semi-arid environments worldwide remains particularly challenging. We used a combination of greenhouse and field experiments to assess the potential role of a woody species, Ulmus pumila, in the restoration of degraded soils associated with coal-mining activities in the northwest China. We investigated how various combinations of water-nitrogen-phosphorus (W-N-P) resources affect multiple growth parameters in U. pumila. We found that several plant growth traits significantly improved with W-N applications, regardless of P inputs. Moderate-to-highest W-N-P doses increased net photosynthesis and transpiration rates, water use efficiency, stomatal conductance, chlorophyll and carotenoid contents under greenhouse conditions. A combination of high W together with low N-P applications led to high relative water content and net photosynthetic rates under field conditions. Increasing of N-P doses under W-shortage condition, aided U. pumila to enhance osmotic adjustments by increasing contents of proline and soluble sugar and also boost the activity of superoxide dismutase, peroxidase and catalase in leaf tissues to reduce accumulation of reactive oxygen species and malondialdehyde content in all conditions of greenhouse and field. Our study is the first to assess the optimum W-N-P resources in U. pumila and demonstrate that optimum growth performance could be obtained under W supplements corresponding to 90 mm year-1, N and P at 110 and 45 kg ha-1, respectively, under field condition. These findings can have far reaching implications for vegetation restoration of degraded areas associated with coal-mining activities across arid and semi-arid regions worldwide.

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 (C_i, E, g_s, and P_N), and selected chlorophyll fluorescence parameters (F_v/F_m, F_v/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.

Genome-Wide Identification of Maize Aquaporin and Functional Analysis During Seed Germination and Seedling Establishment

Water uptake facilitates the initiation of seed germination. It is presumed that aquaporin (AQP)-mediated water inflow contributes to seed germination, but the genetic evidence is still lacking. This study aimed at genome-wide identification of ZmAQPs and further determined the physiological functions. Following a comprehensive search, a total of 41 ZmAQPs were identified according to the latest genome database. Through bioinformatic approaches, the physicochemical characteristics, phylogenetic relationships, and structural features of ZmAQPs were analyzed. The gene expression analysis of 20 high-resolution and multi-tissues samples showed that ZmAQPs had distinct spatiotemporal and tissue-specific expression profiles during seed germination and early seedling development. We then focused on the aquaporin of maize tonoplast intrinsic protein 3 (ZmTIP3), which is specifically expressed in germinating seed. A mutant zmtip3-1 with disruption of the ZmTIP3-1 gene showed shorter shoot and root length, and decreased seedling dry weight compared with the control (W22). The result revealed that ZmTIP3-1 improved the absolute content of seed protein and promoted storage reserves mobilization, suggesting that ZmTIP3 may be a positive regulator of seed vigor. This work provides valuable clues for understanding the function and possible regulatory mechanism of ZmAQPs in seed germination and seedling growth.

The Mechanism of Metal Homeostasis in Plants: A New View on the Synergistic Regulation Pathway of Membrane Proteins, Lipids and Metal Ions

Heavy metal stress (HMS) is one of the most destructive abiotic stresses which seriously affects the growth and development of plants. Recent studies have shown significant progress in understanding the molecular mechanisms underlying plant tolerance to HMS. In general, three core signals are involved in plants' responses to HMS; these are mitogen-activated protein kinase (MAPK), calcium, and hormonal (abscisic acid) signals. In addition to these signal components, other regulatory factors, such as microRNAs and membrane proteins, also play an important role in regulating HMS responses in plants. Membrane proteins interact with the highly complex and heterogeneous lipids in the plant cell environment. The function of membrane proteins is affected by the interactions between lipids and lipid-membrane proteins. Our review findings also indicate the possibility of membrane protein-lipid-metal ion interactions in regulating metal homeostasis in plant cells. In this review, we investigated the role of membrane proteins with specific substrate recognition in regulating cell metal homeostasis. The understanding of the possible interaction networks and upstream and downstream pathways is developed. In addition, possible interactions between membrane proteins, metal ions, and lipids are discussed to provide new ideas for studying metal homeostasis in plant cells.

Interactions of nanoparticles and salinity stress at physiological, biochemical and molecular levels in plants: A review

Salinity stress is one of the most destructive non-biological stresses in plants that has adversely affected many agricultural lands in the world. Salinity stress causes many morphological, physiological, epigenetic and genetic changes in plants by increasing sodium and chlorine ions in the plant cells. The plants can alleviate this disorder to some extent through various mechanisms and return the cell to its original state, but if the salt dose is high, the plants may not be able to provide a proper response and can die due to salt stress. Nowadays, scientists have offered many solutions to this problem. Nanotechnology is one of the most emerging and efficient technologies that has been entered in this field and has recorded very brilliant results. Although some studies have confirmed the positive effects of nontechnology on plants under salinity stress, there is no the complete understanding of the relationship and interaction of nanoparticles and intracellular mechanisms in the plants. In the review paper, we have tried to reach a conclusion from the latest articles that how NPs could help salt-stressed plants to recover their cells under salt stress so that we can take a step towards clearing the existing ambiguities for researchers in this field.

Does silicon really matter for the photosynthetic machinery in plants…?

Silicon (Si) is known to alleviate the adverse impact of different abiotic and biotic stresses by different mechanisms including morphological, physiological, and genetic changes. Photosynthesis, one of the most important physiological processes in the plant is sensitive to different stress factors. Several studies have shown that Si ameliorates the stress effects on photosynthesis by protecting photosynthetic machinery and its function. In stressed plants, several photosynthesis-related processes including PSII maximum photochemical quantum yield (Fv/Fm), the yield of photosystem II (φPSII), electron transport rates (ETR), and photochemical quenching (qP) were observed to be regulated when supplemented with Si, which indicates that Si effectively protects the photosynthetic machinery. In addition, studies also suggested that Si is capable enough to maintain the uneven swelling, disintegrated, and missing thylakoid membranes caused during stress. Furthermore, several photosynthesis-related genes were also regulated by Si supplementation. Taking into account the key impact of Si on the evolutionarily conserved process of photosynthesis in plants, this review article is focused on the aspects of silicon and photosynthesis interrelationships during stress and signaling pathways. The assemblages of this discussion shall fulfill the lack of constructive literature related to the influence of Si on one of the most dynamic and important processes of plant life i.e. photosynthesis.

Silicon Fertilization: A Step towards Cadmium-Free Fragrant Rice

Soil contamination with toxic cadmium (Cd) is becoming a serious global problem and poses a key hazard to environments and the health of human beings worldwide. The present study investigated the effects of foliar applications of three forms of silicate chemicals (calcium silicate, sodium silicate, and potassium silicate) at four rates (0.25%, 0.5%, 0.75%, and 1.0%) at tillering stage on rice growth and the accumulation of Cd under Cd stress (30 mg kg^-1). The results showed that Cd stress reduced the yield-related traits and enlarged Cd contents in different rice organs. The leaf gas exchange attributes and yield traits were enhanced, and the Cd accumulation and bioaccumulation factor in rice organs were reduced, especially in grains, through silicon application. In shoots, roots, and grains, foliar spray of Si reduced Cd contents by 40.3%, 50.7%, and 47.9%, respectively. The effectiveness of silicate compounds in reducing Cd toxicity varied with the kind of chemicals and doses of foliar applications. Foliar application of potassium silicate, at a rate of 0.5%, at tillering stage, showed the best effectiveness in improving grain yield, while mitigating Cd accumulation in rice grains. The outcome of this study provides a promising practicable approach in alleviating Cd toxicity in rice and preventing the entrance of Cd into the food chain.

Transcriptome and Metabolome Analyses Reveal Potential Salt Tolerance Mechanisms Contributing to Maintenance of Water Balance by the Halophytic Grass Puccinellia nuttalliana

Elevated soil salinity exacerbated by human activities and global climate change poses serious threats to plant survival. Although halophytes provide many important clues concerning salt tolerance in plants, some unanswered questions remain to be addressed, including the processes of water and solute transport regulation. We performed high-throughput RNA-sequencing in roots and metabolome characterizations in roots and leaves of Puccinellia nuttalliana halophytic grass subjected to 0 (control) and 150 mM NaCl. In RNAseq, a total of 31 Gb clean bases generated were de novo assembled into 941,894 transcripts. The PIP2;2 and HKT1;5 transcript levels increased in response to the NaCl treatment implying their roles in water and ion homeostasis. Several transcription factors, including WRKY39, DEK3, HY5, and ABF2, were also overexpressed in response to NaCl. The metabolomic analysis revealed that proline and dopamine significantly increased due to the upregulation of the pathway genes under salt stress, likely contributing to salt tolerance mechanisms. Several phosphatidylcholines significantly increased in roots suggesting that the alterations of membrane lipid composition may be an important strategy in P. nuttalliana for maintaining cellular homeostasis and membrane integrity under salt stress. In leaves, the TCA cycle was enriched suggesting enhanced energy metabolism to cope with salt stress. Other features contributing to the ability of P. nuttalliana to survive under high salinity conditions include salt secretion by the salt glands and enhanced cell wall lignification of the root cells. While most of the reported transcriptomic, metabolomics, and structural alterations may have consequences to water balance maintenance by plants under salinity stress, the key processes that need to be further addressed include the role of the changes in the aquaporin gene expression profiles in the earlier reported enhancement of the aquaporin-mediated root water transport.

Alleviation of Cadmium Phytotoxicity Using Silicon Fertilization in Wheat by Altering Antioxidant Metabolism and Osmotic Adjustment

Humans are facing very serious health threats from food contamination with cadmium (Cd), and Cd uptake by wheat is amongst the main causes of Cd entrance into the food chain. The current study examined the effect of foliar application (0, 1.50, 3.00 and 4.00 mM) of various silicate chemicals (calcium silicate and potassium silicate) on wheat growth and Cd addition by wheat under Cd stress 20 mg kg−1 of soil using CdCl2. The results revealed that under control conditions, the application of Si improved all the growth, physiological, biochemical and quality attributes by reducing malondialdehyde contents and electrolyte leakage. Under Cd stress, the supplementation of Si conferred a better growth rate, gaseous exchange for metabolic activity and maintained the tissues’ turgor and membranes’ stabilities compared to those obtained under control (without Si). The enzymatic activities (superoxide dismutase, peroxidase and catalase) also show rapid action by the application of Si supplement, which were associated with elevated osmoprotectant contents and antioxidants, having role in antioxidant defense against Cd stress. These results suggested that a 4.50 mM concentration of Si supplement (potassium silicate) works effectively against Cd stress. The given results showed that Si supplement is beneficial for the enhancement of many metabolic activities that takes places in plants during the growth period that proved a feasible approach in controlling the Cd concentration within wheat plants and, ultimately, in humans.

Foliar application of silicon boosts growth, photosynthetic leaf gas exchange, antioxidative response and resistance to limited water irrigation in sugarcane (Saccharum officinarum L.)

Plant cell and water relationship regulates morphological, physiological and biochemical characteristics to optimize carboxylation for enhanced biomass yield in sugarcane. Insufficient water irrigation is one of the serious problems to impair potential yield of agriculturally important sugarcane cash crop by loss in plant performance. Our study aims to reveal consequences of foliar spray of silicon (Si) using calcium metasilicate powder (Wollastonite, CaO.SiO₂) to alleviate the adverse effects of limited water irrigation in sugarcane. Silicon (0, 50, 100 and 500 ppm) was applied as foliar spray on normally grown 45 days old sugarcane plants. Further, these plants were raised at half field capacity (50%) using water irrigation precisely up to 90 days under open environmental variables. Consequently, restricted irrigation impaired plant growth-development, leaf relative water content (%), photosynthetic pigments, SPAD unit, photosynthetic performance, chlorophyll fluorescence variable yield (Fv/Fm) and biomass yield. Notably, it has enhanced values of proline, hydrogen peroxide (H₂O₂), malondialdehyde (MDA), antioxidative defense enzyme molecules viz., catalase (CAT), ascorbate peroxidase (APx) and superoxide dismutase (SOD). The foliar spray of Si defended sugarcane plants from limited water irrigation stress as Si quenched harmful effect of water-deficit and also enhanced the operation of antioxidant defense machinery for improved sugarcane plant performance suitably favored stomatal dynamics for photosynthesis and plant productivity.

Silicon enhancement for endorsement of Xanthomonas albilineans infection in sugarcane

Silicon (Si) is considered to be a plant growth and development regulator element as well as provide the regulatory response against various biotic stressors. However, the potential mechanism of Si enhancement to regulate plant disease resistance remains to be studied. Therefore, the current study evaluated the effects of Si application on the performance of sugarcane against Xanthomonas albilineans (Xa) infection. Si was applied exogenously (0, 3.85 and 7.70 g Si/kg soil) and the results show that plant height, stem circumference and leaf width of siliconized sugarcane have been improved, which effectively reduced the disease index (0.17-0.21) and incidence (58.2%-69.1%) after Xa infection. Lowest values of MDA (348.5 nmol g^-1 FW) and H₂O₂ (3539.4 mmol/L) were observed in 7.70 g Si/kg soil followed by in 3.85 g Si/kg soil (MDA: 392.6 nmol g^-1 FW and H₂O₂: 3134.6 mmol/L) than that of the control. Whereas, PAL enzyme activity (50.8 mmol/L), JA (230.2 mmol/L) and SA (2.7 ug mL^-1) contents were significantly higher in 7.70 g Si/kg soil followed by in 3.85 g Si/kg soil (PAL: 46.3 mmol/L, JA: 182.7 mmol/L and SA: 2.4 ug mL^-1) as compared to control. The lower MDA, H₂O₂ level and higher enzymatic activities were associated with the highest expression levels of their metabolic pathway associated genes i.e., ShMAPK1, ShLOX, ShPAL, ShAOS, ShAOC, ShC4H, ShCAT, Sh4CL and ShNPR1 (22.08, 15.56, 10.42, 3.35, 2.54, 2.14, 1.82, 1.67 and 1.22 folds, respectively) in 7.70 g Si/kg soil as compared to other experimental units and control. Overall, the results of current study indicates that siliconized sugarcane more actively regulates disease resistance through modulation of growth and MDA, H₂O₂, SA and JA associated metabolic pathways.

Quantification of Silicon in Rice Based on an Electrochemical Sensor via an Amplified Electrocatalytic Strategy

Silicon plays a very important role in the growth of rice. The study of the relationship between rice and silicon has become a hot area in the last decade. Currently, the silica-molybdenum blue spectrophotometric method is mostly used for the determination of silicon content in rice. However, the results of this method vary greatly due to the different choices of reducing agents, measurement wavelengths and color development times. In this work, we present for the first time an electrochemical sensor for the detection of silicon content in rice. This electrochemical analysis technique not only provides an alternative detection strategy, but also, due to the rapid detection by electrochemical methods and the miniaturization of the instrument, it is suitable for field testing. Methodological construction using electrochemical techniques is a key objective. The silicon in rice was extracted by HF and becomes silica after pH adjustment. The silica was then immobilized onto the glassy carbon surface. These silica nanoparticles provided additional specific surface area for adsorption of sodium borohydride and Ag ions, which in turn formed Ag nanoparticles to fabricate an electrochemical sensor. The proposed electrochemical sensor can be used for indirect measurements of 10-400 mg/L of SiO₂, and thus, the method can measure 4.67-186.8 mg/g of silicon. The electrochemical sensor can be used to be comparable with the conventional silicon-molybdenum blue spectrophotometric method. The RSD of the current value was only 3.4% for five sensors. In practical use, 200 samples of glume, leaf, leaf sheath and culm were tested. The results showed that glume had the highest silicon content and culm had the lowest silicon content. The linear correlation coefficients for glume, leaf, leaf sheath and culm were 0.9841, 0.9907, 0.9894 and 0.993, respectively.

Mitigation of climate change and environmental hazards in plants: Potential role of the beneficial metalloid silicon

In the last decades, the concentration of atmospheric CO₂ and the average temperature have been increasing, and this trend is expected to become more severe in the near future. Additionally, environmental stresses including drought, salinity, UV-radiation, heavy metals, and toxic elements exposure represent a threat for ecosystems and agriculture. Climate and environmental changes negatively affect plant growth, biomass and yield production, and also enhance plant susceptibility to pests and diseases. Silicon (Si), as a beneficial element for plants, is involved in plant tolerance and/or resistance to various abiotic and biotic stresses. The beneficial role of Si has been shown in various plant species and its accumulation relies on the root's uptake capacity. However, Si uptake in plants depends on many biogeochemical factors that may be substantially altered in the future, affecting its functional role in plant protection. At present, it is not clear whether Si accumulation in plants will be positively or negatively affected by changing climate and environmental conditions. In this review, we focused on Si interaction with the most important factors of global change and environmental hazards in plants, discussing the potential role of its application as an alleviation strategy for climate and environmental hazards based on current knowledge.

Investigation of Defensive Role of Silicon during Drought Stress Induced by Irrigation Capacity in Sugarcane: Physiological and Biochemical Characteristics

Water stress may become one of the most inevitable factors in years to come regulating crop growth, development, and productivity globally. The application of eco-friendly stress mitigator may sustain physiological fitness of the plants as uptake and accumulation of silicon (Si) found to alleviate stress with plant performance. Our study focused on the mitigative effects of Si using calcium metasilicate (wollastonite powder, CaO·SiO₂) in sugarcane (Saccharum officinarum L.) prior to the exposure of water stress created by the retention of 50-45% soil moisture capacity. Si (0, 50, 100, and 500 ppm L^-1) was supplied through soil irrigation in S. officinarum L. grown at about half of the soil moisture capacity for a period of 90 days. Water stress impaired plant growth, biomass, leaf relative water content, SPAD value, photosynthetic pigments capacity, and photochemical efficiency (F _v/F _m) of photosystem II. The levels of antioxidative defense-induced enzymes, viz., catalase, ascorbate peroxidase, and superoxide dismutase, enhanced. Silicon-treated plants expressed positive correlation with their performance index. A quadratic nonlinear relation observed between loss and gain (%) in physiological and biochemical parameters during water stress upon Si application. Si was found to be effective in restoring the water stress injuries integrated to facilitate the operation of antioxidant defense machinery in S. officinarum L. with improved plant performance index and photosynthetic carbon assimilation.

Biological silicon nanoparticles improve Phaseolus vulgaris L. yield and minimize its contaminant contents on a heavy metals-contaminated saline soil

The synthesis of biological silicon nano-particles (Bio-Si-NPs) is an eco-friendly and low-cost method. There is no study focusing on the effect of Bio-Si-NPs on the plants grown on saline soil contaminated with heavy metals. In this study, an attempt was made to synthesis Bio-Si-NPs using potassium silica florid substrate, and the identified Aspergillus tubingensis AM11 isolate that separated from distribution systems of the potable water. A two-year field trial was conducted to compare the protective effects of Bio-Si-NPs (2.5 and 5.0 mmol/L) and potassium silicate (10 mmol/L) as a foliar spray on the antioxidant defense system, physio-biochemical components, and the contaminants contents of Phaseolus vulgaris L. grown on saline soil contaminated with heavy metals. Our findings showed that all treatments of Bio-Si-NPs and potassium silicate significantly improved plant growth and production, chlorophylls, carotenoids, transpiration rate, net photosynthetic rate, stomatal conductance, membrane stability index, relative water content, free proline, total soluble sugars, N, P, K, Ca²⁺, K⁺/Na⁺, and the activities of peroxidase, catalase, ascorbic peroxidase and superoxide oxide dismutase. Application of Bio-Si-NPs and potassium silicate significantly decreased electrolyte leakage, malondialdehyde, H₂O₂, O₂^•-, Na⁺, Pb, Cd, and Ni in leaves and pods of Phaseolus vulgaris L. compared to control. Bio-Si-NPs were more effective compared to potassium silicate. Application of Bio-Si-NPs at the rate of 5 mmol/L was the recommended treatment to enhance the performance and reduce heavy metals content on plants grown on contaminated saline soils.

Foliar Nourishment with Nano-Selenium Dioxide Promotes Physiology, Biochemistry, Antioxidant Defenses, and Salt Tolerance in Phaseolus vulgaris

Novel strategic green approaches are urgently needed to raise the performance of plants subjected to stress. Two field-level experimental attempts were implemented during two (2019 and 2020) growing seasons to study the possible effects of exogenous nourishment with selenium dioxide nanoparticles (Se-NPs) on growth, physio-biochemical ingredients, antioxidant defenses, and yield of Phaseolus vulgaris (L.) plant growing on a salt-affected soil (EC = 7.55–7.61 dS m⁻¹). At 20, 30, and 40 days from seeding, three foliar sprays were applied to plants with Se-NPs at a rate of 0.5, 1.0, or 1.5 mM. The experimental design was accomplished in randomized complete plots. The data indicate noteworthy elevations in indicators related to growth and yield; pigments related to effective photosynthesis, osmoprotectant (free proline and soluble sugars), nutrient and Se contents, K⁺/Na⁺ ratio, cell integrity (water content and stability of membranes), all enzyme activities; and all features related to leaf anatomy induced by Se-NPs foliar spray. Conversely, marked lowering in markers of Na⁺ content-induced oxidative stress (superoxide radical and hydrogen peroxide) and their outcomes in terms of ionic leakage and malondialdehyde were reported by foliar nourishment with Se-NPS compared to spraying leaves with water as an implemented control. The best results were recorded with Se-NPs applied at 1.0 mM, which mitigated the negative effects of soil salinity (control results). Therefore, the outcomes of this successful study recommend the use of Se-NPs at a rate of 1.0 mM as a foliar spray to grow common beans on saline soils with EC up to 7.55–7.61 dS m⁻¹.

Mitigation of saline conditions in watermelon with mycorrhiza and silicon application

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Salt stress effects agronomic traits and uptake of minerals.

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Salt stress also enhanced the oxidative stress biomarkers like hydrogen peroxide (H₂O₂).

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Supplementation of Mycorrhiza enhances the agronomical traits and alleviates slat stress.

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Silicon application also mitigates the salt stress through modulating antioxidant enzymes.

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The combination of Mycorrhiza and Silicon were more effective than their individual effect.

Citrullus lanatus L. is critical vegetable for salinity stress. Arbuscular mycorrhizal fungi (AMF) and silicon treatments are known to help as bio-ameliorator of saline soils that can improve salinity tolerance in plants. But their combined effect has never been examined on watermelon therefore, present study investigated the effect of inoculation with the Arbuscular mycorrhizal fungi (AMF) along with silicon on the growth and yield parameters, antioxidant enzyme activities, pigment and mineral content of Citrullus lanatus L. plants grown during salt stress conditions. Outcomes from the study point out that salt stressed watermelon plants showed the best morphological and biochemical values when inoculated with Silicon (4 mM) + Glomus mosseae + Gigaspora gigantean. In addition, the plants inoculated by similar treatment demonstrated less osmotic activity, electrolyte leakage, as well as peroxide content. Treatments comprising Silicon (4 mM) with either Glomus mosseae and Gigaspora gigantean also performed significantly similar for most of the traits studied in the present investigation and better than the treatment only with either one of Glomus mosseae and Gigaspora gigantean. Antioxidant efficiency of melon was certainly appreciably enhanced after incubation with AMF and Si combination in salinity stress. Overall, the application of mycorrhiza and silicon can be considered to overcome the salinity stress in watermelon.

Silicon biology in crops under abiotic stress: A paradigm shift and cross-talk between genomics and proteomics

Silicon is a beneficial element to improve the biological process, growth, development, and crop productivity. The review mainly focuses on the advantage of crops supplemented with silicon, how Si alleviate abiotic stress as well as regulate the genes and proteins involved in metabolic and biological functions in plants. Abiotic stress causes damage to the proteins, nucleic acids, affect transpiration rate, stomatal conductance, alter the nutrient balance, and cell desiccation which could reduce the growth and development of the plants. To overcome from this problem researchers, focus on beneficial element like silicon to protect the plants against various abiotic stresses. The previous review reports are based on the application of silicon on salinity and drought stress, plant defense mechanism, the elevation of plant metabolism, enhancement of the biochemical and physiological properties, regulation of secondary metabolites and plant hormone. Here, we discuss about the silicon uptake and accumulation in plants, and silicon regulates the reactive oxygen species under abiotic stress, further we mainly focus on the genes and proteins which play a vital role in plants with silicon supplementation. The study can help the researchers to focus further on plants to improve the advancement in them under abiotic stress.

Silicon alleviates salt stress-induced potassium deficiency by promoting potassium uptake and translocation in rice (Oryza sativa L.)

Under salt stress, plants suffer from potassium (K) deficiency caused by excess salts in growth substrate. Silicon (Si) can promote K status in many plant species under salt stress, however, the underlying mechanisms remain unclear. In this study, we assessed the effects of Si on K homeostasis in rice under salt stress and investigated the mechanisms behind using two low-Si rice mutants (lsi1 and lsi2) and their wild types (WTs). After five days' treatment with Si, plant growth was improved and salt stress-induced K deficiency was alleviated in WTs but not in mutants. Simultaneously, Si significantly enhanced K accumulation content, K uptake index and shoot K distribution rate in WTs but not in mutants. Besides, Si enhanced K concentration in xylem sap in WTs but not in mutants. Scanning ion-selected electrode technique (SIET) analysis showed net K influx rate was raised by Si addition under salt stress in WTs but not in mutants. Moreover, Si up-regulated the expression of genes responsible for K uptake (OsAKT1 and OsHAK1) and xylem loading (OsSKOR) in WTs but not in mutants. Overall, our results strongly indicate that Si can improve K uptake and translocation by up-regulating the expression of relevant genes, thereby promoting K status and alleviating salt stress in rice.

Exogenously Used 24-Epibrassinolide Promotes Drought Tolerance in Maize Hybrids by Improving Plant and Water Productivity in an Arid Environment

The influence of 24-epibrassinolide (EBR24), applied to leaves at a concentration of 5 μM, on plant physio-biochemistry and its reflection on crop water productivity (CWP) and other agronomic traits of six maize hybrids was field-evaluated under semi-arid conditions. Two levels of irrigation water deficiency (IWD) (moderate and severe droughts; 6000 and 3000 m3 water ha-1, respectively) were applied versus a control (well-watering; 9000 m3 water ha-1). IWD reduced the relative water content, membrane stability index, photosynthetic efficiency, stomatal conductance, and rates of transpiration and net photosynthesis. Conversely, antioxidant enzyme activities and osmolyte contents were significantly increased as a result of the increased malondialdehyde content and electrolyte leakage compared to the control. These negative influences of IWD led to a reduction in CWP and grain yield-related traits. However, EBR24 detoxified the IWD stress effects and enhanced all the above-mentioned parameters. The evaluated hybrids varied in drought tolerance; Giza-168 was the best under moderate drought, while Fine-276 was the best under severe drought. Under IWD, certain physiological traits exhibited a highly positive association with yield and yield-contributing traits or CWP. Thus, exogenously using EBR24 for these hybrids could be an effective approach to improve plant and water productivity under reduced available water in semi-arid environments.

Influence of silicon and chitosan on growth and physiological attributes of maize in a saline field

Soil salinity is the main constraint for crop productivity in many parts of the world. Application of silicon (Si) and chitosan (Chi) can improve crop growth under saline soil conditions. The current study was aimed to examine the effects of Si and Chi on mitigation of salinity, morphological and physiological attributes as well as the antioxidant system of maize (Zea mays L.) under saline soil conditions. A field experiment was conducted that comprised of nine treatments as follows: (i) Control (no amendment), (ii) Silicon 40 kg ha^-1 (Si1), (iii) Chitosan 15 kg ha^-1 (Chi1), (iv) Si1 + Chi1, (v) Silicon 80 kg ha^-1 (Si2), (vi) Chitosan 30 kg ha^-1 (Chi2), (vii) Si2 + Chi2, (viii) Si1 + Chi2 and (ix) Si2 + Chi1. Application of Si and Chi substantially improved the morphological and physiological attributes as well as antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) of maize plants, and combined application of Si and Chi was more effective when compared with Si and Chi treatments separately. Membrane stability index was improved by 25%, relative water content by 26%, chlorophyll a by 69% and b by 56% with combined application of Si and chitosan (Si2 + Chi2) compared with control. The SOD, POD and CAT increased by 36%, 38% and 65% with Si2 + Chi2 compared with control. The results suggest that Si and Chi application is the possible option for alleviating salinity stress in maize plant. Further research is suggested to examine Si and Chi effects on various crop's growth.

Roles of Si and SiNPs in Improving Thermotolerance of Wheat Photosynthetic Machinery via Upregulation of PsbH, PsbB and PsbD Genes Encoding PSII Core Proteins

Photosystem II is extremely susceptible to environmental alterations, particularly high temperatures. The maintenance of an efficient photosynthetic system under stress conditions is one of the main issues for plants to attain their required energy. Nowadays, searching for stress alleviators is the main goal for maintaining photosynthetic system productivity and, thereby, crop yield under global climate change. Potassium silicate (K2SiO3, 1.5 mM) and silicon dioxide nanoparticles (SiO2NPs, 1.66 mM) were used to mitigate the negative impacts of heat stress (45 °C, 5 h) on wheat (Triticum aestivum L.) cv. (Shandawelly) seedlings. The results showed that K2SiO3 and SiO2NPs diminished leaf rolling symptoms and electrolyte leakage (EL) of heat-stressed wheat leaves. Furthermore, the maximum quantum yield of photosystem II (Fv/Fm) and the performance index (PIabs), as well as the photosynthetic pigments and organic solutes including soluble sugars, sucrose, and proline accumulation, were increased in K2SiO3 and SiO2NPs stressed leaves. At the molecular level, RT-PCR analysis showed that K2SiO3 and SiO2NPs treatments stimulated the overexpression of PsbH, PsbB, and PsbD genes. Notably, this investigation indicated that K2SiO3 was more effective in improving wheat thermotolerance compared to SiO2NPs. The application of K2SiO3 and SiO2NPs may be one of the proposed approaches to improve crop growth and productivity to tolerate climatic change.

Physio-Biochemical and Agronomic Responses of Faba Beans to Exogenously Applied Nano-Silicon Under Drought Stress Conditions

Nano-silicon application is an efficient novel approach to mitigate the deleterious impacts of drought stress on field crops, which is expected to increase owing to climate change, especially in arid regions. Two-season field studies investigated the influence of foliar-applied nano-silicon (0.5, 1, and 1.5 mM) on physiological and biochemical attributes and their impacts on crop water productivity (CWP) and the agronomic traits of faba beans (Vicia faba). The plants were evaluated under two irrigation regimes: well-watered (100% ETc giving 406 mm ha^-1) and drought stress (65% ETc giving 264 mm ha^-1). It was found that drought stress significantly decreased gas exchange (leaf net photosynthetic rate, stomatal conductance, and rate of transpiration), water relations (relative water content and membrane stability index), nutrient uptake (N, P, K⁺, and Ca⁺²), flavonoids, and phenolic content. In contrast, drought stress significantly increased oxidative stress (H₂O₂ and O 2 · - ) and enzymatic and non-enzymatic antioxidant activities compared with the well-watered treatment. These influences of drought stress were negatively reflected in seed yield-related traits and CWP. However, foliar treatment with nano-silicon, particularly with 1.5 mM, limited the devastating impact of drought stress and markedly enhanced all the aforementioned parameters. Therefore, exogenously applied nano-silicon could be used to improve the CWP and seed and biological yields of faba bean plants under conditions with low water availability in arid environments.

Ameliorative role of Bacillus subtilis FBL-10 and silicon against lead induced stress in Solanum melongena

The continuous deterioration of arable lands by metal pollution compels finding suitable strategies to increase plant tolerance under contaminated regimes. Current study was designed to examine the synergistic role of Bacillus subtilis FBL-10 and silicon (Si) with respect to mitigation of lead (Pb) induced phytotoxicity in Solanum melongena L. Lead stress (75 mg kg^-1) reduced chlorophyll (Chl) content, photosynthetic rate and gas exchange characteristics of S. melongena plants. The Si and B. subtilis FBL-10 individually upgraded all the above-mentioned growth attributes. However, co-application of Si (50 mg kg^-1) and B. subtilis FBL-10 significantly improved biochemical and growth attributes of Pb challenged plants. The abridged levels of oxidative markers including hydrogen peroxide (H₂O₂), and malondialdehyde (MDA) besides reduced Pb accumulation in foliage tissues, were recorded in Si and microbe assisted plants. Furthermore, plants inoculated with B. subtilis FBL-10 alone or in combination with Si showed increment in total soluble proteins, photosynthetic rate and gas exchange attributes. The inoculated plants treated with Si exhibited higher level of auxins and improved activity of antioxidant enzymes under Pb stress. Present research elucidates interactive role of B. subtilis FBL-10 and Si in reduction of Pb toxicity in S. melongena plants. Alone application of Si or B. subtilis FBL-10 was less effective for attenuation of Pb stress; however, synergism between both phyto-protectants demonstrated fabulous ability for Pb stress assuagement. Consequently, executions of field studies become indispensable to comprehend the efficacy of Si applied alone or in combination with plant growth promoting bacteria (PGPB) like B. subtilis FBL-10. From current research, it is concluded that the interaction of Si and PGPB seems an auspicious technique and eco-friendly approach to enhance metal tolerance in crop plants.