The controversies of silicon's role in plant biology

Improving soybean drought tolerance via silicon-induced changes in growth, physiological, biochemical, and root characteristics

Drought-induced osmotic stress is a significant constraint to soybean growth and yield, necessitating the development of effective mitigation strategies. Silicon acts as an important strategy to mitigate the negative stress effects of drought stress. The study was aimed to evaluate the potential of soil-applied silicon in alleviating drought stress in soybean. Two field capacities were tested: control (85% FC) and drought (50% FC), with four silicon application rates (0, 100, 200, and 300 kg ha-1) applied at sowing. Drought stress significantly affected the morphological parameters in soybean as plant height, leaf area, and water potential were reduced by 25%, 20%, and 36%, respectively, while root length increased as compared to control-85% FC. However, drought stress reduced root density, surface area, and biomass as compared to control-85% FC. Additionally, drought reduced photosynthetic rates, chlorophyll a and b levels, and stomatal conductance, while increasing malondialdehyde and hydrogen peroxide. The natural plant defense system was upregulated, with increased activity of phenolics, soluble proteins, and antioxidant enzymes like catalase, superoxide dismutase, and peroxidase. However, silicon applications, especially at 200 kg ha-1, significantly alleviated the negative effects of drought stress by improving morphophysiological and biochemical traits in soybeans. Compared to the control, Si200 increased plant height, root length, photosynthetic rate, and water potential by 22%, 39%, 23%, and 17%, respectively, as compared to control. Furthermore, silicon reduced malondialdehyde and hydrogen peroxide levels by 21% and 10%, enhancing plant resilience. Silicon supplementation also boosted biochemical attributes, with total soluble proteins, phenolics, and antioxidant enzyme activities increasing by 30%, 55%, 19%, 24%, and 31%, respectively, under drought conditions. In crux, silicon at 200 kg ha-1 effectively mitigated the effects of drought stress in soybean, becoming a more sustainable approach to sustain crop yield and food security.

Silicon priming triggers differential physiological, ionomic and metabolic responses in olive (Olea europaea L.) cultivars with different tolerance to salinity

Salinity stress can negatively influence the growth potential and productivity of olive trees affecting photosynthesis and, disturbing ions homeostasis and essential metabolic pathways. Silicon (Si) is proposed as exogenous pretreatment for mitigate the salinity impact on olive plants. One-year old 'Frantoio' (salt-tolerant) and 'Leccino' (salt-sensitive) plants (n = 5) were grown in pots filled with sand and clay and pretreated for 28 days with 10 mg L-1 of Si(OH)4 then, for 51 days with 100 mM NaCl (12.15 g for each plant) and compared to control plants. The following hypotheses have been tested: i) Si pretreatment enhances photosynthetic performance by regulating stomatal closure and decreasing water loss; ii) Si reduces Na+ uptake and accumulation in new leaves; iii) Si improve the biosynthesis of compatible osmolytes that have a role in the regulation of the osmotic stress induced by salinity. The Si priming effect in olive tree was cultivar dependent. In 'Frantoio' Si induce a rapid early decrease of stomatal conductance increasing the intrinsic water use efficiencies (intWUE) not observed in 'Leccino' plants. In 'Leccino' the key Si effect was the reduction of Na+ accumulation in new leaves (-58 %) and maintenance of the K+ concentration under salinity. Specific interactions between Si and NaCl and the number of polyphenols affected were higher in 'Frantoio' than in 'Leccino'. Among the key mechanisms related to the Si-mediated tolerance to salt stress we can conclude that photosynthesis and Na+ uptake are the two principals involved in the responses of salinity to 'Frantoio' and 'Leccino' cultivars.

Across 33 broad-leaved deciduous woody species, silicon enhances leaf lamina stiffness but not tensile strength whereas cellulose enhances both

Silicon (Si) has been hypothesized to be a metabolically cheaper substitute for carbon-based cell wall components to support leaves. However, how the biomechanical function of Si, deposited as amorphous silica, differs from cell wall components remains untested. Here, we tested the hypothesis that species with higher leaf Si concentrations have stiffer but more brittle leaf lamina. We measured the mechanical properties, including modulus of elasticity (E), tensile strength (σmax), and maximum strain (εmax), tissue density, and the concentrations of Si and cell wall components for 33 deciduous broad-leaved woody species. Multiple regression results showed that tissue density, Si concentration, and cellulose concentration contributed positively to E and negatively to εmax. By contrast, tissue density and cellulose concentration, but not Si concentration, contributed to σmax. No significant contribution of lignin concentration to mechanical properties was detected. These results suggest that Si might function as a substitute for cellulose to increase stiffness but not the strength of a lamina. Greater Si concentration decreased εmax without increasing σmax, which made the lamina more brittle. The brittleness associated with Si might explain a potential cost or disadvantage of using Si, which would elucidate the trade-offs between species with different leaf Si concentrations.

The silicon efflux transporter BEC1 is essential for bloom formation and stress tolerance in cucumber

Silicon (Si) plays a crucial role in plant growth, development, and stress tolerance. However, in some consumable plant products, such as fruits, Si deposition leads to the formation of a white powdery layer known as bloom, which diminishes glossiness and consumer appeal. Despite its significance, the genetic basis of bloom formation remains largely unexplored. Here, we identified a unique cucumber backbone parent line exhibiting bloomless fruit, which was designated blooml ess cucumber 1 (bec1). Map-based cloning of the bec1 locus revealed that BEC1, harboring a natural C-to-T variation at the 754th base of its coding region, is a strong candidate gene for the bloomless trait. Functional validation through gene-editing mutants and BEC1::BEC1-GFP transgenic lines confirmed that BEC1, encoding a Si efflux transporter, is responsible for bloom formation. Mutation of BEC1 impaired Si uptake, thereby preventing the deposition of Si on the surface of glandular trichomes and resulting in bloomless fruits. Additionally, Si deficiency in BEC1 mutants compromised resistance to Corynespora cassiicola and chilling stress. Interestingly, grafting bec1 scions onto bloom rootstocks restored the Si accumulation and stress resistance, while maintaining bloomless phenotype. Overall, our findings elucidate the role of BEC1 in bloom formation and provide a valuable genetic target for breeding bloomless cucumber with enhanced stress resilience.

Silicon alleviates aluminum-induced inhibition of photosynthetic and growth attributes in rice by modulating competitive pathways between ethylene and polyamines and activating antioxidant defense

Silicon (Si) has been reported to mitigate aluminium (Al3+) toxicity in rice; however, the mechanism underlying this beneficial effect has not been fully elucidated. In this study, Si addition increased the total level of both free and conjugated putrescine (Put) content in rice leaves by 89.3 % through up-regulation of the key synthesis genes in both of arginine decarboxylase (ADC) and ornithine decarboxylase (ODC) pathways under Al stress. The production of total Put increased by 10.3 % under Si treatment but decreased by 11.7 % under Al treatment compared to the control. Similarly, Si increased total spermidine (Spd) and spermine (Spm) levels by 154.9 % and 83.5 %, respectively, through up-regulation of S-adenosyl-Met-decarboxylase genes (SAMDC1 and SAMDC2), spermidine synthase genes (SPDS1 and SPDS2), and spermine synthase gene (SPMS) under Al stress. Compared with Al treatment alone, Si significantly increased the levels of free, conjugated and total polyamines (PAs) in leaves under Al stress by 106.1 %, 86.6 % and 99.3 %, respectively. The increase of PAs induced by Si maintained redox balance and improved photosynthetic capacity, ultimately increasing rice growth by 28.6 % under Al stress. Conversely, Si reduced Al-induced increase in 1-aminocyclopropane-1-carboxylate (ACC) content and ethylene production by 23.9 % and 43.8 %, respectively, through down-regulation of ACC synthase genes (ACS1 and ACS2) and ACC oxidase ACO genes (ACO1 and ACO4). In addition, Si mitigated the Al-induced oxidative damage by reducing the accumulation of reactive oxygen species (ROS) through activation of enzymatic (superoxide dismutase and catalase) and non-enzymatic (ascorbate-glutathione cycle) antioxidant defence systems. We therefore propose that Si attenuates Al-induced damage on rice photosynthetic apparatus by modulating competitive interactions between ethylene and PA biosynthesis and activating ROS scavenging capacity.

New Insights into the Synergistic Interaction Between Pseudomonas qingdaonensis NZ 1 and Silicon to Mitigate Drought Stress in Rice

The current study assessed the synergistic effects of PGPR and Si in alleviating drought stress in rice. Bacteria were isolated from Phragmites australis inhabiting an urban riverbank. Among the isolated strains, Pseudomonas qingdaonensis NZ 1 showed promising results under in vitro drought stress induced by PEG-6000 (-0.28 MPa). To further investigate the synergistic effect of Pseudomonas qingdaonensis NZ 1 and silicon, a plant growth experiment was conducted comprising the control (dH2O) and plants treated with NZ 1, Si (1 mM), and NZ 1+Si under normal and drought stress conditions. The results revealed that NZ 1+Si-treated plants showed improved plant growth parameters, chlorophyll contents, relative water contents, antioxidant potential, and nutrient uptake under normal and drought conditions. Moreover, endogenous abscisic acid and jasmonic acid levels were substantially reduced, while the salicylic acid level was increased in NZ 1+Si-treated plants. Moreover, the relative expression of the ABA metabolic genes OsNCED3 and OsCYP707A6 and transcription factors OsbZIP23 and OsDREB1B were significantly altered. Furthermore, the leaf Si, calcium, potassium, and phosphorus contents were increased in NZ 1+Si-treated drought-stressed plants, along with the upregulation of OsLSi1. The combined application of NZ 1 and Si offers a sustainable agricultural strategy to effectively mitigate the detrimental effects of drought.

Silicon-Mediated Modulation of Olive Leaf Phytochemistry: Genotype-Specific and Stress-Dependent Responses

Secondary metabolites in olive (Olea europaea L.) leaves constitute a complex framework wherein phenylpropanoids, terpenoids, and secoiridoids in particular, serve as major contributors to olive plant resilience. Silicon (Si) stands as a mediator of defense mechanisms in plants, enhancing their protective responses and adaptability. A field trial on one-year-old plantlets of two metabolically distinct olive genotypes was conducted to investigate the effects of foliar-applied Si on the phytochemical profiles of locally treated leaves. Silicon's systemic effects in juvenile leaves were also appraised. We accounted for intervarietal differences in nutrient uptake and conducted in situ measurements of physiological indices. The peak of the summer season and the onset of autumn were chosen as the two sampling time points. Intense summer conditions prompted metabolic adjustments that resulted in phytochemical profiles unique to each cultivar. These profiles were further significantly altered by Si while remaining genotype-specific, with substantial increases in prominent compounds like oleuropein (105% and 252%) and verbascoside (62% and 126%), depending on the genotype. As the pressure from environmental factors eased, the differences in Si-mediated phytochemical responses emerged. Silicon had a limited effect on the phytochemical profile of the resilient cultivar which acquired a metabolic steady-state, while it significantly altered the profile of its metabolically more versatile counterpart, resulting with a progressive increase in its oleuropein (37%) and verbascoside (26%) levels. These effects extended to untreated, juvenile leaves as well. While effective in altering and improving the phytochemical composition of olive leaves, Si acted in a manner that adhered to each genotype's metabolic foundation. The intensity of environmental constraints, along with each cultivar's inherent sensitivity to them, seems to be tied to silicon's capacity to mediate significant phytochemical alterations. The extent of silicon's prophylactic function may therefore be dependent on a genotype's metabolic foundation and overall sensitivity, and as such it seems inseparable from stress and its intensity.

Silicon-Mediated Interactions Between Plant Antagonists

The prolonged arms race between plants and their antagonists has resulted in the evolution of multiple plant defence mechanisms to combat attacks by pests and pathogens. Silicon (Si) accumulation occurs mainly in grasses and provides a physical barrier against antagonists. Biochemical pathways may also be involved in Si-mediated plant resistance, although the precise mode of action in this case is less clear. Most studies have focussed on Si-based effects against single attackers. In this review, we consider how Si-based plant resistance operates when simultaneously and/or sequentially attacked by insect herbivores, fungal phytopathogens, and plant parasitic nematodes and how the plant hormones jasmonic acid (JA) and salicylic acid (SA) are involved. Si defence may mediate both intra- and interspecific competition and facilitation. Si has been found to impact plant-mediated interactions between insect herbivores within the same feeding guild and across different feeding guilds, with varying patterns of JA and SA. These results suggest that hormonal crosstalk may play a role in the Si-mediated effects, although this finding varied between studies. While some reports support the notion that JA is linked to Si responses, others indicate that Si supplementation reduces JA production. In terms of phytopathogens, SA has not been found to be involved in Si-mediated defences. Improving our understanding of Si-mediated plant defence could be beneficial for sustainable agriculture under future climates.

Exploring silica accumulation in bamboo leaves: a study on phytolith morphology and epidermal patterning in the tropical giant bamboo Dendrocalamus copelandii

BACKGROUND AND AIMS

Bamboo is a grass in the Poaceae family with various applications. Bamboo leaves can accumulate high silica. However, silica deposition in bamboo has received limited study. Therefore, this research investigated silica accumulation in Dendrocalamus copelandii leaves. The study includes the localization of silica through phytolith morphology, examination of the distribution patterns of phytoliths in epidermal tissues, analysis of silica accumulation within specialized silica cells (short cells) and analysis of silicon concentration across various leaf developmental stages.

METHODS

We used imaging techniques, including differential interference contrast and a scanning electron microscope incorporating an energy-dispersive X-ray spectrometer, to investigate silica accumulation in bamboo leaves. We also analysed the silicon concentration using inductively coupled plasma-optical emission spectroscopy.

KEY RESULTS

Leaves of D. copelandii exhibited 11 phytolith morphotypes, namely Bilobate, Polylobate, Saddle, Acute, Acute bulbosus, Microhair, Stomata, Bulliform flabellate, Elongate sinuate, Elongate entire and Tracheary. Most of these phytoliths were found in short cells (Bilobate, Polylobate and Saddle) of epidermal tissues. The short cells were arranged transversely along the leaf length. Bilobate phytoliths were found in both the abaxial and adaxial epidermis, whereas the Saddle morphotype was found only in the abaxial epidermis. Silica accumulation in the short cells of unexpanded leaves begins at the leaf apex, spreads to the middle and base positions, and accumulates initially in the abaxial epidermis, then the adaxial epidermis. Moreover, bamboo leaves accumulate a higher silicon concentration as they age.

CONCLUSIONS

Phytolith morphotypes and silica accumulation in epidermal short cells are key factors in understanding silica deposition. Leaf age and climate significantly impact the silicon concentration in bamboo leaves. Our findings are informative for archaeological studies and for plant taxonomical classification. The results are also applicable for biotechnological applications.

Effect of Hoagland's nutrient solution strengths and sodium silicate on growth, yield and biochemical parameters of Carla (Momordica Charantia L.) under hydroponic conditions

The medicinal species of Carla (Momoradica charantia) is one of the medicinal plants in Cucurbitaceae family, which has shown significant effects on the control of diabetes, blood pressure, high cholesterol and liver failure due to its valuable alkaloid and glycosidic compounds. In order to investigate the effect of different strengths of Hoagland's nutrient solution and different levels of sodium silicate on yield components, biochemical characteristics and photosynthetic pigments of the medicinal plant Carla under hydroponic conditions, a factorial experiment in the form of a completely randomized design with three replications was carried out in the Department of Medicinal Plants of Arak University. The first factor included the concentrations of nutrient solution at four levels (¼, ½, 1 and 2 strength of Hoagland's nutrient solution) and the second factor included sodium silicate spraying at four levels (0, 50, 100 and 150 mg L- 1) taken from the source of sodium silicate. The results showed that different strengths of Hoagland's nutrient solution and different concentrations of sodium silicate had a significant effect on all growth and morphological traits. The results of the experiment showed an increase in the number of flowers and fruits in double strength Hoagland concentration compared to the control (full strength), and the lowest amounts of these traits were observed at ¼ strength Hoagland concentration. In addition, the maximum numbers of flowers and fruit, fruit diameter, fruit length, and fruit weight were obtained at concentration of 100 mg L- 1 sodium silicate, and the minimum values of these traits were recorded at ¼ strength Hoagland's solution. The highest amounts of chlorophyll b and a were seen in double strength Hoagland's solution and the lowest amounts were seen in ¼ strength Hoagland. Moreover, the amount of carotenoid was the highest in ¼ strength Hoagland and the lowest in double strength Hoagland. The maximum and minimum values of chlorophyll b and a were obtained at concentrations of 150 and 0 mg/kg sodium silicate, respectively. In general, it was found that double strength Hoagland was more effective than other concentrations on yield components and morphological parameters, and flowering and fruit harvesting times were also reduced in the mentioned treatment. On the other hand, sodium silicate at 100 and 150 mg L- 1 had more obvious effects on the evaluated traits and the reduction of flowering and fruit harvesting times.

The interaction of nutrient uptake with biotic and abiotic stresses in plants

Plants depend heavily on efficient nutrient uptake and utilization for optimal growth and development. However, plants are constantly subjected to a diverse array of biotic stresses, such as pathogen infections, insect pests, and herbivory, as well as abiotic stress like drought, salinity, extreme temperatures, and nutrient imbalances. These stresses significantly impact the plant's ability to take up nutrient and use it efficiency. Understanding how plants maintain nutrient uptake and use efficiency under biotic and abiotic stress conditions is crucial for improving crop resilience and sustainability. This review explores the recent advancements in elucidating the mechanisms underlying nutrient uptake and utilization efficiency in plants under such stress conditions. Our aim is to offer a comprehensive perspective that can guide the breeding of stress-tolerant and nutrition-efficient crop varieties, ultimately contributing to the advancement of sustainable agriculture.

Anatomical and Trait Analyses Reveal a Silicon-Carbon Trade-Off in the Epidermis of Sedges

In recent years, the detection of numerous negative correlations between silicon (Si) and carbon (C)-based compounds in plants has suggested trade-offs between different stress resistance and/or mechanical support strategies. However, nearly all studies have involved whole-leaf analysis, and it is unclear how the trade-off operates mechanistically, at the cellular level. Here we combined leaf trait measurements and microscopic analyses (electron microscopy with elemental X-ray mapping and X-ray microtomography) of 17 species from a high-Si family: Cyperaceae. Accumulation of Si was strongly negatively correlated with C-based compounds, particularly tannins. Our microscopical investigations showed that the accumulation of phenolics and deposition of silica were mutually exclusive in the outer epidermal cell walls. This trade-off was independent of that between the construction of tough, sclerenchyma-rich leaves and growth potential (the leaf economics spectrum). We also identified a strong negative correlation between Si and accumulation of epicuticular waxes. Previous whole leaf analyses were, in effect, hiding the locations of the trade-off between Si and C-based compounds in plants. The epidermal location of this trade-off and the specific involvement of tannins and waxes suggest the existence of different strategies to resist environmental stresses. Our study provides key insights into plant Si utilization and highlights the multidimensionality of plant stress resistance strategies.

Silicon uptake and transport mechanisms in plants: processes, applications and challenges in sustainable plant management

Silicon (Si) is an abundant element in the earth's crust essential for plant growth and development. Recent studies silicon's potential for improving plant resilience to numerous biotic stressors, notably fungal diseases. This review seeks to offer a comprehensive understanding of the processes and advantages of silicon-induced systemic resistance in plants, with a special focus on its interactions with fungal pathogens. Furthermore, we investigate the effect of silicon on plant physiological and biochemical changes, such as enhanced lignification, strengthening of physical barriers, and activation of antioxidant systems. Additionally, we examine the influence of silicon on microbial populations within the rhizosphere and its effects on mycorrhizal associations. Lastly, we discuss the potential applications and challenges of integrating silicon-based strategies in sustainable plant disease management. This review provides valuable insights into using silicon as a novel approach to enhance plant systemic resistance against fungal pathogens, offering prospects for developing eco-friendly and efficient agricultural practices.

Species-specific modulation of nitro-oxidative stress and root growth in monocots by silica nanoparticle pretreatment under copper oxide nanoparticle stress

BACKGROUND

Abiotic stressors such as heavy metals and nanoparticles pose significant challenges to sustainable agriculture, with copper oxide nanoparticles (CuO NPs) known to inhibit root growth and induce oxidative stress in plants. While silica nanoparticles (SiO2 NPs) have been shown to increase abiotic stress tolerance, their role in mitigating CuO NP-induced stress in crops, especially monocots, remains poorly understood. This study addresses this critical knowledge gap by investigating how SiO2 NP pretreatment modulates CuO NP-induced stress responses, with a particular focus on root growth inhibition and nitro-oxidative stress pathways.

RESULTS

Using an in vitro semihydroponic system, seeds were pretreated with varying concentrations of SiO2 NPs (100-800 mg/L) before exposure to CuO NPs at levels known to inhibit root growth by 50%. SiO2 NP pretreatment alleviated CuO NP-induced root growth inhibition in sorghum, wheat, and rye but intensified it in triticale. These responses are associated with species-specific alterations in reactive signaling molecules, including a reduction in nitric oxide levels and an increase in hydrogen sulfide in sorghum, a decrease in superoxide anion levels in rye, and elevated hydrogen peroxide levels in wheat. Protein tyrosine nitration, a marker of nitro-oxidative stress, was reduced in most cases, further indicating the stress-mitigating role of SiO2 NPs. These signaling molecules were selected for their established roles in mediating oxidative and nitrosative stress responses under abiotic stress conditions.

CONCLUSIONS

SiO2 NP pretreatment modulates CuO NP-induced stress responses through species-specific regulation of reactive oxygen and nitrogen species, demonstrating its potential as a tool for enhancing crop resilience. These findings advance the understanding of nanoparticle‒plant interactions and provide a foundation for future applications of nanotechnology in sustainable agriculture.

CLINICAL TRIAL NUMBER

Not applicable.

Silicon mitigates the adverse effects of drought on Lolium perenne physiological, morphometric and anatomical characters

Limited water resources and natural drought may result in reduced water availability for the population's needs and the maintenance of the proper vegetation condition. Understanding the impact of drought on turfgrass species is essential to developing strategies that enhance the adaptability of plants to drought stress. It is vital for maintaining green areas in cities under changing climatic conditions. Therefore, studies on the ability of turfgrasses to recover after periods of drought without irrigation are becoming increasingly essential. We conducted research to determine the possibility of reducing the negative impact of drought stress on the photosynthetic efficiency, the morphometric features of plant shoots and roots, and the distribution of biomass of Lolium perenne lawn cultivars in the initial period of growth by applying biostimulant with silicon. We also investigated how drought and silicon (Si) application affect the leaf and root anatomical structure of L. perenne plants. Studies on the influence of drought on the physiological, biometric parameters and anatomical characteristics of two L. perenne cultivars were carried out under two levels of soil moisture (well-watered plants-control and drought caused by the cessation of watering) and also two variants of Si application (with and without Si application). Plants were exposed to drought in the tillering phase for 21 days. After this time, all plants were provided with optimal soil moisture conditions for the next 14 days (recovery period). Measurements of physiological parameters and biometric features of plants were evaluated in four terms: after 7, 14 and 21 days of drought and after recovery. Drought stress in L. perenne cvs. resulted in decreasing values of physiological parameters, especially maximal fluorescence, the quantum efficiency of photosystem II and photosynthetic electron transport rate compared with the values of features in well-watered plants. These adverse impacts were reflected in decreased biomass-related traits: shoot number, shoots and roots biomass, as well as area and length of roots. The application of Si reduced the detrimental effects of drought by accelerating plant growth after stress and increasing the values of most of the investigated physiological parameters. Under drought stress conditions, Si application led to the development of two-cell-layer exodermis, which reduced the water losses in L. perenne roots and shoots and, as a result, improved the drought tolerance of plants.

Endophytic microbial communities and functional shifts in Hemarthria compressa grass in response to Silicon and Selenium amendment

BACKGROUND

Hemarthria compressa, a widely cultivated forage grass, is critical for supporting livestock production and maintaining the ecological balance in grassland ecosystems. Enhancing its stress resistance and productivity is crucial for sustainable grassland utilization and development. Silicon (Si) and Selenium (Se) are recognized as beneficial nutrients that promote plant growth and stress tolerance, and modulate of plant-microorganism interactions. However, the intricate linkages between the endophytes shifts and host grass growth induced by Si/Se amendments are poorly understood. In this study, a pot experiment was conducted to examine the effects of foliar-applied Si/Se on the growth and nutritional quality of H. compressa grass, as well as the composition, diversity and potential functions of endophytic bacteria in leaves.

RESULTS

Both Si and Se treatments significantly improved grass biomass by approximately 17%. Nutritional quality was also improved, with Si application increased plant Si and neutral detergent fiber contents by 25.6% and 5.8%, while Se significantly enhanced the grass Se content from 0.055 mg kg-1 to 0.636 mg kg-1. Furthermore, Si/Se amendments altered the structure of the leaf endophytic bacterial community, resulting in an increased alpha diversity and a more modularized co-occurrence network. Moreover, both Si and Se treatments enriched plant growth-promoting bacterial genera such as Brevundimonas and Truepera. Metabolic function analysis revealed that Si application promoted chlorophyllide biosynthesis by 152%, several carbon metabolism pathways by 35-152%, and redox-related pathways by 57-93%, while the starch biosynthesis pathway was downregulated by 79% of the endophytic bacterial community. In contrast, Se application mainly enhanced starch degradation, CMP-legionamine biosynthesis by 71% and TCA cycle-related pathways by 23-58%, while reducing L-threonine metabolism by 98%. These specific functional changes in the endophytic bacteria induced by Si/Se amendments were closely linked with the observed growth promotion and stress resistance of the host H. compressa grass.

CONCLUSIONS

Si and Se amendments not only enhanced the growth and nutritional quality of H. compressa grass, but also altered the community structure and functional traits of endophytic bacteria in grass. The enrichment of beneficial endophytes and the modification of community metabolic functions within the endophytic community may play important synergistic effects on improving grass growth.

Impact of straw returning on soil ecology and crop yield: A review

Several studies have demonstrated the effect of straw return on enhancing soil ecology, promoting sustainable agricultural practices, and cumulative effects on plant yield. Recent studies have focused on straw return methods and their impact on soil nutrient cycling and the overall physicochemical composition of the soil. Despite the substantial progress and successes, several research gaps in these studies require further investigations to harness the full potential of straw return. This review provides a thorough examination of straw diversity and decomposition mechanisms, the effects of straw on soil microorganisms, the interactions between cellulolytic nitrogen-fixing microbes and lignocellulose biomass, as well as nutrient mineralization, organic matter content, and their influence on plant growth and yield. This review also examined the effects of straw return on plant pathogens and its allelopathic impact on plant growth, highlighting research gaps to encourage further studies that could fully realize the potential benefits of straw return in agricultural fields for optimal plant growth.

Convergent evidence for the temperature-dependent emergence of silicification in terrestrial plants

Research on silicon (Si) biogeochemistry and its beneficial effects for plants has received significant attention over several decades, but the reasons for the emergence of high-Si plants remain unclear. Here, we combine experimentation, field studies and analysis of existing databases to test the role of temperature on the expression and emergence of silicification in terrestrial plants. We first show that Si is beneficial for rice under high temperature (40 °C), but harmful under low temperature (0 °C), whilst a 2 °C increase results in a 37% increase in leaf Si concentrations. We then find that, globally, the average distribution temperature of high-Si plant clades is 1.2 °C higher than that of low-Si clades. Across China, leaf Si concentrations increase with temperature in high-Si plants (wheat and rice), but not in low-Si plants (weeping willow and winter jasmine). From an evolutionary perspective, 77% of high-Si families (>10 mg Si g-1 DW) originate during warming episodes, while 86% of low-Si families (<1 mg Si g-1 DW) originate during cooling episodes. On average, Earth's temperature during the emergence of high-Si families is 3 °C higher than that of low-Si families. Taken together, our evidence suggests that plant Si variation is closely related to global and long-term climate change.

Silicon Effects Depend upon Insect Herbivore Guild and Has Limited Influence on Gall-Inducing Insects of Bauhinia brevipes

Silicon (Si) is a widely recognized element in plant defense, often enhancing resistance to herbivory by strengthening cell walls and deterring feeding by external herbivores. However, its impact on internal, endophytic herbivores, such as gall-inducing insects, remains underexplored. This study investigates the role of silicon in Bauhinia brevipes, focusing on its effects on herbivory by insects. We hypothesize that while silicon strengthens plant tissues and reduces feeding by external herbivores, it may have a limited effect on internal feeders, such as gall-inducing insects. Our results indicate that silicon accumulation in leaves significantly reduces herbivory by chewing insects but has no direct effect on the occurrence of gall-inducing insects. Silicon content in galled tissues was lower compared to healthy leaves, suggesting that gall-inducing insects may manipulate silicon distribution to mitigate its defensive effects. Our results indicate that hypersensitivity reactions were positively influenced by silicon, highlighting the role of this element in enhancing localized defense mechanisms. Our findings reveal silicon's tissue-specific roles in plant defense, emphasizing the need for more research on its nuanced interactions with endophytic herbivores and implications for ecological applications. This research contributes to the literature on silicon's multifaceted role in plant-herbivore interactions and its potential applications in sustainable pest management.

Silicon transport and its "homeostasis" in rice

Silicon (Si), the most abundant mineral element in soil, functions as a beneficial element for plant growth. Higher Si accumulation in the shoots is required for high and stable production of rice, a typical Si-accumulating plant species. During the last two decades, great progresses has been made in the identification of Si transporters involved in uptake, xylem loading and unloading as well as preferential distribution and deposition of Si in rice. In addition to these transporters, simulation by mathematical models revealed several other key factors required for efficient uptake and distribution of Si. The expression of Lsi1, Lsi2 and Lsi3 genes is down-regulated by Si deposition in the shoots rather than in the roots, but the exact mechanisms underlying this down-regulation are still unknown. In this short review, we focus on Si transporters identified in rice and discuss how rice optimizes Si accumulation ("homeostasis") through regulating Si transporters in response to the fluctuations of this element in the soil solution.

Effects of Silicon Concentration and Synthesis Duration on Lignin Structure: A Spectroscopic and Microscopic Study

Silicon (Si) is a highly abundant mineral in Earth's crust. It plays a vital role in plant growth, providing mechanical support, enhancing grain yield, facilitating mineral nutrition, and aiding stress response mechanisms. The intricate relationship between silicification and lignin chemistry significantly impacts cell wall structure. Yet, the precise influence of Si on lignin synthesis remains elusive. This study investigated the interaction between Si and lignin model compounds during in vitro synthesis. Employing spectroscopic and microscopic analyses, we delineated how Si concentrations modulate lignin polymerization dynamics, particularly affecting molecular conformation and aggregation behavior over time. Fluctuations in the polymer structure are directly related to both the synthesis time and the concentration of silica. Our results demonstrate that lower Si concentrations promote the aggregation of lignin oligomers into larger particles, while higher concentrations increase the possibility of oligomer repulsion, thus preventing particle growth. These findings elucidate the intricate interplay between Si and lignin, which is crucial for understanding plant cell wall structure and stress resilience. Moreover, the results provide insights for developing lignin-silica materials with increasing applications in industry and medicine.

A novel layered culture device reveals spatial dynamics of root element uptake and optimal silicon application site for mitigating chromium uptake by rice

Understanding root uptake mechanisms for various elements is crucial for optimizing heavy metal remediation strategies and enhancing plant-nutrient interactions. However, simple and effective methods to differentiate the contributions of specific root segments in element uptake are lacking. Here, we developed a layered culture device consisting of a culture box and a plant suspension mechanism, which isolates different root segments through solid media and waterproof coating. Then, we used the device to investigate the roles of distinct root segments (0-1 cm and 1-2 cm from the tip) in heavy metal chromium (Cr) and beneficial element silicon (Si) uptake in rice. The results indicated that the 0-1 cm root segment contributed approximately 58% of leaf Cr(VI), with higher efflux compared to the 1-2 cm segment. Conversely, the 1-2 cm root segment served as the primary source of leaf Si and Cr(III), accounting for 62% and 54%, respectively. The translocation factors for Cr(VI) were similar for both segments (0.039 and 0.032), while the Cr(III) translocation factor for the 0-1 cm root segment (0.061) was 2.8 times that of the 1-2 cm segment. Notably, Si application to the 0-1 cm segment most effectively alleviated Cr (III) and Cr (VI) stress, boosting shoot length, fresh weight, and chlorophyll concentration and reducing Cr concentrations in roots and leaves by 24.7%-65.7%. In contrast, Si application to the 1-2 cm segment had minimal impact on rice growth or Cr uptake. These results suggest a deep Si application strategy for remediating Cr-contaminated soil. The innovative device provides a scientific foundation for distinguishing element uptake contributions of different root segments and enhancing the utilization efficiency of remediation materials and nutrient management in agriculture.

Transient Expression of Nicotiana tabacum Silicon-Induced Histidine-Rich Defensins in N. benthamiana Limits Necrotic Lesion Development Caused by Phytopathogenic Fungi

Silicon (Si) supplementation permits plants to better deter infection. Supplementing hydroponically propagated Nicotiana tabacum with 1 mM potassium silicate (K2SiO3) reduced necrotic lesion development on detached leaves by both Botrytis cinerea and Sclerotinia sclerotiorum. Previously, a family of Si-induced genes was identified in N. tabacum. These genes were members of the solanaceous histidine-rich defensin (HRD) superfamily and were termed NtHRD1s (the first identified family of N. tabacum HRDs). Defensins were originally identified to participate in innate immunity. Thus, the NtHRD1s were tested for antimicrobial effects on plant pathogens. Transient expression of NtHRD1 genes within N. benthamiana leaves restricted the development of necrotic lesions caused by B. cinerea and S. sclerotiorum. Thus, the NtHRD1s may be an additional Si-responsive factor conferring beneficial effects on plants. [Formula: see text] Copyright © 2025 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Contrasting effects of arsenic on mycorrhizal-mediated silicon and phosphorus uptake by rice

Silicon (Si) and arbuscular mycorrhizal fungi (AMF) increase plant resistance to various environmental stresses, including heavy metal (and metalloid) toxicity. Although Si and AMF each independently enhance plant tolerance, the nature of their interactions and their combined impacts on nutrient uptake, especially in the context of toxic elements such as arsenic (As), remains to be elucidated. This study investigated AMF-mediated regulation of plant nutrient uptake under As stress using rice, a model Si-accumulating plant. Experiments were conducted under As-free and As stress conditions, incorporating AMF inoculation and silicic acid application, with a focus on nutrient uptake and transporter expression. Without As, AMF inoculation increased shoot Si content by 44%, while invariance was common under As toxicity stress (10 μM of As(III)). Despite As presence, AMF increased Lsi1 expression with Si application, elevating As content in roots and shoots by 38% and 55%, respectively. Introduction of As stress amplified AMF role in phosphorus (P) uptake from 13% to 38%, correlating with up-regulated P transporter expression. Three-way ANOVA of interactions among As, Si, and AMF on P and As uptake by rice revealed that As amplified AMF potential to increase P uptake while weakening promotive effect on Si uptake. Silicon reduced As absorption, while AMF increased As uptake, but the elevated As were potentially retained within fungal hyphae, limiting transfer to rice plants. Overall, As toxicity stress had contrasting effects on P- and Si-promoting roles of AMF. These findings contribute to our understanding of plant-fungal interactions under heavy metal stress.

Rhizobacteria and silicon modulate defense, oxidative stress, and suppress blast disease in upland rice plants in low phosphorus soils under field conditions

MAIN CONCLUSION

Rhizobacteria and silicon fertilization synergism suppress leaf and panicle Blast, and mitigates biotic stress in rice plants. Association of bioagents and silicon is synergistic for mitigating leaf and panicle blast and low phosphorus (P) levels in upland rice, under greenhouse conditions. This study aimed to evaluate the potential of the bioagents and silicon interaction on blast disease severity suppression in upland rice plants, under field low P conditions. The experiment was conducted during two growing seasons (E1 and E2), in randomized block design with four replications, and consisted of five treatments, combining a mix of three rhizobacteria, BRM 32114 and BRM62523 (Serratia marcescens), and BRM32110 (Bacillus toyonensis), and three application methods (seed treatment, drenching, spraying). Calcium and magnesium silicate (2 t/ha) was applied over a low soil P, 30 days before sowing. Leaf blast (LBS) and panicle blast (PBS), area under the disease progress curve (AUDPC), activity of enzymes related to oxidative stress, pathogenesis-related (PR), biochemical indicators such as hydrogen peroxide, chlorophyll a and b, carotenoids, and grain yield (GY), were assessed. Bioagents and silicon suppressed LBS by 77.93 and PBS by 62.37%, reduced AUDPC by 77.3 (LBS) and 60.6% (PBS). The yield in E1 was 25% higher than in E2. The treatments statistically differ only in E2, the yield with bioagents and silicon (2435.72 kg ha-1) was 71.95% higher compared to the absolute control. All enzymatic activities related to oxidative stress and PR proteins were modulated by bioagents and silicon association. The association of rhizobacteria and silicon exhibited a synergistic effect, and represents a bioprotective combination to reduce the effects of different stresses and indirectly reduces the use of chemical inputs.

The effect of silicon supplementation and drought stress on the deposition of callose and chemical components in the cell walls of the Brassica napus roots

BACKGROUND

Silicon has an important role in regulating water management in plants. It is deposited in cell walls and creates a mechanical barrier against external factors. The aim of this study was to determine the role of silicon supplementation in the synthesis and distribution of callose in oilseed rape roots and to characterize the modifications of cell wall structure of these organs after exposure to drought stress. Histological and ultrastructural analyses were performed to determine the changes in the distribution of arabinogalactan proteins, pectins, and extensin in roots of Brassica napus growing under drought and supplemented with silicon. Callose deposition and the accumulation of callose synthase protein were assessed, followed by transcriptional analysis of callose synthase genes.

RESULTS

The results showed that silicon supplementation under drought conditions alter the direction of cortex cell differentiation, promoting fiber formation and proliferation of callose-depositing cells in the roots of the tested plants. This was reflected in an increase in the level of callose synthase and a decrease in the transcriptional activity of the gene encoding this enzyme, indicating regulation based on negative feedback under drought stress. The changes in abundance and distribution of investigated arabinogalactan proteins, pectins and extensin in roots of Si supplemented plants growing under drought stress were observed, indicating cell walls remodeling.

CONCLUSION

Silicon supplementation in oilseed rape roots induced significant changes in cell wall composition, including increased callose deposition and altered pectins and arabinogalactan proteins distribution. These modifications, along with the formation of fibres in the root cortex, likely contribute to enhanced cell wall strength providing a physical barrier against water loss and mechanical stress, as a probable defence mechanism induced during drought stress.

Direct determination of silicon overestimates the accumulation and translocation of SiO2 nanoparticles in rice seedlings

Silica nanoparticles (SiO2 NPs) have numerous applications in agriculture, but may also pose significant risks to plants. Nevertheless, their bioaccumulation, an important determinant of their risks, was often not accurately measured due to the lack of reliable methods. In this study, the accumulation in rice seedlings of SiO2 NPs of different sizes without and with a gold nanoparticle core (Au@SiO2 NPs) was examined. Potential interference from SiO2 NP dissolution was minimized by lowering the pH of the uptake medium, which did not result in any observable adverse bioeffects. Under this condition, the direct determination of Si showed the significant accumulation of SiO2 NPs in roots and shoots and a decrease in the accumulation of SiO2 NPs in shoots with increasing particle size. However, when accumulation was monitored using Au@SiO2 NPs, SiO2 NP accumulation was significantly higher when measured by direct Si determination than by Au determination, indicating that the former overestimates the accumulation of SiO2 NPs. Consequently, unlike direct Si determination, tracking the gold nanoparticle core revealed an increase in SiO2 NP accumulation in shoots with increasing particle size. Overall, accurate determination of SiO2 NP bioaccumulation is imperative for appropriate bioapplications and reliable biosafety assessments of these particles.

Unlocking the role of silicon against biotic stress in plants

The requirement for agricultural crops continues to enhance with the continuous growth of the human population globally. Plant pathogenic diseases outbreaks are enhancing and threatening food security and safety for the vulnerable in different regions worldwide. Silicon (Si) is considered a non-essential element for plant growth. It regulates the biological functions, plant development and productivity, and balance the defense mechanism in response to fungal, bacterial and pest attacks. The optimum crop yield can be achieved by applying Si in agricultural systems through different methods to replace or minimize the use of synthetic fertilizers. This approach can be effective on crop production during limited resources, extreme climates, pests and diseases, and environmental pollution. Silicon can be applied as foliar spray, priming of seeds, soil water irrigation, soil amendment and soilless medium (hydroponic) to enhance plant performance and stress tolerance capacity during stress conditions. This article summarized the effective roles of Si and the ability to perform in agroecosystems for better crop production, food security and safety for sustainable agriculture in the future.

Silicon regulation of manganese homeostasis in plants: mechanisms and future prospective

Manganese (Mn), a plant micronutrient element, is an important component of metalloprotein involved in multiple metabolic processes, such as photosynthesis and scavenging reactive oxygen species (ROS). Its disorder (deficiency or excess) affects the Mn-dependent metabolic processes and subsequent growth and development of plants. The beneficial element of Si has a variety of applications in agricultural fields for plant adaptation to various environmental stresses, including Mn disorder. The probable mechanisms for Si alleviation of Mn toxicity in plants are summarized as follows: (1) Si alters the rhizosphere acidification, root exudates and microorganisms to decrease the bioavailability of Mn in the rhizosphere; (2) Si down-regulates Mn transporter gene and reinforces the apoplastic barriers for inhibiting the Mn uptake and translocation; and (3) Si promotes the Mn deposition onto cell wall and Mn compartmentation into vacuole. Under Mn-deficient conditions, the probable mechanisms for Si promotion of Mn absorption in some plants remain an open question. Moreover, scavenging ROS is a common mechanism for Si alleviating Mn disorder. This minireview highlights the current understanding and future perspectives of Si regulation of manganese homeostasis in plants.

Enhancing crop disease management through integrating biocontrol bacteria and silicon fertilizers: Challenges and opportunities

To achieve sustainable disease management in agriculture, there's a growing interest in using beneficial microorganisms as alternatives to chemical pesticides. Bacteria, in particular, have been extensively studied as biological control agents, but their inconsistent performance and limited availability hinder broader adoption. Research continues to explore innovative biocontrol technologies, which can be enhanced by combining silicon (Si) with biocontrol plant growth-promoting rhizobacteria (PGPR). Both biocontrol PGPR and Si demonstrate effectiveness in reducing plant disease under stress conditions, potentially leading to synergistic effects when used together. This review examines the individual mechanisms by which biocontrol PGPR and Si fertilizers manage plant diseases, emphasizing their roles in enhancing plant defense and decreasing disease incidence. Various Si fertilizer sources allow for flexible application methods, suitable for different target diseases and plant species. However, challenges exist, such as inconsistent soil Si data, lack of standardized soil tests, and limited availability of Si fertilizers. Addressing these issues necessitates collaborative efforts to develop improved Si fertilizers and tailored application strategies for specific cropping systems. Additionally, exploring silicate-solubilizing biocontrol bacteria to enhance Si availability in soils introduces intriguing research avenues. Investigating these bacteria's diversity and mechanisms can optimize Si access for plants and bolster disease resistance. Overall, combining biocontrol PGPR and Si fertilizers or silicate-solubilizing biocontrol bacteria shows promise for sustainable agriculture, enhancing crop productivity while reducing reliance on chemical inputs and promoting environmental sustainability.

The interaction effect of water deficit stress and nanosilicon on phytochemical and physiological characteristics of hemp (Cannabis sativa L.)

Different practical approaches have been employed to attenuate the destructive impacts of water deficit stress on plants, such as utilization of humic acid, salicylic acid, algae extract, mulching, and microorganisms, as well as silicon application. Nanosilicon significantly moderates the ruinous effects of abiotic and biotic stress in plants through some physiological processes. In this study, the interaction effect of drought stress and nanosilicon on phytochemical and physiological characteristics of hemp (Cannabis sativa L.) was investigated, wherein the four-week-old seedlings were subjected to irrigation treatments at four levels, including 100% (control), 80% (mild stress), 60% (moderate stress), and 40% (severe stress) of field capacity and nanosilicon at three concentrations (0, 0.5, and 1.5 mM) was foliar applied every 10 days in a factorial completely randomized design experiment with three replications for 30 days. Phytochemical and physiological analyses such as photosynthetic pigments, total phenolic and flavonoid content, and antioxidant enzyme activities were conducted. The results indicated that the highest content of Cannabidiol and Tetrahydrocannabinol was achieved using 1.5 mM (1.89%) and 0.5 mM (0.63%) nanosilicon treatments, respectively, under moderate stress. The plants subjected to severe drought stress without nanosilicon application displayed the lowest values of chlorophyll a (0.50 mg/g FW) and b (0.20 mg/g FW). The use of nanosilicon excited the activation of antioxidant enzymes, wherein the plants treated with nanosilicon and drought stress exhibited significantly higher SOD, POD, and APX activities compared to the control. Under all drought stress levels, foliar application of nanosilicon at the highest concentration decreased proline content. The results proposed that the application of 1.5 mM nanosilicon, as a more efficient concentration, improved drought tolerance in hemp plants.

Effect of silicon on the distribution and speciation of uranium in sunflower (Helianthus annuus)

Sunflower (Helianthus annuus) can potentially be used for uranium (U) phytoremediation. However, the factors influencing the absorption of U and its subsequent distribution within plant tissues remain unclear, including the effect of silicon (Si) which is known to increase metal tolerance. Here, using hydroponics, the effect of Si on the distribution and speciation of U in sunflower was examined using synchrotron-based X-ray fluorescence and fluorescence-X-ray absorption near-edge spectroscopy. It was found that ∼88 % of U accumulates within the root regardless of treatments. Without the addition of Si, most of the U appeared to bind to epidermis within the roots, whereas in the leaves, U primarily accumulated in the veins. The addition of Si alleviated U phytotoxicity and decreased U concentration in sunflower by an average of 60 %. In the roots, Si enhanced U distribution in cell walls and impeded its entry into cells, likely due to increased callose deposition. In the leaves, Si induced the sequestration of U in trichomes. However, Si did not alter U speciation and U remained in the hexavalent form. These results provide information on U accumulation and distribution within sunflower, and suggest that Si could enhance plant growth under high U stress.

Plant Silicon Defences Suppress Herbivore Performance, but Mode of Feeding Is Key

The performance of herbivorous animals depends on the nutritional and defensive traits of the plants they consume. The uptake and deposition of biogenic silicon in plant tissues is arguably the most basic and ubiquitous anti-herbivore defence used by plants, especially grasses. We conducted meta-analyses of 150 studies reporting how vertebrate and invertebrate herbivores performed when feeding on silicon-rich plants relative to those feeding on low-silicon plants. Silicon levels were 52% higher and 32% more variable in silicon-rich plants compared to plants with low silicon, which resulted in an overall 33% decline in herbivore performance. Fluid-feeding herbivore performance was less adversely impacted (-14%) than tissue-chewing herbivores, including mammals (-45%), chewing arthropods (-33%) and plant-boring arthropods (-39%). Fluid-feeding arthropods with a wide diet breadth or those feeding on perennial plant species were mostly unaffected by silicon defences. Unlike many other plant defences, where diet specialisation often helps herbivores overcome their effects, silicon negatively impacts chewing herbivores regardless of diet breadth. We conclude that silicon defences primarily target chewing herbivores and impact vertebrate and invertebrate herbivores to a similar degree.

Silicon improves salt resistance by enhancing ABA biosynthesis and aquaporin expression in Nicotiana tabacum L

Silicon (Si) can significantly improve the salt tolerance of plants, but its mechanism remains unclear. In this study, role of abscisic acid (ABA) in Si derived salt resistance in tobacco seedling was investigated. Under salt stress, the photosynthetic rate, stomatal conductance, and transpiration rate of tobacco seedlings were reduced by 86.17%, 80.63%, and 67.54% respectively, resulting in a decrease in biomass. The application of Si found to mitigate these stress-induced markers. However, positive role of Si was mainly attributed to the enhanced expression of aquaporin genes, which helped in enhancing root hydraulic conductance (Lpr) and ultimately maintaining the leaf relative water content (RWC). Moreover, sodium tungstate, an ABA biosynthesis inhibitor, was used to test the role of ABA on Si-regulating Lpr. The results indicated that the improvement of Lpr by Si was diminished in the presence of ABA inhibitor. In addition, it was observed that the ABA content was increased due to the Si-upregulated of ABA biosynthesis genes, namely NtNCED1 and NtNCED5. Conversely, the expression of ABA metabolism gene NtCYP7O7A was found to be reduced by Si. Together, this study suggested that Si increased ABA content, leading to enhanced efficiency of water uptake by the roots, ultimately facilitating an adequate water supply to maintain leaf water balance. As a result, there was an improvement in salt resistance in tobacco seedling.

How does silicon alleviate Cd-induced phytotoxicity in barley, Hordeum vulgare L.?

Toxic heavy metal accumulation in edible plants has become a problem worth worrying about for human health. Cadmium is one of the most toxic metals presenting high bioavailability in the environment. The main route of transfer of Cd to humans is the consumption of contaminated food which suggests that reducing of Cd absorption by plants could reduce this risk. In this context, it was suggested that silicon supply would be able to limit the transfer of Cd to the plants. Thus, this work evaluated the effects of 0.5 mM Si on Cd absorption and accumulation in barley (Hordeum vulgare L.). Plants were grown hydroponically for 21 days in the presence of 0 and 15 μM Cd2+ combined or not with 0.5 mM Si. Analyses were related to growth and photosynthesis parameters, Cd accumulation in organs and Cd subcellular distribution in the shoots. Results showed that, under Cd alone, plants showed severe toxicity symptoms as chlorosis and necrosis and produced significantly less biomass as compared to control. 0.5 mM Si in the medium culture significantly reduced Cd-induced toxicity by mitigating symptoms and restoring growth, photosynthesis, and nutrition. Si also induced a significant reduction of Cd concentration in plants and changed its sub-cellular compartmentalization by enhancing fixation to cell walls and reducing the Cd concentration in the cytoplasmic and organelles fractions. These data suggest that the application of Si could significantly increase Cd tolerance and reduce the risk of the Cd accumulation in edible plants.

Colonization by the endophytic fungus Phyllosticta fallopiae combined with the element Si promotes the growth of Dendrobium nobile

Endophytic fungi can promote plant growth and development, particularly of Orchidaceae species. Previously, we found that the endophytic fungus Phyllosticta fallopiae DN14, collected from Dendrobium nobile growing on rocks in a wild habitat, significantly promoted growth of its host plant D. nobile, an important herb in Chinese traditional medicine that contains the bioactive component dendrobine. Phyllosticta was positively correlated with FW and dendrobine content of D. nobile and with Si content of the epiphytic matrix. Si is also highly beneficial for the growth and productivity of many plants. Here, we co-cultured D. nobile with P. fallopiae DN14 in half-strength Murashige and Skoog medium with and without various concentrations of Si to investigate the effects of DN14 and Si on plant fresh weight and dendrobine content. We also explored the effects of DN14 infection and colonization on host plant growth, Si accumulation and transport, and expression of key genes, as well as the interaction between DN14 and Si. The combination of DN14 and Si promoted the lignification of D. nobile roots, stems, and leaves and markedly increased the thickening of xylem cell walls. Co-culture with DN14 increased transport of Si from roots to stems and from stems to leaves. Transcriptome sequencing and qRT-PCR analyses showed that enhancement of D. nobile growth by DN14 and Si may involve upregulation of plant hormone-related genes (AUX/IAA and MYC) and lignin biosynthesis genes (HCT, PAL1, and PAL2). Insoluble Si promoted the growth of DN14, perhaps through downregulation of genes (e.g., FBP, MPI, RPIAD) related to carbohydrate metabolism, and DN14 in turn promoted the transformation of insoluble Si into soluble Si for plant uptake. These findings demonstrate that endophytic fungi and Si can improve the growth of D. nobile and therefore show promise as organic amendments for commercial cultivation.

Silicon and selenium alleviate cadmium toxicity in Artemisia selengensis Turcz by regulating the plant-rhizosphere

Soil cadmium (Cd) pollution has emerged as a pressing concern due to its deleterious impacts on both plant physiology and human well-being. Silicon (Si) is renowned for its ability to mitigate excessive Cd accumulation within plant cells and reduce the mobility of Cd in soil, whereas Selenium (Se) augments plant antioxidant capabilities and promotes rhizosphere microbial activity. However, research focusing on the simultaneous utilization of Si and Se to ameliorate plant Cd toxicity through multiple mechanisms within the plant-rhizosphere remains comparatively limited. This study combined hydroponic and pot experiments to investigate the effects of the combined application of Si and Se on Cd absorption and accumulation, as well as the growth and rhizosphere of A. selengensis Turcz under Cd stress. The results revealed that a strong synergistic effect was observed between both Si and Se. The combination of Si and Se significantly increased the activity and content of enzymes and non-enzyme antioxidants within A. selengensis Turcz, reduced Cd accumulation and inhibiting its translocation from roots to shoots. Moreover, Si and Se application improved the levels of reducing sugar, soluble protein, and vitamin C, while reducing nitrite content and Cd bioavailability. Furthermore, the experimental results showed that the combination of Si and Se not only increased the abundance of core rhizosphere microorganisms, but also stimulated the activity of soil enzymes, which effectively limited the migration of Cd in the soil. These findings provided valuable insights into the effective mitigation of soil Cd toxicity to plants and also the potential applications in improving plant quality and safety.

Mechanisms of Arbuscular Mycorrhizal Fungi Increasing Silicon Uptake by Rice

Arbuscular mycorrhizal fungi (AMF) influence silicon (Si) uptake by plants, but the mechanisms remain unclear. This study investigated the mechanisms of AMF-mediated Si uptake by rice, a model Si-accumulating plant, and explored the tripartite interactions among AMF, Si, and phosphorus (P). AMF inoculation increased shoot Si content by 97% when supplied with silicic acid and by 29% with calcium silicate and upregulated expression of Si transporters Lsi1 and Lsi2 in roots. Supplying Si only to AMF hyphae increased the root Si content by 113%, indicating direct Si uptake by hyphae. Mechanisms of AMF-induced Si uptake were elucidated: 1) direct Si uptake by hyphae, 2) increased silicate dissolution, and 3) upregulation of Si transporters. Silicon application also increased AMF colonization by 28%, and the absence of interactions was observed on P uptake. Altogether, AMF support Si acquisition and Si fosters AMF colonization in rice, whereas the P uptake depends more on AMF than on Si.

Silicon mitigates salinity effects on sorghum-sudangrass (Sorghum bicolor × Sorghum sudanense) by enhancing growth and photosynthetic efficiency

The aim of this study was to investigate whether silicon (Si) supply was able to alleviate the harmful effects caused by salinity stress on sorghum-sudangrass (Sorghum bicolor ×Sorghum sudanense ), a species of grass raised for forage and grain. Plants were grown in the presence or absence of 150mM NaCl, supplemented or not with Si (0.5mM Si). Biomass production, water and mineral status, photosynthetic pigment contents, and gas exchange parameters were investigated. Special focus was accorded to evaluating the PSI and PSII. Salinity stress significantly reduced plant growth and tissue hydration, and led to a significant decrease in all other studied parameters. Si supply enhanced whole plant biomass production by 50%, improved water status, decreased Na+ and Cl- accumulation, and even restored chlorophyll a , chlorophyll b , and carotenoid contents. Interestingly, both photosystem activities (PSI and PSII) were enhanced with Si addition. However, a more pronounced enhancement was noted in PSI compared with PSII, with a greater oxidation state upon Si supply. Our findings confirm that Si mitigated the adverse effects of salinity on sorghum-sudangrass throughout adverse approaches. Application of Si in sorghum appears to be an efficient key solution for managing salt-damaging effects on plants.

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.

Nitrogen and Silicon Contribute to Wheat Defense's to Pyrenophora tritici-repentis, but in an Independent Manner

Nitrogen (N) and silicon (Si) are mineral elements that have shown a reduction in the damage caused by tan spot (Pyrenophora tritici-repentis (Ptr)) in wheat. However, the effects of these elements were studied separately, and the N and Si interaction effect on wheat resistance to tan spot remains elusive. Histocytological and biochemical defense responses against Ptr in wheat leaves treated with Si (+Si) at low (LN) and high N (HN) inputs were investigated. Soil amendment with Si reduced the tan spot severity in 18% due to the increase in the leaf Si concentration (around 30%), but it was affected by the N level used. The superoxide dismutase (SOD) activity was higher in +Si plants and inoculated with Ptr, leading to early and higher H2O2 and callose accumulation in wheat leaf. Interestedly, phenylalanine ammonia-lyase (PAL) activity was induced by the Si supplying, being negatively affected by the HN rate. Meanwhile, catalase (CAT), and peroxidase (POX) activities showed differential response patterns according to the Si and N rates used. Tan spot severity was reduced by both elements, but their interaction does not evidence synergic effects in this disease's control. Wheat plants from -Si and HN and +Si and LN treatments recorded lower tan spot severity.

Enhancing Salt Stress Tolerance in Tomato (Solanum lycopersicum L.) through Silicon Application in Roots

Soil salinization poses a significant threat to agricultural productivity, necessitating innovative agronomic strategies to mitigate its impact. This study focuses on improving salt stress resistance in tomato plants through the application of silicon (Si) in roots. A greenhouse experiment was carried out under normal conditions (control, and 1 and 4 mM Si) and under salinity stress (salt control, and 1 and 4 mM Si). Various parameters were analyzed in leaves and roots. Under normal conditions, tomato plants grown in non-saline conditions exhibited some toxicity when exposed to Na2SiO3. As for the experiments under salt stress conditions, Si mitigated oxidative damage, preserving root cell membrane integrity. The concentration of malondialdehyde was reduced by 69.5%, that of proline was reduced by 56.4% and there was a 57.6% decrease in catalase activity for tomato plants treated with 1 mM Si under salt stress. Furthermore, Fe uptake and distribution, under salt conditions, increased from 91 to 123 mg kg-1, the same concentration as that obtained for the normal control. In all cases, the lower dose produced better results under normal conditions than the 4 mM dose. In summary, this research provides a potential application of Si in non-fertigated crop systems through a radicular pathway.

Equisetum arvense as a silica fertilizer

The aim was to use the agricultural weed and silica (Si) hyperaccumulator Equisetum arvense as Si fertilizer in plant cultivation. We investigated (1) the Si uptake in various Equisetum species, (2) where Si accumulates in the Equisetum plant, (3) processing methods to release as much Si as possible from dried, ground E. arvense plants and (4) which treatment yields gives the highest uptake of Si in young wheat plants cultivated in soil containing ground E. arvense. The results showed that E. arvense containes 22% Si and was among the best Si accumulators. Equisetum arvense accumulates Si as both soluble and firmly bound fractions. Amorphous silica (SiO2) accumulates in the outer cell walls of epidermis of the entire plant. Regarding the processing method, a longer treatment time, greater concentration of Equisetum, boiling, and the addition of sodium bicarbonate increased the Si availability in ground, dried E. arvense. The addition of untreated, ground, dried E. arvense to the soil, corresponding to 160 kg Si ha-1, increased the available Si in the soil and the Si uptake in wheat plants by five-fold, compared with the control. Boiling the ground E. arvense increased the Si uptake by 10 times, and the of sodium bicarbonate increased the availability and uptake by 40 times, compared with the control. In conclusion, dried, ground E. arvense can be used as a Si fertilizer as is, after boiling for a slightly better effect, or with sodium bicarbonate (up to a similar amount as the ground material) for best effect.

The Beneficial Effects of Soluble Silicon Fertilizer in Dendrobium Orchids: Silicon-Augmented Resistance against Damage by Insect Pests and Fungal Pathogens

The effects of soluble silicon fertilization on monocots and dicots have been widely studied. However, little is known regarding its effects on protecting epiphytes against insect and fungal pests. The efficacy of silicon fertilizer to reduce damage by thrips pest complexes, namely: Thrips palmi Karny, Frankliniella occidentalis Pergande, Chaetanaphothrips orchidii Moulton, and Chaetanaphothrips signipennis Bagnall (Thysanoptera: Thripidae), and the fungal pathogens: Botrytis cinerea Persoon (Helotiales: Sclerotiniaceae) and Fusarium spp. Link (Hypocreales: Nectriaceae) was examined during a nine-month greenhouse trial in Hawaii. The trial assessed yield, quality, and pest damage across three common varieties of dendrobiums. All replicates received additional soluble silicon fertilizer applications alternating weekly between soil drench and foliar (50 mg Si/plant) applications. Yield, quality, and spray length, pest damage, plant vigor, SPAD, and leaf temperature were measured. Data were analyzed using a generalized linear model (glm) with repeated measures followed by post-hoc pair-wise comparisons in R, version 4.3.1. Treatment effects were significant at p < 0.001 for the majority of the explanatory variables including: marketable yield, spray length, thrips damage, and fungal damage. Overall, the lavender variety ('Uniwai Supreme') benefited the most from silicon applications with a 73.0% increase in marketable yield, compared to the white variety ('Uniwai Mist'), which had an increase of 50.6% marketable sprays in contrast to its untreated control. Si benefits conferred to the purple variety ('Uniwai Royale') were intermediate to the lavender and white varieties. Although the magnitude of Si benefits varied among the varieties, all dendrobium varieties significantly benefited from silicon fertilization.

Co-foliar application of zinc and nano-silicon to rice helps in reducing cadmium exposure risk: Investigations through in-vitro digestion with human cell line bioavailability assay

Foliar application of zinc (Zn) or silicon nanoparticles (Si-NPs) may exert regulatory effects on cadmium (Cd) accumulation in rice grains, however, their impact on Cd bioavailability during human rice consumption remains elusive. This study comprehensively investigated the application of Zn with or without Si-NPs in reducing Cd accumulation in rice grains as well to exactly evaluate the potential risk of Cd exposure resulting from the rice consumption by employing field experiment as well laboratory bioaccessibility and bioavailability assay. Sole Zn (ZnSO4) or in combination with Si (ZnSO4 +Si and ZnO+Si) efficiently lowered the Cd concentration in rice grains. However, the impact of bioaccessible (0.1215-0.1623 mg kg-1) and bioavailable Cd (0.0245-0.0393 mg kg-1) during simulated human rice consumption depicted inconsistent trend. The straw HCl-extractable fraction of Cd (FHCl-Cd) exhibited a significant correlation with total, bioaccessible, and bioavailable Cd in grains, indicating the critical role of FHCl-Cd in Cd accumulation and translocation from grains to human. Additionally, foliar spraying of Zn+Si raised the nutritional value of rice grains, leading to increased protein content and reduced phytic acid concentration. Overall, this study demonstrates the potential of foliar application of ZnSO4 +Si in mitigating the Cd levels in rice grains and associated health risks upon consumption.

The adsorption-diffusion model and biomimetic simulation reveal the switchable roles of silicon in regulating toxic metal uptake in rice roots

Soil contamination by heavy metals has become a serious threat to global food security. The application of silicon (Si)-based materials is a simple and economical method for producing safe crops in contaminated soil. However, the impact of silicon on the heavy-metal concentration in plant roots, which are the first line in the chain of heavy-metal entering plants and causing stress and the main site of heavy-metal deposition in plants, remains puzzling. We proposed a process-based model (adsorption-diffusion model) to explain the results of a collection of 28 experiments on alleviating toxic metal stress in plants by Si. Then we evaluated the applicability of the model in Si-mitigated trivalent chromium (Cr[III]) stress in rice, taking into account variations in experimental conditions such as Cr(III) concentration, stress duration, and Si concentration. It was found that the adsorption-diffusion model fitted the experimental data well (R2 > 0.9). We also verified the binding interaction between Si and Cr in the cell wall using SEM-EDS and XPS. In addition, we designed a simplified biomimetic device that simulated the Si in cell wall to analyze the dual-action switch of Si from increasing Cr(III) adsorption to blocking Cr(III) diffusion. We found that the adsorption of Cr(III) by Si decreased from 58% to 7% as the total amount of Cr(III) increased, and finally the diffusion blocking effect of Si dominated. This study deepens our understanding of the role of Si in mitigating toxic metal stress in plants and is instructive for the research and use of Si-based materials to improve food security.

Silicon nanoparticles in sustainable agriculture: synthesis, absorption, and plant stress alleviation

Silicon (Si) is a widely recognized beneficial element in plants. With the emergence of nanotechnology in agriculture, silicon nanoparticles (SiNPs) demonstrate promising applicability in sustainable agriculture. Particularly, the application of SiNPs has proven to be a high-efficiency and cost-effective strategy for protecting plant against various biotic and abiotic stresses such as insect pests, pathogen diseases, metal stress, drought stress, and salt stress. To date, rapid progress has been made in unveiling the multiple functions and related mechanisms of SiNPs in promoting the sustainability of agricultural production in the recent decade, while a comprehensive summary is still lacking. Here, the review provides an up-to-date overview of the synthesis, uptake and translocation, and application of SiNPs in alleviating stresses aiming for the reasonable usage of SiNPs in nano-enabled agriculture. The major points are listed as following: (1) SiNPs can be synthesized by using physical, chemical, and biological (green synthesis) approaches, while green synthesis using agricultural wastes as raw materials is more suitable for large-scale production and recycling agriculture. (2) The uptake and translocation of SiNPs in plants differs significantly from that of Si, which is determined by plant factors and the properties of SiNPs. (3) Under stressful conditions, SiNPs can regulate plant stress acclimation at morphological, physiological, and molecular levels as growth stimulator; as well as deliver pesticides and plant growth regulating chemicals as nanocarrier, thereby enhancing plant growth and yield. (4) Several key issues deserve further investigation including effective approaches of SiNPs synthesis and modification, molecular basis of SiNPs-induced plant stress resistance, and systematic effects of SiNPs on agricultural ecosystem.

Silicon improves root functioning and water management as well as alleviates oxidative stress in oilseed rape under drought conditions

Introduction

The aim of our study was to examine how silicon regulates water uptake by oilseed rape roots under drought conditions and which components of the antioxidant system take part in alleviating stress-induced ROS generation in the roots.

Methods

The study analyzed mainly the changes in the roots and also some changes in the leaves of oilseed rape plants, including total silicon content, relative water content, osmotic potential, stomatal conductance, abscisic acid level, the accumulation of BnPIP1, BnPIP2-1-7 and BnTIP1 aquaporins, and the activity of antioxidant enzymes.

Results and discussion

It was shown that plants growing in well-watered conditions and supplemented with silicon accumulate smaller amounts of this element in the roots and also have higher relative water content in the leaves compared to the control plants. It was demonstrated for the first time that BnTIP1 accumulation in oilseed rape roots is reduced under drought compared to wellwatered plants, and that this effect is intensified in plants supplemented with silicon. In addition, it was shown that silicon supplementation of oilseed rape increases catalase activity in the roots, which correlates with their high metabolic activity under drought and ultimately stimulates their growth. It was shown that silicon improves water balance in oilseed rape plants subjected to drought stress, and that an important role in these processes is played by tonoplast aquaporins. In addition, it was demonstrated that silicon reduces oxidative stress in roots under drought conditions by increasing the activity of catalase.

Growth Enhancement and Resistance of Banana Plants to Fusarium Wilt Disease as Affected by Silicate Compounds and Application Frequency

The amendment of soils with silicate (Si) compounds is essential to promote growth performance and control Fusarium wilt disease in bananas. Two successive greenhouse trials were conducted at the experimental farm of the University of Putra Malaysia. The treatments were arranged in split plots using a randomized complete block design (RCBD) with four replicates to investigate the effects of Si compounds and application frequency on controlling FOC. Si compounds were used at a constant concentration of 0.1%: T0 (control), T1 (13% SiO2:20% K2O), T2 (26.6% SiO2:13.4% K2O) and T3 (36.2% SiO2:17% Na2O). There were three application frequencies by day intervals (DI): 0DI (without any application), 7DI (12× within 12 weeks after transplanting (WAT)), 15DI (6× within 12 WAT) and 30DI (3× within 12 WAT). From these findings, we observed that the photosynthesis rate started to increase from 10.6 to 19.4 µmol CO2 m-2s-1, when the total chlorophyll content started to increase from 3.85 to 7.61 mgcm-2. The transpiration rate started to increase from a value of 1.94 to 4.31 mmol H2O m-2s-1, when the stomata conductance started to increase from 0.237 to 0.958 mmol m-2s-1. The proline content started to increase from 22.89 to 55.07 µmg-1, when the relative water content started to increase from 42.92 to 83.57%.

A New Type of Quantum Fertilizer (Silicon Quantum Dots) Promotes the Growth and Enhances the Antioxidant Defense System in Rice Seedlings by Reprogramming the Nitrogen and Carbon Metabolism

To promote the growth and yield of crops, it is necessary to develop an effective silicon fertilizer. Herein, a new type of 2 nm silicon quantum dot (SiQD) was developed, and the phenotypic, biochemical, and metabolic responses of rice seedlings treated with SiQDs were investigated. The results indicated that the foliar application of SiQDs could significantly improve the growth of rice seedlings by increasing the uptake of nutrient elements and activating the antioxidative defense system. Furthermore, metabolomics revealed that the supply of SiQDs could significantly up-regulate several antioxidative metabolites (oxalic acid, maleic acid, glycine, lysine, and proline) by reprogramming the nitrogen- and carbon-related biological pathways. The findings provide a new strategy for developing an effective and promising quantum fertilizer in agriculture.