One-step construction of multiplexed enzymatic biosensors using light-addressable electrochemistry on a single silicon photoelectrode

The multiplexed detection of metabolites in parallel within a single biosensor plate is sufficiently valuable but also challenging. Herein, we combine the inherent light addressability of silicon with the high selectivity of enzymes, for the construction of multiplexed photoelectrochemical enzymatic biosensors. To conduct a stable electrochemistry and reagentless biosensing on silicon, a new strategy involving the immobilization of both redox mediators and enzymes using an amide bond-based hydrogel membrane was proposed. The membrane characterization results demonstrated a covalent coupling of ferrocene mediator to hydrogel, in which the mediator acted as not only a signal generator but also a renewable sacrifice agent. By adding corresponding enzymes on different spots of hydrogel membrane modified silicon and recording local photocurrents with a moveable light pointer, this biosensor setup was used successfully to detect multiple metabolites, such as lactate, glucose, and sarcosine, with good analytical performances. The limits of detection of glucose, sarcosine and lactate were found to be 179 μM, 16 μM, and 780 μM with the linear ranges of 0.5-2.5 mM, 0.3-1.5 mM, and 1.0-3.0 mM, respectively. We believe this proof-of-concept study provides a simple and rapid one-step immobilization approach for the fabrication of reagentless enzymatic assays with silicon-based light-addressable electrochemistry.

Yolk shell structured YS-Si@N-doped carbon derived from covalent organic frameworks for enhanced lithium storage

Silicon (Si) has ultra-high theoretical capacity (4200 mAh g-1) and accordingly is widely studied as anode materials for lithium-ion batteries (LIBs). However, its huge volume expansion during charging/discharging is a fatal challenge. The preparation of Si-based composite materials with yolk shell structure is the key to solving the Si volume expansion. Here, N-doped carbon-coated Si nanoparticles (SiNPs) nanocomposites (YS-Si@NC-60) with yolk shell structure derived from covalent organic frameworks (COFs) was prepared. N-doped carbon shells derived from COFs not only maintain the well-ordered nanosized pores of COFs, which facilitates the transport of Li+ to contact with internal SiNPs, but also provide more extra active sites for Li+ storage. Most importantly, the internal void can effectively alleviate the damage effect of SiNPs volume expansion. The obtained YS-Si@NC-60 as a LIBs anode show high cyclic stability and Li+ storage performances. At 0.1 A g-1, the capacity is 1446 mAh g-1 after 110 cycles, and initial coulomb efficiency is as high as 82.2 %. The excellent performance can be attributed to the unique yolk shell structure. This simple and template-free strategy provides a new idea for preparing Si-C nanocomposites with yolk shell structure.

A nine-month repeat-dose intravaginal ring (Ovaprene) irritation study in sheep

OBJECTIVES

Ovaprene is a novel, investigational, intravaginal hormone-free monthly ring contraceptive designed for use in women of reproductive age to be worn over multiple weeks (one menstrual cycle). The objective of this work was to evaluate the safety of Ovaprene during a nine-month repeat-dose sheep study.

STUDY DESIGN

In addition to traditional safety endpoints such as histopathological evaluation of the sheep female reproductive tract, vaginal fluids were collected and tested for released iron over time. Also, the amount of iron in the rings was assessed following removal, and serum iron levels were measured. There were four sheep in each group (Ovaprene group and sham group).

RESULTS

There were no macroscopic clinical findings. There was minimal to mild, mixed or mononuclear cell infiltration present in all levels of vagina (cranial, mid, and caudal) from all animals including sham controls based on post-study necropsy. The female reproductive tract from animals treated with the Ovaprene ring was comparable to the sham controls. The concentrations of serum iron in sheep treated with Ovaprene ring were similar compared to a sham treated animal. The average amount of ferrous gluconate released from Ovaprene over the 29-day period of use was 175 mg of the approximately 512 mg nominally loaded into the rings.

CONCLUSIONS

Overall, the Ovaprene devices were well-tolerated in female sheep.

IMPLICATIONS

This study should support a chronic (e.g., one year) contraceptive efficacy study in women.

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.

Cytokinin and indole-3-acetic acid crosstalk is indispensable for silicon mediated chromium stress tolerance in roots of wheat seedlings

The rising heavy metal contamination of soils imposes toxic impacts on plants as well as other life forms. One such highly toxic and carcinogenic heavy metal is hexavalent chromium [Cr(VI)] that has been reported to prominently retard the plant growth. The present study investigated the potential of silicon (Si, 10 µM) to alleviate the toxicity of Cr(VI) (25 µM) on roots of wheat (Triticum aestivum L.) seedlings. Application of Si to Cr(VI)-stressed wheat seedlings improved their overall growth parameters. This study also reveals the involvement of two phytohormones, namely auxin and cytokinin and their crosstalk in Si-mediated mitigation of the toxic impacts of Cr(VI) in wheat seedlings. The application of cytokinin alone to wheat seedlings under Cr(VI) stress reduced the intensity of toxic effects of Cr(VI). In combination with Si, cytokinin application to Cr(VI)-stressed wheat seedlings significantly minimized the decrease induced by Cr(VI) in different parameters such as root-shoot length (10.8% and 13%, respectively), root-shoot fresh mass (11.3% and 10.1%, respectively), and total chlorophyll and carotenoids content (13.4% and 6.8%, respectively) with respect to the control. This treatment also maintained the regulation of proline metabolism (proline content, and P5CS and PDH activities), ascorbate-glutathione (AsA-GSH) cycle and nutrient homeostasis. The protective effect of Si and cytokinin against Cr(VI) stress was minimized upon supplementation of an inhibitor of polar auxin transport- 2,3,5-triiodobenzoic acid (TIBA) which suggested a potential involvement of auxin in Si and cytokinin-mediated mitigation of Cr(VI) toxicity. The exogenous addition of a natural auxin - indole-3-acetic acid (IAA) confirmed auxin is an active member of a signaling cascade along with cytokinin that aids in Si-mediated Cr(VI) toxicity alleviation as IAA application reversed the negative impacts of TIBA on wheat roots treated with Cr(VI), cytokinin and Si. The results of this research are also confirmed by the gene expression analysis conducted for nutrient transporters (Lsi1, CCaMK, MHX, SULT1 and ZIP1) and enzymes involved in the AsA-GSH cycle (APX, GR, DHAR and MDHAR). The overall results of this research indicate towards possible induction of a crosstalk between cytokinin and IAA upon Si supplementation which in turn stimulates physiological, biochemical and molecular changes to exhibit protective effects against Cr(VI) stress. Further, the information obtained suggests probable employment of Si, cytokinin and IAA alone or combined in agriculture to maintain plant productivity under Cr(VI) stress and data regarding expression of key genes can be used to develop new crop varieties with enhanced resistance against Cr(VI) stress together with its reduced load in seedlings.

Influence of Silicon Supplementation on Growth, Immunity, Antioxidant, Hormonal Profile and Bone Health Biomarkers in Pre-ruminant Crossbred Calves

Silicon (Si), a newer trace element, is believed to be important for healthy bone formation and to decrease bone resorption, improving the quality of bone by manipulating several hormones and enzymes. Therefore, the current investigation was conducted to determine the impact of Si supplementation on growth, immunity, antioxidant, hormonal profile and biomarkers of bone health in pre-ruminant crossbred calves. Twenty-four crossbred calves (5-7 days) were selected on the basis of their body weight (BW 31.65 ± 0.46 kg) and divided into 4 groups (n = 6) and fed as per ICAR (2013) feeding standards except that these were additionally supplemented with 0 (Si0), 50 (Si50), 100 (Si100) and 150 (Si150) mg of Si/kg dry matter (DM) in four respective groups for 90 days. Every month, peripheral blood samples were drawn (0, 30, 60 and 90 days post supplementing with Si) and analysed for antioxidant status, hormonal profile and bone health biomarkers. It is reported that dietary Si supplementation improved (P < 0.05) net body weight gain (kg), average daily gain (g) and average dry matter intake (kg), whereas feed intake (kg/100 kg BW), was not altered due to Si supplementation. Structural growth measurements were significantly higher (P < 0.05) in Si100 and Si150 groups as compared to Si50 and control groups. However, immune response (humoral as well as cell-mediated immunity), erythrocytic antioxidant enzymes (superoxide dismutase, SOD, glutathione peroxidase, GPx and catalase), plasma ferric reducing total antioxidant power (FRAP) activity and the plasma concentration of total immunoglobulins (TIg) remained unaffected by Si supplementation. Silicon increased (P < 0.05) the concentration of plasma growth hormone (GH), vitamin D3, bone alkaline phosphatase (BALP) and osteocalcin (OCN) in Si100 and Si150 groups, but the levels of calcitonin, parathyroid hormone (PTH) and hydroxyproline (HYP) remained similar among all the groups. As a result of the current investigation, it can be inferred that the inclusion of 100 and 150 mg of Si/kg DM was effective in improving the growth performance, growth hormone, vitamin D3 and bone health status in pre-ruminant calves. However, supplementation of 150 mg of Si/kg DM had no additional benefit; therefore 100 mg of Si/kg DM is the optimum level of Si supplementation in pre-ruminant calves.

Rice physical defenses and their role against insect herbivores

MAIN CONCLUSION

Understanding surface defenses, a relatively unexplored area in rice can provide valuable insight into constitutive and induced defenses against herbivores. Plants have evolved a multi-layered defense system against the wide range of pests that constantly attack them. Physical defenses comprised of trichomes, wax, silica, callose, and lignin, and are considered as the first line of defense against herbivory that can directly affect herbivores by restricting or deterring them. Most studies on physical defenses against insect herbivores have been focused on dicots compared to monocots, although monocots include one of the most important crops, rice, which half of the global population is dependent on as their staple food. In rice, Silica is an important element stimulating plant growth, although Silica has also been found to impart resistance against herbivores. However, other physical defenses in rice including wax, trichomes, callose, and lignin are less explored. A detailed exploration of the morphological structures and functional consequences of physical defense structures in rice can assist in incorporating these resistance traits in plant breeding and genetic improvement programs, and thereby potentially reduce the use of chemicals in the field. This mini review addresses these points with a closer look at current literature and prospects on rice physical defenses.

Well-Dispersed Bi nanoparticles for promoting the lithium storage performance of Si Anode: Effect of the bridging Bi nanoparticles

Silicon (Si) is considered a promising anode material for lithium-ion batteries (LIBs) due to its high theoretical specific capacity of up to 4200 mAh/g. However, the poor cycling and rate performances of Si induced by the low intrinsic electronic conductivity and large volume expansion during the lithiation/delithiation process limit its practical application. Herein, a novel silicon/bismuth@nitrogen-doped carbon (Si/Bi@NC) composite with nanovoids was synthesized and investigated as an advanced anode material for LIBs. In such a structure, ultrafine bismuth nanoparticles coupled with an N-doped carbon layer were introduced to modify the surface of Si nanoparticles. Subsequently, the lithiated LixBi has excellent high ionic conductivity and acts as a fast transport bridge for lithium ions. The introduced carbon coating layer and nanovoids can buffer the volume expansion of Si during the lithiation/delithiation process, thus maintaining structural stability during the cycling process. As a result, the Si/Bi@NC composite exhibits excellent electrochemical performance, providing a relatively high capacity of 955.8 mAh/g at 0.5 A/g after 450 cycles and excellent rate performance with a high capacity of 477.8 mAh/g even at 10.0 A/g. Furthermore, the assembled full cell with LiFePO4 as cathode and pre-lithium Si/Bi@NC as anode can provide a high capacity of 138.8 mAh/g at 1C after 90 cycles, exhibiting outstanding cycling performance.

Preparation and characterization of green silicon nanoparticles and their effects on growth and lead (Pb) accumulation in maize (Zea mays L.)

The excessive accumulation of heavy metals, particularly lead (Pb) in agricultural soils, is a growing problem worldwide and needs urgent attention. This study aimed to prepare green silicon (Si) NPs using extract of Chenopodium quinoa leaves and evaluated their effects on Pb uptake and growth of maize (Zea mays L.). The results indicated that Pb exposure negatively affected the growth and chlorophyll contents of maize varieties, while SiNPs positively affected these attributes. Pb alone increased the electrolyte-leakage (EL), hydrogen-peroxide (H2O2) and selected antioxidant enzyme activities in leaves, whereas SiNPs decreased EL and H2O2 concentrations and further enhanced the enzyme activities as compared to their respective treatments without SiNPs. Pb-only treatments led to an increase in Pb concentrations and total Pb uptake in both shoots and roots. In contrast, SiNPs resulted in reduced Pb concentrations, with a concurrent decrease in total Pb uptake in shoots compared to the control treatment. The findings demonstrated that foliar application of SiNPs can mitigate the toxic effects of Pb in maize plants by triggering the antioxidant enzyme system and reducing the oxidative stress. Taken together, SiNPs have the potential to enhance maize production in Pb-contaminated soils. However, future research and application efforts should prioritize key aspects such as optimizing NPs synthesis, understanding positive mechanisms of green-synthesized NPs, and conducting multiple crop tests and real-world field trials.

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.

Structural assessment of OsNIP2;1 highlighted critical residues defining solute specificity and functionality of NIP class aquaporins

INTRODUCTION

Nodulin-26-like intrinsic proteins (NIPs) are integral membrane proteins belonging to the aquaporin family, that facilitate the transport of neutral solutes across the bilayer. The OsNIP2;1 a member of NIP-III class of aquaporins is permeable to beneficial elements like silicon and hazardous arsenic. However, the atomistic cross-talk of these molecules traversing the OsNIP2;1 channel is not well understood.

OBJECTIVE

Due to the lack of genomic variation but the availability of high confidence crystal structure, this study aims to highlight structural determinants of metalloid permeation through OsNIP2;1.

METHODS

The molecular simulations, combined with site-directed mutagenesis were used to probe the role of specific residues in the metalloid transport activity of OsNIP2;1.

RESULTS

We drew energetic landscape of OsNIP2;1, for silicic and arsenous acid transport. Potential Mean Force (PMF) construction illuminate three prominent energetic barriers for metalloid passage through the pore. One corresponds to the extracellular molecular entry in the channel, the second located on ar/R filter, and the third size constriction in the cytoplasmic half. Comparative PMF for silicic acid and arsenous acid elucidate a higher barrier for silicic acid at the cytoplasmic constrict resulting in longer residence time for silicon. Furthermore, our simulation studies explained the importance of conserved residues in loop-C and loop-D with a direct effect on pore dynamics and metalloid transport. Next we assessed contribution of predicted key residues for arsenic uptake, by functional complementation in yeast. With the aim of reducing arsenic uptake while maintaining beneficial elements uptake, we identified novel OsNIP2;1 mutants with substantial reduction in arsenic uptake in yeast.

CONCLUSION

We provide a comprehensive assessment of pore lining residues of OsNIP2;1 with respect to metalloid uptake. The findings will expand mechanistic understanding of aquaporin's metalloid selectivity and facilitate variant interpretation to develop novel alleles with preference for beneficial metalloid species and reducing hazardous ones.

Silicon reduces toxicity and accumulation of arsenic and cadmium in cereal crops: A meta-analysis, mechanism, and perspective study

Arsenic (As) and cadmium (Cd) are two toxic metal(loid)s that pose significant risks to food security and human health. Silicon (Si) has attracted substantial attention because of its positive effects on alleviating the toxicity and accumulation of As and Cd in crops. However, our current knowledge of the comprehensive effects and detailed mechanisms of Si amendment is limited. In this study, a global meta-analysis of 248 original articles with over 7000 paired observations was conducted to evaluate Si-mediated effects on growth and As and Cd accumulation in rice (Oryza sativa L.), wheat (Triticum aestivum L.), and maize (Zea mays L.). Si application increases the biomass of these crops under As and/or Cd contamination. Si amendment also decreased shoot As and Cd accumulation by 24.1 % (20.6 to 27.5 %) and 31.9 % (29.0 to 31.9 %), respectively. Furthermore, the Si amendment reduced the human health risks posed by As (2.6 %) and Cd (12.9 %) in crop grains. Si-induced inhibition of Cd accumulation is associated with decreased Cd bioavailability and the downregulation of gene expression. The regulation of gene expression by Si addition was the driving factor limiting shoot As accumulation. Overall, our analysis demonstrated that Si amendment has great potential to reduce the toxicity and accumulation of As and/or Cd in crops, providing a scientific basis for promoting food safety globally.

Metagenomic and biochemical analyses reveal the potential of silicon to alleviate arsenic toxicity in rice (Oryza sativa L.)

Arsenic (As) pollution in agricultural systems poses a serious threat to crop productivity and food safety. Silicon (Si) has been reported to mitigate toxic effects of heavy metals in plants. However, the mechanisms behind Si-mediated alleviation of As toxicity in rice (Oryza sativa L.) remain poorly understood. Here, we performed metagenomic and biochemical analyses to investigate the potential of Si in alleviating As toxicity to rice plants. As exposure reduced plant growth, chlorophyll contents, antioxidant enzyme levels and soil enzymes activity, while increasing reactive oxygen species (ROS) activity and inducing alterations in the rhizosphere microbiome of rice seedlings. Silicon amendments enhanced rice growth (24%), chlorophyll a (25%), and chlorophyll b (26.7%), indicating enhanced photosynthetic capacity. Si amendments also led to the upregulation of antioxidant enzymes viz., superoxide dismutase (15.4%), and peroxidase (15.6%), resulting in reduced ROS activity and oxidative stress compared to the As-treated control. Furthermore, Si treatment reduced uptake and translocation of As in rice plants, as evidenced by the analysis of elemental contents. Microscopic examination of leaf and root ultrastructure showed that Si mitigated As-induced cellular damage and maintained normal morphology. Metagenomic analysis of the rice rhizosphere microbiome revealed that Si application modulated composition and diversity of microbial communities e.g., Proteobacteria, Actinobacteria, and Firmicutes. Additionally, Si amendments upregulated the relative expression levels of OsGSH, OsPCs, OsNIP1;1 and OsNIP3;3 genes, while the expression levels of the OsLis1 and OsLis2 genes were significantly downregulated compared with As-treated rice plants. Overall, these findings contribute to our understanding of Si-mediated plant resilience to As stress and offer potential strategies for sustainable agriculture in As-contaminated regions.

Asymmetric metamaterial sandwich structure with NIM characteristics for THz imaging application

This study presented a unique, miniaturised asymmetric interconnected vertical stripe (IVS) design for terahertz (THz) frequency applications. Therefore, this research aimed to achieve a frequency response of 0 to 10 THz using a 5 × 5 µm2 Silicon (Si) substrate material. Meanwhile, various parametric examinations were conducted to investigate variations in the performance. For example, the unit cell selection process was carefully examined by using various design structures and modifying the structure by adding split gaps and connecting bars between vertical stripes. Furthermore, the proposed sandwich structure design was used to compute the absorbance and reflectance properties. All the analytical examinations were executed utilising the Computer Simulation Technology (CST) 2019 software. The introduced IVS metamaterial exhibits negative index behaviour and has a single resonance frequency of 5.23 THz with an acceptable magnitude of - 24.38 dB. Additionally, the quadruple-layer IVS structure exhibits optimised transmission coefficient behaviour between 3 and 6 THz and 7 to 9 THz, respectively. However, the magnitude of the transmission coefficient increased with the number of material layers. Besides that, the absorbance study shows that using a quadruple-layer structure obtains unique and promising results. Overall, the proposed asymmetric IVS metamaterial design achieves the required performance by using a compact structure rather than extending the dimensions of the design.

Synergistic influence of selenium and silicon supplementation prevents the oxidative effects of arsenic stress in wheat

Influence of supplementation of selenium (Se, 1 and 5 µM) and silicon (Si, 0.1 and 0.5 mM) was investigated in wheat under arsenic (30 µM As) stress. Plants grown under As stress exhibited a significant decline in growth parameters however, Se and Si supplementation mitigated the decline significantly. Treatment of Se and Si alleviated the reduction in the intermediate components of chlorophyll biosynthesis pathway and the content of photosynthetic pigments. Arsenic stressed plants exhibited increased reactive oxygen species accumulation and the NADPH oxidase activity which were lowered significantly due to Se and Si treatments. Moreover, Se and Si supplementation reduced lipid peroxidation and activity of lipoxygenase and protease under As stress. Supplementation of Se and Si significantly improved the antioxidant activities and the content of cysteine, tocopherol, reduced glutathione and ascorbic acid. Treatment of Se and Si alleviated the reduction in nitrate reductase activity. Exogenously applied Se and Si mitigated the reduction in mineral elements and reduced As accumulation. Hence, supplementation of Se and Si is beneficial in preventing the alterations in growth and metabolism of wheat under As stress.

New Aspects of Femtosecond Laser Ablation of Si in Water: A Material Perspective

We report a study of the role of material's conductivity in determining the morphology of nanoparticles and nanostructures produced by ultrafast laser ablation of solids. Nanoparticles and textured surfaces formed by laser ablation display a wide variation in size and morphology depending on the material. In general, these qualities can be grouped as to material type, insulator, semiconductor, or metal; although each has many other different material properties that make it difficult to identify the critical material factor. In this report, we study these nanoparticle/ surface structural characteristics as a function of silicon (Si) resistivity, thus honing-in on this critical parameter and its effects. The results show variations in morphology, optical and non-linear properties of Si nanoparticles. The yield of colloidal Si nanoparticles increased with an increase in the conductivity of Si. Laser-induced periodic surface structures (LIPSS) formed on ablated substrates are also found to be sensitive to the initial conductivity of the material. Further, the laser ablation of Gamma-irradiated Si has been investigated to verify the influence of altered conductivity on the formation of Si nanoparticles. These observations are interpreted using the basic mechanisms of the laser ablation process in a liquid and its intricate relation with the initial density of states and thermal conductivities of the target material.

Silicon nanoparticles (SiNPs) stimulated secondary metabolism and mitigated toxicity of salinity stress in basil (Ocimum basilicum) by modulating gene expression: a sustainable approach for crop protection

The underlying mechanisms through which silicon oxide nanoparticles (SiNPs) can confer salinity resistance to plants are poorly understood. This study explored the efficacy of supplementing nutrient solution with SiNPs (20-30 nm; 10 mg kg-1 soil) to stimulate metabolism and alleviate the risks associated with salinity (0.73 g kg-1 soil) in basil seedlings. For this purpose, variations in photosynthetic indices, proline osmoprotectant, antioxidant markers, phenylpropanoid metabolism, and transcriptional behaviors of genes were investigated. SiNPs increased shoot fresh weight (38%) and mitigated the risk associated with the salinity stress by 14%. SiNPs alleviated the inhibitory effects of salinity on the total chlorophyll concentration by 15%. The highest increase (twofold) in proline content was recorded in the SiNP-treated seedlings grown under salinity. The nano-supplement enhanced the activity of enzymatic antioxidants, including peroxidase (2.5-fold) and catalase (4.7-fold). SiNPs induced the expression of gamma-cadinene synthase (CDS) and caffeic acid O-methyltransferase (COMT) genes by 6.5- and 18.3-fold, respectively. SiNPs upregulated the eugenol synthase (EGS1) and fenchol synthase (FES) genes by six- and nine-fold, respectively. Salinity transcriptionally downregulated the geraniol synthase (GES) gene, while this gene displayed an upward trend in response to SiNPs by eight-fold. The nano-supplement transcriptionally stimulated the R-linalool synthase (LIS) gene by 3.3-fold. The terpinolene synthase (TES) gene displayed a similar trend to that of the GES gene. The highest expression (25-fold) of the phenylalanine ammonia-lyase (PAL) gene was recorded in seedlings supplemented with SiNPs. The physiological and molecular assessments demonstrated that employing SiNPs is a sustainable strategy for improving plant primary/secondary metabolism and crop protection.

Silicon, a quasi-essential element: Availability in soil, fertilizer regime, optimum dosage, and uptake in plants

The essentiality of silicon (Si) has always been a matter of debate as it is not considered crucial for the lifecycles of most plants. But beneficial effects of endogenous Si and its supplementation have been observed in many plants. Silicon plays a pivotal role in alleviating the biotic and abiotic stress in plants by acting as a physical barrier as well as affecting molecular pathways involved in stress tolerance, thus widely considered as "quasi-essential". In soil, most of Si is found in complex forms as mineral silicates which is not available for plant uptake. Monosilicic acid [Si(OH)4] is the only plant-available form of silicon (PAS) present in the soil. The ability of a plant to uptake Si is positively correlated with the PAS concentration of the soil. Since many cultivated soils often lack a sufficient amount of PAS, it has become common practice to supplement Si through the use of Si-based fertilizers in various crop cultivation systems. This review outlines the use of natural and chemical sources of Si as fertilizer, different regimes of Si fertilization, and conclude by identifying the optimum concentration of Si required to observe the beneficial effects in plants. Also, the different mathematical models defining the mineral dynamics for Si uptake at whole plant scale considering various natural factors like plant morphology, mineral distribution, and transporter expression have been discussed. Information provided here will further help in increasing understanding of Si role and thereby facilitate efficient exploration of the element as a fertilizer in crop production.

Silicon a key player to mitigate chromium toxicity in plants: Mechanisms and future prospective

Chromium is a serious heavy metal (HM) and its concentration in plant-soil interface is soaring due to anthropogenic activities, unregulated disposals, and lack of efficient treatments. High concentration of Cr is toxic to ecosystems and human health. Cr stress also diminishes the plant performance by changing the plant's vegetative and reproductive development that ultimately affects sustainable crop production. Silicon (Si) is the second-most prevalent element in the crust of the planet, and has demonstrated a remarkable potential to minimize the HM toxicity. Amending soils with Si mitigates adverse effects of Cr by improving plant physiological, biochemical, and molecular functioning and ensuring better Cr immobilization, compartmentation, and co-precipitation. However, there is no comprehensive review on the role of Si to mitigate Cr toxicity in plants. Thus, in this present review; the discussion has been carried on; 1) the source of Cr, 2) underlying mechanisms of Cr uptake by plants, 3) how Si affects the plant functioning to reduce Cr toxicity, 4) how Si can cause immobilization, compartmentation, and co-precipitation 5) strategies to improve Si accumulation in plants to counter Cr toxicity. We also discussed the knowledge gaps and future research needs. The present review reports up-to-date knowledge about the role of Si to mitigate Cr toxicity and it will help to get better crop productivity in Cr-contaminated soils. The findings of the current review will educate the readers on Si functions in reducing Cr toxicity and will offer new ideas to develop Cr tolerance in plants through the use of Si.

Ecological stoichiometry of C, N, P and Si of Karst Masson pine forests: Insights for the forest management in southern China

Ecological stoichiometry is an effective method to study the stoichiometric relations and laws of elements in biogeochemical cycle, widely used in studies on nutrient cycles, limiting elements and nutrient utilization efficiency in ecosystems. To explore C, N, P, and Si stoichiometric characteristics and reveal these nutrient cycle processes and mechanisms in the karst Masson pine forests, the typical Masson pine forests of the three different stand ages in southern China were selected as the research objects and the C, N, P, and Si stoichiometric characteristics of soil-plant-litter continuum were studied. The followed results and conclusions were obtained: 1) Content range of TOC (total organic carbon), TN (total N), TP (Total P) and TSi (total Si) of the Masson pine forests was 288.31-334.61, 0.34-6.66, 0.11-1.05, and 0.76-11.4 g·kg-1, respectively. And the ratio range of C:N, C:P, C:Si, N:P, N:Si, and P:Si was 49.95-913.57, 99.98-2872.18, 22.48-429.31, 1.85-6.33, 0.17-6.01, and 0.04-0.91, respectively. 2) The significant differences in C, N, P, and Si stoichiometric characteristics were present between different organs or different forest ages. Leaves had the highest N and P content, while roots were the best enriched organ of Si element. Si content and C:Si were obviously correlated with forest age. 3) Significant N limitation was present in the Masson pine forests. And in the young and middle-aged forests, N limitation was more obvious. 4) The litter nutrients mainly came from branches. And the litter decomposed fast, which played an important role in the nutrient return of barren karst soil. The present results not only revealed the stoichiometric characteristics and cycling processes of C, N, P, and Si elements in the Masson pine forests, but also provided important scientific bases for the artificial management of Masson pine plantations in southern China.

Silicon ameliorates cadmium (Cd) toxicity in pearl millet by inducing antioxidant defense system

Cadmium (Cd) stress is a significant environmental pollutant that can negatively impact crop yield and growth, and is a serious global issue. However, silicon (Si) has been shown to have a potential function in alleviating the effects of several abiotic stress conditions on crops, including Cd stress. This study investigated the effectiveness of applying silicon to soil as a method for reducing cadmium toxicity in pearl millet (IP14599) seedlings. Seeds of IP14599 were treated with Si + Cd element which cumulated to a combination of 9 treatments. Different Cd concentration of (0, 200, and 300 mg/kg-1) was taken and manually mixed into a sieved soil prior to planting and Si (0, 100 and 200 mg/kg-1) was selectively introduced till after attaining 12 days of seedling emergence. The physiochemical parameters of Cd stressed plants investigated includes chlorophyll, gas exchange attributes, proline, relative water contents, malondialdehyde (MDA) content and antioxidant enzymes (superoxide dismutase (SOD),catalase (CAT), ascorbate peroxidase (APX), peroxidase (POD). Our result revealed that the metal (Cd) caused serious oxidative impairment thereby reducing photosynthetic performance, increased activity of MDA and Cd content in the roots and leaves of IP14599.In addition, Si increased the growth pattern and antioxidant defense action thereby mitigating the Cd toxicity. The results revealed that at Si 200, Si significantly increased the chlorophyll, carotenoids and plant height at 122 %, 69 % and 128 % under the Cd 200 and Cd 300 mg/kg-1 treatment, respectively. The single treatment at Si100 and Si 200 decreased ROS by 29 %, and 37 % respectively and MDA decreased by 33 % and 43 % in contrast to Cd 200 and 300 treatments, respectively. However, Si200 showed significant increase in the activities of APX 97 %, SOD by 89 %, CAT 35 % and POD 86 % as compared to single Si, Cd or combine Cd + Si treatment. Also, a gradual decline in Cd level in both the leaf and root was present when exposed to high concentrations of Si at Si200 and 300 mg/kg-1. Our findings revealed that Si might significantly increase the capacity to tolerate Cd stress in crop plants. Therefore, the study revealed that Si has the potential to alleviate Cd-induced toxicity by reducing Cd assimilation and enhancing the growth attributes of IP14599 plants.

Unveiling mechanisms of silicon-mediated resistance to chromium stress in rice using a newly-developed hierarchical system

Silicon (Si) has been well-known to enhance plant resistance to heavy-metal stress. However, the mechanisms by which silicon mitigates heavy-metal stress in plants are not clear. In particular, information regarding the role of Si in mediating resistance to heavy-metal stress at a single cell level is still lacking. Here, we developed a hierarchical system comprising the plant, protoplast, and suspension cell subsystems to investigate the mechanisms by which silicon helps to alleviate the toxic effects of trivalent chromium [Cr(III)] in rice. Our results showed that in whole-plant subsystem silicon reduced shoot Cr(III) concentration, effectively alleviating Cr(III) stress in seedlings and causing changes in antioxidant enzyme activities similar to those observed at lower Cr(III) concentrations without silicon added. However, in protoplast subsystem lacking the cell wall, no silicon deposition occurred, leading to insignificant changes in cell survival or antioxidation processes under Cr(III) stress. Conversely, in suspension cell subsystem, silicon supplementation substantially improved cell survival and changes in antioxidant enzyme activities under Cr(III) stress. This is due to the fact that >95% of silicon was on the cell wall, reducing Cr(III) concentration in cells by 7.7%-10.4%. Collectively, the results suggested that the silicon deposited on the cell wall hindered Cr(III) bio-uptake, which consequently delayed Cr(III)-induced changes in antioxidant enzyme activities. This research emphasizes the significance of cell walls in Si-alleviated heavy-metal stress and deepens our understanding of silicon functioning in plants. Furthermore, the hierarchical system has great potential for application in studying the functioning of other elements in plant cell walls.

Foliar spraying of Zn/Si affects Cd accumulation in paddy grains by regulating the remobilization and transport of Cd in vegetative organs

The reduction of cadmium (Cd) accumulation in rice grains through biofortification of essential nutrients like zinc (Zn) and silicon (Si) is an area of study that has gained significant attention. However, there is limited understanding of the mechanism of Zn/Si interaction on Cd accumulation and remobilization in rice plants. This work used a pot experiment to examine the effects of Zn and Si applied singly or in combination on the physiological metabolism of Cd in different rice organs under Cd stress. The results revealed that: Zn/Si application led to a significant decrease in root Cd concentration and reduce the value of Tf Soil-Root in filling stage. The content of phytochelatin (PCs, particularly PC2) and glutathione (GSH) in roots, top and basal nodes were increased with Zn/Si treatment application. Furthermore, Zn/Si treatment promoted the distribution of Cd in cell wall during Cd stress. These findings suggest that Zn/Si application facilitates the compartmentalization of Cd within subcellular structures and enhances PCs production in vegetative organs, thereby reducing Cd remobilization. Zn/Si treatment upregulated the metabolism of amino acid components involved in osmotic regulation, secondary metabolite synthesis, and plant chelating peptide synthesis in vegetative organs. Additionally, it significantly decreased the accumulation of Cd in globulin, albumin, and glutelin, resulting in an average reduction of 50.87% in Cd concentration in milled rice. These results indicate that Zn/Si nutrition plays a crucial role in mitigating heavy metal stress and improving the nutritional quality of rice by regulating protein composition and coordinating amino acid metabolism balance.

Regulation of rhizosphere microenvironment by rice husk ash for reducing the accumulation of cadmium and arsenic in rice

It is important to reduce Cd and As content in brown rice in contaminated paddy soils. We conducted research on the effects of rice husk ash (RHA) on the Cd and As in the rhizosphere microenvironment (soil, porewater, and iron plaque) and measured the Cd, As, and Si content in rice plants. The main elements in RHA were Si (29.64%) and O (69.17%), which had the maximum adsorption capacity for Cd was 42.49 mg/kg and for As was 18.62 mg/kg. Soil pH and available Si content increased, while soil available Cd and As decreased following application of 0.5%-2% RHA. RHA promote the transformation of Cd to insoluble fraction, while As was transformed from a poorly soluble form to a more active one. RHA reduced Cd content and increased Si content in porewater, and reduced As only at the later rice growth stages. RHA increased the amount of iron plaque, thereby decreasing the Cd content in iron plaque, while increased the As content in it. Cd and inorganic As content in brown rice were decreased, to 0.31 mg/kg and 0.18 mg/kg, respectively. The decrease of Cd in brown rice was due to the decrease of Cd mobility in soil, thereby reducing root accumulation, while the decrease of As in brown rice was affected by the transport from roots to stems. Therefore, RHA can be considered as a safe and efficient in-situ remediation amendment for Cd and As co-contaminated paddy soil.

Exogenous application of silicon and selenium improves the tolerance of tomato plants to calcium nitrate stress

Silicon (Si) and selenium (Se) can improve the tolerance of plants to NaCl-induced salt stress. However, few studies are available on their regulatory effects on plants' tolerance to calcium nitrate stress, which often occurs in protected facilities, causing secondary soil salinization. In this study, we report the effects of Si (6 mM) and Se (20 μM) applied separately or in combination on the growth, photosynthesis, oxidative damage, and nitrogen metabolism of tomato plants, as well as fruit quality under calcium nitrate stress. The results showed that applications of Si or Se alone or in combination improved the plant growth and photosynthetic performance and reduced oxidative damage of the stressed plants. Applications of Si and Se did not decrease the calcium accumulation in leaves of the stressed plants. Under calcium nitrate stress, the concentrations of NO3-, NO2- and NH4+ in leaves were significantly increased, while the activities of nitrogen assimilation-related enzymes (including nitrate reductase, nitrite reductase, glutamine synthase, glutamine-2-oxoglutarate aminotransferase and glutamate dehydrogenase) were decreased. Applications of Si and Se, especially their combined treatment, decreased the NO3-, NO2-, and NH4+ concentrations and enhanced the activities of nitrogen assimilation-related enzymes in the stressed plants. Applied Si and Se also decreased the nitrate and titratable acid concentrations and increased vitamin levels in tomato fruits under calcium nitrate stress. It is suggested that Si and Se improved the tomato plant growth and fruit quality under calcium nitrate stress by alleviating oxidative damage and promoting both photosynthesis and nitrogen assimilation.

Uncovering the dominant role of root lignin accumulation in silicon-induced resistance to drought in tomato

The role of lignin accumulation in silicon-induced resistance has not been fully elucidated. Based on the finding that the root cell wall is protected by silicon, this study explored the role of lignin accumulation in silicon-induced drought resistance in tomato. The decreased silicon concentration of the root confirmed the dominant role of lignin accumulation in silicon-induced drought resistance. The lignin monomer content in the root was enhanced by silicon, and was accompanied by the enhancement of drought resistance. Histochemical and transcriptional analyses of lignin showed that lignin accumulation was promoted by silicon under drought stress. In addition, in the root zone, silicon-induced lignin accumulation increased as the distance from the root tip increased under drought stress. Surprisingly, the Dwarf gene was upregulated by silicon in the roots. Micro Tom Dwarf gene mutation and Micro Tom-d + Dwarf gene functional complementation were further used to confirm that Dwarf regulates the spatial accuracy of SHR expression in the root. Therefore, root lignin accumulation plays a dominant role in silicon-induced drought resistance in tomato and the regulation of spatial accuracy of root lignification by silicon under drought stress is through the BR pathway, thereby avoiding the inhibition of root growth caused by root lignification.

Single-Crystal Silicon Nanotubes, Hollow Nanocones, and Branched Nanotube Networks

We report a general approach for the synthesis of single-crystal silicon nanotubes, involving epitaxial deposition of silicon shells on germanium nanowire templates followed by removal of the germanium template by selective wet etching. By exploiting advances in the synthesis of germanium nanowires, we were able to rationally tune the nanotube internal diameters (5-80 nm), wall thicknesses (3-12 nm), and taper angles (0-9°) and additionally demonstrated branched silicon nanotube networks. Field effect transistors fabricated from p-type nanotubes exhibited a strong gate effect, and fluid transport experiments demonstrated that small molecules could be electrophoretically driven through the nanotubes. These results demonstrate the suitability of silicon nanotubes for the design of nanoelectrofluidic devices.

Broadband Tunable Infrared Light Emission from Metal-Oxide-Semiconductor Tunnel Junctions in Silicon Photonics

Broadband near-infrared light emitting tunnel junctions are demonstrated with efficient coupling to a silicon photonic waveguide. The metal oxide semiconductor devices show long hybrid photonic-plasmonic mode propagation lengths of approximately 10 μm and thus can be integrated into an overcoupled resonant cavity with quality factor Q ≈ 49, allowing for tens of picowatt near-infrared light emission coupled directly into a waveguide. The electron inelastic tunneling transition rate and the cavity mode density are modeled, and the transverse magnetic (TM) hybrid mode excitation rate is derived. The results coincide well with polarization resolved experiments. Additionally, current-stressed devices are shown to emit unpolarized light due to radiative recombination inside the silicon electrode.

Solvent Extraction of PDMS Tubing as a New Method for the Capture of Volatile Organic Compounds from Headspace

Polydimethylsiloxane (PDMS) tubing is increasingly being used to collect volatile organic compounds (VOCs) from static biological headspace. However, analysis of VOCs collected using PDMS tubing often deploys thermal desorption, where samples are considered as 'one-offs' and cannot be used in multiple experiments. In this study, we developed a static headspace VOC collection method using PDMS tubing which is solvent-based, meaning that VOC extracts can be used multiple times and can be linked to biological activity. Using a synthetic blend containing a range of known semiochemicals (allyl isothiocyanate, (Z)-3-hexen-1-ol, 1-octen-3-one, nonanal, (E)-anethol, (S)-bornyl acetate, (E)-caryophyllene and pentadecane) with differing chemical and physicochemical properties, VOCs were collected in static headspace by exposure to PDMS tubing with differing doses, sampling times and lengths. In a second experiment, VOCs from oranges were collected using PDMS sampling of static headspace versus dynamic headspace collection. VOCs were eluted with diethyl ether and analysed using gas chromatography - flame ionization detector (GC-FID) and coupled GC - mass spectrometry. GC-FID analysis of collected samples showed that longer PDMS tubes captured significantly greater quantities of compounds than shorter tubes, and that sampling duration significantly altered the recovery of all tested compounds. Moreover, greater quantities of compounds were recovered from closed compared to open systems. Finally, analysis of orange headspace VOCs showed no qualitative differences in VOCs recovered compared to dynamic headspace collections, although quantities sampled using PDMS tubing were lower. In summary, extraction of PDMS tubing with diethyl ether solvent captures VOCs from the headspace of synthetic blends and biological samples, and the resulting extracts can be used for multiple experiments linking VOC content to biological activity.

Silicon and arbuscular mycorrhizal fungi alleviate chromium toxicity in Brassica rapa by regulating Cr uptake, antioxidant defense expression, the glyoxalase system, and secondary metabolites

The potential contribution of silicon (Si) (300 mg kg-1 potash silica) or arbuscular mycorrhizal fungi (AMF) (Rhizophagus irregularis) to reduce chromium toxicity (Cr; 0 and 300 mg kg-1) in Brassica rapa was examined in this work. Under Cr stress, Si and AMF were used separately and in combination (no Si, or AMF, Si, AMF, and Si + AMF). Brassica rapa growth, colonization, photosynthesis, and physio-biochemical characteristics decreased under Cr stress. Oxidative stress was a side effect of Cr stress and was associated with high levels of methylglyoxal (MG), hydrogen peroxide (H2O2), lipid peroxidation (MDA), and maximum lipoxygenase activity (LOX). On the other hand, quantitative real-time PCR analyses of gene expression showed that under Cr stress, the expression of genes for secondary metabolites and antioxidant enzymes was higher than that under the control. The co-application of Si and AMF activated the plant defense system by improving the antioxidative enzymes activities, the potassium citrate and glutathione pool, the glyoxalase system, metabolites, and genes encoding these enzymes under Cr stress. Under the influence of Cr stress, oxidative stress was reduced by the coordinated control of the antioxidant and glyoxalase systems. However, the restricted Cr uptake and root and shoot accumulation of Si and AMF co-applied to only Cr-stressed plants was more significant. In summary, Si and AMF applied together successfully counteract the deleterious effects of Cr stress and restore growth and physio-biochemical characteristics. As a result, the beneficial effects of the combined Si and AMF application may be attributed to mycorrhizae-mediated enhanced Si absorption and metal resistance.

Effects of carbon-silicon structure on photochemical activity of biochars

Biochar has raised increasing concerns because of its great environmental impacts. It is known that the photocatalytic property of biochar is related to its carbon component and dissolved black carbon, but the effect of silicon component is ignored, and the effect of silicon and carbon phases was far less studied. This study systematically explored the photochemistry of silicon-rich and silicon-deficient biochar under light irradiation by using hexavalent chromium (Cr(VI)) and sulfadiazine as representative pollutants for photoreduction and photooxidation, respectively. It was found that biochar had photoreduction activity under the enhancement of electron donors, and 80.1% Cr(VI) can be removed by biochar with crystalline silicon and carbon (i.e., RH900) after 12 h irradiation. Meanwhile after low temperature pyrolysis, biochar with amorphous silicon and carbon (i.e., RH600) had great photooxidation capacity, and 71.90% organic pollutant was degraded within 24 h. The reaction was illustrated by transient photocurrent response, and hydroxyl radical generation measurement, and other tests. A new photochemical mechanism of the synergy between silicon and carbon model was proposed to elucidate the redox reactions of pollutants under the light. Graphitic carbon or crystalline silicon formed under high temperature played a role of valence band which was excited under light irradiation and the effect of electron donors to benefit photoreduction, while amorphous silicon formed under low temperature facilitated photooxidation process by increasing reactive oxygen species concentration. This study provided a gist for biochar production and application in the field of photocatalysis, and contributed to the broader understanding of biochar geochemical behavior in natural sunlit system.

Silicon (Si) mitigates the negative effects of iron deficiency in common bean (Phaseolus vulgaris L.) by improving photosystem activities and nutritional status

Silicon (Si) is the second most abundant element in the Earth's crust after oxygen. Its beneficial impact on crop development and yield, particularly under stressful conditions such as iron (Fe) deficiency, has been well documented. Fe deficiency is a critical constraint that limits crop production globally. The objective of this study was to investigate the effects of silicon (Na2SiO3) on common bean (Phaseolus vulgaris L. 'Coco Rose' variety) under iron-deficient conditions. The common bean plants were subjected to six treatments, which included three sufficient iron treatments (50 μM Fe) each paired with three varying silicon concentrations (0, 0.25, and 0.5 mM Si), and three iron-deficient treatments (0.1 μM Fe) each associated with the same silicon concentrations (0, 0.25, and 0.5 mM Si). The results indicate that iron deficiency had a negative impact on almost all the measured parameters. However, under silicon treatments, especially with 0.5 mM Si, the depressive effects of iron deficiency were significantly mitigated. The addition of 0.5 mM Si alleviated leaf chlorosis and improved biomass production, nutritional status, photosynthetic pigment content, photosynthetic gas exchange, and photosystem (PSI and PSII) activities. Interestingly, a greater beneficial effect of silicon was observed on PSII compared to PSI. This was accompanied by a significant augmentation in leaf iron concentration by 42%. Therefore, by enhancing the photosystem activities and nutritional status, among other mechanisms, silicon is capable of mitigating the adverse effects of iron-deficient conditions, making it a successful and effective solution to cope with this nutritional stress.

Functions of silicon and phytolith in higher plants

Silicon (Si) is abundant in the lithosphere, and previous studies have confirmed that silicon plays an important role in plant growth. Higher plants absorb soluble silicon from soil through roots which is deposited in plant tissues mainly in the form of phytoliths. Based on previous studies, the research progress in silicon and phytoliths in the structural protection, enhancement on photosynthesis and transpiration of plants and plant growth and stress resistance was reviewed. Meanwhile, gaps in phytolith research, including phytolith morphology and function, impact of diverse environmental factors coupling with phytoliths, phytolith characteristics at different stages of plant development and phytoliths in regional vegetation are identified. The paper intends to promote the wider application of phytolith research findings and provides reference for further research on phytoliths.

Efficient genome editing by controlled release of Cas9 ribonucleoprotein in plant cytosol using polymer-modified microneedle array

Direct delivery of genome-editing proteins into plant tissues could be useful in obtaining DNA-free genome-edited crops obviating the need for backcrossing to remove vector-derived DNA from the host genome as in the case of genetically modified organisms generated using DNA vector. Previously, we successfully delivered Cas9 ribonucleoprotein (RNP) into plant tissue by inserting microneedle array (MNA) physisorbed with Cas9 RNPs. Here, to enhance protein delivery and improve genome-editing efficiency, we introduced a bioactive polymer DMA/HPA/NHS modification to the MNA, which allowed strong bonding between the proteins and MNA. Compared with other modifying agents, this MNA modification resulted in better release of immobilized protein in a plant cytosol-mimicking environment. The delivery of Cas9 RNPs in Arabidopsis thaliana reporter plants was improved from 4 out of 17 leaf tissues when using unmodified MNAs to 9 out of 17 when using the polymer-modified MNAs. Further improvements in delivery efficiency can be envisaged by optimizing the polymer modification conditions, which could have significant implications for the development of more effective plant genome editing techniques.

Silicon-phosphorus pathway mitigates heavy metal stress by buffering rhizosphere acidification

Heavy metal pollution threatens food security, and rhizosphere acidification will increase the bioavailability of heavy metals. As a beneficial element in plants, silicon can relieve heavy metal stress. However, less attention has been paid to its effects on plant rhizosphere processes. Here, we show that for Japonica (Nipponbare and Oochikara) and Indica (Jinzao 47) rice cultivars, the degree of root acidification was significantly reduced after silicon uptake, and the total organic carbon, citric acid, and malic acid concentrations in rice root exudates were significantly reduced. We further confirmed the results by q-PCR that the expressions of proton pump and organic acid secretion genes were down-regulated by 35-61 % after silicon treatment. Intriguingly, phosphorus allocation, an intensively studied mechanism of rhizosphere acidification, was altered by silicon treatment. Specifically, among total phosphorus in rice seedlings, the soluble proportion increased from 52.0 % to 61.7 %, while cell wall phosphorus decreased from 48.0 % to 32.3 %. Additionally, silicon-mediated alleviation of rhizosphere acidification has positive effects on relieving heavy metal stress. Simulation revealed that low acidification of the nutrient solution resulted in a decrease in bioavailable heavy metal concentrations, thereby reducing rice uptake. We further confirmed that the impediment of rhizosphere acidification led to free-state Cr3+ in solutions decreasing by 43 % and contributed up to 63 % of silicon's mitigation of Cr(III) stress. Overall, we propose a novel mechanism in which silicon reduces heavy metal absorption by increasing plant soluble phosphorus concentration and buffering rhizosphere acidification. This paper provides a unique insight into the role of silicon in plants and, more importantly, a theoretical reference for the rational application of silicon fertilizer to improve phosphorus utilization efficiency, alleviate heavy metal stress, and balance soil pH.

Comparative effects of silicon and silicon nanoparticles on the antioxidant system and cadmium uptake in tomato under cadmium stress

Cadmium (Cd) pollution is an important threat to agricultural production globally. Silicon (Si) and silicon nanoparticles (Si NPs) can mitigate Cd stress in plants. However, the mechanisms underlying the impacts of Si and Si NPs on Cd resistance, particularly in low-Si accumulators, remain inadequately understood. Accordingly, we conducted a comparative investigation into the roles of Si and Si NPs in regulating the antioxidant system (enzymes and antioxidants) and Cd uptake (influx rate, symplastic and apoplastic pathways) in tomato (a typical low-Si accumulator). The results revealed that Si and Si NPs improved tomato growth under Cd stress, and principal component analysis (PCA) demonstrated that Si NPs were more effective than Si. For oxidative damage, redundancy analysis (RDA) results showed that Si NPs ameliorated oxidative damage in both shoots and roots, whereas Si predominantly alleviated oxidative damage in roots. Simultaneously, Si and Si NPs regulated antioxidant enzymes and nonenzymatic antioxidants with distinct targets and strengths. Furthermore, Si and Si NPs decreased Cd concentration in tomato shoot, root, and xylem sap, while Si NPs induced a more significant decline in shoot and xylem sap Cd. Noninvasive microtest and quantitative estimation of trisodium-8-hydroxy-1,3,6-pyrenetrisulfonic (PTS, an apoplastic tracer) showed that Si and Si NPs reduced the Cd influx rate and apoplastic Cd uptake, while Si NPs induced a more significant reduction. Moreover, Si regulated the expression of genes responsible for Cd uptake (NRAMP2 and LCT1) and compartmentalization (HMA3), while Si NPs reduced the expression of NRAMP2. In conjunction with RDA, the results showed that Si and Si NPs decreased Cd uptake mainly by regulating the symplastic and apoplastic pathways, respectively. Overall, our results indicate that Si NPs is more effective in promoting tomato growth and alleviating oxidative damage than Si in tomato under Cd stress by modulating the antioxidant system and reducing apoplastic Cd uptake.

N-Heterocyclic Olefins on a Silicon Surface

The adsorption of N-heterocyclic olefins (NHOs) on silicon is investigated in a combined scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory study. We find that both of the studied NHOs bind covalently, with ylidic character, to the silicon adatoms of the substrate and exhibit good thermal stability. The adsorption geometry strongly depends on the N-substituents: for large N-substituents, an upright adsorption geometry is favored, while a flat-lying geometry is found for the NHO with smaller wingtips. These different geometries strongly influence the quality and properties of the obtained monolayers. The upright geometry leads to the formation of ordered monolayers, whereas the flat-lying NHOs yield a mostly disordered, but denser, monolayer. The obtained monolayers both show large work function reductions, as the higher density of the flat-lying monolayer is found to compensate for the smaller vertical dipole moments. Our findings offer new prospects in the design of tailor-made ligand structures in organic electronics and optoelectronics, catalysis, and material science.

CycloSiFA: The Next Generation of Silicon-Based Fluoride Acceptors for Positron Emission Tomography (PET)

The ring-opening Si-fluorination of a variety of azasilole derivatives cyclo-1-(iPr2 Si)-4-X-C6 H3 -2-CH2 NR (4: R=2,6-iPr2 C6 H3 , X=H; 4 a: R=2,4,6-Me3 C6 H2 , X=H; 9: R=2,6-iPr2 C6 H3 , X=tBuMe2 SiO; 10: R=2,6-iPr2 C6 H3 , X=OH; 13: R=2,6-iPr2 C6 H3 , X=HCCCH2 O; 22: R=2,6-iPr2 C6 H3 , X=tBuMe2 SiCH2 O) with different 19 F-fluoride sources was studied, optimized and the experience gained was used in a translational approach to create a straightforward 18 F-labelling protocol for the azasilole derivatives [18 F]6 and [18 F]14. The latter constitutes a potential clickable CycloSiFA prosthetic group which might be used in PET tracer development using Cu-catalysed triazole formation. Based on our findings, CycloSiFA has the potential to become a new entry into non-canonical labelling methodologies for radioactive PET tracer development.

Neutral and Anionic Square Planar Palladium(0) Complexes Stabilized by a Silicon Z-Type Ligand

Anionic [Pd(0)-X]- ate complex were proposed as key intermediates in Pd-catalyzed cross-coupling for decades, but their isolation remained elusive. Herein, a chelating Lewis acidic bis(amidophenolato)silane is introduced as a strong Z-type ligand which enables the characterization of the first anionic [Pd(0)-X]- ate complex. Intriguingly, these compounds and the neutral L-Pd(0) analogs exhibit a square planar coordination that is highly unusual for a d10 metal. Theoretical methods scrutinize the interaction between the Lewis acidic Si(IV) center and the late transition metal, while reactivity studies shed light on the potential role of anionic additives in oxidative addition reactions.

The effect of rice residue management on rice paddy Si, Fe, As, and methane biogeochemistry

Rice production results in residues of straw and husk, and the management of these residues has implications for the sustainability of the rice agroecosystem. Rice straw is typically incorporated into soil either as fresh residue or is burned prior to incorporation. Rice husk is not typically returned to rice fields. However, rice husk contains high levels of silicon, which has been shown to decrease rice accumulation of arsenic. In this work, we studied the resulting biogeochemical changes in rice paddy soils when paddies were amended with either straw or burned straw and either no husk, husk, or burned husk over two years. Using a full-factorial design, we observed that the higher lability of rice straw carbon controlled redox-sensitive processes despite the application of husk and straw at similar carbon rates. Amending paddies with straw, rather than burned straw, increased porewater Fe and As, plant As, and methane emissions regardless of husk amendment. Husk addition provided insignificant Si to the plant despite its high concentration of Si, suggesting limited short-term mobility of Si and that long-term additions of husk or higher rates may need to be studied.

Modulation of metal transporters, oxidative stress and cell abnormalities by synergistic application of silicon and titanium oxide nanoparticles: A strategy for cadmium tolerance in rice

Heavy metals, especially cadmium (Cd), cause severe toxicity symptoms in crop plants. Applying nanoparticles (NPs) as nano-fertilizers is a novel approach to mitigating plants' Cd stress. However, knowledge about the combinational use of silicon (Si) and titanium dioxide (TiO2) NPs to mitigate Cd stress, especially in rice, must be highlighted. TiO2-NPs (15 mg L-1) and Si-NPs (2.5 mM) were applied alone and in combination to rice plants grown without (control; no Cd stress) and with (100 μM) Cd concentration. Results revealed that compared to the control plants, root length, shoot length, shoot fresh weight, and root dry weight of rice seedlings were significantly decreased by 25.43%, 26.64%, 34.13%, and 29.87% under Cd exposure. However, the synergistic effect of TiO2- and Si-NPs increased rice plants' shoot length, root length, root dry weight, and shoot fresh weight by 24.62%, 29.81%, 36.16%, and 33.07%, respectively, under the Cd-toxicity. The concentration of malondialdehyde (MDA) and H2O2 were amplified due to Cd stress, which leads to damage to the subcellular structures. Si and TiO2-NPs co-application improved the anti-oxidative enzymatic activities (catalase, peroxidase, superoxide dismutase) and an elevated concentration of non-enzymatic glutathione in Cd-exposed rice. The Cd accumulation was condensed by 21.37% and 19.7% in the shoot, while 48.31% and 45.65% in root tissues under Si-NPs + Cd and TiO2-NPs + Cd treatments compared to Cd-alone treated seedlings, respectively. The expression patterns of metal transporters, such as OsNramp1 and OsHMA3, were the highest when rice plants were cultivated under Cd stress and significantly reduced when treated with sole and combined Si- and TiO2-NPs treatments. In conclusion, combining Si- and TiO2-NPs significantly improved the antioxidant enzymatic activities, chlorophyll contents, biomass production, and reduced cellular damage. Despite limitations, our findings guide future research, addressing risks, optimizing concentrations, and assessing long-term effects that can balance agricultural progress with environmental sustainability.

Silicon nanoparticles alleviate cadmium toxicity in rice (Oryza sativa L.) by modulating the nutritional profile and triggering stress-responsive genetic mechanisms

This study investigated the physiological and molecular responses of rice genotype '9311' to Cd stress and the mitigating effects of silicon oxide nanoparticles (SiO NPs). Cd exposure severely hindered plant growth, chlorophyll content, photosynthesis, and Cd accumulation. However, SiO NPs supplementation, particularly the SiONP100 treatment, significantly alleviated Cd-induced toxicity, mitigating the adverse effects on plant growth while maintaining chlorophyll content and photosynthetic attributes. The SiONP100 treatment also reduced Cd accumulation, indicating a preference for Si uptake in genotype 9311. Complex interactions among Cd, Si, Mg, Ca, and K were uncovered, with fluctuations in MDA and H2O2 contents. Distinct morphological changes in stomatal aperture and mesophyll cell structures were observed, including changes in starch granules, grana thylakoids, and osmophilic plastoglobuli. Moreover, following SiONP100 supplementation, genotype 9311 increased peroxidase, superoxide dismutase, and catalase activities by 56%, 44%, and 53% in shoots and 62%, 49%, and 65% in roots, respectively, indicating a robust defense mechanism against Cd stress. Notably, OsNramp5, OsHMA3, OsSOD-Cu/Zn, OsCATA, OsCATB, and OsAPX1 showed significant expression after SiO NPs treatment, suggesting potential Cd translocation within rice tissues. Overall, SiO NPs supplementation holds promise for enhancing Cd tolerance in rice plants while maintaining essential physiological functions.

A Binary Silicon-Centered Organoboron Catalyst with Superior Performance to That of Its Bifunctional Analogue

This work reported that a silicon-centered alkyl borane/ammonium salt binary (two-component) catalyst exhibits much higher activity than its bifunctional analogue (one-component) for the ring-opening polymerization of propylene oxide, showing 7.3 times the activity of its bifunctional analogue at a low catalyst loading of 0.01 mol %, and even 15.3 times the activity at an extremely low loading of 0.002 mol %. By using 19 F NMR spectroscopy, control experiments, and theoretical calculation we discovered that the central silicon atom displays appropriate electron density and a larger intramolecular cavity, which is useful to co-activate the monomer and to deliver propagating chains, thus leading to a better intramolecular synergic effect than its bifunctional analogue. A unique two-pathway initiation mode was proposed to explain the unusual high activity of the binary catalytic system. This study breaks the traditional impression of the binary Lewis acid/nucleophilic catalyst with poor activity because of the increase in entropy.

Silicon-based nanoparticles for mitigating the effect of potentially toxic elements and plant stress in agroecosystems: A sustainable pathway towards food security

Due to their size, flexibility, biocompatibility, large surface area, and variable functionality nanoparticles have enormous industrial, agricultural, pharmaceutical and biotechnological applications. This has led to their widespread use in various fields. The advancement of knowledge in this field of research has altered our way of life from medicine to agriculture. One of the rungs of this revolution, which has somewhat reduced the harmful consequences, is nanotechnology. A helpful ingredient for plants, silicon (Si), is well-known for its preventive properties under adverse environmental conditions. Several studies have shown how biogenic silica helps plants recover from biotic and abiotic stressors. The majority of research have demonstrated the benefits of silicon-based nanoparticles (Si-NPs) for plant growth and development, particularly under stressful environments. In order to minimize the release of brine, heavy metals, and radioactive chemicals into water, remove metals, non-metals, and radioactive components, and purify water, silica has also been used in environmental remediation. Potentially toxic elements (PTEs) have become a huge threat to food security through their negative impact on agroecosystem. Si-NPs have the potentials to remove PTEs from agroecosystem and promote food security via the promotion of plant growth and development. In this review, we have outlined the various sources and ecotoxicological consequences of PTEs in agroecosystems. The potentials of Si-NPs in mitigating PTEs were extensively discussed and other applications of Si-NPs in agriculture to foster food security were also highlighted.

Thiol-Specific Silicon-Containing Conjugating Reagent: β-Silyl Alkynyl Carbonyl Compounds

Site-specific modification of thiol-containing biomolecules has been recognized as a versatile and powerful strategy for probing our biological systems and discovering novel therapeutics. The addition of lipophilic silicon moiety opens up new avenues for multi-disciplinary research with broad applications in both the medicinal and material sciences. However, adhering to the strict biocompatibility requirements, and achieving the introduction of labile silicon handle and high chemo-selectivity have been formidable. In this paper, we report silicon-based conjugating reagents including β-trialkylsilyl and silyl ether-tethered alkynones that selectively react with thiols under physiological conditions. The pH-neutral, metal-free and additive-free reaction yields stable products with broad substrate compatibility and full retention of silicon handles in most cases. Besides simple aliphatic and aromatic thiols, this approach is applicable in the labeling of thiols present in proteins, sugars and payloads, thereby expanding the toolbox of thiol conjugation.

Interference of Parenteral Nutrition Components in Silicon-Mediated Protection Against Aluminum Bioaccumulation

Aluminum and silicon are contaminants found in formulations used to prepare parenteral nutrition. Both elements are leached from glass containers, mainly during the heating cycle for sterilization. Insoluble and biologically inactive species of hydroxyaluminosilicates have been shown to form in solutions containing Al and Si. Therefore, this interaction may play an important role in protecting the body against Al toxicity. In this study, the bioavailability of Al in the presence of Si, calcium gluconate (Gluc.), and potassium phosphate (Phosf.) was investigated in rats. The rats were divided into 10 groups of 5 animals each: control, Al, Si, Al + Si, Gluc, Gluc + Al, Gluc + Al + Si, Phosf, Phosf + Al, and Phosf + Al + Si. The doses, consisting of 0.5 mg/kg/day Al and 2 mg/kg/day Si in the presence or absence of Gluc. or Phosf., were intraperitoneally administered for 3 months. Tissues were analyzed for Al and Si content. Al accumulated in the liver, kidneys, and bones, and the simultaneous administration of Si decreased Al accumulation in these tissues. The presence of Si reduced the amount of Al present by 72% in the liver, by 45% in the kidneys, and by 16% in bone. This effect was lees pronounced in the presence of parenteral nutrition compounds though. Si tissue accumulation was also observed, mainly when administered together with phosphate. These results suggest that Si may act as a protector against Al toxicity, by either reducing Al absorption or increasing its excretion, probably through hydroxyaluminosilicates formation. The presence of calcium gluconate and potassium phosphate decreases or inhibits this effect.

Removal of silicon-containing contaminants from TEM specimens

Contaminant-free specimens are an essential prerequisite for high-quality electron microscopy. Silicon is the second most abundant element in the earth's crust with similar chemical properties to that of carbon. However, as a potential source of contamination, silicon has been occasionally reported but not specifically addressed in the electron microscopy community to date. This work highlights the widespread presence of silicon-containing contaminants on TEM specimens, and proposes a general solution for this type of contaminants by using SF6 as a silicon remover. After the treatment, both hydrocarbons and silicon-containing contaminants were removed and no further electron beam showering was needed for most of the specimens to achieve time-invariant imaging. It is expected that this method could be beneficial not only for electron microscopes but also for other surface-sensitive analytical instruments.

Silica sources for arsenic mitigation in rice: machine learning-based predictive modeling and risk assessment

Arsenic (As) is a well-known human carcinogen, and the consumption of rice is the main pathway for the South Asian people. The study evaluated the impact of the amendments involving CaSiO3, SiO2 nanoparticles, silica solubilizing bacteria (SSB), and rice straw compost (RSC) on mitigation of As toxicity in rice. The translocation of As from soil to cooked rice was tracked, and the results showed that RSC and its combination with SSB were the most effective in reducing As loading in rice grain by 53.2%. To determine the risk of dietary exposure to As, the average daily intake (ADI), hazard quotient (HQ), and incremental lifetime cancer risk (ILCR) were computed. The study observed that the ADI was reduced to one-third (0.24 μg kg-1bw) under RSC+SSB treatments compared to the control. An effective prediction model was established using random forest model and described the accumulation of As by rice grains depend on bioavailable As, P, and Fe which explained 48.5, 5.07%, and 2.6% of the variation in the grain As, respectively. The model anticipates that to produce As benign rice grain, soil should have P and Fe concentration more than 30 mg kg-1 and 12 mg kg-1, respectively if soil As surpasses 2.5 mg kg-1.

Effects of metal amendment and metalloid supplementation on foliar defences are plant accession-specific in the hyperaccumulator Arabidopsis halleri

Soil pollution by metals and metalloids as a consequence of anthropogenic industrialisation exerts a seriously damaging impact on ecosystems. However, certain plant species, termed hyperaccumulators, are able to accumulate extraordinarily high concentrations of these metal(loid)s in their aboveground tissues. Such hyperaccumulation of metal(loid)s is known to act as a defence against various antagonists, such as herbivores and pathogens. We investigated the influences of metal(loid)s on potential defence traits, such as foliar elemental, organic and mechanical defences, in the hyperaccumulator plant species Arabidopsis halleri (Brassicaceae) by artificially amending the soil with common metallic pollutants, namely cadmium (Cd) and zinc (Zn). Additionally, unamended and metal-amended soils were supplemented with the metalloid silicon (Si) to study whether Si could alleviate metal excess. Individuals originating from one non-/low- and two moderately to highly metal-contaminated sites with different metal concentrations (hereafter called accessions) were grown for eight weeks in a full-factorial design under standardised conditions. There were significant interactive effects of metal amendment and Si supplementation on foliar concentrations of certain elements (Zn, Si, aluminium (Al), iron (Fe), potassium (K) and sulfur (S), but these were accession-specific. Profiles of glucosinolates, characteristic organic defences of Brassicaceae, were distinct among accessions, and the composition was affected by soil metal amendment. Moreover, plants grown on metal-amended soil contained lower concentrations of total glucosinolates in one of the accessions, which suggests a potential trade-off between inorganic defence acquisition and biosynthesis of organic defence. The density of foliar trichomes, as a proxy for the first layer of mechanical defence, was also influenced by metal amendment and/or Si supplementation in an accession-dependent manner. Our study highlights the importance of examining the effects of co-occurring metal(loid)s in soil on various foliar defence traits in different accessions of a hyperaccumulating species.

Experimental evaluation of usable specimen thickness of Si for lattice imaging by transmission electron microscopy at 300 kV

We evaluated the usable specimen thickness of Si for lattice imaging on a transmission electron microscopy (TEM) instrument operating at 300 kV and equipped with a complementary metal-oxide-semiconductor camera by using an original reference material (RM) and comparing the lattice images obtained from Si patterns of the RM with various thicknesses. Lattice images of the {111} planes of crystalline Si are successfully observed for patterns with thicknesses of up to 508 nm. However, the contrast of these lattice fringes at a thickness of 508 nm is not distinct, even when recorded using a longer exposure time (5.0 s) than that required to obtain lattice images of patterns with thicknesses of 316 nm or less (0.5 s). Based on these results, we conclude that the practical thickness of crystalline Si specimens for accurate structural analysis and TEM magnification calibration via lattice imaging is less than approximately 500 nm under the experimental conditions.