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

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

Role of the GLP2-Wnt1 axis in silicon-rich alkaline mineral water maintaining intestinal epithelium regeneration in piglets under early-life stress.

Stress-induced intestinal epithelial injury (IEI) and a delay in repair in infancy are predisposing factors for refractory gut diseases in adulthood, such as irritable bowel syndrome (IBS). Hence, it is necessary to develop appropriate mitigation methods for mammals when experiencing early-life stress (ELS). Weaning, as we all know, is a vital procedure that all mammalian newborns, including humans, must go through. Maternal separation (MS) stress in infancy (regarded as weaning stress in animal science) is a commonly used ELS paradigm. Drinking silicon-rich alkaline mineral water (AMW) has a therapeutic effect on enteric disease, but the specific mechanisms involved have not been reported. Herein, we discover the molecular mechanism by which silicon-rich AMW repairs ELS-induced IEI by maintaining intestinal stem cell (ISC) proliferation and differentiation through the glucagon-like peptide (GLP)2-Wnt1 axis. Mechanistic study showed that silicon-rich AMW activates GLP2-dependent Wnt1/ß-catenin pathway, and drives ISC proliferation and differentiation by stimulating Lgr5+ ISC cell cycle passage through the G1-S-phase checkpoint, thereby maintaining intestinal epithelial regeneration and IEI repair. Using GLP2 antagonists (GLP23-33) and small interfering RNA (SiWnt1) in vitro, we found that the GLP2-Wnt1 axis is the target of silicon-rich AMW to promote intestinal epithelium regeneration. Therefore, silicon-rich AMW maintains intestinal epithelium regeneration through the GLP2-Wnt1 axis in piglets under ELS. Our research contributes to understanding the mechanism of silicon-rich AMW promoting gut epithelial regeneration and provides a new strategy for the alleviation of ELS-induced IEI.

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 Supplementation for Bone Health: An Umbrella Review Attempting to Translate from Animals to Humans.

Studies have attempted to demonstrate the benefits of silicon on bone health using a wide range of Si amounts-provided in the diet or through supplementation-and several different animal species. Previous studies in humans have also demonstrated a positive correlation between Si intake and bone health measures. The aim of the current review is to determine the effective levels of Si intake or supplementation that influence bone health to better inform future study designs and guidelines. Articles were identified using one of two search terms: "silicon AND bone" or "sodium zeolite A AND bone". Articles were included if the article was a controlled research study on the effect of Si on bone health and/or mineral metabolism and was in English. Articles were excluded if the article included human subjects, was in vitro, or studied silica grafts for bone injuries. Silicon type, group name, Si intake from diet, Si supplementation amount, animal, and age at the start were extracted when available. Dietary Si intake, Si supplementation amount, and the amount of Si standardized on a kg BW basis were calculated and presented as overall mean ± standard deviations, medians, minimums, and maximums. Studies that left out animal weights, amount of food or water consumed, or nutrient profiles of the basal diet were excluded from these calculations. Standardized Si intakes ranged from 0.003 to 863 mg/kg BW, at times vastly exceeding current human Si intake recommendations (25 mg/d). The lack of data provided by the literature made definitively determining an effective threshold of supplementation for skeletal health difficult. However, it appears that Si consistently positively influences bone and mineral metabolism by around 139 mg Si/kg BW/d, which is likely unfeasible to attain in humans and large animal species. Future studies should examine this proposed threshold more directly and standardize supplemental or dietary Si intakes to kg BW for better study replication and translation.

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.

Differential Expression of Stress Adaptation Genes in a Diatom Ulnaria acus under Different Culture Conditions.

Diatoms are a group of unicellular eukaryotes that are essential primary producers in aquatic ecosystems. The dynamic nature of their habitat necessitates a quick and specific response to various stresses. However, the molecular mechanisms of their physiological adaptations are still underexplored. In this work, we study the response of the cosmopolitan freshwater diatom Ulnaria acus (Bacillariophyceae, Fragilariophycidae, Licmophorales, Ulnariaceae, Ulnaria) in relation to a range of stress factors, namely silica deficiency, prolonged cultivation, and interaction with an algicidal bacterium. Fluorescent staining and light microscopy were used to determine the physiological state of cells under these stresses. To explore molecular reactions, we studied the genes involved in the stress response-type III metacaspase (MC), metacaspase-like proteases (MCP), death-specific protein (DSP), delta-1-pyrroline-5-carboxylate dehydrogenase (ALDH12), and glutathione synthetase (GSHS). We have described the structure of these genes, analyzed the predicted amino acid sequences, and measured their expression dynamics in vitro using qRT-PCR. We demonstrated that the expression of UaMC1, UaMC3, and UaDSP increased during the first five days of silicon starvation. On the seventh day, it was replaced with the expression of UaMC2, UaGSHS, and UaALDH. After 45 days of culture, cells stopped growing, and the expression of UaMC1, UaMC2, UaGSHS, and UaDSP increased. Exposure to an algicidal bacterial filtrate induced a higher expression of UaMC1 and UaGSHS. Thus, we can conclude that these proteins are involved in diatoms' adaptions to environmental changes. Further, these data show that the molecular adaptation mechanisms in diatoms depend on the nature and exposure duration of a stress factor.

Hydraulic retention time governed the micro/nanostructures of titanium-incorporated diatoms and their photocatalytic activity.

Titanium-incorporated diatoms are promising biomaterials to photodegrade micropollutants such as pharmaceuticals and personal care products (PPCPs). Hydraulic retention time (HRT) is a key parameter for diatom cultivation and the incorporation of titanium into diatom frustules. This study assessed how HRT governs the micro/nanostructures, titania (TiO2) content and distribution, and the photocatalytic activity of titanium-incorporated diatom frustules. We cultivated a diatom strain Stephanodiscus hantzschii using a feed solution containing titanium(IV) in membrane bioreactors (MBRs) at a solids retention time (SRT) of 10 d and staged HRTs from 24 to 12 and to 6 h. The decrease in HRT reduced the porosity of diatom frustules but increased their silicon and titania contents. When the HRT decreased from 24 to 12 and to 6 h, the specific surface areas of the diatom decreased from 37.65 ± 3.19 to 31.53 ± 3.71 and to 18.43 ± 2.69 m2·g-1 frustules, while the titanium (Ti) contents increased from 53 ± 14 to 71 ± 9 and to 85 ± 13 mg Ti·g-1 frustules. The increase in the influent flow rates of the MBRs with decreasing HRTs likely enhanced nutrient diffusion inside the diatom valve pores, facilitating the uptake and incorporation of silicon and titanium. The titanium-incorporated frustules were effective in removing two representative PPCPs, bisphenol A (BPA) and N,N-diethyl-meta-toluamide (DEET), from water. As photocatalytic activity depends on the amount of titanium, decreasing the HRT substantially increased the photocatalytic activity of the titanium-incorporated frustules. In batch tests under ultraviolet light, frustules from the diatom cultivated at HRTs of 24, 12, and 6 h had the pseudo-first-order removal (mainly through photodegradation) rate constants of BPA of 0.376, 0.456, and 0.683 h-1, respectively. Under the same experimental condition, the pseudo-first-order removal rate constants of DEET by the frustules cultivated at HRTs of 24, 12, and 6 h increased from 0.270 to 0.330 and to 0.480 h-1.

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.

Editing Silicon Transporter Genes to Reduce Arsenic Accumulation in Rice.

Rice is a dominant source of inorganic arsenic (As) exposure for populations consuming rice as a staple food. Decreasing As accumulation in rice grain is important for improving food safety. Arsenite [As(III)], the main form of As in paddy soil porewater, is taken up inadvertently by OsLsi1 and OsLsi2, the two key transporters for silicon (Si) uptake in rice roots. Here, we investigated whether editing OsLsi1 or OsLsi2 can decrease As accumulation in rice grain without compromising grain yield. We used the CRISPR-Cas9 technology to edit the promoter region of OsLsi1 and the C-terminal coding sequence of OsLsi1 and OsLsi2, and we generated a total of 27 mutants. Uptake and accumulation of Si and As were evaluated in both short-term hydroponic experiments and in a paddy field. Deletion of 1.2-2 kb of the OsLsi1 promoter suppressed OsLsi1 expression in roots and Si uptake markedly and did not affect As(III) uptake or grain As concentration. Some of the OsLsi1 and OsLsi2 coding sequence mutants showed large decreases in the uptake of Si and As(III) as well as large decreases in Si accumulation in rice husks. However, only OsLsi2 mutants showed significant decreases (by up to 63%) in the grain total As concentration. Editing OsLsi2 mainly affected the accumulation of inorganic As in rice grain with little effect on the accumulation of dimethylarsenate (DMA). Grain yields of the OsLsi2 mutants were comparable to those of the wild type. Editing OsLsi2 provides a promising way to reduce As accumulation in rice grain without compromising the grain yield.

Effects and mechanisms of glyphosate as phosphorus nutrient on element stoichiometry and metabolism in the diatom Phaeodactylum tricornutum.

The ability to utilize dissolved organic phosphorus (DOP) gives phytoplankton competitive advantages in P-limited environments. Our previous research indicates that the diatom Phaeodactylum tricornutum could grow on glyphosate, a DOP with carbon-phosphorus (C-P) bond and an herbicide, as sole P source. However, direct evidence and mechanism of glyphosate utilization are still lacking. In this study, using physiological and isotopic analysis, combined with transcriptomic profiling, we demonstrated the uptake of glyphosate by P. tricornutum and revealed the candidate responsible genes. Our data showed a low efficiency of glyphosate utilization by P. tricornutum, suggesting that glyphosate utilization costs energy and that the alga possessed an herbicide-resistant type of 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase. Compared to the P-limited cultures, the glyphosate-grown P. tricornutum cells up-regulated genes involved in DNA replication, cell growth, transcription, translation, carbon metabolism, and many genes encoding antioxidants. Additionally, cellular C and silicon (Si) increased remarkably while cellular nitrogen (N) declined in the glyphosate-grown P. tricornutum, leading to higher Si:C and Si:N ratios, which corresponded to the up-regulation of genes involved in the C metabolism and Si uptake and the down-regulation of those encoding N uptake. This has the potential to enhance C and Si export to the deep sea when P is limited but phosphonate is available. In sum, our study documented how P. tricornutum could utilize the herbicide glyphosate as P nutrient and how glyphosate utilization may affect the element content and stoichiometry in this diatom, which have important ecological implications in the future ocean.IMPORTANCEGlyphosate is the most widely used herbicide in the world and could be utilized as phosphorus (P) source by some bacteria. Our study first revealed that glyphosate could be transported into Phaeodactylum tricornutum cells for utilization and identified putative genes responsible for glyphosate uptake. This uncovers an alternative strategy of phytoplankton to cope with P deficiency considering phosphonate accounts for about 25% of the total dissolved organic phosphorus (DOP) in the ocean. Additionally, accumulation of carbon (C) and silicon (Si), as well as elevation of Si:C ratio in P. tricornutum cells when grown on glyphosate indicates glyphosate as the source of P nutrient has the potential to result in more C and Si export into the deep ocean. This, along with the differential ability to utilize glyphosate among different species, glyphosate supply in dissolved inorganic phosphorus (DIP)-depleted ecosystems may cause changes in phytoplankton community structure. These insights have implications in evaluating the effects of human activities (use of Roundup) and climate change (potentially reducing DIP supply in sunlit layer) on phytoplankton in the future ocean.

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 nano silicon fertilizer on the lodging resistance characteristics of wheat basal second stem node.

The application of nano fertilizers is one of the hotspots in current agricultural production. In this study, nano silicon materials were mixed with compound fertilizers to make nano silicon fertilizer. The effects of different amounts of nano silicon application on the breaking-resistance strength, lodging-resistance index, lignin accumulation, lignin synthesis related enzymes, and the relative expression of lignin synthesis related genes in the second stem node of wheat were mainly studied. Four treatments were set up: CK (750 kg·ha-1 compound fertilizer), T1 (750 kg·ha-1 compound fertilizer + 0.9 kg·ha-1 nano silicon), T2 (750 kg·ha-1 compound fertilizer + 1.8 kg·ha-1 nano silicon), T3 (750 kg·ha-1 compound fertilizer + 2.7 kg·ha-1 nano silicon). The results of the two-year experiment showed that the breaking-resistance strength, lodging-resistance index, lignin accumulation in the second stem node of wheat treated with nano silicon fertilizer were higher than CK. In the first year of the experiment, the lignin accumulation of T2 was 130.73%, 5.14% and 7.25% higher than that of CK, T1 and T3 respectively at the maturity stage. In the second year of the experiment, the lignin accumulation of T2 was 20.33%, 11.19% and 9.89% higher than that of CK, T1 and T3 respectively at the maturity stage. And the activities of PAL, 4CL, CAD, and related gene expression levels were also higher than CK. And among them, T2 performed the best, indicating that the application of nano silicon fertilizer is beneficial for improving the lodging resistance of wheat stems and is of great significance for improving the quality of wheat.

Silicon nutrition improves the quality and yield of rice under dry cultivation.

BACKGROUND: Dry cultivation of rice is a water-saving, emission reduction and labor-saving rice farming method. However, the development of rice under dry cultivation is hampered by the limitations of dry cultivation on rice yield and rice quality. We hypothesized that additional silicon (Si) would be a measure to address these limitations or challenges. RESULTS: In the present study, we set up field trials with three treatments: flooded cultivation (W), dry cultivation (D) and dry cultivation plus Si. Yield and quality were reduced under D treatment compared to W treatment. The addition of Si promoted root development, increased plant height and leaf area, increased photosynthetic enzyme activity, net photosynthetic rate and SPAD values, and increased biomass under dry crop conditions. Under the drought conditions, silica up-regulated the expression of AGPSI, SBEI, SBEIIb, SSI and SSII-1 genes and the activities of ADP-glucose pyrophosphorylase (AGPase), soluble starch synthetase (SSS) and starch branching enzyme (SBE) enzymes, which reduced protein, amylose, chalkiness percentage and chalkiness degree, increased brown rice rate, milled rice rate and head milled rice rate, and also improved rice quality. In addition, the increase of AGPase, SSS and SBE enzyme activities promoted the filling rate and the number of spikes was guaranteed, whereas the yield was improved by promoting the seed setting rate and 1000-grain weight. CONCLUSION: The results of the present study indicate that adding appropriate amounts of Si fertilizer can improve the yield and quality of rice under dry cultivation by regulating source supply capacity and grain starch synthesis. © 2023 Society of Chemical Industry.

Anonic Silicon Hydrogels Affect the Concentration of Proteins in Tears during Wear.

PURPOSE: The objective of this study was to quantitatively assess the concentration of human tear proteins in patients wearing contact lenses of various ionicities and determine whether differences were related to the incidence of corneal infiltrative events (CIE). METHODS: 24 subjects (samples) were randomly selected for spectral count analysis to obtain protein concentrations using LCMS analysis. The subjects were neophyte and ametropic with ages between 18 and 40; 6 wore control lenses, 8 wore TestLens1, and 10 wore TestLens2. 16 subjects experienced CIEs during the study. RESULTS: A pairwise multiple hypothesis test identified 7 proteins that significantly differed in concentration between TestLens1 and control, and 11 proteins that differed between TestLens2 and control. Of the 12 unique proteins, 9 were at increased concentration and 3 were at lower concentration in the tears of test lens wearers compared to the control lens group. Bootstrap clustering confirmed these findings, showing 3 similar clusters to the original sample groups which separated people wearing control lenses from those wearing TestLens1 or TestLens2 with 83% accuracy and between TestLens1 and TestLens2 with 45% accuracy. Permutation testing identified 5 proteins that had significantly changed in concentration between people wearing TestLens2 and Control lenses. There was no difference in protein concentrations between those subjects who experienced a CIE and those who did not. CONCLUSION: Wearing contact lenses of different ionicities can affect the concentration of proteins in the tear film. The current study did not find any associations of the concentration of proteins with CIEs. Future tests with increased sample size are needed to establish any relations between these changes and clinical performance.

Dynamics of Humic Acid, Silicon, and Biochar under Heavy Metal, Drought, and Salinity with Special Reference to Phytohormones, Antioxidants, and Melatonin Synthesis in Rice.

This study aimed to develop a biostimulant formulation using humic acid (HA), silicon, and biochar alone or in combination to alleviate the lethality induced by combined heavy metals (HM-C; As, Cd, and Pb), drought stress (DS; 30-40% soil moisture), and salt stress (SS; 150 mM NaCl) in rice. The results showed that HA, Si, and biochar application alone or in combination improved plant growth under normal, DS, and SS conditions significantly. However, HA increased the lethality of rice by increasing the As, Cd, and Pb uptake significantly, thereby elevating lipid peroxidation. Co-application reduced abscisic acid, elevated salicylic acid, and optimized the Ca2+ and Si uptake. This subsequently elevated the K+/Na+ influx and efflux by regulating the metal ion regulators (Si: Lsi1 and Lsi2; K+/Na+: OsNHX1) and increased the expressions of the stress-response genes OsMTP1 and OsNramp in the rice shoots. Melatonin synthesis was significantly elevated by HM-C (130%), which was reduced by 50% with the HA + Si + biochar treatment. However, in the SS- and DS-induced crops, the melatonin content showed only minor differences. These findings suggest that the biostimulant formulation could be used to mitigate SS and DS, and precautions should be taken when using HA for heavy metal detoxification.

Gene Duplication, Shifting Selection, and Dosage Balance of Silicon Transporter Proteins in Marine and Freshwater Diatoms.

Numerous factors shape the evolution of protein-coding genes, including shifts in the strength or type of selection following gene duplications or changes in the environment. Diatoms and other silicifying organisms use a family of silicon transporters (SITs) to import dissolved silicon from the environment. Freshwaters contain higher silicon levels than oceans, and marine diatoms have more efficient uptake kinetics and less silicon in their cell walls, making them better competitors for a scarce resource. We compiled SITs from 37 diatom genomes to characterize shifts in selection following gene duplications and marine-freshwater transitions. A deep gene duplication, which coincided with a whole-genome duplication, gave rise to two gene lineages. One of them (SIT1-2) is present in multiple copies in most species and is known to actively import silicon. These SITs have evolved under strong purifying selection that was relaxed in freshwater taxa. Episodic diversifying selection was detected but not associated with gene duplications or habitat shifts. In contrast, genes in the second SIT lineage (SIT3) were present in just half the species, the result of multiple losses. Despite conservation of SIT3 in some lineages for the past 90-100 million years, repeated losses, relaxed selection, and low expression highlighted the dispensability of SIT3, consistent with a model of deterioration and eventual loss due to relaxed selection on SIT3 expression. The extensive but relatively balanced history of duplications and losses, together with paralog-specific expression patterns, suggest diatoms continuously balance gene dosage and expression dynamics to optimize silicon transport across major environmental gradients.

Abiogenic silicon: Interaction with potentially toxic elements and its ecological significance in soil and plant systems.

Abiogenic silicon (Si), though deemed a quasi-nutrient, remains largely inaccessible to plants due to its prevalence within mineral ores. Nevertheless, the influence of Si extends across a spectrum of pivotal plant processes. Si emerges as a versatile boon for plants, conferring a plethora of advantages. Notably, it engenders substantial enhancements in biomass, yield, and overall plant developmental attributes. Beyond these effects, Si augments the activities of vital antioxidant enzymes, encompassing glutathione (GSH), catalase (CAT), superoxide dismutase (SOD), and peroxidase (POD), among others. It achieves through the augmentation of reactive oxygen species (ROS) scavenging gene expression, thus curbing the injurious impact of free radicals. In addition to its effects on plants, Si profoundly ameliorates soil health indicators. Si tangibly enhances soil vitality by elevating soil pH and fostering microbial community proliferation. Furthermore, it exerts inhibitory control over ions that could inflict harm upon delicate plant cells. During interactions within the soil matrix, Si readily forms complexes with potentially toxic metals (PTEs), encapsulating them through Si-PTEs interactions, precipitative mechanisms, and integration within colloidal Si and mineral strata. The amalgamation of Si with other soil amendments, such as biochar, nanoparticles, zeolites, and composts, extends its capacity to thwart PTEs. This synergistic approach enhances soil organic matter content and bolsters overall soil quality parameters. The utilization of Si-based fertilizers and nanomaterials holds promise for further increasing food production and fortifying global food security. Besides, gaps in our scientific discourse persist concerning Si speciation and fractionation within soils, as well as its intricate interplay with PTEs. Nonetheless, future investigations must delve into the precise functions of abiogenic Si within the physiological and biochemical realms of both soil and plants, especially at the critical juncture of the soil-plant interface. This review seeks to comprehensively address the multifaceted roles of Si in plant and soil systems during interactions with PTEs.

A silicon transporter gene required for healthy growth of rice on land.

Silicon (Si) is the most abundant mineral element in the earth's crust. Some plants actively accumulate Si as amorphous silica (phytoliths), which can protect plants from stresses. Here, we report a gene (SIET4) that is required for the proper accumulation and cell-specific deposition of Si in rice and show that it is essential for normal growth. SIET4 is constitutively expressed in leaves and encodes a Si transporter. SlET4 polarly localizes at the distal side of epidermal cells and cells surrounding the bulliform cells (motor cells) of the leaf blade, where Si is deposited. Knockout of SIET4 leads to the death of rice in the presence but not absence of Si. Further analysis shows that SIET4 knockout induces abnormal Si deposition in mesophyll cells and the induction of hundreds of genes related to various stress responses. These results indicate that SIET4 is required for the proper export of Si from leaf cells to the leaf surface and for the healthy growth of rice on land.

Identification of VrNIP2-1 aquaporin with novel selective filter regulating the transport of beneficial as well as hazardous metalloids in mungbean (Vigna radiata L.).

Nodulin 26-like intrinsic protein (NIP) subfamily of aquaporins (AQPs) in plants, is known to be involved in the uptake of metalloids including boron, germanium (Ge), arsenic (As), and silicon (Si). In the present study, a thorough evaluation of 55 AQPs found in the mungbean genome, including phylogenetic distribution, sequence homology, expression profiling, and structural characterization, contributed to the identification of VrNIP2-1 as a metalloid transporter. The pore-morphology of VrNIP2-1 was studied using molecular dynamics simulation. Interestingly, VrNIP2-1 was found to harbor an aromatic/arginine (ar/R) selectivity filter formed with ASGR amino acids instead of GSGR systematically reported in metalloid transporters (NIP2s) in higher plants. Evaluation of diverse cultivars showed a high level of Si accumulation in leaves indicating functional Si transport in mungbean. In addition, heterologous expression of VrNIP2-1 in yeast revealed As(III) and GeO2 transport activity. Similarly, VrNIP2-1 expression in Xenopus oocytes confirmed its Si transport ability. The metalloid transport activity with unique structural features will be helpful to better understand the solute specificity of NIP2s in mungbean and related pulses. The information provided here will also serve as a basis to improve Si uptake while restricting hazardous metalloids like As in plants.

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.