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Root border cells (RBCs) and their mucilage are considered to play an important role in protecting root tip from aluminum (Al) toxicity, but their interactions with silicon (Si) under Al stress still remain unclear. Here, we investigated the effect of Si on the formation of RBCs under Al stress and the related detoxification mechanism in hydroponically grown rice (Oryza sativa L.). The results showed that Si could prevent the separation of RBCs from each other by increasing the degree of pectin methylesterification in root tip cell wall, thereby keeping more RBCs around the root tip. Also, Si maintained the viability of RBCs, increased the amount of mucilage, and reduced the content of total Al and free Al in root tips. Moreover, the RBCs accumulated more Al and Si simultaneously than root tip in the Al treatments with Si supply. Overall, these results indicated that Si reduced the toxicity of Al to RBCs through formation of Si–Al complex on the RBCs, thereby improving the viability of RBCs and promoting the secretion of mucilage. Concomitantly, Si, RBCs and their mucilage could form a protective sheath at the root tip, which prevented Al from diffusing into the root tip, thereby alleviating Al toxicity in rice root tips. [Display omitted] • Si kept more RBCs around the root tip under Al stress. • Si improved the viability of RBCs and promoted the production of mucilage. • The formation of Si–Al complex on the RBCs reduced the toxicity of Al to root tip. • A protective sheath formed by RBCs and mucilage prevented Al from entering root tip. [ABSTRACT FROM AUTHOR]

Silicon (Si), as a beneficial element for a number of crops, can significantly improve the growth and yield of crops partly through silicon-enhanced resistance to biotic and/or abiotic stress. However, the mechanisms of Si-improved growth and fruit quality of horticultural crops, in particular, remain poorly understood. In the present study, two-year field experiments were conducted aimed at testing the effects of different sources of silicate fertilizers applied on table grape yield, fruit quality and fruit commercial characteristics during storage period. For this, two table grape cultivars were tested with treatments including: (I) no silicate fertilizer (control), (II) steel slag fertilizer and (III) water-cooling slag fertilizer. The application rate of silicate fertilizer was 600 kg SiO 2 ha −1 . Fruit yield, cluster weight, berry weight, berry size ( i.e. length and width) were significantly increased by application of silicon fertilizers ( P < 0.05) in both cultivars. Table grape fruit yield was 13.5% higher in the treatment with either water-cooling slag fertilizer or steel-slag fertilizer than in the control across the two years tested. Silicon fertilization significantly improved fruit total soluble solids, the ratio of total soluble solids to titratable acidity (TSS/TA) and fruit firmness. Applying silicate fertilizer significantly extended the fruit shelf-life by decreasing fruit respiratory intensity, decay incidence and weight loss ( P < 0.05). Water-cooling slag fertilizer did not show a significant difference from steel slag fertilizer in grape yield and fruit quality. Our findings suggest that silicate fertilizer could prolong fruit shelf-life and increase the yield and quality of grape in a calcareous grey desert soil. [ABSTRACT FROM AUTHOR]

Due to the frequent occurrence of extreme weather and severe environmental pollution, food security and human survival are at risk. Silicon, a key element in plant nutrition and environmental remediation, has a variety of applications in combatting various forms of abiotic and biotic stress and fostering healthy plants and soils. To establish a silicon-based defense barrier for plants, we firstly summarized and grouped the mechanisms of silicon functioning in plants: 1) molecular regulation and overall strengthening, 2) physical barrier and apoplastic obstruction, and 3) energy conservation. Additionally, the types and applications of silicon-based materials as soil remediation materials and fertilizers were discussed. Then, the challenges to build up such a barrier were analyzed in terms of silicon absorption and transportation, deposition and aggregation, and perception and regulation. An "external + internal" strategy was proposed to accelerate the establishment of a silicon-based barrier to enhance plants' resistance to extreme weather and environmental pollution, including high temperatures, drought, ultraviolet radiation, salt, heavy metals, nutrient deficiencies, new pollutants, and biotic stress. Finally, this paper emphasized the contribution of silicon barrier to healthy Soil-Plant-Atmosphere system that eventually benefit human health. This paper highlights the current understanding and future perspectives of silicon-related research in Soil-Plant-Atmosphere system, providing a reference for the application of silicon-based materials in environmental and agricultural fields. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • Si reduces toxic metal concentration in shoots but sometimes increases it in roots. • The adsorption-diffusion model was developed to explain the effect of Si in roots. • Si exhibited dual roles in roots by increasing adsorption and blocking diffusion. • The intensity and duration of stress and Si concentration affected Si's function. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • A hierarchical system was developed to explore the Si functioning mechanism. • The system includes three subsystems: plant, protoplast, and suspended cell. • Si affects rice seedlings' antioxidant enzyme activity by reducing Cr(III) uptake. • Silicon presents different roles on protoplasts and suspension cells. • 95% of Si is on cell walls of suspension cells and acts as a defense barrier. [ABSTRACT FROM AUTHOR]

Background and aims: Silicon (Si) is known to alleviate aluminum (Al) toxicity in a number of plant species; however, the mechanisms of Si-triggered Al detoxification have not been elucidated, especially in rice (Oryza sativa). We investigated the interactions between Si and Al in root and the role of cell wall polysaccharides in rice resistance to Al. Methods: Rice seedlings were grown in 0.5 mM CaCl2 solution with or without 50 µM Al and 1.0 mM H4SiO4 for 24 h. The cell expansion and oxidative injury of root were measured by histochemical analyses; Al accumulation and distribution in root apices were determined by inductively coupled plasma mass spectrometry (ICP-MS); the degree of pectin methylesterification was analyzed by immunofluorescence, and the expression of genes (e.g. OsPME) related to Al resistance was measured by quantitative real-time PCR. Results: Si relieved the inhibition of cell elongation and oxidative injury caused by Al and significantly reduced Al content (by about 41 %) in cell wall (CW). Meanwhile, Si inhibited pectin methylesterase (PME) activity and its gene expression, thereby increasing the degree of pectin methylesterification, and reduced the content of hemicellulose, which was the main binding site for Al in CW, under Al stress. Furthermore, Si decreased the non-exchangeable Al fraction of CW in root, but did not change the cation exchange capacity of CW. Conclusions: Si reduces the deposition of Al in the cell wall of rice root apex by decreasing both the degree of pectin demethylesterification and the content of hemicellulose, thereby alleviating Al stress. [ABSTRACT FROM AUTHOR]

Silicon (Si) can alleviate salt stress by decreasing Na+ bypass flow in rice (Oryza sativa L.), however, the mechanisms underpinning remain veiled. In this study, we investigated the roles of OsLsi1 and OsLsi2 in Si-induced reduction of bypass flow and its resultant alleviation of salt stress by using lsi1 and lsi2 mutants (defective in OsLsi1 and OsLsi2, respectively) and their wild types (WTs). Under salt stress, Si promoted plant growth and decreased root-to-shoot Na+ translocation in WTs, but not in mutants. Simultaneously, quantitative estimation and fluorescent visualization of trisodium-8-hydroxy-1,3,6-pyrenetrisulphonic (PTS, an apoplastic tracer) showed Si reduced bypass flow in WTs, but not in mutants. Energy-dispersive X-ray microanalysis (EDX) showed Si was deposited at root endodermis in WTs, but not in mutants. Moreover, results obtained from root split experiment using lsi1 WT showed down-regulated expression of Si transport genes (OsLsi1 and OsLsi2) in root accelerated Si deposition at root endodermis. In summary, our results reveal that Si deposition at root endodermis and its resultant reduction of Na+ bypass flow is modulated by OsLsi1 and OsLsi2 and regulated by the expression of OsLsi1 and OsLsi2 , implying that root Si deposition could be an active and physiologically-regulated process in rice. • Si deposition at root endodermis reduces Na+ bypass flow and alleviates salt stress. • Root Si deposition is modulated by OsLsi1 and OsLsi2. • Down-regulated OsLsi1 and OsLsi2 accelerated endodermis Si deposition. • Si deposition in root could be an active and physiologically-regulated process. [ABSTRACT FROM AUTHOR]

Trivalent chromium [Cr(III)] is a threat to the environment and crop production. Silicon (Si) has been shown to be effective in mitigating Cr(III) toxicity in rice. However, the mechanisms by which Si reduces Cr(III) uptake in rice are unclear. Herein, we hypothesized that the ability of Si to obstruct Cr(III) diffusion via apoplastic bypass is related to silicic acid polymerization, which may be affected by Cr(III) in rice roots. To test this hypothesis, we employed hydroponics experiments on rice (Oryza sativa L.) and utilized apoplastic bypass tracer techniques, as well as model simulations, to investigate 1) the effect of Si on Cr(III) toxicity and its obstruction capacity via apoplastic bypass, 2) the effect of Cr(III) on silicic acid polymerization, and 3) the relationship between the degree of silicic acid polymerization and its Cr(III) obstruction capacity. We found that Si reversed the damage caused by Cr(III) stress in rice. Si exerted an obstruction effect in the apoplast, significantly decreasing the share of Cr(III) uptake via the apoplastic bypass from 18% to 11%. Moreover, Cr(III) reduced silica particles' radii and increased Si concentration in roots. Modeling revealed that a 5-fold reduction in their radii decreased the diffusion of Cr(III) in apoplast by approximately 17%. We revealed that Cr(III) promoted silicic acid polymerization, resulting in the formation of a higher number of Si particles with a smaller radius in roots, which in turn increased the ability of Si to obstruct Cr(III) diffusion. This negative feedback regulatory mechanism is novel and crucially important for maintaining homeostasis in rice, unveiling the unique role of Si under Cr(III) ion stress and providing a theoretical basis for promoting the use of Si fertilizer in the field. [Display omitted] • Si in rice mitigates Cr(III) stress by obstructing Cr(III) uptake via apoplastic bypass. • Cr(III) reduces Si particle radius and increases root Si concentration. • A great number of smaller Si particles can improve their obstructing effect. • Si in rice alleviates Cr(III) stress via a negative feedback regulatory mechanism. [ABSTRACT FROM AUTHOR]

This study evaluated the effect of silicate fertilizer on denitrification and associated gene abundance in a paddy soil. A consecutive trial from 2013 to 2015 was conducted including the following treatments: control (CK), mineral fertilizer (NPK), NPK plus sodium metasilicate (NPK + MSF), and NPK plus slag-based silicate fertilizer (NPK + SSF). Real-time quantitative PCR (qPCR) was used to analyze the abundances of nirS, nirK, and nosZ genes. Potential NO emissions and ammonium and nitrate concentrations were related to the nirS and nirK gene abundance. Compared with the NPK treatments, the addition of a Si fertilizer decreased NO emission rates and denitrification potential by 32.4-66.6 and 22.0-59.2%, respectively, which were probably related to increased rice productivity, soil Fe availability, and soil N depletion. The abundances of nirS and nirK genes were decreased by 17.7-35.8% and 21.1-43.5% with addition of silicate fertilizers, respectively. Rates of total NO and NO from denitrification (DeNO) emission were positively correlated with the nirS and nirK gene abundance. Nitrate, exchangeable NH , and Fe concentrations were the main factors regulating the nirS and nirK gene abundance. Silicate fertilization during rice growth may serve as an effective approach to decreasing NO emissions. [ABSTRACT FROM AUTHOR]

Background and aims: We investigated the effects of silicon (Si) on chlorophyll concentration, photosynthesis, leaf chloroplast ultrastructure, and expression of genes involved in photosynthesis to elucidate the mechanisms through which Si mediated alleviation of manganese (Mn) toxicity in rice ( Oryza sativa L.). Methods: Rice seedlings were grown hydroponically with normal Mn (6.7 μM) or high Mn (2 mM) concentrations, both with (1.5 mM) and without Si supplementation. Leaf chloroplast ultrastructure was observed by scanning and transmission electron microscopy. Differentially expressed genes relating to photosynthesis were identified by high-throughput sequencing, and their relative expression levels were evaluated by real-time quantitative PCR. Results: Chlorophyll and carotenoid concentrations and net photosynthesis decreased with chloroplast degradation under high Mn stress. High Mn concentrations may have inhibited photosynthesis through several mechanisms, including suppressing chlorophyll and ATP synthesis, decreasing light-harvesting processes, impairing photosystem I (PSI) stability and structure, and slowing activity of phosphoribulokinase. Si enhanced Mn tolerance efficiently by increasing chlorophyll concentration, light-use efficiency, and ATP concentration as well as by stabilizing the structure of PSI and promoting CO assimilation. Conclusions: Our findings suggest active involvement of Si in Mn detoxification, ranging from physiological responses to gene expression. [ABSTRACT FROM AUTHOR]

It is well documented that slag-based silicon fertilizers have beneficial effects on the growth and disease resistance of rice. However, their effects vary greatly with sources of slag and are closely related to availability of silicon (Si) in these materials. To date, few researches have been done to compare the differences in plant performance and disease resistance between different slag-based silicon fertilizers applied at the same rate of plant-available Si. In the present study both steel and iron slags were chosen to investigate their effects on rice growth and disease resistance under greenhouse conditions. Both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to examine the effects of slags on ultrastructural changes in leaves of rice naturally infected by Bipolaris oryaze, the causal agent of brown spot. The results showed that both slag-based Si fertilizers tested significantly increased rice growth and yield, but decreased brown spot incidence, with steel slag showing a stronger effect than iron slag. The results of SEM analysis showed that application of slags led to more pronounced cell silicification in rice leaves, more silica cells, and more pronounced and larger papilla as well. The results of TEM analysis showed that mesophyll cells of slag-untreated rice leaf were disorganized, with colonization of the fungus (Bipolaris oryzae), including chloroplast degradation and cell wall alterations. The application of slag maintained mesophyll cells relatively intact and increased the thickness of silicon layer. It can be concluded that applying slag-based fertilizer to Si-deficient paddy soil is necessary for improving both rice productivity and brown spot resistance. The immobile silicon deposited in host cell walls and papillae sites is the first physical barrier for fungal penetration, while the soluble Si in the cytoplasm enhances physiological or induced resistance to fungal colonization. [ABSTRACT FROM AUTHOR]

Accumulation of arsenite [As(III)] and dimethylarsinic acid (DMA) in rice grainsposes a threat to human health. Although silicon (Si) has been reported to reduce As uptake, the mechanisms involved are not fully understood. In this study, we first confirmed that the concurrent addition of Si and As in solution decreased As accumulation in rice. Then, the effect of Si previously deposited in shoots by the pretreatment of rice seedlings with Si for one week was investigated by using lsi2 mutant and its wild type. The uptake of both As(III) and DMA decreased in rice subjected concurrently to Si and As (III)/DMA in solution, without effects on OsLsi1 and OsLsi2 expression. This concurrent treatment also decreased total As concentration in the root cell walls and xylem sap, which might have restrained apoplastic transport of As to shoots. Silicon previously deposited in the shoots decreased root-to-shoot As(III) translocation and down-regulated OsLsi1 , OsLsi2 and OsNRAMP1 , but did not affect As concentration in the roots, and had no effect on DMA uptake and accumulation in shoots and roots either. This study sheds light on the role of silicon in solution and rice shoots in As(Ⅲ) and DMA uptake and transport by rice. ga1 • Silicon added to arsenite or dimethylarsinic acid solutions decreased rice arsenic concentrations. • Silicon previously deposited in shoots decreased shoot arsenite concentrations. • It downregulated OsLsi1 , OsLsi2 and OsNRAMP1 under arsenite exposure. • Silicon previously deposited in shoots did not affect rice dimethylarsinic acid concentrations. [ABSTRACT FROM AUTHOR]

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

The two-layer nanotubes consisted of carbon atoms on the outside layer and silicon atoms on the inside layer (CNT@SiNT) show a series of diversity in the shape transitions, for instance transforming from a circle through an oval to a rectangle. In this paper, we investigate this geometric change from three perspectives. In the first aspect, we stationary time, followed by quantize in the three-dimensional Z-axis of nanotubes. In the second aspect, we stationary Z-axis, followed by quantize in the time. Finally, we tracked distance of nanotubes flattest section and roundest section. At the stationary time, the overall image of different Z-axis distance distributions is similar to a plan view of multiple ice creams, regardless of whether CNT or SiNT are on the same Z-axis, their slice plans are circle or rectangle of the projection of the Z-axis section on the XOY plane. In the stationary Z-axis, the nanotubes periodically change from a circle to an oval, and then from an oval to a rectangle at different times. Most remarkably, the distance value of deformation which we track the flattest and roundest is a constant value, and in the same distance period, there is only one roundest circle and one longest rectangle at different section and different time. The geometric analysis provided theoretical reference for the preparation of various devices and semiconductor nano-heterojunctions. [ABSTRACT FROM AUTHOR]

Abiotic and biotic stresses are the major factors limiting plant growth worldwide. Plants exposed to abiotic and biotic stresses often cause reduction in plant biomass as well as crop yield, resulting in plant biomass carbon loss. As a beneficial and quasi-essential element, silicon accumulation in rhizosphere and plants can alleviate the unfavorable effects of the major forms of abiotic and biotic stress through several resistance mechanisms and thus increases plant biomass accumulation and crop yield. The beneficial effects of silicon on plant growth and crop yield have been widely reviewed over the last years. However, carbon accumulation of silicon-associated plant biomass under abiotic and biotic stresses has not yet been systematically addressed. This review article focuses on both the main mechanisms of silicon-mediated alleviation of abiotic and biotic stresses and their effects on plant biomass carbon accumulation in terrestrial ecosystems. The major points are the following: (1) the recovery of plant biomass via silicon mediation usually exhibits a bell-shaped response curve to abiotic stress severity and an S-shaped response curve to biotic stress severity; (2) although carbon concentration of plant biomass decreases with silicon accumulation, more than 96% of the recovered plant biomass contributes to plant biomass carbon accumulation; (3) silicon-mediated recovery generally increases plant biomass carbon by 35% and crop yield by 24%. In conclusion, silicon can improve plant growth and enhance plant biomass carbon accumulation under abiotic and biotic stresses in terrestrial ecosystems. [ABSTRACT FROM AUTHOR]