Versatile role of silicon in cereals: Health benefits, uptake mechanism, and evolution

Elucidating the underlying mechanisms of silicon to suppress the effects of nitrogen deficiency in pepper plants

In many regions, nitrogen (N) deficiency limits pepper cultivation, presenting significant cultivation challenges. This study investigates the impact of N deficiency and silicon (Si) supplementation on physiological responses and antioxidant modulation in pepper plants, focusing particularly on the homeostasis of carbon (C), nitrogen, and phosphorus (P), and their effects on growth and biomass production. Conducted in a factorial design, the experiment examined pepper plants under conditions of N sufficiency and deficiency, with and without Si supplementation (0.0 mM and 2.0 mM). Results showed that N deficiency sensitizes pepper plants, leading to increased electrolyte leakage (39.59%) and disrupted C, N, and P homeostasis. This disruption manifests as reductions in photosynthetic pigments (-64.53%), photochemical efficiency (-14.92%), and the synthesis of key metabolites such as total free amino acids (-86.97%), sucrose (-53.88%), and soluble sugars (-39.96%), ultimately impairing plant growth. However, Si supplementation was found to alleviate these stresses. It modulated the antioxidant system, enhanced the synthesis of ascorbic acid (+30.23), phenolic compounds (+33.19%), and flavonoids (+7.52%), and reduced cellular electrolyte leakage (-25.02%). Moreover, Si helped establish a new homeostasis of C, N, and P, optimizing photosynthetic and nutritional efficiency by improving the utilization of C (+17.46%) and N (+13.20%). These Si-induced modifications in plant physiology led to increased synthesis of amino acids (+362.20%), soluble sugars (+51.34%), and sucrose (77.42%), thereby supporting enhanced growth of pepper plants. These findings elucidate the multifaceted biological roles of Si in mitigating N deficiency effects, offering valuable insights for more sustainable horticultural practices.

Unveiling silicon-mediated cadmium tolerance mechanisms in mungbean (Vigna radiata (L.) Wilczek): Integrative insights from gene expression, antioxidant responses, and metabolomics

Cadmium (Cd), one of the most phytotoxic heavy metals, is a major contributor to yield losses in several crops. Silicon (Si) is recognized for its vital role in mitigating Cd toxicity, however, the specific mechanisms governing this mitigation process are still not fully understood. In the present study, the effect of Si supplementation on mungbean (Vigna radiata (L.) Wilczek) plants grown under Cd stress was investigated to unveil the intricate pathways defining Si derived stress tolerance. Non-invasive leaf imaging technique revealed improved growth, biomass, and photosynthetic efficiency in Si supplemented mungbean plants under Cd stress. Further, physiological and biochemical analysis revealed Si mediated increase in activity of glutathione reductase (GR), ascorbate peroxidase (APX), and catalase (CAT) enzymes involved in reactive oxygen species (ROS) metabolism leading to mitigation of cellular damage and oxidative stress. Untargeted metabolomic analysis using liquid chromatography coupled with mass spectrometry (LC-MS/MS) provided insights into Si mediated changes in metabolites and their respective pathways under Cd stress. Alteration in five different metabolic pathways with major changes in flavanols and flavonoids biosynthesis pathway which is essential for controlling plants antioxidant defense system and oxidative stress management were observed. The information reported here about the effects of Si on photosynthetic efficiency, antioxidant responses, and metabolic changes will be helpful in understanding the Si-mediated resistance to Cd stress in plants.

Exploring Aluminum Tolerance Mechanisms in Plants with Reference to Rice and Arabidopsis: A Comprehensive Review of Genetic, Metabolic, and Physiological Adaptations in Acidic Soils

Aluminum (Al) makes up a third of the Earth's crust and is a widespread toxic contaminant, particularly in acidic soils. It impacts crops at multiple levels, from cellular to whole plant systems. This review delves into Al's reactivity, including its cellular transport, involvement in oxidative redox reactions, and development of specific metabolites, as well as the influence of genes on the production of membrane channels and transporters, alongside its role in triggering senescence. It discusses the involvement of channel proteins in calcium influx, vacuolar proton pumping, the suppression of mitochondrial respiration, and the initiation of programmed cell death. At the cellular nucleus level, the effects of Al on gene regulation through alterations in nucleic acid modifications, such as methylation and histone acetylation, are examined. In addition, this review outlines the pathways of Al-induced metabolic disruption, specifically citric acid metabolism, the regulation of proton excretion, the induction of specific transcription factors, the modulation of Al-responsive proteins, changes in citrate and nucleotide glucose transporters, and overall metal detoxification pathways in tolerant genotypes. It also considers the expression of phenolic oxidases in response to oxidative stress, their regulatory feedback on mitochondrial cytochrome proteins, and their consequences on root development. Ultimately, this review focuses on the selective metabolic pathways that facilitate Al exclusion and tolerance, emphasizing compartmentalization, antioxidative defense mechanisms, and the control of programmed cell death to manage metal toxicity.

New insight into the mechanisms of preferential encapsulation of metal(loid)s by wheat phytoliths under silicon nanoparticle amendment

Silicon nanoparticles (SiNPs) have been widely used to immobilize toxic trace metal(loid)s (TTMs) in contaminated croplands. However, the effect and mechanisms of SiNP application on TTM transportation in response to phytolith formation and phytolith-encapsulated-TTM (PhytTTM) production in plants are unclear. This study demonstrates the promotion effect of SiNP amendment on phytolith development and explores the associated mechanisms of TTM encapsulation in wheat phytoliths grown on multi-TTM contaminated soil. The bioconcentration factors between organic tissues and phytoliths of As and Cr (> 1) were significantly higher than those of Cd, Pb, Zn and Cu, and about 10 % and 40 % of the total As and Cr that bioaccumulated in wheat organic tissues were encapsulated into the corresponding phytoliths under high-level SiNP treatment. These observations demonstrate that the potential interaction of plant silica with TTMs is highly variable among elements, with As and Cr being the two most strongly concentrated TTMs in the phytoliths of wheat treated with SiNPs. The qualitative and semi-quantitative analyses of the phytoliths extracted from wheat tissues suggest that the high pore space and surface area (≈ 200 m² g^-1) of phytolith particles could have contributed to the embedding of TTMs during silica gel polymerization and concentration to form PhytTTMs. The abundant SiO functional groups and high silicate-minerals in phytoliths are dominant chemical mechanisms for the preferential encapsulation of TTMs (i.e., As and Cr) by wheat phytoliths. Notably, the organic carbon and bioavailable Si of soils and the translocation of minerals from soil to plant aerial parts can impact TTM sequestration by phytoliths. Thus, this study has implications for the distribution or detoxification of TTMs in plants via preferential PhytTTM production and biogeochemical cycling of PhytTTMs in contaminated cropland following exogenous Si supplementation.

Iron plaque formation, characteristics, and its role as a barrier and/or facilitator to heavy metal uptake in hydrophyte rice (Oryza sativa L.)

The persistent bioavailability of toxic metal(oids) (TM) is undeniably the leading source of serious environmental problems. Through the transfer of these contaminants into food networks, sediments and the aquatic environmental pollution by TM serve as key routes for potential risks to soil and human health. The formation of iron oxyhydroxide plaque (IP) on the root surface of hydrophytes, particularly rice, has been linked to the impact of various abiotic and biotic factors. Radial oxygen loss has been identified as a key driver for the oxidation of rhizosphere ferrous iron (Fe²⁺) and its subsequent precipitation as low-to-high crystalline and/or amorphous Fe minerals on root surfaces as IP. Considering that each plant species has its unique capability of creating an oxidised rhizosphere under anaerobic conditions, the abundance of rhizosphere Fe²⁺, functional groups from organic matter decomposition and variations in binding capacities of Fe oxides, thus, impacting the mobility and interaction of several contaminants as well as toxic/non-toxic metals on the specific surface areas of the IP. More insight from wet extraction and advanced synchrotron-based analytical techniques has provided further evidence on how IP formation could significantly affect the fate of plant physiology and biomass production, particularly in contaminated settings. Collectively, this information sets the stage for the possible implementation of IP and related analytical protocols as a strategic framework for the management of rice and other hydrophytes, particularly in contaminated sceneries. Other confounding variables involved in IP formation, as well as operational issues related to some advanced analytical processes, should be considered.

Exogenous silicon enhances resistance to 1,2,4-trichlorobenzene in rice

Environmental contamination with 1,2,4-trichlorobenzene (TCB) is a threat to rice growth, and ultimately, to human health. Silicon (Si) plays an important role in plants' stress responses. However, little is known about the effects of Si on the TCB tolerance of rice plants. We investigated the effects of Si on the morphological, physiological, and molecular characteristics of rice plants under TCB stress. First, we compared the TCB tolerance of 13 rice cultivars by measuring seven growth-related and 13 physiological indices across four treatments. Then, six cultivars with contrasting TCB tolerance were selected to study the expression of Si transport and detoxification related genes. Compared with the control, the TCB treatment resulted in decreased growth indices, chlorophyll content, and antioxidant enzyme activities, and increased the superoxide anion content and root electrical conductivity. Application of Si improved rice growth, chlorophyll content and alleviated oxidative damage caused by TCB. The alleviating effect of Si ranged from 4.1 % to 56.72 % among the cultivars, with the strongest alleviating effect on Wuyujing 36. The transcript levels of genes encoding Si transporters and detoxification enzymes were higher in tolerant cultivars than in sensitive cultivars. The TCB treatment induced the expression of GST and Lsi2 in roots and HO-1 in leaves; these genes as well as Lsi1 were differentially expressed in roots and/or leaves in the TCB + Si treatment. Lsi1 played a key role in Si-mediated TCB tolerance in Wuyujing 36. The joint analysis of gene transcript levels in TCB and TCB + Si treatments confirmed that all six genes were associated with TCB tolerance, especially Lsi1 and Lsi2 in roots and GST and CuZn-SOD in leaves. Si can increase rice plants' resistance to TCB stress by improving growth and enhancing superoxide dismutase (SOD) activity and chlorophyll content, and by up-regulating genes involved in Si transport and detoxification.

Silicon as a Smart Fertilizer for Sustainability and Crop Improvement

Silicon (Si), despite being abundant in nature, is still not considered a necessary element for plants. Si supplementation in plants has been extensively studied over the last two decades, and the role of Si in alleviating biotic and abiotic stress has been well documented. Owing to the noncorrosive nature and sustainability of elemental Si, Si fertilization in agricultural practices has gained more attention. In this review, we provide an overview of different smart fertilizer types, application of Si fertilizers in agriculture, availability of Si fertilizers, and experiments conducted in greenhouses, growth chambers, and open fields. We also discuss the prospects of promoting Si as a smart fertilizer among farmers and the research community for sustainable agriculture and yield improvement. Literature review and empirical studies have suggested that the application of Si-based fertilizers is expected to increase in the future. With the potential of nanotechnology, new nanoSi (NSi) fertilizer applications may further increase the use and efficiency of Si fertilizers. However, the general awareness and scientific investigation of NSi need to be thoughtfully considered. Thus, we believe this review can provide insight for further research into Si fertilizers as well as promote Si as a smart fertilizer for sustainability and crop improvement.

Role of silicon in elevating resistance against sheath blight and blast diseases in rice (Oryza sativa L.)

Rice blast caused by Magnaporthe oryzae and sheath blight caused by Rhizoctonia solani, are the two major diseases of rice that cause enormous losses in rice production worldwide. Identification and utilization of broad-spectrum resistance resources have been considered sustainable and effective strategies. However, the majority of the resistance genes and QTLs identified have often been found to be race-specific, and their resistance is frequently broken down due to continuous exposure to the pathogen. Therefore, integrated approaches to improve plant resistance against such devastating pathogen have great importance. Silicon (Si), a beneficial element for plant growth, has shown to provide a prophylactic effect against many pathogens. The application of Si helps the plants to combat the disease-causing pathogens, either through its deposition in different parts of the plant or through modulation/induction of specific defense genes by yet an unknown mechanism. Some reports have shown that Si imparts resistance to rice blast and sheath blight. The present review summarizes the mechanism of Si transport and deposition and its effect on rice growth and development. A special emphasis has been given to explore the existing evidence showing Si mediated blast and sheath blight resistance and the mechanism involved in resistance. This review will help to understand the prophylactic effects of Si against sheath blight and blast disease at the mechanical, physiological, and genetic levels. The information provided here will help develop a strategy to explore Si derived benefits for sustainable rice production.