Comparative study of silicon and selenium to modulate chloroplast pigments levels, Hill activity, photosynthetic parameters and carbohydrate metabolism under arsenic stress in rice seedlings

Integrated application of selenium and silica reduce arsenic accumulation and enhance the level of metabolites in rice grains

In this study, rice plants were co-exposed to selenium (Se) and silica (Si) under arsenic (As) stress to evaluate As accumulation in rice grains, associated cancer risk, and its impact on the types and numbers of grain metabolites. A total of 58 metabolites were identified, of which, 19 belong to sugars, and drastically altered during different treatments. Arsenic exposure significantly reduced monosaccharides, i.e., D-glucose (83%) >D-galactose (60%) >D-fructose (57%) >D-ribose (29%) but increased that monosaccharide units which have antioxidant properties (i.e. α-D-glucopyranoside and melibiose). However, the levels of D-galactose, fructose, and ribose were significantly increased during co-supplementation of selenite (SeIV) and Si under As stress. Other groups of rice grain metabolites, like sugar alcohols, organic acids, polyphenols, carboxylic acids, fatty acids, and phytosterols, were also significantly altered by As exposure and increased in grains of SeIV and Si supplemented rice compared to alone As exposure. In brief, rice growing in As-affected areas may have a low level of different metabolites. However, supplementation by selenite (SeIV) with Si not only increased metabolites and amylose/amylopectin ratio but also reduced ∼90% of As accumulation in grains. Thus, the use of SeIV with Si might be advantageous for the locals to provide a healthy diet of rice and limit As-induced cancer risk up to 10-fold.

Chloroplast antioxidant reactions associated with zinc-alleviating effects on iron toxicity in wheat seedlings

This study aimed to explore the mechanism by which Zn retards Fe toxicity by analyzing the morphological, photosynthetic, and chloroplast physiological parameters of wheat seedlings treated with either single or combined Zn and Fe. Different behavior of the seedlings was observed under untreated and treated conditions. The most discriminating quantitative traits were associated with leaf area, biomass dry mass and fresh mass, net photosynthetic rate, intercellular CO2 concentration, stomatal conductance, transpiration rate of seedlings, Hill reaction, Mg2+-ATPase and Ca2+-ATPase activities, malondialdehyde and O2 ·- contents, and glutathione reductase, ascorbate peroxidase, peroxidase, and superoxide dismutase activities and their gene expression in the seedling chloroplast. The obtained findings suggest the important function of an appropriate Zn concentration in preventing Fe toxicity. Therefore, a thorough evaluation of the effects of Zn on Fe-stressed plant growth is beneficial for sustainable agriculture.

Silicon alleviates the toxicity of microplastics on kale by regulating hormones, phytochemicals, ascorbate-glutathione cycling, and photosynthesis

Kale is rich in various essential trace elements and phytochemicals, including glucosinolate and its hydrolyzed product isothiocyanate, which have significant anticancer properties. Nowadays, new types of pollutant microplastics (MP) pose a threat to global ecosystems due to their high bioaccumulation and persistent degradation. Silicon (Si) is commonly used to alleviate abiotic stresses, offering a promising approach to ensure safe food production. However, the mechanisms through which Si mitigates MP toxicity are unknown. In this study, a pot culture experiments was conducted to evaluate the morphogenetic, physiological, and biochemical responses of kale to Si supply under MP stress. The results showed that MP caused the production of reactive oxygen species, inhibited the growth and development of kale, and reduced the content of phytochemicals by interfering with the photosynthetic system, antioxidant defense system, and endogenous hormone regulation network. Si mitigated the adverse effects of MP by enhancing the photosynthetic capacity of kale, regulating the distribution of substances between primary and secondary metabolism, and strengthening the ascorbate-glutathione (AsA-GSH) cycling system.

Gene identification, expression analysis, and molecular docking of SAT and OASTL in the metabolic pathway of selenium in Cardamine hupingshanensis

KEY MESSAGE

Identification of selenium stress-responsive expression and molecular docking of serine acetyltransferase (SAT) and O-acetyl serine (thiol) lyase (OASTL) in Cardamine hupingshanensis. A complex coupled with serine acetyltransferase (SAT) and O-acetyl serine (thiol) lyase (OASTL) is the key enzyme that catalyzes selenocysteine (Sec) synthesis in plants. The functions of SAT and OASTL genes were identified in some plants, but it is still unclear whether SAT and OASTL are involved in the selenium metabolic pathway in Cardamine hupingshanensis. In this study, genome-wide identification and comparative analysis of ChSATs and ChOASTLs were performed. The eight ChSAT genes were divided into three branches, and the thirteen ChOASTL genes were divided into four branches by phylogenetic analysis and sequence alignment, indicating the evolutionary conservation of the gene structure and its association with other plant species. qRT-PCR analysis showed that the ChSAT and ChOASTL genes were differentially expressed in different tissues under various selenium levels, suggesting their important roles in Sec synthesis. The ChSAT1;2 and ChOASTLA1;2 were silenced by the VIGS system to investigate their involvement in selenium metabolites in C. hupingshanensis. The findings contribute to understanding the gene functions of ChSATs and ChOASTLs in the selenium stress and provide a reference for further exploration of the selenium metabolic pathway in plants.

Unveiling the significance of foliar-applied silicon, selenium and phosphorus for the management and remediation of arsenic in two different rice genotypes

Under paddy soil conditions, rice plants are vulnerable to arsenic (As) accumulation, thus causing potential threat to human health. Here we investigated the influence of foliar-applied phosphorus (P: 10 and 20 mg L-1), silicon (Si: 0.6 and 1.5 g L-1) and selenium (Se: 5 and 10 mg L-1) on As accumulation, morphological and physiological attributes of two contrasting rice genotypes (KSK-133 and Super Basmati) under As stress (25 mg kg-1 as arsenate). Silicon foliar dressing significantly (p < 0.05) reduced grain As uptake (up to 67%) and improved rice growth and chlorophyll content (28-66%) in both rice genotypes over their controls. Phosphorus foliar application resulted in a notable decrease (17%) in grain As uptake of coarse rice genotype (KSK-133), while it slightly increased grain As uptake in the fine one (Super Basmati; 6%) compared to controls. However, foliar-applied Se did not show significant effects on rice plants growth attributes and As uptake in both genotypes. Similarly, biochemical and enzymatic attributes (i.e., lipid peroxidation, electrolyte leakage, peroxidase and catalase) were improved with Si application in rice plants, except for P treatment that was only effective for coarse one. Foliar-applied Si also resulted in reduced cancer risk and hazard quotient (< 0.10) for both rice genotypes. This study advances our understanding on critical role of different foliar-applied nutrients and rice genotypes, which is imperative to develop effective As remediation and management strategies in coarse and fine rice genotypes and protect human health.

Interactive effects of selenium and arsenic on phenolic constituents and antioxidant activity in rice (Oryza sativa L.)

Arsenic (As) is a heavy toxic metalloid found in air, water and soil that adversely affects the plant growth by inducing oxidative stress in plants. Its contamination of rice is a serious problem throughout the world. Selenium (Se) is a beneficial micronutrient for plants that acts as an antioxidant at low doses and protect the plants against number of environmental stresses either by modulating the primary metabolic pathways or regulating the production of phenolic compounds. In the present investigation, effect of Se on different phenolics, enzymes related to their metabolism and antioxidative potential were studied in As stressed rice leaves. Rice plants were grown in pots containing sodium arsenate (2-10 mg As(V) kg-1 soil) and sodium selenate (0.5-1 mg Se kg-1 soil), both alone and in combination and leaf samples were analyzed for various biochemical parameters. Phenolic constituents increased in rice leaves with As(V) treatment from 2 to 5 mg kg-1 soil and leaves exposed to As(V) @ 5 mg kg-1 soil exhibited 1.7, 1.9 and 2.5 fold increase in total phenolics, o-dihydroxyphenols and flavonols, respectively at grain filling stage. Binary application of Se + As improved various phenolic constituents, FRAP, reducing power and antioxidant activities as compared to control. PAL, TAL and PPO activities increased from 1.3 to 4.6 fold in combined As + Se treatment at both the stages. Anthocyanin contents showed a decline (10.8 fold) with increasing As doses and its content improved at both the stages with maximum increase of 3.76 fold with As5+Se1 combination. Binary application of As + Se improved gallic acid, chlorogenic acid, 3-hydroxy benzoic acid and kaempferol contents than control whereas catechin and coumaric acid showed the reverse trend. Application of Se can modulate phenolic constituents in leaf and grains of rice Cv PR126 due to As stress that helped plants to adapt to excess As and resulted in improved plant growth.

Modulation of plant photosynthetic processes during metal and metalloid stress, and strategies for manipulating photosynthesis-related traits

Metals constitute vital elements for plant metabolism and survival, acting as essential co-factors in cellular processes which are indispensable for plant growth and survival. Excess or deficient provision of metal/metalloids puts plant's life and survival at risk, thus considered a potent stress for plants. Chloroplasts as an organelle with a high metal demand form a pivotal site within the metal homeostasis network. Therefore, the metal-mediated electron transport chain (ETC) in chloroplasts is a primary target site of metal/metalloid-induced stresses. Both excess and deficient availability of metal/metalloids threatens plant's photosynthesis in several ways. Energy demands from the photosynthetic carbon reactions should be in balance with energy output of ETC. Malfunctioning of ETC components as a result of metal/metalloid stress initiates photoinhiition. A feedback inhibition from carbon fixation process also impedes the ETC. Metal stress impairs antioxidant enzyme activity, pigment biosynthesis, and stomatal function. However, genetic manipulations, nutrient management, keeping photostasis, and application of phytohormones are among strategies for coping with metal stress. Consequently, a comprehensive understanding of the underlying mechanisms of metal/metalloid stress, as well as the exploration of potential strategies to mitigate its impact on plants are imperative. This review offers a mechanistic insight into the disruption of photosynthesis regulation by metal/metalloids and highlights adaptive approaches to ameliorate their effects on plants. Focus was made on photostasis, nutrient interactions, phytohormones, and genetic interventions for mitigating metal/metalloid stresses.

Regulatory effects of silicon nanoparticles on the growth and photosynthesis of cotton seedlings under salt and low-temperature dual stress

BACKGROUND

Silicon nanoparticles (SiO2-NPs) play a crucial role in plants mitigating abiotic stress. However, the regulatory mechanism of SiO2-NPs in response to multiple stress remains unclear. The objectives of this study were to reveal the regulatory mechanism of SiO2-NPs on the growth and photosynthesis in cotton seedlings under salt and low-temperature dual stress. It will provide a theoretical basis for perfecting the mechanism of crop resistance and developing the technology of cotton seedling preservation and stable yield in arid and high salt areas.

RESULTS

The results showed that the salt and low-temperature dual stress markedly decreased the plant height, leaf area, and aboveground biomass of cotton seedlings by 9.58%, 15.76%, and 39.80%, respectively. While SiO2-NPs alleviated the damage of the dual stress to cotton seedling growth. In addition to reduced intercellular CO2 concentration, SiO2-NPs significantly improved the photosynthetic rate, stomatal conductance, and transpiration rate of cotton seedling leaves. Additionally, stomatal length, stomatal width, and stomatal density increased with the increase in SiO2-NPs concentration. Notably, SiO2-NPs not only enhanced chlorophyll a, chlorophyll b, and total chlorophyll content, but also slowed the decrease of maximum photochemical efficiency, actual photochemical efficiency, photochemical quenching of variable chlorophyll, and the increase in non-photochemical quenching. Moreover, SiO2-NPs enhanced the activities of ribulose-1,5-bisphosphate carboxylase/oxygenase and phosphoenolpyruvate carboxylase, improved leaf water potential, and decreased abscisic acid and malondialdehyde content. All the parameters obtained the optimal effects at a SiO2-NPs concentration of 100 mg L- 1, and significantly increased the plant height, leaf area, and aboveground biomass by 7.68%, 5.37%, and 43.00%, respectively. Furthermore, significant correlation relationships were observed between photosynthetic rate and stomatal conductance, stomatal length, stomatal width, stomatal density, chlorophyll content, maximum photochemical efficiency, actual photochemical efficiency, photochemical quenching of variable chlorophyll, and Rubisco activity.

CONCLUSION

The results suggested that the SiO2-NPs improved the growth and photosynthesis of cotton seedlings might mainly result from regulating the stomatal state, improving the light energy utilization efficiency and electron transport activity of PSII reaction center, and inducing the increase of Rubisco activity to enhance carbon assimilation under the salt and low-temperature dual stress.

Regulatory Mechanisms Underlying Arsenic Uptake, Transport, and Detoxification in Rice

Arsenic (As) is a metalloid environmental pollutant ubiquitous in nature that causes chronic and irreversible poisoning to humans through its bioaccumulation in the trophic chain. Rice, the staple food crop for 350 million people worldwide, accumulates As more easily compared to other cereal crops due to its growth characteristics. Therefore, an in-depth understanding of the molecular regulatory mechanisms underlying As uptake, transport, and detoxification in rice is of great significance to solving the issue of As bioaccumulation in rice, improving its quality and safety and protecting human health. This review summarizes recent studies on the molecular mechanisms of As toxicity, uptake, transport, redistribution, regulation, and detoxification in rice. It aims to provide novel insights and approaches for preventing and controlling As bioaccumulation in rice plants, especially reducing As accumulation in rice grains.

Silicon-mediated alleviation of cadmium toxicity in soil-plant system: historical review

The contamination of crops by Cd is a worldwide problem that needs to be addressed for minimizing risk for human health. Today, numerous investigations have demonstrated that Si plays a role in reducing Cd toxicity and accumulation in cultivated plants. The evolution of scientific understanding - the Cd behavior in soil and in plant is discussed for the first time. Our analysis evidences that the research on Si-Cd interactions in the soil-plant system has quickened only in recent years, although basic interactions between silicic acid and Cd cations in aqueous systems were studied over 40-50 years ago. Today, numerous direct and indirect mechanisms of the Si impact on mobility and translocation of Cd in soil and in plants are reported. More productive studies in this area are those that considered the soil-plant system as a whole. Analysis of the development of the Cd-Si-related ideas suggests the prospects of further studies aimed at finding synergetic action of Si and other substances on Cd behavior in the soil-plant system.

Screening of Durum Wheat Cultivars for Selenium Response under Contrasting Environments, Based on Grain Yield and Quality Attributes

In the literature, little information is available on the effect of Selenium (Se) on durum wheat yield and grain quality performances. A field investigation was conducted to explore the effect of exogenous Se foliar supply on two types of durum wheat germplasm; i.e., 16 advanced lines and nine modern varieties. The Se effect was assessed on grain yield as well as on technological quality traits (moisture, protein and gluten contents, Zeleny sedimentation index, and deformation energy) in two contrasting environments in Tunisia, namely Kef–Boulifa (semi-arid region) and Beja (sub-humid region). The results displayed significant effects of environments, Se foliar application, and cultivars on grain yield and quality attributes. For grain yield performance, the beneficial effect of Se was more pronounced under the Kef–Boulifa environment, and conversely for the grain quality. A genetic variation was observed within and among the two environments under both Se treatments (with and without Se). Notably, the Se-treated advanced lines displayed the highest grain yield under Kef–Boulifa and Beja conditions. Although these cultivars showed better grain quality in both sites, the modern varieties valorized the Se foliar application better. Cultivars that recorded the highest values for the studies attributes were not necessarily those that valorized the Se supply better. Interestingly, some advanced lines have noted superiority compared to the modern varieties. In this study, cultivars that combine both good yield and good grain quality were determined for semi-arid (L11, L1, Dhahbi, and Maali) and sub-humid (L2, L14, L6, L3, Salim, and INRAT 100) zones. The screening results provide genetic material that could be exploited in breeding programs to improve Se use efficiency.