An insight into the role of silicon on retaliation to osmotic stress in finger millet (Eleusine coracana (L.) Gaertn)

Revitalization of small millets for nutritional and food security by advanced genetics and genomics approaches

Small millets, also known as nutri-cereals, are smart foods that are expected to dominate food industries and diets to achieve nutritional security. Nutri-cereals are climate resilient and nutritious. Small millet-based foods are becoming popular in markets and are preferred for patients with celiac and diabetes. These crops once ruled as food and fodder but were pushed out of mainstream cultivation with shifts in dietary habits to staple crops during the green revolution. Nevertheless, small millets are rich in micronutrients and essential amino acids for regulatory activities. Hence, international and national organizations have recently aimed to restore these lost crops for their desirable traits. The major goal in reviving these crops is to boost the immune system of the upcoming generations to tackle emerging pandemics and disease infestations in crops. Earlier periods of civilization consumed these crops, which had a greater significance in ethnobotanical values. Along with nutrition, these crops also possess therapeutic traits and have shown vast medicinal use in tribal communities for the treatment of diseases like cancer, cardiovascular disease, and gastrointestinal issues. This review highlights the significance of small millets, their values in cultural heritage, and their prospects. Furthermore, this review dissects the nutritional and therapeutic traits of small millets for developing sustainable diets in near future.

Combination of Biochemical, Molecular, and Synchrotron-Radiation-Based Techniques to Study the Effects of Silicon in Tomato (Solanum Lycopersicum L.)

The work focused on the analysis of two cultivars of tomato (Solanum lycopersicum L.), Aragon and Gladis, under two different treatments of silicon, Low, 2 L of 0.1 mM CaSiO3, and High, 0.5 mM CaSiO3, weekly, for 8 weeks, under stress-free conditions. We subsequently analyzed the morphology, chemical composition, and elemental distribution using synchrotron-based µ-XRF techniques, physiological, and molecular aspects of the response of the two cultivars. The scope of the study was to highlight any significant response of the plants to the Si treatments, in comparison with any response to Si of plants under stress. The results demonstrated that the response was mainly cultivar-dependent, also at the level of mitochondrial-dependent oxidative stress, and that it did not differ from the two conditions of treatments. With Si deposited mainly in the cell walls of the cells of fruits, leaves, and roots, the treatments did not elicit many significant changes from the point of view of the total elemental content, the physiological parameters that measured the oxidative stress, and the transcriptomic analyses focalized on genes related to the response to Si. We observed a priming effect of the treatment on the most responsive cultivar, Aragon, in respect to future stress, while in Gladis the Si treatment did not significantly change the measured parameters.

Comparison of selenite and selenate in alleviation of drought stress in Nicotiana tabacum L

Exogenous selenium (Se) improves the tolerance of plants to abiotic stress. However, the effects and mechanisms of different Se species on drought stress alleviation are poorly understood. This study aims to evaluate and compare the different effects and mechanisms of sodium selenate (Na2SeO4) and sodium selenite (Na2SeO3) on the growth, photosynthesis, antioxidant system, osmotic substances and stress-responsive gene expression of Nicotiana tabacum L. under drought stress. The results revealed that drought stress could significantly inhibit growth, whereas both Na2SeO4 and Na2SeO3 could significantly facilitate the growth of N. tabacum under drought stress. However, compared to Na2SeO3, Se application as Na2SeO4 induced a significant increase in the root tip number and number of bifurcations under drought stress. Furthermore, both Na2SeO4 and Na2SeO3 displayed higher levels of photosynthetic pigments, better photosynthesis, and higher concentrations of osmotic substances, antioxidant enzymes, and stress-responsive gene (NtCDPK2, NtP5CS, NtAREB and NtLEA5) expression than drought stress alone. However, the application of Na2SeO4 showed higher expression levels of the NtP5CS and NtAREB genes than Na2SeO3. Both Na2SeO4 and Na2SeO3 alleviated many of the deleterious effects of drought in leaves, which was achieved by reducing stress-induced lipid peroxidation (MDA) and H2O2 content by enhancing the activity of antioxidant enzymes, while Na2SeO4 application showed lower H2O2 and MDA content than Na2SeO3 application. Overall, the results confirm the positive effects of Se application, especially Na2SeO4 application, which is markedly superior to Na2SeO3 in the role of resistance towards abiotic stress in N. tabacum.

Multifaceted roles of silicon in mitigating environmental stresses in plants

Food security relies on plant productivity and plant's resilience to climate change driven environmental stresses. Plants employ diverse adaptive mechanisms of stress-signalling pathways, antioxidant defense, osmotic adjustment, nutrient homeostasis and phytohormones. Over the last few decades, silicon has emerged as a beneficial element for enhancing plant growth productivity. Silicon ameliorates biotic and abiotic stress conditions by regulating the physiological, biochemical and molecular responses. Si-uptake and transport are facilitated by specialized Si-transporters (Lsi1, Lsi2, Lsi3, and Lsi6) and, the differential root anatomy has been shown to reflect in the varying Si-uptake in monocot and dicot plants. Silicon mediates a number of plant processes including osmotic, ionic stress responses, metabolic processes, stomatal physiology, phytohormones, nutrients and source-sink relationship. Further studies on the transcriptional and post-transcriptional regulation of the Si transporter genes are required for better uptake and transport in spatial mode and under different stress conditions. In this article, we present an account of the availability, uptake, Si transporters and, the role of Silicon to alleviate environmental stress and improve plant productivity.

Fascinating regulatory mechanism of silicon for alleviating drought stress in plants

Plants confront several environmental stresses that are crucial in defining plant productivity. Among these environmental stresses, drought stress is recognized as the foremost abiotic factor which affects the food security around the globe due to its negative impact on the plant development, and quality of plant products. Because of this, drought stress has gained an imperative appearance in the field of plant sciences in recent years. Silicon (Si), an agronomically essential mineral nutrient, is recognized highly advantageous in enhancing plant growth at various phases of plant life cycle under water deficit circumstances. Si has been considered extensively useful in mitigating harmful consequences of drought stress by enhancing root H₂O absorption, regulating uptake of nutrients, reducing transpiration rate, improving photosynthetic activity, increment in the production of compatible solutes and by elevating plant antioxidant defense functioning. Si also known to improve plant endurance to limited water availability by inducing the functioning of various stress associated genes. To maximize the potential benefits and sustainable efficiency of Si in agriculture, it is of crucial importance to gain knowledge about the underlying mechanisms of how Si counteract stress conditions. Various findings suggested that Si increases the plant's immune system against drought stress, and application of Si is an important approach to shield plants from adverse stress conditions and soil nutrient depletion. This paper shows that Si has imperative and noteworthy impacts on improving plant tolerance to drought stress via maintaining cellular homeostasis. Present review mainly provides an insight into silicon role as beneficial element to alleviate drought stress in plants by regulating their morphological, physicochemical and molecular characteristics.

Silicon-induced mitigation of drought stress in peanut genotypes (Arachis hypogaea L.) through ion homeostasis, modulations of antioxidative defense system, and metabolic regulations

Drought stress considered as a major environmental constraint that frequently limits crop production globally. In the current investigation, drought stress-induced alterations in growth, ion homeostasis, photosynthetic pigments, organic osmolytes, reactive oxygen species (ROS) generation, antioxidative components, and metabolic profile were examined in order to assess the role of silicon (Si) in mitigation of drought effects and to understand the drought adaptive mechanism in two contrasting peanut genotypes (GG7: fast growing and tall, TG26: slow growing and semi-dwarf). Si application significantly improved the leaf chlorophyll content, relative water content % (RWC %), growth and biomass in GG7 compared with TG26 genotype under water stress. Si supplementation considerably promotes the uptake and transport of mineral nutrients under drought condition in both the genotypes, which eventually promote plant growth. Exogenous application of Si protects the photosynthetic pigments from oxidative damage by reducing membrane lipid peroxidation and either maintained or reduced H₂O₂ accumulation in both the genotypes. The activity of enzymatic antioxidants like superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX), and glutathione reductase (GR) and non-enzymatic antioxidants like ascorbate (AsA) and glutathione (GSH) were either maintained or increased in both the genotypes in response to Si under drought as compared to those without Si. Silicon-induced higher accumulation of metabolites mainly sugars and sugar alcohols (talose, mannose, fructose, sucrose, cellobiose, trehalose, pinitol, and myo-inositol), amino acids (glutamic acid, serine, histidine, threonine, tyrosine, valine, isoleucine, and leucine) in GG7 genotype as compared to TG26, provides osmo-protection. Moreover, Si application increased phytohormones levels such as indole-3-acetic acid (IAA), gibberellic acid (GA₃), jasmonic acid (JA), and zeatin in GG7 genotype under drought stress compared to non-Si treated seedlings suggesting its involvement in signaling pathways for drought adaptation and tolerance. Noteworthy increment in polyphenols (chlorogenic acid, caffeic acid, ellagic acid, rosmarinic acid, quercetin, coumarin, naringenin, and kaempferol) in the Si treated seedlings of GG7 genotype as compared to TG26 under drought stress suggests an efficient mechanism of ROS sequestration in GG7 genotype. Our findings provide comprehensive information on physiological, biochemical, and metabolic dynamics associated with Si-mediated water stress tolerance in peanut. This study indicates that the drought tolerance efficacy of peanut genotypes can be improved by Si application.

Enhancement of Nicotiana tabacum Resistance Against Dehydration-Induced Leaf Senescence via Metabolite/Phytohormone-Gene Regulatory Networks Modulated by Melatonin

Melatonin (MEL) is a pleiotropic agent with crucial functions reported in a variety of stress responses and developmental processes. Although MEL involvement in plant defense against natural leaf senescence has been widely reported, the precise regulatory mechanisms by which it delays stress-induced senescence remain unclear. In this study, we found that foliar spraying of melatonin markedly ameliorated dehydration-induced leaf senescence in Nicotiana tabacum, accompanied by attenuated oxidative damage, expression of senescence-related genes, and reduced endogenous ABA production. Metabolite profiling indicated that melatonin-treated plants accumulated higher concentrations of sugars, sugar alcohol, and organic acids, but fewer concentrations of amino acids in the leaves, than untreated plants after exposure to dehydration. Gene expression analysis revealed that the delayed senescence of stressed plants achieved by melatonin treatment might be partially ascribed to the upregulated expression of genes involved in ROS scavenging, chlorophyll biosynthesis, photosynthesis, and carbon/nitrogen balances, and downregulated expression of senescence-associated genes. Furthermore, hormone responses showed an extensively modulated expression, complemented by carotenoid biosynthesis regulation to achieve growth acceleration in melatonin-treated plants upon exposure to dehydration stress. These findings may provide more comprehensive insights into the role of melatonin in alleviating leaf senescence and enhancing dehydration resistance.

Characterization of influx and efflux silicon transporters and understanding their role in the osmotic stress tolerance in finger millet (Eleusine coracana (L.) Gaertn.)

Over the last decade, silicon (Si) has been widely accepted as a beneficial element for plant growth. The advantages plant derives from the Si are primarily based on the uptake and transport mechanisms. In the present study, the Si uptake regime was studied in finger millet (Eleusine coracana (L). Gaertn.) under controlled and stress conditions. The finger millet can efficiently uptake Si and accumulate it by more than 1% of dry weight in the leaf tissues, thus categorized as a Si accumulator. Subsequent evaluation with the single root assay revealed a three-fold higher Si uptake under osmatic stress than control. These results suggest that Si alleviated the PEG-induced stress by regulating the levels of osmolytes and antioxidant enzymes. Further, to understand the molecular mechanism involved in Si uptake, the Si influx (EcoLsi1 and EcoLsi6) and efflux transporters (EcoLsi2 and EcoLsi3) were identified and characterized. The comparative phylogenomic analysis of the influx transporter EcoLsi1 with other monocots revealed conserved features like aromatic/arginine (Ar/R) selectivity filters and pore morphology. Similarly, Si efflux transporter EcoLsi3 is highly homologous to other annotated efflux transporters. The transcriptome data revealed that the expression of both influx and efflux Si transporters was elevated due to Si supplementation under stress conditions. These findings suggest that stress elevates Si uptake in finger millet, and its transport is also regulated by the Si transporters. The present study will be helpful to better explore Si derived benefits in finger millet.