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Silicon (Si) is the most copious element of existence in the lithosphere but still it has not been added into the essential element list. The imperative role of Si in triggering growth and development of plants has been identified. It is of paramount importance in regulating overall physiological and metabolic characteristics of the plants. Being considered as a non-essential element, it has been known to occur at about 30%, majority of its presence is there in rocks as mineral salts. It has been regarded as multitalented or quasi-element on earth's crust that can be efficiently taken up by plants and translocated further towards aerial parts via transpiration phenomenon. It has also been known to mitigate different biotic and abiotic stressed conditions from plants as the need of the hour owing to its eco-friendly nature. However, the mechanisms associated with their stress attenuation are associated with Reactive Oxygen Species (ROS) scavenging, activation of antioxidative defense responses and phytohormonal signaling. Also, biotic stress factors can be ameliorated through accumulation of Si within epidermal tissues or pathogenesis-related host defense mechanisms. To explore further, omics-mediated studies have been further discussed to shed light on the stress mitigating processes. Further, to improve our understanding for Si-mediated benefits in plants we need to explore the molecular mechanisms of Si uptake, transport and gene expression studies revealing their mitigate properties. In the present review, we have evolved the Si-based studies in plants associated with its transport, uptake and accumulation. Apart from this, we have also discussed about their role in ameliorating stresses from plants by activating their defenses. Moreover, their roles in plant hormonal crosstalk have also been elucidated. Above all, we have also revealed the role of Si-Nanoparticles (SiNPs) in improving stress potential of plants along with stimulation of plant productivities via omics-based approaches.

Soil amendments are known to promote several plant growth parameters. In many agro-ecosystems, water scarcity and drought induced phosphorus deficiency limits crop yield significantly. Considering the climate change scenario, drought and related stress factors will be even more severe endangering the global food security. Therefore, two parallel field trials were conducted to examine at what extent soil amendment of leonardite and humic acid would affect drought and phosphorus tolerance of maize. The treatments were: control (C: 100% A pan and 125 kg P ha −1 ), P deficiency (phosphorus stress (PS): 62.5 kg P ha −1 ), water deficit stress (water stress (WS): 67% A pan), and PS + WS (67% A pan and 62.5 kg P ha −1 ). Three organic amendments were (i) no amendment, (ii) 625 kg S + 750 kg leonardite ha −1 and (iii) 1250 kg S + 37.5 kg humic acid ha −1 ) tested on stress treatments. Drought and P deficiency reduced plant biomass, grain yield, chlorophyll content, F v /F m , RWC and antioxidant activity (superoxide dismutase, peroxidase, and catalase), but increased electrolyte leakage and leaf H 2 O 2 in maize plants. The combined stress of drought and P deficiency decreased further related plant traits. Humic acid and leonardite enhanced leaf P and yield in maize plants under PS. A significant increase in related parameters was observed with humic acid and leonardite under WS. The largest increase in yield and plant traits in relation to humic acid and leonardite application was observed under combined stress situation. The use of sulfur-enriched amendments can be used effectively to maintain yield of maize crop in water limited calcareous soils.

Cadmium stress is one of the chief environmental cues that can substantially reduce plant growth. In the present research, we studied the effect of jasmonic acid (JA) and gibberellic acid (GA 3 ) applied individually and/or in combination to chickpea ( Cicer arietinum ) plants exposed to 150 µM cadmium sulphate. Cadmium stress resulted in reduced plant growth and pigment contents. Moreover, chickpea plants under cadmium contamination displayed higher levels of electrolytic leakage, H 2 O 2, and malonaldehyde, as well as lower relative water content. Plants primed with JA (1 nM) and those foliar-fed with GA 3 (10 –6  M) showed improved metal tolerance by reducing the accumulation of reactive oxygen species, malonaldehyde and electrolytic leakage, and increasing relative water content. . Osmoprotectants like proline and glycinebetaine increased under cadmium contamination. Additionally, the enzymatic activities and non-enzymatic antioxidant levels increased markedly under Cd stress, but application of JA as well as of GA 3 further improved these attributes. Enzymes pertaining to the ascorbate glutathione and glyoxylase systems increased significantly when the chickpea plants were exposed to Cd. However, JA and GA 3 applied singly or in combination showed improved enzymatic activities as well as nutrient uptake, whereas they reduced the metal accumulation in chickpea plants. Taken together, our findings demonstrated that JA and GA 3 are suitable agents for regulating Cd stress resistance in chickpea plants.

Due to their versatile applications, ZnONPs have been formulated by several approaches, including green chemistry methods. In the current study, convenient and economically viable ZnONPs were produced using Elaeagnus angustifolia (EA) leaf extracts. The phytochemicals from E. angustifolia L. are believed to serve as a non-toxic source of reducing and stabilizing agents. The physical and chemical properties of ZnONPs were investigated employing varying analytical techniques (UV, XRD, FT-IR, EDX, SEM, TEM, DLS and Raman). Strong UV–Vis absorption at 399 nm was observed for green ZnONPs. TEM, SEM and XRD analyses determined the nanoscale size, morphology and crystalline structure of ZnONPs, respectively. The ZnONPs were substantiated by evaluation using HepG2 (IC 50 : 21.7 µg mL −1 ) and HUH7 (IC 50 : 29.8 µg mL −1 ) cancer cell lines and displayed potential anticancer activities. The MTT cytotoxicity assay was conducted using Leishmania tropica “KWH23” (promastigotes: IC 50 , 24.9 µg mL −1 ; and amastigotes: IC 50 , 32.83 µg mL −1 ). ZnONPs exhibited excellent antimicrobial potencies against five different bacterial and fungal species via the disc-diffusion method, and their MIC values were calculated. ZnONPs were found to be biocompatible using human erythrocytes and macrophages. Free radical scavenging tests revealed excellent antioxidant activities. Enzyme inhibition assays were performed and revealed excellent potential. These findings suggested that EA@ZnONPs have potential applications and could be used as a promising candidate for clinical development.

Plant leaves offer an exclusive windowpane to uncover the changes in organs, tissues, and cells as they advance towards the process of senescence and death. Drought-induced leaf senescence is an intricate process with remarkably coordinated phases of onset, progression, and completion implicated in an extensive reprogramming of gene expression. Advancing leaf senescence remobilizes nutrients to younger leaves thereby contributing to plant fitness. However, numerous mysteries remain unraveled concerning leaf senescence. We are not still able to correlate leaf senescence and drought stress to endogenous and exogenous environments. Furthermore, we need to decipher how molecular mechanisms of the leaf senescence and levels of drought tolerance are advanced and how is the involvement of SAGs in drought tolerance and plant fitness. This review provides the perspicacity indispensable for facilitating our coordinated point of view pertaining to leaf senescence together with inferences on progression of whole plant aging. The main segments discussed in the review include coordination between hormonal signaling, leaf senescence, drought tolerance, and crosstalk between hormones in leaf senescence regulation.

Brassinosteroids (BRs) are an important group of plant steroidal hormones that are actively involved in a myriad of key growth and developmental processes from germination to senescence. Moreover, BRs are known for their effective role in alleviation of stress-induced changes in normal metabolism via the activation of different tolerance mechanisms. Efforts to improve plant growth through exogenous application of BRs (through different modes such as foliar spray, presowing seed treatment, or through root growing medium) have gained considerable ground world over. It has been widely demonstrated that the exogenous application of BRs to stressed plants imparts the stress tolerance mechanisms. In BR-induced regulation of physio-biochemical processes in plants, interaction (crosstalk) of BRs with other phytohormones has been reported. This crosstalk may fine-tune the effective roles of other hormones in regulating stress tolerance. The multifaceted role of BRs consolidated so far has reflected their immense potential to help plants in counteracting the stress-induced changes. The effects of introgression and up- and down-regulation of BR-related genes reported so far to improve crop productivity have been presented here. Strong evidence exists that BRs are involved in signal transduction particularly in the regulation of the mitogen-activated protein kinase (MAPK) cascade, which in turn is involved in controlled development, cell death, and the perception of pathogen-associated molecular pattern (PAMP) signaling. How far BRs are involved in signal transduction pathways operative under stressful environments has also been comprehensively discussed in this review.

Mung bean is an important pulse crop. It is highly nutritive but is vulnerable to salinity stress. Therefore, the present study was aimed to investigate the protective effect of silicon (Si) against salt stress-induced damage to mung bean plants. Mung bean plants treated with NaCl (0, 50 and 100 mM) showed considerable declines in length and dry weights of shoots and roots. Chlorophyll-a (chl-a), chl-b, total chl, carotenoids and leaf relative water content (LRWC) decreased under NaCl stress. However, supplementation with Si in the form of sodium silicate (Na2SiO3) to NaCl-stressed plants ameliorated the adverse effects of NaCl on growth, biomass, pigment synthesis and leaf relative water content (LRWC). Silicon (Si)-supplemented plants exhibited enhanced chl-fluorescence and gas exchange parameters under normal (non-stress) as well as NaCl stress conditions. Salt-induced decline in the frequency of stomata and number of leaves per plant under salt stress was significantly recovered with Si supplementation. In addition, application of Si increased the levels of proline and glycine betaine in mung bean plants. Furthermore, histochemical staining tests showed that the levels of superoxide radicals and H2O2 increased with NaCl treatments, which thereby resulted in increased lipid peroxidation (LPO) and electrolyte leakage. Contrarily, decreased levels of H2O2, lipid peroxidation (measured as MDA content), and electrolyte leakage in Si-supplemented plants under NaCl stress indicated the stress mitigating role of Si. The activities of key antioxidant enzymes (SOD, CAT, APX and GR) under NaCl stress showed an increase under the NaCl regime. However, application of Si further boosted the activities of all four antioxidant enzymes in NaCl-stressed plants. The enhanced Na+ uptake and Na+/K+ ratio in mung bean plants accompanied by decreased K+ and Ca2+ uptake under NaCl stress were reversed with Si supplementation thereby resulting in enhanced accumulation of K+ and Ca2+ and decreased Na+. In conclusion, Si supplementation mitigated the negative effects of NaCl on mung bean plants through modifications in uptake of inorganic nutrients, osmolyte production and the antioxidant defence system.

Reactive oxygen species (ROS) and nitric oxide (NO) are produced in all aerobic life forms under both physiological and adverse conditions. Unregulated ROS/NO generation causes nitro-oxidative damage, which has a detrimental impact on the function of essential macromolecules. ROS/NO production is also involved in signaling processes as secondary messengers in plant cells under physiological conditions. ROS/NO generation takes place in different subcellular compartments including chloroplasts, mitochondria, peroxisomes, vacuoles, and a diverse range of plant membranes. This compartmentalization has been identified as an additional cellular strategy for regulating these molecules. This assessment of subcellular ROS/NO metabolisms includes the following processes: ROS/NO generation in different plant cell sites; ROS interactions with other signaling molecules, such as mitogen-activated protein kinases (MAPKs), phosphatase, calcium (Ca2+), and activator proteins; redox-sensitive genes regulated by the iron-responsive element/iron regulatory protein (IRE-IRP) system and iron regulatory transporter 1(IRT1); and ROS/NO crosstalk during signal transduction. All these processes highlight the complex relationship between ROS and NO metabolism which needs to be evaluated from a broad perspective.

Environmental pollution by alkaline salts, such as Na 2 CO 3 , is a permanent problem in agriculture. Here, we examined the putative role of jasmonic acid (JA) in improving Na 2 CO 3 -stress tolerance in maize seedlings. Pretreatment of maize seedlings with JA was found to significantly mitigate the toxic effects of excessive Na 2 CO 3 on photosynthesis- and plant growth-related parameters. The JA-induced improved tolerance could be attributed to decreased Na uptake and Na 2 CO 3 -induced oxidative damage by lowering the accumulation of reactive oxygen species and malondialdehyde. JA counteracted the salt-induced increase in proline and glutathione content, and significantly improved ascorbic acid content and redox status. The major antioxidant enzyme activities were largely stimulated by JA pretreatment in maize plants exposed to excessive alkaline salts. Additionally, increased activities of glyoxalases I and II were correlated with reduced levels of methylglyoxal in JA-pretreated alkaline-stressed maize plants. These results indicated that modifying the endogenous Na + and K + contents by JA pretreatment improved alkaline tolerance in maize plants by inhibiting Na uptake and regulating the antioxidant and glyoxalase systems, thereby demonstrating the important role of JA in mitigating heavy metal toxicity. Our findings may be useful in the development of alkali stress tolerant crops by genetic engineering of JA biosynthesis.

Cadmium (Cd) is considered to be one of the most toxic pollutants persistent in soil for thousands of years and is ranked on seventh position among all environmental pollutants. The higher concentration of Cd in plants inhibits their growth and metabolism and further enters the food chain. Cd toxicity initiates redox actions in plants by inducing oxidative stress through the production of free radicals. It alters mineral uptake by disturbing water potential or affects the microbial population in soils, opening and closing of stomata, transpiration, photosynthesis, antioxidant levels, sugar metabolism and productivities. It also causes chlorosis, mineral deficiencies, inhibition of nitrate reductase activity and ammonia assimilation in several plant species. The plants have adopted a number of mechanisms to facilitate reduction in the amount of ROS. They possess series of antioxidative defence responses to scavenge reactive oxygen species (ROS) levels. Furthermore, specific mechanisms such as such as efflux, immobilization, stabilization, complexation, sequestration and detoxification are generally observed to combat the Cd stresses. Moreover, endogenous phytohormonal signalling during stressed conditions within plants has also been focussed. Cd stimulates various hormonal signalling pathways and regulates many physiological processes in plants that in turn ameliorate Cd stress. Strikingly, phytohormones play an imperative role during signal transduction pathway along with regulating overall growth and development of plants under toxic conditions. Moreover, plant hormones boost antioxidant activities and plummet oxidative damage from plants along with maintaining cellular homeostasis. This review encompasses the ecotoxicological aspects of Cd within plants and plant responses to tackle such adversities.