Exogenous Silicon Attenuates Cadmium-Induced Oxidative Stress in Brassica napus L. by Modulating AsA-GSH Pathway and Glyoxalase System

Overexpression of dehydroascorbate reductase gene IbDHAR1 improves the tolerance to abiotic stress in sweet potato

Dehydroascorbate reductase (DHAR), an indispensable enzyme in the production of ascorbic acid (AsA) in plants, is vital for plant tolerance to various stresses. However, there is limited research on the stress tolerance functions of DHAR genes in sweet potato (Ipomoea batatas [L.] Lam). In this study, the full-length IbDHAR1 gene was cloned from the leaves of sweet potato cultivar Xu 18. The IbDHAR1 protein is speculated to be located in both the cytoplasm and the nucleus. As revealed by qRT-PCR, the relative expression level of IbDHAR1 in the proximal storage roots was much greater than in the other tissues, and could be upregulated by high-temperature, salinity, drought, and abscisic acid (ABA) stress. The results of pot experiments indicated that under high salinity and drought stress conditions, transgenic Arabidopsis and sweet potato plants exhibited decreases in H2O2 and MDA levels. Conversely, the levels of antioxidant enzymes APX, SOD, POD, and ACT, and the content of DHAR increased. Additionally, the ratio of AsA/DHA was greater in transgenic lines than in the wild type. The results showed that overexpression of IbDHAR1 intensified the ascorbic acid-glutathione cycle (AsA-GSH) and promoted the activity of the related antioxidant enzyme systems to improve plant stress tolerance and productivity.

Application of CuNPs and AMF alleviates arsenic stress by encompassing reduced arsenic uptake through metabolomics and ionomics alterations in Elymus sibiricus

Recent studies have exhibited a very promising role of copper nanoparticles (CuNPs) in mitigation of abiotic stresses in plants. Arbuscular mycorrhizae fungi (AMF) assisted plants to trigger their defense mechanism against abiotic stresses. Arsenic (As) is a non-essential and injurious heavy-metal contaminant. Current research work was designed to elucidate role of CuNPs (100, 200 and 300 mM) and a commercial inoculum of Glomus species (Clonex® Root Maximizer) either alone or in combination (CuNPs + Clonex) on physiology, growth, and stress alleviation mechanisms of E. sibiricus growing in As spiked soils (0, 50, and 100 mg Kg- 1 soil). Arsenic induced oxidative stress, enhanced biosynthesis of hydrogen peroxide, lipid peroxidation and methylglyoxal (MG) in E. sibiricus. Moreover, As-phytotoxicity reduced photosynthetic activities and growth of plants. Results showed that individual and combined treatments, CuNPs (100 mM) as well as soil inoculation of AMF significantly enhanced root growth and shoot growth by declining As content in root tissues and shoot tissues in As polluted soils. E. sibiricus plants treated with CuNPs (100 mM) and/or AMF alleviated As induced phytotoxicity through upregulating the activity of antioxidative enzymes such as catalase (CAT) and superoxide dismutase (SOD) besides the biosynthesis of non-enzymatic antioxidants including phytochelatin (PC) and glutathione (GSH). In brief, supplementation of CuNPs (100 mM) alone or in combination with AMF reduced As uptake and alleviated the As-phytotoxicity in E. sibiricus by inducing stress tolerance mechanism resulting in the improvement of the plant growth parameters.

Physiology and transcriptomic analysis revealed the mechanism of silicon promoting cadmium accumulation in Sedum alfredii Hance

Silicon (Si) effectively promote the yield of many crops, mainly due to its ability to enhance plants resistance to stress. However, how Si helps hyperaccumulators to extract Cadmium (Cd) from soil has remained unclear. In this study, Sedum alfredii Hance (S. alfredii) was used as material to study how exogenous Si affected biomass, Cd accumulation, antioxidation, cell ultrastructure, subcellular distribution and changes in gene expression after Cd exposure. The study has shown that as Si concentration increases (1, 2 mM), the shoot biomass of plants increased by 33.1%-63.6%, the Cd accumulation increased by 31.9%-96.6%, and the chlorophyll, carotenoid content, photosynthetic gas exchange parameters significantly increased. Si reduced Pro and MDA, promoted the concentrations of SOD, CAT and POD to reduce antioxidant stress damage. In addition, Si promoted GSH and PC to chelate Cd in vacuoles, repaired damaged cell ultrastructure, improved the fixation of Cd and cell wall (especially in pectin), and reduced the toxic effects of Cd. Transcriptome analysis found that genes encoding Cd detoxification, Cd absorption and transport were up-regulated by Si supplying, including photosynthetic pathways (PSB, LHCB, PSA), antioxidant defense systems (CAT, APX, CSD, RBOH), cell wall biosynthesis such as pectinesterase (PME), chelation (GST, MT, NAS, GR), Cd absorption (Nramp3, Nramp5, ZNT) and Cd transport (HMA, PCR). Our result revealed the tentative mechanism of Si promotes Cd accumulation and enhances Cd tolerance in S. alfredii, and thereby provides a solid theoretical support for the practical use of Si fertilizer in phytoextraction.

Pb uptake, accumulation, and translocation in plants: Plant physiological, biochemical, and molecular response: A review

Lead (Pb) is a highly toxic contaminant that is ubiquitously present in the ecosystem and poses severe environmental issues, including hazards to soil-plant systems. This review focuses on the uptake, accumulation, and translocation of Pb metallic ions and their toxicological effects on plant morpho-physiological and biochemical attributes. We highlight that the uptake of Pb metal is controlled by cation exchange capacity, pH, size of soil particles, root nature, and other physio-chemical limitations. Pb toxicity obstructs seed germination, root/shoot length, plant growth, and final crop-yield. Pb disrupts the nutrient uptake through roots, alters plasma membrane permeability, and disturbs chloroplast ultrastructure that triggers changes in respiration as well as transpiration activities, creates the reactive oxygen species (ROS), and activates some enzymatic and non-enzymatic antioxidants. Pb also impairs photosynthesis, disrupts water balance and mineral nutrients, changes hormonal status, and alters membrane structure and permeability. This review provides consolidated information concentrating on the current studies associated with Pb-induced oxidative stress and toxic conditions in various plants, highlighting the roles of different antioxidants in plants mitigating Pb-stress. Additionally, we discussed detoxification and tolerance responses in plants by regulating different gene expressions, protein, and glutathione metabolisms to resist Pb-induced phytotoxicity. Overall, various approaches to tackle Pb toxicity have been addressed; the phytoremediation techniques and biochar amendments are economical and eco-friendly remedies for improving Pb-contaminated soils.

Physiological and biochemical responses of Leersia hexandra Swartz to nickel stress: Insights into antioxidant defense mechanisms and metal detoxification strategies

Phytoremediation is widely considered as a cost-effective method for managing heavy metal soil pollution. Leersia hexandra Swartz shows a promising potential for the remediation of heavy metals pollution, including chromium (Cr), copper (Cu), and nickel (Ni). It is vital to understand the physiological and biochemical responses of L. hexandra to Ni stress to elucidate the mechanisms underlying Ni tolerance and accumulation. Here, we examined the metabolic and transcriptomic responses of L. hexandra exposed to 40 mg/L Ni for 24 h and 14 d. After 24-h Ni stress, gene expression of glutathione metabolic cycle (GSTF1, GSTU1 and MDAR4) and superoxide dismutase (SODCC2) was significantly increased in plant leaves. Furthermore, after 14-d Ni stress, the ascorbate peroxidase (APX7), superoxide dismutase (SODCP and SOD1), and catalase (CAT) gene expression was significantly upregulated, but that of glutathione metabolic cycle (EMB2360, GSTU1, GSTU6, GSH2, GPX6, and MDAR2) was downregulated. After 24-h Ni stress, the differentially expressed metabolites (DEMs) were mainly flavonoids (45%) and flavones (20%). However, after 14-d Ni stress, the DEMs were mainly carbohydrates and their derivatives (34%), amino acids and derivatives (15%), and organic acids and derivatives (8%). Results suggest that L. hexandra adopt distinct time-dependent antioxidant and metal detoxification strategies likely associated with intracellular reduction-oxidation balance. Novel insights into the molecular mechanisms responsible for Ni tolerance in plants are presented.

Regulation of rhizosphere microenvironment by rice husk ash for reducing the accumulation of cadmium and arsenic in rice

It is important to reduce Cd and As content in brown rice in contaminated paddy soils. We conducted research on the effects of rice husk ash (RHA) on the Cd and As in the rhizosphere microenvironment (soil, porewater, and iron plaque) and measured the Cd, As, and Si content in rice plants. The main elements in RHA were Si (29.64%) and O (69.17%), which had the maximum adsorption capacity for Cd was 42.49 mg/kg and for As was 18.62 mg/kg. Soil pH and available Si content increased, while soil available Cd and As decreased following application of 0.5%-2% RHA. RHA promote the transformation of Cd to insoluble fraction, while As was transformed from a poorly soluble form to a more active one. RHA reduced Cd content and increased Si content in porewater, and reduced As only at the later rice growth stages. RHA increased the amount of iron plaque, thereby decreasing the Cd content in iron plaque, while increased the As content in it. Cd and inorganic As content in brown rice were decreased, to 0.31 mg/kg and 0.18 mg/kg, respectively. The decrease of Cd in brown rice was due to the decrease of Cd mobility in soil, thereby reducing root accumulation, while the decrease of As in brown rice was affected by the transport from roots to stems. Therefore, RHA can be considered as a safe and efficient in-situ remediation amendment for Cd and As co-contaminated paddy soil.

Foliar spraying of exogenous uniconazole (S3307) at the flowering stage as an effective method to resist low-temperature stress on mung bean [Vigna radiata (L.) Wilczek]

Low temperature is one of the major constraints on agricultural productivity worldwide and is likely to further increase. Several adaptations and mitigation strategies are required to cope with low-temperature stress. Uniconazole (S3307) could play a significant role in the alleviation of abiotic stress in plants. In this study, the effects of S3307 on the reactive oxygen species (ROS) and antioxidant metabolism were studied in the leaves of mung bean [Vigna radiata (L.) Wilczek]. The experimental results showed that the low-temperature induced accumulation of superoxide anion (O2-) production rate, and malonaldehyde (MDA) contents. Increased proline content and enzymatic antioxidants, including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), were found to alleviate oxidative damage under low temperatures. While, S3307 could reduce O2- production rate and MDA contents and increase the activities of SOD, POD, and CAT, slowed the decrease in ascorbic acid (AsA), dehydroascorbic acid (DHA), glutathione (GSH), and oxidized glutathione (GSSG), and promoted increase in soluble sugars (SS), soluble proteins (SP), and proline (Pro) content under low-temperature. At the same time, low temperature leads to lower 100 grain weight and number of grains per plant, which eventually causes yield reduction decreased. Foliar spraying of S3307 could alleviate the yield loss caused by low temperature, and the increase of S3307 treatment was 5.1%-12.5% and 6.3%-32.9% for the two varieties, respectively, compared with CK. In summary, exogenous S3307 pretreatment enhances plant tolerance to low-temperature by improving the antioxidant enzyme activities, increased non-enzymatic antioxidants content, and decreased O2- production rate and MDA contents and inducing alterations in endogenous S3307, and reduce the decrease in mung bean yield.

Modulations of functional traits of Spinacia oleracea plants exposed to cadmium stress by using H2S as an antidote: a regulatory mechanism

The present study is based on the application of H2S as an exogenous antidote in Spinacia oleracea (spinach) plants grown in Cd-contaminated (50 ppm) soil. The different doses of H2S in the form of NaHS (10, 50, 100, 200, and 500 μM) have been applied as a foliar spray to regulate the physiological attributes under Cd toxicity. Over to control, the plants grown in Cd alone showed a reduction in the fresh biomass by 48% with more production of oxidative biomarkers (H2O2, SOR, and MDA content) and antioxidative enzymes (SOD, POD, APX, and GR). Further, with the exogenous application of H2S, among all the doses the fresh biomass was found to be maximally increased at 100 μM dose by 76%, and the Cd content was reduced significantly by 25% in the shoot compared to plants grown in Cd treated soil alone. With the decrease in Cd content in the shoot, the production of H2O2, SOR, and MDA content was reduced by 52%, 40%, and 38% respectively, at 100 μM compared to the plants grown in Cd-treated soil. The activities of estimated antioxidative enzymes showed a reduction in their activities up to 100 μM. Whereas, Glutathione reductase (GR) and Phytochelatins (PCs) showed different trends with their higher values in plants treated with NaHS in the presence of Cd. At 100 μM the GR and PCs, respectively showed 48% and 37% increment over Cd-treated plants alone. At this dose, the relative expression of SOD, POD, APX, GR, and PCS5 (Phytochelatin synthetase enzyme) genes, and other functional activities (SEM and fluorescence kinetics) supported the best performance of plants at 100 μM. Therefore, among all the doses, 100 μM dose of H2S has significantly reduced the Cd toxicity by maintaining the growth and other functional traits of plants. The correlation analysis also supported the result by showing a relationship between H2S application and Cd uptake. So, with this strategy, the plants grown in metal-contaminated fields can be improved qualitatively as well as quantitatively. With further experimentation, the mode of application could be explored to increase its efficiency and to promote this strategy at a wider scale.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01389-3.

Elevated carbon dioxide concentrations increase the risk of Cd exposure in rice

Since the Industrial Revolution, crops have been exposed to various changes in the environment, including elevated atmospheric carbon dioxide (CO2) concentration and cadmium (Cd) pollution in soil. However, information about how combined changes affect crop is limited. Here, we have investigated the changes of japonica and indica rice subspecies seedlings under elevated CO2 level (1200 ppm) and Cd exposure (5 μM Cd) conditions compared with ambient CO2 level (400 ppm) and without Cd exposure in CO2 growth chambers with hydroponic experiment. The results showed that elevated CO2 levels significantly promoted seedling growth and rescued the growth inhibition under Cd stress. However, the elevated CO2 levels led to a significant increase in the shoot Cd accumulation of the two rice subspecies. Especially, the increase of shoot Cd accumulation in indica rice was more than 50% compared with control. Further investigation revealed that the decreases in the photosynthetic pigments and photosynthetic rates caused by Cd were attenuated by the elevated CO2 levels. In addition, elevated CO2 levels increased the non-enzymatic antioxidants and significantly enhanced the ascorbate peroxidase (APX) and glutathione reductase (GR) activities, alleviating the lipid peroxidation and reactive oxygen species (ROS) accumulation induced by Cd. Overall, the research revealed how rice responded to the elevated CO2 levels and Cd exposure, which can help modify agricultural practices to ensure food security and food safety in a future high-CO2 world.

Algal Bio-Stimulants Enhance Salt Tolerance in Common Bean: Dissecting Morphological, Physiological, and Genetic Mechanisms for Stress Adaptation

Salinity adversely affects the plant's morphological characteristics, but the utilization of aqueous algal extracts (AE) ameliorates this negative impact. In this study, the application of AE derived from Chlorella vulgaris and Dunaliella salina strains effectively reversed the decline in biomass allocation and water relations, both in normal and salt-stressed conditions. The simultaneous application of both extracts in salt-affected soil notably enhanced key parameters, such as chlorophyll content (15%), carotene content (1%), photosynthesis (25%), stomatal conductance (7%), and transpiration rate (23%), surpassing those observed in the application of both AE in salt-affected as compared to salinity stress control. Moreover, the AE treatments effectively mitigated lipid peroxidation and electrolyte leakage induced by salinity stress. The application of AE led to an increase in GB (6%) and the total concentration of free amino acids (47%) by comparing with salt-affected control. Additionally, salinity stress resulted in an elevation of antioxidant enzyme activities, including superoxide dismutase, ascorbate peroxidase, catalase, and glutathione reductase. Notably, the AE treatments significantly boosted the activity of these antioxidant enzymes under salinity conditions. Furthermore, salinity reduced mineral contents, but the application of AE effectively counteracted this decline, leading to increased mineral levels. In conclusion, the application of aqueous algal extracts, specifically those obtained from Chlorella vulgaris and Dunaliella salina strains, demonstrated significant efficacy in alleviating salinity-induced stress in Phaseolus vulgaris plants.

The regulatory metabolic networks of the Brassica campestris L. hairy roots in response to cadmium stress revealed from proteome studies combined with a transcriptome analysis

Brassica campestris L., a cadmium (Cd) hyperaccumulating herbaceous plant, is considered as a promising candidate for the bioremediation of Cd pollution. However, the molecular mechanisms regulating these processes remain unclear. The present work, using proteome studies combined with a transcriptome analysis, was carried out to reveal the response mechanisms of the hairy roots of Brassica campestris L. under Cd stress. Significant tissue necrosis and cellular damage occurred, and Cd accumulation was observed in the cell walls and vacuoles of the hairy roots. Through quantitative proteomic profiling, a total of 1424 differentially expressed proteins (DEPs) were identified, and are known to be enriched in processes including phenylalanine metabolism, plant hormone signal transduction, cysteine and methionine metabolism, protein export, isoquinoline alkaloid biosynthesis and flavone biosynthesis. Further studies combined with a transcriptome analysis found that 118 differentially expressed genes (DEGs) and their corresponding proteins were simultaneously up- or downregulated. Further Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analysis of the 118 shared DEGs and DEPs indicated their involvement in calcium, ROS and hormone signaling-mediated response, including regulation of carbohydrate and energy metabolism, biosynthesis of GSH, PCs and phenylpropanoid compounds that play vital roles in the Cd tolerance of Brassica campestris L. Our findings contribute to a better understanding of the regulatory networks of Brassica campestris L. under Cd stress, as well as provide valuable information on candidate genes (e.g., BrPAL, BrTAT, Br4CL, BrCDPK, BrRBOH, BrCALM, BrABCG1/2, BrVIP, BrGCLC, BrilvE, BrGST12/13/25). These results are of particular importance to the subsequent development of promising transgenic plants that will hyperaccumulate heavy metals and efficient phytoremediation processes.

The SbbHLH041-SbEXPA11 Module Enhances Cadmium Accumulation and Rescues Biomass by Increasing Photosynthetic Efficiency in Sorghum

In plants, expansin genes are responsive to heavy metal exposure. To study the bioremediary potential of this important gene family, we discovered a root-expressed expansin gene in sorghum, SbEXPA11, which is notably upregulated following cadmium (Cd) exposure. However, the mechanism underlying the Cd detoxification and accumulation mediated by SbEXPA11 in sorghum remains unclear. We overexpressed SbEXPA11 in sorghum and compared wild-type (WT) and SbEXPA11-overexpressing transgenic sorghum in terms of Cd accumulation and physiological indices following Cd. Compared with the WT, we found that SbEXPA11 mediates Cd tolerance by exerting reactive oxygen species (ROS)-scavenging effects through upregulating the expression of antioxidant enzymes. Moreover, the overexpression of SbEXPA11 rescued biomass production by increasing the photosynthetic efficiency of transgenic plants. In the pot experiment with a dosage of 10 mg/kg Cd, transgenic sorghum plants demonstrated higher efficacy in reducing the Cd content of the soil (8.62 mg/kg) compared to WT sorghum plants (9.51 mg/kg). Subsequent analysis revealed that the SbbHLH041 transcription factor has the ability to induce SbEXPA11 expression through interacting with the E-box located within the SbEXPA11 promoter. These findings suggest that the SbbHLH041-SbEXPA11 cascade module may be beneficial for the development of phytoremediary sorghum varieties.

Exogenous application of glutathione enhanced growth, nutritional orchestration and physiochemical characteristics of Brassica oleracea L. under lead stress

A major obstacle to agricultural production and yield quality is heavy metal contamination of the soil and water, which leads to lower productivity and quality of crops. The situation has significantly worsened as a result of the growing population and subsequent rise in food consumption. The growth of nutrient-rich plants is hampered by lead (Pb) toxicity in the soil. Brassica oleracea L. (broccoli) is a prominent vegetable crop in the Brassicaceae family subjected to a number of biotic and abiotic stresses that dramatically lower crop yields. Seed priming is a novel, practicable, and cost-effective method that can improve various abiotic stress tolerances. Many plant metabolic activities depend on the antioxidant enzyme glutathione (GSH), which also chelates heavy metals. Keeping in view the stress mitigation potential of GSH, current research work was designed to inspect the beneficial role of seed priming with GSH on the growth, morphological and gas exchange attributes of broccoli seedlings under Pb stress. For this purpose, broccoli seeds were primed with 25, 50, and 75 µM L-1 GSH. Plant growth and photosynthetic activity were adversely affected by Pb stress. Furthermore, Pb stress enhanced proline levels along with reduced protein and phenol content. The application of GSH improved growth traits, total soluble proteins, chlorophyll content, mineral content, and gas exchange parameters. The involvement of GSH in reducing Pb concentrations was demonstrated by an improved metal tolerance index and lower Pb levels in broccoli plants. The results of the current study suggest that GSH can be used as a strategy to increase broccoli tolerance to Pb by enhancing nutrient uptake, growth and proline.

Integrated physio-biochemical and transcriptomic analysis revealed mechanism underlying of Si-mediated alleviation to cadmium toxicity in wheat

Cadmium (Cd) contamination has resulted in serious reduction of crop yields. Silicon (Si), as a beneficial element, regulates plant growth to heavy metal toxicity mainly through reducing metal uptake and protecting plants from oxidative injury. However, the molecular mechanism underlying Si-mediated Cd toxicity in wheat has not been well understood. This study aimed to reveal the beneficial role of Si (1 mM) in alleviating Cd-induced toxicity in wheat (Triticum aestivum) seedlings. The results showed that exogenous supply of Si decreased Cd concentration by 67.45% (root) and 70.34% (shoot), and maintained ionic homeostasis through the function of important transporters, such as Lsi, ZIP, Nramp5 and HIPP. Si ameliorated Cd-induced photosynthetic performance inhibition through up-regulating photosynthesis-related genes and light harvesting-related genes. Si minimized Cd-induced oxidative stress by decreasing MDA contents by 46.62% (leaf) and 75.09% (root), and helped re-establish redox homeostasis by regulating antioxidant enzymes activities, AsA-GSH cycle and expression of relevant genes through signal transduction pathway. The results revealed molecular mechanism of Si-mediated wheat tolerance to Cd toxicity. Si fertilizer is suggested to be applied in Cd contaminated soil for food safety production as a beneficial and eco-friendly element.

Abscisic acid (ABA) alleviates cadmium toxicity by enhancing the adsorption of cadmium to root cell walls and inducing antioxidant defense system of Cosmos bipinnatus

Cadmium (Cd) pollution is a global problem affecting soil ecology and plant growth. Abscisic acid (ABA) acts as a growth and stress hormone, regulates cell wall synthesis, and plays an important role in plant responses to stress. There are few studies on the mechanisms behind abscisic acid alleviation of cadmium stress in Cosmos bipinnatus, especially in regards to regulation of the root cell wall. This study examined the effects of different concentrations of abscisic acid at different concentrations of cadmium stress. Through adding 5 μmol/L and 30 μmol/L cadmium, followed by spraying 10 μmol/L and 40 μmol/L ABA in a hydroponic experiment, it was found that under two concentrations of cadmium stress, low concentration of ABA improved root cell wall polysaccharide, Cd, and uronic acid content. Especially in pectin, after the application of low concentration ABA, the cadmium concentration was significantly increased by 1.5 times and 1.2 times compared with the Cd concentration under Cd5 and Cd30 treatment alone, respectively. Fourier-Transform Infrared spectroscopy (FTIR) demonstrated that cell wall functional groups such as -OH and -COOH were increased with exposure to ABA. Additionally, the exogenous ABA also increased expression of three kinds of antioxidant enzymes and plant antioxidants. The results of this study suggest that ABA could reduce Cd stress by increasing Cd accumulation, promoting Cd adsorption on the root cell wall, and activating protective mechanisms. This result could help promote application of C. bipinnatus for phytostabilization of cadmium-contaminated soil.

Biochar-Mediated Control of Metabolites and Other Physiological Responses in Water-Stressed Leptocohloa fusca

We investigated biochar-induced drought tolerance in Leptocohloa fusca (Kallar grass) by exploring the plant defense system at physiological level. L. fusca plants were exposed to drought stress (100%, 70%, and 30% field capacity), and biochar (BC), as an organic soil amendment was applied in two concentrations (15 and 30 mg kg-1 soil) to induce drought tolerance. Our results demonstrated that drought restricted the growth of L. fusca by inhibiting shoot and root (fresh and dry) weight, total chlorophyll content and photosynthetic rate. Under drought stress, the uptake of essential nutrients was also limited due to lower water supply, which ultimately affected metabolites including amino and organic acids, and soluble sugars. In addition, drought stress induced oxidative stress, which is evidenced by the higher production of reactive oxygen species (ROS) including hydrogen peroxide (H2O2), superoxide ion (O2-), hydroxyl ion (OH-), and malondialdehyde (MDA). The current study revealed that stress-induced oxidative injury is not a linear path, since the excessive production of lipid peroxidation led to the accumulation of methylglyoxal (MG), a member of reactive carbonyl species (RCS), which ultimately caused cell injury. As a consequence of oxidative-stress induction, the ascorbate-glutathione (AsA-GSH) pathway, followed by a series of reactions, was activated by the plants to reduce ROS-induced oxidative damage. Furthermore, biochar considerably improved plant growth and development by mediating metabolites and soil physio-chemical status.

The mechanism of silicon on alleviating cadmium toxicity in plants: A review

Cadmium is one of the most toxic heavy metal elements that seriously threaten food safety and agricultural production worldwide. Because of its high solubility, cadmium can easily enter plants, inhibiting plant growth and reducing crop yield. Therefore, finding a way to alleviate the inhibitory effects of cadmium on plant growth is critical. Silicon, the second most abundant element in the Earth's crust, has been widely reported to promote plant growth and alleviate cadmium toxicity. This review summarizes the recent progress made to elucidate how silicon mitigates cadmium toxicity in plants. We describe the role of silicon in reducing cadmium uptake and transport, improving plant mineral nutrient supply, regulating antioxidant systems and optimizing plant architecture. We also summarize in detail the regulation of plant water balance by silicon, and the role of this phenomenon in enhancing plant resistance to cadmium toxicity. An in-depth analysis of literature has been conducted to identify the current problems related to cadmium toxicity and to propose future research directions.

In vitro application of proline in potato tubers under newly emerging bacteria Lelliottia amnigena infection

Biotic stress deleteriously affects growth, development, and productivity in plants. Proline (Pro) plays a significant role in enhancing plant resistance to pathogen infection. However, its effects on reducing Lelliottia amnigena-induced oxidative stress in potato tubers remain unknown. The present study aims to evaluate the in vitro Pro treatment in potato tubers exposed to a newly emerging bacterium, L. amnigena. Sterilized healthy potato tubers were inoculated with 0.3 mL of L. amnigena suspension (3.69 × 10⁷ CFU mL^-1) 24 h before Pro (5.0 mM) application. The L. amnigena treatment significantly increased the contents of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) in the potato tubers by 80.6 and 85.6%, respectively, compared to the control. Application of proline (Pro) decreased MDA and H₂O₂ contents by 53.6 and 55.9%, respectively, compared to the control. Application of Pro to L. amnigena-stressed potato tubers increased the activities of NADPH oxidase (NOX), superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), polyphenol oxidase (PPO), phenylalanine ammonia-lyase (PAL), cinnamyl alcohol dehydrogenase (CAD), 4-coumaryl-CoA ligase (4CL) and cinnamate-4-hydroxylase (C4H) C4H by 94.2, 96.3, 97.3, 97.1, 96.6, 79.3, 96.4, 93.6, and 96.2%, respectively, compared to the control. In comparison to the control, the genes PAL, SOD, CAT, POD, and NOX were significantly increased in the Pro-treated tubers at 5.0 mM concentration. Tubers treated with Pro + L. amnigena increased the transcript levels of PAL, SOD, CAT, POD, and NOX by 2.3, 2.2, 2.3, 2.5, and 2.8-fold respectively, compared to the control. Our findings suggested that pretreatment of tubers with Pro might reduce lipid peroxidation and oxidative stress by enhancing enzymatic antioxidant activity and gene expression.

Effect of Thallium(I) on Growth, Nutrient Absorption, Photosynthetic Pigments, and Antioxidant Response of Dittrichia Plants

Dittrichia plants were exposed to thallium (Tl) stress (10, 50, and 100 µM) for 7 days. The Tl toxicity altered the absorption and accumulation of other nutrients. In both the roots and the leaves, there was a decline in K, Mg, and Fe content, but an increase in Ca, Mn, and Zn. Chlorophylls decreased, as did the photosynthetic efficiency, while carotenoids increased. Oxidative stress in the roots was reflected in increased lipid peroxidation. There was more production of superoxide (O2.−), hydrogen peroxide (H2O2), and nitric oxide (NO) in the roots than in the leaves, with increases in both organs in response to Tl toxicity, except for O2.− production in the roots, which fluctuated. There was increased hydrogen sulfide (H2S) production, especially in the leaves. Superoxide dismutase (SOD), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), monodehydroascorbate reductase (MDHAR), and glutathione reductase (GR) showed increased activities, except for APX and MDHAR in the roots and GR in the leaves. The components of the ascorbate–glutathione cycle were affected. Thus, ascorbate (AsA) increased, while dehydroascorbate (DHA), reduced glutathione (GSH), and oxidized glutathione (GSSG) decreased, except for in the roots at 100 µM Tl, which showed increased GSH. These Tl toxicity-induced alterations modify the AsA/DHA and GSH/GSSG redox status. The NO and H2S interaction may act by activating the antioxidant system. The effects of Tl could be related to its strong affinity for binding with -SH groups, thus altering the functionality of proteins and the cellular redox state.

Involvement of abscisic acid in silicon-mediated enhancement of copper stress tolerance in Artemisia annua

Heavy metal (HM) toxicity is a well-known hazard which causes deleterious impact on the growth and development of plants. The impact of abscisic acid (ABA) in presence of silicon (Si) on plant development and quality traits has largely gone unexplored. The effects of ABA and Si on the growth, yield, and quality characteristics of Artemisia annua L. plants growing under copper (Cu) stress (20 and 40 mg kg^-1) were investigated in a pot experiment. During this investigation, Cu stress caused severe damage to the plants but exogenous administration of Si and ABA ameliorated the harmful effects of Cu toxicity, and the plants displayed higher biomass and improved physio-biochemical attributes. Copper accumulated in the roots and shoots and its toxicity caused oxidative stress as demonstrated by the increased 2-thiobarbituric acid reactive substance (TBARS) content. It also resulted in the increased activity of antioxidant enzymes, however, the exogenous Si and ABA supplementation decreased the buildup of reactive oxygen species (ROS) and lipid peroxidation, alleviating the oxidative damage produced by HM stress. Copper toxicity had a considerable negative impact on glandular trichome density, ultrastructure as well as artemisinin production. However, combined Si and ABA enhanced the size and density of glandular trichomes, resulting in higher artemisinin production. Taken together, our results demonstrated that exogenous ABA and Si supplementation protect A. annua plants against Cu toxicity by improving photosynthetic characteristics, enhancing antioxidant enzyme activity, protecting leaf structure and integrity, avoiding excess Cu deposition in shoot and root tissues, and helping in enhanced artemisinin biosynthesis. Our results indicate that the combined application of Si and ABA improved the overall growth of plants and may thus be used as an effective approach for the improvement of growth and yield of A. annua in Cu-contaminated soils.

Attenuation of negative effects caused by a combination of heat and cadmium stress in Arabidopsis thaliana deficient in jasmonic acid synthesis

Due to recent global warming, heat stress can simultaneously occur with cadmium (Cd) stress in regions suffering from metal pollution. In this study, we investigated the effects of heat, Cd and their combination on the growth and physiological characteristics of Arabidopsis thaliana. Arabidopsis plants were more susceptible to a combination of heat and Cd stress than to each stress applied individually, although the accumulation of Cd in shoots was comparable between plants subjected to Cd stress and the combined stress. Plants subjected to this stress combination showed a dramatic reduction in the accumulation of the photosynthetic reaction center proteins in photosystem II as well as a tendency toward enhanced lipid peroxidation, suggesting that the negative effects of a combination of heat and Cd stresses might be caused by oxidative damage accompanied by damage to the photosynthetic apparatus. Interestingly, aos and lox3 mutants deficient in jasmonic acid (JA) synthesis showed attenuation of the negative effects caused by a combination of heat and Cd stresses on the growth and maximum quantum efficiency of photosystem II. The roles of JA might be altered when heat stress is combined with Cd stress, despite its significance in the tolerance of plants to Cd stress when individually applied, which has been shown in previous studies.

Regulatory Mechanisms of Plant Growth-Promoting Rhizobacteria and Plant Nutrition against Abiotic Stresses in Brassicaceae Family

Extreme environmental conditions, such as abiotic stresses (drought, salinity, heat, chilling and intense light), offer great opportunities to study how different microorganisms and plant nutrition can influence plant growth and development. The intervention of biological agents such as plant growth-promoting rhizobacteria (PGPRs) coupled with proper plant nutrition can improve the agricultural importance of different plant species. Brassicaceae (Cruciferae) belongs to the monophyletic taxon and consists of around 338 genera and 3709 species worldwide. Brassicaceae is composed of several important species of economical, ornamental and food crops (vegetables, cooking oils, forage, condiments and industrial species). Sustainable production of Brassicas plants has been compromised over the years due to several abiotic stresses and the unbalanced utilization of chemical fertilizers and uncertified chemicals that ultimately affect the environment and human health. This chapter summarized the influence of PGPRs and nutrient management in the Brassicaceae family against abiotic stresses. The use of PGPRs contributed to combating climate-induced change/abiotic factors such as drought, soil and water salinization and heavy metal contamination that limits the general performance of plants. Brassica is widely utilized as an oil and vegetable crop and is harshly affected by abiotic stresses. Therefore, the use of PGPRs along with proper mineral nutrients management is a possible strategy to cope with abiotic stresses by improving biochemical, physiological and growth attributes and the production of brassica in an eco-friendly environment.

Grape Berry Responses to Sequential Flooding and Heatwave Events: A Physiological, Transcriptional, and Metabolic Overview

Grapevine cultivation, such as the whole horticulture, is currently challenged by several factors, among which the extreme weather events occurring under the climate change scenario are the most relevant. Within this context, the present study aims at characterizing at the berry level the physiological response of Vitis vinifera cv. Sauvignon Blanc to sequential stresses simulated under a semi-controlled environment: flooding at bud-break followed by multiple summer stress (drought plus heatwave) occurring at pre-vèraison. Transcriptomic and metabolomic assessments were performed through RNASeq and NMR, respectively. A comprehensive hormone profiling was also carried out. Results pointed out a different response to the heatwave in the two situations. Flooding caused a developmental advance, determining a different physiological background in the berry, thus affecting its response to the summer stress at both transcriptional levels, with the upregulation of genes involved in oxidative stress responses, and metabolic level, with the increase in osmoprotectants, such as proline and other amino acids. In conclusion, sequential stress, including a flooding event at bud-break followed by a summer heatwave, may impact phenological development and berry ripening, with possible consequences on berry and wine quality. A berry physiological model is presented that may support the development of sustainable vineyard management solutions to improve the water use efficiency and adaptation capacity of actual viticultural systems to future scenarios.

Determination and Quantification of Phytochemicals from the Leaf Extract of Parthenium hysterophorus L. and Their Physio-Biochemical Responses to Several Crop and Weed Species

This current investigation was undertaken both in laboratory and glasshouse for documentation and quantification of phytochemicals from different parts of the parthenium (Parthenium hysterophorus L.) plant through LC-MS and HPLC to study their effect on two crops namely, Bambara groundnut (Vigna subterranean L.) and maize (Zea mays L.), and six different types of weed e.g., Digitaria sanguinalis, Eleusine indica, Ageratum conyzoides, Cyperus iria, Euphorbia hirta, and Cyperus difformis. The parthenium methanolic leaf extracts at 25, 50, 75, and 100 g L^-1 were sprayed in the test crops and weeds to assess their physiological and biochemical reactions after 6, 24, 48, and 72 h of spraying these compounds (HAS). The LC-MS analysis confirmed seven types of phytochemicals (caffeic acid, ferulic acid, vanillic acid, parthenin, chlorogenic acid, quinic acid, and p-anisic acid) in the parthenium leaf extract that were responsible for the inhibition of tested crops and weeds. From the HPLC analysis, higher amounts in leaf methanol extracts (40,752.52 ppm) than those of the stem (2664.09 ppm) and flower extracts (30,454.33 ppm) were recorded. Parthenium leaf extract at 100 g L^-1 had observed higher phytotoxicity on all weed species except C. difformis. However, all crops were found safe under this dose of extraction. Although both crops were also affected to some extent, they could recover from the stress after a few days. The photosynthetic rate, transpiration rate, stomatal conductance, carotenoid and chlorophyll content were decreased due to the application of parthenium leaf extract. However, when parthenium leaf extract was applied at 100 g L^-1 for 72 h, the malondialdehyde (MDA) and proline content were increased in all weeds. Enzymatic antioxidant activity (e.g., superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) contents) were also elevated as a result of the sprayed parthenium leaf extract. The negative impact of physiological and biochemical responses as a consequence of the parthenium leaf extract led the weed species to be stressed and finally killed. The current findings show the feasibility of developing bioherbicide from the methanolic extract of parthenium leaf for controlling weeds, which will be cost-effective, sustainable, and environment friendly for crop production during the future changing climate.

Interactions between hydrogen sulphide and rhizobia modulate the physiological and metabolism process during water deficiency-induced oxidative defense in soybean

Hydrogen sulphide (H₂ S), a new gas signal molecule, participates in the regulation of various abiotic stresses in plants. However, how the tandem working of H₂ S and rhizobia affects the adaptation of soybean to water deficiency is still unclear. In this study, we investigated the adaptation mechanism of H₂ S and rhizobia in soybean to water deficiency. Our results revealed that H₂ S and rhizobia jointly enhanced the leaf chlorophyll content and relative water content in plants, and caused an increase in the biomass of soybean seedlings under water deficiency. Besides, in the absence of water, H₂ S enhanced the biomass by affecting the number of nodules and nitrogenase activity during vegetative growth. The expression of nodulation marker genes including early nodulin 40 (GmENOD40), ERF required for nodulation (GmERN) and nodulation inception genes (GmNIN1a, GmNIN2a and GmNIN2b) were upregulated by H₂ S and rhizobia in the nodules. Moreover, the combined effect of H₂ S and rhizobia was proved to affect the enzyme activities and gene expression level of antioxidants, as well as osmotic protective substance content and related gene expression levels under water deficiency in soybean seedlings. In addition, the metabolomic results suggested that the combined effect of H₂ S and rhizobia remarkably promoted the contents of lipids and lipid-like molecules. Our results indicated that H₂ S and rhizobia synergistically reduced the oxidative damage caused by water deficiency through increasing the accumulation of metabolites and strengthening the plant antioxidant capacity.

Nitric Oxide Made a Major Contribution to the Improvement of Quality in Button Mushrooms (Agaricus bisporus) by the Combined Treatment of Nitric Oxide with 1-MCP

Browning is one of the major effects of shelf-life responsible for the reduction in the commercial value of the button mushrooms (Agaricus bisporus). In this study, the individual and the combined effects of exogenous sodium nitroprusside (SNP, a nitric oxide donor) and 1-methylcyclopropene (1-MCP) on the quality of button mushrooms were evaluated. The results demonstrated that mushrooms treated with SNP+1-MCP promoted reactive oxygen species (ROS) metabolism thereby protecting cell membrane integrity, hindering polyphenol oxidase (PPO) binding to phenolic compounds, and downregulating the PPO activity. In addition, the SNP+1-MCP treatment effectively maintained quality (firmness, color, total phenol, and flavonoid) and mitigated oxidative damage by reducing ROS accumulation and malondialdehyde production through the stimulation of the antioxidant enzymes activities and the enhancement of ascorbic acid (AsA) and glutathione (GSH) contents. Moreover, the correlation analysis validated the above results. The SNP+1-MCP treatment was observed to be more prominent on maintaining quality than the individual effects of SNP followed by 1-MCP, suggesting that the combination of NO and 1-MCP had synergistic effects in retarding button mushrooms senescence, and NO signaling molecules might be predominant in the synergy.

Short-term responses of Spinach (Spinacia oleracea L.) to the individual and combinatorial effects of Nitrogen, Phosphorus and Potassium and silicon in the soil contaminated by boron

While of lesser prevalence than boron (B) deficient soils, B-rich soils are important to study as they can cause B toxicity in the field and subsequently decrease crop yields in different regions of the world. We have conducted the present study to examine the role of the individual or combined application of silicon (Si) and NPK fertilizer in B-stressed spinach plants (Spinacia oleracea L.). S. oleracea seedlings were subjected to different NPK fertilizers, namely, low NPK (30 kg ha-2) and normal NPK (60 kg ha-2)], which were also supplemented by Si (3 mmol L-1), for varying levels of B in the soil i.e., 0, 250, and 500 mg kg-1. Our results illustrated that the increasing levels of B in the soil caused a substantial decrease in the plant height, number of leaves, number of stems, leaf area, plant fresh weight, plant dry weight, chlorophyll a, chlorophyll b, total chlorophyll, carotenoid content, net photosynthesis, stomatal conductance, transpiration rate, magnesium content in the roots, magnesium contents in the shoots, phosphorus content in the roots, phosphorus content in the leaves in the shoots, iron content in the roots, iron content in the shoots, calcium content in the roots, and calcium content in the shoots. However, B toxicity in the soil increased the concentration of malondialdehyde, hydrogen peroxide, and electrolyte leakage which were also manifested by the increasing activities of enzymatic [superoxidase dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX)], and non-enzymatic antioxidants (phenolic, flavonoid, ascorbic acid, and anthocyanin content). B toxicity in the soil further increased the concentration of organic acids in the roots such as oxalic acid, malic acid, formic acid, citric acid, acetic acid, and fumaric acid. The addition of Si and fertilizer levels in the soil significantly alleviated B toxicity effects on S. oleracea by improving photosynthetic capacity and ultimately plant growth. The increased activity of antioxidant enzymes in Si and NPK-treated plants seems to play a role in capturing stress-induced reactive oxygen species, as was evident from the lower levels of oxidative stress indicators, organic acid exudation, and B concentration in the roots and shoots of Si and NPK-treated plants. Research findings, therefore, suggested that the Si and NPK application can ameliorate B toxicity in S. oleracea seedlings and result in improved plant growth and composition under metal stress as depicted by the balanced exudation of organic acids.

Silicon-mediated metabolic upregulation of ascorbate glutathione (AsA-GSH) and glyoxalase reduces the toxic effects of vanadium in rice

Although beneficial metalloid silicon (Si) has been proven to reduce the toxicity of several heavy metals, there is a lack of understanding regarding Si potential function in mitigating phytotoxicity induced by vanadium (V). In this study, effect of Si (1.5 mM) on growth, biomass production, V uptake, reactive oxygen species (ROS), methylglyoxal (MG) formation, selected antioxidants enzymes activities, glyoxalase enzymes under V stress (35 mg L^-1) was investigated in hydroponic experiment. The results showed that V stress reduced rice growth, caused V accumulation in rice. Addition of Si to the nutritional medium increased plant growth, biomass yield, root length, root diameter, chlorophyll parameters, photosynthetic assimilation, ion leakage, antioxidant enzymes activities under V stress. Notably, Si sustained V-homeostasis and alleviated V caused oxidative stress by boosting ascorbate (AsA) levels and the activity of antioxidant enzymes in V stressed rice plants. Furthermore, Si protected rice seedlings against the harmful effects of methylglyoxal by increasing the activity of glyoxalase enzymes. Additionally, Si increased the expression of numerous genes involved in the detoxification of reactive oxygen species (e.g., OsCuZnSOD1, OsCaTB, OsGPX1, OsAPX1, OsGR2, and OsGSTU37) and methylglyoxal (e.g., OsGLYI-1 and OsGLYII-2). The findings supported that Si can be applied to plants to minimize the V availability to plant, and also induced V stress tolerance.

Does silicon help to alleviate water deficit stress and in the recovery of Dipteryx alata seedlings?

Water deficit to causes serious problems in the growth and development of plants, impairing their metabolism. Thus, it is necessary to use agents that can mitigate plant damage. This study assesses the potential of silicon to mitigate water deficit stress in Dipteryx alata Vogel seedlings and to help in their recovery after the resumption of irrigation. The study analyzed four water regimes: (I) Continuous irrigation; (II) Water deficit without Si; (III) Water deficit + 0.75 mL Si; and (IV) Water deficit + 1.50 mL Si. Seedlings were evaluated in four periods: (1) (T0 - time zero) at the beginning of the experiment, before irrigation suspension; (2) (P0) when the photosynthetic rates (A) of seedlings under irrigation suspension reached values close to zero, period in which irrigation was resumed; (3) (REC) when A reached values ​​close to those of seedlings under continuous irrigation, characterizing the recovery period; and (4) (END) 45 days after REC, when seedlings were kept under continuous irrigation, similar to the control. Application of 0.75 mL Si alleviates damage to the photosynthetic apparatus of D. alata seedlings that remain longer under water deficit, and contributes to faster physiological recovery after the resumption of irrigation. D. alata seedlings have recovery potential after the stress period, regardless of Si application.

Co-inoculation of halotolerant potassium solubilizing Bacillus licheniformis and Aspergillus violaceofuscus improves tomato growth and potassium uptake in different soil types under salinity

Soil salinity is an important stress that negatively affects crop growth and productivity, causing extensive agricultural losses, worldwide. Potassium (K) solubilizing microorganisms (KSMs) can impart abiotic stress tolerance in plants in addition to nutrient solubilization. In this study, the salinity tolerance of KSMs Bacillus licheniformis and Aspergillus violaceofuscus originating from saxicolous habitats was examined using different concentrations of NaCl (0, 25, 50, 75, 100, and 125 mM) under in vitro conditions. The results indicated that both KSMs were capable of tolerating salinity. As B. licheniformis had a maximum growth in 100 mM NaCl at 37 °C, A. violaceofuscus had the maximum biomass and catalase (CAT) activity at 75 mM NaCl. However, maximum proline content was detected at 100 mM NaCl in both KSMs. Further, the ability of these KSMs to promote tomato growth individually and in combination with the presence or absence of mica was also examined in unsterilized or sterilized Alfisol and Vertisol soils under induced salinity in greenhouse conditions. The results of the greenhouse study revealed that inoculation of KSMs along with/without mica amendment significantly improved the morphological and physiological characteristics of tomato plants under salinity. Plant height, leaf area, biomass, relative water content, proline content, and CAT activity of dual inoculated plants were significantly higher than non-inoculated plants. Significant correlations existed between various soil, plant growth, soil pH and available K. From the results, it could be concluded that B. licheniformis and A. violaceofuscus are potential candidates for improving crop production in saline-stressed soils.

Alleviative mechanisms of silicon solubilizing Bacillus amyloliquefaciens mediated diminution of arsenic toxicity in rice

Silicon (Si) has gained considerable attention for its utility in improved plant health under biotic and abiotic stresses through alteration of physiological and metabolic processes. Its interaction with arsenic (As) has been the compelling area of research amidst heavy metal toxicity. However, microbe mediated Si solubilization and their role for reduced As uptake is still an unexplored domain. Foremost role of Bacillus amyloliquefaciens (NBRISN13) in impediment of arsenite (AsIII) translocation signifies our work. Reduced grain As content (52-72%) during SN13 inoculation under feldspar supplementation (Si+SN+As) highlight the novel outcome of our study. Upregulation of Lsi1, Lsi2 and Lsi3genes in Si+SN+As treated rice plants associated with restricted As translocation, frames new propositions for future research on microbemediated reduced As uptake through increased Si transport. In addition to low As accumulation, alleviation of oxidative stress markers by modulation of defense enzyme activities and differential accumulation of plant hormones was found to be associated with improved growth and yield. Thus, our findings confer the potential role of microbe mediated Si solubilization in mitigation of As stress to restore plant growth and yield.

Comparative study on the influence of silicon and selenium to mitigate arsenic induced stress by modulating TCA cycle, GABA, and polyamine synthesis in rice seedlings

Arsenic contamination of groundwater is a major concern for its usage in crop irrigation in many regions of the world. Arsenic is absorbed by rice plants mainly from arsenic contaminated water during irrigation. It hampers growth and agricultural productivity. The aim of the study was to mitigate the toxic effects of arsenate (As-V) [25 μM, 50 μM, and 75 μM] by silicon (Si) [2 mM] and selenium (Se) [5 μM] amendments on the activity of the TCA cycle, synthesis of γ-aminobutyric acid (GABA) and polyamines (PAs) in rice (Oryza sativa L. cv. MTU-1010) seedlings and to identify which chemical was more potential to combat this threat. As(V) application decreased the activities of tested respiratory enzymes and increased the levels of organic acids (OAs) in the test seedlings. Application of Si with As(V) and Se with As(V) increased the activities of respiratory enzymes and the levels of OAs. The effects were more pronounced during Si amendments. The activities of GABA synthesizing enzymes along with accumulation of GABA were increased under As(V) stress. During joint application of Si with As(V) and Se with As(V) the activity and the level of said parameters were decreased that indicating defensive role of these chemicals to resist As(V) toxicity in rice and Si amendments showed greater potential to reduce As(V) induced damages in the test seedlings. PAs trigger tolerance mechanism against As(V) in plants. PAs such as putrescine, spermidine and spermine were synthesized more during Si and Se amendments in As(V) contaminated rice seedlings to combat the toxic effects of As(V). Si amendments substantially modulated the toxic effects caused by As(V) over Se amendments in the As(V) challenged test seedlings. Thus, in future application of Si enriched fertilizer will be beneficial to grow rice plants with normal vigor in arsenic contaminated soil.

Multidimensional Role of Silicon to Activate Resilient Plant Growth and to Mitigate Abiotic Stress

Sustainable agricultural production is critically antagonistic by fluctuating unfavorable environmental conditions. The introduction of mineral elements emerged as the most exciting and magical aspect, apart from the novel intervention of traditional and applied strategies to defend the abiotic stress conditions. The silicon (Si) has ameliorating impacts by regulating diverse functionalities on enhancing the growth and development of crop plants. Si is categorized as a non-essential element since crop plants accumulate less during normal environmental conditions. Studies on the application of Si in plants highlight the beneficial role of Si during extreme stressful conditions through modulation of several metabolites during abiotic stress conditions. Phytohormones are primary plant metabolites positively regulated by Si during abiotic stress conditions. Phytohormones play a pivotal role in crop plants' broad-spectrum biochemical and physiological aspects during normal and extreme environmental conditions. Frontline phytohormones include auxin, cytokinin, ethylene, gibberellin, salicylic acid, abscisic acid, brassinosteroids, and jasmonic acid. These phytohormones are internally correlated with Si in regulating abiotic stress tolerance mechanisms. This review explores insights into the role of Si in enhancing the phytohormone metabolism and its role in maintaining the physiological and biochemical well-being of crop plants during diverse abiotic stresses. Moreover, in-depth information about Si's pivotal role in inducing abiotic stress tolerance in crop plants through metabolic and molecular modulations is elaborated. Furthermore, the potential of various high throughput technologies has also been discussed in improving Si-induced multiple stress tolerance. In addition, a special emphasis is engrossed in the role of Si in achieving sustainable agricultural growth and global food security.

A tau class glutathione-S-transferase (OsGSTU5) confers tolerance against arsenic toxicity in rice by accumulating more arsenic in root

Arsenic (As) considered as one of the hazardous metalloid that hampers various physiological activities in rice. To study the mechanism of As tolerance in rice, one differentially expressed tau class glutathione-S-transferase (OsGSTU5) has been selected and transgenic rice plants with knockdown (KD) and overexpressing (OE) OsGSTU5 were generated. Our results suggested that KD lines became less tolerant to As stress than WT plants, while OE lines showed enhanced tolerance to As. Under As toxicity, OE and KD lines showed enhanced and reduced antioxidant activities such as, SOD, PRX and catalase, respectively indicating its role in ROS homeostasis. In addition, higher malondialdehyde content, poor photosynthetic parameters and higher reactive oxygen species (ROS) in KD plant, suggests that knockdown of OsGSTU5 renders KD plants more susceptible to oxidative damage. Also, the relative expression profile of various transporters such as OsABCC1 (As sequestration), Lsi2 and Lsi6 (As translocaters) and GSH dependent activity of GSTU5 suggests that GSTU5 might help in chelation of As with GSH and sequester it into the root vacuole using OsABCC1 transporter and thus limits the upward translocation of As towards shoot. This study suggests the importance of GSTU5 as a good target to improve the As tolerance in rice.

Silicon-induced alterations in the expression of aquaporins and antioxidant system activity in well-watered and drought-stressed oilseed rape

Progressing climate change necessitates the search for solutions of plant protection against the effects of water deficit. One of these solutions could be silicon supplementation. The aim of the study was to verify the hypothesis that silicon changes aquaporin expression and antioxidant system activity in a direction which may alleviate the effects of drought stress in oilseed rape. The accumulation of BnPIP1, BnPIP2-1-7 and BnTIP1;1 aquaporins and the expression of their genes, the level of catalase, superoxide dismutase activities and hydrogen peroxide content as well as total non-enzymatic antioxidant activity were analyzed in leaf tissue from control and silicon-treated oilseed rape plants growing under well-watered and drought conditions. Silicon was applied in two forms - pure silicon and a silicon complex. It was shown that under drought conditions, both pure silicon and the silicon complex (with Fe) significantly increased the accumulation of aquaporins and improved the activity of enzymatic and non-enzymatic components of the antioxidant system, while under well-watered conditions, these effects were observed only in the case of the silicon complex. The presented study proves that silicon supplementation in oilseed rape improves the regulation of water management and contributes to the protection against oxidative stress caused by drought.

Silicon Fertigation Regimes Attenuates Cadmium Toxicity and Phytoremediation Potential in Two Maize (Zea mays L.) Cultivars by Minimizing Its Uptake and Oxidative Stress

Silicon (Si) is an important plant-derived metabolite that is significantly involved in maintaining the stability of a plant’s metabiological, structural and physiological characteristics under the abiotic stressed environment. We conducted the present study using maize (Zea mays L.) cultivars (Sadaf and EV-20) grown in sand artificially contaminated with cadmium (500 µM) in Hoagland’s nutrient solution to investigate its efficiency. Results from the present study evidenced that the toxic concentration of Cd in sand significantly reduced shoot length, root length, shoot fresh weight, root fresh weight, shoot dry weight and root dry weight by 88, 94, 89, 86 99 and 99%, respectively, in Sadaf while decreasing by 98, 97, 93, 99, 84 and 91%, respectively, in EV-20. Similarly, Cd toxicity decreased total chlorophyll and carotenoid content in both varieties of Z. mays. Moreover, the activities of various antioxidants (superoxidase dismutase, peroxidase and catalase) increased under the toxic concentration of Cd in sand which was manifested by the presence of membrane permeability, malondialdehyde (MDA), and hydrogen peroxide (H2O2). Results additionally showed that the toxic effect of Cd was more severe in EV-20 compared with Sadaf under the same conditions of environmental stresses. In addition, the increased concentration of Cd in sand induced a significantly increased Cd accumulation in the roots (141 and 169 mg kg−1 in Sadaf and EV-20, respectively), and shoots (101 and 141 mg kg−1 in Sadaf and EV-20, respectively), while; EV-20 accumulated higher amounts of Cd than Sadaf, with the values for both bioaccumulation factor (BAF) and translocation factor (TF) among all treatments being less than 1. The subsequent negative results of Cd injury can be overcome by the foliar application of Si which not only increased plant growth and biomass, but also decreased oxidative damage induced by the higher concentrations of MDA and H2O2 under a Cd-stressed environment. Moreover, external application of Si decreased the concentration of Cd in the roots and shoots of plants, therefore suggesting that the application of Si can ameliorate Cd toxicity in Z. mays cultivars and results in improved plant growth and composition under Cd stress by minimizing oxidative damage to membrane-bound organelles.

Outstanding Questions on the Beneficial Role of Silicon in Crop Plants

Silicon (Si) is widely accepted as a beneficial element for plants. Despite the substantial progress made in understanding Si transport mechanisms and modes of action in plants, several questions remain unanswered. In this review, we discuss such outstanding questions and issues commonly encountered by biologists studying the role of Si in plants in relation to Si bioavailability. In recent years, advances in our understanding of the role of Si-solubilizing bacteria and the efficacy of Si nanoparticles have been made. However, there are many unknown aspects associated with structural and functional features of Si transporters, Si loading into the xylem, and the role of specialized cells like silica cells and compounds preventing Si polymerization in plant tissues. In addition, despite several 1,000 reports showing the positive effects of Si in high as well as low Si-accumulating plant species, the exact roles of Si at the molecular level are yet to be understood. Some evidence suggests that Si regulates hormonal pathways and nutrient uptake, thereby explaining various observed benefits of Si uptake. However, how Si modulates hormonal pathways or improves nutrient uptake remains to be explained. Finally, we summarize the knowledge gaps that will provide a roadmap for further research on plant silicon biology, leading to an exploration of the benefits of Si uptake to enhance crop production.

Potassium and melatonin-mediated regulation of fructose-1,6-bisphosphatase (FBPase) and sedoheptulose-1,7- bisphosphatase (SBPase) activity improve photosynthetic efficiency, carbon assimilation and modulate glyoxalase system accompanying tolerance to cadmium stress in tomato seedlings

The mechanism of the combined action of potassium (K) and melatonin (Mel) in modulating tolerance to cadmium (Cd) stress in plants is not well understood. The present study reveals the synergistic role of K and Mel in enhancing physiological and biochemical mechanisms of Cd stress tolerance in tomato seedlings. The present findings reveal that seedlings subjected to Cd toxicity exhibited disturbed nutrients balance [nitrogen (N) and potassium (K)], chlorophyll (Chl) biosynthesis [reduced δ-aminolevulinic acid (δ-ALA) content and δ-aminolevulinic acid dehydratase (δ-ALAD) activity], pathway of carbon fixation [reduced fructose-1,6-bisphosphatase (FBPase) and sedoheptulose-1,7- bisphosphatase (SBPase) activity] and photosynthesis process in tomato seedlings. However, exogenous application of K and Mel alone as well as together improved physiological and biochemical mechanisms in tomato seedlings, but their combined application proved best by efficiently improving nutrient uptake, photosynthetic pigments biosynthesis (increased Chl a and b, and Total Chl), carbon flow in Calvin cycle, activity of Rubisco, carbonic anhydrase activity, and accumulation of total soluble carbohydrates content in seedlings under Cd toxicity. Furthermore, the combined treatment of K and Mel suppressed overproduction of reactive oxygen species (hydrogen peroxide and superoxide), Chl degradation [reduced chlorophyllase (Chlase) activity] and methylglyoxal content in Cd-stressed tomato seedlings by upregulating glyoxalase (increased glyoxalase I and glyoxalase II activity) and antioxidant systems (increased ascorbate-glutathione metabolism). Thus, the present study provides stronger evidence that the co-application of K and Mel exhibited synergistic roles in mitigating the toxic effect of Cd stress by increasing glyoxalase and antioxidant systems and also by improving photosynthetic efficiency in tomato seedlings.

Exogenous melatonin improves cadmium tolerance in Solanum nigrum L. without affecting its remediation potential

Although Solanum nigrum L. is a phytoremediator for different metals, its growth and physiology are still influenced by toxic levels of cadmium (Cd). Thus, the development of eco-friendly strategies to enhance its tolerance, maintaining remediation potential is of special interest. The present work aimed to evaluate the effects of exogenous application of melatonin (MT) in the physiological and biochemical responses of S. nigrum and remediation potential exposed to Cd. After 30 days of exposure, the results revealed that Cd-mediated inhibitory effects on biomass and photosynthetic pigment synthesis were efficiently mitigated upon application of melatonin, without affecting Cd accumulation. Higher levels of Cd were found in roots, regardless of the pretreatment with the melatonin. Foliar application of melatonin, however, induced distinctive effects, lowering malondialdehyde (MDA), relative electrical conductivity (REL), and proline levels in shoots. These changes contributed to improvements in the water status, photosynthetic pigment synthesis, and biomass production of S. nigrum under Cd stresses. Overall, our results indicate a protective effect of melatonin on S. nigrum response to excess Cd, contributing to a better tolerance and growth rate, without disturbing its phytoremediation potential.Novelty statementAlthough Solanum nigrum L. is a phytoremediator for different metals, its growth and physiology are still influenced by toxic levels of cadmium. This study evaluated the potential of melatonin to boost S. nigrum defence against Cd toward a better growth rate and remediation potential.

Characterization of cadmium accumulation in the cell walls of leaves in a low-cadmium rice line and strengthening by foliar silicon application

Cadmium (Cd) remobilization in leaves is affected by whether Cd is stored in nonlabile subcellular compartments, which might be regulated by silicon (Si) application. However, the underlying mechanism is still far from being completely understood. In this research, the Cd distribution pattern in leaves and a Cd-binding characterization in the cell wall of the low-Cd rice line YaHui2816 were investigated through one hydroponic experiment with 10 μM Cd in solutions. Foliar Si application was further adopted to explore its influence on the Cd accumulation in the cell walls of leaves in YaHui2816. Most of the Cd (69.4%) was distributed in the cell walls of YaHui2816 leaves, whereas the isolated cell walls of leaves from YaHui2816 exhibited a lower capacity for Cd chemisorption than the contrasting line C268A, which was resulted from its fewer relative peak areas of functional groups in the cell wall, such as carboxyl CO and OH stretching. Foliar Si application significantly increased the Cd concentration in leaves and various cell wall fractions (pectin, hemicellulose 1 and residue) by 191% and 137-160%, respectively. RNA-seq analysis revealed that foliar Si application depressed the expression of the metal transporters OsZIP7 and OsZIP8, up-regulated the expression of genes participating in the glutathione metabolism and the cellulose synthesis. Overall, the influence of foliar Si application on Cd-accumulation in the cell wall of leaves in a low-Cd rice line was demonstrated in this research, which inspires further avenues to ensure the food safety of rice grains.

Exogenous silicon enhances the systemic defense of cucumber leaves and roots against CA-induced autotoxicity stress by regulating the ascorbate-glutathione cycle and photosystem II

Cinnamic acid (CA), one of the main autotoxins secreted by cucumber roots during continuous cropping, inhibits plant growth and reduces yield. Silicon (Si) is an environmentally friendly element that alleviates abiotic stresses in plants, but the mechanism underlying its resistance to autotoxicity remain unclear. Here, we used 0.8 mmol L^-1 CA to study the effects of Si application on the growth, chlorophyll fluorescence, and ascorbate-glutathione (AsA-GSH) cycle of cucumber seedlings under CA inducing conditions. Our results indicated that CA significantly induced photoinhibition and overaccumulation of reactive oxygen species (ROS), thereby inhibiting cucumber growth. Treatment with 1.0 mmol L^-1 Si improved plant height, stem diameter and biomass accumulation, and protected the photosynthetic electron transport function of photosystem II in the presence of CA. Similarly, Si application maintained the ROS status by increasing ascorbate (AsA) and glutathione (GSH) production, as well as the ratios of AsA/DHA and GSH/GSSG in both leaves and roots during CA stress. In addition, Si application in CA-treated seedlings enhanced the activity of key enzymes such as ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR), glutathione S-transferase (GST), and the transcription of several enzyme genes (CsAPX, CsMDHAR and CsGR） from the AsA-GSH cycle. These results suggest that exogenous Si enhances CA tolerance in cucumber seedlings by protecting photosystem II activity, upregulating AsA-GSH pathway, and reducing ROS levels.

Unraveling the effects of arbuscular mycorrhizal fungi on cadmium uptake and detoxification mechanisms in perennial ryegrass (Lolium perenne)

Cadmium (Cd) is a major environmental pollutant and one of the most toxic metals in the environment. Arbuscular mycorrhizal fungi (AMF) assisted phytoremediation can be used to remove Cd from polluted soils but the role of AMF, which mediate in Cd accumulation and tolerance, remains poorly understood. Here we inoculated Lolium perenne with two different AMF species (Glomus etunicatum and Glomus mosseae). Mycorrhizal L. perenne and non-mycorrhizal controls were exposed to Cd stress and we tested the effects of AMF mycorrhization on Cd uptake and subsequent tolerance, as well as the underlying mechanisms. Mycorrhizal infection increased root Cd²⁺ uptake and we observed that net Cd²⁺ influx was coupled with net Ca²⁺ influx. The inactivation of Ca²⁺ transporter channels decreased Cd²⁺ uptake in non-inoculated roots to a greater extent than in inoculated roots, indicating that AMF activates additional ion transport channels. In consequence, inoculated plants exhibited higher Cd accumulation in both roots and shoots than non-inoculated controls. However, AMF-inoculated plants showed higher chlorophyll concentrations, photosynthesis, and growth under Cd, indicating lower Cd toxicity in AMF-inoculated plants, despite the increase in Cd uptake. We observed that AMF-inoculated favored the isolation of Cd within cell walls and vacuoles, and had higher concentrations of superoxide dismutase activity and glutathione concentration in roots than non-inoculated plants, consequently experiencing less stress upon Cd exposure. Our results highlight the potential and mechanism of AMF for enhancing phytoremediation of L. perenne in heavy metal contaminated environments.

Regulation of antioxidant defense and glyoxalase systems in cyanobacteria

Oxidative stress is common consequence of abiotic stress in plants as well as cyanobacteria caused by generation of reactive oxygen species (ROS), an inevitable product of respiration and photosynthetic electron transport. ROS act as signalling molecule at low concentration however, when its production exceeds the endurance capacity of antioxidative defence system, the organisms suffer oxidative stress. A highly toxic metabolite, methylglyoxal (MG) is also produced in cyanobacteria in response to various abiotic stresses which consequently augment the ensuing oxidative damage. Taking recourse to the common lineage of eukaryotic plants and cyanobacteria, it would be worthwhile to explore the regulatory role of glyoxalase system and antioxidative defense mechanism in combating abiotic stress in cyanobacteria. This review provides comprehensive information on the complete glyoxalase system (GlyI, GlyII and GlyIII) in cyanobacteria. Furthermore, it elucidates the recent understanding regarding the production of ROS and MG, noteworthy link between intracellular MG and ROS and its detoxification via synchronization of antioxidants (enzymatic and non-enzymatic) and glyoxalase systems using glutathione (GSH) as common co-factor.

Foliar Supplementation of Clove Fruit Extract and Salicylic Acid Maintains the Performance and Antioxidant Defense System of Solanum tuberosum L. under Deficient Irrigation Regimes

A field trial was conducted twice (in 2020 and 2021) to evaluate the effect of clove fruit extract (CFE) and/or salicylic acid (SA), which were used as a foliar nourishment, on growth and yield traits, as well as physiological and biochemical indices utilizing potato (Solanum tuberosum L.) plants irrigated with deficient regimes in an arid environment. Three drip irrigation regimes [e.g., well watering (7400 m3 ha−1), moderate drought (6200 m3 ha−1), and severe drought (5000 m3 ha−1)] were designed for this study. The tested growth, yield, and photosynthetic traits, along with the relative water content, were negatively affected, whereas markers of oxidative stress (hydrogen peroxide and superoxide), electrolyte leakage, and peroxidation of membrane lipids (assessed as malondialdehyde level) were augmented along with increased antioxidative defense activities under drought stress. These effects were gradually increased with the gradual reduction in the irrigation regime. However, under drought stress, CFE and/or SA significantly enhanced growth characteristics (fresh and dry weight of plant shoot and plant leaf area) and yield components (average tuber weight, number of plant tubers, and total tuber yield). In addition, photosynthetic attributes (chlorophylls and carotenoids contents, net photosynthetic and transpiration rates, and stomatal conductance) were also improved, and defensive antioxidant components (glutathione, free proline, ascorbate, soluble sugars, and α-tocopherol levels, and activities of glutathione reductase, peroxidase, superoxide dismutase, catalase, and ascorbate peroxidase) were further enhanced. The study findings advocate the idea of using a CFE+SA combined treatment, which was largely efficient in ameliorating potato plant growth and productivity by attenuating the limiting influences of drought stress in dry environments.

Endogenous nitric oxide and its potential sources regulate glutathione-induced cadmium stress tolerance in maize plants

It was aimed to assess that up to what extent endogenous nitric oxide (NO) and its sources are involved in glutathione (GSH)-mediated tolerance of maize plants to cadmium (Cd) stress. The Cd-stressed maize plants were sprayed with or without GSH (1.0 mM) once every week for two weeks. Before initiating the stress treatment, the Cd-stressed plants sprayed with GSH were supplied with or without 0.1 mM, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO; a NO scavenger) for two weeks or with 0.1 mM sodium tungstate (ST; a nitrate reductase inhibitor), or 0.1 mM NG-nitro-L-arginine methyl ester hydrochloride (L-NAME). Cadmium stress suppressed the activities of dehydroascorbate reductase, monodehydroascorbate reductase, and glyoxalase II, while increased leaf NO, Cadmium content, proline, oxidative stress, the activities of glutathione reductase, ascorbate peroxidase, the key enzymes of oxidative defense system, glyoxalase I, NR and NOS. GSH reduced oxidative stress and tissue Cd²⁺ content, but it improved growth, altered water relations, and additionally increased proline levels, activities of the AsA-GSH cycle, key enzymatic antioxidants, glyoxalase I and II, NR and NOS as well as NO content. The cPTIO and ST supplementation abolished the beneficial effects of GSH by reducing the activities of NO and NR. However, L-NAME did not retreat the favorable effects of GSH, although it reduced the NOS activity without eliminating NO content, suggesting that NR might be a prospective source of NO generated by GSH in Cd-stressed plants, which in turn accelerated the activities of antioxidant enzymes.

Effect of exogenous silicon and methyl jasmonate on the alleviation of cadmium-induced phytotoxicity in tomato plants

In the present study, a hydroponic experiment was performed to evaluate the effect of exogenous silicon (Si) and methyl jasmonate (MeJA) on the mitigation of Cd toxicity in tomato seedlings. The results revealed that Cd-stressed plants exhibited growth inhibition, increased lipid peroxidation, and impaired photosynthetic pigment accumulation. However, Si and MeJA applied alone or in combination significantly ameliorated the above-mentioned adverse effects induced by Cd. Among all treatments, Cd+Si+MeJA treatment elevated the dry mass of roots, stems, and leaves by 317.39%, 110.85%, and 119.71%, respectively. The chlorophyll a, chlorophyll b, and carotenoid contents in Cd+Si+MeJA-treated group were dramatically elevated (p < 0.05). Meanwhile, the malondialdehyde content in roots and shoots were reduced by 32.24% and 69.94%, respectively. The Si and MeJA applied separately or in combination also resulted in a prominent decrease of Cd influxes in tomato roots; therefore, a reduction of Cd content in tomato tissues were detected, and the Cd concentration in tomato roots were decreased by 27.19%, 25.18%, and 17.51% in Cd+Si, Cd+MeJA and Cd+Si+MeJA-treated plants, respectively. Moreover, in Cd+Si+MeJA-treated group, the percentage of Cd in cell wall fraction was enhanced while that in organelle fraction was decreased as compared with Cd-stressed plants. Collectively, our findings indicated that Si and MeJA application provide a beneficial role in enhancing Cd tolerance and reducing Cd uptake in tomato plants.

Interactive effects of gibberellic acid and NPK on morpho-physio-biochemical traits and organic acid exudation pattern in coriander (Coriandrum sativum L.) grown in soil artificially spiked with boron

It was aimed to examine the role of gibberellic acid (GA₃) and NPK fertilizer in alleviating boron (B) toxicity in coriander (Coriandrum sativum L.) plants. Two weeks old C. sativum seedlings were subjected to different NPK fertilizers [low NPK (30 kg ha^-1) and normal NPK (60 kg ha^-1)], which were also supplied by GA₃ (50 mg L^-1), under varying levels of B i.e., 0, 200 and 400 mg kg^-1 in the soil. Results revealed that B toxicity led to a substantial decreased in the plant growth and biomass, photosynthetic pigments, gas exchange characteristics, sugars and essential nutrients in the roots and shoots of C. sativum seedlings. However, B toxicity boosted the production of reactive oxygen species (ROS) by increasing the contents of malondialdehyde (MDA), which is the indication of oxidative stress in C. sativum seedlings and was also manifested by hydrogen peroxide (H₂O₂) contents and electrolyte leakage (EL) to the membrane bounded organelles. Although, activities of various antioxidative enzymes like superoxidase dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX), non-enzymatic antioxidants like phenolic, flavonoid, ascorbic acid and anthocyanin contents and organic acids from the roots such as oxalic acid, malic acid, formic acid, citric acid, acetic acid and fumaric acid contents were increased with the increasing levels of B in the soil. The application if NPK and GA₃ mitigated B toxicity by stimulated plant growth and biomass, photosynthetic efficiency, nutritional status and antioxidant machinery of the plant by decreasing MDA contents, H₂O₂ initiation and EL (%) in the roots and leaves of C. sativum seedlings. In addition, the application of NPK and GA₃ further decreased the organic acids exudation contents in the roots C. sativum seedlings. Research findings, therefore, suggested that NPK and GA₃ application can ameliorate B toxicity in C. sativum seedlings and resulted in improved plant growth and composition under B stress as depicted by balanced contents of organic acids.

Exploring the significant contribution of silicon in regulation of cellular redox homeostasis for conferring stress tolerance in plants

Silicon (Si), a bioactive metalloid is beneficial for plant growth and development. It also plays a key role in the amelioration of different abiotic and biotic stresses. Extensive studies have elucidated the morpho-physiological, biochemical and molecular background of Si-mediated stress tolerance in plants. However, the mechanism acquired by Si to enhance stress tolerance in plants is still unheeded. Present review summarized the prospective mechanisms of Si in acquisition of stress tolerance with emphasis on its interactions with secondary messengers. Silicon usually modulates the different gene expressions in plants under stress conditions rather than acting as a direct signal or secondary messengers. Silicon regulates the production and accumulation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in plants under stress conditions. Furthermore, Si also activates the antioxidant defence system in plants; thereby, maintaining the cellular redox homeostasis and preventing the oxidative damage of cells. Silicon also up-regulates the synthesis of hydrogen sulfide (H₂S) or acts synergistically with nitric oxide (NO), consequently conferring stress tolerance in plants. Overall, the review may provide a progressive understanding of the role of Si in conservation of the redox homeostasis in plants.

Silicon-mediated abiotic and biotic stress mitigation in plants: Underlying mechanisms and potential for stress resilient agriculture

Silicon (Si) is a beneficial macronutrient for plants. The Si supplementation to growth media mitigates abiotic and biotic stresses by regulating several physiological, biochemical and molecular mechanisms. The uptake of Si from the soil by root cells and subsequent transport are facilitated by Lsi1 (Low silicon1) belonging to nodulin 26-like major intrinsic protein (NIP) subfamily of aquaporin protein family, and Lsi2 (Low silicon 2) belonging to putative anion transporters, respectively. The soluble Si in the cytosol enhances the production of jasmonic acid, enzymatic and non-enzymatic antioxidants, secondary metabolites and induces expression of genes in plants under stress conditions. Silicon has been found beneficial in conferring tolerance against biotic and abiotic stresses by scavenging the reactive oxygen species (ROS) and regulation of different metabolic pathways. In the present review, Si transporters identified in various plant species and mechanisms of Si-mediated abiotic and biotic stress tolerance have been presented. In addition, role of Si in regulating gene expression under various abiotic and biotic stresses as revealed by transcriptome level studies has been discussed. This provides a deeper understanding of various mechanisms of Si-mediated stress tolerance in plants and may help in devising strategies for stress resilient agriculture.

Protective role of tebuconazole and trifloxystrobin in wheat (Triticum aestivum L.) under cadmium stress via enhancement of antioxidant defense and glyoxalase systems

Cadmium (Cd) is a toxic metal and an environmental pollutant that significantly reduces plant growth and productivity. Proper management can ameliorate dysfunction and improve the plant growth and productivity exposed to Cd. Therefore, the present study was conducted to explore the protective role of the fungicides tebuconazole (TEB) and trifloxystrobin (TRI) in helping wheat (Triticum aestivum L. cv. Norin 61) seedlings to tolerate Cd. Five-day-old hydroponically grown seedlings were allowed to mild (0.25 mM CdCl₂) and severe (0.5 mM CdCl₂) Cd stress separately and with the fungicides (2.75 µM TEB + 1.0 µM TRI) for the next four days. Compared to control, the level of H₂O₂ in the seedlings exposed to mild and severe Cd stress alone increased by 81 and 112%, respectively. The accumulation of Cd also increased in the wheat seedlings along with declining mineral nutrients under Cd stress. The protective effect of TEB and TRI was observed with the enhancement of the antioxidant defense and methylglyoxalase systems and reduction in oxidative damage. Applying TEB and TRI reduced MDA (by 9 and 18%), EL (by 21 and 17%), MG (by 12 and 17%), and LOX activity (by 37 and 27%), respectively, relative to Cd stress alone. Cadmium uptake also decreased in the shoots (by 48 and 50%, respectively) and roots (by 23 and 25%, respectively) of the fungicide-treated wheat seedlings under mild and severe Cd stress, relative to stress alone. These results indicate the exogenous application of TEB and TRI is a promising approach to improve Cd tolerance in wheat plants. Further investigation is needed under field conditions and for other crop species to determine the Cd-tolerance induced by TEB and TRI application.