Enhancement of soybean tolerance to water stress through regulation of nitrogen and antioxidant defence mechanisms mediated by the synergistic role of salicylic acid and thiourea.

Water stress (WS) poses a significant threat to global food and energy security by adversely affecting soybean growth and nitrogen metabolism. This study explores the synergistic effects of exogenous salicylic acid (SA, 0.5 mM) and thiourea (TU, 400 mg L-1), potent plant growth regulators, on soybean responses under WS conditions. The treatments involved foliar spraying for 3 days before inducing WS by reducing soil moisture to 50% of field capacity, followed by 2 weeks of cultivation under normal or WS conditions. WS significantly reduced plant biomass, chlorophyll content, photosynthetic efficiency, water status, protein content, and total nitrogen content in roots and leaves. Concurrently, it elevated levels of leaf malondialdehyde, H2O2, proline, nitrate, and ammonium. WS also triggered an increase in antioxidant enzyme activity and osmolyte accumulation in soybean plants. Application of SA and TU enhanced the activities of key enzymes crucial for nitrogen assimilation and amino acid synthesis. Moreover, SA and TU improved plant growth, water status, chlorophyll content, photosynthetic efficiency, protein content, and total nitrogen content, while reducing oxidative stress and leaf proline levels. Indeed, the simultaneous application of SA and TU demonstrated a heightened impact compared to their separate use, suggesting a synergistic interaction. This study underscores the potential of SA and TU to enhance WS tolerance in soybean plants by modulating nitrogen metabolism and mitigating oxidative damage. These findings hold significant promise for improving crop productivity and quality in the face of escalating water limitations due to climate change.

Citric acid and hydrogen sulfide cooperate to mitigate chromium stress in tomato plants by modulating the ascorbate-glutathione cycle, chromium sequestration, and subcellular allocation of chromium.

The study aimed to investigate the role of hydrogen sulfide (H2S) in regulating chromium stress (Cr-S) tolerance of tomato plants treated with citric acid (CA). Prior to the Cr treatment, tomato plants were foliar-fed with CA (100 µM) daily for 3 days. Subsequently, the plants were grown for another ten days in a hydroponic system in a 50 µM Cr (VI) solution. Chromium treatment reduced photosynthetic pigments and plant biomass, but boosted the levels of hydrogen peroxide (H2O2) malondialdehyde (MDA), H2S, phytochelatins (PCs), and glutathione (GSH), electrolyte leakage (EL), and antioxidant enzyme activity in tomato plants. However, the foliar spray of CA mitigated the levels of H2O2, MDA, and EL, promoted plant growth and chlorophyll content, enhanced antioxidant enzymes' activities, and increased H2S production in Cr-S-tomato plants. CA also increased the levels of GSH and PCs, potentially reducing the toxicity of Cr through regulated sequestration. Additionally, the application of sodium hydrogen sulfide (NaHS), a donor of H2S, improved CA-induced Cr stress tolerance. The addition of CA promoted Cr accumulation in root cell wall and leaf vacuoles to suppress its toxicity. To assess the involvement of H2S in CA-mediated Cr-S tolerance, 0.1 mM hypotaurine (HT), an H2S scavenger, was provided to the control and Cr-S-plants along with CA and CA + NaHS. HT reduced the beneficial effects of CA by decreasing H2S production in tomato plants. However, the NaHS addition with CA + HT inverted the adverse impacts of HT, indicating that H2S is required for CA-induced Cr-S tolerance in tomato plants.

Interactive effect of silicon and zinc on cadmium toxicity alleviation in wheat plants.

Silicon (Si) and Zinc (Zn) have been frequently used to alleviate cadmium (Cd) toxicity, which are feasible strategies for crop safety production. However, the mechanisms underlying the interaction of Si and Zn on alleviating Cd toxicity are not well understood. A hydroponic system was adopted to evaluate morphological, physiological-biochemical responses, and related gene expression of wheat seedlings to Si (1 mM) and Zn (50 µM) addition under Cd stress (10 µM). Cd induced obvious inhibition of wheat growth by disturbing photosynthesis and chlorophyll synthesis, provoking generation of reactive oxygen species (ROS) and interfering ion homeostasis. Cd concentration was decreased by 68.3%, 43.1% and 73.3% in shoot, and 78.9%, 44.1% and 85.8% in root by Si, Zn, and combination of Si with Zn, relative to Cd only, respectively. Si and Zn effectively ameliorated Cd toxicity and enhanced wheat growth; but single Si or combination of Si with Zn had more efficient ability on alleviating Cd stress than only Zn, indicating Si and Zn have synergistic effect on Cd toxicity; Interaction of them alleviated oxidative stress by reducing ROS content, improving AsA-GSH cycle and antioxidant enzymes activities, and regulating Cd into vacuole through PC-Cd complexes transported by HMA3 transporter. Our results suggest that fertilizers including Si and Zn should be made to reduce Cd content, which will beneficial for food production and safety.

Melatonin enhanced the heavy metal-stress tolerance of pepper by mitigating the oxidative damage and reducing the heavy metal accumulation.

Heavy metals (HMs), like vanadium (V), chromium (Cr), cadmium (Cd), and nickel (Ni) toxicity due to anthropogenic, impair plant growth and yield, which is a challenging issue for agricultural production. Melatonin (ME) is a stress mitigating molecule, which alleviates HM-induced phytotoxicity, but the possible underlying mechanism of ME functions under HMs' phytotoxicity is still unclear. Current study uncovered key mechanisms for ME-mediated HMs-stress tolerance in pepper. HMs toxicity greatly reduced growth by impeding leaf photosynthesis, root architecture system, and nutrient uptake. Conversely, ME supplementation markedly enhanced growth attributes, mineral nutrient uptake, photosynthetic efficiency, as measured by chlorophyll content, gas exchange elements, chlorophyll photosynthesis genes' upregulation, and reduced HMs accumulation. ME treatment showed a significant decline in the leaf/root V, Cr, Ni, and Cd concentration which was about 38.1/33.2%, 38.5/25.9%, 34.8/24.9%, and 26.6/25.1%, respectively, when compared with respective HM treatment. Furthermore, ME remarkably reduced the ROS (reactive oxygen species) accumulation, and reinstated the integrity of cellular membrane via activating antioxidant enzymes (SOD, superoxide dismutase; CAT, catalase; APX, ascorbate peroxidase; GR, glutathione reductase; POD, peroxidase; GST, glutathione S-transferase; DHAR, dehydroascorbate reductase; MDHAR, monodehydroascorbate reductase) and as well as regulating ascorbate-glutathione (AsA-GSH) cycle. Importantly, oxidative damage showed efficient alleviations through upregulating the genes related to key defense such as SOD, CAT, POD, GR, GST, APX, GPX, DHAR, and MDHAR; along with the genes related to ME biosynthesis. ME supplementation also enhanced the level of proline and secondary metabolites, and their encoding genes expression, which may control excessive H2O2 (hydrogen peroxide) production. Finally, ME supplementation enhanced the HM stress tolerance of pepper seedlings.

Alleviation of arsenic toxicity in pepper plants by aminolevulinic acid and heme through modulating its sequestration and distribution within cell organelles.

Aminolevulinic acid (ALA) is essential for chlorophyll and heme synthesis. However, whether heme interacts with ALA to elicit antioxidants in arsenic (As)-exposed plants is still unknown. ALA was applied daily to pepper plants for 3 days prior to beginning As stress (As-S). Then, As-S was initiated for 14 days by employing sodium hydrogen arsenate heptahydrate (0.1 mM AsV). Arsenic treatment decreased photosynthetic pigments (chl a by 38% and chl b by 28%), biomass by 24%, and heme by 47% content, but it elevated contents of malondialdehyde (MDA) by 3.3-fold, hydrogen peroxide (H2O2) by 2.3-fold, glutathione (GSH), methylglyoxal (MG), and phytochelatins (PCs) and electrolyte leakage (EL) by 2.3-fold along with enhanced subcellular As concentration in the pepper plant's roots and leaves. The supplementation of ALA to the As-S-pepper seedlings enhanced the amount of chlorophyll, heme content, and antioxidant enzyme activity as well as plant growth, while it reduced the levels of H2O2, MDA, and EL. ALA boosted GSH and phytochelates (PCs) in the As-S-seedlings by controlling As sequestration and rendering it harmless. The addition of ALA enhanced the amount of As that accumulated in the root vacuoles and reduced the poisonousness of the soluble As in the vacuoles. The ALA treatment facilitated the deposition and fixation of As in the vacuoles and cell walls, thereby reducing the transport of As to other cell organelles. This mechanism may have contributed to the observed decrease in As accumulation in the leaves. The administration of 0.5 mM hemin (H) (a source of heme) significantly enhanced ALA-induced arsenic stress tolerance. Hemopexin (Hx, 0.4 µg L-1), a heme scavenger, was treated with the As-S plants along with ALA and ALA + H to observe if heme was a factor in ALA's increased As-S tolerance. Heme synthesis/accumulation in the pepper plants was reduced by Hx, which counteracted the positive effects of ALA. Supplementation of H along with ALA + Hx reversed the negative effects of Hx, demonstrating that heme is required for ALA-induced seedling As-S tolerance.

Gibberellic acid mitigates nickel stress in soybean by cell wall fixation and regulating oxidative stress metabolism and glyoxalase system.

It is broadly known that excessive concentration of nickel (Ni) causes venomous effects on plant health as well as food security. The underlying gibberellic acid (GA) mechanism to overcome Ni-induced stress is still unclear. Our outcomes represented the potential role of gibberellic acid (GA) to boost the soybean stress tolerance mechanism against Ni toxicity. GA elevated the seed germination, plant growth, biomass indices, and photosynthetic machinery as well as relative water contents under Ni-induced stress in soybean. We found that the GA lowered the Ni uptake, and distribution in the soybean plants, as well as GA, can decrease the Ni fixation in the root cell wall by lowering the hemicelluloses content. However, it reduces the MDA level, over-generation of ROS, electrolyte leakage, and methylglyoxal contents by up-surging the level of antioxidant enzyme, and glyoxalase I and glyoxalase II activities. Furthermore, GA regulates the antioxidant-related (CAT, SOD, APX, and GSH) and phytochelatins (PCs) genes expression to sequester the excessive Ni to the vacuoles and efflux the Ni outer the cell. Hence, less Ni was translocated toward shoots. Overall, GA augmented cell wall Ni elimination, and the antioxidant defense mechanism possibly upgraded the soybean tolerance against Ni stress.

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.

Nitric oxide mitigates vanadium toxicity in soybean (Glycine max L.) by modulating reactive oxygen species (ROS) and antioxidant system.

Vanadium (V) induced hazardous effects posturing a serious concern on crop production as well as food security. However, the nitric oxide (NO)-mediated alleviation of V-induced oxidative stress in soybean seedlings is still unknown. Therefore, this research was designed to explore the effects of exogenous NO to mitigate the V-induced phytotoxicity in soybean plants. Our upshots disclosed that NO supplementation considerably improved the plant biomass, growth, and photosynthetic attributes by regulating the carbohydrates, and plants biochemical composition, which further improved the guard cells, and stomatal aperture of soybean leaves. Additionally, NO regulated the plant hormones, and phenolic profile which restricted the V contents absorption (65.6%), and translocation (57.9%) by maintaining the nutrient acquisition. Furthermore, it detoxified the excessive V contents, and upsurged the antioxidants defense mechanism to lower the MDA, and scavenge ROS production. The molecular analysis further verified the NO-based regulation of lipid, sugar production, and degradation as well as detoxification mechanism in the soybean seedlings. Exclusively, we elaborated very first time the behind mechanism of V-induced oxidative stress alleviation by exogenous NO, hence illustrating the NO supplementation role as a stress alleviating agent for soybean grown in V contaminated areas to elevate the crop development and production.

Benzylaminopurine and Abscisic Acid Mitigates Cadmium and Copper Toxicity by Boosting Plant Growth, Antioxidant Capacity, Reducing Metal Accumulation and Translocation in Bamboo [Pleioblastus pygmaeus (Miq.)] Plants.

An in vitro experiment was conducted to determine the influence of phytohormones on the enhancement of bamboo resistance to heavy metal exposure (Cd and Cu). To this end, one-year-old bamboo plants (Pleioblastus pygmaeus (Miq.) Nakai.) contaminated by 100 µM Cd and 100 µM Cu both individually and in combination were treated with 10 µM, 6-benzylaminopurine and 10 µM abscisic acid. The results revealed that while 100 µM Cd and 100 µM Cu accelerated plant cell death and decreased plant growth and development, 10 µM 6-benzylaminopurine and 10 µM abscisic acid, both individually and in combination, increased plant growth by boosting antioxidant activities, non-antioxidants indices, tyrosine ammonia-lyase activity (TAL), as well as phenylalanine ammonia-lyase activity (PAL). Moreover, this combination enhanced protein thiol, total thiol, non-protein, glycine betaine (GB), the content of proline (Pro), glutathione (GSH), photosynthetic pigments (Chlorophyll and Carotenoids), fluorescence parameters, dry weight in shoot and root, as well as length of the shoot. It was then concluded that 6-benzyl amino purine and abscisic acid, both individually and in combination, enhanced plant tolerance under Cd and Cu through several key mechanisms, including increased antioxidant activity, improved photosynthesis properties, and decreased metals accumulation and metal translocation from root to shoot.

The involvement of hydrogen sulphide in melatonin-induced tolerance to arsenic toxicity in pepper (Capsicum annuum L.) plants by regulating sequestration and subcellular distribution of arsenic, and antioxidant defense system.

Melatonin (MT) and hydrogen sulphide (H2S) are recognised as vital biomolecules actively taking part in plant defence systems as free radical scavengers and antioxidants against a myriad of biotic and abiotic stressors. However, it has been yet unknown in plants subjected to arsenic (As) toxicity whether or not H2S interacts with MT to regulate endogenous antioxidant defence system. Prior to beginning As stress (As-S) treatments, MT (0.10 mM) was applied externally to plants daily for three days. AsS was then started for two weeks with As(V) (0.1 mM as Na2HAsO4·7H2O). The treatment of As reduced plant biomass (24.4%) and chlorophyll a (51.7%), chlorophyll b (25.9%), while it increased subcellular As in roots and leaves, levels of glutathione (GSH), hydrogen peroxide (H2O2), malondialdehyde (MDA), methylglyoxal (MG), H2S and phytochelatins (PCs) in pepper plants. In As-stressed pepper plants, the application of MT increased plant biomass (16.3%), chlorophyll a (52.7%), chlorophyll b (28.2%), antioxidant enzymes' activities, and H2S accumulation, while it lowered the concentrations of MDA and H2O2. In As-treated plants, GSH and phytochelatins (PCs) were increased by MT by regulating As sequestration to make it harmless. The addition of MT increased As accumulation in the vacuoles of roots and caused the soluble fraction of As in vacuoles to become less toxic to vital organelles. MT-induced tolerance to As stress was further enhanced using NaHS, a source of H2S. Hypotaurine (0.1 mM HT), a H2S scavenger, was applied to the control and As-stressed plants together with MT and MT + NaHS to determine whether H2S was implicated in MT-induced increased As-S tolerance. By reducing H2S generation in pepper plants, HT counteracted the beneficial effects of MT, whereas the addition of NaHS to MT + HT restored the negative effects of HT, proving that H2S is necessary for the pepper plants As-stress tolerance caused by MT.

Combined application of asparagine and thiourea improves tolerance to lead stress in wheat by modulating AsA-GSH cycle, lead detoxification and nitrogen metabolism.

Lead (Pb), like other heavy metals, is not essentially required for optimal plant growth; however, plants uptake it from the soil, which poses an adverse effect on growth and yield. Asparagine (Asp) and thiourea (Thi) are known to assuage the negative impacts of heavy metal pollution on plant growth; however, combined application of Asp and Thi has rarely been tested to discern if it could improve wheat yield under Pb stress. Thus, this experimentation tested the role of individual and combined applications of Asp (40 mM) and Thi (400 mg/L) in improving wheat growth under lead (Pb as PbCl2, 0.1 mM) stress. Lead stress significantly reduced plant growth, chlorophyll contents and photosystem system II (PSII) efficiency, whereas it increased Pb accumulation in the leaves and roots, leaf proline contents, phytochelatins, and oxidative stress related attributes. The sole or combined application of Asp and Thi increased the vital antioxidant biomolecules/enzymes, including reduced glutathione (GSH), ascorbic acid (AsA), ascorbate peroxsidase (APX), catalase (CAT), superoxide dismutase (SOD), glutathione S-transferase (GST), dehydroascorbate reductase (DHAR), and glutathione reductase (GR). Furthermore, the sole or the combined application of Asp and Thi modulated nitrogen metabolism by stimulating the activities of nitrate and nitrite reductase, glutamate synthase (GOGAT) and glutamine synthetase (GS). Asp and Thi together led to improve plant growth and vital physiological processes, but lowered down Pb accumulation compared to those by their sole application. The results suggest that Asp and Thi synergistically can improve wheat growth under Pb-toxicity.

Protective mechanisms of sulfur against arsenic phytotoxicity in Brassica napus by regulating thiol biosynthesis, sulfur-assimilation, photosynthesis, and antioxidant response.

The contamination of agricultural soils with Arsenic (As) is a significant environmental stress that restricts plant growth, metabolism, and productivity worldwide. The present study examined the role of elemental sulfur (S0) in protecting Brassica napus plants from Arsenic (As) toxicity. Arsenic (100, and 200 mg As kg-1 soil) in soil caused detrimental effects on five Brassica napus cultivars (Neelam, Teri-Uttam Jawahar, Him Sarson, GSC-101, and NUDB 26-11). The As toxicity inhibited the growth and photosynthesis indices in all cultivars with more deterioration effects in NUDB 26-11. Plant absorption and uptake of As caused the generation of oxidative injury by accumulating the reactive oxygen species (ROS), which simultaneously decreased the plant defence capability and ultimately the photosynthesis. Application of sulfur (S0, 100 or 200 mg S kg-1 soil) alleviated the negative impacts and toxicity of As on the photosynthesis and growth matrices of plants, especially under high S level. S0 also boosted the antioxidant potential of plants and toned-down lipid peroxidation and ROS aggravation such as superoxide anion (O2•-) and H2O2, hydrogen peroxide, in As affected plants. In general, S0 at 200 mg kg-1 soil more perceptibly increased the functionality of antioxidant enzymes, and non-enzymatic antioxidants, metal chelators and non-protein thiols. Further amendment of soil with S0 at fifteen days before seed sowing affected by As-induced toxic effects (added to soil at the time of sowing) considerably intensified the endogenous hydrogen sulfide (H2S) content and its regenerating enzymes D-cysteine desulfhydrase (DCD) and L-cysteine desulfhydrase (LCD) that further strengthened the defense capability of plants to withstand As-stress. Our results suggest the role of H2S in the S-induced defense operation of the B. napus plants in restraining As toxicity. The current study shows that S0 as a source of S might be used to promote the growth of B. napus plants in polluted agricultural soils.

Drought-tolerant Bacillus megaterium isolated from semi-arid conditions induces systemic tolerance of wheat under drought conditions.

KEY MESSAGE: A detailed study of the response of wheat plants, inoculated with drought-tolerant PGPR is studied which would be beneficial to achieve genetic improvement of wheat for drought tolerance. Drought stress, a major challenge under current climatic conditions, adversely affects wheat productivity. In the current study, we observed the response of wheat plants, inoculated with drought-tolerant plant growth-promoting rhizobacteria (PGPR) Bacillus megaterium (MU2) and Bacillus licheniformis (MU8) under induced drought stress. In vitro study of 90 rhizobacteria exhibited 38 isolates showed one or more plant growth-promoting properties, such as solubilization of phosphorus, potassium, and exopolysaccharide production. Four strains revealing the best activities were tested for their drought-tolerance ability by growing them on varying water potentials (- 0.05 to - 0.73 MPa). Among them, two bacterial strains Bacillus megaterium and Bacillus licheniformis showed the best drought-tolerance potential, ACC deaminase activities, IAA production, and antagonistic activities against plant pathogens. Additionally, these strains when exposed to drought stress (- 0.73 MPa) revealed the induction of three new polypeptides (18 kDa, 35 kDa, 30 kDa) in Bacillus megaterium. We determined that 106 cells/mL of Bacillus megaterium and Bacillus licheniformis were enough to induce drought tolerance in wheat under drought stress. These drought-tolerant strains increased the germination index (11-46%), promptness index (16-50%), seedling vigor index (11-151%), fresh weight (35-192%), and dry weight (58-226%) of wheat under irrigated and drought stress. Moreover, these strains efficiently colonized the wheat roots and increased plant biomass, relative water content, photosynthetic pigments, and osmolytes. Upon exposure to drought stress, Bacillus megaterium inoculated wheat plants exhibited improved tolerance by enhancing 59% relative water content, 260, 174 and 70% chlorophyll a, b and carotenoid, 136% protein content, 117% proline content and 57% decline in MDA content. Further, activities of defense-related antioxidant enzymes were also upregulated. Our results revealed that drought tolerance was more evident in Bacillus megaterium as compared to Bacillus licheniformis. These strains could be effective bioenhancer and biofertilizer for wheat cultivation in arid and semi-arid regions. However, a detailed study at the molecular level to deduce the mechanism by which these strains alleviate drought stress in wheat plants needs to be explored.

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.

Silicon elevated cadmium tolerance in wheat (Triticum aestivum L.) by endorsing nutrients uptake and antioxidative defense mechanisms in the leaves.

Numerous abiotic stressors including heavy metal stresses, specifically cadmium (Cd) stress in agricultural bio-system hinder the plant adequate growth. The present study was aimed to reveal the protective role of silicon (Si) application with two levels and to recognize the optimum level of Si for wheat plants grown hydroponically under three different levels of Cd toxicities. In methodology, we used nine treatments with three levels of Si (0, 1, and 3 mmol L-1; Na2SiO3) against three levels of Cd (0, 50, 200 µmol L-1; CdCl2) with three biological replicates. The results of our study demonstrated that Si incorporation with the advantage of 3 mmol L-1 in cultured media with Cd50 and Cd200 demolished the toxic effects of Cd on the leaves of wheat plants by increasing plant dry biomass by 88% and 262%, leaf area by 48% and 57%, total chlorophyll contents by 120% and 74%, catalase (CAT) activity by 92% and 110%, superoxide dismutase (SOD) activity by 62% and 78%, peroxidase (POD) activity by 66% and 40%, ascorbic acid (AsA) contents by 33% and 34%, glutathione (GHS) contents by 39% and 30% and reduced MDA contents by 56% and 50%, H2O2 contents by 61% and 66%, and EL contents by 56% and 47% as parallel to Cd corresponding levels. In addition, Si incorporation with the advantage of 3 mmol L-1 significantly increased relative water contents (RWC) to maintain the cell turgor pressure and protect the plant from wilting and cells flaccid and enhanced membrane stability index (MSI) to protect the plant from logging under damaging effects of Cd toxicities. Based on the present findings, Si can be considered a quasi-essential element that enhanced wheat tolerance against Cd toxicity by limiting uptake, accumulation, and translocation of Cd and through regulating antioxidative defense mechanisms.

Synthesis and Characterization of Na-Zeolites from Textile Waste Ash and Its Application for Removal of Lead (Pb) from Wastewater.

Massive production of carcinogenic fly ash waste poses severe threats to water bodies due to its disposal into drains and landfills. Fly ash can be a source of raw materials for the synthesis of adsorbents. Rag fly ash as a new class of raw materials could be a cheap source of Al and Si for the synthesis of Na-zeolites. In this work, NaOH activation, via a prefusion- and postfusion-based hydrothermal strategy, was practiced for the modification of rag fly ash into Na-zeolite. Morphology, surface porosity, chemical composition, functionality, mineral phases, and crystallinity, in conjunction with ion exchangeability of the tailored materials, were evaluated by SEM, ICP-OES, XRF, FTIR, XRD, and cation exchange capacity (CEC) techniques. Rag fly ash and the synthesized Na-zeolites were applied for the removal of Pb (II) from synthetic wastewater by varying the reaction conditions, such as initial metal ion concentration, mass of adsorbent, sorption time, and pH of the reaction medium. It was observed that Na-zeolite materials (1 g/100 mL) effectively removed up to 90-98% of Pb (II) ions from 100 mg/L synthetic solution within 30 min at pH ≈ 8. Freundlich adsorption isotherm favors the multilayer heterogeneous adsorption mechanism for the removal of Pb (II). It is reasonable to conclude that recycling of textile rag fly ash waste into value-added Na-zeolites for the treatment of industrial wastewater could be an emergent move toward achieving sustainable and green remediation.

Combined use of different nanoparticles effectively decreased cadmium (Cd) concentration in grains of wheat grown in a field contaminated with Cd.

Cadmium (Cd) accumulation in arable lands has become a serious matter for food security. Among various approaches, the application of nanoparticles (NPs) for remediation of contaminated water and soils is attaining more popularity worldwide. The current field experiment was executed to explore the impacts of single and combined use of ZnO NPs, Fe NPs and Si NPs on wheat growth and Cd intake by plants in a Cd-contaminated field. Wheat was sown in a field which was contaminated with Cd and was irrigated with the raw-city-effluent while NPs were applied as foliar spray alone and in all possible combinations. The data revealed that straw and grain yields were enhanced in the presence of NPs over control. Chlorophyll, carotenoids contents and antioxidants activities were enhanced while electrolyte leakage was reduced with all NPs over control. In comparison with control, Cd uptake in wheat straw was reduced by 84% and Cd uptake in grain was reduced by 99% in T8 where all three NPs were foliar-applied simultaneously. Zinc (Zn) and iron (Fe) contents were increased in those plants where ZnO and Fe NPs were exogenously applied which revealed that ZnO and Fe NPs enhanced the bio-fortification of Zn and Fe in wheat grains. Overall, foliar application of different NPs is beneficial for better wheat growth, yield, nutrients uptake and to lessen the Cd intake by plants grown in Cd-contaminated soil under real field conditions.

Effect of green and chemically synthesized titanium dioxide nanoparticles on cadmium accumulation in wheat grains and potential dietary health risk: A field investigation.

A field study was designed to explore the impacts of foliar-applied chemically and green synthesized titanium dioxide nanoparticles (TiO2 NPs) on cadmium (Cd) uptake in wheat plants. The wheat was grown in field which was contaminated with Cd and plants were subjected to foliar episodes of TiO2 NPs during plant growth period. Leaf extracts of two plant species (Trianthema portulacastrum, Chenopodium quinoa) were used for green synthesis while sol-gel method was used for chemical preparation of TiO2 NPs. Results showed that TiO2 NPs significantly enhanced the plant height, length of spikes photosynthesis, and straw and grain yield compared to control. TiO2 NPs minimized the oxidative burst in leaves and improved the enzyme activities than control. Cadmium concentrations of straw, roots and grains decreased after TiO2 NPs treatments than control. The grain Cd contents were below recommended threshold (0.2 mg Cd /kg grain DW) for cereals upon NPs exposure. The health risk index by the dietary use of grains for adults was below threshold upon NPs exposure. Overall, foliar use of TiO2 NPs prepared from plant extracts was appropriate in minimizing Cd contents in wheat grains, thereby reducing risk of Cd to human health via food chain.

Foliar exposure of zinc oxide nanoparticles improved the growth of wheat (Triticum aestivum L.) and decreased cadmium concentration in grains under simultaneous Cd and water deficient stress.

A pot study was conducted to explore the effectiveness of zinc oxide nanoparticles (ZnO NPs) foliar exposure on growth and development of wheat, zinc (Zn) and cadmium (Cd) uptake in Cd-contaminated soil under various moisture conditions. Four different levels (0, 25, 50, 100 mg/L) of these NPs were foliar-applied at different time periods during the growth of wheat. Two soil moisture regimes (70% and 35% of water holding capacity) were maintained from 6 weeks of germination till plant harvesting. The results revealed that the growth of wheat increased with ZnO NPs treatments. The best results were found in 100 mg/L ZnO NPs under normal moisture level. The lowest Cd and highest Zn concentrations were also examined when 100 mg/L NPs were applied without water deficit stress. In grain, Cd concentrations decreased by 26%, 81% and 87% in normal moisture while in water deficit conditions, the Cd concentrations decreased by 35%, 66% and 81% compared to control treatment when ZnO NPs were used at 25, 50 and 100 mg/L. The foliar exposure of ZnO NPs boosted up the leaf chlorophyll contents and also decreased the oxidative stress and enhanced the leaf superoxide dismutase and peroxidase activities than the control. It can be suggested that foliar use of ZnO NPs might be an efficient way for increasing wheat growth and yield with maximum Zn and minimum Cd contents under drought stress while decreasing the chances of NPs movement to other environmental compartment which may be possible in soil applied NPs.

Effects of biochar, farm manure, and pressmud on mineral nutrients and cadmium availability to wheat (Triticum aestivum L.) in Cd-contaminated soil.

The contamination of agricultural soils with cadmium (Cd) is one of the serious worldwide concerns for food security. Biochar and organic manures have been known for enhancing plant growth and minimizing toxic trace element stress in plants. However, less is known about the effect of different organic amendments on Cd and uptake of essential nutrients by wheat. Thus, the effects of rice straw biochar (RSB), maize stalk biochar (MSB), farmyard manure (FYM), and pressmud (PRM) at a rate of 1% w/w were tested for Cd immobilization in soil and mineral nutrient availability to wheat crop grown in Cd-spiked soil (6.0 mg kg1 ). The amendments were added in Cd-spiked soil before 12 days of seed sowing and wheat plants were harvested after maturity (115 days after sowing). The findings revealed that the use of amendments improved the number of grains per spike, straw and grain yield of wheat relative to control treatment. The treatments minimized the Cd and enhanced the contents of zinc (Zn), nitrogen (N), phosphorus (P), and potassium (K) in the leaves and grain of the wheat plants. Cadmium concentrations decreased by 35, 38, 68, and 63% in wheat grain, and grain yield increased by 19, 31, 68, and 58% with the application of FYM, PRM, MSB, and RSB, respectively. Overall, the application of MSB was more efficient in decreasing Cd concentrations in leaf and grains of wheat as compared to other conventional organic amendments.