Mitigation of arsenate toxicity by indole-3-acetic acid in brinjal roots: Plausible association with endogenous hydrogen peroxide

Arabidopsis thaliana YUC1 reduced fluoranthene accumulation by modulating IAA content and antioxidant enzyme activities

Indole-3-acetic acid (IAA) can regulate plant growth and thus modulate the accumulation of polycyclic aromatic hydrocarbons (PAHs). However, the effect of endogenous IAA on PAHs accumulation and its influencing factors remains unclear. To unravel this, two different IAA expression genotypes of Arabidopsis thaliana, i.e., IAA-underproducing yucca1D [YUC1] mutant and wild type [WT]) were selected and treated with different fluoranthene (Flu) concentrations (0 mg/L [CK], 5 mg/L [Flu5], and 20 mg/L [Flu20]) to reveal the impact mechanism of endogenous IAA on Flu uptake by plants. The results indicated that under Flu5 treatment, the bioconcentration factors (BCF) and translocation factors (TF) of Flu in WT were 41.4 % and 14.3 % higher than those in YUC1. Similarly, under Flu20 treatment, the BCF and TF of Flu in WT were also 42.2 % and 8.2 % higher than those in YUC1. In addition, the BCF and TF were 72.5 % and 35.8 % higher under Flu5 treatment compared to Flu20 treatment for WT, and 73.4 % and 28.6 % higher respectively for YUC1. Moreover, WT exhibited higher plant growth (biomass, root morphology indicators [root length, root area and number of tips]) and IAA content compared to YUC1 under identical Flu treatments. Plant growth and IAA content declined with the increase of Flu concentration in both YUC1 and WT leaves compared with CK treatment. Conversely, in WT roots, root biomass and morphology indicators promoted followed by a decrease as the concentration of Flu increased. Additionally, the antioxidant enzyme activities (SOD, POD, and CAT) of WT were 11.1 %, 16.7 %, and 28.9 % higher than those of YUC1 under Flu5 treatment, and 13.6 %, 12.9 %, and 26.5 % higher under Flu20 treatment. Compared with CK treatment, SOD and POD activities promoted with increasing Flu concentration, whereas CAT activities decreased. Variability separation analysis revealed that level of IAA primarily influenced Flu accumulation in WT or under Flu5 treatments, whereas antioxidant enzyme activity primarily affected Flu accumulation in YUC1 or under Flu20 treatments. Exploring the relationship between the IAA synthesis gene YUCCA and IAA levels, alongside Flu accumulation, could yield novel insights into the regulation of PAH accumulation in plants.

Regulation of arsenate stress by nitric oxide and hydrogen sulfide in Oryza sativa seedlings: Implication of sulfur assimilation, glutathione biosynthesis, and the ascorbate-glutathione cycle and its genes

Seed priming by nitric oxide (NO) and hydrogen sulphide (H2S) in combating against abiotic stress in plants is well documented. However, knowledge of fundamental mechanisms of their crosstalk is scrambled. Therefore, the reported study examined the probable role of NO and H2S in the mitigation of arsenate toxicity (As(V)) in rice seedlings and whether their potential signalling routes crossover. Results report that As(V) toxicity limited shoot and root length growth with more As accumulation in roots. As(V) further caused elevated reactive oxygen species levels, inhibited ascorbate-glutathione cycle enzymes and relative gene expression of its enzymes and thus, causing lipid and protein oxidation. These results correlate with reduced nitric oxide synthase-like and L-cysteine desulfhydrase activity along with endogenous NO and H2S. While, L-NAME or PAG augmented As(V) toxicity, and addition of SNP or NaHS effectively reversed their respective effects. Furthermore, SNP under PAG or NaHS under L-NAME were able to pacify As(V) stress, implicating that endogenous NO and H2S efficiently ameliorate As(V) toxicity but without their shared signaling in rice seedlings.

Arbuscular mycorrhizae reduced arsenic induced oxidative stress by coordinating nutrient uptake and proline-glutathione levels in Cicer arietinum L. (chickpea)

Accumulation of Arsenic (As) generates oxidative stress by reducing nutrients availability in plants. Arbuscular mycorrhizal (AM) symbiosis can impart metalloid tolerance in plants by enhancing the synthesis of sulfur (S)-rich peptides (glutathione- GSH) and low-molecular-weight nitrogenous (N) osmolytes (proline- Pro). The present study, therefore investigated the efficiency of 3 AM fungal species (Rhizoglomus intraradices-Ri, Funneliformis mosseae -Fm and Claroideoglomus claroideum- Cc) in imparting As (arsenate-AsV -40 at 60 mg kg-1 and arsenite- AsIII at 5 and 10 mg kg-1) tolerance in two Cicer arietinum (chickpea) genotypes (HC 3 and C 235). As induced significantly higher negative impacts in roots than shoots, which was in accordance with proportionately higher reactive oxygen species (ROS) in the former, with AsIII more toxic than AsV. Mycorrhizal symbiosis overcame oxidative stress by providing the host plants with necessary nutrients (P, N, and S) through enhanced microbial enzyme activities (MEAs) in soil, which increased the synthesis of Pro and GSH and established a redox balance in the two genotypes. This coordination between nutrient status, Pro-GSH levels, and antioxidant defense was stronger in HC 3 than C 235 due to its higher responsiveness to the three AM species. However, Ri was most beneficial in inducing redox homeostasis, followed by Fm and Cc, since the Cicer arietinum-Ri combination displayed the maximum ability to boost antioxidant defense mechanisms and establish a coordination with Pro synthesis. Thus, the results highlighted the importance of selecting specific chickpea genotypes having an ability to establish effective mycorrhizal symbiosis for imparting As stress tolerance.

Copper exposure causes alteration in the intestinal microbiota and metabolites in Takifugu rubripes

Copper is an environmental pollutant, and copper in aquatic environments mainly comes from soil and water. It enters the environment through atmospheric deposition, sewage discharge, and industrial production, and enters aquatic organisms, causing toxicity. Takifugu rubripes (T. rubripes) is a marine fish with high economic value. Due to the toxic effects of heavy metals on aquatic organisms such as fish, it can affect the gut community and metabolites of fish. The gut is an important channel for fish to communicate with the outside world and a necessary pathway for the metabolism of nutrients and toxic substances in the fish body. Studies have shown that due to changes in global water emissions and the high sensitivity of aquatic organisms to the environment, copper may pose greater potential hazards to aquatic organisms. Copper poses a greater risk to aquatic species than other heavy metals and metal/metal like pollutants (such as cadmium, lead, mercury, arsenic, etc.) . In order to elucidate the effects of copper exposure on the gut of T. rubripes. In this study, we exposed T. rubripes to 0, 50, 100, or 500 μg/L of copper for three days, the effects of copper exposure on the gut microbiota structure and metabolites of the T. rubripes were investigated using 16 S rRNA gene and metabolomics techniques. The research results indicate that with the increase copper concentration, the intestinal tissue of T. rubripes undergoes significant damage. 16 S rRNA sequencing results show that copper exposure alters the structure and metabolites of intestinal microbiota. Copper exposure of 100 and 500 μg/L inhibited the colonization of the bacterial gut, disrupted the intestinal barrier, and made the fish susceptible to the pathogens. Liquid chromatography-mass spectrometry analysis showed that copper regulated the production of metabolites such as L-histidine, arachidonic acid, and L-glutamic acid, which are related to energy and immunity. Microbiome-metabolome correlation analysis showed that Subdoligranulum, Family_XIII_AD3011_group, and Clostridium_sensu_stricto_1 were the key bacteria for copper ion intervention, and they might up-regulate the levels of metabolites such as indole-3-acetic acid, 3-indoleacrylic acid, and 5-hydroxyindole in the tryptophan metabolism pathway. In summary, our research has demonstrated that copper exposure can cause pathological changes in the intestinal tissue of the T. rubripes. High concentrations of copper ions can affect the colonization of the T. rubripes microbiota in the intestine, damage the fish's immune system, and alter the structure and metabolites of the intestinal microbiota, this can lead to intestinal metabolic dysfunction. providing a reference for the evaluation of the biological toxicity effects of heavy metal elements in the marine environment. This study provides a reference for evaluating the biological toxicity effects of heavy metal elements in marine environments.

Nitric oxide acts upstream of indole-3-acetic acid in ameliorating arsenate stress in tomato seedlings

After their discovery, nitric oxide (NO) and indole-3-acetic acid (IAA) have been reported as game-changing cellular messengers for reducing abiotic stresses in plants. But, information regarding their shared signaling in regulating metal stress is still unclear. Herein, we have investigated about the joint role of NO and IAA in mitigation of arsenate [As(V)] toxicity in tomato seedlings. Arsenate being a toxic metalloid increases the NPQ level and cell death while decreasing the biomass accumulation, photosynthetic pigments, chlorophyll a fluorescence, endogenous NO content in tomato seedlings. However, application of IAA or SNP to the As(V) stressed seedlings improved growth together with less accumulation of arsenic and thus, preventing cell death. Interestingly, addition of c-PTIO, {2-(4-carboxyphenyl)-4, 4, 5, 5-tetramethylimidazoline-1-oxyl-3-oxide, a scavenger of NO} and 2, 3, 5-triidobenzoic acid (TIBA, an inhibitor of polar auxin transport) further increased cell death and inhibited activity of GST, leading to As(V) toxicity. However, addition of IAA to SNP and TIBA treated seedlings reversed the effect of TIBA resulting into decreased As(V) toxicity. These findings demonstrate that IAA plays a crucial and advantageous function in NO-mediated reduction of As(V) toxicity in seedlings of tomato. Overall, this study concluded that IAA might be acting as a downstream signal for NO-mediated reduction of As(V) toxicity in tomato seedlings.

The implication of LPS/TLR4 and FXR receptors in hepatoprotective efficacy of indole-3-acetic acid and chenodeoxycholic acid

AIM

Valproic acid (VPA) belongs to the first-generation antiepileptic drugs, yet its prolonged use can cause life-threatening liver damage. The importance of our study is to investigate the protective effect of indole-3-acetic acid (IAA), chenodeoxycholic acid (CDCA) and their combination on VPA-induced liver injury focusing on lipopolysaccharides (LPS)/toll-like receptor 4 (TLR4) pathway and farnesoid X receptor (FXR).

METHODS

Thirty rats were randomly assigned into five groups, normal control group, VPA group received 500 mg/kg of VPA intraperitoneally. The remaining groups were orally treated with either 40 mg/kg of IAA, 90 mg/kg of CDCA, or a combination of both, along with VPA. All treatments were administered one hour after the administration of VPA for three weeks.

KEY FINDINGS

VPA group showed significant elevations in the liver weight/body weight ratio, serum aminotransferases, triglyceride, and total cholesterol levels. Hepatic glutathione (GSH) level and superoxide dismutase (SOD) activity were significantly decreased, while malondialdehyde (MDA) level, tumor necrosis factor-α (TNF-α), interleukin-1beta (IL-1β), lipopolysaccharide (LPS) and caspase 3 were significantly increased. Likewise, immunohistochemical analysis revealed that TLR4 expression was elevated, whereas FXR expression was downregulated in hepatocytes. IAA substantially ameliorated all previously altered parameters, whereas CDCA treatment showed a partial improvement compared to IAA. Surprisingly, combination therapy of IAA with CDCA showed an additive effect only in the hepatic expression of TLR4 and FXR proteins.

SIGNIFICANCE

IAA could be a promising protective agent against VPA-induced liver injury.

Co-application of copper nanoparticles and metal tolerant Bacillus sp. for improving growth of spinach plants in chromium contaminated soil

Chromium (Cr) is classified as a toxic metal as it exerts harmful effects on plants and human life. Bacterial-assisted nano-phytoremediation is an emerging and environment friendly technique that can be used for the detoxification of such pollutants. In current study, pot experiment was conducted in which spinach plants were grown in soil containing chromium (0, 5, 10, 20 mgkg-1) and treated with selected strain of Bacillus sp. and Cu-O nanoparticle (CuONPs). Data related to plant's growth, physiological parameters, and biochemical tests was collected and analyzed using an appropriate statistical test. It was observed that under chromium stress, all plant's growth parameters were significantly enhanced in response to co-application of CuONPs and Bacillus sp. Similarly, higher levels of catalase, superoxide dismutase, malondialdehyde, and hydrogen peroxide were also observed. However, contents of anthocyanin, carotenoid, total chlorophyll, chlorophyll a & b, were lowered under chromium stress, which were raised in response to the combined application of CuONPs and Bacillus sp. Moreover, this co-application has significant positive effect on total soluble protein, free amino acid, and total phenolics. From this study, it was evident that combined application of Bacillus sp. and CuONP alleviated metal-induced toxicity in spinach plants. The findings from current study may provide new insights for agronomic research for the utilization of bacterial-assisted nano-phytoremediation of contaminated sites.

Physiological and transcriptomic analyses reveal that phytohormone pathways and glutathione metabolism are involved in the arsenite toxicity response in tomatoes

The main forms of inorganic arsenic (As) in soil are arsenate [As(V)] and arsenite [As(III)]. Both forms inhibit plant growth. Here, we investigate the effects of As(III) toxicity on the growth of tomatoes by integrating physiological and transcriptomic analyses. As(III) toxicity induces oxidative damage, inhibits photosynthetic efficiency, and reduces soluble sugar levels. As(III) toxicity leads to reductions in auxin, cytokinin and jasmonic acid contents by 29 %, 39 % and 55 %, respectively, but leads to increases in the ethylene precursor 1-amino-cyclopropane carboxylic acid, abscisic acid and salicylic acid contents in roots, by 116 %, 79 % and 39 %, respectively, thereby altering phytohormone signalling pathways. The total glutathione, reduced glutathione (GSH) and oxidized glutathione (GSSG) contents are reduced by 59 %, 49 % and 94 % in roots; moreover, a high GSH/GSSG ratio is maintained through increased glutathione reductase activity (increased by 214 %) and decreased glutathione peroxidase activity (decreased by 40 %) in the roots of As(III)-treated tomato seedlings. In addition, As(III) toxicity affects the expression of genes related to the endoplasmic reticulum stress response. The altered expression of aquaporins and ABCC transporters changes the level of As(III) accumulation in plants. A set of hub genes involved in modulating As(III) toxicity responses in tomatoes was identified via a weighted gene coexpression network analysis. Taken together, these results elucidate the physiological and molecular regulatory mechanism underlying As(III) toxicity and provide a theoretical basis for selecting and breeding tomato varieties with low As(III) accumulation. Therefore, these findings are expected to be helpful in improving food safety and to developing sustainable agricultural.

Concentration-dependent mechanisms of fluoranthene uptake by ryegrass

Fluoranthene (Flu) uptake by plants is affected by plant growth and environmental concentration. Although plant growth processes, including substance synthesis and antioxidant enzyme activities, have been reported to regulate Flu uptake, their contributions have been poorly evaluated. Moreover, the effect of Flu concentration is little known. Here, low concentrations (0, 1, 5, and 10 mg/L) and high concentrations (20, 30, and 40 mg/L) of Flu were set to compare the changes in Flu uptake by ryegrass (Lolium multiflorum Lam.). Indices of plant growth (biomass, root length, root area, root tip number, and photosynthesis and transpiration rates), substance synthesis (indole acetic acid [IAA] content), and antioxidant enzyme activities (superoxide dismutase [SOD], peroxidase [POD], and catalase [CAT]) were recorded to unravel the mechanism of Flu uptake. Findings suggested that the Langmuir model fitted Flu uptake by ryegrass well. Flu absorption capacity in the root was stronger than that that in the leaf. Flu bioconcentration and translocation factors increased then reduced with the increase in Flu concentration and reached the maximum value under 5 mg/L Flu treatment. Plant growth and IAA content had the same pattern as before bioconcentration factor (BCF). SOD and POD activities increased then decreased with Flu concentration and reached their highest levels under 30 and 20 mg/L Flu treatments, respectively, whereas CAT activity decreased continuously and reached its lowest level under 40 mg/L Flu treatment. Variance partitioning analysis indicated that IAA content had the greatest significant effect on Flu uptake under low-concentration Flu treatments, whereas antioxidant enzyme activities had the greatest significant effect on Flu uptake under high-concentration Flu treatments. Revealing the concentration-dependent mechanisms of Flu uptake could provide a basis for regulating pollutant accumulation in plants.

Negative Impacts of Arsenic on Plants and Mitigation Strategies

Arsenic (As) is a metalloid prevalent mainly in soil and water. The presence of As above permissible levels becomes toxic and detrimental to living organisms, therefore, making it a significant global concern. Humans can absorb As through drinking polluted water and consuming As-contaminated food material grown in soil having As problems. Since human beings are mobile organisms, they can use clean uncontaminated water and food found through various channels or switch from an As-contaminated area to a clean area; but plants are sessile and obtain As along with essential minerals and water through roots that make them more susceptible to arsenic poisoning and consequent stress. Arsenic and phosphorus have many similarities in terms of their physical and chemical characteristics, and they commonly compete to cause physiological anomalies in biological systems that contribute to further stress. Initial indicators of arsenic's propensity to induce toxicity in plants are a decrease in yield and a loss in plant biomass. This is accompanied by considerable physiological alterations; including instant oxidative surge; followed by essential biomolecule oxidation. These variables ultimately result in cell permeability and an electrolyte imbalance. In addition, arsenic disturbs the nucleic acids, the transcription process, and the essential enzymes engaged with the plant system's primary metabolic pathways. To lessen As absorption by plants, a variety of mitigation strategies have been proposed which include agronomic practices, plant breeding, genetic manipulation, computer-aided modeling, biochemical techniques, and the altering of human approaches regarding consumption and pollution, and in these ways, increased awareness may be generated. These mitigation strategies will further help in ensuring good health, food security, and environmental sustainability. This article summarises the nature of the impact of arsenic on plants, the physio-biochemical mechanisms evolved to cope with As stress, and the mitigation measures that can be employed to eliminate the negative effects of As.

Melatonin involves hydrogen sulfide in the regulation of H+-ATPase activity, nitrogen metabolism, and ascorbate-glutathione system under chromium toxicity

Contamination of soils with chromium (Cr) jeopardized agriculture production globally. The current study was planned with the aim to better comprehend how melatonin (Mel) and hydrogen sulfide (H₂S) regulate antioxidant defense system, potassium (K) homeostasis, and nitrogen (N) metabolism in tomato seedlings under Cr toxicity. The data reveal that application of 30 μM Mel to the seedlings treated with 25 μM Cr has a positive effect on H₂S metabolism that resulted in a considerable increase in H₂S. Exogenous Mel improved phytochelatins content and H⁺-ATPase activity with an associated increase in K content as well. Use of tetraethylammonium chloride (K⁺-channel blocker) and sodium orthovanadate (H⁺-ATPase inhibitor) showed that Mel maintained K homeostasis through regulating H⁺-ATPase activity under Cr toxicity. Supplementation of the stressed seedlings with Mel substantially scavenged excess reactive oxygen species (ROS) that maintained ROS homeostasis. Reduced electrolyte leakage and lipid peroxidation were additional signs of Mel's ROS scavenging effects. In addition, Mel also maintained normal functioning of nitrogen (N) metabolism and ascorbate-glutathione (AsA-GSH) system. Improved level of N fulfilled its requirement for various enzymes that have induced resilience during Cr stress. Additionally, the AsA-GSH cycle's proper operation maintained redox equilibrium, which is necessary for the biological system to function normally. Conversely, 1 mM hypotaurine (H₂S scavenger) abolished the Mel-effect and again Cr-induced impairment on the above-mentioned parameters was observed even in presence of Mel. Therefore, based on the observed findings, we concluded that Mel needs endogenous H₂S to alleviate Cr-induced impairments in tomato seedlings.

Combined application of plant growth-promoting bacteria and iron oxide nanoparticles ameliorates the toxic effects of arsenic in Ajwain (Trachyspermum ammi L.)

Soil contamination with toxic heavy metals [such as arsenic (As)] is becoming a serious global problem because of the rapid development of the social economy. Although plant growth-promoting bacteria (PGPB) and nanoparticles (NPs) are the major protectants to alleviate metal toxicity, the study of these chemicals in combination to ameliorate the toxic effects of As is limited. Therefore, the present study was conducted to investigate the combined effects of different levels of Providencia vermicola (5 ppm and 10 ppm) and iron oxide nanoparticles (FeO-NPs) (50 mg/l^-1 and 100 mg/l^-1) on plant growth and biomass, photosynthetic pigments, gas exchange attributes, oxidative stress and response of antioxidant compounds (enzymatic and non-enzymatic), and their specific gene expression, sugars, nutritional status of the plant, organic acid exudation pattern As accumulation from the different parts of the plants, and electron microscopy under the soil, which was spiked with different levels of As [0 μM (i.e., no As), 50 μM, and 100 μM] in Ajwain (Trachyspermum ammi L.) seedlings. Results from the present study showed that the increasing levels of As in the soil significantly (p< 0.05) decreased plant growth and biomass, photosynthetic pigments, gas exchange attributes, sugars, and nutritional contents from the roots and shoots of the plants, and destroyed the ultra-structure of membrane-bound organelles. In contrast, increasing levels of As in the soil significantly (p< 0.05) increased oxidative stress indicators in term of malondialdehyde, hydrogen peroxide, and electrolyte leakage, and also increased organic acid exudation patter in the roots of T. ammi seedlings. The negative impact of As toxicity can overcome the application of PGPB (P. vermicola) and FeO-NPs, which ultimately increased plant growth and biomass by capturing the reactive oxygen species, and decreased oxidative stress in T. ammi seedlings by decreasing the As contents in the roots and shoots of the plants. Our results also showed that the FeO-NPs were more sever and showed better results when we compared with PGPB (P. vermicola) under the same treatment of As in the soil. Research findings, therefore, suggest that the combined application of P. vermicola and FeO-NPs can ameliorate As toxicity in T. ammi seedlings, resulting in improved plant growth and composition under metal stress, as depicted by balanced exudation of organic acids.

Plant hormones and neurotransmitter interactions mediate antioxidant defenses under induced oxidative stress in plants

Due to global climate change, abiotic stresses are affecting plant growth, productivity, and the quality of cultivated crops. Stressful conditions disrupt physiological activities and suppress defensive mechanisms, resulting in stress-sensitive plants. Consequently, plants implement various endogenous strategies, including plant hormone biosynthesis (e.g., abscisic acid, jasmonic acid, salicylic acid, brassinosteroids, indole-3-acetic acid, cytokinins, ethylene, gibberellic acid, and strigolactones) to withstand stress conditions. Combined or single abiotic stress disrupts the normal transportation of solutes, causes electron leakage, and triggers reactive oxygen species (ROS) production, creating oxidative stress in plants. Several enzymatic and non-enzymatic defense systems marshal a plant's antioxidant defenses. While stress responses and the protective role of the antioxidant defense system have been well-documented in recent investigations, the interrelationships among plant hormones, plant neurotransmitters (NTs, such as serotonin, melatonin, dopamine, acetylcholine, and γ-aminobutyric acid), and antioxidant defenses are not well explained. Thus, this review discusses recent advances in plant hormones, transgenic and metabolic developments, and the potential interaction of plant hormones with NTs in plant stress response and tolerance mechanisms. Furthermore, we discuss current challenges and future directions (transgenic breeding and genome editing) for metabolic improvement in plants using modern molecular tools. The interaction of plant hormones and NTs involved in regulating antioxidant defense systems, molecular hormone networks, and abiotic-induced oxidative stress tolerance in plants are also discussed.

Transcription Factor AtOFP1 Involved in ABA-Mediated Seed Germination and Root Growth through Modulation of ROS Homeostasis in Arabidopsis

Ovate family proteins (OFPs) are valued as a family of transcription factors that are unique to plants, and they play a pluripotent regulatory role in plant growth and development, including secondary-cell-wall synthesis, DNA repair, gibberellin synthesis, and other biological processes, via their interaction with TALE family proteins. In this study, CHIP-SEQ was used to detect the potential target genes of AtOFP1 and its signal-regulation pathways. On the other hand, Y2H and BIFC were employed to prove that AtOFP1 can participate in ABA signal transduction by interacting with one of the TALE family protein called AtKNAT3. ABA response genes are not only significantly upregulated in the 35S::HAOFP1 OE line, but they also show hypersensitivity to ABA in terms of seed germination and early seedling root elongation. In addition, the AtOFP1-regulated target genes are mainly mitochondrial membranes that are involved in the oxidative–phosphorylation pathway. Further qRT-PCR results showed that the inefficient splicing of the respiratory complex I subunit genes NAD4 and NAD7 may lead to ROS accumulation in 35S::HA-AtOFP1 OE lines. In conclusion, we speculated that the overexpression of AtOFP1 may cause the ABA hypersensitivity response by increasing the intracellular ROS content generated from damage to the intima systems of mitochondria.

Exogenously-applied L-glutamic acid protects photosynthetic functions and enhances arsenic tolerance through increased nitrogen assimilation and antioxidant capacity in rice (Oryza sativa L.)

L-Glutamic acid (Glu) is used as an effective bio-stimulant to reduce arsenic (As) stress in plants. The role of Glu was studied in the protection of photosynthesis and growth of rice (Oryza sativa L. Japonica Type Taipie-309) plants grown with 50 μM As stress by studying the oxidative stress, photosynthetic and growth characteristics. Among the Glu concentrations (0, 2.5, 5 and 10 μM), 10 μM Glu maximally enhanced photosynthesis and growth parameters with the least cellular oxidative stress level. The supplementation of 10 μM Glu resulted in the reduced effects of As stress on gas exchange parameters, PSII activity and growth attributes through enhancement of antioxidant and proline metabolism. The enzymes of nitrogen (N) assimilation, such as nitrate reductase, nitrite reductase, glutamine synthetase and glutamate synthase were increased with Glu treatment under As stress. The Glu-induced metabolite synthesis showed the role of various metabolites in As stress responses. The role of Glu as a signalling molecule in reducing the adverse effects of As through accelerating the antioxidant enzymes, PSII activity, proline metabolism and nitrogen assimilation has been discussed.

Coumarin-Mediated Growth Regulations, Antioxidant Enzyme Activities, and Photosynthetic Efficiency of Sorghum bicolor Under Saline Conditions

Secondary metabolites, such as phenolic compounds, play an important role in alleviating salinity-induced negative effects in plants. The present study focused on seed priming and foliar application of a potent phenolic compound, coumarin, to induce salinity tolerance in Sorghum bicolor var. SS-77. Based on pilot experiment, 100 mg L^-1 concentration of coumarin was applied to mitigate the negative effects of salinity on Sorghum, grown at 0, 100, and 200 mM NaCl under netted greenhouse conditions. Coumarin was applied to each salinity treatment in four different ways (i) non-primed control (NP), (ii) seed priming (COP), (iii) foliar application (COF), and (iv) a combination of seed priming and foliar application (COPF). Salinity stress significantly reduced the plant growth, biochemical attributes, and photosynthetic efficiency of Sorghum, whereas coumarin treatments (COP, COF, and COPF) showed a significant increase (P< 0.01) in above-mentioned parameters at all salinities. Among all, the combined treatment (COPF) showed maximum increase in growth, biochemicals, photosynthetic pigments, antioxidant enzymes, and photosynthetic efficiency parameters. Therefore, it is suggested that a combination of seed priming and foliar spray of 10 mg L^-1 coumarin is more suitable than their individual applications. It is an environment friendly and economically feasible approach that will be used to improve salinity tolerance of Sorghum and helpful to get considerable biomass from saline degraded lands to fulfill food, fodder, and energy demands of the ever-growing population.

Antioxidants as modulators of arsenic-induced oxidative stress tolerance in plants: An overview

Arsenic (As) is a highly toxic contaminant in the environment. Although both inorganic and organic types of arsenic exist in the environment, the most common inorganic forms of As that adversely affect plants are arsenite (As III) and arsenate (As V). Despite no evidence for As being essential for plant growth, exposure of roots to this element can cause its uptake primarily via transporters responsible for the transport of essential mineral nutrients. Arsenic exposure even at low concentrations disturbs the plant normal functioning via excessive generation of reactive oxygen species, a condition known as oxidative stress leading to an imbalance in the redox system of the plant. This is associated with considerable damage to the cell components thereby impairing normal cellular functions and activation of several cell survival and cell death pathways. To counteract this oxidative disorder, plants possess natural defense mechanisms such as chemical species and enzymatic antioxidants. This review considers how different types of antioxidants participate in the oxidative defense mechanism to alleviate As stress in plants. Since the underlying phenomena of oxidative stress tolerance are not yet fully elucidated, the potential for "Omics" technologies to uncover molecular mechanisms are discussed. Various strategies to improve As-induced oxidative tolerance in plants such as exogenous supplementation of effective growth regulators, protectant chemicals, transgenic approaches, and genome editing are also discussed thoroughly in this review.

Synergistic application of silver nanoparticles and indole acetic acid alleviate cadmium induced stress and improve growth of Daucus carota L

Cadmium (Cd) is one of the major hazardous elements that is very toxic to the health of both human and plants. The toxicity of Cd causes plants to suffer by disabling their overall physiological mechanisms. Therefore, present study was intended to investigate the synergistic role of AgNPs and IAA in improving the resilience against Cd toxicity and underlaying physiological and biochemical mechanisms in carrot (Daucus carota L.) plants. Also, the existence of genotypic variation for Cd tolerance in D. carota was also studied. The results revealed that Cd stress decreased plant growth attributes like root diameter, root length, root weight, shoot weight, shoot length, leaves fresh weight and leaves dry weight. Nonetheless, AgNPs and IAA mitigated Cd stress by detoxifying reactive oxygen species (ROS). Additionally, the application of AgNPs and IAA boosted plant growth through reducing the level of malondialdehyde (MDA). Enhancement in the activity of phenol synthesizing and oxidizing enzymes including peroxidase, polyphenol oxidase and phenylalanine ammonia-lyase was also observed by application of AgNPs and IAA. The increased activities of antioxidant enzymes including POX, PPO and PAL by the combined application of AgNPs and IAA advocate stress ameliorative role against Cd stress in plants. The enhanced Cd content was detected in the roots as compared to shoots of treated plants. Pre breed 22 was found as a Cd tolerant genotype.

Molybdenum-induced endogenous nitric oxide (NO) signaling coordinately enhances resilience through chlorophyll metabolism, osmolyte accumulation and antioxidant system in arsenate stressed-wheat (Triticum aestivum L.) seedlings

There is little information available to decipher the interaction between molybdenum (Mo) and nitric oxide (NO) in mitigating arsenic (As^V) stress in plants. The present work highlights the associative role of exogenous Mo and endogenous NO signaling in regulating As^V tolerance in wheat seedlings. Application of Mo (1 μM) on 25-day-old wheat seedlings grown in the presence (5 μM) or absence of As^V stress caused improvement of photosynthetic pigment metabolism, reduction of electrolytic leakage and reactive oxygen species (ROS), and higher accumulation of osmolytes (proline and total soluble sugars). The molybdenum treatment upregulated antioxidative enzymes, such as superoxide dismutase, ascorbate peroxidase and glutathione reductase. In addition, the accumulation of nonenzymatic antioxidants (ascorbate and glutathione) was correlated with an increase in ascorbate peroxidase and glutathione reductase activity. The application of cPTIO (endogenous NO scavenger; 100 μM) reversed the Mo-mediated effects, thus indicating that endogenous NO may accompany Mo-induced mitigation of As^V stress. Mo treatment stimulated the accumulation of endogenous NO in the presence of As^V stress. Thus, it is evident that Mo and NO-mediated As^V stress tolerance in wheat seedlings are primarily operative through chlorophyll restoration, osmolytes accumulation, reduced electrolytic leakage, and ROS homeostasis.

Molybdenum and hydrogen sulfide synergistically mitigate arsenic toxicity by modulating defense system, nitrogen and cysteine assimilation in faba bean (Vicia faba L.) seedlings

Hydrogen sulfide (H₂S) has emerged as a potential gasotransmitter in plants with a beneficial role in stress amelioration. Despite the various known functions of H₂S in plants, not much information is available to explain the associative role of molybdenum (Mo) and hydrogen sulfide (H₂S) signaling in plants under arsenic toxicity. In view to address such lacunae in our understanding of the integrative roles of these biomolecules, the present work attempts to decipher the roles of Mo and H₂S in mitigation of arsenate (AsV) toxicity in faba bean (Vicia faba L.) seedlings. AsV-stressed seedlings supplemented with exogenous Mo and/or NaHS treatments (H₂S donor) showed resilience to AsV toxicity manifested by reduction of apoptosis, reactive oxygen species (ROS) content, down-regulation of NADPH oxidase and GOase activity followed by upregulation of antioxidative enzymes in leaves. Fluorescent localization of ROS in roots reveals changes in its intensity and spatial distribution in response to MO and NaHS supplementation during AsV stress. Under AsV toxicity conditions, seedlings subjected to Mo + NaHS showed an increased rate of nitrogen metabolism evident by elevation in nitrate reductase, nitrite reductase and glutamine synthetase activity. Furthermore, the application of Mo and NaHS in combination positively upregulates cysteine and hydrogen sulfide biosynthesis in the absence and presence of AsV stress. Mo plus NaHS-supplemented seedlings exposed to AsV toxicity showed a substantial reduction in oxidative stress manifested by reduced ELKG, lowered MDA content and higher accumulation of proline in leaves. Taken together, the present findings provide substantial evidence on the synergetic role of Mo and H₂S in mitigating AsV stress in faba bean seedlings. Thus, the application of Mo and NaHS reveals their agronomic importance to encounter heavy metal stress for management of various food crops.

Role of exogenously applied putrescine in amelioration of cadmium stress in Coriandrum sativum by modulating antioxidant system

Abiotic stress reduces the plant growth and biomass production. Putrescine (Put) may be applied to alleviate numerous types of abiotic stresses in plants. The present research was intended to evaluate the role of exogenously applied Put in extenuation of cadmium (Cd) stress in coriander plants. Coriander seeds primed with 0.25, 0.5, and1 mM Put were allowed to grow in 50 mg kg^-1 Cd contaminated soil for one month. Put treatment improved seed germination, gas exchange attributes, root growth and shoot growth of coriander. The improved activity of stress-responsive enzymes such as superoxide dismutase, catalase and peroxidase, besides amplification of proline was observed in Put treated seedlings under Cd stress. In addition, a reduced amount of total soluble protein and sugars content were noticed in Cd stressed seedlings. Nevertheless, Put reduced MDA level in treated plants. Our results demonstrated that Put mitigated Cd induced stress by modulating antioxidants and photosynthetic activity of coriander plants.Novelty statement Most of the researchers have studied the role of endogenous putrescine in alleviation of plant stress. However, during current study, we primed coriander seeds with putrescine. Our results elucidated very promising role of exogenously applied putrescine in stress mitigation and growth improvement of coriander seedlings under Cd stress. The findings of current study advocate the application of putrescine for stress alleviation in crop plants.

Heat stress-mediated effects on the morphophysiological, biochemical, and ultrastructural parameters of germinating Melanoxylon brauna Schott. seeds

The present study showed that the heat stress (40 °C) caused changes in morphophysiological, biochemical, and ultrastructural parameters to the seeds Melanoxylon brauna, ultimately leading to loss of germination capacity. Temperature is an abiotic factor that influences seed germination. In the present study, we investigated morphophysiological, biochemical, and ultrastructural changes during the germination of Melanoxylon brauna seeds under heat stress. Seed germination was evaluated at constant temperatures of 25 and 40 °C. The samples consisted of seeds soaked in distilled and ionized water for 48 and 96 h at both temperatures. For the evaluation of internal morphology, the seeds were radiographed. Ultrastructural parameters were assessed using transmission electron microscopy (TEM). The production of reactive oxygen species (ROS), content of malondialdehyde (MDA) and glucose, carbonylated proteins, and activity of the enzymes (superoxide dismutase-SOD, ascorbate peroxidase-APX, catalase-CAT, peroxidase-POX, glucose-6-phosphate dehydrogenase-G6PDH, lipase, α- and β-amylase, and protease) were measured by spectrophotometric analysis. An 82% reduction in the germination of M. brauna seeds was observed at 25 °C, and 0% at 40 °C. TEM showed that seeds submitted to heat stress (40 °C) had poorly developed mitochondria and significantly reduced respiration rates. The content of ROS and protein carbonylation in seeds subjected to 40 °C increased compared to that at 25 °C. The activity of antioxidant enzymes, namely SOD, APX, CAT, and POX, was significantly reduced in seeds subjected to heat stress. Glucose content, G6PDH, and lipase activity also decreased when the seeds were exposed to heat stress. Conversely, α- and β-amylase enzymes and the protease increased due to the increase in temperature. Our data showed that the increase in temperature caused an accumulation of ROS, increasing the oxidative damage to the seeds, which led to mitochondrial dysfunction, ultimately leading to loss of germination.

Ascorbate and glutathione independently alleviate arsenate toxicity in brinjal but both require endogenous nitric oxide

In this study, we have explored the possible role of ascorbic acid (ASC) and glutathione (GSH) in alleviating arsenate (As^V ) toxicity in brinjal roots. Moreover, we have also focused our attention on the possible involvement of endogenous nitric oxide (NO) in accomplishing this task. As^V treatment negatively impacts the length and fresh weight of roots and shoots as well as the dry weight and fitness of roots, and this was accompanied by greater As accumulation in roots and shoots of brinjal. As^V treatment also declined the endogenous NO level by inhibiting Nitric Oxide Synthase-like (NOS-like) activity. Furthermore, As^V stimulated oxidative stress markers, caused protein damage by their carbonylation due to downregulation in antioxidants [particularly ascorbate (AsA)-GSH cycle], leading to disturbed cellular redox status. This, collectively, led to root cell death in brinjal. However, the addition of either ASC or GSH rescued brinjal roots from the toxic effects of As^V in. Interestingly, lycorine (an inhibitor of ASC biosynthesis) further increased As^V toxicity, while ASC rescued its effects. Moreover, buthionine sulphoximine (BSO, an inhibitor of GSH biosynthesis) interestingly increased further As^V toxicity, while GSH rescued the plant from the As toxic effects. An interesting notion of this study was that GSH rescued the toxic effect of lycorine, while ASC rescued the toxic effect of BSO, though the As^V toxicity mediated by either ASC or GSH was always accompanied by high endogenous NO level and NOS-like activity. All together, these results suggest that ASC and GSH independently mitigate As^V toxicity in brinjal roots, but both might be dependent on endogenous NO for accomplishing the As^V toxicity alleviatory tasks.

Selenium Supplementation and Crop Plant Tolerance to Metal/Metalloid Toxicity

Selenium (Se) supplementation can restrict metal uptake by roots and translocation to shoots, which is one of the vital stress tolerance mechanisms. Selenium can also enhance cellular functions like membrane stability, mineral nutrition homeostasis, antioxidant response, photosynthesis, and thus improve plant growth and development under metal/metalloid stress. Metal/metalloid toxicity decreases crop productivity and uptake of metal/metalloid through food chain causes health hazards. Selenium has been recognized as an element essential for the functioning of the human physiology and is a beneficial element for plants. Low concentrations of Se can mitigate metal/metalloid toxicity in plants and improve tolerance in various ways. Selenium stimulates the biosynthesis of hormones for remodeling the root architecture that decreases metal uptake. Growth enhancing function of Se has been reported in a number of studies, which is the outcome of improvement of various physiological features. Photosynthesis has been improved by Se supplementation under metal/metalloid stress due to the prevention of pigment destruction, sustained enzymatic activity, improved stomatal function, and photosystem activity. By modulating the antioxidant defense system Se mitigates oxidative stress. Selenium improves the yield and quality of plants. However, excessive concentration of Se exerts toxic effects on plants. This review presents the role of Se for improving plant tolerance to metal/metalloid stress.