Lead-induced stress, which triggers the production of nitric oxide (NO) and superoxide anion (O2·-) in Arabidopsis peroxisomes, affects catalase activity

Nitric oxide in plants: an insight on redox activity and responses toward abiotic stress signaling

Plants, as sessile organisms, are subjected to diverse abiotic stresses, including salinity, desiccation, metal toxicity, thermal fluctuations, and hypoxia at different phases of plant growth. Plants can activate messenger molecules to initiate a signaling cascade of response toward environmental stresses that results in either cell death or plant acclimation. Nitric oxide (NO) is a small gaseous redox-active molecule that exhibits a plethora of physiological functions in growth, development, flowering, senescence, stomata closure and responses to environmental stresses. It can also facilitate alteration in protein function and reprogram the gene profiling by direct or indirect interaction with different target molecules. The bioactivity of NO can be manifested through different redox-based protein modifications including S-nitrosylation, protein nitration, and metal nitrosylation in plants. Although there has been considerable progress in the role of NO in regulating stress signaling, still the physiological mechanisms regarding the abiotic stress tolerance in plants remain unclear. This review summarizes recent advances in understanding the emerging knowledge regarding NO function in plant tolerance against abiotic stresses. The manuscript also highlighted the importance of NO as an abiotic stress modulator and developed a rational design for crop cultivation under a stress environment.

Unlocking the versatility of nitric oxide in plants and insights into its molecular interplays under biotic and abiotic stress

In plants, nitric oxide (NO) has become a versatile signaling molecule essential for mediating a wide range of physiological processes under various biotic and abiotic stress conditions. The fundamental function of NO under various stress scenarios has led to a paradigm shift in which NO is now seen as both a free radical liberated from the toxic product of oxidative metabolism and an agent that aids in plant sustenance. Numerous studies on NO biology have shown that NO is an important signal for germination, leaf senescence, photosynthesis, plant growth, pollen growth, and other processes. It is implicated in defense responses against pathogensas well as adaptation of plants in response to environmental cues like salinity, drought, and temperature extremes which demonstrates its multifaceted role. NO can carry out its biological action in a variety of ways, including interaction with protein kinases, modifying gene expression, and releasing secondary messengers. In addition to these signaling events, NO may also be in charge of the chromatin modifications, nitration, and S-nitrosylation-induced posttranslational modifications (PTM) of target proteins. Deciphering the molecular mechanism behind its essential function is essential to unravel the regulatory networks controlling the responses of plants to various environmental stimuli. Taking into consideration the versatile role of NO, an effort has been made to interpret its mode of action based on the post-translational modifications and to cover shreds of evidence for increased growth parameters along with an altered gene expression.

Evidence for dual targeting control of Arabidopsis 6-phosphogluconate dehydrogenase isoforms by N-terminal phosphorylation

The oxidative pentose-phosphate pathway (OPPP) retrieves NADPH from glucose-6-phosphate, which is important in chloroplasts at night and in plastids of heterotrophic tissues. We previously studied how OPPP enzymes may transiently locate to peroxisomes, but how this is achieved for the third enzyme remained unclear. By extending our genetic approach, we demonstrated that Arabidopsis isoform 6-phosphogluconate dehydrogenase 2 (PGD2) is indispensable in peroxisomes during fertilization, and investigated why all PGD-reporter fusions show a mostly cytosolic pattern. A previously published interaction of a plant PGD with thioredoxin m was confirmed using Trxm2 for yeast two-hybrid (Y2H) and bimolecular fluorescent complementation (BiFC) assays, and medial reporter fusions (with both ends accessible) proved to be beneficial for studying peroxisomal targeting of PGD2. Of special importance were phosphomimetic changes at Thr6, resulting in a clear targeting switch to peroxisomes, while a similar change at position Ser7 in PGD1 conferred plastid import. Apparently, efficient subcellular localization can be achieved by activating an unknown kinase, either early after or during translation. N-terminal phosphorylation of PGD2 interfered with dimerization in the cytosol, thus allowing accessibility of the C-terminal peroxisomal targeting signal (PTS1). Notably, we identified amino acid positions that are conserved among plant PGD homologues, with PTS1 motifs first appearing in ferns, suggesting a functional link to fertilization during the evolution of seed plants.

Phytocompounds and Regulation of Flavonoids in In Vitro-Grown Safflower Plant Tissue by Abiotic Elicitor CdCl2

In this study, a Gas chromatography-mass spectrometry (GC-MS) investigation of embryogenic callus and somatic embryo regenerated shoots of Carthamus tinctorius revealed the presence of a variety of sugars, sugar acids, sugar alcohols, fatty acids, organic acids, and amino acids of broad therapeutic value. The in vitro developed inflorescence contained a wide range of active compounds. In embryogenic calluses, important flavonoids like naringenin, myricetin, kaempferol, epicatechin gallate, rutin, pelargonidin, peonidin, and delphinidin were identified. To augment the synthesis of active compounds, the effect of cadmium chloride (CdCl2) elicitation was tested for various treatments (T1-T4) along with a control (T0). Varying concentrations of CdCl2 [0.05 mM (T1), 0.10 mM (T2), 0.15 mM (T3), and 0.20 mM (T4)] were added to the MS medium, and flavonoid accumulation was quantified through ultra-high-pressure liquid chromatography-tandem mass spectroscopy (UHPLC-MS/MS). The flavonoids naringenin, kaempferol, epicatechin gallate, pelargonidin, cyanidin, and delphinidin increased by 6.7-, 1.9-, 3.3-, 2.1-, 1.9-, and 4.4-fold, respectively, at T3, whereas quercetin, myricetin, rutin, and peonidin showed a linear increase with the increase in CdCl2 levels. The impacts of stress markers, i.e., ascorbate peroxidase (APX), catalase (CAT), and superoxide dismutase (SOD), on defense responses in triggering synthesis were also evaluated. The maximum APX and SOD activity was observed at T3, while CAT activity was at its maximum at T2. The impact of elicitor on biochemical attributes like protein, proline, sugar, and malondialdehyde (MDA) content was investigated. The maximum protein, proline, and sugar accumulation was noted at high elicitor dose T4, while the maximum MDA content was noted at T3. These elevated levels of biochemical parameters indicated stress in culture, and the amendment of CdCl2 in media thus could be a realistic approach for enhancing secondary metabolite synthesis in safflower.

Nitric oxide (NO) modulates low temperature-stress signaling via S-nitrosation, a NO PTM, inducing ethylene biosynthesis inhibition leading to enhanced post-harvest shelf-life of agricultural produce

Low temperature (cold) stress is one of the major abiotic stress conditions affecting crop productivity worldwide. Nitric oxide (NO) is a dynamic signaling molecule that interacts with various stress regulators and provides abiotic stress tolerance. Stress enhanced NO contributes to S-nitrosothiol accumulation which causes oxidation of the -SH group in proteins leading to S-nitrosation, a post-translational modification. Cold stress induced in vivo S-nitrosation of > 240 proteins majorly belonging to stress/signaling/redox (myrosinase, SOD, GST, CS, DHAR), photosynthesis (RuBisCO, PRK), metabolism (FBA, GAPDH, TPI, SBPase), and cell wall modification (Beta-xylosidases, alpha-l-arabinogalactan) in different crop plants indicated role of NO in these important cellular and metabolic pathways. NO mediated regulation of a transcription factor CBF (C-repeat Binding Factor, a transcription factor) at transcriptional and post-translational level was shown in Solanum lycopersicum seedlings. NO donor priming enhances seed germination, breaks dormancy and provides tolerance to stress in crops. Its role in averting stress, promoting seed germination, and delaying senescence paved the way for use of NO and NO releasing compounds to prevent crop loss and increase the shelf-life of fruits and vegetables. An alternative to energy consuming and expensive cold storage led to development of a storage device called "shelf-life enhancer" that delays senescence and increases shelf-life at ambient temperature (25-27 °C) using NO donor. The present review summarizes NO research in plants and exploration of NO for its translational potential to improve agricultural yield and post-harvest crop loss.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01371-z.

Identification of lead-binding proteins as carriers and potential molecular targets associated with systolic blood pressure

Lead (Pb) exposure is well recognized as a significant environmental factor associated with the high incidence of cardiovascular diseases. However, the carriers and molecular targets of Pb in human blood remain to be understood, especially for a real Pb exposure scenario. In this study, a total of 350 blood samples were collected from the smelting workers and systematically analyzed using metallomics and metalloproteomics approaches. The results showed that the majority of Pb (∼99.4%) could be presented in the blood cells. Pb in the cytoplasm of blood cells accounted for approximately 83.1% of the total blood Pb, with nearly half of Pb being bound to proteins. Pb-binding proteins in the blood of workers were identified as hemoglobin, catalase, haptoglobin, δ-aminolevulinic acid dehydratase, and peroxiredoxin-2. Multiple linear regression analysis demonstrated that higher levels of Pb bound to proteins (Mix-bound Pb and Protein-bound Pb) were positively associated with higher systolic blood pressure (p < 0.05). However, the association between blood lead level, Pb levels in the blood cells and systolic blood pressure was not observed (p > 0.05). This study suggested that Pb bound to proteins could be a suitable biomarker for indicating the potential risk of occupational hypertension.

The synergy of halotolerant PGPB and mauran mitigates salt stress in tomato (Solanum lycopersicum) via osmoprotectants accumulation

Salinity stress is one of the major abiotic factors limiting sustainable agriculture. Halotolerant plant growth-promoting bacteria (PGPB) increased salt stress tolerance in plants, but the mechanisms underlying the tolerance are poorly understood. This study investigated the PGP activity of four halotolerant bacteria under salinity stress and the tomato salt-tolerance mechanisms induced by the synergy of these bacteria with the exopolysaccharide (EPS) mauran. All PGPB tested in this study were able to offer a significant improvement of tomato plant biomass under salinity stress; Peribacillus castrilensis N3 being the most efficient one. Tomato plants treated with N3 and the EPS mauran showed greater tolerance to NaCl than the treatment in the absence of EPS and PGPB. The synergy of N3 with mauran confers salt stress tolerance in tomato plants by increasing sodium transporter genes' expression and osmoprotectant content, including soluble sugars, polyols, proline, GABA, phenols and the polyamine putrescine. These osmolytes together with the induction of sodium transporter genes increase the osmotic adjustment capacity to resist water loss and maintain ionic homeostasis. These findings suggest that the synergy of the halotolerant bacterium N3 and the EPS mauran could enhance tomato plant growth by mitigating salt stress and could have great potential as an inductor of salinity tolerance in the agriculture sector.

Overexpression of Zostera japonica J protein gene ZjDjB1 in Arabidopsis enhanced the tolerance to lead stress

BACKGROUND

Among the heavy metal pollution in soil, lead pollution is particularly prominent. The lead in contaminated soil will not only cause damage to plants, animals and microorganisms, but also seriously affect the progress of the entire ecosystem. Under lead stress, the abundance of DnaJ protein in plants will increase. However, little is known about the role of DnaJ in lead stress.

METHODS AND RESULTS

We used transgenic Arabidopsis that overexpressed DnaJ gene ZjDjB1 of Zostera japonica as material to study the role of DnaJ in the mechanism of lead induced stress response. Under lead stress, the seedlings and adult plants of transgenic ZjDjB1 Arabidopsis have higher tolerance to lead stress than wild type. Under lead stress, the content of NO and O2^·- free radicals in transgenic ZjDjB1 Arabidopsis was lower than that of wild type. The negative effect of catalase in transgenic ZjDjB1 Arabidopsis under lead stress was weaker than that of wild type. The expression of ABC transporter of mitochondrion 3 (ATM3; systematic name: ABCB25) in transgenic ZjDjB1 Arabidopsis under lead stress was higher than that in wild type.

CONCLUSIONS

These results confirmed that ZjDjB1, the DnaJ gene of Z. japonica, was involved in the reaction mechanism to lead pollution, which might improve the tolerance of plants to lead stress by maintaining catalase activity and increasing the expression level of ATM3 under lead stress.

Auxin Crosstalk with Reactive Oxygen and Nitrogen Species in Plant Development and Abiotic Stress

The phytohormone auxin acts as an important signaling molecule having regulatory functions during the growth and development of plants. Reactive oxygen species (ROS) are also known to perform signaling functions at low concentrations; however, over-accumulation of ROS due to various environmental stresses damages the biomolecules and cell structures and leads to cell death, and therefore, it can be said that ROS act as a double-edged sword. Nitric oxide (NO), a gaseous signaling molecule, performs a wide range of favorable roles in plants. NO displays its positive role in photomorphogenesis, root growth, leaf expansion, seed germination, stomatal closure, senescence, fruit maturation, mitochondrial activity and metabolism of iron. Studies have revealed the early existence of these crucial molecules during evolution. Moreover, auxin, ROS and NO together show their involvement in various developmental processes and abiotic stress tolerance. Redox signaling is a primary response during exposure of plants to stresses and shows a link with auxin signaling. This review provides updated information related to crosstalk between auxin, ROS and NO starting from their evolution during early Earth periods and their interaction in plant growth and developmental processes as well as in the case of abiotic stresses to plants.

Warhorses in soil bioremediation: Seed biopriming with PGPF secretome to phytostimulate crop health under heavy metal stress

The fungal symbiosis with the plant root system is importantly recognized as a plant growth promoting fungi (PGPFs), as well as elicitor of plant defence against different biotic and abiotic stress conditions. Thus PGPFs are playing as a key trouper in enhancing agricultural quality and increased crop production and paving a way towards a sustainable agriculture. Due to increased demand of food production, the over and unscientific usage of chemical fertilizers has led to the contamination of soil by organic and inorganic wastes impacting on soil quality, crops quality effecting on export business of agricultural products. The application of microbial based consortium like plant growth promoting fungi is gaining worldwide importance due to their multidimensional activity. These activities are through plant growth promotion, induction of systemic resistance, disease combating and detoxification of organic and inorganic toxic chemicals, a heavy metal tolerance ability. The master key behind these properties exhibited by PGPFs are attributed towards various secretory biomolecules (secondary metabolites or enzymes or metabolites) secreted by the fungi during interaction mechanism. The present review is focused on the multidimensional role PGPFs as elicitors of Induced systemic resistance against phytopathogens as well as heavy metal detoxifier through seed biopriming and biofortification methods. The in-sights on PGPFs and their probable mechanistic nature contributing towards plants to withstand heavy metal stress and stress alleviation by activating of various stress regulatory pathways leading to secretion of low molecular weight compounds like organic compounds, glomalin, hydrophobins, etc,. Thus projecting the importance of PGPFs and further requirement of research in developing PGPFs based molecules and combining with trending Nano technological approaches for enhanced heavy metal stress alleviations in plant and soil as well as establishing a sustainable agriculture.

Assay of Reactive Oxygen/Nitrogen Species (ROS/RNS) in Arabidopsis Peroxisomes Through Fluorescent Protein Containing a Type 1 Peroxisomal Targeting Signal (PTS1)

Plant peroxisomes have an active nitro-oxidative metabolism. However, the assay of reactive oxygen and nitrogen species (ROS/RNS) could be a challenge since the purification of peroxisomes is technically a high time-consuming approach that needs to be optimized for each tissue/organ (root, leaf, fruit) and plant species. Arabidopsis thaliana, as a model plant for biochemical and molecular studies, has become a useful tool to study the basic metabolism, including also that of ROS/RNS. The combination of specific fluorescent probes with Arabidopsis plants expressing a fluorescent protein containing a type 1 peroxisomal targeting signal (PTS1) is a powerful tool to address the profile of ROS/RNS in peroxisomes by confocal laser scanning microscope (CLSM). This chapter provides a detailed description to detect the content and distribution of ROS and RNS in Arabidopsis peroxisomes, together with a critical analysis of their potentialities and limitations, since these approaches require appropriate controls to corroborate the obtained data.

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.

The Role of NO in the Amelioration of Heavy Metal Stress in Plants by Individual Application or in Combination with Phytohormones, Especially Auxin

Since the time of the Industrial Revolution, the accumulation of various heavy metals (HMs), such as cadmium (Cd), arsenic (As), lead (Pb), chromium (Cr), mercury (Hg), copper (Cu), zinc (Zn), nickel (Ni), etc., has increased substantially in the soil, causing a real risk to all kinds of consumers in the food chain. Moreover, excess HM accumulation is considered a major factor in decreasing plant growth and productivity. A number of recent studies have exhibited the astonishing impact of nitric oxide (NO), a multifunctional, gaseous signal molecule, on alleviating the destructive effects of HMs. Many reports revealed the noteworthy contribution of NO in reducing HM uptake and toxicity levels. In the present review, focus is given to the contribution of NO to decrease the toxicity levels of different HMs in a variety of plant species and their accumulation in those species. Simultaneously, this review also demonstrates the effects of NO on HM-stressed species, by its use both individually and along with auxin, a plant-growth-promoting phytohormone. Different perspectives about the reaction to the co-application of NO and auxin, as well as the differential role of NO to overcome HM stress, have been expanded.

Reactive Oxygen Species, Antioxidant Responses and Implications from a Microbial Modulation Perspective

Simple Summary

Environmental conditions are subject to unprecedented changes due to recent progressive anthropogenic activities on our planet. Plants, as the frontline of food security, are susceptible to these changes, resulting in the generation of unavoidable byproducts of metabolism (ROS), which eventually affect their productivity. The response of plants to these unfavorable conditions is highly intricate and depends on several factors, among them are the species/genotype tolerance level, intensity, and duration of stress factors. Defensive mechanisms in plant systems, by nature, are concerned primarily with generating enzymatic and non-enzymatic antioxidants. In addition to this, plant-microbe interactions have been found to improve immune systems in plants suffering from drought and salinity stress.

Abstract

Plants are exposed to various environmental stresses in their lifespan that threaten their survival. Reactive oxygen species (ROS), the byproducts of aerobic metabolism, are essential signalling molecules in regulating multiple plant developmental processes as well as in reinforcing plant tolerance to biotic and abiotic stimuli. However, intensified environmental challenges such as salinity, drought, UV irradiation, and heavy metals usually interfere with natural ROS metabolism and homeostasis, thus aggravating ROS generation excessively and ultimately resulting in oxidative stress. Cellular damage is confined to the degradation of biomolecular structures, including carbohydrates, proteins, lipids, pigments, and DNA. The nature of the double-edged function of ROS as a secondary messenger or harmful oxidant has been attributed to the degree of existing balance between cellular ROS production and ROS removal machinery. The activities of enzyme-based antioxidants, catalase (CAT, EC 1.11.1.6), monodehydroascorbate reductase (MDHAR, E.C.1.6.5.4), dehydroascorbate reductase (DHAR, EC 1.8.5.1), superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11), glutathione reductase (GR, EC 1.6.4.2), and guaiacol peroxidase (GPX, EC 1.11.1.7); and non-enzyme based antioxidant molecules, ascorbate (AA), glutathione (GSH), carotenoids, α-tocopherol, prolines, flavonoids, and phenolics, are indeed parts of the defensive strategies developed by plants to scavenge excess ROS and to maintain cellular redox homeostasis during oxidative stress. This review briefly summarises current knowledge on enzymatic and non-enzymatic antioxidant machinery in plants. Moreover, additional information about the beneficial impact of the microbiome on countering abiotic/biotic stresses in association with roots and plant tissues has also been provided.

Subtoxic levels of some heavy metals cause differential root-shoot structure, morphology and auxins levels in Arabidopsis thaliana

Contamination of soil by heavy metals severely affects plant growth and causes soil pollution. While effects on plant growth have been investigated for metals taken individually or in groups, less is known about their comparative effects. In this study Arabidopsis thaliana seedlings were grown for 14 days in Petri dishes containing medium contaminated by six common heavy metals (Hg, Cd, Pb, Cu, Ni and Zn), at the minimum concentrations defined as toxic by the most recent EU legislation on contamination of agricultural soils. (a) Root structure and morphology, (b) metal composition and translocation, and (c) the levels of indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) were analyzed. Metals accumulated more in roots than in shoots, with concentrations that differed by several orders of magnitude depending on the metal: Cd (ca. 700 × and ca. 450 × in roots and shoots, respectively), Hg (150 × , 80 × ), Ni (50 × , 20 × ), Cu (48 × , 20 × ), Zn (23 × , 6 × ), and Pb (9 × , 4 × ). Responses were significant for at least nine of the ten root parameters (with the exception of Hg), and five of the six shoot parameters (with the exception of Zn). Cu and Zn induced respectively the strongest responses in root hormonal (up to ca. 240% the control values for IBA, 190% for IAA) and structural parameters (up to 210% for main root length, 330% for total lateral root length, 220% for number of root tips, 600% for total root surface, and from 2.5° to 26.0° of root growth angle). Regarding the shoots, the largest changes occurred for shoot height (down to 60% for Ni), rosette diameter (down to 45% for Hg), leaf number (up to 230% for Zn) and IBA (up to 240% for Pb and Cu). A microscope analysis revealed that shape and conformation of root hairs were strongly inhibited after Cd exposure, and enhanced under Hg and Pb. The results could have positive applications such as for defining toxicity thresholds (in phytoremediation) and acceptable concentration levels (for policies) for some of the most common heavy metals in agricultural soils.

Spermine-Mediated Tolerance to Selenium Toxicity in Wheat (Triticum aestivum L.) Depends on Endogenous Nitric Oxide Synthesis

Excess selenium (Se) causes toxicity, and nitric oxide (NO)’s function in spermine (Spm)-induced tolerance to Se stress is unknown. Using wheat plants exposed to 1 mM sodium selenate—alone or in combination with either 1 mM Spm, 0.1 mM NO donor sodium nitroprusside (SNP) or 0.1 mM NO scavenger cPTIO—the potential beneficial effects of these compounds to palliate Se-induced stress were evaluated at physiological, biochemical and molecular levels. Se-treated plants accumulated Se in their roots (92%) and leaves (95%) more than control plants. Furthermore, Se diminished plant growth, photosynthetic traits and the relative water content and increased the levels of malondialdehyde, H₂O₂, osmolyte and endogenous NO. Exogenous Spm significantly decreased the levels of malondialdehyde by 28%, H₂O₂ by 37% and electrolyte leakage by 42%. Combined Spm/NO treatment reduced the Se content and triggered plant growth, photosynthetic traits, antioxidant enzymes and glyoxalase systems. Spm/NO also upregulated MTP1, MTPC3 and HSP70 and downregulated TaPCS1 and NRAMP1 (metal stress-related genes involved in selenium uptake, translocation and detoxification). However, the positive effects of Spm on Se-stressed plants were eliminated by the NO scavenger. Accordingly, data support the notion that Spm palliates selenium-induced oxidative stress since the induced NO elicits antioxidant defence upregulation but downregulates Se uptake and translocation. These findings pave the way for potential biotechnological approaches to supporting sustainable wheat crop production in selenium-contaminated areas.

Alleviation of Chlorpyrifos Toxicity in Maize (Zea mays L.) by Reducing Its Uptake and Oxidative Stress in Response to Soil-Applied Compost and Biochar Amendments

Chlorpyrifos (CP) is a pesticide used extensively in agricultural crops. Residual CP has been found in a variety of soils, vegetables and fruits indicating a serious danger to humans. Therefore, it is necessary to restrict its entry into agricultural products for food safety. A wire-house pot experiment was conducted with maize plants in biochar- and compost-amended soil (at 0.25% and 0.50%, respectively, in weight-by-weight composition) contaminated with 100 and 200 mg kg⁻¹ of CP, respectively. Results indicated toxicity at both CP levels (with 84% growth reduction) at CP 200 mg kg⁻¹. However, application of compost and biochar at the 0.50% level improved the fresh weight (2.8- and 4-fold, respectively). Stimulated superoxide dismutase (SOD) and peroxidase (POX) activities and depressed catalase (CAT) activity were recorded in response to CP contamination and were significantly recovered by the amendments. Both amendments significantly decreased the CP phytoavailability. With biochar, 91% and 76% reduction in the CP concentration in maize shoots and with compost 72% and 68% reduction was recorded, at a 0.50% level in 100 and 200 mg kg⁻¹ contaminated treatments respectively. Compost accelerated the CP degradation in postharvest soil. Therefore, biochar and compost amendments can effectively be used to decrease CP entry in agricultural produce by reducing its phytoavailability.

Interplay of hydrogen peroxide and nitric oxide: systemic regulation of photosynthetic performance and nitrogen metabolism in cadmium challenged cyanobacteria

In the present study, the potential role of hydrogen peroxide (H₂O₂) and nitric oxide (NO) has been well recorded in the induction of cadmium (Cd) stress tolerance in cyanobacteria. In this regard, H₂O₂ and SNP (sodium nitroprusside, NO donor), were applied to Nostoc muscorum and Anabaena sp. exposed to Cd (6 µM) stress, to analyze different physiological and biochemical parameters. Results revealed that treatment of Cd reduced the growth, pigment contents, photosynthetic oxygen yield and performance of PS II photochemistry (decreased chlorophyll a fluorescence parameters, i.e., ФP_o, Ψ_o, ФE_o, PI_ABS along with F_v/F_o and increased the energy flux parameters, i.e., ABS/RC, TR_o/RC, ET_o/RC, DI_o/RC along with F_o/F_v. Similarly, uptake of nitrate (NO₃ ^-) and nitrite (NO₂ ^-), as well as the activities of nitrate and ammonia assimilating enzymes along with carbohydrate content, were severely affected by Cd toxicity and notwithstanding this, glutamate dehydrogenase (GDH) activity exhibited reverse trend. Exogenous application of a very low dose (1 µM) of H₂O₂ (only for 3 h) and NO (SNP; 10 µM) notably counteracted Cd-induced toxicity. Nevertheless, the positive impact of H₂O₂ got reversed under the treatment of PTIO (NO scavenger) and _LNAME (inhibitor of nitric oxide synthase; NOS) while NO could work efficiently even in the presence of NAC (H₂O₂ scavenger) and DPI (inhibitor of NADPH oxidase); hence indicated towards the H₂O₂ mediated NO signaling in averting Cd induced toxicity in test cyanobacteria. In conclusion, current finding demonstrated a positive cross-talk between H₂O₂ and NO for providing tolerance to cyanobacteria against Cd stress.

Response to Static Magnetic Field-Induced Stress in Scenedesmus obliquus and Nannochloropsis gaditana

Magnetic fields in biological systems is a promising research field; however, their application for microalgae has not been fully exploited. This work aims to measure the enzymatic activity and non-enzymatic activity of two microalgae species in terms of superoxide dismutase (SOD), catalase (CAT), and carotenoids, respectively, in response to static magnetic fields-induced stress. Two magnet configurations (north and south) and two exposure modes (continuous and pulse) were applied. Two microalgae species were considered, the Scenedesmus obliquus and Nannochloropsis gaditana. The SOD activity increased by up to 60% in S. obliquus under continuous exposure. This trend was also found for CAT in the continuous mode. Conversely, under the pulse mode, its response was hampered as the SOD and CAT were reduced. For N. gaditana, SOD increased by up to 62% with the south configuration under continuous exposure. In terms of CAT, there was a higher activity of up to 19%. Under the pulsed exposure, SOD activity was up to 115%. The CAT in this microalga was increased by up to 29%. For N. gaditana, a significant increase of over 40% in violaxanthin production was obtained compared to the control, when the microalgae were exposed to SMF as a pulse. Depending on the exposure mode and species, this methodology can be used to produce oxidative stress and obtain an inhibitory or enhanced response in addition to the significant increase in the production of antioxidant pigments.

Peroxisomal PEX7 Receptor Affects Cadmium-Induced ROS and Auxin Homeostasis in Arabidopsis Root System

Peroxisomes are important in plant physiological functions and stress responses. Through the production of reactive oxygen and nitrogen species (ROS and RNS), and antioxidant defense enzymes, peroxisomes control cellular redox homeostasis. Peroxin (PEX) proteins, such as PEX7 and PEX5, recognize peroxisome targeting signals (PTS1/PTS2) important for transporting proteins from cytosol to peroxisomal matrix. pex7-1 mutant displays reduced PTS2 protein import and altered peroxisomal metabolism. In this research we analyzed the role of PEX7 in the Arabidopsis thaliana root system exposed to 30 or 60 μM CdSO₄. Cd uptake and translocation, indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) levels, and reactive oxygen species (ROS) and reactive nitrogen species (RNS) levels and catalase activity were analyzed in pex7-1 mutant primary and lateral roots in comparison with the wild type (wt). The peroxisomal defect due to PEX7 mutation did not reduce Cd-uptake but reduced its translocation to the shoot and the root cell peroxisomal signal detected by 8-(4-Nitrophenyl) Bodipy (N-BODIPY) probe. The trend of nitric oxide (NO) and peroxynitrite in pex7-1 roots, exposed/not exposed to Cd, was as in wt, with the higher Cd-concentration inducing higher levels of these RNS. By contrast, PEX7 mutation caused changes in Cd-induced hydrogen peroxide (H₂O₂) and superoxide anion (O₂^●-) levels in the roots, delaying ROS-scavenging. Results show that PEX7 is involved in counteracting Cd toxicity in Arabidopsis root system by controlling ROS metabolism and affecting auxin levels. These results add further information to the important role of peroxisomes in plant responses to Cd.

Nephroprotective effect of naringin in methotrexate induced renal toxicity in male rats

The current work aims to study the nephroprotective potential of naringin (NG), a flavanone derived from citrus fruits, in methotrexate (MTX)-induced renal toxicity. Thirty male rats were divided into five groups; control group (IP saline), MTX group (IP single dose, 20 mg/kg), and three groups co-treated with MTX and naringin (IP daily dose; 20, 40, and 80 mg/kg, respectively). Kidney tissues were used to investigate renal function, oxidative stress, lipid peroxidation, and caspase-3 activity. Biochemical cytokine analysis was performed in addition to ultrastructural examinations of kidney tissue. When compared to the MTX-treated rats, MTX+NG significantly reduced the levels of urea, creatinine, MDA, NO, TNFα, IL-6, and caspase-3 activity. A significant increase in the levels of the antioxidant enzymes and GSH were also noted. Additionally, naringin ameliorated the apparent ultrastructural changes observed in the glomeruli and renal tubules of MTX-intoxicated rats. Noticeable structural improvements of glomerular lesions, proximal, and distal convoluted tubular epithelium were observed in MTX+NG treated animals, including podocytes with regular foot processes, perfectly organized filtration barrier, no signs of GBM thickening, organized brush border, and normal architecture of microvilli. Naringin (80 mg/kg) had the maximum amelioration effect. To the best of our knowledge, this is the first study to investigate the ultrastructural manifestations of naringin and/or MTX on the kidney of rats. Taken all, naringin has a potent therapeutic effect and can be used in adjuvant therapy to prevent MTX-induced nephrotoxicity. Nevertheless, the molecular mechanism underlying the nephroprotective capacity of naringin needs further investigation.

Silicon induces adventitious root formation in rice under arsenate stress with involvement of nitric oxide and indole-3-acetic acid

Arsenic (As) negatively affects plant development. This study evaluates how the application of silicon (Si) can favor the formation of adventitious roots in rice under arsenate stress (AsV) as a mechanism to mitigate its negative effects. The simultaneous application of AsV and Si up-regulated the expression of genes involved in nitric oxide (NO) metabolism, cell cycle progression, auxin (IAA, indole-3-acetic acid) biosynthesis and transport, and Si uptake which accompanied adventitious root formation. Furthermore, Si triggered the expression and activity of enzymes involved in ascorbate recycling. Treatment with L-NAME (NG-nitro L-arginine methyl ester), an inhibitor of NO generation, significantly suppressed adventitious root formation, even in the presence of Si; however, supplying NO in the growth media rescued its effects. Our data suggest that both NO and IAA are essential for Si-mediated adventitious root formation under AsV stress. Interestingly, TIBA (2,3,5-triiodobenzoic acid), a polar auxin transport inhibitor, suppressed adventitious root formation even in the presence of Si and SNP (sodium nitroprusside, an NO donor), suggesting that Si is involved in a mechanism whereby a cellular signal is triggered and that first requires NO formation, followed by IAA biosynthesis.

Comparative transcriptome profiling and co-expression network analysis uncover the key genes associated withearly-stage resistance to Aspergillus flavus in maize

BACKGROUND

The fungus Aspergillus flavus (A. flavus) is a serious threat to maize (Zea mays) production worldwide. It causes considerable yield and economic losses, and poses a health risk to humans and livestock due to the high toxicity of aflatoxin. However, key genes and regulatory networks conferring maize resistance to A. flavus are not clear, especially at the early stage of infection. Here, we performed a comprehensive transcriptome analysis of two maize inbred lines with contrasting resistance to A. flavus infection.

RESULTS

The pairwise comparisons between mock and infected kernels in each line during the first 6 h post inoculation (hpi) showed that maize resistance to A. flavus infection was specific to the genotype and infection stage, and defense pathways were strengthened in the resistant line. Further comparison of the two maize lines revealed that the infection-induced up-regulated differentially expressed genes (DEGs) in the resistant line might underlie the enhanced resistance. Gene co-expression network analysis by WGCNA (weighted gene co-expression network analysis) identified 7 modules that were significantly associated with different infection stages, and 110 hub genes of these modules. These key regulators mainly participate in the biosynthesis of fatty acid and antibiotics. In addition, 90 candidate genes for maize resistance to A. flavus infection and/or aflatoxin contamination obtained in previous studies were confirmed to be differentially expressed between the resistant and susceptible lines within the first 6 hpi.

CONCLUSION

This work unveiled more A. flavus resistance genes and provided a detailed regulatory network of early-stage resistance to A. flavus in maize.

Catalase (CAT) Gene Family in Rapeseed (Brassica napus L.): Genome-Wide Analysis, Identification, and Expression Pattern in Response to Multiple Hormones and Abiotic Stress Conditions

Catalase (CAT) is an antioxidant enzyme expressed by the CAT gene family and exists in almost all aerobic organisms. Environmental stresses induce the generation of reactive oxygen species (ROS) that eventually hinder plant growth and development. The CAT enzyme translates the hydrogen peroxide (H₂O₂) to water (H₂O) and reduce the ROS levels to shelter the cells’ death. So far, the CAT gene family has not been reported in rapeseed (Brassica napus L.). Therefore, a genome-wide comprehensive analysis was conducted to classify the CAT genes in the rapeseed genome. The current study identified 14 BnCAT genes in the rapeseed genome. Based on phylogenetic and synteny analysis, the BnCATs belong to four groups (Groups I–IV). A gene structure and conserved motif analysis showed that Group I, Group II, and Group IV possess almost the same intron/exon pattern, and an equal number of motifs, while Group III contains diverse structures and contain 15 motifs. By analyzing the cis-elements in the promoters, we identified five hormone-correlated responsive elements and four stress-related responsive elements. Further, six putative bna-miRNAs were also identified, targeting three genes (BnCAT4, BnCAT6, and BnCAT8). Gene ontology (GO) enrichment analysis showed that the BnCAT genes were largely related to cellular organelles, ROS response, stimulus response, stress response, and antioxidant enzymes. Almost 10 BnCAT genes showed higher expression levels in different tissues, i.e., root, leaf, stem, and silique. The expression analysis showed that BnCAT1–BnCAT3 and BnCAT11–BnCAT13 were significantly upregulated by cold, salinity, abscisic acid (ABA), and gibberellic acid (GA) treatment, but not by drought and methyl jasmonate (MeJA). Notably, most of the genes were upregulated by waterlogging stress, except BnCAT6, BnCAT9, and BnCAT10. Our results opened new windows for future investigations and provided insights into the CAT family genes in rapeseed.

Loss of function of the chloroplast membrane K+/H+ antiporters AtKEA1 and AtKEA2 alters the ROS and NO metabolism but promotes drought stress resilience

Potassium (K⁺) exerts key physiological functions such as osmoregulation, stomatal movement, membrane transport, protein synthesis and photosynthesis among others. Previously, it was demonstrated in Arabidopsis thaliana that the loss of function of the chloroplast K⁺Efflux Antiporters KEA1 and KEA2, located in the inner envelope membrane, provokes inefficient photosynthesis. Therefore, the main goal of this study was to evaluate the potential impact of the loss of function of those cation transport systems in the metabolism of reactive oxygen and nitrogen species (ROS and RNS). Using 14-day-old seedlings from Arabidopsis double knock-out kea1kea2 mutants, ROS metabolism and NO content in roots and green cotyledons were studied at the biochemical level. The loss of function of AtKEA1 and AtKEA2 did not cause oxidative stress but it provoked an alteration of the ROS homeostasis affecting some ROS-generating enzymes. These included glycolate oxidase (GOX) and NADPH-dependent superoxide generation activity, enzymatic and non-enzymatic antioxidants and both NADP-isocitrate dehydrogenase and NADP-malic enzyme activities. NO content, analyzed by confocal laser scanning microscopy (CLSM), was negatively affected in both photosynthetic and non-photosynthetic organs in kea1kea2 mutant seedlings. Furthermore, the S-nitrosoglutathione reductase (GSNOR) protein expression and activity were downregulated in kea1kea2 mutants, whereas the tyrosine nitrated protein profile, analyzed by immunoblot, was unaffected but the relative expression of each immunoreactive band changed. Moreover, kea1kea2 mutants showed an increased photorespiratory pathway and stomata closure, thus promoting a higher resilience to drought stress. Data suggest that the chloroplast osmotic balance and integrity maintained by AtKEA1 and AtKEA2 are necessary to keep the balance of ROS/RNS metabolism. Moreover, these data open new questions about how endogenous NO generation might be affected by the K⁺/H⁺ transport located in the chloroplasts.

Signaling Toward Reactive Oxygen Species-Scavenging Enzymes in Plants

Reactive oxygen species (ROS) are signaling molecules essential for plant responses to abiotic and biotic stimuli as well as for multiple developmental processes. They are produced as byproducts of aerobic metabolism and are affected by adverse environmental conditions. The ROS content is controlled on the side of their production but also by scavenging machinery. Antioxidant enzymes represent a major ROS-scavenging force and are crucial for stress tolerance in plants. Enzymatic antioxidant defense occurs as a series of redox reactions for ROS elimination. Therefore, the deregulation of the antioxidant machinery may lead to the overaccumulation of ROS in plants, with negative consequences both in terms of plant development and resistance to environmental challenges. The transcriptional activation of antioxidant enzymes accompanies the long-term exposure of plants to unfavorable environmental conditions. Fast ROS production requires the immediate mobilization of the antioxidant defense system, which may occur via retrograde signaling, redox-based modifications, and the phosphorylation of ROS detoxifying enzymes. This review aimed to summarize the current knowledge on signaling processes regulating the enzymatic antioxidant capacity of plants.

Lead (Pb)-resistant bacteria inhibit Pb accumulation in dill (Anethum graveolens L.) by improving biochemical, physiological, and antioxidant enzyme response of plants

The accumulation of heavy metal in the soil is a serious concern for sustainable food production due to their toxic effects on plants and other living things. The strategies are required on urgent bases for the management of metal-contaminated soils. Thus, the microbes from the genus Pseudomonas were characterized for different traits and lead (Pb)-resistant ability and their effects were assessed on growth, photosynthesis, antioxidant capacity, and Pb uptake by dill (Anethum graveolens L.). Furthermore, soil basal respiration and induced respiration in soil were also assessed under microbes and Pb stress. Among the tested three strains, Pseudomonas P159 and P150 were more tolerant to Pb stress than Pseudomonas P10, whereas P159 showed the highest values for phosphorus (P), siderophore, auxin, and hydrogen cyanide production. The bacterial inoculation increased the plant shoot dry weights, carbohydrates, proline, and chlorophyll contents under Pb stress. The catalase (CAT) and peroxidase (POD) activities of the plants were higher in bacterial-treated plants than control. The bacterial inoculation decreased Pb concentration in plants, and the response varied with the type of microbes. The bacterial strains enhanced the soil basal and induced respiration than respective Pb treatments alone. Overall, Pseudomonas P159 is potentially suitable for the remediation of Pb-contaminated soils. Graphical abstract.

Salicylic acid-induced nitric oxide enhances arsenic toxicity tolerance in maize plants by upregulating the ascorbate-glutathione cycle and glyoxalase system

The role of nitric oxide (NO) in salicylic acid (SA)-induced tolerance to arsenic (As) stress in maize plants is not reported in the literature. Before starting As stress (AsS) treatments, SA (0.5 mM) was sprayed to the foliage of maize plants. Thereafter, AsV (0.1 mM as sodium hydrogen arsenate heptahydrate) stress (AsS) was initiated and during the stress period, sodium nitroprusside (SNP 0.1 mM), a NO donor, was sprayed individually or in combination with SA. Furthermore, cPTIO (0.1 mM) was also applied as a NO scavenger during the stress period. Arsenic stress led to significant reductions in plant growth, photosynthesis, water relation parameters and endogenous NO content, but it increased hydrogen peroxide, malondialdehyde, electrolyte leakage, methylglyoxal, proline, the activities of major antioxidant enzymes, and leaf and root As content. The combined treatment of SA+SNP was more effective to reverse oxidative stress related parameters and reduce the As content in both leaves and roots, with a concomitant increase in antioxidant defense system, the ascorbate-glutathione (AsA-GSH) cycle-related enzymes, glyoxalase system enzymes, plant growth, and photosynthetic traits. The beneficial effects of SA were completely abolished with cPTIO supply by blocking the NO synthesis in AsS-maize plants, indicating that NO effectively participated in SA-improved tolerance to AsS in maize plants.

Additional calcium and sulfur manages hexavalent chromium toxicity in Solanum lycopersicum L. and Solanum melongena L. seedlings by involving nitric oxide

In recent years, nutrient management has gained much attention for mitigating metal stress. But, role of nutrients like calcium (Ca) and sulfur (S) in mitigating Cr(VI) toxicity along with their mechanism of action are still limited. Therefore, the present study was performed to explore role of Ca and S in ameliorating Cr(VI) toxicity in 21 days old seedlings of Solanum lycopersicum L. and Solanum melongena L. Chromium (VI) reduced tolerance index and altered root traits due to greater Cr accumulation in the cell wall and cellular organelles due to down-regulation in thiols and phytochelatins that lead to alterations in photosynthesis. However, Ca or S stimulated vacuolar sequestration of Cr(VI) and reduced its uptake at the cell wall. This was coincided with up-regulation in glutathione-S-transferase activity, and amounts of thiols and phytochelatins. Cr(VI) caused oxidative stress together with up-regulation in superoxide dismutase and catalase, and proline metabolism while Ca and S reversed these effects. Chromium (VI) inhibited nitrate reductase activity while Ca and S reversed this response. NG-nitro-l-arginine methyl ester augmented Cr(VI) toxicity but sodium nitroprusside (SNP) mitigated Cr(VI) toxicity. Overall results show that Ca and S both are able in ameliorating Cr(VI) toxicity and require nitric oxide for this task.

Nitric oxide is essential for cadmium-induced peroxule formation and peroxisome proliferation

Nitric oxide (NO) and nitrosylated derivatives are produced in peroxisomes, but the impact of NO metabolism on organelle functions remains largely uncharacterised. Double and triple NO-related mutants expressing cyan florescent protein (CFP)-SKL (nox1 × px-ck and nia1 nia2 × px-ck) were generated to determine whether NO regulates peroxisomal dynamics in response to cadmium (Cd) stress using confocal microscopy. Peroxule production was compromised in the nia1 nia2 mutants, which had lower NO levels than the wild-type plants. These findings show that NO is produced early in the response to Cd stress and was involved in peroxule production. Cd-induced peroxisomal proliferation was analysed using electron microscopy and by the accumulation of the peroxisomal marker PEX14. Peroxisomal proliferation was inhibited in the nia1 nia2 mutants. However, the phenotype was recovered by exogenous NO treatment. The number of peroxisomes and oxidative metabolism were changed in the NO-related mutant cells. Furthermore, the pattern of oxidative modification and S-nitrosylation of the catalase (CAT) protein was changed in the NO-related mutants in both the absence and presence of Cd stress. Peroxisome-dependent signalling was also affected in the NO-related mutants. Taken together, these results show that NO metabolism plays an important role in peroxisome functions and signalling.

Plant Peroxisomes: A Factory of Reactive Species

Plant peroxisomes are organelles enclosed by a single membrane whose biochemical composition has the capacity to adapt depending on the plant tissue, developmental stage, as well as internal and external cellular stimuli. Apart from the peroxisomal metabolism of reactive oxygen species (ROS), discovered several decades ago, new molecules with signaling potential, including nitric oxide (NO) and hydrogen sulfide (H2S), have been detected in these organelles in recent years. These molecules generate a family of derived molecules, called reactive nitrogen species (RNS) and reactive sulfur species (RSS), whose peroxisomal metabolism is autoregulated through posttranslational modifications (PTMs) such as S-nitrosation, nitration and persulfidation. The peroxisomal metabolism of these reactive species, which can be weaponized against pathogens, is susceptible to modification in response to external stimuli. This review aims to provide up-to-date information on crosstalk between these reactive species families and peroxisomes, as well as on their cellular environment in light of the well-recognized signaling properties of H2O2, NO and H2S.

Effects of Antimony on Reactive Oxygen and Nitrogen Species (ROS and RNS) and Antioxidant Mechanisms in Tomato Plants

This research studies the effects that Sb toxicity (0.0, 0.5, and 1.0 mM) has on the growth, reactive oxygen and nitrogen species, and antioxidant systems in tomato plants. Sb is accumulated preferentially in the roots, with little capacity for its translocation to the leaves where the concentration is much lower. The growth of the seedlings is reduced, with alteration in the content in other nutrients. There is a decrease in the content of Fe, Mg, and Mn, while Cu and Zn increase. The contents in chlorophyll a and b decrease, as does the photosynthetic efficiency. On the contrary the carotenoids increase, indicating a possible action as antioxidants and protectors against Sb. The phenolic compounds do not change, and seem not to be involved in the defense response of the tomato against the stress by Sb. The water content of the leaves decreases while that of proline increases in response to the Sb toxicity. Fluorescence microscopy images and spectrofluorometric detection showed increases in the production of O2.-, H2O2, NO, and ONOO-, but not of nitrosothiols. The Sb toxicity induces changes in the SOD, POX, APX, and GR antioxidant activities, which show a clear activation in the roots. In leaves, only the SOD and APX increase. The DHAR activity is inhibited in roots but undergoes no changes in the leaves, as is also the case for the POX and GR activities. Ascorbate increases while GSH decreases in the roots. The total AsA + DHA content increases in the roots, but the total GSH + GSSG content decreases, while neither is altered in the leaves. Under Sb toxicity increases the expression of the SOD, APX, and GR genes, while the expression of GST decreases dramatically in roots but increases in leaves. In addition, an alteration is observed in the pattern of the growth of the cells in the elongation zone, with smaller and disorganized cells. All these effects appear to be related to the ability of the Sb to form complexes with thiol groups, including GSH, altering both redox homeostasis and the levels of auxin in the roots and the quiescent center.

Roles of nitric oxide in heavy metal stress in plants: Cross-talk with phytohormones and protein S-nitrosylation

Heavy metal (HM) stress is a major hazard, which significantly affects plant growth and development. In order to confront HM stress, plants directly or indirectly regulate the levels of endogenous nitric oxide (NO), a redox-related signaling molecule involved in wide range of plant growth and development as well as in response to HM stress. In addition, there is now compelling experimental evidence that NO usually mediates signaling processes through interactions with different biomolecules like phytohormones to regulate HM tolerance. Apart from phytohormones, NO partly operates through posttranslational modification of proteins, notably via S-nitrosylation in response to HM stress. Recently, the roles of S-nitrosylation as a regulator of plant responses to HM stress and S-nitrosylated candidates have also been established and detected. Here, we describe the roles of NO in confronting HM phytotoxicity in plants with a particular focus on the presentation and discussion of recent data obtained in this field, which involves in the function of various phytohormones and S-nitrosylation during plant responses to HM stress. Additionally, both importance and challenges of future work are outlined in order to further elucidate the specific mechanisms underlying the roles of NO in plant responses to HM stress.

Burkholderia phytofirmans PsJN and tree twigs derived biochar together retrieved Pb-induced growth, physiological and biochemical disturbances by minimizing its uptake and translocation in mung bean (Vigna radiata L.)

Anthropogenic activities like industrial mining, refining and smelting release substantial amounts of lead (Pb) into the soil causing potential ecological menaces to environment, soil productivity and food security. Present pot scale study was undertaken to investigate the effects of tree twigs-derived biochar and a bacterium Burkholderia phytofirmans PsJN on Pb accumulation, growth, physiological, biochemical and antioxidative defense responses of mung bean grown in Pb spiked soil. The original soil was spiked with Pb (600 mg kg^-1) and amended with biochar (1% w/w). Upon screening in laboratory, B. phytofirmans PsJN exhibited high Pb tolerance and was able to grow at high Pb concentrations. Surface-disinfected seeds of mung bean were inoculated with B. phytofirmans PsJN and sown in pots along with un-inoculated seeds. Data were collected for various growth, physiological and biochemical parameters from fully matured harvested plants. Application of biochar and B. phytofirmans PsJN ameliorated Pb induced negative impacts in mung bean both individually and in combination, but better growth, physiological and seed quality responses were observed with their combined use. Compared with respective controls, their combined use increased the following parameters in normal and Pb spiked soils, respectively: plant height (69% and 159%), root dry weight (97% and 130%), shoot dry weight (42% and 104%), number of pods (70% and 210%), grains weight (58% and 194%) and number of root nodules (71% and 255%). Moreover, combined use increased chlorophyll contents (27% and 37%), photosynthetic rate (93% and 204%), transpiration rate (42% and 132%), stomatal conductance (70% and 218%), sub-stomatal conductance (93% and 148%) and water use efficiency (35% and 43%). In addition, combined application of biochar and B. phytofirmans PsJN retarded Pb-induced oxidative stress by intensifying antioxidant enzyme activities and reducing activities of reactive oxygen species. Similarly, considerable reduction in Pb uptake, translocation and bioaccumulation in mung bean was noticed in Pb spiked soil due to applied amendments. Furthermore, their combined use resulted in considerable increase in grain quality parameters (protein, fat, ash) both in normal and Pb-spiked soils. Therefore, it can be inferred that interactive use of biochar and B. phytofirmans PsJN provides an efficient innovative strategy to repossess Pb induced growth, physiological, biochemical and oxidative disturbances in mung bean.

Recent progress in the knowledge on the alleviating effect of nitric oxide on heavy metal stress in plants

Recently, nitric oxide (NO), a redox-related signaling molecule, is considered to be a key regulator in plant growth and development as well as response to abiotic stresses. Heavy metal (HM) stress is one of the most serious threats to affect crop growth and production. HM stress attributes to the production of reactive oxygen species (ROS), leading to oxidative stress in plants. Thus, to minimize the toxic effects of HM stress, plants directly or indirectly activate different ROS-scavenging mechanisms comprised antioxidative enzymes and non-enzymatic antioxidants. Understanding the roles of NO is essential to elucidate how NO activates the appropriate set of responses to HM stress. Moreover, the regulation of key genes or proteins is very important in response to stress stimuli. Therefore, here we focus on the recent knowledge concerning the alleviating effect of NO on HM stress, covering from HM iron accumulation to antioxidant system to related gene and protein expression.

Assessment of Subcellular ROS and NO Metabolism in Higher Plants: Multifunctional Signaling Molecules

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

Lead toxicity induced phytotoxic effects on mung bean can be relegated by lead tolerant Bacillus subtilis (PbRB3)

Being a primary toxic heavy metal, lead (Pb) contamination presents an imposing environmental and public health concern worldwide. A Bacillus subtilis PbRB3, displaying higher Pb tolerance, was isolated from the textile effluent. The bacterial culture was able to remove >80% of Pb from culture solution. Upon screening in the presence of Pb, PbRB3 strain exhibited significant plant growth promoting potential. A 3 weeks long pot experiment was established to examine the capability of PbRB3 strain for physiological and biochemical traits, and Pb accumulation tendency of mung bean at 250 and 500 mg kg^-1 of Pb toxicity, respectively. With respect to control treatments, photosynthetic pigments, protein synthesis, net assimilation rate, transpiration rate and stomatal conductance were significantly constrained by Pb toxicity levels. Intrinsic and instantaneous water use efficiencies were considerably improved in inoculated plants under Pb toxicity. Compared to inoculated control, significantly higher superoxide dismutase activity in both Pb toxicity treatments, while higher malondialdehyde contents only at Pb500 treatment was recorded with PbRB3 inoculation. Catalase activity between Pb250 and Pb500 treatments was comparable at both inoculation level. Moreover, PbRB3 inoculation led to significantly higher peroxidase activity under Pb toxicity treatments compared to inoculated control. The PbRB3 inoculation led to comparable differences in root Pb content between Pb250 and Pb500 treatments. These results suggest that inoculation of Pb tolerant, Bacillus subtilis PbRB3, could be employed to improve mung bean growth potential and adaptation against Pb toxicity, and thereby accelerated Pb rhizoaccumulation from metal contaminated environment.

Nitric Oxide Enhances Cytotoxicity of Lead by Modulating the Generation of Reactive Oxygen Species and Is Involved in the Regulation of Pb2+ and Ca2+ Fluxes in Tobacco BY-2 Cells

Lead is a heavy metal known to be toxic to both animals and plants. Nitric oxide (NO) was reported to participate in plant responses to different heavy metal stresses. In this study, we analyzed the function of exogenous and endogenous NO in Pb-induced toxicity in tobacco BY-2 cells, focusing on the role of NO in the generation of reactive oxygen species (ROS) as well as Pb²⁺ and Ca²⁺ fluxes using non-invasive micro-test technology (NMT). Pb treatment induced BY-2 cell death and rapid NO and ROS generation, while NO burst occurred earlier than ROS accumulation. The elimination of NO by 2-4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) resulted in a decrease of ROS, and the supplementation of NO by sodium nitroprusside (SNP) caused an increased accumulation of ROS. Furthermore, the addition of exogenous NO stimulated Pb²⁺ influx, thus promoting Pb uptake in cells and aggravating Pb-induced toxicity in cells, whereas the removal of endogenous NO produced the opposite effect. Moreover, we also found that both exogenous and endogenous NO enhanced Pb-induced Ca²⁺ effluxes and calcium homeostasis disorder. These results suggest that exogenous and endogenous NO played a critical regulatory role in BY-2 cell death induced by Pb stress by promoting Pb²⁺ influx and accumulation and disturbing calcium homeostasis.

Short-Term Low Temperature Induces Nitro-Oxidative Stress that Deregulates the NADP-Malic Enzyme Function by Tyrosine Nitration in Arabidopsis thaliana

Low temperature (LT) negatively affects plant growth and development via the alteration of the metabolism of reactive oxygen and nitrogen species (ROS and RNS). Among RNS, tyrosine nitration, the addition of an NO₂ group to a tyrosine residue, can modulate reduced nicotinamide-dinucleotide phosphate (NADPH)-generating systems and, therefore, can alter the levels of NADPH, a key cofactor in cellular redox homeostasis. NADPH also acts as an indispensable electron donor within a wide range of enzymatic reactions, biosynthetic pathways, and detoxification processes, which could affect plant viability. To extend our knowledge about the regulation of this key cofactor by this nitric oxide (NO)-related post-translational modification, we analyzed the effect of tyrosine nitration on another NADPH-generating enzyme, the NADP-malic enzyme (NADP-ME), under LT stress. In Arabidopsis thaliana seedlings exposed to short-term LT (4 °C for 48 h), a 50% growth reduction accompanied by an increase in the content of superoxide, nitric oxide, and peroxynitrite, in addition to diminished cytosolic NADP-ME activity, were found. In vitro assays confirmed that peroxynitrite inhibits cytosolic NADP-ME2 activity due to tyrosine nitration. The mass spectrometric analysis of nitrated NADP-ME2 enabled us to determine that Tyr-73 was exclusively nitrated to 3-nitrotyrosine by peroxynitrite. The in silico analysis of the Arabidopsis NADP-ME2 protein sequence suggests that Tyr73 nitration could disrupt the interactions between the specific amino acids responsible for protein structure stability. In conclusion, the present data show that short-term LT stress affects the metabolism of ROS and RNS, which appears to negatively modulate the activity of cytosolic NADP-ME through the tyrosine nitration process.

Reactive oxygen species, auxin and nitric oxide in metal-stressed roots: toxicity or defence

The presented review is a summary on the current knowledge about metal induced stress response in plants, focusing on the roles of reactive oxygen species, auxin and nitric oxide in roots. The article focuses mainly on the difference between defence and toxicity symptoms of roots during metal-induced stress. Nowadays, pollution of soils by heavy metals is a rapidly growing issue, which affects agriculture and human health. In order to deal with these problems, we must first understand the basic mechanisms and responses to environmental conditions in plants growing under such conditions. Studies so far show somewhat conflicting data, interpreting the same stress responses as both symptoms of defence and toxicity. Therefore, the aim of this review is to give a report about current knowledge of heavy metal-induced stress research, and also to differentiate between toxicity and defence, and outline the challenges of research, focusing on reactive oxygen and nitrogen species, auxin, and the interplay among them. There are still remaining questions on how reactive oxygen and nitrogen species, as well as auxin, can activate either symptoms of toxicity or defence, and adaptation responses.

Sweet Pepper (Capsicum annuum L.) Fruits Contain an Atypical Peroxisomal Catalase That is Modulated by Reactive Oxygen and Nitrogen Species

During the ripening of sweet pepper (Capsicum annuum L.) fruits, in a genetically controlled scenario, enormous metabolic changes occur that affect the physiology of most cell compartments. Peroxisomal catalase gene expression decreases after pepper fruit ripening, while the enzyme is also susceptible to undergo post-translational modifications (nitration, S-nitrosation, and oxidation) promoted by reactive oxygen and nitrogen species (ROS/RNS). Unlike most plant catalases, the pepper fruit enzyme acts as a homodimer, with an atypical native molecular mass of 125 to 135 kDa and an isoelectric point of 7.4, which is higher than that of most plant catalases. These data suggest that ROS/RNS could be essential to modulate the role of catalase in maintaining basic cellular peroxisomal functions during pepper fruit ripening when nitro-oxidative stress occurs. Using catalase from bovine liver as a model and biotin-switch labeling, in-gel trypsin digestion, and nanoliquid chromatography coupled with mass spectrometry, it was found that Cys377 from the bovine enzyme could potentially undergo S-nitrosation. To our knowledge, this is the first report of a cysteine residue from catalase that can be post-translationally modified by S-nitrosation, which makes it especially important to find the target points where the enzyme can be modulated under either physiological or adverse conditions.

Hydrogen sulfide: A novel component in Arabidopsis peroxisomes which triggers catalase inhibition

Plant peroxisomes have the capacity to generate different reactive oxygen and nitrogen species (ROS and RNS), such as H₂ O₂ , superoxide radical (O₂ ^· - ), nitric oxide and peroxynitrite (ONOO^- ). These organelles have an active nitro-oxidative metabolism which can be exacerbated by adverse stress conditions. Hydrogen sulfide (H₂ S) is a new signaling gasotransmitter which can mediate the posttranslational modification (PTM) persulfidation. We used Arabidopsis thaliana transgenic seedlings expressing cyan fluorescent protein (CFP) fused to a canonical peroxisome targeting signal 1 (PTS1) to visualize peroxisomes in living cells, as well as a specific fluorescent probe which showed that peroxisomes contain H₂ S. H₂ S was also detected in chloroplasts under glyphosate-induced oxidative stress conditions. Peroxisomal enzyme activities, including catalase, photorespiratory H₂ O₂ -generating glycolate oxidase (GOX) and hydroxypyruvate reductase (HPR), were assayed in vitro with a H₂ S donor. In line with the persulfidation of this enzyme, catalase activity declined significantly in the presence of the H₂ S donor. To corroborate the inhibitory effect of H₂ S on catalase activity, we also assayed pure catalase from bovine liver and pepper fruit-enriched samples, in which catalase activity was inhibited. Taken together, these data provide evidence of the presence of H₂ S in plant peroxisomes which appears to regulate catalase activity and, consequently, the peroxisomal H₂ O₂ metabolism.

PMAP-23 triggers cell death by nitric oxide-induced redox imbalance in Escherichia coli

BACKGROUND

Antibiotic resistance is a global problem and there is an urgent need to augment the arsenal against pathogenic bacteria. The emergence of different drug resistant bacteria is threatening human lives to be pushed toward the pre-antibiotic era. Antimicrobial peptides (AMPs) are a host defense component against infectious pathogens in response to innate immunity. PMAP-23, an AMP derived from porcine myeloid, possesses antibacterial activity. It is currently not clear how the antibacterial activity of PMAP-23 is manifested.

METHODS

The disruptive effect of nitric oxide (NO) on the catalase activity, reactive oxygen species (ROS) production, DNA oxidation and apoptosis-like death were evaluated using the NO generation inhibitor.

RESULTS

In this investigation, PMAP-23 generates NO in a dose dependent manner. NO deactivated catalase and this antioxidant could not protect Escherichia coli against ROS, especially hydroxyl radical. This redox imbalance was shown to induce oxidative stress, thus leading to DNA strand break. Consequently, PMAP-23 treated E. coli cells resulted in apoptosis-like death. These physiological changes were inhibited when NO generation was inhibited. In the ΔdinF mutant, the levels of DNA strand break sharply increased and the cells were more sensitive to PMAP-23 than wild type.

CONCLUSION

Our data strongly indicates that PMAP-23 mediates apoptosis-like cell death through affecting intracellular NO homeostasis. Furthermore, our results demonstrate that DinF functioned in protection from oxidative DNA damage.

GENERAL SIGNIFICANCE

The identification of PMAP-23 antibacterial activity and mechanism provides a promising antibacterial agent, supporting the role of NO in cell death regulation.

The role of endogenous nitric oxide in melatonin-improved tolerance to lead toxicity in maize plants

Melatonin (MT) and nitric oxide (NO) are known as scavengers of free radicals and an antioxidant against biotic and abiotic stresses in plant defense systems. However, whether NO interplays role in MT-induced antioxidant defense remains to be determined in the plants exposed to lead (Pb) toxicity. So, two experiments were designed to evaluate the role of NO in MT-mediated tolerance of maize plants to Pb stress. In the initial experiment, prior to starting different treatments, a solution of 0.05- or 0.10-mM MT was sprayed every other day for a period of 10 days to the leaves of maize plants exposed to Pb stress (0.1-mM PbCl₂). Pb toxicity significantly caused reduction in plant biomass (both fresh and dry), PSII maximum efficiency (F_v/F_m), total chlorophyll, leaf potassium (K), calcium (Ca), and leaf water potential, but it resulted in increased levels of proline, hydrogen peroxide (H₂O₂), malondialdehyde (MDA), electron leakage (EL), leaf Pb, and endogenous NO. An addition experiment was set up to further understand whether NO played role in mitigation of Pb toxicity in maize plants by MT using scavengers of NO and cPTIO combined with the MT treatments. MT-induced tolerance to Pb toxicity was totally eliminated by cPTIO by reversing endogenous NO. The present results clearly indicated that MT mediated the endogenous NO to improve tolerance of maize plants to Pb toxicity. This evidence was also supported by the increases of H₂O₂ and MDA and reduces some antioxidant enzyme activities tested as well as the plant growth inhibition and increased leaf Pb content by application of MT combined with cPTIO.

Lead induces oxidative stress in Pisum sativum plants and changes the levels of phytohormones with antioxidant role

The interaction of lead (Pb) with plant hormonal balance and oxidative stress remains under discussion. To evaluate how Pb induces oxidative stress, and modulates the antioxidant enzymes and the phytohormones pool, four-week old Pisum sativum plants were exposed during 28 days to 10, 100 and 500 mg kg-1 Pb in soil. In comparison to leaves, roots showed higher Pb accumulation, oxidative damages and changes in phytohormone pools. Contrarily to leaves, where glutathione reductase (GR) and ascorbate peroxidase (APX) activities were more stimulated than catalase (CAT) and superoxide dismutase (SOD), roots showed a stimulation of SOD, GR and APX in all doses, and of CAT in the highest dose. While protein oxidation occurred in roots even at lower Pb-doses, lipid peroxidation and membrane permeability also occurred but at 500 mg kg-1 and in both organs, accompanied by increases of H2O2. Jasmonic acid (JA) responded in both organs even at lowest Pb-doses, while salicylic acid (SA) and abscisic acid (ABA, only in leaves), increased particularly at the concentration of 500 mg Pb kg-1. In conclusion, and compared with leaves, roots showed oxidative damage even at 10 mg Pb Kg-1, being proteins a first oxidative-target, although there is a stimulation of the antioxidant enzymes. Also, JA is mobilized prior to oxidative stress changes are detected, and may play a protective role (activating antioxidant enzymes), while the mobilization of SA is particularly relevant in cells expressing oxidative damage. Other hormones, like indolacetic acid and ABA may have a low protective role against Pb toxicity.

Vitexin protects against ischemia/reperfusion-induced brain endothelial permeability

Brain endothelial permeability plays a crucial role in blood-brain barrier (BBB), but the permeability enhancement in cerebral ischemia reperfusion (I/R). Vitexin has certain neuroprotective effects, but the effect brain endothelial permeability in I/R injury was unknown. In this study, the effects of Vitexin on endothelial permeability and the underlying mechanisms in human brain microvascular endothelial cells (HBMEc) I/R injury model were investigated. Cell viability, lactate dehydrogenase (LDH), inflammation and apoptosis were detected. The effects of Vitexin on BBB integrity tight junction, matrix metalloproteinases (MMP) were also investigated. The mechanism was confirmed by PI3K inhibitor and NOS inhibitor in normal or eNOS siRNA transfection HBMEc. Vitexin significantly reduced LDH, Caspase 3 level, alleviated inflammation, also could maintain BBB integrity, increased tight junction proteins expression and inhibited MMP. The mechanism is related to reduction of intracellular NO and ONOO^-, regulated eNOS, iNOS activity. Vitexin significantly preserved eNOS phosphorylation in response to the activated Akt. Moreover, combined with PI3K inhibitor or low dosage of NOS inhibitor, totally abolished Vitexin-induced eNOS phosphorylation, the protected effect was also attenuated, but still significantly between model cells. However, combined with high dosage NOS inhibitor which both inhibited the eNOS phosphorylation and iNOS, the protected effect of Vitexin was abrogated. In addition, eNOS silencing cells were used to further clarify the regulatory role of Vitexin on iNOS. Our findings showed that Vitexin could play a protective role in I/R-induced brain endothelial permeability by simultaneously increase eNOS phosphorylation and inhibit iNOS.

Impact of Nitric Oxide (NO) on the ROS Metabolism of Peroxisomes

Nitric oxide (NO) is a gaseous free radical endogenously generated in plant cells. Peroxisomes are cell organelles characterized by an active metabolism of reactive oxygen species (ROS) and are also one of the main cellular sites of NO production in higher plants. In this mini-review, an updated and comprehensive overview is presented of the evidence available demonstrating that plant peroxisomes have the capacity to generate NO, and how this molecule and its derived products, peroxynitrite (ONOO⁻) and S-nitrosoglutathione (GSNO), can modulate the ROS metabolism of peroxisomes, mainly throughout protein posttranslational modifications (PTMs), including S-nitrosation and tyrosine nitration. Several peroxisomal antioxidant enzymes, such as catalase (CAT), copper-zinc superoxide dismutase (CuZnSOD), and monodehydroascorbate reductase (MDAR), have been demonstrated to be targets of NO-mediated PTMs. Accordingly, plant peroxisomes can be considered as a good example of the interconnection existing between ROS and reactive nitrogen species (RNS), where NO exerts a regulatory function of ROS metabolism acting upstream of H₂O₂.