Interplay of reactive oxygen species and nitric oxide: nitric oxide coordinates reactive oxygen species homeostasis

Nitric oxide production and protein S-nitrosation in algae

Key roles for nitric oxide in signalling processes and plant physiological processes are now well established. In particular, the identification and functional characterisation of proteins regulated by S-nitrosation, a NO-dependent post-translational modification, provided remarkable insights into the subtle mechanisms by which NO mediates its effects. Nevertheless, and despite the considerable progress in understanding NO signalling, the question of how plant cells produce NO is not yet fully resolved. Interestingly, there is now compelling evidence that algae constitute promising biological models to investigate NO production and functions in plants. This article reviews recent highlights of research on NO production in algae and provides an overview of S-nitrosation in these organisms at the proteome level.

Nanoscale materials and NO-ROS homeostasis in plants: trilateral dynamics

Nanoparticles (NPs) have garnered increasing attention for their applications in agriculture and plant science, particularly for their interactions with reactive oxygen species (ROS) and nitric oxide (•NO). NPs, owing to their novel physicochemical properties, can be used to uniquely modulate ROS levels, enabling great control over redox homeostasis and signaling cascades. In addition, NPs may act as carriers for •NO donors, thus facilitating controlled and synchronized release and targeted delivery of •NO within plant systems. This opinion article provides insights into the current state of knowledge regarding NP interactions with ROS and •NO homeostasis in plants, highlighting key findings and knowledge gaps, as well as outlining future research directions in this rapidly expanding and potentially transformative field of research.

Emerging concern of nano-pollution in agro-ecosystem: Flip side of nanotechnology

Nanomaterials (NMs) have proven to be a game-changer in agriculture, showcasing their potential to boost plant growth and safeguarding crops. The agricultural sector has widely adopted NMs, benefiting from their small size, high surface area, and optical properties to augment crop productivity and provide protection against various stressors. This is attributed to their unique characteristics, contributing to their widespread use in agriculture. Human exposure from various components of agro-environmental sectors (soil, crops) NMs residues are likely to upsurge with exposure paths may stimulates bioaccumulation in food chain. With the aim to achieve sustainability, nanotechnology (NTs) do exhibit its potentials in various domains of agriculture also have its flip side too. In this review article we have opted a fusion approach using bibliometric based analysis of global research trend followed by a holistic assessment of pros and cons i.e. toxicological aspect too. Moreover, we have also tried to analyse the current scenario of policy associated with the application of NMs in agro-environment.

Nitric oxide: an old drug but with new horizons in ophthalmology-a narrative review

Background and Objective

Based on basic knowledge and prior research on nitric oxide (NO), the potential of NO for treating eye diseases is reviewed, and the possibility of NO-based eye drops in clinical practice and the future potential of NO in ophthalmology are discussed.

Methods

A PubMed search was performed for English-language original reports and reviews using the following key words: nitric oxide, eye, ocular, and drug.

Key Content and Findings

NO is synthesized in the human body by NO synthase (NOS) from L-arginine or through enzyme-dependent reduction of dietary nitrate. Three types of NOS (eNOS, nNOS, and iNOS) are abundantly expressed in the eye under normal physiologic or pathologic conditions. The biological effect of NO in the eye is dose dependent. Low intraocular NO concentrations, produced by eNOS or nNOS, have various cellular effects, including vasodilation, intraocular pressure (IOP) regulation, and neuroprotection. iNOS induced under pathologic ocular conditions produces high NO concentrations in the local environment and mediates tissue inflammation, ocular cell apoptosis, and neurodegeneration. In particular, increased iNOS has been reported in glaucoma and retinal ischemic or degenerative diseases. NO plays a vital role in ocular injury. NO can facilitate ocular surface wound healing while eradicating pathogens such as bacteria and Acanthamoeba in chemical burns or infectious keratitis. Furthermore, NO has antifibrotic activity via the cyclic guanosine monophosphate (cGMP) signaling pathway. NO causes smooth muscle relaxation, which can be used to inhibit myopia progression in children. NO can be a stem cell modulator and may help in treating ocular stem cell disorders.

Conclusions

Because of its diverse biologic effects, NO can be a key player in regulating ocular inflammation in various ocular diseases, aiding ocular surface wound healing, controlling IOP in glaucoma, alleviating retinal disease, and suppressing myopia progression. Although there remain limitations to the effective use of highly unstable state, gaseous NO, the role of NO in the field of ophthalmology can be greatly expanded through the development of novel NO donors and effective delivery platforms.

An activated form of NB-ARC protein RLS1 functions with cysteine-rich receptor-like protein RMC to trigger cell death in rice

A key event that follows pathogen recognition by a resistance (R) protein containing an NB-ARC (nucleotide-binding adaptor shared by Apaf-1, R proteins, and Ced-4) domain is hypersensitive response (HR)-type cell death accompanied by accumulation of reactive oxygen species and nitric oxide. However, the integral mechanisms that underlie this process remain relatively opaque. Here, we show that a gain-of-function mutation in the NB-ARC protein RLS1 (Rapid Leaf Senescence 1) triggers high-light-dependent HR-like cell death in rice. The RLS1-mediated defense response is largely independent of salicylic acid accumulation, NPR1 (Nonexpressor of Pathogenesis-Related Gene 1) activity, and RAR1 (Required for Mla12 Resistance 1) function. A screen for suppressors of RLS1 activation identified RMC (Root Meander Curling) as essential for the RLS1-activated defense response. RMC encodes a cysteine-rich receptor-like secreted protein (CRRSP) and functions as an RLS1-binding partner. Intriguingly, their co-expression resulted in a change in the pattern of subcellular localization and was sufficient to trigger cell death accompanied by a decrease in the activity of the antioxidant enzyme APX1. Collectively, our findings reveal an NB-ARC-CRRSP signaling module that modulates oxidative state, the cell death process, and associated immunity responses in rice.

Transcriptome Analysis Reveals the Mechanisms of Tolerance to High Concentrations of Calcium Chloride Stress in Parachlorella kessleri

Salt stress is one of the abiotic stress factors that affect the normal growth and development of higher plants and algae. However, few research studies have focused on calcium stress, especially in algae. In this study, the mechanism of tolerance to high calcium stress of a Parachlorella kessleri strain was explored by the method of transcriptomics combined with physiological and morphological analysis. Concentrations of CaCl₂ 100 times (3.6 g/L) and 1000 times (36 g/L) greater than the standard culture were set up as stresses. The results revealed the algae could cope with high calcium stress mainly by strengthening photosynthesis, regulating osmotic pressure, and inducing antioxidant defense. Under the stress of 3.6 g/L CaCl₂, the algae grew well with normal cell morphology. Although the chlorophyll content was significantly reduced, the photosynthetic efficiency was well maintained by up-regulating the expression of some photosynthesis-related genes. The cells reduced oxidative damage by inducing superoxide dismutase (SOD) activities and selenoprotein synthesis. A large number of free amino acids were produced to regulate the osmotic potential. When in higher CaCl₂ stress of 36 g/L, the growth and chlorophyll content of algae were significantly inhibited. However, the algae still slowly grew and maintained the same photosynthetic efficiency, which resulted from significant up-regulation of massive photosynthesis genes. Antioxidant enzymes and glycerol were found to resist oxidative damage and osmotic stress, respectively. This study supplied algal research on CaCl₂ stress and provided supporting data for further explaining the mechanism of plant salt tolerance.

BR-Mediated Protein S-Nitrosylation Alleviated Low-Temperature Stress in Mini Chinese Cabbage (Brassica rapa ssp. pekinensis)

Brassinosteroids (BRs), a novel plant hormone, are widely involved in plant growth and stress response processes. Nitric oxide (NO), as an important gas signaling molecule, can regulate target protein activity, subcellular localization and function in response to various stresses through post-translational S-nitrosylation modifications. However, the relationship between BR and NO in alleviating low-temperature stress of mini Chinese cabbage remains unclear. The hydroponic experiment combined with the pharmacological and molecular biological method was conducted to study the alleviating mechanism of BR at low temperature in mini Chinese cabbage. The results showed that low temperature inhibited the growth of mini Chinese cabbage seedlings, as evidenced by dwarf plants and yellow leaves. Treatment with 0.05 mg/L BR and 50 µM NO donor S-nitrosoglutathione (GSNO) significantly increased the leaf area, stem diameter, chlorophyll content, dry and fresh weight and proline content. Meanwhile, the malondialdehyde (MDA) content in 0.05 mg/L BR- and 50 µM GSNO-treated leaves were significantly lower than those in other treated leaves under low-temperature conditions. In addition, BR and GSNO applications induced an increase in NO and S-nitrosothiol (SNO) levels in vivo under low-temperature stress. Similarly, spraying BR after the elimination of NO also increased the level of S-nitrosylation in vivo, while spraying GSNO after inhibiting BR biosynthesis decreased the level of NO and SNO in vivo. In contrast, the S-nitrosoglutathione reductase (BrGSNOR) relative expression level and GSNOR enzyme activity were downregulated and inhibited by BR treatment, GSNO treatment and spraying BR after NO clearance, while the relative expression level of BrGSNOR was upregulated and GSNOR enzyme activity was also increased when spraying GSNO after inhibiting BR synthesis. Meanwhile, the biotin switch assay showed that exogenous BR increased the level of total nitrosylated protein in vivo under low-temperature stress. These results suggested that BR might act as an upstream signal of NO, induced the increase of NO content in vivo and then induced the protein S-nitrosylation modification to alleviate the damage of mini Chinese cabbage seedlings under low-temperature stress.

Nano-priming as emerging seed priming technology for sustainable agriculture-recent developments and future perspectives

Nano-priming is an innovative seed priming technology that helps to improve seed germination, seed growth, and yield by providing resistance to various stresses in plants. Nano-priming is a considerably more effective method compared to all other seed priming methods. The salient features of nanoparticles (NPs) in seed priming are to develop electron exchange and enhanced surface reaction capabilities associated with various components of plant cells and tissues. Nano-priming induces the formation of nanopores in shoot and helps in the uptake of water absorption, activates reactive oxygen species (ROS)/antioxidant mechanisms in seeds, and forms hydroxyl radicals to loosen the walls of the cells and acts as an inducer for rapid hydrolysis of starch. It also induces the expression of aquaporin genes that are involved in the intake of water and also mediates H2O2, or ROS, dispersed over biological membranes. Nano-priming induces starch degradation via the stimulation of amylase, which results in the stimulation of seed germination. Nano-priming induces a mild ROS that acts as a primary signaling cue for various signaling cascade events that participate in secondary metabolite production and stress tolerance. This review provides details on the possible mechanisms by which nano-priming induces breaking seed dormancy, promotion of seed germination, and their impact on primary and secondary metabolite production. In addition, the use of nano-based fertilizer and pesticides as effective materials in nano-priming and plant growth development were also discussed, considering their recent status and future perspectives.

Scavenging of nitric oxide up-regulates photosynthesis under drought in Festuca arundinacea and F. glaucescens but reduces their drought tolerance

Nitric oxide (NO) has been proven to be involved in the regulation of many physiological processes in plants. Though the contribution of NO in plant response to drought has been demonstrated in numerous studies, this phenomenon remains still not fully recognized. The research presented here was performed to decipher the role of NO metabolism in drought tolerance and the ability to recover after stress cessation in two closely related species of forage grasses, important for agriculture in European temperate regions: Festuca arundinacea and F. glaucescens. In both species, two genotypes with distinct levels of drought tolerance were selected to compare their physiological reactions to simulated water deficit and further re-watering, combined with a simultaneous application of NO scavenger, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO). The results clearly indicated a strong relationship between scavenging of NO in leaves and physiological response of both analyzed grass species to water deficit and re-watering. It was revealed that NO generated under drought was mainly located in mesophyll cells. In plants with reduced NO level a higher photosynthetic capacity and delay in stomatal closure under drought, were observed. Moreover, NO scavenging resulted also in the increased membrane permeability and higher accumulation of ROS in cells of analyzed plants both under drought and re-watering. This phenomena indicate that lower NO level might reduce drought tolerance and the ability of F. arundinacea and F. glaucescens to recover after stress cessation.

Indium induces nitro-oxidative stress in roots of wheat (Triticum aestivum)

The entrance of indium, an emerging contaminant from electronics, into the agroecosystem inevitably causes its accumulation in crops and raises exposure risk of humans via food chain. This study investigated indium uptake and toxicological effects in wheat plants under a worst-case scenario. Inhibition of root growth is a primary manifestation of indium toxicity and most absorbed indium accumulated in wheat roots with only a tiny portion reaching the leaves. The enhancement of reactive oxygen species (ROS), lipid peroxidation and protein oxidation in roots suggest that indium caused oxidative stress. Additionally, we found the levels of nitric oxide and peroxyinitrite, two major reactive nitrogen species (RNS), also increased in wheat roots under indium stress. These changes were accompanied by a raise in protein tyrosine nitration, thereby provoking nitrosative stress. The increase in peroxyinitrite and S-nitrosoglutathione content, S-nitrosoglutathione reductase activity as well as a concomitant reduction in glutathione concentrations suggest a rigorous metabolic interplay between ROS and RNS. Moreover, indium simultaneously triggered alteration in protein carbonylation and nitration. Overall, our results suggest that indium induced nitro-oxidative stress which probably contributes to toxicological effects in wheat plants, which are helpful in reducing the potential risk from emerging contaminants analogous to indium to humans.

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.

Influence of Haptoglobin Polymorphism on Stroke in Sickle Cell Disease Patients

This review outlines the current clinical research investigating how the haptoglobin (Hp) genetic polymorphism and stroke occurrence are implicated in sickle cell disease (SCD) pathophysiology. Hp is a blood serum glycoprotein responsible for binding and removing toxic free hemoglobin from the vasculature. The role of Hp in patients with SCD is critical in combating blood toxicity, inflammation, oxidative stress, and even stroke. Ischemic stroke occurs when a blocked vessel decreases oxygen delivery in the blood to cerebral tissue and is commonly associated with SCD. Due to the malformed red blood cells of sickle hemoglobin S, blockage of blood flow is much more prevalent in patients with SCD. This review is the first to evaluate the role of the Hp polymorphism in the incidence of stroke in patients with SCD. Overall, the data compiled in this review suggest that further studies should be conducted to reveal and evaluate potential clinical advancements for gene therapy and Hp infusions.

Molecular Mechanisms of Nitric Oxide (NO) Signaling and Reactive Oxygen Species (ROS) Homeostasis during Abiotic Stresses in Plants

Abiotic stressors, such as drought, heavy metals, and high salinity, are causing huge crop losses worldwide. These abiotic stressors are expected to become more extreme, less predictable, and more widespread in the near future. With the rapidly growing human population and changing global climate conditions, it is critical to prevent global crop losses to meet the increasing demand for food and other crop products. The reactive gaseous signaling molecule nitric oxide (NO) is involved in numerous plant developmental processes as well as plant responses to various abiotic stresses through its interactions with various molecules. Together, these interactions lead to the homeostasis of reactive oxygen species (ROS), proline and glutathione biosynthesis, post-translational modifications such as S-nitrosylation, and modulation of gene and protein expression. Exogenous application of various NO donors positively mitigates the negative effects of various abiotic stressors. In view of the multidimensional role of this signaling molecule, research over the past decade has investigated its potential in alleviating the deleterious effects of various abiotic stressors, particularly in ROS homeostasis. In this review, we highlight the recent molecular and physiological advances that provide insights into the functional role of NO in mediating various abiotic stress responses in plants.

Redox feedback regulation of ANAC089 signaling alters seed germination and stress response

The interplay between the phytohormone abscisic acid (ABA) and the gasotransmitter nitric oxide (NO) regulates seed germination and post-germinative seedling growth. We show that GAP1 (germination in ABA and cPTIO 1) encodes the transcription factor ANAC089 with a critical membrane-bound domain and extranuclear localization. ANAC089 mutants lacking the membrane-tethered domain display insensitivity to ABA, salt, and osmotic and cold stresses, revealing a repressor function. Whole-genome transcriptional profiling and DNA-binding specificity reveals that ANAC089 regulates ABA- and redox-related genes. ANAC089 truncated mutants exhibit higher NO and lower ROS and ABA endogenous levels, alongside an altered thiol and disulfide homeostasis. Consistently, translocation of ANAC089 to the nucleus is directed by changes in cellular redox status after treatments with NO scavengers and redox-related compounds. Our results reveal ANAC089 to be a master regulator modulating redox homeostasis and NO levels, able to repress ABA synthesis and signaling during Arabidopsis seed germination and abiotic stress.

The AtCRK5 Protein Kinase Is Required to Maintain the ROS NO Balance Affecting the PIN2-Mediated Root Gravitropic Response in Arabidopsis

The Arabidopsis AtCRK5 protein kinase is involved in the establishment of the proper auxin gradient in many developmental processes. Among others, the Atcrk5-1 mutant was reported to exhibit a delayed gravitropic response via compromised PIN2-mediated auxin transport at the root tip. Here, we report that this phenotype correlates with lower superoxide anion (O2•-) and hydrogen peroxide (H2O2) levels but a higher nitric oxide (NO) content in the mutant root tips in comparison to the wild type (AtCol-0). The oxidative stress inducer paraquat (PQ) triggering formation of O2•- (and consequently, H2O2) was able to rescue the gravitropic response of Atcrk5-1 roots. The direct application of H2O2 had the same effect. Under gravistimulation, correct auxin distribution was restored (at least partially) by PQ or H2O2 treatment in the mutant root tips. In agreement, the redistribution of the PIN2 auxin efflux carrier was similar in the gravistimulated PQ-treated mutant and untreated wild type roots. It was also found that PQ-treatment decreased the endogenous NO level at the root tip to normal levels. Furthermore, the mutant phenotype could be reverted by direct manipulation of the endogenous NO level using an NO scavenger (cPTIO). The potential involvement of AtCRK5 protein kinase in the control of auxin-ROS-NO-PIN2-auxin regulatory loop is discussed.

Antioxidant Activity Evaluation of FlexirubinType Pigment from Chryseobacterium artocarpi CECT 8497 and Related Docking Study

The current research is focused on studying the biological efficacy of flexirubin, a pigment extracted from Chryseobacterium artocarpi CECT 8497.Different methods such as DPPH, H₂O_2, NO^•, O₂^•−, ^•OH, lipid peroxidation inhibition by FTC and TBA, ferric reducing and ferrous chelating activity were carried out to evaluate the antioxidant activity of flexirubin. Molecular docking was also carried out, seeking the molecular interactions of flexirubin and a standard antioxidant compound with SOD enzyme to figure out the possible flexirubin activity mechanism. The new findings revealed that the highest level of flexirubin exhibited similar antioxidant activity as that of the standard compound according to the H₂O₂, ^•OH, O₂^•−, FTC and TBA methods. On the other hand, flexirubin at the highest level has shown lower antioxidant activity than the positive control according to the DPPH and NO• and even much lower when measured by the FRAP method. Molecular docking showed that the interaction of flexirubin was in the binding cavity of the SOD enzyme and did not affect its metal-binding site. These results revealed that flexirubin has antioxidant properties and can be a useful therapeutic compound in preventing or treating free radical-related diseases.

Nitric oxide signaling in the plant nucleus: the function of nitric oxide in chromatin modulation and transcription

Nitric oxide (NO) is involved in a vast number of physiologically important processes in plants, such as organ development, stress resistance, and immunity. Transduction of NO bioactivity is generally achieved by post-translational modification of proteins, with S-nitrosation of cysteine residues as the predominant form. While traditionally the subcellular location of the factors involved was of lesser importance, recent studies identified the connection between NO and transcriptional activity and thereby raised the question about the route of NO into the nuclear sphere. Identification of NO-affected transcription factors and chromatin-modifying histone deacetylases implicated the important role of NO signaling in the plant nucleus as a regulator of epigenetic mechanisms and gene transcription. Here, we discuss the relationship between NO and its directly regulated protein targets in the nuclear environment, focusing on S-nitrosated chromatin modulators and transcription factors.

Nitric oxide production and signalling in algae

Nitric oxide (NO) was the first identified gaseous messenger and is now well established as a major ubiquitous signalling molecule. The rapid development of our understanding of NO biology in embryophytes came with the partial characterization of the pathways underlying its production and with the decrypting of signalling networks mediating its effects. Notably, the identification of proteins regulated by NO through nitrosation greatly enhanced our perception of NO functions. In comparison, the role of NO in algae has been less investigated. Yet, studies in Chlamydomonas reinhardtii have produced key insights into NO production through the identification of NO-forming nitrite reductase and of S-nitrosated proteins. More intriguingly, in contrast to embryophytes, a few algal species possess a conserved nitric oxide synthase, the main enzyme catalysing NO synthesis in metazoans. This latter finding paves the way for a deeper characterization of novel members of the NO synthase family. Nevertheless, the typical NO-cyclic GMP signalling module transducing NO effects in metazoans is not conserved in algae, nor in embryophytes, highlighting a divergent acquisition of NO signalling between the green and the animal lineages.

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.

Nitric Oxide Releasing Hydrogel Nanoparticles Decreases Epithelial Cell Injuries Associated With Airway Reopening

Acute respiratory distress syndrome (ARDS) is an acute inflammatory lung condition. It is characterized by disruption of gas exchange inside the alveoli, accumulation of protein edema, and an increase in lung stiffness. One major cause of ARDS is a lung infection, such as SARS-COV-2 infection. Lungs of ARDS patients need to be mechanically ventilated for airway reopening. Consequently, ventilation might damage delicate lung tissue leading to excess edema, known as ventilator-induced lung injury (VILI). Mortality of COVID-19 patients under VILI seems to be higher than non-COVID patients, necessitating effective preventative therapies. VILI occurs when small air bubbles form in the alveoli, injuring epithelial cells (EPC) due to shear stress. Nitric oxide (NO) inhalation was suggested as a therapy for ARDS, however, it was shown that it is not effective because of the extremely short half-life of NO. In this study, NO-releasing nanoparticles were produced and tested in an in vitro model, representing airways in the deep lung. Cellular injuries were quantified via fluorescent live/dead assay. Atomic force microscopy (AFM) was used to assess cell morphology. qRT-PCR was performed to assess the expression of inflammatory markers, specifically IL6 and CCL2. ELISA was performed to assess IL6 and confirm qRT-PCR results at the protein level. Finally, ROS levels were assessed in all groups. Here, we show that NO delivery via nanoparticles enhanced EPC survival and recovery, AFM measurements revealed that NO exposure affect cell morphology, while qRT-PCR demonstrated a significant downregulation in IL6 and CCL2 expression when treating the cells to NO both before and after shear exposure. ELISA results for IL6 confirmed qRT-PCR data. ROS experiment results support our findings from previous experiments. These findings demonstrate that NO-releasing nanoparticles can be used as an effective delivery approach of NO to deep lung to prevent/reduce ARDS associated inflammation and cell injuries. This information is particularly useful to treat severe ARDS due to COVID-19 infection. These nanoparticles will be useful when clinically administrated to COVID-19 patients to reduce the symptoms originating from lung distress.

Discovery of an ultraspecific triuret hydrolase (TrtA) establishes the triuret biodegradation pathway

Triuret (carbonyldiurea) is an impurity found in industrial urea fertilizer (<0.1% w/w) that is applied, worldwide, around 300 million pounds each year on agricultural lands. In addition to anthropogenic sources, endogenous triuret has been identified in amoeba and human urine, the latter being diagnostic for hypokalemia. The present study is the first to describe the metabolic breakdown of triuret, which funnels into biuret metabolism. We identified the gene responsible for triuret decomposition (trtA) in bacterial genomes, clustered with biuH, which encodes biuret hydrolase and has close protein sequence homology. TrtA is a member of the isochorismatase-like hydrolase (IHL) protein family, similarly to BiuH, and has a catalytic efficiency (k_cat/K_M) of 6 x 10⁵ M⁻¹s⁻¹, a K_M for triuret of 20 μM, and exquisite substrate specificity. Indeed, TrtA has four orders of magnitude less activity with biuret. Crystal structures of TrtA in apo and holo form were solved and compared with the BiuH structure. The high substrate selectivity was found to be conveyed by second shell residues around each active site. Mutagenesis of residues conserved in TrtA to the alternate consensus found in BiuHs revealed residues critical to triuret hydrolase activity but no single mutant evolved more biuret activity, and likely a combination of mutations is required to interconvert between TrtA, BiuH functions. TrtA-mediated triuret metabolism is relatively rare in recorded genomes (1–2%), but is largely found in plant-associated, nodulating, and endophytic bacteria. This study suggests functions for triuret hydrolase in certain eukaryotic intermediary processes and prokaryotic intermediary or biodegradative metabolism

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.

Systematic analysis of SmWD40s, and responding of SmWD40-170 to drought stress by regulation of ABA- and H2O2-induced stomal movement in Salvia miltiorrhiza bunge

WD40 proteins play crucial roles in response to abiotic stress. By screening the genome sequences of Salvia miltiorrhiza Bunge, 225 SmWD40 genes were identified and divided into 9 subfamilies (I-IX). Physiological, biochemical, gene structure, conserved protein motif and GO annotation analyses were performed on SmWD40 family members. The SmWD40-170 was found in 110 SmWD40 genes that contain drought response elements, SmWD40-170 was one of these genes whose response in terms of expression under drought was significant. The expression of SmWD40-170 was also up-regulated by ABA and H₂O₂. Through observed the stomatal phenotype of SmWD40-170 transgenic lines, the stomatal closure was abolished under dehydration, ABA and H₂O₂ treatment in SmWD40-170 knockdown lines. Abscisic acid (ABA), as the key phytohormone, elevates reactive oxygen species (ROS) levels under drought stress. The ABA-ROS interaction mediated the generation of H₂O₂ and the activation of anion channel in guard cells. The osmolality alteration of guard cells further accelerated the stomatal closure. As a second messenger, nitric oxide (NO) regulated ABA signaling, the NO stimulated protein kinase activity inhibited the K⁺ influx which result in stomatal closure. These NO-relevant events were essential for ABA-induced stomatal closure. The reduction of NO production was also observed in the guard cells of SmWD40-170 knockdown lines. The abolished of stomatal closure attributed to the SmWD40-170 deficiency induced the reduction of NO content. In general, the SmWD40-170 is a critical drought response gene in SmWD40 gene family and regulates ABA- and H₂O₂-induced stomatal movement by affecting the synthesis of NO.

Matrix Redox Physiology Governs the Regulation of Plant Mitochondrial Metabolism through Posttranslational Protein Modifications

Mitochondria function as hubs of plant metabolism. Oxidative phosphorylation produces ATP, but it is also a central high-capacity electron sink required by many metabolic pathways that must be flexibly coordinated and integrated. Here, we review the crucial roles of redox-associated posttranslational protein modifications (PTMs) in mitochondrial metabolic regulation. We discuss several major concepts. First, the major redox couples in the mitochondrial matrix (NAD, NADP, thioredoxin, glutathione, and ascorbate) are in kinetic steady state rather than thermodynamic equilibrium. Second, targeted proteomics have produced long lists of proteins potentially regulated by Cys oxidation/thioredoxin, Met-SO formation, phosphorylation, or Lys acetylation, but we currently only understand the functional importance of a few of these PTMs. Some site modifications may represent molecular noise caused by spurious reactions. Third, different PTMs on the same protein or on different proteins in the same metabolic pathway can interact to fine-tune metabolic regulation. Fourth, PTMs take part in the repair of stress-induced damage (e.g., by reducing Met and Cys oxidation products) as well as adjusting metabolic functions in response to environmental variation, such as changes in light irradiance or oxygen availability. Finally, PTMs form a multidimensional regulatory system that provides the speed and flexibility needed for mitochondrial coordination far beyond that provided by changes in nuclear gene expression alone.

Low endogenous NO levels in roots and antioxidant systems are determinants for the resistance of Arabidopsis seedlings grown in Cd

Cadmium (Cd), which is a toxic non-essential heavy metal capable of entering plants and thus the food chain, constitutes a major environmental and health concern worldwide. An understanding of the tools used by plants to overcome Cd stress could lead to the production of food crops with lower Cd uptake capacity and of plants with greater Cd uptake potential for phytoremediation purposes in order to restore soil efficiency in self-sustaining ecosystems. The signalling molecule nitric oxide (NO), whose function remains unclear, has recently been involved in responses to Cd stress. Using different mutants, such as nia1nia2, nox1, argh1-1 and Atnoa1, which were altered in NO metabolism, we analysed various parameters related to reactive oxygen and nitrogen species (ROS/RNS) metabolism and seedling fitness following germination and growth under Cd treatment conditions for seven days. Seedling roots were the most affected, with an increase in ROS and RNS observed in wild type (WT) seedling roots, leading to increased oxidative damage and fitness loss. Mutants that showed lower NO levels in seedling roots under Cd stress were more resistant than WT seedlings due to the maintenance of antioxidant systems which protect against oxidative damage.

Proteomic Changes during MCMV Infection Revealed by iTRAQ Quantitative Proteomic Analysis in Maize

Maize chlorotic mottle virus (MCMV) has been occurring frequently worldwide and causes severe yield losses in maize (Zea mays). To better investigate the destructive effects of MCMV infection on maize plants, isobaric tagging for relative and absolute quantitation (iTRAQ)-based comparative proteomic analysis was performed on MCMV infected maize cv. B73. A total of 972 differentially abundant proteins (DAPs), including 661 proteins with increased abundance and 311 proteins with reduced abundance, were identified in response to MCMV infection. Functional annotations of DAPs and measurement of photosynthetic activity revealed that photosynthesis was decreased, while the abundance of ribosomal proteins, proteins related to stress responses, oxidation-reduction and redox homeostasis was altered significantly during MCMV infection. Two DAPs, disulfide isomerases like protein ZmPDIL-1 and peroxiredoxin family protein ZmPrx5, were further analyzed for their roles during MCMV infection through cucumber mosaic virus-based virus-induced gene silencing (CMV-VIGS). The accumulation of MCMV was suppressed in ZmPDIL-1-silenced or ZmPrx5-silenced B73 maize, suggesting ZmPDIL-1 and ZmPrx5 might enhance host susceptibility to MCMV infection.

Melatonin-Nitric Oxide Crosstalk and Their Roles in the Redox Network in Plants

Melatonin, an amine hormone highly conserved during evolution, has a wide range of physiological functions in animals and plants. It is involved in plant growth, development, maturation, and aging, and also helps ameliorate various types of abiotic and biotic stresses, including salt, drought, heavy metals, and pathogens. Melatonin-related growth and defense responses of plants are complex, and involve many signaling molecules. Among these, the most important one is nitric oxide (NO), a freely diffusing amphiphilic biomolecule that can easily cross the cell membrane, produce rapid signal responses, and participate in a wide variety of physiological reactions. NO-induced S-nitrosylation is also involved in plant defense responses. NO interacts with melatonin as a long-range signaling molecule, and helps regulate plant growth and maintain oxidative homeostasis. Exposure of plants to abiotic stresses causes the increase of endogenous melatonin levels, with the consequent up-regulation of melatonin synthesis genes, and further increase of melatonin content. The application of exogenous melatonin causes an increase in endogenous NO and up-regulation of defense-related transcription factors, resulting in enhanced stress resistance. When plants are infected by pathogenic bacteria, NO acts as a downstream signal to lead to increased melatonin levels, which in turn induces the mitogen-activated protein kinase (MAPK) cascade and associated defense responses. The application of exogenous melatonin can also promote sugar and glycerol production, leading to increased levels of salicylic acid and NO. Melatonin and NO in plants can function cooperatively to promote lateral root growth, delay aging, and ameliorate iron deficiency. Further studies are needed to clarify certain aspects of the melatonin/NO relationship in plant physiology.

Improvement in lipid production in Monoraphidium sp. QLY-1 by combining fulvic acid treatment and salinity stress

The effects of the combined treatment of fulvic acid (FA) and salinity stress on lipid production in Monoraphidium sp. QLY-1 at multiple levels was investigated in this study. The results indicated that the highest lipid content (59.53%) in QLY-1 was achieved by combining FA treatment and salinity stress. Compared with the control group and FA addition alone, the group treated with both FA and salinity stress had increased contents of reactive oxygen species (ROS), antioxidases, and nitric oxide (NO). Additionally, the addition of FA enhanced the expression levels of mitogen-activated protein kinases (MAPKs) and key genes related to lipid biosynthesis in QLY-1 under salinity stress. Collectively, biochemical analyses indicated that ROS, NO, MAPK, expression of lipid biosynthesis-related genes and antioxidant systems were involved in the lipid biosynthesis pathways of QLY-1 under the combined treatment of FA and salinity stress.

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.

The function of S-nitrosothiols during abiotic stress in plants

Nitric oxide (NO) is an active redox molecule involved in the control of a wide range of functions integral to plant biology. For instance, NO is implicated in seed germination, floral development, senescence, stomatal closure, and plant responses to stress. NO usually mediates signaling events via interactions with different biomolecules, for example the modulation of protein functioning through post-translational modifications (NO-PTMs). S-nitrosation is a reversible redox NO-PTM that consists of the addition of NO to a specific thiol group of a cysteine residue, leading to formation of S-nitrosothiols (SNOs). SNOs are more stable than NO and therefore they can extend and spread the in vivo NO signaling. The development of robust and reliable detection methods has allowed the identification of hundreds of S-nitrosated proteins involved in a wide range of physiological and stress-related processes in plants. For example, SNOs have a physiological function in plant development, hormone metabolism, nutrient uptake, and photosynthesis, among many other processes. The role of S-nitrosation as a regulator of plant responses to salinity and drought stress through the modulation of specific protein targets has also been well established. However, there are many S-nitrosated proteins that have been identified under different abiotic stresses for which the specific roles have not yet been identified. In this review, we examine current knowledge of the specific role of SNOs in the signaling events that lead to plant responses to abiotic stress, with a particular focus on examples where their functions have been well characterized at the molecular level.

Glutathione depletion and dual-model oxygen balance disruption for photodynamic therapy enhancement

Photodynamic therapy (PDT) is a prospective approach to cure tumor diseases. However, tumor micro-environment is notably characterized with severe hypoxia and high expression of glutathione (GSH), which seriously limit its clinical application. Here, based on the characteristics of perfluorocarbon (PFC) to dissolve substantial oxygen (O₂) and the sensitivity of reductive GSH to S-NO group, we designed GSH depletion and dual-model O₂ supply strategies to promote PDT enhancement. The PFC nanoliposomes (FI@Lip) and biocompatible NO donor S-nitrosated human serum albumin (HSA-SNO) were combined to synergistically combat the obstacle of tumor micro-environment, reducing GSH concentration and increasing singlet oxygen (¹O₂) generation. In vitro, after irradiation with NIR laser, the PFC in FI@Lip dissolved more O₂ to increase ¹O₂ generation. In addition, with co-delivery of HSA-SNO, it can effectively promote GSH depletion to recover ¹O₂ level and release NO concurrently to inhibit mitochondrial respiration. This combination strategy of FI@Lip and HSA-SNO obviously relieved intracellular hypoxia and decreased GSH to increase more toxic ¹O₂ generation for PDT enhancement. The present work will play as an enlightening role in PDT design and clinical application in the near future.

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.

Chloroplasts at the Crossroad of Photosynthesis, Pathogen Infection and Plant Defense

Photosynthesis, pathogen infection, and plant defense are three important biological processes that have been investigated separately for decades. Photosynthesis generates ATP, NADPH, and carbohydrates. These resources are utilized for the synthesis of many important compounds, such as primary metabolites, defense-related hormones abscisic acid, ethylene, jasmonic acid, and salicylic acid, and antimicrobial compounds. In plants and algae, photosynthesis and key steps in the synthesis of defense-related hormones occur in chloroplasts. In addition, chloroplasts are major generators of reactive oxygen species and nitric oxide, and a site for calcium signaling. These signaling molecules are essential to plant defense as well. All plants grown naturally are attacked by pathogens. Bacterial pathogens enter host tissues through natural openings or wounds. Upon invasion, bacterial pathogens utilize a combination of different virulence factors to suppress host defense and promote pathogenicity. On the other hand, plants have developed elaborate defense mechanisms to protect themselves from pathogen infections. This review summarizes recent discoveries on defensive roles of signaling molecules made by plants (primarily in their chloroplasts), counteracting roles of chloroplast-targeted effectors and phytotoxins elicited by bacterial pathogens, and how all these molecules crosstalk and regulate photosynthesis, pathogen infection, and plant defense, using chloroplasts as a major battlefield.

AST-120 Reduces Neuroinflammation Induced by Indoxyl Sulfate in Glial Cells

Chronic kidney disease (CKD) involves multiple organ dysfunction, and the neurological complications that are often present in CKD patients support the idea of a crosstalk between the kidneys and the brain. Evidence suggests a possible role for products accumulating in these patients as uremic toxins in various CKD complications, including neurodegeneration. Indoxyl sulfate (IS), derived from tryptophan metabolism, is well-known as a uremic nephron-vascular toxin, and recent evidence suggests it also has a role in the immune response and in neurodegeneration. Inflammation has been associated with neurodegenerative diseases, as well as with CKD. In this study, we demonstrated that sera of CKD patients induced a significant inflammation in astrocyte cells which was proportional to IS sera concentrations, and that the IS adsorbent, AST-120, reduced this inflammatory response. These results indicated that, among the uremic toxins accumulating in serum of CKD patients, IS significantly contributed to astrocyte inflammation. Moreover, being also chronic inflammation associated with CKD, here we reported that IS further increased inflammation and oxidative stress in primary central nervous system (CNS) cells, via Nuclear Factor-κB (NF-κB) and Aryl hydrocarbon Receptor (AhR) activation, and induced neuron death. This study is a step towards elucidating IS as a potential pharmacological target in CKD patients.

Inhibition of NOS- like activity in maize alters the expression of genes involved in H2O2 scavenging and glycine betaine biosynthesis

Nitric oxide synthase-like activity contributes to the production of nitric oxide in plants, which controls plant responses to stress. This study investigates if changes in ascorbate peroxidase enzymatic activity and glycine betaine content in response to inhibition of nitric oxide synthase-like activity are associated with transcriptional regulation by analyzing transcript levels of genes (betaine aldehyde dehydrogenase) involved in glycine betaine biosynthesis and those encoding antioxidant enzymes (ascorbate peroxidase and catalase) in leaves of maize seedlings treated with an inhibitor of nitric oxide synthase-like activity. In seedlings treated with a nitric oxide synthase inhibitor, transcript levels of betaine aldehyde dehydrogenase were decreased. In plants treated with the nitric oxide synthase inhibitor, the transcript levels of ascorbate peroxidase-encoding genes were down-regulated. We thus conclude that inhibition of nitric oxide synthase-like activity suppresses the expression of ascorbate peroxidase and betaine aldehyde dehydrogenase genes in maize leaves. Furthermore, catalase activity was suppressed in leaves of plants treated with nitric oxide synthase inhibitor; and this corresponded with the suppression of the expression of catalase genes. We further conclude that inhibition of nitric oxide synthase-like activity, which suppresses ascorbate peroxidase and catalase enzymatic activities, results in increased H2O2 content.

The effect of NaCl stress on photosynthetic efficiency and lipid production in freshwater microalga-Scenedesmus obliquus XJ002

Rapid industrialization and population growth have increased the world's energy demands, resulting in a shortage of conventional fossil fuels. Thus, there is an urgent need to develop sustainable and renewable forms of energy. Microalgae have emerged as a potential feedstock for biofuel production. Under stress conditions, lipid production is enhanced in algal cells due to changes in the lipid biosynthetic pathways that produce neutral lipids. In this study, we examined the physiological and biochemical effects of salinity stress (0.00, 0.01, 0.10, 0.15, 0.20M) on the freshwater microalga Scenedesmus obliquus XJ002. We found that the biomass and the content of chlorophyll a, b and carotenoids decreased with increasing NaCl concentration. NaCl stress damaged the oxygen evolving complex (OEC) and the PSII (photosystem II) reaction center and subsequently suppressed electron transport at the donor and receptor sides of the reaction center, influencing the absorption, transfer, and application of light energy. Additionally, the total lipid content of cells was significantly increased under NaCl stress treatment. The highest lipid content (32.26%) was found in cells cultured in the presence of 0.20M NaCl, which was about 2.52-fold higher than that of cells grown in medium lacking NaCl (12.82%). In addition to providing insight into the physiological and biochemical responses of S. obliquus XJ002 to salinity stress, these findings show that lipid production, and hence biofuel feedstock production, can be boosted by adjusting salt levels in the growth medium.

Nitric oxide buffering and conditional nitric oxide release in stress response

Nitric oxide (NO) has emerged as an essential biological messenger in plant biology that usually transmits its bioactivity by post-translational modifications such as S-nitrosylation, the reversible addition of an NO group to a protein cysteine residue leading to S-nitrosothiols (SNOs). In recent years, SNOs have risen as key signalling molecules mainly involved in plant response to stress. Chief among SNOs is S-nitrosoglutathione (GSNO), generated by S-nitrosylation of the key antioxidant glutathione (GSH). GSNO is considered the major NO reservoir and a phloem mobile signal that confers to NO the capacity to be a long-distance signalling molecule. GSNO is able to regulate protein function and gene expression, resulting in a key role for GSNO in fundamental processes in plants, such as development and response to a wide range of environmental stresses. In addition, GSNO is also able to regulate the total SNO pool and, consequently, it could be considered the storage of NO in cells that may control NO signalling under basal and stress-related responses. Thus, GSNO function could be crucial during plant response to environmental stresses. Besides the importance of GSNO in plant biology, its mode of action has not been widely discussed in the literature. In this review, we will first discuss the GSNO turnover in cells and secondly the role of GSNO as a mediator of physiological and stress-related processes in plants, highlighting those aspects for which there is still some controversy.

An update on nitric oxide and its benign role in plant responses under metal stress

Pollution due to heavy metal(loid)s has become common menace across the globe. This is due to unprecedented frequent geological changes coupled with increasing anthropogenic activities, and population growth rate. Heavy metals (HMs) presence in the soil causes toxicity, and hampers plant growth and development. Plants being sessile are exposed to a variety of stress and/or a network of different kinds of stresses throughout their life cycle. To sense and transduce these stress signal, the signal reactive nitrogen species (RNS) particularly nitric oxide (NO) is an important secondary messenger next to only reactive oxygen species (ROS). Nitric oxide, a redox active molecule, colourless simple gas, and being a free radical (NO) has the potential in regulating multiple biological signaling responses in a variety of plants. Nitric oxide can counteract HMs-induced ROS, either by direct scavenging or by stimulating antioxidants defense team; therefore, it is also known as secondary antioxidant. The imbalance or cross talk of/between NO and ROS concentration along with antioxidant system leads to nitrosative and oxidative stress, or combination of both i.e., nitro-oxidative stress. Endogenous synthesis of NO also takes place in plants in the presence of heavy metals. During HM stress the different organelles of plant cells can biosynthesize NO in parallel to the ROS, such as in mitochondria, chloroplasts, peroxisomes, cytoplasm, endoplasmic reticulum and apoplasts. In view of the above, an effort has been made in the present review article to trace current knowledge and latest advances in chemical properties, biological roles, mechanism of NO action along with the physiological, biochemical, and molecular changes that occur in plants under different metal stress. A brief focus is also carried on ROS properties, roles, and their production.

WD40-REPEAT 5a functions in drought stress tolerance by regulating nitric oxide accumulation in Arabidopsis

Nitric oxide (NO) generation by NO synthase (NOS) in guard cells plays a vital role in stomatal closure for adaptive plant response to drought stress. However, the mechanism underlying the regulation of NOS activity in plants is unclear. Here, by screening yeast deletion mutants with decreased NO accumulation and NOS-like activity when subjected to H₂ O₂ stress, we identified TUP1 as a novel regulator of NOS-like activity in yeast. Arabidopsis WD40-REPEAT 5a (WDR5a), a homolog of yeast TUP1, complemented H₂ O₂ -induced NO accumulation of a yeast mutant Δtup1, suggesting the conserved role of WDR5a in regulating NO accumulation and NOS-like activity. This note was further confirmed by using an Arabidopsis RNAi line wdr5a-1 and two T-DNA insertion mutants of WDR5a with reduced WDR5a expression, in which both H₂ O₂ -induced NO accumulation and stomatal closure were repressed. This was because H₂ O₂ -induced NOS-like activity was inhibited in the mutants compared with that of the wild type. Furthermore, these wdr5a mutants were more sensitive to drought stress as they had reduced stomatal closure and decreased expression of drought-related genes. Together, our results revealed that WDR5a functions as a novel factor to modulate NOS-like activity for changes of NO accumulation and stomatal closure in drought stress tolerance.

Nanoparticles Alter Secondary Metabolism in Plants via ROS Burst

The particles within the size range of 1 and 100 nm are known as nanoparticles (NPs). NP-containing wastes released from household, industrial and medical products are emerging as a new threat to the environment. Plants, being fixed to the two major environmental sinks where NPs accumulate - namely water and soil, cannot escape the impact of nanopollution. Recent studies have shown that plant growth, development and physiology are significantly affected by NPs. But, the effect of NPs on plant secondary metabolism is still obscure. The induction of reactive oxygen species (ROS) following interactions with NPs has been observed consistently across plant species. Taking into account the existing link between ROS and secondary signaling messengers that lead to transcriptional regulation of secondary metabolism, in this perspective we put forward the argument that ROS induced in plants upon their interaction with NPs will likely interfere with plant secondary metabolism. As plant secondary metabolites play vital roles in plant performance, communication, and adaptation, a comprehensive understanding of plant secondary metabolism in response to NPs is an utmost priority.

Modulation of Protein S-Nitrosylation by Isoprene Emission in Poplar

Researchers have been examining the biological function(s) of isoprene in isoprene-emitting (IE) species for two decades. There is overwhelming evidence that leaf-internal isoprene increases the thermotolerance of plants and protects them against oxidative stress, thus mitigating a wide range of abiotic stresses. However, the mechanisms of abiotic stress mitigation by isoprene are still under debate. Here, we assessed the impact of isoprene on the emission of nitric oxide (NO) and the S-nitroso-proteome of IE and non-isoprene-emitting (NE) gray poplar (Populus × canescens) after acute ozone fumigation. The short-term oxidative stress induced a rapid and strong emission of NO in NE compared with IE genotypes. Whereas IE and NE plants exhibited under nonstressful conditions only slight differences in their S-nitrosylation pattern, the in vivo S-nitroso-proteome of the NE genotype was more susceptible to ozone-induced changes compared with the IE plants. The results suggest that the nitrosative pressure (NO burst) is higher in NE plants, underlining the proposed molecular dialogue between isoprene and the free radical NO Proteins belonging to the photosynthetic light and dark reactions, the tricarboxylic acid cycle, protein metabolism, and redox regulation exhibited increased S-nitrosylation in NE samples compared with IE plants upon oxidative stress. Because the posttranslational modification of proteins via S-nitrosylation often impacts enzymatic activities, our data suggest that isoprene indirectly regulates the production of reactive oxygen species (ROS) via the control of the S-nitrosylation level of ROS-metabolizing enzymes, thus modulating the extent and velocity at which the ROS and NO signaling molecules are generated within a plant cell.

Effects of nitric oxide on mitochondrial oxidative defence in postharvest peach fruits

BACKGROUND

It has been confirmed that the accumulation of reactive oxygen species (ROS) in fruit can cause oxidative damage and nitric oxide (NO) can regulate the accumulation of ROS and the antioxidative defence of fruit. However, little is known about the roles of NO on the antioxidant system in mitochondria of fruit. In this study, Feicheng peach fruits were dipped with 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO) and NO solutions to explore the effects of NO on the membrane permeability transition and antioxidant system in mitochondria of peach fruit.

RESULTS

Treatment with 15 µmol L(-1) NO solution could delay the decrease of mitochondrial permeability transition and decrease the content of ROS in mitochondria. Besides, when the endogenous NO was scavenged by c-PTIO, the ROS in mitochondria increased greatly and superoxide dismutase activity decreased, while the content and activities of peroxidase and catalase changed slightly.

CONCLUSION

By delaying the decrease of mitochondrial permeability transition, 15 µmol L(-1) NO treatment could promote a more stable internal medium in mitochondria of Feicheng peach fruit. The increases in the activities of antioxidant enzymes in mitochondria caused by the remove of endogenous NO suggested that NO also plays an important role in the mitochondrial antioxidant system of Feicheng peach fruit.

NO Promotes Seed Germination and Seedling Growth Under High Salt May Depend on EIN3 Protein in Arabidopsis

The gas molecule nitric oxide (NO) can cooperate with ethylene to tightly modulate plant growth and stress responses. One of the mechanism of their crosstalk is that NO is able to activate ethylene biosynthesis, possibly through post-translational modification of key enzymes such as ACC synthase and oxidase by S-nitrosylation. In this paper, we focus on the crosstalk of NO with ethylene signaling transduction transcription factor EIN3 (Ethylene Insensitive 3) and downstream gene expression in alleviating germination inhibition and growth damage induced by high salt. The Arabidopsis lines affected in ethylene signaling (ein3eil1) and NO biosynthesis (nia1nia2) were employed to compare with the wild-type Col-0 and overexpressing line EIN3ox. Firstly, the obviously inhibited germination, greater ratio of bleached leaves and enhanced electrolyte leakage were found in ein3eil1 and nia1nia2 lines than in Col-0 plants upon high salinity. However, the line EIN3ox obtained a notably elevated ability to germinate and improved seedling resistance. The experiment with SNP alone or plus high salt mostly enhanced the expression of EIN3 transcripts, compared with ACO4 and ACS2. The western blot and transcript analysis found that high-salt-induced EIN3 stabilization and EIN3 transcripts were largely attenuated in the NO biogenesis mutant nia1nia2 plants than in Col-0 ones. This observation was confirmed by simulation experiments with NO scavenger cPTIO to block NO emission. Taken together, our study provides insights that NO promotes seed germination and seedlings growth under salinity may depend on EIN3 protein.

Antioxidant Systems are Regulated by Nitric Oxide-Mediated Post-translational Modifications (NO-PTMs)

Nitric oxide (NO) is a biological messenger that orchestrates a plethora of plant functions, mainly through post-translational modifications (PTMs) such as S-nitrosylation or tyrosine nitration. In plants, hundreds of proteins have been identified as potential targets of these NO-PTMs under physiological and stress conditions indicating the relevance of NO in plant-signaling mechanisms. Among these NO protein targets, there are different antioxidant enzymes involved in the control of reactive oxygen species (ROS), such as H2O2, which is also a signal molecule. This highlights the close relationship between ROS/NO signaling pathways. The major plant antioxidant enzymes, including catalase, superoxide dismutases (SODs) peroxiredoxins (Prx) and all the enzymatic components of the ascorbate-glutathione (Asa-GSH) cycle, have been shown to be modulated to different degrees by NO-PTMs. This mini-review will update the recent knowledge concerning the interaction of NO with these antioxidant enzymes, with a special focus on the components of the Asa-GSH cycle and their physiological relevance.

Stress Sensitivity Is Associated with Differential Accumulation of Reactive Oxygen and Nitrogen Species in Maize Genotypes with Contrasting Levels of Drought Tolerance

Drought stress decreases crop growth, yield, and can further exacerbate pre-harvest aflatoxin contamination. Tolerance and adaptation to drought stress is an important trait of agricultural crops like maize. However, maize genotypes with contrasting drought tolerances have been shown to possess both common and genotype-specific adaptations to cope with drought stress. In this research, the physiological and metabolic response patterns in the leaves of maize seedlings subjected to drought stress were investigated using six maize genotypes including: A638, B73, Grace-E5, Lo964, Lo1016, and Va35. During drought treatments, drought-sensitive maize seedlings displayed more severe symptoms such as chlorosis and wilting, exhibited significant decreases in photosynthetic parameters, and accumulated significantly more reactive oxygen species (ROS) and reactive nitrogen species (RNS) than tolerant genotypes. Sensitive genotypes also showed rapid increases in enzyme activities involved in ROS and RNS metabolism. However, the measured antioxidant enzyme activities were higher in the tolerant genotypes than in the sensitive genotypes in which increased rapidly following drought stress. The results suggest that drought stress causes differential responses to oxidative and nitrosative stress in maize genotypes with tolerant genotypes with slower reaction and less ROS and RNS production than sensitive ones. These differential patterns may be utilized as potential biological markers for use in marker assisted breeding.

The impact of sodium nitroprusside and ozone in kiwifruit ripening physiology: a combined gene and protein expression profiling approach

BACKGROUND AND AIMS

Despite their importance in many aspects of plant physiology, information about the function of oxidative and, particularly, of nitrosative signalling in fruit biology is limited. This study examined the possible implications of O3 and sodium nitroprusside (SNP) in kiwifruit ripening, and their interacting effects. It also aimed to investigate changes in the kiwifruit proteome in response to SNP and O3 treatments, together with selected transcript analysis, as a way to enhance our understanding of the fruit ripening syndrome.

METHODS

Kiwifruits following harvest were pre-treated with 100 μm SNP, then cold-stored (0 °C, relative humidity 95 %) for either 2 or 6 months in the absence or in the presence of O3 (0·3 μL L(-1)), and subsequently were allowed to ripen at 20 °C. The ripening behaviour of fruit was characterized using several approaches: together with ethylene production, several genes, enzymes and metabolites involved in ethylene biosynthesis were analysed. Kiwifruit proteins were identified using 2-D electrophoresis coupled with nanoliquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. Expression patterns of kiwifruit ripening-related genes were also analysed using real-time quantitative reverse transcription-PCR (RT-qPCR).

KEY RESULTS

O3 treatment markedly delayed fruit softening and depressed the ethylene biosynthetic mechanism. Although SNP alone was relatively ineffective in regulating ripening, SNP treatment prior to O3 exposure attenuated the O3-induced ripening inhibition. Proteomic analysis revealed a considerable overlap between proteins affected by both SNP and O3. Consistent with this, the temporal dynamics in the expression of selected kiwifruit ripening-related genes were noticeably different between individual O3 and combined SNP and O3 treatments.

CONCLUSIONS

This study demonstrates that O3-induced ripening inhibition could be reversed by SNP and provides insights into the interaction between oxidative and nitrosative signalling in climacteric fruit ripening.

The impact of sodium nitroprusside and ozone in kiwifruit ripening physiology: a combined gene and protein expression profiling approach

BACKGROUND AND AIMS

Despite their importance in many aspects of plant physiology, information about the function of oxidative and, particularly, of nitrosative signalling in fruit biology is limited. This study examined the possible implications of O3 and sodium nitroprusside (SNP) in kiwifruit ripening, and their interacting effects. It also aimed to investigate changes in the kiwifruit proteome in response to SNP and O3 treatments, together with selected transcript analysis, as a way to enhance our understanding of the fruit ripening syndrome.

METHODS

Kiwifruits following harvest were pre-treated with 100 μm SNP, then cold-stored (0 °C, relative humidity 95 %) for either 2 or 6 months in the absence or in the presence of O3 (0·3 μL L(-1)), and subsequently were allowed to ripen at 20 °C. The ripening behaviour of fruit was characterized using several approaches: together with ethylene production, several genes, enzymes and metabolites involved in ethylene biosynthesis were analysed. Kiwifruit proteins were identified using 2-D electrophoresis coupled with nanoliquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. Expression patterns of kiwifruit ripening-related genes were also analysed using real-time quantitative reverse transcription-PCR (RT-qPCR).

KEY RESULTS

O3 treatment markedly delayed fruit softening and depressed the ethylene biosynthetic mechanism. Although SNP alone was relatively ineffective in regulating ripening, SNP treatment prior to O3 exposure attenuated the O3-induced ripening inhibition. Proteomic analysis revealed a considerable overlap between proteins affected by both SNP and O3. Consistent with this, the temporal dynamics in the expression of selected kiwifruit ripening-related genes were noticeably different between individual O3 and combined SNP and O3 treatments.

CONCLUSIONS

This study demonstrates that O3-induced ripening inhibition could be reversed by SNP and provides insights into the interaction between oxidative and nitrosative signalling in climacteric fruit ripening.