Endogenous Nitric Oxide Content Research Articles

Crosstalk between melatonin and nitric oxide restrains Cadmium-induced oxidative stress and enhances vinblastine biosynthesis in Catharanthus roseus (L) G Don.

Nitric oxide functions downstream of the melatonin in adjusting Cd-induced osmotic and oxidative stresses, upregulating the transcription of D4H and DAT genes, and increasing total alkaloid and vincristine contents. A few studies have investigated the relationship between melatonin (MT) and nitric oxide (NO) in regulating defensive responses. However, it is still unclear how MT and NO interact to regulate the biosynthesis of alkaloids and vincristine in leaves of Catharanthus roseus (L.) G. Don under Cd stress. Therefore, this context was explored in the present study. Results showed that Cd toxicity (200µM) induced oxidative stress, decreased biomass, Chl a, and Chl b content, and increased the content of total alkaloid and vinblastine in the leaves. Application of both MT (100µM) and sodium nitroprusside (200µM SNP, as NO donor) enhanced endogenous NO content and accordingly increased metal tolerance index, the content of total alkaloid and vinblastine. It also upregulated the transcription of two respective genes (D4H and DAT) under non-stress and Cd stress conditions. Moreover, the MT and SNP treatments reduced the content of H2O2 and malondialdehyde, increased the activities of superoxide dismutase and ascorbate peroxidase, enhanced proline accumulation, and improved relative water content in leaves of Cd-exposed plants. The scavenging NO by 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxy l-3-oxide (cPTIO) averted the effects of MT on the content of total alkaloid and vinblastine and antioxidative responses. Still, the effects conferred by NO on attributes mentioned above were not significantly impaired by p-chlorophenylalanine (p-CPA as an inhibitor of MT biosynthesis). These findings and multivariate analyses indicate that MT motivated terpenoid indole alkaloid biosynthesis and mitigated Cd-induced oxidative stress in the leaves of periwinkle in a NO-dependent manner.

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

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

Nitric oxide regulates the lignification and carotenoid biosynthesis of postharvest carrot (Daucus carota L.)

The carrot is an important horticultural crop of the Apiaceae family, possessing considerable nutritional and economic value. Unfortunately, the decline in the postharvest quality has resulted in a decrease in the desirability of carrots and further food wastage. Nitric oxide (NO) plays a crucial role in alleviating the senescence and reducing losses of postharvest horticultural products, but its impact on the postharvest quality of carrots has not been reported. In this study, the effects of treatment with ddH2O, varying concentrations of sodium nitroprusside (SNP), and carboxy-PTIO (cPTIO) on the whiteness index, weight loss, and sensory scoring were evaluated, and a concentration of 1.5 mM SNP treatment preserved the appearance quality of postharvest carrots. Further analysis revealed that SNP treatment led to an increase in endogenous NO content by promoting nitrate reductase activity, which subsequently enhanced the expression of DcPSY1, DcPDS1, DcZDS1, DcCRTISO1, and DcLCYB1 and increased the levels of total carotenoid, α-carotenoid, and β-carotenoid. The alternation of carotenoids both increased abscisic acid (ABA) level by promoting the expression of ABA biosynthesis genes, but also hindered the generation of hydrogen peroxide and superoxide anion. Meanwhile, the expression of lignin biosynthesis genes was downregulated in SNP treatment group, resulting in postharvest carrots with lower lignin content and a lower degree of cell lignification. Overall, our findings provide a theoretical basis for the application of NO in the postharvest preservation of carrots and shed light on the role of NO in regulating the synthesis mechanisms of carotenoids and lignin in postharvest carrots.

Nitric Oxide in Plant Functioning: Metabolism, Signaling, and Responses to Infestation with Ecdysozoa Parasites.

Nitric oxide (NO) is an important signaling molecule that is involved in a wide range of physiological processes in plants, including responses to biotic and abiotic stresses. Changes in endogenous NO concentration lead to activation/deactivation of NO signaling and NO-related processes. This paper presents the current state of knowledge on NO biosynthesis and scavenging pathways in plant cells and highlights the role of NO in post-translational modifications of proteins (S-nitrosylation, nitration, and phosphorylation) in plants under optimal and stressful environmental conditions. Particular attention was paid to the interactions of NO with other signaling molecules: reactive oxygen species, abscisic acid, auxins (e.g., indole-3-acetic acid), salicylic acid, and jasmonic acid. In addition, potential common patterns of NO-dependent defense responses against attack and feeding by parasitic and molting Ecdysozoa species such as nematodes, insects, and arachnids were characterized. Our review definitely highlights the need for further research on the involvement of NO in interactions between host plants and Ecdysozoa parasites, especially arachnids.

Alleviating the Injuries of NaCl Exposure on Respiratory Activities, Leaf Stomatal and Antioxidant Defense of Silybum marianum L. Seedlings by Exogenous Nitric Oxide

Nitric oxide (NO) is recognized as an endogenous signaling molecule that plays an important role in the defence responses of medicinal plants to NaCl stress. In this study, we investigated the effects of sodium nitroprusside (SNP) as an NO donor at three concentrations (0, 100, and 200 µmol l−1) to alleviate the deleterious effects of salt stress (100 mM NaCl) on leaf gas exchange and biochemical characteristics of Silybum marianum L. seedlings. This study showed that salt stress significantly decreased relative water content (RWC), chlorophyll b content, endogenous NO concentration, maximum quantum yield (Fv/Fm), leaf gas exchange, stomatal size, K+/Na+ ratio, and plant dry weight, and increased malondialdehyde (MDA) content, hydrogen peroxide (H2O2) content, proline content, stomatal density, and enzyme activities. SNP treatment increased Fv/Fm, photosynthetic pigments, K+/Na+ ratio, and dry weights of the shoots and roots of NaCl-exposed plants. The exogenous application of NO increased the proline content under salinity stress more than under stress conditions without SNP application, so that the proline content increased from 32 to 47 µmol g−1. Application of 100 µM SNP also increased endogenous NO concentration (up to 43%) and consequently protected plants against salt stress-induced damage by improving enzyme activity and reducing the H2O2 generation rate (up to 14%) and MDA content (up to 50%) compared to plants treated with NaCl alone. Foliar application of NO to salt-stressed plants increased root and shoot respiration rates from 20 and 12%, respectively, under salinity stress to 57% under the application of SNP and stress conditions, and decreased stomatal conductance by up to 70%, resulting in improved RWC. Increased internal NO generation in plants induced by 100 µM SNP application has the potential to mitigate salinity injury in Silybum marianum L. plants.

Isoenzymatic Pattern of Hydrogen Sulfide (H2S)-Generating L-Cysteine Desulfhydrase (LCD) in Arabidopsis thaliana Seedlings: Effect of Nitric Oxide (NO) and H2S

In higher plants, hydrogen sulfide (H2S) is a recognized signaling molecule that performs multiple regulatory functions. The enzyme L-cysteine desulfhydrase (LCD) catalyzes the conversion of L-cysteine (L-Cys) to pyruvate and ammonium with the concomitant generation of H₂S, and it is considered one of the main sources of H2S in plants. Using non-denaturing polyacrylamide gel electrophoresis (PAGE) in combination with a specific assay for LCD activity, this study aims to identify the potential LCD isozymes in wild-type Arabidopsis thaliana seedlings of 16 days old grown under in vitro conditions, and to evaluate the potential impact of nitric oxide (NO) and H2S on these LCD isozymes. For this purpose, an Atnoa1 mutant characterized to have a low endogenous NO content as well as the exogenous application of H2S were used. Five LCD isozymes were detected, with LCD IV being the isozyme that has the highest activity. However, the LCD V activity was the only one that was positively modulated in the Atnoa1 mutants and by exogenous H2S. To our knowledge, this is the first report showing the different LCD isozymes present in Arabidopsis seedlings and how their activity is affected by NO and H2S content.

Melatonin-mediated endogenous nitric oxide coordinately boosts stability through proline and nitrogen metabolism, antioxidant capacity, and Na+/K+ transporters in tomato under NaCl stress.

The interactions between nitric oxide (NO) and melatonin in alleviating sodium chloride (NaCl) toxicity in plants are poorly comprehended. Here, the associations between the exogenous application of melatonin and endogenous NO levels in inducing tomato seedlings' defense response during NaCl toxicity were investigated. The results indicated that the application of melatonin (150 μM) increased height (23.7%) and biomass (32.2%), improved chlorophyll (a (137%) and b (92.8%)), and proline metabolisms, and reduced the contents of superoxide anion radicals (49.6%), hydrogen peroxide (31.4%), malondialdehyde (38%), and electrolyte leakage (32.6%) in 40-day-old tomato seedlings grown under NaCl (150 mM) treatment. Melatonin increased the antioxidant defense system in NaCl-stressed seedlings by increasing the activity of the antioxidant enzymes. Melatonin also improved N metabolism and endogenous NO content in NaCl-stressed seedlings by upregulating the activity of enzymes implicated in N assimilation. Furthermore, melatonin improved ionic balance and reduced Na content in NaCl-exposed seedlings by upregulating the expression of genes involved in K/Na ratio homeostasis (NHX1-4) and increasing the accumulation of mineral nutrients (P, N, Ca, and Mg). However, the addition of cPTIO (100 μM; an NO scavenger) reversed the beneficial impacts of melatonin, indicating the effective function of NO in melatonin-induced defense mechanisms in NaCl-stressed tomato seedlings. Therefore, our results revealed that melatonin improves the tolerance of tomato plants during NaCl toxicity by mediating internal NO.

Nitric oxide promotes adventitious root formation in cucumber under cadmium stress through improving antioxidant system, regulating glycolysis pathway and polyamine homeostasis.

Cadmium (Cd) as a potentially toxic heavy metal that not only pollutes the environment but also interferes with plant growth. Nitric oxide (NO) regulates plant growth and development as well as abiotic stress response. However, the mechanism underpinning NO-induced adventitious root development under Cd stress remains unclear. In this study, cucumber (Cucumis sativus 'Xinchun No. 4') was used as the experimental material to investigate the effect of NO on the development of adventitious roots in cucumber under Cd stress. Our results revealed that, as compared to Cd stress, 10 μM SNP (a NO donor) could considerably increase the number and length of adventitious roots by 127.9% and 289.3%, respectively. Simultaneously, exogenous SNP significantly increased the level of endogenous NO in cucumber explants under Cd stress. Our results revealed that supplementation of Cd with SNP significantly increased endogenous NO content by 65.6% compared with Cd treatment at 48 h. Furthermore, our study indicated that SNP treatment could improve the antioxidant capacity of cucumber explants under Cd stress by up-regulating the gene expression level of antioxidant enzymes, as well as reducing the levels of malondialdehyde (MDA), hydrogen peroxide (H2O2) and superoxide anion ( ) to alleviate oxidative damage and membrane lipid peroxidation. Application of NO resulted in a decrease of the , MDA, and H2O2 level by 39.6%, 31.4% and 60.8% as compared to Cd-alone treatment, respectively. Besides that, SNP treatment significantly increased the expression level of related genes involved in glycolysis processes and polyamine homeostasis. However, application of NO scavenger 2-(4-carboxy -2-phenyl)-4, 4, 5, 5-tetramethy limidazoline -1-oxyl -3-oxide (cPTIO) and the inhibitor tungstate significantly reversed the positive role of NO in promoting the adventitious root formation under Cd stress. These results suggest that exogenous NO can increase the level of endogenous NO, improve antioxidation ability, promote glycolysis pathway and polyamine homeostasis to enhance the occurrence of adventitious roots in cucumber under Cd stress. In summary, NO can effectively alleviate the damage of Cd stress and significantly promote the development of adventitious root of cucumber under Cd stress.

Enhancing the resistance of peach fruit against Monilinia fructicola using exogenous nitric oxide by activating the gamma-aminobutyric acid shunt

Nitric oxide (NO) can induce plant disease resistance through signal transduction. The gamma-aminobutyric acid (GABA) shunt possesses different response modes for resisting different pathogens. However, the effect of the GABA shunt in NO-induced plant disease resistance is not clear. Herein, the role of the GABA shunt in the resistance of peach fruit induced by NO against Monilinia fructicola infection was investigated together with possible interaction pathways. NO treatment repressed the disease of peach fruit, increased the endogenous NO content, and enhanced the activities and gene expression of GABA shunt enzymes within 48 h, including glutamate decarboxylase (GAD), GABA transaminase (GABA-T) and succinic semialdehyde dehydrogenase (SSADH). However, the NO scavenger 2-(4-carboxyphenyl)− 4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) aggravated the disease of peach fruit, and inhibited the activities and gene expression of GABA shunt enzymes. The above results highlighted the importance of the GABA shunt in NO-induced disease resistance of peach fruit. It was noteworthy that the nitrosylated level of GAD4, GABA-T3 and SSADH was up-regulated at 6 and 12 h in NO-treated fruit compared with the control, which might be related to the enhanced GABA shunt activity. Additionally, NO treatment up-regulated the expression of glutamate receptor (PpGLR) and glutamate dehydrogenase (PpGDH), promoted Ca2+ influx, strengthened the activity of the tricarboxylic acid cycle (TCAC), and raised the ATP content and energy charge. Overall, the data indicated that NO treatment induced peach fruit disease resistance by activating the GABA shunt.

Melatonin facilitates the deposition of suberin polyphenolic and lignin at wounds of potato tubers by mediating nitric oxide and reactive oxygen species

Melatonin (MT), a phytohormone, can enhance plant resistance against biotic and abiotic stresses. However, no studies have been conducted on whether MT influences suberin polyphenolic (SPP) and lignin deposition by mediating nitric oxide (NO) and reactive oxygen species (ROS). Herein, wounded tubers were treated with 50 μmol/L MT, and 25 μmol/L Nω-nitro-L-arginine (L-NNA), a specific inhibitor of nitric oxide synthase. We found that MT upregulated StNR (nitrate reductase) and StNOS (nitric oxide synthase) expression levels, and increased endogenous NO content. Additionally, MT upregulated StNOX (NADPH oxidase) expression and facilitated O2.- and H2O2 production. Moreover, MT upregulated relative expression and enhanced the activities of the main enzyme and products of the phenylpropanoid pathway, and increased peroxidase (POD) activity. MT also elevated the accumulation amount of suberin polyphenolic (SPP) and lignin at the wound tissues, resulting in less weight loss and disease index in wounded potatoes (cv. Atlantic) during healing. In contrast, L-NNA treatment suppressed the influence of MT on the generation of endogenous NO and ROS, the activity of phenylpropanoid metabolism and POD, and SPP and lignin accumulation at wounds. Taken together, MT could promote SPP and lignin deposition at wounds of potato tubers by inducing NO and ROS production and activating phenylpropanoid metabolism. However, L-NNA could eliminate the positive effect of MT.

Nitric oxide mediates melatonin-induced isoflavone accumulation and growth improvement in germinating soybeans under NaCl stress

The involvement of nitric oxide (NO) in exogenous melatonin (MT)-induced isoflavone accumulation and growth improvement in NaCl-stressed soybeans was investigated in this study. The results demonstrated that MT increased the activity of nitrate reductase (NR) and upregulated the relative expression of NR1, NR2, and nitric oxide synthase1, which subsequently led to an increase in NO content. MT and sodium nitroprusside (SNP, as an NO donor) markedly increased isoflavone content by enhancing the activities of cinnamic acid 4-hydroxylase (C4H) and phenylalanine ammonia lyase (PAL), and by upregulating gene expression of C4H, Isoflavone synthase, PAL, and Chalcone isomerase 1A, which are involved in isoflavone biosynthesis. Moreover, MT, as well as SNP, improved the growth and biomass of NaCl-treated soybeans by increasing the activities of superoxide dismutase, catalase, and peroxidase, and reducing the accumulation of H2O2 and O2•− in soybeans under NaCl stress. These MT-induced responses were entirely reversed by the supply of 4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO, a specific scavenger of NO), which in turn considerably decreased endogenous NO content. These results suggest that NO acts as an important downstream signal molecule, mediating MT-induced isoflavone accumulation and growth improvement in NaCl-stressed soybeans.

Enhanced Salt Tolerance of Torreya grandis Genders Is Related to Nitric Oxide Level and Antioxidant Capacity.

Nitric oxide (NO), a bioactive molecule, is often involved in the regulation of physiological and biochemical processes in stressed plants. However, the effects of NO donors on dioecious plants remain unclear. Using a pot experiment, female and male Torreya grandis were used to study the role of sex and NO in salt stress tolerance. In the present study, female and male T. grandis seedlings pretreated with an NO donor (sodium nitroprusside, SNP) were exposed to salt stress, and then leaf relative water content (RWC), photosynthetic pigments, chlorophyll fluorescence parameters, NO and glutathione levels, oxidative damage, and antioxidant enzyme activities were investigated. Female T. grandis plants had better tolerance to salinity, as they were characterized by significantly higher RWC, pigment content, and photochemical activities of photosystem II (PSII) and fewer negative effects associated with higher nitrate reductase (NR) activity and NO content. Pretreatment with an NO donor further increased the endogenous NO content and NR activity of both female and male T. grandis plants compared with salt treatment. Moreover, pretreatment with an NO donor alleviated salt-induced oxidative damage of T. grandis, especially in male plants, as indicated by reduced lipid peroxidation, through an enhanced antioxidant system, including proline and glutathione accumulation, and increased antioxidant enzyme activities. However, the ameliorating effect of the NO donor was not effective in the presence of the NO scavenger (Nω-nitro-L-arginine methyl ester, L-name). In conclusion, enhanced salt tolerance in T. grandis plants is related to nitric oxide levels and the supply of NO donors is an interesting strategy for alleviating the negative effect of salt on T. grandis. Our data provide new evidence to contribute to the current understanding of NO-induced salt stress tolerance.

Changes in Nitric oxide Levels in Basal Forebrain during Sedation with Dexmedetomidine and Sevoflurane

BackgroundPerioperative and critical care settings frequently require periods of prolonged sedation but the effect of sedation on sleep homeostasis is not completely understood. In the ongoing studies in our laboratory, continuous 8 h sedation with dexmedetomidine (DEX) was shown to increase wakefulness (WAKE), decrease slow‐wave sleep (SWS), and nearly eliminate rapid eye movement sleep (REMS) in the post‐sedation period [1]. In contrast, continuous 8 h sedation with sevoflurane (SEVO) did not affect the time spent in WAKE or SWS, but increased REMS in the post‐sedation period [1]. Past studies have shown nitric oxide (NO) in basal forebrain (BF) to be a key modulator of sleep homeostasis. Specifically, NO concentration in BF has been shown to increase with sleep pressure (e.g., during sleep deprivation) and decrease with the reduced sleep need (e.g., during recovery from sleep deprivation). To determine the effect of sedation produced by DEX or SEVO on sleep homeostasis, as inferred from changes in NO levels in BF, we quantified the changes in NO concentration before, during, and after sedation with DEX and SEVO.MethodsAdult male Sprague Dawley rats (N=4 male) were surgically prepared to record electroencephalogram (EEG) and electromyogram and intravenous delivery of DEX via a chronic catheter in jugular vein. In addition, an open flow microperfusion guide cannula was implanted into BF (N=2) or prefrontal cortex (N=2) for collection of perfusates for NO analysis. Prefrontal cortex (PFC) was used as an anatomical control for BF. After at least 15 days of post‐surgical recovery, rats were connected to the EEG recording system and a sampling insert was lowered into BF or PFC to route the perfusate samples directly into a high‐performance liquid chromatograph for online analysis of nitrite and nitrate levels, which are collectively termed as NOx and are considered a surrogate for endogenous NO concentration. The EEG and NOx were recorded during 2 h baseline wake condition, 8 h of sedation with either DEX (0.5‐0.7ug/kg/min) or SEVO (1.5‐3.0%), and 2 h post‐sedation period. Each rat was administered with DEX or SEVO in a counter‐balanced manner and with a washout period of at least 7 days.ResultsThe NOx levels in BF decreased during sedation with DEX (mean ± standard deviation: 0.52 μM ± 0.31 during baseline vs 0.08 μM ± 0.01 during DEX) and SEVO (mean ± standard deviation: 1.58 μM ± 0.16 during baseline vs 0.72 μM ± 0.07 during SEVO). The NOx levels in PFC during sedation with DEX stayed about at the same level as observed during baseline state (2.40 μM ± 1.39 during baseline vs. 3.01 μM ± 0.16 during DEX), but the NOx levels in PFC decreased during sedation with SEVO (1.45 μM ± 1.23 during baseline vs 0.37 μM ± 0.18 during SEVO).ConclusionAlthough these are preliminary data, the decrease in NOx levels in BF after sedation with DEX and SEVO suggest a reduced sleep pressure and is supportive of the changes in sleep homeostasis as described in our previous report.References Parkar A, Liu T, Fryzel A, Groenhout T, Mashour GA and Pal D (2020) Effect of prolonged sedation with dexmedetomidine, midazolam, propofol, or sevoflurane on sleep homeostasis in rat. J Neurosurgical Anesthesiology, Vol 32, No 4, Page 403, Abstract no SNACC‐387.

Nitric Oxide Improves Salt Tolerance of Cyclocarya paliurus by Regulating Endogenous Glutathione Level and Antioxidant Capacity.

Cyclocarya paliurus is commonly used to treat diabetes in China. However, the natural habitats of C. paliurus are typically affected by salt stress. Previous studies showed that nitric oxide (NO) level was related to salt tolerance of C. paliurus, and its synthesis was induced by exogenous hydrogen sulfide. However, the effects of different NO donors in alleviating the negative effect of salt stress are still unclear. In the present study, C. paliurus seedlings pretreated with three NO donors (S-nitroso-N-acetylpenicillamine, SNAP and S-nitrosoglutathione, GSNO and sodium nitroprusside, SNP) were exposed to salt stress, and then, the total biomass, chlorophyll fluorescence parameters, NO and glutathione levels, oxidative damage, and antioxidant enzyme activities were investigated. The results showed that pretreatment of NO donors maintained chlorophyll fluorescence and attenuated the loss of plant biomass under salt stress, and the best performance was observed in C. paliurus under SNP treatment. We also found that pretreatment of NO donors further increased the endogenous NO content and nitrate reductase (NR) activity compared with salt treatment. Moreover, pretreatment with NO donors, especially SNP, alleviated salt-induced oxidative damage, as indicated by lowered lipid peroxidation, through an enhanced antioxidant system including glutathione accumulation and increased antioxidant enzyme activities. The supply of NO donors is an interesting strategy for alleviating the negative effect of salt on C. paliurus. Our data provide new evidence contributing to the current understanding of NO-induced salt stress tolerance.

Nasal and tracheobronchial nitric oxide production and its influence on oxygenation in horses undergoing total intravenous anaesthesia

BackgroundThe present study aimed to investigate the effect of endotracheal intubation on nasal and tracheal endogenous NO concentrations, gas exchange and oxygenation in horses undergoing general anaesthesia. In many species a major part of physiological nitric oxide (NO) production takes place in the nasopharynx. Inhaled NO acts as a pulmonary vasodilator and regulates lung perfusion and endotracheal intubation bypasses the nasopharynx. Six horses were randomly assigned to either the “intubated” (INT) or the “non-intubated” (nINT) treatment group. Horses were premedicated with dexmedetomidine (5 μg/kg IV). Anaesthesia was induced with 2.5 mg/kg ketamine and 0.05 mg/kg diazepam IV, and it was maintained by administration of a triple-drip (100 mg/kg/h guaifenesin, 4 mg/kg/h ketamine, 7 μg/kg/h dexmedetomidine). The horses were spontaneously breathing room air. Heart rate, cardiac output, arterial blood pressure, pulmonary arterial blood pressures and respiratory rate were recorded during a 100-min anaesthesia period. Arterial, venous and mixed venous blood samples were taken every 10 minutes and analysed for partial pressure of oxygen (PO2) and carbon dioxide (PCO2), oxygen saturation and haemoglobin content. Standard oxygenation indices were calculated. Nasal and tracheal endogenous NO concentration was determined by chemiluminescence.ResultsCardiovascular variables, respiratory rate, PO2, PCO2, oxygen saturation, haemoglobin content, CaO2, O2ER, P(a-ET)CO2 and Qs/Qt did not differ significantly between the two treatment groups. The P(A-a)O2 was significantly higher in INT (6.1 ± 0.3 kPa) compared to nINT (4.9 ± 0.1 kPa) (p = 0.045), respectively. The nasal (8.0 ± 6.2 ppb) and tracheal (13.0 ± 6.3 ppb) endogenous NO concentration differed significantly in INT (p = 0.036), but not in nINT (nasal: 16.9 ± 9.0 ppb; tracheal: 18.5 ± 9.5 ppb) (p = 0.215).ConclusionEndotracheal intubation reduces the nasal and tracheal endogenous NO concentration. The influence on pulmonary gas exchange and oxygenation is negligible in horses breathing room air.

24-Epibrassinolide and nitric oxide combined to improve the drought tolerance in kiwifruit seedlings by proline pathway and nitrogen metabolism

24-Epibrassinolide (EBR) and nitric oxide (NO) are redox signaling molecules that participate in plant stress response, but their combined role in drought stress response remains unclear. In this study, potted kiwifruit seedlings grown under drought stress were treated with sodium nitroprusside, a NO donor (SNP, 100 μM), 24-epibrassinolide (EBR, 0.01 mg·L−1), and their combination (S+E), as well as well-watered (CK) and drought treatments (DCK). Results revealed that plant biomass, leaf relative water content, photosynthetic pigment content, and photosynthetic capacity of leaves decreased, whereas MDA, H2O2, relative electrolyte leakage, endogenous NO, proline, and soluble sugar content increased in response to drought stress. The application of SNP and EBR alleviated the above adverse effects caused by drought stress and improved the enzyme activities of glutamine synthetase (GS), reduced the glutamate dehydrogenase (GDH) involved in nitrogen metabolism to maintain plant growth, and regulated the expression of aquaporin genes PIP1;1 and PIP2;2–1 to maintain normal water metabolism. The up-regulation of proline synthesis gene P5CR1 expression and the down-regulation of proline degradation gene ProDH expression caused proline accumulation under drought stress. Overall, the combination of SNP and EBR was more effective than independent SNP or EBR in mitigating drought stress in kiwifruit seedlings.

Nitric oxide inhibits endothelial cell apoptosis by inhibiting cysteine‐dependent SOD1 monomerization

Endothelial cell apoptosis is an important pathophysiology in many cardiovascular diseases. The gasotransmitter nitric oxide (NO) is known to regulate cell survival and apoptosis. However, the mechanism underlying the effect of NO remains unclear. In this research, by targeting cytosolic copper/zinc superoxide dismutase (SOD1) monomerization, we aimed to explore how NO inhibited endothelial cell apoptosis. We showed that treatment with the NO synthase (NOS) inhibitor nomega‐nitro‐l‐arginine methyl ester hydrochloride (L‐NAME) significantly decreased the endogenous NO content of endothelial cells, facilitated the formation of SOD1 monomers, inhibited dismutase activity, and promoted reactive oxygen species (ROS) accumulation in human umbilical vein endothelial cells (HUVECs); by contrast, supplementation with the NO donor sodium nitroprusside (SNP) upregulated NO content, prevented the formation of SOD1 monomers, enhanced dismutase activity, and reduced ROS accumulation in L‐NAME‐treated HUVECs. Mechanistically, tris(2‐carboxyethyl) phosphine hydrochloride (TCEP), a specific reducer of cysteine thiol, increased SOD1 monomer formation, thus preventing the NO‐induced increase in dismutase activity and the decrease in ROS. Furthermore, SNP inhibited HUVEC apoptosis caused by the decrease in endogenous NO, whereas TCEP abolished this protective effect of SNP. In summary, our data reveal that NO protects endothelial cells against apoptosis by inhibiting cysteine‐dependent SOD1 monomerization to enhance SOD1 activity and inhibit oxidative stress.

Hydrogen sulfide alleviates salinity stress in Cyclocarya paliurus by maintaining chlorophyll fluorescence and regulating nitric oxide level and antioxidant capacity

Cyclocarya paliurus is commonly used to treat diabetes in China. However, the natural habitats of C. paliurus are typically affected by salt stress. Hydrogen sulfide (H2S) is a growth regulator that is widely used to enhance plant stress tolerance, but the possible mechanism underlying H2S-alleviated salt stress in C. paliurus remains unclear. C. paliurus seedlings pretreated with NaHS (an H2S donor) were exposed to salt stress, and then, the leaf and total biomass, chlorophyll fluorescence parameters, nitric oxide (NO) content, oxidative damage, and proline and phenolic content were investigated to test the hypothesis that H2S and NO were involved in the salt tolerance of C. paliurus. The results showed that H2S pretreatment maintained chlorophyll fluorescence and attenuated the loss of plant biomass. We also found that H2S pretreatment further increased the endogenous NO content and nitrate reductase activity compared with salt treatment. Moreover, H2S pretreatment alleviated salt-induced oxidative damage, as indicated by lowered lipid peroxidation, through an enhanced antioxidant system including more proline and phenolic accumulation and increased antioxidant enzyme activities. However, C. paliurus leaves treated with the NO scavenger significantly diminished H2S-mediated NO production and alleviation of membrane lipid peroxidation. Thus, we concluded that H2S-induced NO was involved in C. paliurus salt tolerance.

Cryopreserved-pollen viability is regulated by NO-induced programmed cell death.

After cryopreservation, the NO content in pollen increased, inducing programmed cell death as a key reason for reduced viability. Low recovery of biomaterials after cryopreservation is a bottleneck that limits the application of this technology. At present, the mechanism of viability decline after cryopreservation is not fully understood. In this study, the effects of nitric oxide (NO) on programmed cell death (PCD) and its relationship with viability were investigated, using Paeonia lactiflora 'Fen Yu Nu' pollen with significantly decreased viability after cryopreservation. The results showed that: the activity of caspase-3-like and caspase-9-like protease and the apoptosis rate of pollen cells were significantly increased, the expression level of the promoting PCD (pro-PCD) genes was up-regulated, while the expression level of the inhibiting PCD (anti-PCD) genes was down-regulated after preservation in liquid nitrogen (LN); the NO content in pollen cells increased significantly after LN exposure. The correlation analysis showed that NO was significantly correlated with pollen viability and all indicators of PCD. The addition of a NO carrier SNP after LN storage reduced pollen viability, increased endogenous NO content, decreased mitochondrial membrane potential level, activated caspase-3-like and caspase-9-like protease in pollen cells, and increased cell apoptosis rate. The expression levels of pro-PCD genes PDCD2 and ATG8CL were significantly up-regulated, while the expression levels of anti-PCD genes DAD1, BI-1 and LSD1 were significantly down-regulated. The addition of NO scavenger c-PTIO improved pollen viability, and produced the opposite effect of sodium nitroferricyanide (III) dihydrate (SNP), but did not change the mitochondrial membrane potential. These results suggest that NO induced PCD during the cryopreservation of pollen, which was one of the reasons for the significant decrease of pollen viability after cryopreservation.

A Highly Stable Two-Photon Ratiometric Fluorescence Probe for Real-Time Biosensing and Imaging of Nitric Oxide in Brain Tissues and Larval Zebrafish

A Highly Stable Two-Photon Ratiometric Fluorescence Probe for Real-Time Biosensing and Imaging of Nitric Oxide in Brain Tissues and Larval Zebrafish