Moderate modulation by S-nitrosoglutathione of photorespiratory enzymes in pea (Pisum sativum) leaves, compared to the strong effects of high light

When plants are exposed to water stress, photosynthesis is downregulated due to enhanced reactive oxygen species (ROS) and nitric oxide (NO). In contrast, photorespiratory metabolism protected photosynthesis and sustained yield. Modulation of photorespiration by ROS was established, but the effect of NO on photorespiratory metabolism was unclear. We, therefore, examined the impact of externally added NO by using S-nitrosoglutathione (GSNO), a natural NO donor, in leaf discs of pea (Pisum sativum) under dark or light: moderate or high light (HL). Maximum NO accumulation with GSNO was under high light. The presence of 2-4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), a NO scavenger, prevented the increase in NO, confirming the release of NO in leaves. The increase in S-nitrosothiols and tyrosine-nitrated proteins on exposure to GSNO confirmed the nitrosative stress in leaves. However, the changes by GSNO in the activities and transcripts of five photorespiratory enzymes: glycolate oxidase, hydroxypyruvate reductase, catalase, glycerate kinase, and phosphoglycolate phosphatase activities were marginal. The changes in photorespiratory enzymes caused by GSNO were much less than those with HL. Since GSNO caused only mild oxidative stress, we felt that the key modulator of photorespiration might be ROS, but not NO.

Candidate molecules as alternative nitric oxide donors with better antibacterial property against Escherichia coli and Staphylococcus aureus

AIMS

Four nitric oxide (NO) donors, S-nitrosoglutathione (GSNO), S-nitrosocysteine (CySNO), S-nitroso-N-acetylcysteine (SNAC), and 2-(2-S-nitroso propionamide) acetic acid (GAS) were prepared and their physicochemical characteristics were analyzed. Besides, the antibacterial properties of NO donors were investigated against Escherichia coli and Staphylococcus aureus.

METHODS AND RESULTS

UV-visible absorption spectrum and Fourier transform infrared spectrum verified the successful preparation of RSNOs. All NO donors (10 mmol l-1) could release NO continuously, and the amount of NO release was from 80.22 μmol l-1 to 706.63 μmol l-1, in which the release of NO from SNAC was the highest, and the release of NO from NaNO2 was the least. The inhibition zone indicated that all NO donors showed stronger antibacterial activity against E. coli and S. aureus, and the antibacterial ability was in the order of SNAC > GSNO > CySNO > GAS > NaNO2 for both E. coli and S. aureus (P < 0.05). Scanning electron microscopy(SEM) showed that all NO donors could result in varying degrees of damage to cell wall and membrane of both E. coli and S. aureus and the damage of E. coli was more severe.

CONCLUSION

Four alternative NO donors were successfully synthesized. All alternative NO donors showed better antibacterial properties against E. coli and S. aureus than NaNO2.

Synergistic wound repair effects of a composite hydrogel for delivering tumor-derived vesicles and S-nitrosoglutathione

Treating chronic wounds requires transition from proinflammatory M1 to anti-inflammatory M2 dominant macrophages. Based on the role of tumor extracellular vesicles (tEVs) in regulating the phenotypic switching from M1 to M2 macrophages, we propose that tEVs may have a beneficial impact on alleviating the overactive inflammatory microenvironment associated with refractory wounds. On the other hand, as a nitric oxide donor, S-nitrosoglutathione (GSNO) can regulate inflammation, promote angiogenesis, enhance matrix deposition, and facilitate wound healing. In this study, a guar gum-based hydrogel with tEVs and GSNO was designed for the treatment of diabetic refractory wounds. This hybrid hydrogel was formed through the phenyl borate bonds, which can automatically disintegrate in response to the high reactive oxygen species (ROS) level at the site of refractory diabetic wounds, releasing tEVs and GSNO. We conducted a comprehensive evaluation of this hydrogel in vitro, which demonstrated excellent performance. Meanwhile, using a full-thickness excision model in diabetic mice, the wounds exposed to the therapeutic hydrogel healed completely within 21 days. The increased closure rate was associated with macrophage polarization and collagen deposition, accelerated fibroblast proliferation, and increased angiogenesis in the regenerating tissues. Therefore, this multifunctional hybrid hydrogel appears to be promising for clinical applications.

Nitric oxide alleviates salt stress through protein S-nitrosylation and transcriptional regulation in tomato seedlings

NO enhances the resistance of tomato seedlings to salt stress through protein S-nitrosylation and transcriptional regulation, which involves the regulation of MAPK signaling and carbohydrate metabolism. Nitric oxide (NO) regulates various physiological and biochemical processes and stress responses in plants. We found that S-nitrosoglutathione (GSNO) treatment significantly promoted the growth of tomato seedling under NaCl stress, indicating that NO plays a positive role in salt stress resistance. Moreover, GSNO pretreatment resulted in an increase of endogenous NO level, S-nitrosothiol (SNO) content, S-nitrosoglutathione reductase (GSNOR) activity and GSNOR expression under salt stress, implicating that S-nitrosylation might be involved in NO-alleviating salt stress. To further explore whether S-nitrosylation is a key molecular mechanism of NO-alleviating salt stress, the biotin-switch technique and liquid chromatography/mass spectrometry/mass spectrometry (LC-MS/MS) were conducted. A total of 1054 putative S-nitrosylated proteins have been identified, which were mainly enriched in chloroplast, cytoplasm and mitochondrion. Among them, 15 and 22 S-nitrosylated proteins were involved in mitogen-activated protein kinase (MAPK) signal transduction and carbohydrate metabolism, respectively. In MAPK signaling, various S-nitrosylated proteins, SAM1, SAM3, SAM, PP2C and SnRK, were down-regulated and MAPK, MAPKK and MAPKK5 were up-regulated at the transcriptional level by GSNO treatment under salt stress compared to NaCl treatment alone. The GSNO pretreatment could reduce ethylene production and ABA content under NaCl stress. In addition, the activities of enzyme identified in carbohydrate metabolism, their expression at the transcriptional level and the metabolite content were up-regulated by GSNO supplication under salt stress, resulting in the activation of glycolysis and tricarboxylic acid cycle (TCA) cycles. Thus, these results demonstrated that NO might beneficially regulate MAPK signaling at transcriptional levels and activate carbohydrate metabolism at the post-translational and transcriptional level, protecting seedlings from energy deficiency and salinity, thereby alleviating salt stress-induced damage in tomato seedlings. It provides initial insights into the regulatory mechanisms of NO in response to salt stress.

Mechanisms of Regulation of the P-Glycoprotein Transporter Protein Functioning under the Action of Nitric Oxide

Mechanisms of regulation of the P-glycoprotein (Pgp) transporter under the action of nitric oxide (NO) were studied in Caco-2 cells. S-Nitrosoglutathione (GSNO) was used as a NO donor, which was added to the cells at concentrations 1, 10, 50, 100, and 500 µM and incubated for 3, 24, or 72 h. The amount of Pgp was analyzed using Western blotting, activity was determined by monitoring transport of its substrate, fexofenadine. The study showed that a short-term exposure to GSNO for 3 h at 500 µM concentration caused increase in the concentration of peroxynitrite in Caco-2 cells, which reduced the activity, but not the amount of Pgp. Increase in the duration of exposure to 24 h increased the amount and activity of Pgp at GSNO concentrations of 10 and 50 µM, increased the amount without increasing activity at 100 µM concentration, and decreased the amount of the transporter protein at 500 µM. Duration of exposure to GSNO of 72 h at concentration of 10 µM resulted in the increase of the amount and activity of Pgp, while at concentration of 100 and 500 µM it decreased the amount of the transport protein. At the same time, it was shown using specific inhibitors that the increase in the amount of Pgp under the influence of low concentrations of GSNO was realized through the NO-cGMP signaling pathway, and the effect of the higher concentration of GSNO and the respective development of nitrosative stress was realized through Nrf2 and the constitutive androstane receptor.

Improved Polymer Hemocompatibility for Blood-Contacting Applications via S-Nitrosoglutathione Impregnation

Blood-contacting medical devices (BCMDs) are inevitably challenged by thrombi formation, leading to occlusion of flow and device failure. Ideal BCMDs seek to mimic the intrinsic antithrombotic properties of the human vasculature to locally prevent thrombotic complications, negating the need for systemic anticoagulation. An emerging category of BCMD technology utilizes nitric oxide (NO) as a hemocompatible agent, as the vasculature's endothelial layer naturally releases NO to inhibit platelet activation and consumption. In this paper, we report for the first time the novel impregnation of S-nitrosoglutathione (GSNO) into polymeric poly(vinyl chloride) (PVC) tubing via an optimized solvent-swelling method. Material testing revealed an optimized GSNO-PVC material that had adequate GSNO loading to achieve NO flux values within the physiological endothelial NO flux range for a 4 h period. Through in vitro hemocompatibility testing, the optimized material was deemed nonhemolytic (hemolytic index <2%) and capable of reducing platelet activation, suggesting that the material is suitable for contact with whole blood. Furthermore, an in vivo 4 h extracorporeal circulation (ECC) rabbit thrombogenicity model confirmed the blood biocompatibility of the optimized GSNO-PVC. Platelet count remained near 100% for the novel GSNO-impregnated PVC loops (1 h, 91.08 ± 6.27%; 2 h, 95.68 ± 0.61%; 3 h, 97.56 ± 8.59%; 4 h, 95.11 ± 8.30%). In contrast, unmodified PVC ECC loops occluded shortly after the 2 h time point and viable platelet counts quickly diminished (1 h, 85.67 ± 12.62%; 2 h, 54.46 ± 10.53%; 3 h, n/a; 4 h, n/a). The blood clots for GSNO-PVC loops (190.73 ± 72.46 mg) compared to those of unmodified PVC loops (866.50 ± 197.98 mg) were significantly smaller (p < 0.01). The results presented in this paper recommend further investigation in long-term animal models and suggest that GSNO-PVC has the potential to serve as an alternative to systemic anticoagulation in BCMD applications.

S-Nitrosoglutathione-Based Nitric Oxide-Releasing Nanofibers Exhibit Dual Antimicrobial and Antithrombotic Activity for Biomedical Applications

The novel use of nanofibers as a physical barrier between blood and medical devices has allowed for modifiable, innovative surface coatings on devices ordinarily plagued by thrombosis, delayed healing, and chronic infection. In this study, the nitric oxide (NO) donor S-nitrosoglutathione (GSNO) is blended with the biodegradable polymers polyhydroxybutyrate (PHB) and polylactic acid (PLA) for the fabrication of hemocompatible, antibacterial nanofibers tailored for blood-contacting applications. Stress/strain behavior of different concentrations of PHB and PLA is recorded to optimize the mechanical properties of the nanofibers. Nanofibers incorporated with different concentrations of GSNO (10, 15, 20 wt%) are evaluated based on their NO-releasing kinetics. PLA/PHB + 20 wt% GSNO nanofibers display the greatest NO release over 72 h (0.4-1.5 × 10-10  mol mg-1 min-1 ). NO-releasing fibers successfully reduce viable adhered bacterial counts by ≈80% after 24 h of exposure to Staphylococcus aureus. NO-releasing nanofibers exposed to porcine plasma reduce platelet adhesion by 64.6% compared to control nanofibers. The nanofibers are found noncytotoxic (>95% viability) toward NIH/3T3 mouse fibroblasts, and 4',6-diamidino-2-phenylindole and phalloidin staining shows that fibroblasts cultured on NO-releasing fibers have improved cellular adhesion and functionality. Therefore, these novel NO-releasing nanofibers provide a safe antimicrobial and hemocompatible coating for blood-contacting medical devices.

Exposure to a natural nitric oxide donor negatively affects the potential influx of rubidium in potassium-starved Arabidopsis plants

Nitric oxide (NO) and potassium (K⁺) exert a profound influence on the acclimation of plants to multiple stress conditions. A recent report indicated that exogenous addition of an NO donor causes, under conditions of adequate K⁺ supply, a detrimental effect on K⁺ status. It remains unknown whether an exogenous NO source could negatively affect the potential capture of this element when plants are faced with a K⁺ shortage. In this work we offer evidence that, under conditions of K⁺-deprivation, the addition of the naturally occurring NO donor, S-nitrosoglutathione (GSNO), diminishes the potential inward transport of the K⁺-analogue rubidium (Rb⁺) from diluted Rb⁺ concentrations in Arabidopsis thaliana. Studies with the akt1-2 mutant, lacking the AKT1 inward-rectifier K⁺-channel involved in K⁺-uptake, unveiled that the effect of GSNO on Rb⁺-influx involves a non-AKT1 component. In addition, exposure to the NO-donor led to down-regulation of transcripts coding for the AtHAK5 K⁺-transporter, a major component of the K⁺-transport machinery in K⁺-deprived plants. Moreover, studies with the hak5 mutant showed that GSNO could either stimulate Rb⁺-uptake or does not lead to a significant effect on Rb⁺-uptake relative to -K⁺ and to -K⁺ in the presence of decayed GSNO, respectively, thus indicating that the presence of AtHAK5 is required for GSNO exerting an inhibitory effect.

S-Nitrosation impairs activity of stress-inducible aldehyde dehydrogenases from Arabidopsis thaliana

Nitric oxide (NO) is an intracellular messenger that mediates stress responses. Several plant aldehyde dehydrogenase (ALDH) genes are expressed during abiotic stress conditions to reduce the level of cytotoxic aldehydes. We investigated a possible interference between NO and ALDHs, using the isoform ALDH3H1 of Arabidopsis thaliana as model. The physiological NO donor; S-nitrosoglutathione (GSNO), inhibits ALDH3H1 in a time- and concentration-dependent manner. Mutagenesis and ESI-MS/MS analyses show that all Cys residues of ALDH3H1 are targets of GSNO-mediated S-nitrosation. Chemical labelling indicates that the deactivation is due to the conversion of the catalytic thiol into a catalytically non-active nitrosothiol. GSNO has the same effect on the chloroplastic ALDH3I1, suggesting that susceptibility of the catalytic Cys to NO is a common feature of ALDHs. S-Nitrosation and enzymatic inhibition of ALDH were reverted by reducing agents. Our study proves that the function of ALDHs does not exclusively depend on transcriptional regulation, with stress-induced expression, but may be also susceptible to posttranslational regulation through S-nitrosation. We discuss the potential involvement of S-nitrosoglutathione reductase (GSNOR), binding specific cofactors and reducing partners in a protective system of ALDHs in vivo, which will be experimentally corroborated in our forthcoming study.

The Possible Role of the Nitroso-Sulfide Signaling Pathway in the Vasomotoric Effect of Garlic Juice

The beneficial cardiovascular effects of garlic have been reported in numerous studies. The major bioactive properties of garlic are related to organic sulfides. This study aimed to investigate whether garlic juice works exclusively due to its sulfur compounds or rather via the formation of new products of the nitroso-sulfide signaling pathway. Changes in isometric tension were measured on the precontracted aortic rings of adult normotensive Wistar rats. We evaluated NO-donor (S-nitrosoglutathione, GSNO)-induced vasorelaxation and compare it with effects of hydrogen sulfide (H₂S)/GSNO and garlic/GSNO. Incubation with garlic juice increased the maximal GSNO-induced relaxation and markedly changed the character of the relaxant response. Although incubation with an H₂S donor enhanced the maximal vasorelaxant response of GSNO, neither the absolute nor the relative relaxation changed over time. The mixture of GSNO with an H₂S donor evoked a response similar to GSNO-induced relaxation after incubation with garlic juice. This relaxation of the H₂S and GSNO mixture was soluble guanylyl cyclase (sGC) dependent, partially reduced by HNO scavenger and it was adenosine triphosphate-sensitive potassium channels (K_ATP) independent. In this study, we demonstrate for the first time the suggestion that H₂S itself is probably not the crucial bioactive compound of garlic juice but rather potentiates the production of new signaling molecules during the GSNO-H₂S interaction.

S-Nitrosoglutathione Mimics the Beneficial Activity of Endothelial Nitric Oxide Synthase-Derived Nitric Oxide in a Mouse Model of Stroke

BACKGROUND

The nitric oxide (NO)-producing activity of endothelial nitric oxide synthase (eNOS) plays a significant role in maintaining endothelial function and protecting against the stroke injury. However, the activity of the eNOS enzyme and the metabolism of major NO metabolite S-nitrosoglutathione (GSNO) are dysregulated after stroke, causing endothelial dysfunction. We investigated whether an administration of exogenous of GSNO or enhancing the level of endogenous GSNO protects against neurovascular injury in wild-type (WT) and eNOS-null (endothelial dysfunction) mouse models of cerebral ischemia-reperfusion (IR).

METHODS

Transient cerebral ischemic injury was induced by middle cerebral artery occlusion (MCAO) for 60 minutes in male adult WT and eNOS null mice. GSNO (0.1 mg/kg body weight, intravenously) or N6022 (GSNO reductase inhibitor, 5.0 mg/kg body weight, intravenously) was administered 30 minutes before MCAO in preinjury and at the reperfusion in postinjury studies. Brain infarctions, edema, and neurobehavioral functions were evaluated at 24 hours after the reperfusion.

RESULTS

eNOS-null mice had a higher degree (P< .05) of injury than WT. Pre- or postinjury treatment with either GSNO or N6022 significantly reduced infarct volume, improved neurological and sensorimotor function in both WT and eNOS-null mice.

CONCLUSION

Reduced brain infarctions and edema, and improved neurobehavioral functions by pre- or postinjury GSNO treatment of eNOS knock out mice indicate that GSNO can attenuate IR injury, likely by mimicking the eNOS-derived NO-dependent anti-ischemic and anti-inflammatory functions. Neurovascular protection by GSNO/N6022 in both pre- and postischemic injury groups support GSNO as a promising drug candidate for the prevention and treatment of stroke injury.

S-Nitrosylation of CHIP Enhances F508Del-CFTR Maturation

S-nitrosothiols (SNOs) are endogenous signaling molecules that have numerous beneficial effects on the airway via cyclic guanosine monophosphate-dependent and -independent processes. Healthy human airways contain SNOs, but SNO levels are lower in the airways of patients with cystic fibrosis (CF). In this study, we examined the interaction between SNOs and the molecular cochaperone C-terminus Hsc70 interacting protein (CHIP), which is an E3 ubiquitin ligase that targets improperly folded CF transmembrane conductance regulator (CFTR) for subsequent degradation. Both CFBE41o- cells expressing either wild-type or F508del-CFTR and primary human bronchial epithelial cells express CHIP. Confocal microscopy and IP studies showed the cellular colocalization of CFTR and CHIP, and showed that S-nitrosoglutathione inhibits the CHIP-CFTR interaction. SNOs significantly reduced both the expression and activity of CHIP, leading to higher levels of both the mature and immature forms of F508del-CFTR. In fact, SNO inhibition of the function and expression of CHIP not only improved the maturation of CFTR but also increased CFTR's stability at the cell membrane. S-nitrosoglutathione-treated cells also had more S-nitrosylated CHIP and less ubiquitinated CFTR than cells that were not treated, suggesting that the S-nitrosylation of CHIP prevents the ubiquitination of CFTR by inhibiting CHIP's E3 ubiquitin ligase function. Furthermore, the exogenous SNOs S-nitrosoglutathione diethyl ester and S-nitro-N-acetylcysteine increased the expression of CFTR at the cell surface. After CHIP knockdown with siRNA duplexes specific for CHIP, F508del-CFTR expression increased at the cell surface. We conclude that SNOs effectively reduce CHIP-mediated degradation of CFTR, resulting in increased F508del-CFTR expression on airway epithelial cell surfaces. Together, these findings indicate that S-nitrosylation of CHIP is a novel mechanism of CFTR correction, and we anticipate that these insights will allow different SNOs to be optimized as agents for CF therapy.

Proteomic Investigation of S-Nitrosylated Proteins During NO-Induced Adventitious Rooting of Cucumber

Nitric oxide (NO) acts an essential signaling molecule that is involved in regulating various physiological and biochemical processes in plants. However, whether S-nitrosylation is a crucial molecular mechanism of NO is still largely unknown. In this study, 50 μM S-nitrosoglutathione (GSNO) treatment was found to have a maximum biological effect on promoting adventitious rooting in cucumber. Meanwhile, removal of endogenous NO significantly inhibited the development of adventitious roots implying that NO is responsible for promoting the process of adventitious rooting. Moreover, application of GSNO resulted in an increase of intracellular S-nitrosothiol (SNO) levels and endogenous NO production, while decreasing the S-nitrosoglutathione reductase (GSNOR) activity during adventitious rooting, implicating that S-nitrosylation might be involved in NO-induced adventitious rooting in cucumber. Furthermore, the identification of S-nitrosylated proteins was performed utilizing the liquid chromatography/mass spectrometry/mass spectrometry (LC-MS/MS) and biotin-switch technique during the development of adventitious rooting. Among these proteins, the activities and S-nitrosylated level of glyceraldehyde-3-phosphate dehydrogenase (GAPDH), tubulin alpha chain (TUA), and glutathione reductase (GR) were further analyzed as NO direct targets. Our results indicated that NO might enhance the S-nitrosylation level of GAPDH and GR, and was found to subsequently reduce these activities and transcriptional levels. Conversely, S-nitrosylation of TUA increased the expression level of TUA. The results implied that S-nitrosylation of key proteins seems to regulate various pathways through differential S-nitrosylation during adventitious rooting. Collectively, these results suggest that S-nitrosylation could be involved in NO-induced adventitious rooting, and they also provide fundamental evidence for the molecular mechanism of NO signaling during adventitious rooting in cucumber explants.

Tomato Root Growth Inhibition by Salinity and Cadmium Is Mediated By S-Nitrosative Modifications of ROS Metabolic Enzymes Controlled by S-Nitrosoglutathione Reductase

S-nitrosoglutathione reductase (GSNOR) exerts crucial roles in the homeostasis of nitric oxide (NO) and reactive nitrogen species (RNS) in plant cells through indirect control of S-nitrosation, an important protein post-translational modification in signaling pathways of NO. Using cultivated and wild tomato species, we studied GSNOR function in interactions of key enzymes of reactive oxygen species (ROS) metabolism with RNS mediated by protein S-nitrosation during tomato root growth and responses to salinity and cadmium. Application of a GSNOR inhibitor N6022 increased both NO and S-nitrosothiol levels and stimulated root growth in both genotypes. Moreover, N6022 treatment, as well as S-nitrosoglutathione (GSNO) application, caused intensive S-nitrosation of important enzymes of ROS metabolism, NADPH oxidase (NADPHox) and ascorbate peroxidase (APX). Under abiotic stress, activities of APX and NADPHox were modulated by S-nitrosation. Increased production of H2O2 and subsequent oxidative stress were observed in wild Solanumhabrochaites, together with increased GSNOR activity and reduced S-nitrosothiols. An opposite effect occurred in cultivated S. lycopersicum, where reduced GSNOR activity and intensive S-nitrosation resulted in reduced ROS levels by abiotic stress. These data suggest stress-triggered disruption of ROS homeostasis, mediated by modulation of RNS and S-nitrosation of NADPHox and APX, underlies tomato root growth inhibition by salinity and cadmium stress.

Glutathione-related substances maintain cardiomyocyte contractile function in hypoxic conditions

Severe hypoxia leads to decline in cardiac contractility and induces arrhythmic events in part due to oxidative damage to cardiomyocyte proteins including ion transporters. This results in compromised handling of Ca2+ ions that trigger heart contractile machinery. Here, we demonstrate that thiol-containing compounds such as N-acetylcysteine (NAC), glutathione ethyl ester (et-GSH), oxidized tetraethylglutathione (tet-GSSG), oxidized glutathione (GSSG) and S-nitrosoglutathione (GSNO) are capable of reducing negative effects of hypoxia on isolated rat cardiomyocytes. Preincubation of cardiomyocytes with 0.1 mM GSNO, 0.5 mM et-GSH, GSSG, tet-GSSG or with 10 mM NAC allows cells 5-times longer tolerate the hypoxic conditions and elicit regular Ca2+ transients in response to electric pacing. The shape of Ca2+ transients generated in the presence of GSNO, et-GSH and NAC was similar to that observed in normoxic control cardiomyocytes. The leader compound, GSNO, accelerated by 34% the recovery of normal contractile function of isolated rat heart subjected to ischemia-reperfusion. GSNO increased glutathionylation of Na,K-ATPase alpha-2 subunit, the principal ion-transporter of cardiac myocyte sarcolemma, which prevents irreversible oxidation of Na,K-ATPase and regulates its function to support normal Ca2+ ion handling in hypoxic cardiomyocytes. Altogether, GSNO appears effective cardioprotector in hypoxic conditions worth further studies toward its cardiovascular application.

Impact of the NO-Sensitive Guanylyl Cyclase 1 and 2 on Renal Blood Flow and Systemic Blood Pressure in Mice

Nitric oxide (NO) modulates renal blood flow (RBF) and kidney function and is involved in blood pressure (BP) regulation predominantly via stimulation of the NO-sensitive guanylyl cyclase (NO-GC), existing in two isoforms, NO-GC1 and NO-GC2. Here, we used isoform-specific knockout (KO) mice and investigated their contribution to renal hemodynamics under normotensive and angiotensin II-induced hypertensive conditions. Stimulation of the NO-GCs by S-nitrosoglutathione (GSNO) reduced BP in normotensive and hypertensive wildtype (WT) and NO-GC2-KO mice more efficiently than in NO-GC1-KO. NO-induced increase of RBF in normotensive mice did not differ between the genotypes, but the respective increase under hypertensive conditions was impaired in NO-GC1-KO. Similarly, inhibition of endogenous NO increased BP and reduced RBF to a lesser extent in NO-GC1-KO than in NO-GC2-KO. These findings indicate NO-GC1 as a target of NO to normalize RBF in hypertension. As these effects were not completely abolished in NO-GC1-KO and renal cyclic guanosine monophosphate (cGMP) levels were decreased in both NO-GC1-KO and NO-GC2-KO, the results suggest an additional contribution of NO-GC2. Hence, NO-GC1 plays a predominant role in the regulation of BP and RBF, especially in hypertension. However, renal NO-GC2 appears to compensate the loss of NO-GC1, and is able to regulate renal hemodynamics under physiological conditions.

iNOS promotes hypothalamic insulin resistance associated with deregulation of energy balance and obesity in rodents

Inducible nitric oxide (iNOS)-mediated S-nitrosation of the metabolic signaling pathway has emerged as a post-translational modification that triggers insulin resistance in obesity and aging. However, the effects of S-nitrosation in controlling energy homeostasis are unknown. Thus, in the present study we aimed to evaluate the effects of S-nitrosation in insulin signaling pathway in the hypothalamus of rodents. Herein, we demonstrated that the intracerebroventricular infusion of the nitric oxide (NO) donor S-nitrosoglutathione (GSNO) promoted hypothalamic insulin signaling resistance and replicated the food intake pattern of obese individuals. Indeed, obesity induced S-nitrosation of hypothalamic IR and Akt, whereas inhibition of iNOS or S-nitrosation of insulin signaling pathway protected against hypothalamic insulin resistance and normalized energy homeostasis. Overall, these findings indicated that S-nitrosation of insulin signaling pathway is required to sustain hypothalamic insulin resistance in obesity.

cGMP signaling inhibits platelet shape change through regulation of the RhoA-Rho Kinase-MLC phosphatase signaling pathway

Essentials Platelet shape change requires cytoskeletal rearrangement via myosin-mediated actin contraction. We investigated whether nitric oxide (NO) affected thrombin-induced platelet shape change. NO inhibits shape change, RhoA/ROCK signalling and myosin light chain (MLC) phosphorylation. NO promotes MLC phosphatase activity, thus prevents MLC phosphorylation and shape change.

SUMMARY

Background Platelet shape change, spreading and thrombus stability require activation of the actin cytoskeleton contractile machinery. The mechanisms controlling actin assembly to prevent unwanted platelet activation are unclear. Objectives We examined the effects of nitric oxide on the signaling pathways regulating platelet actin-myosin activation. Results S-nitrosoglutathione (GSNO) inhibited thrombin-induced platelet shape change and myosin phosphorylation of the myosin light chain (MLC). Because thrombin stimulates phospho-MLC through the RhoA/ ROCK dependent inhibition of MLC phosphatase (MLCP) we examined the effects of NO on this pathway. Thrombin caused the GTP loading and activation of RhoA, leading to the ROCK-mediated phosphorylation of MLCP on threonine 853 (thr853 ), which is known to inhibit phosphatase activity. Treatment of platelets with GSNO blocked ROCK-mediated increases in phosphoMLCP-thr853 induced by thrombin. This effect was mimicked by the direct activator of protein kinase G, 8-pCPT-PET-cGMP, and blocked by the inhibition of guanylyl cyclase, but not inhibitors of protein kinase A. Further exploration of the mechanism demonstrated that GSNO stimulated the association of RhoA with protein kinase G (PKG) and the inhibitory phosphorylation (serine188) of RhoA in a cGMP-dependent manner. Consistent with these observations, in vitro experiments revealed that recombinant PKG caused direct phosphorylation of RhoA. The inhibition of RhoA by GSNO prevented ROCK-mediated phosphorylation and inhibition of MLCP activity. Conclusions These data suggest novel crosstalk between the NO-cGMP-PKG and RhoA/ROCK signaling pathways to control platelet actin remodeling.

S-nitrosoglutathione spraying improves stomatal conductance, Rubisco activity and antioxidant defense in both leaves and roots of sugarcane plants under water deficit

Water deficit is a major environmental constraint on crop productivity and performance and nitric oxide (NO) is an important signaling molecule associated with many biochemical and physiological processes in plants under stressful conditions. This study aims to test the hypothesis that leaf spraying of S-nitrosoglutathione (GSNO), an NO donor, improves the antioxidant defense in both roots and leaves of sugarcane plants under water deficit, with positive consequences for photosynthesis. In addition, the roles of key photosynthetic enzymes ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPC) in maintaining CO₂ assimilation of GSNO-sprayed plants under water deficit were evaluated. Sugarcane plants were sprayed with water or GSNO 100 μM and subjected to water deficit, by adding polyethylene glycol (PEG-8000) to the nutrient solution. Sugarcane plants supplied with GSNO presented increases in the activity of antioxidant enzymes such as superoxide dismutase in leaves and catalase in roots, indicating higher antioxidant capacity under water deficit. Such adjustments induced by GSNO were sufficient to prevent oxidative damage in both organs and were associated with better leaf water status. As a consequence, GSNO spraying alleviated the negative impact of water deficit on stomatal conductance and photosynthetic rates, with plants also showing increases in Rubisco activity under water deficit.

Nitric oxide inhibits the mitochondrial carnitine/acylcarnitine carrier through reversible S-nitrosylation of cysteine 136

S-nitrosylation of the mitochondrial carnitine/acylcarnitine transporter (CACT) has been investigated on the native and the recombinant proteins reconstituted in proteoliposomes, and on intact mitochondria. The widely-used NO-releasing compound, GSNO, strongly inhibited the antiport measured in proteoliposomes reconstituted with the native CACT from rat liver mitochondria or the recombinant rat CACT over-expressed in E. coli. Inhibition was reversed by the reducing agent dithioerythritol, indicating a reaction mechanism based on nitrosylation of Cys residues of the CACT. The half inhibition constant (IC50) was very similar for the native and recombinant proteins, i.e., 74 and 71μM, respectively. The inhibition resulted to be competitive with respect the substrate, carnitine. NO competed also with NEM, correlating well with previous data showing interference of NEM with the substrate transport path. Using a site-directed mutagenesis approach on Cys residues of the recombinant CACT, the target of NO was identified. C136 plays a major role in the reaction mechanism. The occurrence of S-nitrosylation was demonstrated in intact mitochondria after treatment with GSNO, immunoprecipitation and immunostaining of CACT with a specific anti NO-Cys antibody. In parallel samples, transport activity of CACT measured in intact mitochondria, was strongly inhibited after GSNO treatment. The possible physiological and pathological implications of the post-translational modification of CACT are discussed.

S-nitrosoglutathione promotes cell wall remodelling, alters the transcriptional profile and induces root hair formation in the hairless root hair defective 6 (rhd6) mutant of Arabidopsis thaliana

Nitric oxide (NO) exerts pleiotropic effects on plant development; however, its involvement in cell wall modification during root hair formation (RHF) has not yet been addressed. Here, mutants of Arabidopsis thaliana with altered root hair phenotypes were used to assess the involvement of S-nitrosoglutathione (GSNO), the primary NO source, in cell wall dynamics and gene expression in roots induced to form hairs. GSNO and auxin restored the root hair phenotype of the hairless root hair defective 6 (rhd6) mutant. A positive correlation was observed between increased NO production and RHF induced by auxin in rhd6 and transparent testa glabra (ttg) mutants. Deposition of an epitope within rhamnogalacturonan-I recognized by the CCRC-M2 antibody was delayed in root hair cells (trichoblasts) compared with nonhair cells (atrichoblasts). GSNO, but not auxin, restored the wild-type root glycome and transcriptome profiles in rhd6, modulating the expression of a large number of genes related to cell wall composition and metabolism, as well as those encoding ribosomal proteins, DNA and histone-modifying enzymes and proteins involved in post-translational modification. Our results demonstrate that NO plays a key role in cell wall remodelling in trichoblasts and suggest that it also participates in chromatin modification in root cells of A. thaliana.

Nitric Oxide Modulates Histone Acetylation at Stress Genes by Inhibition of Histone Deacetylases

Histone acetylation, which is an important mechanism to regulate gene expression, is controlled by the opposing action of histone acetyltransferases and histone deacetylases (HDACs). In animals, several HDACs are subjected to regulation by nitric oxide (NO); in plants, however, it is unknown whether NO affects histone acetylation. We found that treatment with the physiological NO donor S-nitrosoglutathione (GSNO) increased the abundance of several histone acetylation marks in Arabidopsis (Arabidopsis thaliana), which was strongly diminished in the presence of the NO scavenger 2-4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide. This increase was likely triggered by NO-dependent inhibition of HDAC activity, since GSNO and S-nitroso-N-acetyl-dl-penicillamine significantly and reversibly reduced total HDAC activity in vitro (in nuclear extracts) and in vivo (in protoplasts). Next, genome-wide H3K9/14ac profiles in Arabidopsis seedlings were generated by chromatin immunoprecipitation sequencing, and changes induced by GSNO, GSNO/2-4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide or trichostatin A (an HDAC inhibitor) were quantified, thereby identifying genes that display putative NO-regulated histone acetylation. Functional classification of these genes revealed that many of them are involved in the plant defense response and the abiotic stress response. Furthermore, salicylic acid, which is the major plant defense hormone against biotrophic pathogens, inhibited HDAC activity and increased histone acetylation by inducing endogenous NO production. These data suggest that NO affects histone acetylation by targeting and inhibiting HDAC complexes, resulting in the hyperacetylation of specific genes. This mechanism might operate in the plant stress response by facilitating the stress-induced transcription of genes.

Relationship between Glutathione Peroxidase, Platelet Reactivity, and Reactive Oxygen Species in an Acute Coronary Syndrome Population

Low activity levels of the antioxidant enzyme, glutathione peroxidase (GPx), have been implicated in adverse clinical outcomes in coronary artery disease. A potential mechanistic link for this relationship is that low GPx activity predisposes patients to thrombotic complications due to impaired reactive oxygen species (ROS) metabolism. GPx potentially regulates the bioavailability of nitric oxide (NO) - a potent platelet inhibitor - therefore indirectly affecting platelet activation. This study examined the relationship between levels of GPx activity, ROS, and platelet activation in 51 acute coronary syndrome (ACS) patients. No relationship was observed between GPx activity and platelet reactivity nor between ROS levels and platelet reactivity. However patients with low GPx activity had significantly higher ROS levels (r²=0.1, p<0.05), suggesting a differential capacity to upregulate antioxidant defence in response to oxidative stress. Low levels of GPx activity may contribute to increased clinical risk by an inability to protect against oxidant-mediated damage.

Alteration of blood clot structures by interleukin-1 beta in association with bone defects healing

The quality of hematomas are crucial for successful early bone defect healing, as the structure of fibrin clots can significantly influence the infiltration of cells, necessary for bone regeneration, from adjacent tissues into the fibrin network. This study investigated if there were structural differences between hematomas from normal and delayed healing bone defects and whether such differences were linked to changes in the expression of IL-1β. Using a bone defect model in rats, we found that the hematomas in the delayed healing model had thinner fibers and denser clot structures. Moreover, IL-1β protein levels were significantly higher in the delayed healing hematomas. The effects of IL-1β on the structural properties of human whole blood clots were evaluated by thrombelastograph (TEG), scanning electronic microscopy (SEM), compressive study, and thrombolytic assays. S-nitrosoglutathione (GSNO) was applied to modulate de novo hematoma structure and the impact on bone healing was evaluated in the delayed healing model. We found that GSNO produced more porous hematomas with thicker fibers and resulted in significantly enhanced bone healing. This study demonstrated that IL-1β and GSNO had opposing effects on clot architecture, the structure of which plays a pivotal role in early bone healing.

Neuroprotective Effects of Inhibiting Fyn S-Nitrosylation on Cerebral Ischemia/Reperfusion-Induced Damage to CA1 Hippocampal Neurons

Nitric oxide (NO) can regulate signaling pathways via S-nitrosylation. Fyn can be post-translationally modified in many biological processes. In the present study, using a rat four-vessel-occlusion ischemic model, we aimed to assess whether Fyn could be S-nitrosylated and to evaluate the effects of Fyn S-nitrosylation on brain damage. In vitro, Fyn could be S-nitrosylated by S-nitrosoglutathione (GSNO, an exogenous NO donor), and in vivo, endogenous NO synthesized by NO synthases (NOS) could enhance Fyn S-nitrosylation. Application of GSNO, 7-nitroindazole (7-NI, an inhibitor of neuronal NOS) and hydrogen maleate (MK-801, the N-methyl-d-aspartate receptor (NMDAR) antagonist) could decrease the S-nitrosylation and phosphorylation of Fyn induced by cerebral ischemia/reperfusion (I/R). Cresyl violet staining validated that these compounds exerted neuroprotective effects against the cerebral I/R-induced damage to hippocampal CA1 neurons. Taken together, in this study, we demonstrated that Fyn can be S-nitrosylated both in vitro and in vivo and that inhibiting S-nitrosylation can exert neuroprotective effects against cerebral I/R injury, potentially via NMDAR-mediated mechanisms. These findings may lead to a new field of inquiry to investigate the underlying pathogenesis of stroke and the development of novel treatment strategies.

Exogenous nitric oxide improves sugarcane growth and photosynthesis under water deficit

Nitric oxide (NO)-mediated redox signaling plays a role in alleviating the negative impact of water stress in sugarcane plants by improving root growth and photosynthesis. Drought is an environmental limitation affecting sugarcane growth and yield. The redox-active molecule nitric oxide (NO) is known to modulate plant responses to stressful conditions. NO may react with glutathione (GSH) to form S-nitrosoglutathione (GSNO), which is considered the main reservoir of NO in cells. Here, we investigate the role of NO in alleviating the effects of water deficit on growth and photosynthesis of sugarcane plants. Well-hydrated plants were compared to plants under drought and sprayed with mock (water) or GSNO at concentrations ranging from 10 to 1000 μM. Leaf GSNO sprayed plants showed significant improvement of relative water content and leaf and root dry matter under drought compared to mock-sprayed plants. Additionally, plants sprayed with GSNO (≥ 100 μM) showed higher leaf gas exchange and photochemical activity as compared to mock-sprayed plants under water deficit and after rehydration. Surprisingly, a raise in the total S-nitrosothiols content was observed in leaves sprayed with GSH or GSNO, suggesting a long-term role of NO-mediated responses to water deficit. Experiments with leaf discs fumigated with NO gas also suggested a role of NO in drought tolerance of sugarcane plants. Overall, our data indicate that the NO-mediated redox signaling plays a role in alleviating the negative effects of water stress in sugarcane plants by protecting the photosynthetic apparatus and improving shoot and root growth.

S-Nitrosylation of NF-κB p65 Inhibits TSH-Induced Na(+)/I(-) Symporter Expression

Nitric oxide (NO) is a ubiquitous signaling molecule involved in a wide variety of cellular physiological processes. In thyroid cells, NO-synthase III-endogenously produced NO reduces TSH-stimulated thyroid-specific gene expression, suggesting a potential autocrine role of NO in modulating thyroid function. Further studies indicate that NO induces thyroid dedifferentiation, because NO donors repress TSH-stimulated iodide (I(-)) uptake. Here, we investigated the molecular mechanism underlying the NO-inhibited Na(+)/I(-) symporter (NIS)-mediated I(-) uptake in thyroid cells. We showed that NO donors reduce I(-) uptake in a concentration-dependent manner, which correlates with decreased NIS protein expression. NO-reduced I(-) uptake results from transcriptional repression of NIS gene rather than posttranslational modifications reducing functional NIS expression at the plasma membrane. We observed that NO donors repress TSH-induced NIS gene expression by reducing the transcriptional activity of the nuclear factor-κB subunit p65. NO-promoted p65 S-nitrosylation reduces p65-mediated transactivation of the NIS promoter in response to TSH stimulation. Overall, our data are consistent with the notion that NO plays a role as an inhibitory signal to counterbalance TSH-stimulated nuclear factor-κB activation, thus modulating thyroid hormone biosynthesis.

Targeting the nNOS/peroxynitrite/calpain system to confer neuroprotection and aid functional recovery in a mouse model of TBI

Traumatic brain injury (TBI) derails nitric oxide (NO)-based anti-inflammatory and anti-excitotoxicity mechanisms. NO is consumed by superoxide to form peroxynitrite, leading to decreased NO bioavailability for S-nitrosoglutathione (GSNO) synthesis and regulation of neuroprotective pathways. Neuronal peroxynitrite is implicated in neuronal loss and functional deficits following TBI. Using a contusion mouse model of TBI, we investigated mechanisms for the opposed roles of GSNO versus peroxynitrite for neuroprotection and functional recovery. TBI was induced by controlled cortical impact (CCI) in adult male mice. GSNO treatment at 2h after CCI decreased the expression levels of phospho neuronal nitric oxide synthase (pnNOS), alpha II spectrin degraded products, and 3-NT, while also decreasing the activities of nNOS and calpains. Treatment of TBI with FeTPPS, a peroxynitrite scavenger, had effects similar to GSNO treatment. GSNO treatment of TBI also reduced neuronal degeneration and improved neurobehavioral function in a two-week TBI study. In a cell free system, SIN-1 (a peroxynitrite donor and 3-nitrotyrosinating agent) increased whereas GSNO (an S-nitrosylating agent) decreased calpain activity, and these activities were reversed by, respectively, FeTPPS and mercuric chloride, a cysteine-NO bond cleaving agent. These data indicate that peroxynitrite-mediated activation and GSNO-mediated inhibition of the deleterious nNOS/calpain system play critical roles in the pathobiology of neuronal protection and functional recovery in TBI disease. Given GSNO׳s safety record in other diseases, its neuroprotective efficacy and promotion of functional recovery in this TBI study make low-dose GSNO a potential candidate for preclinical evaluation.

Loss of GSNOR1 Function Leads to Compromised Auxin Signaling and Polar Auxin Transport

Cross talk between phytohormones, nitric oxide (NO), and auxin has been implicated in the control of plant growth and development. Two recent reports indicate that NO promoted auxin signaling but inhibited auxin transport probably through S-nitrosylation. However, genetic evidence for the effect of S-nitrosylation on auxin physiology has been lacking. In this study, we used a genetic approach to understand the broader role of S-nitrosylation in auxin physiology in Arabidopsis. We compared auxin signaling and transport in Col-0 and gsnor1-3, a loss-of-function GSNOR1 mutant defective in protein de-nitrosylation. Our results showed that auxin signaling was impaired in the gsnor1-3 mutant as revealed by significantly reduced DR5-GUS/DR5-GFP accumulation and compromised degradation of AXR3NT-GUS, a useful reporter in interrogating auxin-mediated degradation of Aux/IAA by auxin receptors. In addition, polar auxin transport was compromised in gsnor1-3, which was correlated with universally reduced levels of PIN or GFP-PIN proteins in the roots of the mutant in a manner independent of transcription and 26S proteasome degradation. Our results suggest that S-nitrosylation and GSNOR1-mediated de-nitrosylation contribute to auxin physiology, and impaired auxin signaling and compromised auxin transport are responsible for the auxin-related morphological phenotypes displayed by the gsnor1-3 mutant.

Nitric oxide augments single Ca(2+) channel currents via cGMP-dependent protein kinase in Kenyon cells isolated from the mushroom body of the cricket brain

Behavioral and pharmacological studies in insects have suggested that the nitric oxide (NO)/cyclic GMP (cGMP) signaling pathway is involved in the formation of long-term memory (LTM) associated with olfactory learning. However, the target molecules of NO and the downstream signaling pathway are still not known. In this study, we investigated the action of NO on single voltage-dependent Ca(2+) channels in the intrinsic neurons known as Kenyon cells within the mushroom body of the cricket brain, using the cell-attached configuration of the patch-clamp technique. Application of the NO donor S-nitrosoglutathione (GSNO) increased the open probability (NPO) of single Ca(2+) channel currents. This GSNO-induced increase was blocked by ODQ, a soluble guanylate cyclase (sGC) inhibitor, suggesting that the NO generated by GSNO acts via sGC to raise cGMP levels. The membrane-permeable cGMP analog 8-Bro-cGMP also increased the NPO of single Ca(2+) channel currents. Pretreatment of cells with KT5823, a protein kinase G blocker, abolished the excitatory effect of GSNO. These results suggest that NO augments the activity of single Ca(2+) channels via the cGMP/PKG signaling pathway. To gain insight into the physiological role of NO, we examined the effect of GSNO on action potentials of Kenyon cells under current-clamp conditions. Application of GSNO increased the frequency of action potentials elicited by depolarizing current injections, indicating that NO acts as a modulator resulting in a stimulatory signal in Kenyon cells. We discuss the increased Ca(2+) influx through these Ca(2+) channels via the NO/cGMP signaling cascade in relation to the formation of olfactory LTM.

Elevation of NO production increases Fe immobilization in the Fe-deficiency roots apoplast by decreasing pectin methylation of cell wall

Cell wall is the major component of root apoplast which is the main reservoir for iron in roots, while nitric oxide (NO) is involved in regulating the synthesis of cell wall. However, whether such regulation could influence the reutilization of iron stored in root apoplast remains unclear. In this study, we observed that iron deficiency elevated NO level in tomato (Solanum lycopersicum) roots. However, application of S-nitrosoglutathione, a NO donor, significantly enhanced iron retention in root apoplast of iron-deficient plants, accompanied with a decrease of iron level in xylem sap. Consequently, S-nitrosoglutathione treatment increased iron concentration in roots, but decreased it in shoots. The opposite was true for the NO scavenging treatment with 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO). Interestingly, S-nitrosoglutathione treatment increased pectin methylesterase activity and decreased degree of pectin methylation in root cell wall of both iron-deficient and iron-sufficient plants, which led to an increased iron retention in pectin fraction, thus increasing the binding capacity of iron to the extracted cell wall. Altogether, these results suggested that iron-deficiency-induced elevation of NO increases iron immobilization in root apoplast by decreasing pectin methylation in cell wall.

The use of nanoparticles to deliver nitric oxide to hepatic stellate cells for treating liver fibrosis and portal hypertension

Polymeric nanoparticles are designed to transport and deliver nitric oxide (NO) into hepatic stellate cells (HSCs) for the potential treatment of both liver fibrosis and portal hypertension. The nanoparticles, incorporating NO donor molecules (S-nitrosoglutathione compound), are designed for liver delivery, minimizing systemic delivery of NO. The nanoparticles are decorated with vitamin A to specifically target HSCs. We demonstrate, using in vitro and in vivo experiments, that the targeted nanoparticles are taken up specifically by rat primary HSCs and the human HSC cell line accumulating in the liver. When nanoparticles, coated with vitamin A, release NO in liver cells, we find inhibition of collagen I and α-smooth muscle actin (α-SMA), fibrogenic genes associated with activated HSCs expression in primary rat liver and human activated HSCs without any obvious cytotoxic effects. Finally, NO-releasing nanoparticles targeted with vitamin A not only attenuate endothelin-1 (ET-1) which elicites HSC contraction but also acutely alleviates haemodynamic disorders in bile duct-ligated-induced portal hypertension evidenced by decreasing portal pressure (≈20%) and unchanging mean arterial pressure. This study clearly shows, for the first time, the potential for HSC targeted nanoparticle delivery of NO as a treatment for liver diseases with proven efficacy for alleviating both liver fibrosis and portal hypertension.

β-Cyclodextrin-hemin complex-induced lateral root formation in tomato: involvement of nitric oxide and heme oxygenase 1

β-Cyclodextrin-hemin complex-induced tomato lateral root formation was associated with nitric oxide and heme oxygenase 1 by modulating cell cycle regulatory genes. β-Cyclodextrin-hemin complex (β-CDH), a complex by combining β-cyclodextrin (β-CD) with hemin, a heme oxygenase 1 (HO1) inducer, was a trigger of cucumber adventitious root formation by enhancing HO1 gene expression. In this report, our results identified the previously unknown function of β-CDH in plants: the inducer of tomato lateral root (LR) formation. β-CDH-triggered LR formation is hemin-specific, since β-CD failed to induce LR development. Because nitric oxide (NO) is involved in LR formation, the correlation of β-CDH with NO and HO1 was investigated. Our analysis suggested that β-CDH induced an increase in endogenous NO production, followed by up-regulation of tomato HO1 gene and LR formation, all of which were mimicked by hemin and two NO-releasing compounds (SNP and GSNO). The induction of HO1 gene expression and LR formation triggered by β-CDH or hemin were significantly blocked by an inhibitor of HO1. Further results revealed that both β-CDH- and SNP-stimulated HO1 gene expression and thereafter LR formation were sensitive to the removal of NO with a potent NO scavenger, and the responses of SNP were significantly blocked by an inhibitor of HO1. Molecular evidence illustrated that representative cell cycle regulatory genes, including SlCDKA1, SlCYCA3;1, SlCYCA2;1, and SlCYCD3;1, were significantly up-regulated by β-CDH and SNP, but obviously blocked when seedlings were co-treated with the scavenger of NO or the inhibitor of HO1. In summary, our physiological and molecular evidence demonstrated that both NO and HO1 were involved in the β-CDH-induced LR formation with, at least partially, HO1 acting downstream of NO signaling.

Nitric oxide suppresses the inhibitory effect of abscisic acid on seed germination by S-nitrosylation of SnRK2 proteins

Nitric oxide (NO) plays important roles in plant development, and biotic and abiotic stress responses. In a recent study, we showed that endogenous NO negatively regulates abscisic acid (ABA) signaling in guard cells by inhibiting sucrose nonfermenting 1 (SNF1)-related protein kinase 2.6 (SnRK2.6)/open stomata 1(OST1) through S-nitrosylation. Application of NO breaks seed dormancy and alleviates the inhibitory effect of ABA on seed germination and early seedling growth, but it is unclear how NO functions at the stages of seed germination and early seedling development. Here, we show that like SnRK2.6, SnRK2.2 can be inactivated by S-nitrosoglutathione (GSNO) treatment through S-nitrosylation. SnRK2.2 and the closely related SnRK2.3 are known to play redundant roles in ABA inhibition of seed germination in Arabidopsis. We found that treatment with the NO donor SNP phenocopies the snrk2.2snrk2.3 double mutant in conferring ABA insensitivity at the stages of seed germination and early seedling growth. Our results suggest that NO negatively regulates ABA signaling in germination and early seedling growth through S-nitrosylation of SnRK2.2 and SnRK2.3.

Differential transcriptomic analysis by RNA-Seq of GSNO-responsive genes between Arabidopsis roots and leaves

S-Nitrosoglutathione (GSNO) is a nitric oxide-derived molecule that can regulate protein function by a post-translational modification designated S-nitrosylation. GSNO has also been detected in different plant organs under physiological and stress conditions, and it can also modulate gene expression. Thirty-day-old Arabidopsis plants were grown under hydroponic conditions, and exogenous 1 mM GSNO was applied to the root systems for 3 h. Differential gene expression analyses were carried out both in roots and in leaves by RNA sequencing (RNA-seq). A total of 3,263 genes were identified as being modulated by GSNO. Most of the genes identified were associated with the mechanism of protection against stress situations, many of these having previously been identified as target genes of GSNO by array-based methods. However, new genes were identified, such as that for methionine sulfoxide reductase (MSR) in leaves or different miscellaneous RNA (miscRNA) genes in Arabidopsis roots. As a result, 1,945 GSNO-responsive genes expressed differently in leaves and roots were identified, and 114 of these corresponded exclusively to one of these organs. In summary, it is demonstrated that RNA-seq extends our knowledge of GSNO as a signaling molecule which differentially modulates gene expression in roots and leaves under non-stress conditions.

Dual regulation of cytosolic ascorbate peroxidase (APX) by tyrosine nitration and S-nitrosylation

Post-translational modifications (PTMs) mediated by nitric oxide (NO)-derived molecules have become a new area of research, as they can modulate the function of target proteins. Proteomic data have shown that ascorbate peroxidase (APX) is one of the potential targets of PTMs mediated by NO-derived molecules. Using recombinant pea cytosolic APX, the impact of peroxynitrite (ONOO-) and S-nitrosoglutathione (GSNO), which are known to mediate protein nitration and S-nitrosylation processes, respectively, was analysed. While peroxynitrite inhibits APX activity, GSNO enhances its enzymatic activity. Mass spectrometric analysis of the nitrated APX enabled the determination that Tyr5 and Tyr235 were exclusively nitrated to 3-nitrotyrosine by peroxynitrite. Residue Cys32 was identified by the biotin switch method as S-nitrosylated. The location of these residues on the structure of pea APX reveals that Tyr235 is found at the bottom of the pocket where the haem group is enclosed, whereas Cys32 is at the ascorbate binding site. Pea plants grown under saline (150 mM NaCl) stress showed an enhancement of both APX activity and S-nitrosylated APX, as well as an increase of H2O2, NO, and S-nitrosothiol (SNO) content that can justify the induction of the APX activity. The results provide new insight into the molecular mechanism of the regulation of APX which can be both inactivated by irreversible nitration and activated by reversible S-nitrosylation.

Exogenous nitric oxide potentiate DNA damage and alter DNA repair in cells exposed to ionising radiation

The aim of this study was to investigate impact of exogenous nitric oxide (NO) on generation of different types of DNA damages, their transformation, and specificity of DNA repair in cells treated with ionizing radiation (IR).

METHODS

levels of single-strand and double-strand breaks assessed in peripheral blood lymphocytes (PBL) isolated from healthy humans and treated in vitro with NO donor -- S-nitrosoglutathione (GSNO) and IR. The rate of DNA repair estimated after 30 and 60 min of PBL treatment. The visualization and measuring the number of prompt and delayed DNA damages, including strand breaks, apurinic and thermolabile sites performed with single-cell gel electrophoresis.

RESULTS

IR caused dose-dependent generation of single strand breaks (SSBs), double strand breaks (DSBs), and heat-labile sites (HLS) in cell DNA. However, particularly destructive was combined treatment IR with GSNO as NO donor that leads to a significant increase of DNA damage and a dose-dependent inhibition of the DNA repair rate. Obtained data proofs the ability of NO to inhibit fast and slow stages of SSBs, DSBs, and HLS repair resulting in significant growth of genotoxic effect. DNA breaks generation from HLS is able to affect DSBs yields especially in cells with altered DNA repair. The process of DNA repair of delayed DSBs formed from HLS was quite different from removal of DNA damages occurring immediately after treatment and was characterized by IR dose dependent inhibition of DNA repair.

CONCLUSION

High level of DNA strand breaks, that are generated after the combined treatment with NO and IR, are accumulated for quite a long time after exposure due to altered DNA repair, indicating the development of genetic instability and increase of carcinogenic risk for organism exposed to combination of harmful environmental factors.

The effects of thiol modulators on nitrergic nerve- and S-nitrosothiols-induced relaxation in duodenum

BACKGROUND

The aim of this study was to investigate whether thiols are involved in the nitrergic neurotransmission in mouse duodenum.

METHODS

The effects of thiol-modulating agents, ethacrynic acid (100 μM), a non-specific sulfhydryl alkylator, and diamide (100 μM), an alkylating agent that oxidizes protein sulfhydryl groups and depletes intracellular glutathione, on relaxations to nitrergic stimulation (electrical field stimulation, EFS;10 Hz, 25 V, 1 ms, 15 s-train), S-nitrosoglutathione (GSNO; 5 μM), S-nitroso-acetylpenicillamine (SNAP; 5 μM), and S-nitrosocysteine (CysNO; 10 μM) were investigated. Moreover, the effects of buthionine sulfoximine (100 μM), an inhibitor of γ-glutamylcysteine synthetase, and sulfobromophthalein (100 μM), an inhibitor of glutathione-S-transferase, were studied on relaxant responses to EFS and S-nitrosothiols in mouse duodenum.

RESULTS

Exogenous free thiol, glutathione (GSH, 100 μM) did not influence relaxation to EFS, GSNO, SNAP, and CysNO. Ethacrynic acid and diamide significantly decreased relaxation of duodenum to EFS, GSNO, SNAP, and CysNO. This inhibition was prevented by addition of GSH. Buthionine sulfoximine and sulfobromophthalein significantly decreased relaxation to EFS and GSNO but did not influence relaxation to SNAP and CysNO. The inhibitory effect of buthionine sulfoximine and sulfobromophthalein on the relaxant response to EFS and GSNO was prevented by addition of GSH.

CONCLUSIONS

These results suggest that relaxation to nitrergic stimulation is thiol-dependent, and nitrosothiols, possibly S-nitrosoglutathione may play a role, as an intermediate compound in nitrergic neurotransmission in mouse duodenum.

Yeast flavohemoglobin protects against nitrosative stress and controls ferric reductase activity

The role of Saccharomyces cerevisiae flavohemoglobin (Yhb1) is controversial and far from understood. This study compares the effects of nitrosative and oxidative challenge on the yeast mutant lacking the YHB1 gene. Growth of the mutant was impaired by nitrosoglutathione and peroxynitrite, whereas increased sensitivity to reactive oxygen species was not observed. Increased levels of intracellular NO(*) after incubation with NO(*) donors were found in the mutants cells as compared to the wild-type cells. Deletion of the YHB1 gene was found to augment the reduction of Fe(3+) by yeast cells which suggests that flavohemoglobin participates in regulation of the activity of plasma membrane ferric reductase(s).

Proteomic analysis of S-nitrosylated proteins in potato plant

Nitric oxide (NO) has various functions in physiological responses in plants, such as development, hormone signaling and defense. The mechanism of how NO regulates physiological responses has not been well understood. Protein S-nitrosylation, a redox-related modification of cysteine thiol by NO, is known to be one of the important post-translational modifications to regulate activity and interactions of proteins. To elucidate NO function in plants, proteomic analysis of S-nitrosylated proteins in potato (Solanum tuberosum) was performed. Detection and functional analysis of internal S-nitrosylated proteins is technically demanding because of the instability and reversibility of the protein S-nitrosylation. By using a modified biotin switch assay optimized for potato tissues, and nano liquid chromatography combined with mass spectrometry, approximately 80 S-nitrosylated candidate proteins were identified in S-nitrosoglutathione-treated potato leaves and tuber extracts. Identified proteins included redox-related enzymes, defense-related proteins and metabolic enzymes. Some of identified proteins were synthesized in Escherichia coli, and S-nitrosylation of recombinant proteins was confirmed in vitro. Dehydroascorbate reductase 1 (DHAR1, EC 1.8.5.1), one of the identified S-nitrosylated target proteins, showed glutathione-dependent dehydroascorbate-reducing activity. Either point mutation in a target cysteine of S-nitrosylation or treatment with an NO donor, S-nitroso-L-cysteine, significantly reduced the activity of DHAR1, indicating that DHAR1 is negatively regulated by S-nitrosylation of the cysteine residue essential for the enzymatic activity. These results show that the modified method developed in this study can be used to identify proteins regulated by S-nitrosylation in potato tissues.

Proteomic analysis of S-nitrosylated proteins in potato plant

Nitric oxide (NO) has various functions in physiological responses in plants, such as development, hormone signaling and defense. The mechanism of how NO regulates physiological responses has not been well understood. Protein S-nitrosylation, a redox-related modification of cysteine thiol by NO, is known to be one of the important post-translational modifications to regulate activity and interactions of proteins. To elucidate NO function in plants, proteomic analysis of S-nitrosylated proteins in potato (Solanum tuberosum) was performed. Detection and functional analysis of internal S-nitrosylated proteins is technically demanding because of the instability and reversibility of the protein S-nitrosylation. By using a modified biotin switch assay optimized for potato tissues, and nano liquid chromatography combined with mass spectrometry, approximately 80 S-nitrosylated candidate proteins were identified in S-nitrosoglutathione-treated potato leaves and tuber extracts. Identified proteins included redox-related enzymes, defense-related proteins and metabolic enzymes. Some of identified proteins were synthesized in Escherichia coli, and S-nitrosylation of recombinant proteins was confirmed in vitro. Dehydroascorbate reductase 1 (DHAR1, EC 1.8.5.1), one of the identified S-nitrosylated target proteins, showed glutathione-dependent dehydroascorbate-reducing activity. Either point mutation in a target cysteine of S-nitrosylation or treatment with an NO donor, S-nitroso-L-cysteine, significantly reduced the activity of DHAR1, indicating that DHAR1 is negatively regulated by S-nitrosylation of the cysteine residue essential for the enzymatic activity. These results show that the modified method developed in this study can be used to identify proteins regulated by S-nitrosylation in potato tissues.

[Nitrogen oxide is involved in the regulation of the Fe-S cluster assembly in proteins and the formation of biofilms by Escherichia coli cells]

The functions of nitrogen oxide (NO) in the regulation of the reversible processes of Fe-S cluster assembly in proteins and the formation of Escherichia coli biofilms have been investigated. S-nitrosoglutathione (GSNO) and crystalline nitrosyl complexes of iron with sulfur-containing aliphatic ligands cisaconite (CisA) and penaconite have been used as NO donors for the first time. Wild-type E. coli cells of the strain MC4100, mutants deltaiscA and deltasufA, and the double paralog mutant deltaiscA/sufA with deletions in the alternative pathways of Fe2+ supply for cluster assembly (all derived from the above-named strain) were used in this study. Plankton growth of bacterial cultures, the mass of mature biofilms, and the expression of the SoxRS[2Fe-2S] regulon have been investigated and shown to depend on strain genotype, the process of Fe-S cluster assembly in iron-sulfur proteins, NO donor structure, and the presence of Fe2+ chelator ferene in the incubation medium. The antibiotic ciprofloxacine (CF) was used as an inhibitor of E. coli biofilm formation in the positive control. NO donors regulating Fe-S cluster assembly in E. coli have been shown to control plankton growth of the cultures and the process of mature biofilm formation; toxic doses of NO caused a dramatic (3- to 4-fold) stimulation of cell entry into biofilms as a response to nitrosative stress; NO donors CisA and GSNO in physiological concentrations suppressed the formation of mature biofilms, and the activity of these compounds was comparable to that of CE Regulation of both Fe-S cluster assembly in iron-sulfur proteins and biofilm formation by NO is indicative of the connection between these processes in E. coli.

Quantitative site-specific reactivity profiling of S-nitrosylation in mouse skeletal muscle using cysteinyl peptide enrichment coupled with mass spectrometry

S-nitrosylation, the formation of S-nitrosothiol (SNO), is an important reversible thiol oxidation event that has been increasingly recognized for its role in cell signaling. Although many proteins susceptible to S-nitrosylation have been reported, site-specific identification of physiologically relevant SNO modifications remains an analytical challenge because of the low abundance and labile nature of this modification. Herein we present further improvement and optimization of the recently reported resin-assisted cysteinyl peptide enrichment protocol for SNO identification and its application to mouse skeletal muscle to identify specific cysteine sites sensitive to S-nitrosylation by a quantitative reactivity profiling strategy. Our results indicate that the protein- and peptide-level enrichment protocols provide comparable specificity and coverage of SNO-peptide identifications. S-nitrosylation reactivity profiling was performed by quantitatively comparing the site-specific SNO modification levels in samples treated with S-nitrosoglutathione, an NO donor, at two different concentrations (i.e., 10 and 100 μM). The reactivity profiling experiments led to the identification of 488 SNO-modified sites from 197 proteins with specificity of ∼95% at the unique peptide level, i.e., ∼95% of enriched peptides contain cysteine residues as the originally SNO-modified sites. Among these sites, 281 from 145 proteins were considered more sensitive to S-nitrosylation based on the ratios of observed SNO levels between the two treatments. These SNO-sensitive sites are more likely to be physiologically relevant. Many of the SNO-sensitive proteins are localized in mitochondria, contractile fiber, and actin cytoskeleton, suggesting the susceptibility of these subcellular compartments to redox regulation. Moreover, these observed SNO-sensitive proteins are primarily involved in metabolic pathways, including the tricarboxylic acid cycle, glycolysis/gluconeogenesis, glutathione metabolism, and fatty acid metabolism, suggesting the importance of redox regulation in muscle metabolism and insulin action.

Temporal and pharmacological characterization of angiostatin release and generation by human platelets: implications for endothelial cell migration

Platelets play an important role in thrombosis and in neo-vascularisation as they release and produce factors that both promote and suppress angiogenesis. Amongst these factors is the angiogenesis inhibitor angiostatin, which is released during thrombus formation. The impact of anti-thrombotic agents and the kinetics of platelet angiostatin release are unknown. Hence, our objectives were to characterize platelet angiostatin release temporally and pharmacologically and to determine how angiostatin release influences endothelial cell migration, an early stage of angiogenesis. We hypothesized anti-platelet agents would suppress angiostatin release but not generation by platelets. Human platelets were aggregated and temporal angiostatin release was compared to vascular endothelial growth factor (VEGF). Immuno-gold electron microscopy and immunofluorescence microscopy identified α-granules as storage organelles of platelet angiostatin. Acetylsalicylic acid, MRS2395, GPIIb/IIIa blocking peptide, and aprotinin were used to characterize platelet angiostatin release and generation. An endothelial cell migration assay was performed under hypoxic conditions to determine the effects of pharmacological platelet and angiostatin inhibition. Compared to VEGF, angiostatin generation and release from α-granules occurred later temporally during platelet aggregation. Consequently, collagen-activated platelet releasates stimulated endothelial cell migration more potently than maximally-aggregated platelets. Platelet inhibitors prostacyclin, S-nitroso-glutathione, acetylsalicylic acid, and GPIIb/IIIa blocking peptide, but not a P2Y12 inhibitor, suppressed angiostatin release but not generation. Suppression of angiostatin generation in the presence of acetylsalicylic acid enhanced platelet-stimulated endothelial migration. Hence, the temporal and pharmacological modulation of platelet angiostatin release may have significant consequences for neo-vascularization following thrombus formation.

Effect of S-nitrosoglutathione on renal mitochondrial function: a new mechanism for reversible regulation of manganese superoxide dismutase activity?

Mitochondria are at the heart of all cellular processes as they provide the majority of the energy needed for various metabolic processes. Nitric oxide has been shown to have numerous roles in the regulation of mitochondrial function. Mitochondria have enormous pools of glutathione (GSH≈5-10 mM). Nitric oxide can react with glutathione to generate a physiological molecule, S-nitrosoglutathione (GSNO). The impact GSNO has on mitochondrial function has been intensively studied in recent years, and several mitochondrial electron transport chain complex proteins have been shown to be targeted by GSNO. In this study we investigated the effect of GSNO on mitochondrial function using normal rat proximal tubular kidney cells (NRK cells). GSNO treatment of NRK cells led to mitochondrial membrane depolarization and significant reduction in activities of mitochondrial complex IV and manganese superoxide dismutase enzyme (MnSOD). MnSOD is a critical endogenous antioxidant enzyme that scavenges excess superoxide radicals in the mitochondria. The decrease in MnSOD activity was not associated with a reduction in its protein levels and treatment of NRK cell lysate with dithiothreitol (a strong sulfhydryl-group-reducing agent) restored MnSOD activity to control values. GSNO is known to cause both S-nitrosylation and S-glutathionylation, which involve the addition of NO and GS groups, respectively, to protein sulfhydryl (SH) groups of cysteine residues. Endogenous GSH is an essential mediator in S-glutathionylation of cellular proteins, and the current studies revealed that GSH is required for MnSOD inactivation after GSNO or diamide treatment in rat kidney cells as well as in isolated kidneys. Further studies showed that GSNO led to glutathionylation of MnSOD; however, glutathionylated recombinant MnSOD was not inactivated. This suggests that a more complex pathway, possibly involving the participation of multiple proteins, leads to MnSOD inactivation after GSNO treatment. The major highlight of these studies is the fact that dithiothreitol can restore MnSOD activity after GSNO treatment. To our knowledge, this is the first study showing that MnSOD activity can be reversibly regulated in vivo, through a mechanism involving thiol residues.

Iron is involved in the maintenance of circadian period length in Arabidopsis

The homeostasis of iron (Fe) in plants is strictly regulated to maintain an optimal level for plant growth and development but not cause oxidative stress. About 30% of arable land is considered Fe deficient because of calcareous soil that renders Fe unavailable to plants. Under Fe-deficient conditions, Arabidopsis (Arabidopsis thaliana) shows retarded growth, disordered chloroplast development, and delayed flowering time. In this study, we explored the possible connection between Fe availability and the circadian clock in growth and development. Circadian period length in Arabidopsis was longer under Fe-deficient conditions, but the lengthened period was not regulated by the canonical Fe-deficiency signaling pathway involving nitric oxide. However, plants with impaired chloroplast function showed long circadian periods. Fe deficiency and impaired chloroplast function combined did not show additive effects on the circadian period, which suggests that plastid-to-nucleus retrograde signaling is involved in the lengthening of circadian period under Fe deficiency. Expression pattern analyses of the central oscillator genes in mutants defective in CIRCADIAN CLOCK ASSOCIATED1/LATE ELONGATED HYPOCOTYL or GIGANTEA demonstrated their requirement for Fe deficiency-induced long circadian period. In conclusion, Fe is involved in maintaining the period length of circadian rhythm, possibly by acting on specific central oscillators through a retrograde signaling pathway.

Regulation of guard cell photosynthetic electron transport by nitric oxide

Nitric oxide (NO) is one of the key elements in the complex signalling pathway leading to stomatal closure by inducing reversible protein phosphorylation and Ca(2+) release from intracellular stores. As photosynthesis in guard cells also contributes to stomatal function, the aim of this study was to explore the potential role of NO as a photosynthetic regulator. This work provides the first description of the reversible inhibition of the effect of NO on guard cell photosynthetic electron transport. Pulse amplitude modulation (PAM) chlorophyll fluorescence measurements on individual stomata of peeled abaxial epidermal strips indicated that exogenously applied 450nM NO rapidly increases the relative fluorescence yield, followed by a slow and constant decline. It was found that NO instantly decreases photochemical fluorescence quenching coefficients (qP and qL), the operating quantum efficiency of photosystem II (ΦPSII), and non-photochemical quenching (NPQ) to close to zero with different kinetics. NO caused a decrease in NPQ, which is followed by a slow and continuous rise. The removal of NO from the medium surrounding the epidermal strips using a rapid liquid perfusion system showed that the effect of NO on qP and ΦPSII, and thus on the linear electron transport rate through PSII (ETR), is reversible, and the constant rise in NPQ disappears, resulting in a near steady-state value. The reversible inhibition by NO of the ETR could be restored by bicarbonate, a compound known to compete with NO for one of the two coordination sites of the non-haem iron (II) in the QAFe(2+)QB complex.

Shoot to root communication is necessary to control the expression of iron-acquisition genes in Strategy I plants

Previous research showed that auxin, ethylene, and nitric oxide (NO) can activate the expression of iron (Fe)-acquisition genes in the roots of Strategy I plants grown with low levels of Fe, but not in plants grown with high levels of Fe. However, it is still an open question as to how Fe acts as an inhibitor and which pool of Fe (e.g., root, phloem, etc.) in the plant acts as the key regulator for gene expression control. To further clarify this, we studied the effect of the foliar application of Fe on the expression of Fe-acquisition genes in several Strategy I plants, including wild-type cultivars of Arabidopsis [Arabidopsis thaliana (L.) Heynh], pea [Pisum sativum L.], tomato [Solanum lycopersicon Mill.], and cucumber [Cucumis sativus L.], as well as mutants showing constitutive expression of Fe-acquisition genes when grown under Fe-sufficient conditions [Arabidopsis opt3-2 and frd3-3, pea dgl and brz, and tomato chln (chloronerva)]. The results showed that the foliar application of Fe blocked the expression of Fe-acquisition genes in the wild-type cultivars and in the frd3-3, brz, and chln mutants, but not in the opt3-2 and dgl mutants, probably affected in the transport of a Fe-related repressive signal in the phloem. Moreover, the addition of either ACC (ethylene precursor) or GSNO (NO donor) to Fe-deficient plants up-regulated the expression of Fe-acquisition genes, but this effect did not occur in Fe-deficient plants sprayed with foliar Fe, again suggesting the existence of a Fe-related repressive signal moving from leaves to roots.

Quantification of mitochondrial S-nitrosylation by CysTMT⁶ switch assay

S-nitrosylation (SNO) is an important oxidative posttranslational modification in the regulation of cardiac mitochondria. SNO modification of several mitochondrial proteins has been associated with cardiac preconditioning and improved cell survival following ischemia/reperfusion injury. Due to their labile nature, SNO modifications are challenging to study using traditional biochemical techniques; particularly, the identification of individual modified cysteine residues. Here, we describe the details of the cysTMT(6) switch assay, a variation of the classic biotin switch protocol. The cysTMT(6) reagent provides a simplified and powerful approach to SNO detection by combining unambiguous identification of the modified cysteine residue and relative quantification of up to six samples by mass spectrometry analysis.

The proteome response of potato leaves to priming agents and S-nitrosoglutathione

The primed mobilization for more potent defense responses to subsequent stress has been shown for many plant species, but there is a growing need to identify reliable molecular markers for this unique phenomenon. In the present study a proteomic approach was used to screen similarities in protein abundance in leaves of primed potato (Solanum tuberosum L.) treated with four well-known inducers of plant resistance, i.e. β-aminobutyric acid (BABA), γ-aminobutyric acid (GABA), Laminarin and 2,6-dichloroisonicotinic acid (INA), respectively. Moreover, to gain insight into the importance of nitric oxide (NO) in primed protein accumulation the potato leaves were supplied by S-nitrosoglutathione (GSNO), as an NO donor. The comparative analysis, using two-dimensional electrophoresis and mass spectrometry, revealed that among 25 proteins accumulated specifically after BABA, GABA, INA and Laminarin treatments, 13 proteins were accumulated also in response to GSNO. Additionally, overlapping proteomic changes between BABA-primed and GSNO-treated leaves showed 5 protein spots absent in the proteome maps obtained in response to the other priming agents. The identified 18 proteins belonged, in most cases, to functional categories of primary metabolism. The selected proteins including three redox-regulated enzymes, i.e. glyceraldehyde 3-phosphate dehydrogenase, carbonic anhydrase, and fructose-bisphosphate aldolase, were discussed in relation to the plant defence responses. Taken together, the overlapping effects in the protein profiles obtained between priming agents, GSNO and cPTIO treatments provide insight indicating that the primed potato exhibits unique changes in the primary metabolism, associated with selective protein modification via NO.