Nitrosative stress in plants

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.

Polyamines reprogram oxidative and nitrosative status and the proteome of citrus plants exposed to salinity stress

The interplay among polyamines (PAs) and reactive oxygen and nitrogen species (RNS and ROS) is emerging as a key issue in plant responses to salinity. To address this question, we analysed the impact of exogenous PAs [putrescine (Put), spermidine (Spd) and spermine (Spm)] on the oxidative and nitrosative status in citrus plants exposed to salinity. PAs partially reversed the NaCl-induced phenotypic and physiological disturbances. The expression of PA biosynthesis (ADC, SAMDC, SPDS and SPMS) and catabolism (DAO and PAO) genes was systematically up-regulated by PAs. In addition, PAs altered the oxidative status in salt-stressed plants as inferred by changes in ROS production and redox status accompanied by regulation of transcript expression and activities of various antioxidant enzymes. Furthermore, NaCl-induced up-regulation of NO-associated genes, such as NR, NADde, NOS-like and AOX, along with S-nitrosoglutathione reductase and nitrate reductase activities, was partially restored by PAs. Protein carbonylation and tyrosine nitration are depressed by specific PAs whereas protein S-nitrosylation was elicited by all PAs. Furthermore, we identified 271 S-nitrosylated proteins that were commonly or preferentially targeted by salinity and individual PAs. This work helps improve our knowledge on the plant's response to environmental challenge.

Aluminum induces cross-resistance of potato to Phytophthora infestans

The phenomenon of cross-resistance allows plants to acquire resistance to a broad range of stresses after previous exposure to one specific factor. Although this stress-response relationship has been known for decades, the sequence of events that underpin cross-resistance remains unknown. Our experiments revealed that susceptible potato (Solanum tuberosum L. cv. Bintje) undergoing aluminum (Al) stress at the root level showed enhanced defense responses correlated with reduced disease symptoms after leaf inoculation with Phytophthora infestans. The protection capacity of Al to subsequent stress was associated with the local accumulation of H2O2 in roots and systemic activation of salicylic acid (SA) and nitric oxide (NO) dependent pathways. The most crucial Al-mediated changes involved coding of NO message in an enhanced S-nitrosothiol formation in leaves tuned with an abundant SNOs accumulation in the main vein of leaves. Al-induced distal NO generation was correlated with the overexpression of PR-2 and PR-3 at both mRNA and protein activity levels. In turn, after contact with a pathogen we observed early up-regulation of SA-mediated defense genes, e.g. PR1, PR-2, PR-3 and PAL, and subsequent disease limitation. Taken together Al exposure induced distal changes in the biochemical stress imprint, facilitating more effective responses to a subsequent pathogen attack.

A probable crosstalk between Ca⁺², reactive oxygen species accumulation and scavenging mechanisms and modulation of protein kinase C activity during seed development in sunflower

Seed development in sunflower involves a gradual dehydration and accumulation of oil bodies in the cells of developing cotyledons during transition from 30 to 40 DAA stage. Reactive oxygen species (ROS) content decreased with seed maturation. NO content and NO contributed by putative nitric oxide synthase, however, did not change markedly. Superoxide dismutase (SOD) activity exhibited a peak at 30 DAA stage, indicating its scavenging role at the mid-stage of seed development. H₂O₂ produced as a result of SOD action is subsequently scavenged primarily by elevation of GR activity. Significant temporal differences were evident in GR and POD activity during seed development. Protein kinase C (PKC) activity also showed modulation during early stages of embryo and seed development. Use of PKC-specific fluorescent probe, Fim-1, and PKC inhibitors (staurosporine and bisindoylmaleamide) provided evidence for increase in PKC activity at 40 DAA stage with an increase in protein concentration (50 to 200 µg). Endogenous calcium content also increased with seed maturation. Tissue homogenates from 40 DAA stage showed enhanced fluorescence due to Fim-1-PKC binding in presence of calcium ions and its lowering due to calcium chelating agent (BAPTA). Western blot analysis revealed an increase in the intensity of 2 bands representing PKC with the advancement of seed maturation and their further upregulation by calcium. Present findings, thus, provide new information on the biochemical regulation of seed development in sunflower, with evidence for a possible correlation between calcium, ROS, their scavenging enzymes and "conventional" PKC activity.

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.

Peroxynitrite (ONOO-) is endogenously produced in arabidopsis peroxisomes and is overproduced under cadmium stress

BACKGROUND AND AIMS

Peroxisomes are subcellular compartments involved in multiple cellular metabolic pathways. Peroxynitrite (ONOO(-)) is a nitric oxide-derived molecule which is a nitrating species that causes nitration of proteins. This study used cell biology techniques to explore the potential presence of peroxynitrite in peroxisomes and evaluated its content under stress conditions (excess cadmium).

METHODS

Peroxynitrite, nitric oxide and superoxide anion were studied using cell-permeable specific fluorescent probes by confocal laser scanning microscopy in Arabidopsis thaliana transgenic plants expressing cyan fluorescent protein through the addition of peroxisomal targeting signal 1 (PTS1), which enables peroxisomes to be visualized in vivo. Key Results When no stress was applied, peroxynitrite was clearly localized in the peroxisomes of roots and stomatal guard cells. Under cadmium (150 μm) stress, the generation of peroxynitrite, nitric oxide and the superoxide anion (O2(·-)) increased and was localized in peroxisomes and the cytosol, participating in the generation of nitro-oxidative stress.

CONCLUSIONS

The results show that peroxisomes are an endogenous source of peroxynitrite, which is over-produced under cadmium stress, suggesting that the metabolism of reactive nitrogen species in peroxisomes could participate in the mechanism of the response to this heavy metal.

Effect of abiotic stress stimuli on S-nitrosoglutathione reductase in plants

S-nitrosylation of protein cysteine thiol groups has recently emerged as a widespread and important reversible post-translational protein modification, involved in redox signalling pathways of nitric oxide and reactive nitrogen species. S-nitrosoglutathione reductase (GSNOR), member of class III alcohol dehydrogenase family (EC 1.1.1.1), is considered the key enzyme in the catabolism of major low molecular S-nitrosothiol, S-nitrosoglutathione, and hence to control the level of protein S-nitrosylation. Changes of GSNOR activity after exposure to different abiotic stress conditions, including low and high temperature, continuous dark and de-etiolation, and mechanical injury, were investigated in important agricultural plants. Significantly higher GSNOR activity was found under normal conditions in leaves of Cucumis spp. genotype sensitive to biotrophic pathogen Golovinomyces cichoracearum. GSNOR activity was generally increased in all studied plants by all types of stress conditions. Strong down-regulation of GSNOR was observed in hypocotyls of etiolated pea plants, which did not recover to values of green plants even 168 h after the transfer of etiolated plants to normal light regime. These results point to important role of GSNOR during normal plant development and in plant responses to several types of abiotic stress conditions.

Inhibition of peroxisomal hydroxypyruvate reductase (HPR1) by tyrosine nitration

BACKGROUND

Protein tyrosine nitration is a post-translational modification (PTM) mediated by nitric oxide-derived molecules. Peroxisomes are oxidative organelles in which the presence of nitric oxide (NO) has been reported.

METHODS

We studied peroxisomal nitroproteome of pea leaves by high-performance liquid chromatography with tandem mass spectrometry (LC-MS/MS) and proteomic approaches.

RESULTS

Proteomic analysis of peroxisomes from pea leaves detected a total of four nitro-tyrosine immunopositive proteins by using an antibody against nitrotyrosine. One of these proteins was found to be the NADH-dependent hydroxypyruvate reductase (HPR). The in vitro nitration of peroxisomal samples caused a 65% inhibition of HPR activity. Analysis of recombinant peroxisomal NADH-dependent HPR1 activity from Arabidopsis in the presence of H2O2, NO, GSH and peroxynitrite showed that the ONOO(-) molecule caused the highest inhibition of activity (51% at 5mM SIN-1), with 5mM H2O2 having no inhibitory effect. Mass spectrometric analysis of the nitrated recombinant HPR1 enabled us to determine that, among the eleven tyrosine present in this enzyme, only Tyr-97, Tyr-108 and Tyr-198 were exclusively nitrated to 3-nitrotyrosine by peroxynitrite. Site-directed mutagenesis confirmed Tyr198 as the primary site of nitration responsible for the inhibition on the enzymatic activity by peroxynitrite.

CONCLUSION

These findings suggest that peroxisomal HPR is a target of peroxynitrite which provokes a loss of function.

GENERAL SIGNIFICANCE

This is the first report demonstrating the peroxisomal NADH-dependent HPR activity involved in the photorespiration pathway is regulated by tyrosine nitration, indicating that peroxisomal NO metabolism may contribute to the regulation of physiological processes under no-stress conditions.

Nitric oxide and phytohormone interactions: current status and perspectives

Nitric oxide (NO) is currently considered a ubiquitous signal in plant systems, playing significant roles in a wide range of responses to environmental and endogenous cues. During the signaling events leading to these plant responses, NO frequently interacts with plant hormones and other endogenous molecules, at times originating remarkably complex signaling cascades. Accumulating evidence indicates that virtually all major classes of plant hormones may influence, at least to some degree, the endogenous levels of NO. In addition, studies conducted during the induction of diverse plant responses have demonstrated that NO may also affect biosynthesis, catabolism/conjugation, transport, perception, and/or transduction of different phytohormones, such as auxins, gibberellins, cytokinins, abscisic acid, ethylene, salicylic acid, jasmonates, and brassinosteroids. Although still not completely elucidated, the mechanisms underlying the interaction between NO and plant hormones have recently been investigated in a number of species and plant responses. This review specifically focuses on the current knowledge of the mechanisms implicated in NO-phytohormone interactions during the regulation of developmental and metabolic plant events. The modifications triggered by NO on the transcription of genes encoding biosynthetic/degradative enzymes as well as proteins involved in the transport and signal transduction of distinct plant hormones will be contextualized during the control of developmental, metabolic, and defense responses in plants. Moreover, the direct post-translational modification of phytohormone biosynthetic enzymes and receptors through S-nitrosylation will also be discussed as a key mechanism for regulating plant physiological responses. Finally, some future perspectives toward a more complete understanding of NO-phytohormone interactions will also be presented and discussed.

Cross-talk interactions of exogenous nitric oxide and sucrose modulates phenylpropanoid metabolism in yellow lupine embryo axes infected with Fusarium oxysporum

The aim of the study was to examine cross-talk of exogenous nitric oxide (NO) and sucrose in the mechanisms of synthesis and accumulation of isoflavonoids in embryo axes of Lupinus luteus L. cv. Juno. It was verified whether the interaction of these molecules can modulate the defense response of axes to infection and development of the pathogenic fungus Fusarium oxysporum f. sp. lupini. Sucrose alone strongly stimulated a high level of genistein glucoside in axes pretreated with exogenous nitric oxide (SNP or GSNO) and non-pretreated axes. As a result of amplification of the signal coming from sucrose and GSNO, high isoflavonoids accumulation was observed (+Sn+GSNO). It needs to be stressed that infection in tissues pretreated with SNP/GSNO and cultured on the medium with sucrose (+Si+SNP/+Si+GSNO) very strongly enhances the accumulation of free isoflavone aglycones. In +Si+SNP axes phenylalanine ammonia-lyase activity was high up to 72h. As early as at 12h in +Si+SNP axes an increase was recorded in gene expression level of the specific isoflavonoid synthesis pathway. At 24h in +Si+SNP axes a very high total antioxidant capacity dependent on the pool of fast antioxidants was noted. Post-infection generation of semiquinone radicals was lower in axes with a high level of sucrose than with a deficit.

Nitrosative responses in citrus plants exposed to six abiotic stress conditions

Nitrosative status has emerged as a key component in plant response to abiotic stress; however, knowledge on its regulation by different environmental conditions remains unclear. The current study focused on nitrosative responses in citrus plants exposed to various abiotic stresses, including continuous light, continuous dark, heat, cold, drought and salinity. Morphological observations and physiological analysis showed that abiotic stress treatments were sensed by citrus plants. Furthermore, it was revealed that nitrosative networks are activated by environmental stress factors in citrus leaves as evidenced by increased nitrite (NO) content along with the release of NO and superoxide anion (O₂⁻) in the vascular tissues. The expression of genes potentially involved in NO production, such as NR, AOX, NADHox, NADHde, PAO and DAO, was affected by the abiotic stress treatments demonstrating that NO-derived nitrosative responses could be regulated by various pathways. In addition, S-nitrosoglutathione reductase (GSNOR) and nitrate reductase (NR) gene expression and enzymatic activity displayed significant changes in response to adverse environmental conditions, particularly cold stress. Peroxynitrite (ONOO⁻) scavenging ability of citrus plants was elicited by continuous light, dark or drought but was suppressed by salinity. In contrast, nitration levels were elevated by salinity and suppressed by continuous light or dark. Finally, S-nitrosylation patterns were enhanced by heat, cold or drought but were suppressed by dark or salinity. These results suggest that the nitrosative response of citrus plants is differentially regulated depending on the stress type and underscore the importance of nitrosative status in plant stress physiology.

Nuclear accumulation of cytosolic glyceraldehyde-3-phosphate dehydrogenase in cadmium-stressed Arabidopsis roots

NAD-dependent glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a ubiquitous enzyme involved in the glycolytic pathway. It has been widely demonstrated that mammalian GAPDH, in addition to its role in glycolysis, fulfills alternative functions mainly linked to its susceptibility to oxidative posttranslational modifications. Here, we investigated the responses of Arabidopsis (Arabidopsis thaliana) cytosolic GAPDH isoenzymes GAPC1 and GAPC2 to cadmium-induced stress in seedlings roots. GAPC1 was more responsive to cadmium than GAPC2 at the transcriptional level. In vivo, cadmium treatments induced different concomitant effects, including (1) nitric oxide accumulation, (2) cytosolic oxidation (e.g. oxidation of the redox-sensitive Green fluorescent protein2 probe), (3) activation of the GAPC1 promoter, (4) GAPC1 protein accumulation in enzymatically inactive form, and (5) strong relocalization of GAPC1 to the nucleus. All these effects were detected in the same zone of the root tip. In vitro, GAPC1 was inactivated by either nitric oxide donors or hydrogen peroxide, but no inhibition was directly provided by cadmium. Interestingly, nuclear relocalization of GAPC1 under cadmium-induced oxidative stress was stimulated, rather than inhibited, by mutating into serine the catalytic cysteine of GAPC1 (C155S), excluding an essential role of GAPC1 nitrosylation in the mechanism of nuclear relocalization, as found in mammalian cells. Although the function of GAPC1 in the nucleus is unknown, our results suggest that glycolytic GAPC1, through its high sensitivity to the cellular redox state, may play a role in oxidative stress signaling or protection in plants.

Hydrogen sulfide induces systemic tolerance to salinity and non-ionic osmotic stress in strawberry plants through modification of reactive species biosynthesis and transcriptional regulation of multiple defence pathways

Hydrogen sulfide (H2S) has been recently found to act as a potent priming agent. This study explored the hypothesis that hydroponic pretreatment of strawberry (Fragaria × ananassa cv. Camarosa) roots with a H2S donor, sodium hydrosulfide (NaHS; 100 μM for 48 h), could induce long-lasting priming effects and tolerance to subsequent exposure to 100mM NaCI or 10% (w/v) PEG-6000 for 7 d. Hydrogen sulfide pretreatment of roots resulted in increased leaf chlorophyll fluorescence, stomatal conductance and leaf relative water content as well as lower lipid peroxidation levels in comparison with plants directly subjected to salt and non-ionic osmotic stress, thus suggesting a systemic mitigating effect of H2S pretreatment to cellular damage derived from abiotic stress factors. In addition, root pretreatment with NaHS resulted in the minimization of oxidative and nitrosative stress in strawberry plants, manifested via lower levels of synthesis of NO and H(2)O(2) in leaves and the maintenance of high ascorbate and glutathione redox states, following subsequent salt and non-ionic osmotic stresses. Quantitative real-time RT-PCR gene expression analysis of key antioxidant (cAPX, CAT, MnSOD, GR), ascorbate and glutathione biosynthesis (GCS, GDH, GS), transcription factor (DREB), and salt overly sensitive (SOS) pathway (SOS2-like, SOS3-like, SOS4) genes suggests that H2S plays a pivotal role in the coordinated regulation of multiple transcriptional pathways. The ameliorative effects of H2S were more pronounced in strawberry plants subjected to both stress conditions immediately after NaHS root pretreatment, rather than in plants subjected to stress conditions 3 d after root pretreatment. Overall, H2S-pretreated plants managed to overcome the deleterious effects of salt and non-ionic osmotic stress by controlling oxidative and nitrosative cellular damage through increased performance of antioxidant mechanisms and the coordinated regulation of the SOS pathway, thus proposing a novel role for H2S in plant priming, and in particular in a fruit crop such as strawberry.

Rapid auxin-induced nitric oxide accumulation and subsequent tyrosine nitration of proteins during adventitious root formation in sunflower hypocotyls

Using NO specific probe (MNIP-Cu), rapid nitric oxide (NO) accumulation as a response to auxin (IAA) treatment has been observed in the protoplasts from the hypocotyls of sunflower seedlings (Helianthus annuus L.). Incubation of protoplasts in presence of NPA (auxin efflux blocker) and PTIO (NO scavenger) leads to significant reduction in NO accumulation, indicating that NO signals represent an early signaling event during auxin-induced response. A surge in NO production has also been demonstrated in whole hypocotyl explants showing adventitious root (AR) development. Evidence of tyrosine nitration of cytosolic proteins as a consequence of NO accumulation has been provided by western blot analysis and immunolocalization in the sections of AR producing hypocotyl segments. Most abundant anti-nitrotyrosine labeling is evident in proteins ranging from 25-80 kDa. Tyrosine nitration of a particular protein (25 kDa) is completely absent in presence of NPA (which suppresses AR formation). Similar lack of tyrosine nitration of this protein is also evident in other conditions which do not allow AR differentiation. Immunofluorescent localization experiments have revealed that non-inductive treatments (such as PTIO) for AR develpoment from hypocotyl segments coincide with symplastic and apoplastic localization of tyrosine nitrated proteins in the xylem elements, in contrast with negligible (and mainly apoplastic) nitration of proteins in the interfascicular cells and phloem elements. Application of NPA does not affect tyrosine nitration of proteins even in the presence of an external source of NO (SNP). Tyrosine nitrated proteins are abundant around the nuclei in the actively dividing cells of the root primordium. Thus, NO-modulated rapid response to IAA treatment through differential distribution of tyrosine nitrated proteins is evident as an inherent aspect of the AR development.

Rapid auxin-induced nitric oxide accumulation and subsequent tyrosine nitration of proteins during adventitious root formation in sunflower hypocotyls

Using NO specific probe (MNIP-Cu), rapid nitric oxide (NO) accumulation as a response to auxin (IAA) treatment has been observed in the protoplasts from the hypocotyls of sunflower seedlings (Helianthus annuus L.). Incubation of protoplasts in presence of NPA (auxin efflux blocker) and PTIO (NO scavenger) leads to significant reduction in NO accumulation, indicating that NO signals represent an early signaling event during auxin-induced response. A surge in NO production has also been demonstrated in whole hypocotyl explants showing adventitious root (AR) development. Evidence of tyrosine nitration of cytosolic proteins as a consequence of NO accumulation has been provided by western blot analysis and immunolocalization in the sections of AR producing hypocotyl segments. Most abundant anti-nitrotyrosine labeling is evident in proteins ranging from 25-80 kDa. Tyrosine nitration of a particular protein (25 kDa) is completely absent in presence of NPA (which suppresses AR formation). Similar lack of tyrosine nitration of this protein is also evident in other conditions which do not allow AR differentiation. Immunofluorescent localization experiments have revealed that non-inductive treatments (such as PTIO) for AR develpoment from hypocotyl segments coincide with symplastic and apoplastic localization of tyrosine nitrated proteins in the xylem elements, in contrast with negligible (and mainly apoplastic) nitration of proteins in the interfascicular cells and phloem elements. Application of NPA does not affect tyrosine nitration of proteins even in the presence of an external source of NO (SNP). Tyrosine nitrated proteins are abundant around the nuclei in the actively dividing cells of the root primordium. Thus, NO-modulated rapid response to IAA treatment through differential distribution of tyrosine nitrated proteins is evident as an inherent aspect of the AR development.

Salinity-induced changes in S-nitrosylation of pea mitochondrial proteins

Together with reactive oxygen species, nitric oxide is an essential part of the signal transduction induced by stress conditions. In this work we study the pattern of S-nitrosylated proteins from mitochondria of pea plants subjected to 150mM NaCl for 5 and 14days. A differential pattern of target proteins was found during plant development and salt stress, with a minor number of S-nitrosylated proteins at 14 days specifically some key enzymes related to respiration and photorespiration. At this time of stress, only ATP synthase β subunit, peroxiredoxin and Hsp90 were S-nitrosylated and no changes in protein levels were observed, although the activity of PrxII F may be reduced by S-nitrosylation. The NADH/NAD(+) ratio was also high at 14days but not the NADPH/NADP(+). An enhancement in NO measured by fluorimetry and confocal microscopy was observed in leaves, being part of the NO localized in mitochondria. An increase in mitochondrial GSNOR activity was produced in response to short and long-term NaCl treatment, where a higher number of nitrated proteins were also observed. The results indicated that posttranslational modifications seem to modulate respiratory and photorespiratory pathways, as well as some antioxidant enzymes, through differential S-nitrosylation/denitrosylation in control conditions and under salt stress.

Response of mitochondrial antioxidant system and respiratory pathways to reactive nitrogen species in pea leaves

Nitric oxide (NO) has emerged as an important signaling molecule in plants, but little is known about the effects of reactive nitrogen species in plant mitochondria. In this study, the effects of DETA-NONOate, a pure NO slow generator, and of SIN-1 (3-morpholinosydnonimine), a peroxynitrite producer, on the activities of respiratory pathways, enzymatic and non-enzymatic antioxidants have been investigated in isolated mitochondria from pea leaves. No significant changes in lipid peroxidation, protein oxidation or in ascorbate and glutathione redox state were observed after DETA-NONOate treatments whereas cytochrome pathway (CP) respiration was reversibly inhibited and alternative pathway (AP) respiration showed little inhibition. On the other hand, NO did not affect neither activities of Mn superoxide dismutase (Mn-SOD) nor enzymes involved in the ascorbate and glutathione regeneration in mitochondria except for ascorbate peroxidase (APX), which was reversely inhibited depending on ascorbate concentration. Finally, SIN-1 treatment of mitochondria produced a decrease in CP respiration, an increase in protein oxidation and strongly inhibited APX activity (90%), with glutathione reductase and dehydroascorbate reductase (DHAR) being moderately inhibited (30 and 20%, respectively). This treatment did not affect monodehydroascorbate reductase (MDHAR) and Mn-SOD activities. Results showed that mitochondrial nitrosative stress was not necessarily accompanied by oxidative stress. We suggest that NO-resistant AP and mitochondrial APX may be important components of the H(2) O(2) -signaling pathways under nitrosative stress induced by NO in this organelle. Also, MDHAR and DHAR, via ascorbate regeneration, could constitute an essential antioxidant defense together with Mn-SOD, against NO and ONOO(-) stress in plant mitochondria.

A comparative proteomics analysis of soybean leaves under biotic and abiotic treatments

A comparative proteomic study was made to explore the molecular mechanisms, which underlie soybean root and stem defense response caused by the oomycete Phytophthora sojae strain P6497. Soybean (Glycine max cv. Xinyixiaoheidou) seedling roots were incubated in salicylic acid, methyl jasmonate, 1-amino cyclopropane-1-carboxylic acid, hydrogen peroxide, sodium nitroprusside, vitamin B(1) and P. sojae zoosperm in order to determine whether the corresponding leaves play a role in the defense response at the proteomic level. The results showed that the proteome of leaves had no significant differences. Of the 21 identified proteins identified in the study, 62 % were involved in predominately in energy functions. Those involved in protein synthesis, secondary metabolism and metabolism categories followed in abundance, where proteins involved as transporters and in transcription were the least and represented only 5 %. Those related to energy were shown to be involved in photosynthesis and photorespiration activities. The present study provides important information with regards to proteomic methods aimed to study protein regulations of the soybean-P. sojae pathosystem, especially in terms of host resistance to this pathogen.

Mitochondria are an early target of oxidative modifications in senescing legume nodules

Legume nodule senescence is a poorly understood process involving a decrease in N(2) fixation and an increase in proteolytic activity. Some physiological changes during nodule aging have been reported, but scarce information is available at the subcellular level. Biochemical, immunological and proteomic approaches were used to provide insight into the effects of aging on the mitochondria and cytosol of nodule host cells. In the mitochondria, the oxidative modification of lipids and proteins was associated with a marked decline in glutathione, a reduced capacity to regenerate ascorbate, and upregulation of alternative oxidase and manganese superoxide dismutase. In the cytosol, there were consistent reductions in the protein concentrations of carbon metabolism enzymes, inhibition of protein synthesis and increase in serine proteinase activity, disorganization of cytoskeleton, and a sharp reduction of cytosolic proteins, but no detectable accumulation of oxidized molecules. We conclude that nodule mitochondria are an early target of oxidative modifications and a likely source of redox signals. Alternative oxidase and manganese superoxide dismutase may play important roles in controlling ROS concentrations and the redox state of mitochondria. The finding that specific methionine residues of a cytosolic glutamine synthetase isoform are sulfoxidized suggests a regulatory role of this enzyme in senescing nodules.

Protein tyrosine nitration in pea roots during development and senescence

Protein tyrosine nitration is a post-translational modification mediated by reactive nitrogen species (RNS) that is associated with nitro-oxidative damage. No information about this process is available in relation to higher plants during development and senescence. Using pea plants at different developmental stages (ranging from 8 to 71 days), tyrosine nitration in the main organs (roots, stems, leaves, flowers, and fruits) was analysed using immunological and proteomic approaches. In the roots of 71-day-old senescent plants, nitroproteome analysis enabled the identification a total of 16 nitrotyrosine-immunopositive proteins. Among the proteins identified, NADP-isocitrate dehydrogenase (ICDH), an enzyme involved in the carbon and nitrogen metabolism, redox regulation, and responses to oxidative stress, was selected to evaluate the effect of nitration. NADP-ICDH activity fell by 75% during senescence. Analysis showed that peroxynitrite inhibits recombinant cytosolic NADP-ICDH activity through a process of nitration. Of the 12 tyrosines present in this enzyme, mass spectrometric analysis of nitrated recombinant cytosolic NADP-ICDH enabled this study to identify the Tyr392 as exclusively nitrated by peroxynitrite. The data as a whole reveal that protein tyrosine nitration is a nitric oxide-derived PTM prevalent throughout root development and intensifies during senescence.

Modulating protein function through reversible oxidation: Redox-mediated processes in plants revealed through proteomics

It has been clearly demonstrated that plants redox control can be exerted over virtually every cellular metabolic pathway affecting metabolic homeostasis and energy balance. Therefore, a tight link exists between cellular/compartmental steady-state redox level and cellular metabolism. Proteomics offers a powerful new way to characterize the response and regulation of protein oxidation in different cell types and in relation to cellular metabolism. Compelling evidence revealed in proteomics studies suggests the integration of the redox network with other cellular signaling pathways such as Ca(2+) and/or protein phosphorylation, jasmonic, salicylic, abscisic acids, ethylene, and other phytohormones. Here we review progress in using the various proteomics techniques and approaches to answer biological questions arising from redox signaling and from changes in redox status of the cell. The focus is on reversible redox protein modifications and on three main processes, namely oxidative and nitrosative stress, defense against pathogens, cellular redox response and regulation, drawing on examples from plant redox proteomics studies.

Peroxisomes as cell generators of reactive nitrogen species (RNS) signal molecules

Nitric oxide is a gaseous free radical with a wide range of direct and indirect actions in plant cells. However, the enzymatic sources of NO and its subcellular localization in plants are still under debate. Among the different subcellular compartments where NO has been found to be produced, peroxisomes are the best characterized since in these organelles it has been demonstrated the presence of NO and it has been biochemically characterized a L-arginine-dependent nitric oxide synthase activity. This chapter summarizes the present knowledge of the NO metabolism and its derived reactive nitrogen species (RNS) in plant peroxisomes and how this gaseous free radical is involved in natural senescence, and is released to the cytosol under salinity stress conditions acting as a signal molecule.

Protein tyrosine nitration in higher plants grown under natural and stress conditions

Protein tyrosine nitration is a post-translational modification (PTM) mediated by reactive nitrogen species (RNS) that is linked to nitro-oxidative damages in plant cells. During the last decade, the identification of proteins undergoing this PTM under adverse environmental conditions has increased. However, there is also a basal endogenous nitration which seems to have a regulatory function. The technological advances in proteome analysis have allowed identifying these modified proteins and have shown that the number and identity of the nitrated proteins change among plant species, analysed organs and growing/culture conditions. In this work, the current knowledge of protein tyrosine nitration in higher plants under different situations is reviewed.

Effect of elevated CO₂ on phosphorus nutrition of phosphate-deficient Arabidopsis thaliana (L.) Heynh under different nitrogen forms

Phosphorus (P) nutrition is always a key issue regarding plants responses to elevated CO(2). Yet it is unclear of how elevated CO(2) affects P uptake under different nitrogen (N) forms. This study investigated the influence of elevated CO(2) (800 µl l(-1)) on P uptake and utilization by Arabidopsis grown in pH-buffered phosphate (P)-deficient (0.5 µM) hydroponic culture supplying with 2mM nitrate (NO(3)(-)) or ammonium (NH(4)(+)). After 7 d treatment, elevated CO(2) enhanced the biomass production of both NO(3)(-)- and NH(4) (+)-fed plants but decreased the P amount absorbed per weight of roots and the P concentration in the shoots of plants supplied with NH(4)(+). In comparison, elevated CO(2) increased the amount of P absorbed per weight of roots, as well as the P concentration in plants and alleviated P deficiency-induced symptoms of plants supplied with NO(3)(-). Elevated CO(2) also increased the root/shoot ratio, total root surface area, and acid phosphatase activity, and enhanced the expression of genes or transcriptional factors involving in P uptake, allocation and remobilization in P deficient plants. Furthermore, elevated CO(2) increased the nitric oxide (NO) level in roots of NO(3)(-)-fed plants but decreased it in NH(4)(+)-fed plants. NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO) inhibited plant P acquisition by roots under elevated CO(2). Considering all of these findings, this study concluded that a combination of elevated CO(2) and NO(3)(-) nutrition can induce a set of plant adaptive strategies to improve P status from P-deficient soluble sources and that NO may be a signalling molecule that controls these processes.

Structural and functional characterization of a plant S-nitrosoglutathione reductase from Solanum lycopersicum

S-nitrosoglutathione reductase (GSNOR), also known as S-(hydroxymethyl)glutathione (HMGSH) dehydrogenase, belongs to the large alcohol dehydrogenase superfamily, namely to the class III ADHs. GSNOR catalyses the oxidation of HMGSH to S-formylglutathione using a catalytic zinc and NAD(+) as a coenzyme. The enzyme also catalyses the NADH-dependent reduction of S-nitrosoglutathione (GSNO). In plants, GSNO has been suggested to serve as a nitric oxide (NO) reservoir locally or possibly as NO donor in distant cells and tissues. NO and NO-related molecules such as S-nitrosothiols (S-NOs) play a central role in the regulation of normal plant physiological processes and host defence. The enzyme thus participates in the cellular homeostasis of S-NOs and in the metabolism of reactive nitrogen species. Although GSNOR has recently been characterized from several organisms, this study represents the first detailed biochemical and structural characterization of a plant GSNOR, that from tomato (Solanum lycopersicum). SlGSNOR gene expression is higher in roots and stems compared to leaves of young plants. It is highly expressed in the pistil and stamens and in fruits during ripening. The enzyme is a dimer and preferentially catalyses reduction of GSNO while glutathione and S-methylglutathione behave as non-competitive inhibitors. Using NAD(+), the enzyme oxidizes HMGSH and other alcohols such as cinnamylalcohol, geraniol and ω-hydroxyfatty acids. The crystal structures of the apoenzyme, of the enzyme in complex with NAD(+) and in complex with NADH, solved up to 1.9 Å resolution, represent the first structures of a plant GSNOR. They confirm that the binding of the coenzyme is associated with the active site zinc movement and changes in its coordination. In comparison to the well characterized human GSNOR, plant GSNORs exhibit a difference in the composition of the anion-binding pocket, which negatively influences the affinity for the carboxyl group of ω-hydroxyfatty acids.

Nitric oxide-dependent posttranslational modification in plants: an update

Nitric oxide (NO) has been demonstrated as an essential regulator of several physiological processes in plants. The understanding of the molecular mechanism underlying its critical role constitutes a major field of research. NO can exert its biological function through different ways, such as the modulation of gene expression, the mobilization of second messengers, or interplays with protein kinases. Besides this signaling events, NO can be responsible of the posttranslational modifications (PTM) of target proteins. Several modifications have been identified so far, whereas metal nitrosylation, the tyrosine nitration and the S-nitrosylation can be considered as the main ones. Recent data demonstrate that these PTM are involved in the control of a wide range of physiological processes in plants, such as the plant immune system. However, a great deal of effort is still necessary to pinpoint the role of each PTM in plant physiology. Taken together, these new advances in proteomic research provide a better comprehension of the role of NO in plant signaling.

Fluorogenic tagging of protein 3-nitrotyrosine with 4-(aminomethyl)benzene sulfonate in tissues: a useful alternative to Immunohistochemistry for fluorescence microscopy imaging of protein nitration

Protein tyrosine nitration is a common biomarker of biological aging and diverse pathologies associated with the excessive formation of reactive oxygen and nitrogen species. Recently, we suggested a novel fluorogenic derivatization procedure for the detection of 3-nitrotyrosine (3-NT) using benzylamine derivatives to convert specifically protein- or peptide-bound 3-NT to a highly fluorescent benzoxazole product. In this study, we applied this procedure to fluorogenic derivatization of protein 3-NT in sections from adult rat cerebellum to: (i) test this method for imaging nitrated proteins in fixed brain tissue sections and (ii) compare the chemical approach to immunohistochemical labeling with anti-3-NT antibodies. Immunofluorescence analysis of cerebellar sections using anti-3-NT antibodies showed differential levels of immunostaining in the molecular, Purkinje, and granule cell layers of the cerebellar cortex; in agreement with previous reports, the Purkinje cells were most highly labeled. Importantly, fluorogenic derivatization reactions of cerebellar proteins with 4-(aminomethyl)benzene sulfonic acid (ABS) and K(3)Fe(CN)(6) at pH 9, after sodium dithionite reduction of 3-NT to 3-aminotyrosine, showed a very similar pattern of relative intensity of cell labeling and improved resolution compared with antibody labeling. Our data demonstrate that ABS derivatization may be either a useful alternative to or a complementary approach to immunolabeling in imaging protein nitration in cells and tissues, including under conditions of dual labeling with antibodies to cell proteins, thus allowing for cellular colocalization of nitrated proteins and any protein of interest.

Nitric oxide-mediated stress imprint in potato as an effect of exposure to a priming agent

We investigated how potato exposed to a chemical agent could activate nitric oxide (NO)-dependent events facilitating more potent defense responses to a subsequent pathogen attack. Obtained data revealed that all applied inducers, i.e., β-aminobutyric acid (BABA), γ-aminobutyric acid (GABA), laminarin, or 2,6-dichloroisonicotinic acid (INA), were active stimuli in potentiating NO synthesis in the primed potato. It is assumed, for the mechanism proposed in this paper, that priming involves reversible S-nitrosylated protein (S-nitrosothiols [SNO]) storage as one of the short-term stress imprint components, apart from epigenetic changes sensitized by NO. Based on BABA- and GABA-induced events, it should be stated that a rise in NO generation and coding the NO message in SNO storage at a relatively low threshold together with histone H2B upregulation might create short-term imprint activation, facilitating acquisition of a competence to react faster after challenge inoculation. Laminarin elicited strong NO upregulation with an enhanced SNO pool-altered biochemical imprint in the form of less effective local recall, nevertheless being fully protective in distal responses against P. infestans. In turn, INA showed the most intensified NO generation and abundant formation of SNO, both after the inducer treatment and challenge inoculation abolishing potato resistance against the pathogen. Our results indicate, for the first time, that a precise control of synthesized NO in cooperation with reversible SNO storage and epigenetic modifications might play an important role in integrating and coordinating defense potato responses in the priming phenomenon.

Oxidative and nitrosative-based signaling and associated post-translational modifications orchestrate the acclimation of citrus plants to salinity stress

Reactive oxygen and nitrogen species are involved in a plethora of cellular responses in plants; however, our knowledge on the outcomes of oxidative and nitrosative signaling is still unclear. To better understand how oxidative and nitrosative signals are integrated to regulate cellular adjustments to external conditions, local and systemic responses were investigated in the roots and leaves of sour orange plants (Citrus aurantium L.) after root treatment with hydrogen peroxide (H(2) O(2) ) or sodium nitroprusside (a nitric oxide donor), followed by NaCl stress for 8 days. Phenotypic and physiological data showed that pre-exposure to these treatments induced an acclimation to subsequent salinity stress that was accompanied by both local and systemic H(2) O(2) and nitric oxide (NO) accumulation. Combined histochemical and fluorescent probe approaches showed the existence of a vascular-driven long-distance reactive oxygen species and NO signaling pathway. Transcriptional analysis of genes diagnostic for H(2) O(2) and NO signaling just after treatments or after 8 days of salt stress revealed tissue- and time-specific mechanisms controlling internal H(2) O(2) and NO homeostasis. Furthermore, evidence is presented showing that protein carbonylation, nitration and S-nitrosylation are involved in acclimation to salinity stress. In addition, this work enabled characterization of potential carbonylated, nitrated and nitrosylated proteins with distinct or overlapping signatures. This work provides a framework to better understand the oxidative and nitrosative priming network in citrus plants subjected to salinity conditions.

Detection of S-nitrosothiol and nitrosylated proteins in Arachis hypogaea functional nodule: response of the nitrogen fixing symbiont

To detect the presence of NO, ROS and RNS in nodules of crack entry legumes, we used Arachis hypogaea functional nodule. The response of two cognate partner rhizobia was compared towards NO and GSNO using S. meliloti and Bradyrhizobium sp NC921001. ROS, NO, nitrosothiol and bacteroids were detected by fluorescence microscopy. Redox enzymes and thiol pools were detected biochemically. Nitrosothiols were found to be present but ROS and NO were absent in A. hypogaea nodule. A number of S-nitrosylated proteins were also detected. The total thiol pool and most of the redox enzymes were low in nodule cytosolic extract but these were found to be high in the partner microorganisms indicating partner rhizobia could protect the nodule environment against the nitrosothiols. Both S. meliloti and Bradyrhizobium sp NC921001 were found to contain GSNO reductase. Interestingly, there was a marked difference in growth pattern between S. meliloti and Bradyrhizobium sp in presence of sodium nitroprusside (SNP) and S-nitrosoglutathione (GSNO). Bradyrhizobium sp was found to be much more tolerant to NO donor compounds than the S. meliloti. In contrast, S. meliloti showed resistance to GSNO but was sensitive to SNP. Together our data indicate that nodule environment of crack entry legumes is different than the nodules of infection mode entry in terms of NO, ROS and RNS. Based on our biochemical characterization, we propose that exchange of redox molecules and reactive chemical species is possible between the bacteroid and nodule compartment.

Nitric oxide is involved in light-specific responses of tomato during germination under normal and osmotic stress conditions

BACKGROUND AND AIMS

Nitric oxide (NO) is involved in the signalling and regulation of plant growth and development and responses to biotic and abiotic stresses. The photoperiod-sensitive mutant 7B-1 in tomato (Solanum lycopersicum) showing abscisic acid (ABA) overproduction and blue light (BL)-specific tolerance to osmotic stress represents a valuable model to study the interaction between light, hormones and stress signalling. The role of NO as a regulator of seed germination and ABA-dependent responses to osmotic stress was explored in wild-type and 7B-1 tomato under white light (WL) and BL.

METHODS

Germination data were obtained from the incubation of seeds on germinating media of different composition. Histochemical analysis of NO production in germinating seeds was performed by fluorescence microscopy using a cell-permeable NO probe, and endogenous ABA was analysed by mass spectrometry.

KEY RESULTS

The NO donor S-nitrosoglutathione stimulated seed germination, whereas the NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) had an inhibitory effect. Under WL in both genotypes, PTIO strongly suppressed germination stimulated by fluridone, an ABA inhibitor. The stimulatory effect of the NO donor was also observed under osmotic stress for 7B-1 seeds under WL and BL. Seed germination inhibited by osmotic stress was restored by fluridone under WL, but less so under BL, in both genotypes. This effect of fluridone was further modulated by the NO donor and NO scavenger, but only to a minor extent. Fluorescence microscopy using the cell-permeable NO probe DAF-FM DA (4-amino-5-methylamino-2',7'-difluorofluorescein diacetate) revealed a higher level of NO in stressed 7B-1 compared with wild-type seeds.

CONCLUSIONS

As well as defective BL signalling, the differential NO-dependent responses of the 7B-1 mutant are probably associated with its high endogenous ABA concentration and related impact on hormonal cross-talk in germinating seeds. These data confirm that light-controlled seed germination and stress responses include NO-dependent signalling.

Protein S-nitrosylation: what's going on in plants?

Nitric oxide (NO) is now recognized as a key regulator of plant physiological processes. Understanding the mechanisms by which NO exerts its biological functions has been the subject of extensive research. Several components of the signaling pathways relaying NO effects in plants, including second messengers, protein kinases, phytohormones, and target genes, have been characterized. In addition, there is now compelling experimental evidence that NO partly operates through posttranslational modification of proteins, notably via S-nitrosylation and tyrosine nitration. Recently, proteome-wide scale analyses led to the identification of numerous protein candidates for S-nitrosylation in plants. Subsequent biochemical and in silico structural studies revealed certain mechanisms through which S-nitrosylation impacts their functions. Furthermore, first insights into the physiological relevance of S-nitrosylation, particularly in controlling plant immune responses, have been recently reported. Collectively, these discoveries greatly extend our knowledge of NO functions and of the molecular processes inherent to signal transduction in plants.

Nitric oxide implication in cadmium-induced programmed cell death in roots and signaling response of yellow lupine plants

The sequence of events leading to the programmed cell death (PCD) induced by heavy metals in plants is still the object of extensive investigation. In this study we showed that roots of 3-day old yellow lupine (Lupinus luteus L.) seedlings exposed to cadmium (Cd, 89μM CdCl(2)) resulted in PCD starting from 24h of stress duration, which was evidenced by TUNEL-positive reaction. Cd-induced PCD was preceded by a relatively early burst of nitric oxide (NO) localized mainly in the root tips. Above changes were accompanied by the NADPH-oxidase-dependent superoxide anion (O(2)(·-)) production. However, the concomitant high level of both NO and O(2)(·-) at the 24th h of Cd exposure did not provoke an enhanced peroxynitrite formation. The treatment with the NADPH-oxidase inhibitor and NO-scavenger significantly reduced O(2)(·-) and NO production, respectively, as well as diminished the pool of cells undergoing PCD. The obtained data indicate that boosted NO and O(2)(·-) production is required for Cd-induced PCD in lupine roots. Moreover, we found that in roots of 14-day old lupine plants the NO-dependent Cd-induced PCD was correlated with the enhanced level of the post-stress signals in leaves, including distal NO cross-talk with hydrogen peroxide.

Nitric oxide as a critical factor for perception of UV-B irradiation by microtubules in Arabidopsis

Influence of ultraviolet-B (UV-B) as an abiotic stress factor on plant microtubules (MTs) and involvement of nitric oxide (NO) as a secondary messenger mediating plant cell response to environmental stimuli were investigated in this study. Taking into account that endogenous NO content in plant cells has been shown to be increased under a broad range of abiotic stress factors, the effects of UV-B irradiation and also the combined action of UV-B and NO donor sodium nitroprusside (SNP) or NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO) on the MTs organization in different root cells of Arabidopsis thaliana were tested. Subsequently, realization of the MT-mediated processes such as root growth and development was studied under these conditions. Arabidopsis thaliana seedlings expressing the chimeric gene gfp-map4 were exposed to the enhanced UV-B with or without SNP or c-PTIO pretreatment. The UV-B irradiation alone led to a dose-dependent root growth inhibition and to morphological alterations of the primary root manifested in their swelling and excessive root hair formation. Moreover, dose-dependent randomization and depolymerization of MTs in both epidermal and cortical cells under the enhanced UV-B were found. However, SNP pretreatment of the UV-B irradiated A. thaliana seedlings recovered the UV-B inhibited root growth as compared to c-PTIO pretreatment. It has been shown that in 24 h after UV-B irradiation the organization of MTs in root epidermal cells of SNP-pretreated A. thaliana seedlings was partially recovered, whereas in c-PTIO-pretreated ones the organization of MTs has not been distinctly improved. Therefore, we suppose that the enhanced NO levels in plant cells can protect MTs organization as well as MT-related processes of root growth and development against disrupting effects of UV-B.

Arsenic triggers the nitric oxide (NO) and S-nitrosoglutathione (GSNO) metabolism in Arabidopsis

Environmental contamination by arsenic constitutes a problem in many countries, and its accumulation in food crops may pose health complications for humans. Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are involved at various levels in the mechanism of responding to environmental stress in higher plants. Using Arabidopsis seedlings exposed to different arsenate concentrations, physiological and biochemical parameters were analyzed to determine the status of ROS and RNS metabolisms. Arsenate provoked a significant reduction in growth parameters and an increase in lipid oxidation. These changes were accompanied by an alteration in antioxidative enzymes and the nitric oxide (NO) metabolism, with a significant increase in NO content, S-nitrosoglutathione reductase (GSNOR) activity and protein tyrosine nitration as well as a concomitant reduction in glutathione and S-nitrosoglutathione (GSNO) content. Our results indicate that 500 μM arsenate (AsV) causes nitro-oxidative stress in Arabidopsis, being the glutathione reductase and the GSNOR activities clearly affected.

NADP-dependent isocitrate dehydrogenase from Arabidopsis roots contributes in the mechanism of defence against the nitro-oxidative stress induced by salinity

NADPH regeneration appears to be essential in the mechanism of plant defence against oxidative stress. Plants contain several NADPH-generating dehydrogenases including isocitrate dehydrogenase (NADP-ICDH), glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH), and malic enzyme (ME). In Arabidopsis seedlings grown under salinity conditions (100 mM NaCl) the analysis of physiological parameters, antioxidant enzymes (catalase and superoxide dismutase) and content of superoxide radical (O₂^∙−), nitric oxide (NO), and peroxynitrite (ONOO⁻) indicates a process of nitro-oxidative stress induced by NaCl. Among the analysed NADPH-generating dehydrogenases under salinity conditions, the NADP-ICDH showed the maximum activity mainly attributable to the root NADP-ICDH. Thus, these data provide new insights on the relevance of the NADP-ICDH which could be considered as a second barrier in the mechanism of response against the nitro-oxidative stress generated by salinity.

Metabolism of reactive oxygen species and reactive nitrogen species in pepper (Capsicum annuum L.) plants under low temperature stress

Low temperature is an environmental stress that affects crop production and quality and regulates the expression of many genes, and the level of a number of proteins and metabolites. Using leaves from pepper (Capsicum annum L.) plants exposed to low temperature (8 °C) for different time periods (1 to 3 d), several key components of the metabolism of reactive nitrogen and oxygen species (RNS and ROS, respectively) were analysed. After 24 h of exposure at 8 °C, pepper plants exhibited visible symptoms characterized by flaccidity of stems and leaves. This was accompanied by significant changes in the metabolism of RNS and ROS with an increase of both protein tyrosine nitration (NO(2) -Tyr) and lipid peroxidation, indicating that low temperature induces nitrosative and oxidative stress. During the second and third days at low temperature, pepper plants underwent cold acclimation by adjusting their antioxidant metabolism and reverting the observed nitrosative and oxidative stress. In this process, the levels of the soluble non-enzymatic antioxidants ascorbate and glutathione, and the activity of the main NADPH-generating dehydrogenases were significantly induced. This suggests that ascorbate, glutathione and the NADPH-generating dehydrogenases have a role in the process of cold acclimation through their effect on the redox state of the cell.

Transfer of a Redox-Signal through the Cytosol by Redox-Dependent Microcompartmentation of Glycolytic Enzymes at Mitochondria and Actin Cytoskeleton

The cytosolic glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.12, GapC) plays an important role in glycolysis by providing the cell with ATP and NADH. Interestingly, despite its glycolytic function in the cytosol, GAPDH was reported to possess additional non-glycolytic activities, correlating with its nuclear, or cytoskeletal localization in animal cells. In transiently transformed mesophyll protoplasts from Arabidopsis thaliana colocalization and interaction of the glycolytic enzymes with the mitochondria and with the actin cytoskeleton was visualized by confocal laser scanning microscopy (cLSM) using fluorescent protein fusions and by bimolecular fluorescence complementation, respectively. Yeast two-hybrid screens, dot-blot overlay assays, and co-sedimentation assays were used to identify potential protein-protein interactions between two cytosolic GAPDH isoforms (GapC1, At3g04120; GapC2, At1g13440) from A. thaliana with the neighboring glycolytic enzyme, fructose 1,6-bisphosphate aldolase (FBA6, At2g36460), the mitochondrial porin (VDAC3; At5g15090), and actin in vitro. From these experiments, a mitochondrial association is suggested for both glycolytic enzymes, GAPDH and aldolase, which appear to bind to the outer mitochondrial membrane, in a redox-dependent manner. In addition, both glycolytic enzymes were found to bind to F-actin in co-sedimentation assays, and lead to bundling of purified rabbit actin, as visualized by cLSM. Actin-binding and bundling occurred reversibly under oxidizing conditions. We speculate that such dynamic formation of microcompartments is part of a redox-dependent retrograde signal transduction network for adaptation upon oxidative stress.

The changes of nitric oxide production during the growth of Microcystis aerugrinosa

This study characterized the changes of nitric oxide (NO) production during the growth of Microcystis aerugrinosa, a cyanobacterium which usually cause cyanobacterial blooms. Results showed a drastic NO release accompanying with cell density and Chl-a content sharp rises when M. aerugrinosa grew from fifth day to sixth day. Moreover, high N:P ratio accelerated the cyanobacterial growth and NO burst. Sodium nitroprusside, an exogenous NO donor, promoted M. aerugrinosa growth with the optimal concentration of 0.1 mg/L. Experiments by supplementing with sodium nitrite and L-arginine demonstrated NO production in M. aerugrinosa cells was mainly through nitrate reductase (NR) pathway while minorly through NO synthase pathway. All these data suggested M. aerugrinosa produced increasing NO during its growth mainly by NR pathway, during which NO positively regulated the growth of M. aerugrinosa.

Nitric oxide imbalance provokes a nitrosative response in plants under abiotic stress

Nitric oxide (NO), a free radical generated in plant cells, belongs to a family of related molecules designated as reactive nitrogen species (RNS). When an imbalance of RNS takes place for any adverse environmental circumstances, some of these molecules can cause direct or indirect damage at the cellular or molecular level, promoting a phenomenon of nitrosative stress. Thus, this review will emphasize the recent progress in understanding the function of NO and its production under adverse environmental conditions.

Nitric oxide signalling via cytoskeleton in plants

Nitric oxide (NO) in plant cell mediates processes of growth and development starting from seed germination to pollination, as well as biotic and abiotic stress tolerance. However, proper understanding of the molecular mechanisms of NO signalling in plants has just begun to emerge. Accumulated evidence suggests that in eukaryotic cells NO regulates functions of proteins by their post-translational modifications, namely tyrosine nitration and S-nitrosylation. Among the candidates for NO-downstream effectors are cytoskeletal proteins because of their involvement in many processes regulated by NO. This review discusses new insights in plant NO signalling focused mainly on the involvement of cytoskeleton components into NO-cascades. Herein, examples of NO-related post-translational modifications of cytoskeletal proteins, and also indirect NO impact, are discussed. Special attention is paid to plant α-tubulin tyrosine nitration as an emerging topic in plant NO research.

High temperature triggers the metabolism of S-nitrosothiols in sunflower mediating a process of nitrosative stress which provokes the inhibition of ferredoxin-NADP reductase by tyrosine nitration

High temperature (HT) is considered a major abiotic stress that negatively affects both vegetative and reproductive growth. Whereas the metabolism of reactive oxygen species (ROS) is well established under HT, less is known about the metabolism of reactive nitrogen species (RNS). In sunflower (Helianthus annuus L.) seedlings exposed to HT, NO content as well as S-nitrosoglutathione reductase (GSNOR) activity and expression were down-regulated with the simultaneous accumulation of total S-nitrosothiols (SNOs) including S-nitrosoglutathione (GSNO). However, the content of tyrosine nitration (NO(2) -Tyr) studied by high-performance liquid chromatography with tandem mass spectrometry (LC-MS/MS) and by confocal laser scanning microscope was induced. Nitroproteome analysis under HT showed that this stress induced the protein expression of 13 tyrosine-nitrated proteins. Among the induced proteins, ferredoxin-NADP reductase (FNR) was selected to evaluate the effect of nitration on its activity after heat stress and in vitro conditions using 3-morpholinosydnonimine (SIN-1) (peroxynitrite donor) as the nitrating agent, the FNR activity being inhibited. Taken together, these results suggest that HT augments SNOs, which appear to mediate protein tyrosine nitration, inhibiting FNR, which is involved in the photosynthesis process.

Polyamines, polyamine oxidases and nitric oxide in development, abiotic and biotic stresses

Nitric oxide (NO), polyamines (PAs), diamine oxidases (DAO) and polyamine oxidases (PAO) play important roles in wide spectrum of physiological processes such as germination, root development, flowering and senescence and in defence responses against abiotic and biotic stress conditions. This functional overlapping suggests interaction of NO and PA in signalling cascades. Exogenous application of PAs putrescine, spermidine and spermine to Arabidopsis seedlings induced NO production as observed by fluorimetry and fluorescence microscopy using the NO-binding fluorophores DAF-2 and DAR-4M. The observed NO release induced by 1 mM spermine treatment in the Arabidopsis seedlings was very rapid without apparent lag phase. These observations pave a new insight into PA-mediated signalling and NO as a potential mediator of PA actions. When comparing the functions of NO and PA in plant development and abiotic and biotic stresses common to both signalling components it can be speculated that NO may be a link between PA-mediated stress responses filing a gap between many known physiological effects of PAs and amelioration of stresses. NO production indicated by PAs could be mediated either by H(2)O(2), one reaction product of oxidation of PAs by DAO and PAO, or by unknown mechanisms involving PAs, DAO and PAO.