Involvement of NADPH oxidase in sulfur dioxide-induced oxidative stress in plant cells

Repetitive sulfur dioxide exposure in mice models post-deployment respiratory syndrome

Soldiers deployed to Iraq and Afghanistan have a higher prevalence of respiratory symptoms than nondeployed military personnel and some have been shown to have a constellation of findings on lung biopsy termed post-deployment respiratory syndrome (PDRS). Since many of the subjects in this cohort reported exposure to sulfur dioxide (SO2), we developed a model of repetitive exposure to SO2 in mice that phenocopies many aspects of PDRS, including adaptive immune activation, airway wall remodeling, and pulmonary vascular (PV) disease. Although abnormalities in small airways were not sufficient to alter lung mechanics, PV remodeling resulted in the development of pulmonary hypertension and reduced exercise tolerance in SO2-exposed mice. SO2 exposure led to increased formation of isolevuglandins (isoLGs) adducts and superoxide dismutase 2 (SOD2) acetylation in endothelial cells, which were attenuated by treatment with the isoLG scavenger 2-hydroxybenzylamine acetate (2-HOBA). In addition, 2-HOBA treatment or Siruin-3 overexpression in a transgenic mouse model prevented vascular remodeling following SO2 exposure. In summary, our results indicate that repetitive SO2 exposure recapitulates many aspects of PDRS and that oxidative stress appears to mediate PV remodeling in this model. Together, these findings provide new insights regarding the critical mechanisms underlying PDRS.NEW & NOTEWORTHY We developed a mice model of "post-deployment respiratory syndrome" (PDRS), a condition in Veterans with unexplained exertional dyspnea. Our model successfully recapitulates many of the pathological and physiological features of the syndrome, revealing involvement of the ROS-isoLGs-Sirt3-SOD2 pathway in pulmonary vasculature pathology. Our study provides additional knowledge about effects and long-term consequences of sulfur dioxide exposure on the respiratory system, serving as a valuable tool for future PDRS research.

Repetitive Sulfur Dioxide Exposure in Mice Models Post-Deployment Respiratory Syndrome

Soldiers deployed to Iraq and Afghanistan have a higher prevalence of respiratory symptoms than non-deployed military personnel and some have been shown to have a constellation of findings on lung biopsy termed post-deployment respiratory syndrome (PDRS). Since many of the deployers in this cohort reported exposure to sulfur dioxide (SO 2 ), we developed a model of repetitive exposure to SO 2 in mice that phenocopies many aspects of PDRS, including adaptive immune activation, airway wall remodeling, and pulmonary vascular disease (PVD). Although abnormalities in small airways were not sufficient to alter lung mechanics, PVD was associated with the development of pulmonary hypertension and reduced exercise tolerance in SO 2 exposed mice. Further, we used pharmacologic and genetic approaches to demonstrate a critical role for oxidative stress and isolevuglandins in mediating PVD in this model. In summary, our results indicate that repetitive SO 2 exposure recapitulates many aspects of PDRS and that oxidative stress may mediate PVD in this model, which may be helpful for future mechanistic studies examining the relationship between inhaled irritants, PVD, and PDRS.

Adenosine 5' phosphosulfate reductase and sulfite oxidase regulate sulfite-induced water loss in Arabidopsis

Chloroplast-localized adenosine-5'-phosphosulphate reductase (APR) generates sulfite and plays a pivotal role in reduction of sulfate to cysteine. The peroxisome-localized sulfite oxidase (SO) oxidizes excess sulfite to sulfate. Arabidopsis wild type, SO RNA-interference (SO Ri) and SO overexpression (SO OE) transgenic lines infiltrated with sulfite showed increased water loss in SO Ri plants, and smaller stomatal apertures in SO OE plants compared with wild-type plants. Sulfite application also limited sulfate and abscisic acid-induced stomatal closure in wild type and SO Ri. The increases in APR activity in response to sulfite infiltration into wild type and SO Ri leaves resulted in an increase in endogenous sulfite, indicating that APR has an important role in sulfite-induced increases in stomatal aperture. Sulfite-induced H2O2 generation by NADPH oxidase led to enhanced APR expression and sulfite production. Suppression of APR by inhibiting NADPH oxidase and glutathione reductase2 (GR2), or mutation in APR2 or GR2, resulted in a decrease in sulfite production and stomatal apertures. The importance of APR and SO and the significance of sulfite concentrations in water loss were further demonstrated during rapid, harsh drought stress in root-detached wild-type, gr2 and SO transgenic plants. Our results demonstrate the role of SO in sulfite homeostasis in relation to water consumption in well-watered plants.

NADPH Oxidases: The Vital Performers and Center Hubs during Plant Growth and Signaling

NADPH oxidases (NOXs), mostly known as respiratory burst oxidase homologs (RBOHs), are the key producers of reactive oxygen species (ROS) in plants. A lot of literature has addressed ROS signaling in plant development regulation and stress responses as well as on the enzyme's structure, evolution, function, regulation and associated mechanisms, manifesting the role of NOXs/RBOHs as the vital performers and center hubs during plant growth and signaling. This review focuses on recent advances of NOXs/RBOHs on cell growth, hormone interaction, calcium signaling, abiotic stress responses, and immunity. Several primary particles, including Ca2+, CDPKs, BIK1, ROPs/RACs, CERK, FER, ANX, SnRK and SIK1-mediated regulatory mechanisms, are fully summarized to illustrate the signaling behavior of NOXs/RBOHs and their sophisticated and dexterous crosstalks. Diverse expression and activation regulation models endow NOXs/RBOHs powerful and versatile functions in plants to maintain innate immune homeostasis and development integrity. NOXs/RBOHs and their related regulatory items are the ideal targets for crop improvement in both yield and quality during agricultural practices.

A novel colorimetric and ratiometric fluorescent probe for sensing SO2 derivatives and their bio-imaging in living cells

We report a novel fluorescent probe HBN-TCF for the detection of SO2 derivatives. This probe exhibited near-infrared fluorescence emission with an excitation wavelength of 620 nm. After reacting with SO32-, the emission channel at 664 nm decreased, while the new strong emission channel at 482 nm increased (λex = 400 nm), with a large emission distance (Δλ = 182 nm) observed. This probe exhibited the rapid and selective detection of SO2 derivatives compared with other sulfur-containing species and featured a low detection limit (82 nM). This colorimetric and ratiometric fluorescent probe showed high selectivity and sensitivity for detecting SO2 derivatives. The probe was also successfully exploited for the fluorescence imaging of intracellular and exogenous SO2 derivatives in BEL-7402 cells.

Response of gas-exchange characteristics and chlorophyll fluorescence to acute sulfur dioxide exposure in landscape plants

To explore the toxicity and action mechanism of acute sulfur dioxide (SO₂) on urban landscape plants, a simulated SO₂ stress environment by using fumigation chamber involving increasing SO₂ concentration (0, 25, 50, 100, 200 mg m^-3) was carried out among three species. After 72 h of exposure, SO₂-induced oxidative damage indicated by electrolyte leakage increased with higher dose of SO₂. Meanwhile, SO₂ decreased the contents of chlorophyll a, chlorophyll b and carotenoid and increased the contents of sulfur. Net photosynthetic rate (P_n) decreased as a result of stomatal closure when SO₂ dose was lower than 50 mg m^-3, out of this range, non-stomatal limitation play a dominant role in the decline of P_n. Simultaneous measurements of chlorophyll fluorescence imaging (CFI) also revealed that the maximal quantum efficiency of PSII photochemistry in dark-adapted state (F_v/F_m) and the realized operating efficiency of PSII photochemistry (F_q'/F_m') was reduced by SO₂ in a dose-dependent manner. In addition, the maximum quantum efficiency of PSII photochemistry in light-adapted state (F_v'/F_m') and the PSII efficiency factor (F_q'/F_v') decreased when exposure to SO₂. These results implied that acute SO₂ exposure induced photoinhibition of PSII reaction centers in landscape plants. Our study also indicated that different urban landscape plant species resist differently to SO₂: Euonymus kiautschovicus > Ligustrum vicaryi > Syringa oblata according to gas-exchange characteristics and chlorophyll fluorescence responses.

A novel colorimetric and fluorescent probe for simultaneous detection of SO32-/HSO3- and HSO4- by different emission channels and its bioimaging in living cells

A novel fluorescent probe (E)-3-ethyl-2-(4-hydroxystyryl)-1,1-di-methyl-1H-benzo-[e]indolium iodide (probe EDB) based on benzo[e]indolium was synthesized, which provided the simultaneous detection of SO₃^2-/HSO₃^- and HSO₄^- ion with different emission channels. Based on the principle of ion-induced rotation-displaced H-aggregates, when treated with NaHSO₄, a fluorescence enhancement at 580nm was observed with the excitation wavelength at 420nm. While, in the advantage of the nucleophilic addition of SO₃^2- to the vinyl group, strong fluorescence was obtained at 455nm when treated with Na₂SO₃ with the excitation wavelength at 320nm, along with obvious color change by naked eyes. So the probe could be applied to sense SO₃^2-/HSO₃^- and HSO₄^- ion via different excited and emission channels simultaneously. The probe was also applicable for fluorescence imagings of bisulfite and hydrosulfate in HeLa cells.

Attenuation of Sulfur Dioxide Damage to Wheat Seedlings by Co-exposure to Nitric Oxide

The protective function of nitric oxide (NO) has been extensively clarified in plant responses to abiotic stresses. However, little is known about the regulation of NO in plants exposed to sulfur dioxide (SO₂). In the present study, we found that co-exposure to NO significantly attenuated SO₂-induced wheat seedling growth inhibition. Data showed that NO efficiently prevented SO₂-triggered oxidative stress, as indicated by decreasing reactive oxygen species production, lipid peroxidation, and electrolyte leakage. This might be attributed to the regulatory role of NO in antioxidative defense, such as increasing the activities of antioxidative enzymes and the contents of non-enzymatic antioxidants. The SO₂-caused declines in soluble protein and chlorophyll content were efficiently recovered by NO application. Photosynthetic parameters, such as net photosynthetic rate, maximum photochemical efficiency, and actual photochemical efficiency, were protected by NO. In conclusion, this study demonstrated that during SO₂ exposure, co-application of NO can efficiently alleviate plant damage probably by regulating the antioxidative defense, and protecting plant photosynthesis-related process.

Ozone-Sensitive Arabidopsis Mutants with Deficiencies in Photorespiratory Enzymes

An ozone-sensitive mutant was isolated from T-DNA-tagged lines of Arabidopsis thaliana. The T-DNA was inserted at a locus on chromosome 3, where two genes encoding glycolate oxidases, GOX1 and GOX2, peroxisomal enzymes involved in photorespiration, reside contiguously. The amounts of the mutant's foliar transcripts for these genes were reduced, and glycolate oxidase activity was approximately 60% of that of the wild-type plants. No difference in growth and appearance was observed between the mutant and the wild-type plants under normal conditions with ambient air under a light intensity of 100 µmol photons m-2 s-1. However, signs of severe damage, such as chlorosis and ion leakage from the tissue, rapidly appeared in mutant leaves in response to ozone treatment at a concentration of 0.2 µl l-1 under a higher light intensity of 350 µmol photons m-2 s-1 that caused no such symptoms in the wild-type plant. The mutant also exhibited sensitivity to sulfur dioxide and long-term high-intensity light. Arabidopsis mutants with deficiencies in other photorespiratory enzymes such as glutamate:glyoxylate aminotransferase and hydroxypyruvate reductase also exhibited ozone sensitivities. Therefore, photorespiration appears to be involved in protection against photooxidative stress caused by ozone and other abiotic factors under high-intensity light.

Reactive oxygen species and plant resistance to fungal pathogens

Reactive oxygen species (ROS) have been studied for their role in plant development as well as in plant immunity. ROS were consistently observed to accumulate in the plant after the perception of pathogens and microbes and over the years, ROS were postulated to be an integral part of the defence response of the plant. In this article we will focus on recent findings about ROS involved in the interaction of plants with pathogenic fungi. We will describe the ways to detect ROS, their modes of action and their importance in relation to resistance to fungal pathogens. In addition we include some results from works focussing on the fungal interactor and from studies investigating roots during pathogen attack.

The defense potential of glutathione-ascorbate dependent detoxification pathway to sulfur dioxide exposure in Tagetes erecta

Sulfur dioxide (SO2) exposure is associated with increased risk of various damages to plants. However, little is known about the defense response in ornamental plants. In this study, an artificial fumigation protocol was carried out to study the defense potential of the glutathione (GSH)-ascorbate (AsA) dependent detoxification pathway to SO2 exposure in Tagetes erecta. The results show that when the plants were exposed to different doses of SO2 (0, 15, 30, 50 or 80 mg m(-3)) for different times (6, 12, 18, 24 or 33 h), SO2 induced oxidative stress was confirmed by the increased hydrogen peroxide (H2O2), malondialdehyde (MDA) and relative conductivity of membrane (RC) in a dose-dependent manner for different exposure times. However, the increased levels for H2O2, MDA and RC were not significant vis-a-vis the control when SO2 doses and exposure times were lower than 15 mg m(-3)/33 h, 30 mg m(-3)/24 h or 50 mg m(-3)/12 h (p>0.05). The results could be explained by the increases in the content of reduced form of glutathione (GSH), total glutathione (TGSH), ascorbate (AsA), ratio of GSH/GSSG (oxidized form of glutathione), activities of ascorbate peroxidase (APX), glutathione peroxidase (GPX), glutathione reductase (GR) and glutathione S-transferases (GST). On the other hand, exposure to higher doses of SO2 and longer exposure times, the values of the GSH-AsA dependent antioxidative indices decreased significantly (p<0.01), manifested by increased levels of H2O2. Furthermore, the levels of H2O2, MDA and RC varied little when SO2 doses and exposure times reached a 'critical' value (50 mg m(-3)/24 h). The defense ability of T. erecta to SO2 reached nearly extremity. To summarize, the response of T. erecta to elevated SO2 was related to higher H2O2 levels. GSH-AsA dependent detoxification pathway played an important role in against SO2-induced toxicity, although the defense response could not sufficiently alleviate oxidative damage when SO2 doses and exposure times reached critical value.

Gene response in rice plants treated with continuous fog influenced by pH, was similar to that treated with biotic stress

BACKGROUND

Throughout Asia, including Japan, rice plants are cultivated in a wide range of areas from lowlands to highlands and are frequently exposed to fog, including acid fog. Some physiological studies have shown that acid fog can be a stress factor for plants. We analyzed the gene expression profiles of rice plants treated with artificially prepared simulated acid fog (SiAF) or simulated neutral fog (SiNF) for 1 or 7 days.

RESULTS

Microarray analysis results suggested that both the SiAF and the SiNF treatments induced the expression of genes involved in the defense and stress responses in rice plants. Induction of such genes was detected in plants treated with SiAF for 1 day, and the number of induced genes increased in plants treated with SiAF for 7 days. The genes for defense and stress responses were also induced by SiNF for 7 days, although they were not induced by SiNF for 1 day. The gene expression profiles of the SiAF-treated and the SiNF-treated plants were compared to those of plants treated with other stress factors. The comparison revealed that both SiAF and SiNF treatments have similar effects to biotic stresses and ozone stress. The genes encoding NADPH oxidase and germin, which function in apoplasts, were also induced by SiAF, SiNF and biotic stresses.

CONCLUSIONS

These findings suggest that both the SiAF and the SiNF treatments may result in oxidative stress through the apoplastic production of reactive oxygen species.

The determination of sulfite levels and its oxidation in plant leaves

Sulfur is the sixth most abundant element in life and an important building block of proteins and cellular metabolites. Plants like bacteria can synthesize their sulfur-containing biomolecules from sulfate, where sulfite is an intermediate of the sulfur assimilation pathway. Above a certain threshold SO(2)/sulfite is cytotoxic and is rapidly metabolized to avoid damage. However, the existing data show considerable differences in basal sulfite levels both between species and apparent discrepancies in measured levels in the same species. In order to resolve this question we employed a sulfite detection method using chicken sulfite oxidase and developed an independent enzymatic assay, based on the specific detection of sulfite by sulfite reductase and compared those measurements to a modified colorimetric fuchsin-based method, specific for sulfite detection. We show here that when properly used the sulfite levels detected by the three methods can yield identical results. Furthermore, to examine the capacity of the plant to detoxify sulfite we injected sub-lethal sulfite solutions (yet, several folds higher than the basal levels) into Arabidopsis and tomato leaves and monitored the excess sulfite turnover. Within 3h of sulfite injection, more than 80% of the injected sulfite in Arabidopsis and 91% in tomato were oxidized to sulfate, demonstrating the high capacity of the sulfite oxidation mechanism/s in plants.

Sulphur dioxide evokes a large scale reprogramming of the grape berry transcriptome associated with oxidative signalling and biotic defence responses

The grape and wine industries are heavily reliant on sulphite preservatives. However, the view that sulphites act directly on bacterial and fungal pathogens may be simplistic. Mechanisms of sulphur-enhanced defences are largely unknown; many sulphur-rich compounds enhance plant defences and sulphite can also have oxidative consequences via production of H(2)O(2) or sulphitolysis. To investigate the effects of sulphur dioxide (SO(2) ) on fresh table grapes (Vitis vinifera L. 'Crimson Seedless'), transcriptome analysis was carried out on berries treated with SO(2) under commercial conditions for 21 d. We found a broad perturbation of metabolic processes, consistent with a large-scale stress response. Transcripts encoding putative sulphur-metabolizing enzymes indicated that sulphite was directed towards chelation and conjugation, and away from oxidation to sulphate. The results indicated that redox poise was altered dramatically by SO(2) treatment, evidenced by alterations in plastid and mitochondrial alternative electron transfer pathways, up-regulation of fermentation transcripts and numerous glutathione S-transferases, along with a down-regulation of components involved in redox homeostasis. Features of biotic stress were up-regulated, notably signalling via auxin, ethylene and jasmonates. Taken together, this inventory of transcriptional responses is consistent with a long-term cellular response to oxidative stress, similar to the effects of reactive oxygen species.

Analysis of reactive oxygen species in the guard cell of wheat stoma with confocal microscope

Recently, the laser-scanning confocal microscope has become a routine technique and indispensable tool for cell biological studies. Previous studies indicated that reactive oxygen species (ROS) were generated in tobacco epidermal cells with confocal microscope. In the present studies, the probe 2',7'-dichlorof luorescein diacetate (H₂DCF-DA) was used to research the change of ROS in the guard cell of wheat stoma, and catalase (CAT) was used to demonstrate that ROS had been labeled. The laser-scanning mode of confocal microscope was XYT, and the time interval between two sections was 1.6351 s. Sixty optical sections were acquired with the laser-scanning confocal microscope, and CAT (60,000 U mg⁻¹) was added after four optical sections were scanned. Furthermore, the region of interest (ROI) was circled and the fluorescence intensity of ROS was quantified with Leica Confocal Software. The quantitative data were exported and the trend chart was made with software Excell. The results indicated that ROS were produced intracellularly in stomatal guard cells, and the quantified fluorescence intensity of ROS was declined with CAT added. It is a good method to research the instantaneous change of ROS in plant cells with confocal microscope and fluorescence probe H₂DCF-DA.

SsTypA1, a chloroplast-specific TypA/BipA-type GTPase from the halophytic plant Suaeda salsa, plays a role in oxidative stress tolerance

Suaeda salsa is a leaf-succulent euhalophytic plant capable of surviving under seawater salinity. Here, we report the isolation and functional analysis of a novel Suaeda gene (designated as SsTypA1) encoding a member of the TypA/BipA GTPase gene family. The steady-state transcript level of SsTypA1 in S. salsa was up-regulated in response to various external stressors. Expression of SsTypA1 was restricted to the epidermal layers of the leaf and stem in S. salsa, and SsTypA1-green fluorescence protein (GFP) fusion proteins were targeted to the chloroplasts of tobacco leaves. Ectopic over-expression of SsTypA1 rendered the transgenic tobacco plants with significantly increased tolerance to oxidative stress, and this was accompanied by a reduction in H(2)O(2) content. Enzymatic and Western blot analyses revealed that the activity and amount of the thylakoid-bound NAD(P)H dehydrogenase (NDH) complex in the chloroplasts of leaf cells were enhanced. Additionally, an in vitro assay demonstrated that SsTypA1 bound to GTP and possessed GTPase activity that was stimulated by the presence of chloroplast 70S ribosomes. Together, these results suggest that SsTypA1 may play a critical role in the development of oxidative stress tolerance, perhaps as a translational regulator of the stress-responsive proteins involved in reactive oxygen species (ROS) suppression in chloroplast.