O3-induced Oxidative Stress Research Articles

Stress physiology of Moringa oleifera under tropospheric ozone enrichment: An ecotype-specific investigation into growth, nonstructural carbohydrates, and polyphenols.

Ozone (O3) is an oxidative pollutant that significantly threatens plant development and ecological dynamics. The present study explores the impact of O3 on Moringa (Moringa oleifera) ecotypes when exposed to ambient and elevated O3 levels. Elevated O3 concentrations resulted in significant reductions in total biomass for all ecotypes. Photosynthetic parameters, including stomatal conductance (gsto), CO2 assimilation (Pn), and carboxylation efficiency (K), decreased under elevated O3 in some ecotypes, indicating a detrimental effect on carbon assimilation. Nonstructural carbohydrate (NSC) levels in roots varied among ecotypes, with significant reductions in starch content observed under elevated O3, suggesting a potential shift towards soluble sugar accumulation and reallocation for antioxidant defense. Secondary metabolite analysis revealed increased polyphenol production, particularly quercetin derivatives, under elevated O3 in specific ecotypes, highlighting their role in mitigating oxidative stress. Interestingly, the glucosinolate content also varied, with some ecotypes exhibiting increased levels, suggesting a complex regulatory mechanism in response to O3 exposure. The study underscores the intrinsic variability among Moringa ecotypes in response to O3 stress, emphasizing the importance of genetic diversity for adaptation. The findings indicate that Moringa's metabolic plasticity, including shifts in NSC and SM production, plays a crucial role in its defense mechanisms against O3-induced oxidative stress. These insights are vital for optimizing the cultivation and utilization of Moringa in diverse environmental conditions, particularly in regions with elevated O3 levels.

Exogenous application of melatonin protects bean and tobacco plants against ozone damage by improving antioxidant enzyme activities, enhancing photosynthetic performance, and preventing membrane damage

Ozone (O3) pollution is harmful to plants and ecosystems. Several chemicals have been evaluated to protect plants against O3 deleterious effects. However, they are not adequately efficient and/or the environmental safety of their application is questioned. Hence, new chemicals that provide sufficient protection while being safer for environmental application are needed. This study investigates the response of two O3-sensitive plant species (Phaseolus vulgaris L. cv. Pinto and Nicotiana tabacum L. cv. Bel-W3) leaf-sprayed with deionized water (W, control), ethylenediurea (EDU, 1 mM) or melatonin at lower (1 mM) or higher (3 mM) concentrations (Mel_L and Mel_H, respectively), and then exposed to a square wave of 200 ppb O3, lasting 1 day (5 h day−1) for bean and 2 days (8 h day−1) for tobacco. In both species, the photosynthetic activity of O3-exposed plants was about halved. O3-induced membrane damage was also confirmed by increased malondialdehyde (MDA) byproducts compared to control (W). In EDU- and Mel-treated bean plants, the photosynthetic performance was not influenced by O3, leading to reduction of the incidence and severity of O3 visible injury. In bean plants, Mel_L mitigated the detrimental effect of O3 by boosting antioxidant enzyme activities or osmoprotectants (e.g. abscisic acid, proline, and glutathione transferase). In Mel_L-sprayed tobacco plants, O3 negatively influenced the photosynthetic activity. Conversely, Mel_H ameliorated the O3-induced oxidative stress by preserving the photosynthetic performance, preventing membrane damage, and reducing the visible injuries extent. Although EDU performed better, melatonin protected plants against O3 phytotoxicity, suggesting its potential application as a bio-safer and eco-friendlier phytoprotectant against O3. It is worth noting that the content of melatonin in EDU-treated plants remained unchanged, indicating that the protectant mode of action of EDU is not Mel-related.

Modified electrolyte leakage method for testing the oxidative stability of Pinus mugo Turra under ozone-induced stress

Abstract Electrolyte leakage (EL) is the method commonly used to test the cell membrane integrity of plants under stress conditions. The cells of the leaf may be damaged by ozone (O3) entering the intercellular space as an oxidative stress agent. The modified EL method was used to test the oxidative stability (OxS) of plant tissue against O3-induced oxidative stress. The modification includes simulation of the artificial oxidative stress by additional ozonation of plant samples in the laboratory chamber. This modified EL method was applied to Pinus mugo Turra needle samples collected in the subalpine zone of the High Tatra Mts (Western Carpathians), in the years 2019 and 2020. Changes in the chemical composition of samples after artificial ozonation were traced by gas chromatography/mass spectrometry (GC/MS) analysis. In addition, O3 uptake through open stomata was estimated by calculation of the modelled ozone dose (MO3D). We also conducted an inspection of visible injury (VIN) on the needle surface focused on the occurrence of O3-induced symptoms and biotic harmful agents. Regarding OxS results as well as VIN indices, P. mugo needles showed relatively low sensitivity to oxidative stress induced by O3. Therefore MO3D in a range between 14 and 16 mmol m−2 can be considered as O3 dose with minor phytotoxic effect on P. mugo growing in the mountains of central-eastern Europe.

The response of mesophyll conductance to ozone-induced oxidative stress is genotype-dependent in poplar

The CO2 diffusion conductance within the leaf mesophyll (gm) is considered a major limiting factor of photosynthesis. However, the effects of the major secondary air pollutant ozone (O3) on gm have been poorly investigated. Eight genotypes of the economically important tree species Populus × canadensis Moench were exposed to 120 ppb O3 for 21 d. gm showed a genotype-dependent response to O3-induced oxidative stress and was a major limiting factor of net assimilation rate (Anet), ahead of stomatal conductance to CO2 (gsc) and of the maximum carboxylation capacity of the Rubisco enzyme (Vcmax) in half of the tested genotypes. Increased leaf dry mass per area (LMA) and decreased chlorophyll content were linked to the observed gm decrease, but this relationship did not entirely explain the different genotypic gm responses. Moreover, the oxidative stress defence metabolites ascorbate and glutathione were not related to O3 tolerance of gm. However, malondialdehyde probably mitigated the observed gm decrease in some genotypes due to its oxidative stress signalling function. The large variation of gm suggests different regulation mechanisms amongst poplar genotypes under oxidative stress.

Supplementation with omega-3 fatty acids potentiates oxidative stress in human airway epithelial cells exposed to ozone

BackgroundDietary intake of the omega-3 family of polyunsaturated fatty acids (ω-3 FA) is associated with anti-inflammatory effects. However, unsaturated fatty acids are susceptible to oxidation, which produces pro-inflammatory mediators. Ozone (O3) is a tropospheric pollutant that reacts rapidly with unsaturated fatty acids to produce electrophilic and oxidative mediators of inflammation. ObjectiveDetermine whether supplementation with ω-3 FA alters O3-induced oxidative stress in human airway epithelial cells (HAEC). Methods16-HBE cells expressing a genetically encoded sensor of the reduced to oxidized glutathione ratio (GSH/GSSG, EGSH) were supplemented with saturated, monounsaturated, or ω-3 FA prior to exposure to 0, 0.08, 0.1, or 0.3 ppm O3. Lipid peroxidation was measured in cellular lipid extracts and intact cells following O3 exposure. ResultsRelative to cells incubated with the saturated or monounsaturated fatty acids, cells supplemented with ω-3 FA containing 5 or 6 double bonds showed a marked increase in EGSH during exposure to O3 concentrations as low as 0.08 ppm. Consistent with this finding, the concentration of lipid hydroperoxides produced following O3 exposure was significantly elevated in ω-3 FA supplemented cells. DiscussionSupplementation with polyunsaturated ω-3 FA potentiates oxidative responses, as indicated by EGSH, in HAEC exposed to environmentally relevant concentrations of O3. This effect is mediated by the increased formation of lipid hydroperoxides produced by the reaction of O3 with polyunsaturated fatty acids. Given the inflammatory activity of lipid hydroperoxides, these findings have implications for the potential role of ω-3 FA in increasing human susceptibility to the adverse health effects of O3 exposure.

Investigating the effect of methyl jasmonate and melatonin on resistance of Malus crabapple 'Hong Jiu' to ozone stress.

Ozone (O3) is an adverse environmental factor posing damage to ornamental plants. Thus, it is important to seek an effective way of enhancing plant tolerance to O3-induced damage. Methyl jasmonate (MJ) and melatonin (MT) are plant growth regulators (PGRs) involved in plant abiotic stress responses. In this study, compared with the control group of plants without ozone, the influence of exogenous MJ (0, 10, 50, 100, and 150μM) and MT (0, 0.1, 0.5, 2.5, and 12.5μM) on the resistance of Malus crabapple 'Hong Jiu' was evaluated under O3 stress (100 ± 10nL/L for 3h). Our data revealed that levels of MDA were significantly enhanced following O3 treatment compared with plants without O3. O3 induced the activities of antioxidant enzymes and the accumulation of non-enzymatic antioxidants. While lower malondialdehyde (MDA) content, greater activities of antioxidant enzymes, and higher levels of soluble protein and non-enzymatic antioxidants were observed in PGRs-pretreated plants than in non-PGRs-pretreated plants under O3 stress. Based on the above results and air pollution tolerance index (APTI), an exogenous supply of MJ and MT to Malus crabapple 'Hong Jiu' seedlings was protective for O3-induced toxicity. The present study provides new insights into the mechanisms of MJ and MT amelioration of O3-induced oxidative stress damages in Malus crabapple 'Hong Jiu.'

Major Effect of Oxidative Stress on the Male, but Not Female, SP-A1 Type II Cell miRNome.

Pulmonary surfactant protein A (SP-A) plays an important role in surfactant metabolism and lung innate immunity. In humans there are two proteins, SP-A1 and SP-A2, encoded by SFTPA1 and SFTPA2, respectively, which are produced by the alveolar type II cells (T2C). We sought to investigate the differential influence of SP-A1 and SP-A2 in T2C miRNome under oxidative stress (OxS). SP-A knock out (KO) and hTG male and female mice expressing SP-A1 or SP-A2 as well as gonadectomized (Gx) mice were exposed to O3-induced oxidative stress (OxS) or filtered air (FA). Expression of miRNAs and mRNAs was measured in the T2C of experimental animals. (a) In SP-A1 males after normalizing to KO males, significant changes were observed in the miRNome in terms of sex-OxS effects, with 24 miRNAs being differentially expressed under OxS. (b) The mRNA targets of the dysregulated miRNAs included Ago2, Ddx20, Plcg2, Irs1, Elf2, Jak2, Map2k4, Bcl2, Ccnd1, and Vhl. We validated the expression levels of these transcripts, and observed that the mRNA levels of all of these targets were unaffected in SP-A1 T2C but six of these were significantly upregulated in the KO (except Bcl2 that was downregulated). (c) Gondadectomy had a major effect on the expression of miRNAs and in three of the mRNA targets (Irs1, Bcl2, and Vhl). Ccnd1 was upregulated in KO regardless of Gx. (d) The targets of the significantly changed miRNAs are involved in several pathways including MAPK signaling pathway, cell cycle, anti-apoptosis, and other. In conclusion, in response to OxS, SP-A1 and male hormones appear to have a major effect in the T2C miRNome.

Examining Genetic Variation in Maize Inbreds and Mapping Oxidative Stress Response QTL in B73-Mo17 Nearly Isogenic Lines

Screening crop plants under elevated ozone concentrations ([O3]) is a pre-requisite for identification of tolerant lines, but few studies have mapped maize responses to elevated [O3]. B73-Mo17 nearly isogenic lines (NILs) were screened in the field under ambient (~40 ppb) and elevated (~100 ppb) [O3] at the Free Air gas Concentration Enrichment (FACE) research facility in Champaign, IL to identify maize leaf damage QTL associated with variation in O3-induced oxidative stress response. In Mo17 NILs, a significant leaf damage QTL was identified at 161Mb on chromosome 2. To assess the feasibility of high-throughput phenotyping and fine mapping of early season O3 leaf damage QTL, a subset of the nested association mapping founder lines were screened in a growth chamber experiment under ambient and elevated [O3]. Results showed that elevated [O3] decreased the number of green leaves while increasing the number of lesioned and dead leaves. Most lines showed the same general response to elevated [O3], but the degree of damage varied among lines. Next, tolerant and sensitive B73-Mo17 NILs identified from the FACE study, and hybrid crosses of the identified NILs with Mo17 (n= 20) were grown under elevated O3 (~150 ppb) in growth chambers (n=7). In the chambers, O3-sensitive lines could be distinguished from tolerant lines based on leaf lesions, but there was not a continuous degree of damage like that seen in the field. This research identified a repeatable O3-induced leaf damage QTL and developed populations and markers that can be used in future growth chamber fine mapping experiments. These results demonstrate the feasibility of high-throughput phenotyping and fine mapping of O3 leaf damage QTL in a controlled environment.

Cross-talk between physiological and biochemical adjustments by Punica granatum cv. Dente di cavallo mitigates the effects of salinity and ozone stress

Plants are exposed to a broad range of environmental stresses, such as salinity and ozone (O3), and survive due to their ability to adjust their metabolism. The aim of this study was to evaluate the physiological and biochemical adjustments adopted by pomegranate (Punica granatum L. cv. Dente di cavallo) under realistic field conditions. One-year-old saplings were exposed to O3 [two levels denoted as ambient (AO) and elevated (EO) O3 concentrations] and salinity [S (salt, 50 mM NaCl)] for three consecutive months. No salt (NS) plants received distilled water. Despite the accumulation of Na+ and Cl− in the aboveground biomass, no evidence of visible injury due to salt (e.g. tip yellow-brown lesions) was found. The maintenance of leaf water status (i.e. unchanged values of electrolytic leakage and relative water content), the significant increase of abscisic acid, proline and starch content (+98, +65 and +59% compared to AO_NS) and stomatal closure (−24%) are suggested to act as adaptive mechanisms against salt stress in AO_S plants. By contrast, EO_NS plants were unable to protect cells against the negative impact of O3, as confirmed by the reduction of the CO2 assimilation rate (−21%), accumulation of reactive oxygen species (+10 and +225% of superoxide anion and hydrogen peroxide) and malondialdehyde by-product (about 2-fold higher than AO_NS). Plants tried to preserve themselves from further oxidative damage by adopting some biochemical adjustments [i.e. increase in proline content (+41%) and induction of catalase activity (8-fold higher than in AO_NS)]. The interaction of the two stressors induced responses considerably different to those observed when each stressor was applied independently. An analysis of the antioxidant pool revealed that the biochemical adjustments adopted by P. granatum under EO_S conditions (e.g. reduction of total ascorbate; increased activities of superoxide dismutase and catalase) were not sufficient to ameliorate the O3-induced oxidative stress.

Deciphering the main determinants of O3 tolerance in Euramerican poplar genotypes

Tropospheric ozone (O3) is the main secondary pollutant and considered to be the most damaging for growth and productivity. O3 is well known to induce oxidative stress and Reactive Oxygen Species accumulation in leaf tissues. Several mechanisms have been suggested to enable trees to cope with such stress; however, their relative contribution to O3 tolerance is still unclear. Here, ten Euramerican poplar genotypes (Populus deltoides × nigra) were investigated regarding their response to 120 ppb of O3 for 3 weeks in order to determine main mechanisms and identify the key traits and strategies linked to a better tolerance to O3-induced oxidative stress. Results showed that ascorbate peroxidase and ascorbate regeneration through monodehydroascorbate reductase are the main determinants of O3 tolerance in Euramerican poplar, in protecting photosynthesis capacity from oxidative stress and therefore, maintaining growth and productivity. Besides, stomatal closure was harmful in sensitive genotypes, suggesting that avoiding strategy can be further deleterious under chronic ozone. Finally, O3-induced early senescence appeared essential when up scaling leaf-level mechanistic response to whole-plant productivity, in fine-tuning resource reallocation and photosynthesis area.

321 - Cyclic ozone exposure synergizes with aging leading to memory impairment in male apoE3, not apoE4, targeted replacement mice

The etiology of Alzheimer’s disease (AD), an aging-related neurodegenerative disease, is unknown. Recent epidemiology studies suggest that exposure to unhealthy levels of ozone (O3), a highly reactive oxidant and one of most abundant urban pollutant, may be responsible. Whether O3 acts alone or synergizes with other risk factors, such as aging and APOEe4, leading to AD remains to be determined. To test whether O3 exposure, APOEe4, and aging negatively interact leading to AD, we exposed otherwise healthy male apoE4 targeted replacement (TR) mice to a cyclic O3 exposure protocol, which mimics human exposure scenarios, and compared the results to male apoE3 TR mice, which represent the majority of the human population who carries the APOE e3 gene. The results show, surprisingly, that O3 exposure impairs memory of old male apoE3, but not apoE4, mice nor young apoE3 or apoE4 mice. Further studies show that glutathione concentration decreases with increased age and with O3 exposure in the hippocampus of male apoE3 mice, although its concentration is low in male apE4 mice since young age. Cysteine concentration, on the other hand, increases with age in apoE4 mice. The activities of several antioxidant enzymes including thioredoxin 1 are also increased in the hippocampus of old apoE4 mice, compared to old apoE3 mice. This is associated with diminished lipid and protein oxidation, astrocyte activation/inflammation, and neurogenesis in O3 exposed old apoE4 mice. Our results show, for the first time, that APOEe4, a genetic risk factor for AD, actually protects old male mice from O3-induced memory impairment, probably because old apoE4 male mice have developed compensatory mechanisms to combat O3-induced oxidative stress

SP-A2 contributes to miRNA-mediated sex differences in response to oxidative stress: pro-inflammatory, anti-apoptotic, and anti-oxidant pathways are involved

BackgroundHuman innate host defense molecules, surfactant protein A1 (SP-A1), and SP-A2 differentially affect the function and proteome of the alveolar macrophage (AM). We hypothesized that SP-A genes differentially regulate the AM miRNome.MethodsHumanized transgenic mice expressing SP-A1 and SP-A2 were subjected to O3-induced oxidative stress (OxS) or filtered air (FA), AMs were isolated, and miRNA levels were measured.ResultsIn SP-A2 males, we found significant changes in miRNome in terms of sex and sex-OxS effects, with 11 miRNAs differentially expressed under OxS. Their mRNA targets included BCL2, CAT, FOXO1, IL6, NF-kB, SOD2, and STAT3. We followed the expression of these transcripts as well as key cytokines, and we found that (a) the STAT3 mRNA significantly increased at 4 h post OxS and returned to baseline at 18 h post OxS. (b) The anti-oxidant protein SOD2 level significantly increased, but the CAT level did not change after 4 h post OxS compared to control. (c) The anti-apoptotic BCL2 mRNA increased significantly (18 h post OxS), but the levels of the other transcripts were decreased. The presence of the SP-A2 gene had a protective role in apoptosis of AMs under OxS compared to mice lacking SP-A (knockout, KO). (d) Pro-inflammatory cytokine IL-6 protein levels were significantly increased in SP-A2 mice compared to KO (4 and 18 h post OxS), which signifies the role of SP-A2 in pro-inflammatory protein expression. (e) SOD2 and CAT mRNAs changed significantly in OxS indicating a plausible role of SP-A2 in the homeostasis of reactive oxygen species. (f) Gonadectomy of transgenic mice showed that sex hormones contribute to significant changes of the miRNome expression.ConclusionsWe conclude that SP-A2 influences the miRNA-mediated sex-specific differences in response to OxS. In males, these differences pertain to inflammatory, anti-apoptotic, and anti-oxidant pathways.

95 - Interactions Between Gene, Environment, and Aging in Modulation of Brain Redox Potential and Memory

The cause for the late-onset (sporadic) Alzheimer’s disease (AD), which accounts for 95% of AD cases, is unknown and most likely conferred by complex interactions between genetic and environmental risk factors plus aging. How the genetic and environmental risk factors as well as aging interact, leading to AD, however, is unknown. In this study, we explored the potential interactions between ApoE4, a genetic risk factor, O3, an environmental risk factor, and aging in the induction of memory impairment, using human ApoE4 and ApoE3 (the majority of human population carry the ApoE3 gene) targeted replacement (TR) male mice. The results show that exposure to O3 following a cyclic exposure protocol, which mimics human exposure scenarios, impairs memory of old ApoE3 TR mice, although it has no significant effect on the memory of young ApoE3 and ApoE4 or old ApoE4 TR mice. The concentrations of glutathione (GSH), an important antioxidant, decrease with age and with O3 exposure in frontal cortex (FC) and hippocampus, two brain areas affected mainly in AD, in ApoE3 TR mice, but only in FC of ApoE4 TR mice. The GSH and GSSG redox potentials decrease with age in the FC and hippocampus of ApoE3, but not ApoE4, TR mice; O3 exposure, on the other hand, reduces the redox potential in young ApoE3 and old ApoE4 TR mice. Cysteine concentrations decrease with age and with O3 exposure in both FC and hippocampus in ApoE3, but not in ApoE4, TR mice. The cysteine/cystine redox potentials, a major extracellular redox couple, decrease with O3 exposure in both brain areas in young and old ApoE3 TR mice, but only in the frontal cortex of young ApoE4 TR mice. Together, the results suggest that male ApoE3 TR mice are more sensitive to aging- and O3-induced oxidative stress than ApoE4 TR mice, although young ApoE4 mice per se experience increased level of oxidative stress, compared to young ApoE3 TR mice. The results also suggest that increased sensitivity to oxidative stress may underlie memory loss in O3 exposed old ApoE3 TR mice. As ApoE4 mainly affects females, interactions between ApoE4, O3, and aging in modulation of brain oxidative stress levels and memory in females warrant further investigation.

SP‐A2 contributes to miRNA‐mediated sex differences in response to ozone‐induced oxidative stress: pro‐inflammatory, anti‐apoptotic, and anti‐oxidant pathways are involved

Human host defense molecules, surfactant protein‐A1 (SP‐A1) and SP‐A2 differentially affect alveolar macrophage (AM) function and their proteome. We hypothesized, that SP‐A genes differentially regulate the AM miRNome. SP‐A knockout (KO), humanized transgenic mice expressing SP‐A1 and SP‐A2 and SP‐A2 gonadectomized mice were exposed to O3 or filtered air (FA) and AM isolated. Of the miRNAs (n=372) studied, 11 miRNAs were differentially expressed under O3‐induced oxidative stress (OxS) in SP‐A2 males. Their gene targets included IL‐6, STAT3, BCL2, NF‐kB, and FOXO1. a) We observed increase in STAT3 mRNA (p < 0.05) in SP‐A2 after 4hr of O3 exposure (4hrO3). To account for half‐life differences, we measured mRNA after 18hrO3. BCL2 increased (p < 0.05) in SP‐A2 AM, whereas, the other genes significantly decreased compared to FA. TUNEL assay revealed significant decrease and increase in apoptotic cells under OxS in SP‐A2, and KO, respectively, indicating a role for SP‐A2 in apoptosis. b) The IKKβ mRNA level after 18hrO3 decreased significantly in SP‐A2, but not in KO; a number of SP‐A2‐downregulated miRNAs correlated with the upregulation of target genes, TNF‐α, IL‐1β, and IL‐6, indicating a role in pro‐inflammatory gene expression. c) Although FOXO1 did not change, SOD2 and CAT decreased and increased significantly in SP‐A2 and KO, respectively, after 18hrO3, indicating that SP‐A2 contributes to ROS homeostasis by decreasing the expression of anti‐oxidant enzymes. d) Sex hormones contribute to differential miRNA expression, as demonstrated by gonadectomy. Thus, SP‐A2 affects miRNA‐mediated sex‐specific differences in response to OxS by involving inflammatory, anti‐apoptotic, and anti‐oxidant pathways.Support or Funding InformationCHILD fund, Dept of Pediatrics, Penn State University, College of Medicine

Ozone tolerance in lichens: A possible explanation from biochemical to physiological level using Flavoparmelia caperata as test organism

Lichens are among the best biomonitors of airborne pollutants, but surprisingly they reveal high tolerance to ozone (O3). It was recently suggested that this might be due to the high levels of natural defences against oxidative stress, related to their poikilohydric life strategy. The objective of this work is to give a thorough description of the biochemical and physiological mechanisms that are at the basis of the O3-tolerance of lichens. Chlorophyll a fluorescence (ChlaF) emission, histochemical ROS localization in the lichen thallus, and biochemical markers [enzymes and antioxidants involved in the ascorbate/glutathione (AsA/GSH) cycle; hydrogen peroxide (H2O2) and superoxide anion (O2(-))] were used to characterize the response of the epiphytic lichen Flavoparmelia caperata (L.) Hale exposed to O3 (250 ppb, 5 hd(-1), 2 weeks) at different watering regimes and air relative humidity (RH) in a fumigation chamber. After two-week exposure ChlaF was affected by the watering regime but not by O3. The watering regime influenced also the superoxide dismutase activity and the production of ROS. By contrast O3 strongly influenced the AsA/GSH biochemical pathway, decreasing the reduced ascorbate (AsA) content and increasing the enzymatic activity of ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) independently from the watering regime and the relative humidity applied. This study highlights that F. caperata can face the O3-induced oxidative stress thanks to high levels of constitutive enzymatic and non-enzymatic defences against ROS formed naturally during the dehydration-rehydration cycles to which lichens are frequently exposed.

Effects of Exercise on Oxidative Stress in Rats Induced by Ozone

Oxidative stress (OS) induced by acute exercise is reduced by chronic exercise. Ozone (O3) exposure produces OS. The aim of this study was to determine if aerobic exercise (AE) reduced OS produced by O3. A pilot experiment was performed with male Wistar rats submitted to AE (trained to swim 90 min/day). Adaptation to exercise was demonstrated three weeks after training by means of changes in reduced nitrates (NOx) in plasma. Therefore, two-week training was chosen for the following experiments. Six of twelve trained rats were exposed to O3 (0.5 ppm, 4 h/day, one hour before exercise). Two groups of sedentary animals (n = 6 each) were used as controls, one of which was exposed to O3. At the end of the experiments NOx, 8-isoprostane (8-IP), malondialdehyde (MDA), superoxide dismutase (SOD) activity, and carbonyls (CBs) were measured in plasma. CBs did not change in any group. O3-induced OS was manifested by reduced NOx and SOD activity, as well as increased 8-IP and MDA. Exercise significantly blocked O3 effects although SOD was also decreased by exercise (a greater drop occurring in the O3 group). It is concluded that AE protects against OS produced by O3 and the effect is independent of SOD.

Elevated CO2 ameliorated oxidative stress induced by elevated O3 in Quercus mongolica

Using open top chambers, the effects of elevated O3 (80 nmol mol−1) and elevated CO2 (700 μmol mol−1), alone and in combination, were studied on young trees of Quercus mongolica. The results showed that elevated O3 increased malondialdehyde content and decreased photosynthetic rate after 45 days of exposure, and prolonged exposure (105 days) induced significant increase in electrolyte leakage and reduction of chlorophyll content. All these changes were alleviated by elevated CO2, indicating that oxidative stress on cell membrane and photosynthesis was ameliorated. After 45 days of exposure, elevated O3 stimulated activities of superoxide dismutase (SOD, EC 1.15.1.1) and ascorbate peroxidase (APX, EC 1.11.1.11), but the stimulation was dampened under elevated CO2 exposure. Furthermore, ascorbate (AsA) and total phenolics contents were not higher in the combined gas treatment than those in elevated O3 treatment. It indicates that the protective effect of elevated CO2 against O3 stress was achieved hardly by enhancing ROS scavenging ability after 45 days of exposure. After 105 days of exposure, elevated O3 significantly decreased activities of SOD, catalase (CAT, EC 1.11.1.6) and APX and AsA content. Elevated CO2 suppressed the O3-induced decrease, which could ameliorate the oxidative stress in some extent. In addition, elevated CO2 increased total phenolics content in the leaves both under ambient O3 and elevated O3 exposure, which might contribute to the protection against O3-induced oxidative stress as well.

Mechanisms underlying the amelioration of O3-induced damage by elevated atmospheric concentrations of CO2.

There is growing evidence that rising atmospheric CO2 concentrations will reduce or prevent reductions in the growth and productivity of C3 crops attributable to ozone (O3) pollution. In this study, the role of pollutant exclusion in mediating this response was investigated through growth chamber-based investigations on leaves 4 and 7 of spring wheat (Triticum aestivum cv. Hanno). In the core experiments, plants were raised at two atmospheric CO2 concentrations (ambient [350 micro l l(-1)] or elevated CO2 [700 micro l l(-1)] under two O3 regimes (charcoal/Purafil-filtered air [<5 nl l(-1) O3] or ozone-enriched air [75 nl l(-1) 7 h d(-1)]). A subsequent experiment used an additional O3 treatment where the goal was to achieve equivalent daily O3 uptake over the life-span of leaves 4 and 7 under ambient and CO2-enriched conditions, through daily adjustment of exposures based on measured shifts in stomatal conductance. Plant growth and net CO2 assimilation were stimulated by CO2-enrichment and reduced by exposure to O3. However, the impacts of O3 decreased with plant age (i.e. leaf 7 was more resistant to O3 injury than leaf 4); a finding consistent with ontogenic shifts in the tolerance of plant tissue and/or acclimation to O3-induced oxidative stress. In the combined treatment, elevated CO2 protected against the adverse effects of O3 and reduced cumulative O3 uptake (calculated from measurements of stomatal conductance) by c. 10% and 35% over the life-span of leaves 4 and 7, respectively. Analysis of the relationship between O3 uptake and the decline in the maximum in vivo rate of Rubisco carboxylation (Vcmax) revealed the protection afforded by CO2-enrichment to be due, to a large extent, to the exclusion of the pollutant from the leaf interior (as a consequence of the decline in stomatal conductance triggered by CO2-enrichment), but there was evidence (especially from flux-response relationships constructed for leaf 4) that CO2-enrichment resulted in additional effects that alleviated the impacts of ozone-induced oxidative stress on photosynthesis.