Ozone Injury Research Articles

Arbuscular mycorrhizal symbiosis alleviates ozone injury in ozone-tolerant poplar clone but not in ozone-sensitive poplar clone

Tropospheric ozone (O3) is a typical air pollutant with harmful effects on plants, whereas arbuscular mycorrhizal (AM) fungi are ubiquitous plant symbionts that enhance plant resistance to various abiotic stresses. However, whether AM symbiosis decreases plant O3 sensitivity and what the underlying mechanisms are remain unclear. In this study, O3-tolerant poplar clone 107 and O3-sensitive poplar clone 546 were used as test plants. An open-top chamber experiment was conducted to investigate the effects of AM inoculation on plant growth and physiological parameters under O3 enrichment. The results showed that O3 enrichment significantly decreased plant biomass and net photosynthetic rate and increased the leaf shedding rate and malondialdehyde concentration of clone 546. Generally, clone 107 was less responsive to O3 enrichment than clone 546 was. Differences in antioxidant enzyme activity, rather than in specific leaf weight or stomatal conductance, were responsible for the differences in O3 sensitivity between the two clones. AM inoculation significantly increased the biomass and decreased the leaf shedding rate and malondialdehyde concentration of clone 107 but had no significant effect on almost all the indexes of clone 546, suggesting a species-specific mycorrhizal effect on plant O3 sensitivity. Mechanistically, AM symbiosis did not significantly affect nutrient uptake, stomatal conductance, or specific leaf weight of poplar but did significantly increase antioxidant enzyme activity. Linear regression analysis of antioxidant enzyme activities and the effect of O3 on growth and physiological parameters showed that AM symbiosis mediated antioxidant enzyme activities to mitigate O3 injury to the two poplar clones. This study improved the understanding of the protective effects of AM fungi on plants against O3 pollution.

CABI photoguide to: identifying ozone injury on crop leaves.Plantwise PhotosheetsCABIWallingfordUKCABI photoguide to: identifying ozone injury on crop leaves.PerringM.SharpsK.HayesF.HolderA.FosterJ.undated

CABI photoguide to: identifying ozone injury on crop leaves.Plantwise PhotosheetsCABIWallingfordUKCABI photoguide to: identifying ozone injury on crop leaves.PerringM.SharpsK.HayesF.HolderA.FosterJ.undated

Detection of ozone stress in rice cultivars using spectral reflectance

Ozone stress identification in crops through remote sensing is a promising technology that has a major role in predicting stress-related physiological response. The spectral reflectance approach to phenotyping of rice cultivars is a non-destructive and accurate method to assess ozone stress. In this study, the leaf spectral reflectance of 15 rice cultivars was explored to evaluate the photosynthetic capacity under elevated ozone stress. Ozone injury percentage (OIP), a common indicator to identify ozone stress of rice leaves combined with leaf spectral signatures was used to identify the best fit spectral indices. The normalized difference spectral index (NDSI) was used to determine significant wavebands that showed the best correlation with leaf ozone injury. The correlation coefficient (r) between NDSI and OIP were ranged from -0.79 to 1. Normalized difference spectral index, NDSI[R564,R568], and NDSI[R558,R573] were identified as the best Pearson's correlation with leaf ozone injury percentage with correlation coefficient more than 0.96. The evaluated NDSI in visible regions were identified as a sensitive region to ozone injury. Additionally, results were compared with previously established indices and also evaluated for correlation with plant physiological traits. The correlation coefficient of determination (R2) > 0.5 was observed for newly developed spectral indices, NDSI[R564,R568] and NDSI[R558,R573] with physiological traits compared to previously established 20 indices. The highest R2 of 0.674 were observed for the spectral index, NDSI[R558,R573] with photosynthetic rate and R2 of 0.673 for NDSI[R564,R568] with relative chlorophyll content. As a result, the current research has implications for the selection of the best capable spectral regions for early detection of ozone stress in rice cultivars without destructing the crop. The outcome of the present work suggests that newly developed spectral indices could assist in remote sensing technology in monitoring large scale ozone stress and crop modeling studies to ensure food security.

Thermotolerant wheat cultivar (Triticum aestivum L. var. WR544) response to ozone, EDU, and particulate matter interactive exposure.

The present study was conducted to assess the response of thermotolerant wheat cultivar (Triticum aestivum L. var. WR544) to individual and combination of ambient ground level ozone (AO3) and particulate matter (PM) air pollutants with ethylene diurea (EDU) used as an ozone stress mitigator. The four treatment combinations to which wheat cultivars were exposed are T1 (AO3 + PM), T2 (EDU + PM), T3 (AO3-PM), and T4 (EDU-PM). The effect of different treatments on morphological (foliar ozone injury, leaf area, shoot height, number of leaves, and total biomass), biochemical (leaf extract pH, electrical conductivity, relative water content, total chlorophyll, ascorbic acid content), nutritional (leaf carbohydrate content and leaf protein content), and yield (biological yield, economic yield, and harvest index) attributes of the cultivar were monitored. The plants under T1 experienced 20-30% foliar ozone injury and recorded lowest economic yield (0.58g/plant). Plants under T2 and T3 showed visible foliar ozone injury range between 0 and 5% whereas plants under T4 exhibited negligible ozone injuries. EDU-treated plants without PM deposition (T4) exhibited better morphology, leaf protein content, leaf carbohydrate content, biological and economic yield as compared to T1-, T2-, and T3-treated plants but EDU was only partially effective. Despite being a thermotolerant variety, WR544 gets adversely affected by the individual and combined exposure of AO3 and PM air pollutants. These result findings highlighted the need for more detailed study of air quality impact on the thermotolerant cultivars of other key crops to individual and combined air pollutants.

Testing visible ozone injury within a Light Exposed Sampling Site as a proxy for ozone risk assessment for European forests

Biologically meaningful and cost-effective indicators are needed for assessing and monitoring the impacts of tropospheric ozone (O3) on vegetation and are required in Europe by the National Emission Ceilings Directive (2016). However, a clear understanding on the best suited indicators is missing. The MOTTLES (MOnitoring ozone injury for seTTing new critical LEvelS) project set up a new generation network for O3 monitoring in forest plots in order to: 1) estimate the stomatal O3 fluxes (Phytotoxic Ozone Dose above a threshold Y of uptake, PODY); and 2) collect visible foliar O3 injury, both within the forest plot (ITP) and along the Light Exposed Sampling Site (LESS) along the forest edge. Nine forest sites at high O3 risk were selected across Italy over 2017 − 2019 and significant correlations (p < 0.05) were found between the percentage of symptomatic plant species within the LESS, and POD1 (PODY, with Y = 1 nmol O3 m−2 s−1) calculated for mixed forest species (r = 0.53) and with the occurrence and severity of visible foliar O3 injury on the dominant species in the plots (r = 0.65). A generic flux-based critical level for mixed forest species was derived within the LESS and it was recommended using 11 mmol m−2 POD1 as the critical level for forest protection against O3 injury, similar to the critical level obtained in the ITP (12 mmol m−2 POD1). It was concluded that the frequency of symptomatic plant species within a LESS is a suitable and effective plant-response indicator of phytotoxic O3 levels in forest monitoring. LESS is a non-destructive, less complex and less time-consuming approach compared to the ITP for monitoring foliar O3 injury in the long term. Assessing visible foliar O3 injury in the ITP might only underestimate the O3 risk assessment at individual sites. These results are biologically meaningful and useful to monitoring experts and environmental policy makers.

Chitosan Nanoparticles Loaded with N-Acetyl Cysteine to Mitigate Ozone and Other Possible Oxidative Stresses in Durum Wheat.

Modern durum wheat cultivars are more prone to ozone stress because of their high photosynthetic efficiency and leaf gas exchanges that cause a greater pollutant uptake. This, in turn, generates an increased reactive oxygen species (ROS) production that is a challenge to control by the antioxidant system of the plant, therefore affecting final yield, with a reduction up to 25%. With the aim of mitigating oxidative stress in wheat, we used chitosan nanoparticles (CHT-NPs) either unloaded or loaded with the antioxidant compound N-acetyl cysteine (NAC), on plants grown either in a greenhouse or in an open field. NAC-loaded NPs were prepared by adding 0.5 mg/mL NAC to the CHT solution before ionotropic gelation with tripolyphosphate (TTP). Greenhouse experiments evidenced that CHT-NPs and CHT-NPs-NAC were able to increase the level of the leaf antioxidant pool, particularly ascorbic acid (AsA) content. However, the results of field trials, while confirming the increase in the AsA level, at least in the first phenological stages, were less conclusive. The presence of NAC did not appear to significantly affect the leaf antioxidant pool, although the grain yield was slightly higher in NAC-treated parcels. Furthermore, both NAC-loaded and -unloaded CHT-NPs partially reduced the symptom severity and increased the weight of 1000 seeds, thus showing a moderate mitigation of ozone injury.

Correction To: Epidemiological derivation of flux-based critical levels for visible ozone injury in European forests

In the Original publication of the article, the authors found an error in the text “We recommend CLef of 5 and 12 mmol m−2 POD1 for broadleaved species and conifers, respectively” under the section abstract and conclusion

The Biosynthesis of Phenolic Compounds Is an Integrated Defence Mechanism to Prevent Ozone Injury in Salvia officinalis

Specialized metabolites constitute a major antioxidant system involved in plant defence against environmental constraints, such as tropospheric ozone (O3). The objective of this experiment was to give a thorough description of the effects of an O3 pulse (120 ppb, 5 h) on the phenylpropanoid metabolism of sage, at both biochemical and molecular levels. Variable O3-induced changes were observed over time among the detected phenylpropanoid compounds (mostly identified as phenolic acids and flavonoids), likely because of their extraordinary functional diversity. Furthermore, decreases in the phenylalanine ammonia-lyase (PAL), phenol oxidase (PPO), and rosmarinic acid synthase (RAS) activities were reported during the first hours of treatment, probably due to an O3-induced oxidative damage to proteins. Both PAL and PPO activities were also suppressed at 24 h from the beginning of exposure, whereas enhanced RAS activity occurred at the end of treatment and at the recovery time, suggesting that specific branches of the phenolic pathways were activated. The increased RAS activity was accompanied by the up-regulation of the transcript levels of genes like RAS, tyrosine aminotransferase, and cinnamic acid 4-hydroxylase. In conclusion, sage faced the O3 pulse by regulating the activation of the phenolic biosynthetic route as an integrated defence mechanism.

Individual and combined effects of ethylenediurea (EDU) and elevated carbon dioxide (ECO₂), on two rice (Oryza sativa L.) cultivars under ambient ozone

The present field experiment assesses the individual and combined effects of ethylenediurea (EDU, 200 ppm) and elevated CO2 (ECO₂, 550 ppm), on two rice (Oryza sativa L.) cultivars, Sarjoo-52 and Pusa Basmati-1(PB-1) under FACE (Free Air Concentration Enrichment) facility. During the experiment, the mean ambient ozone (AO3) concentration was 60.3 ppb. EDU treated PB-1 cultivar under elevated CO2 showed less discernible ozone (O3) injury, better photosynthetic rate, photosynthetic pigments, and aggregated more plant biomass in comparison to the Sarjoo-52 cultivar. Non-EDU treated plants showed more O3 induced injury symptoms. PB-1 cultivar was found to be more ozone sensitive than Sarjoo-52 under ambient environment. PB-1 responses to EDU for plant length, grains no plant−1, grain weight plant−1 were better than Sarjoo-52 cultivar under ambient CO2. EDU+CO2 treated PB-1 cultivar showed improved antioxidant capacity than the Sarjoo-52 cultivar. EDU treated PB-1 cultivar under elevated CO2, had more economic yield as compared to the Sarjoo-52 cultivar. Essential human dietary nutrients such as Zn, Ca, and Fe were accumulated more in EDU treated grains of PB-1 as compared to a Sarjoo-52 under elevated CO2 condition. EDU and CO₂ showed significant interactive effects on morphological, physiological, yield, and grain quality attributes of both rice varieties. EDU protected rice plants from ambient O3 pollution, improved rice growth, and yield under both ambient and elevated CO2 conditions.

The response of Pinus species to ozone uptake in different climate regions of Europe

Abstract This study is focused on the research of selected Pinus species exposed to high ozone concentrations in the mountain environment. We noticed different values of modelled ozone doses (MOD) up-taken by Mountain pine (Pinus mugo Turra) in the High Tatra Mts (SK–HTMts) and Swiss stone pine (Pinus cembra L.) in the Alpes-Mercantour (FR–AlpMar) during the growing season 2019. The MOD values were obtained by multiplicative DO3SE model, while we also tested a new approach based on modification of input ozone data. The MOD values were obtained by multiplicative DO3SE model, while we also tested a new approach based on modification of input ozone data. Testing has shown that ozone input based on passive sampling may be used in MOD modelling for sites situated in the subalpine zone where the operation of active monitors is limited.. Presented results confirmed the assumption regarding stomatal ozone flux reduction due to the occurrence of soil drought in hot and dry summer weather typical for the Mediterranean climate region. Despite the limitation of stomatal flux, foliar ozone specific injury on two years needles of P. cembra was substantially higher in comparison to the incidence of ozone injury symptoms observed on two years needles of P. mugo in SK–HTMts. It may suggest low phytotoxicity of given MOD or efficient resistance of P. mugo against oxidative stress. In addition, the visible injury index (VINX) covering the broad effect of biotic and abiotic harmful agents was appraised on P. mugo. Percentage of affected surface indicated moderate deterioration of needle injury at the end of the growing season, particularly due to traces of mechanical damage.

Screening of forty Indian Amaranthus hypochondriacus cultivars for tolerance and susceptibility to tropospheric ozone stress

Tropospheric ozone stress adversely affects crop cultivars growth and productivity variably. The variable response of crop cultivars raised the need for identification of ozone (O3) stress-tolerant cultivars as an adaptive option. In the present study, forty cultivars of Amaranthus hypochondriacus were screened for susceptibility and tolerance to ozone stress. The cultivars were exposed to ambient (AO3) and elevated (EO3) ozone levels in free air ozone enrichment (FAOE) facility and monitored for foliar ozone injury symptoms appearance and yield attributes response. Foliar ozone injury symptoms on Amaranthus cultivars were interveinal yellow or black spots. Foliar ozone injury was observed in almost half of the cultivars and the maximum foliar injury (> 75%) was observed in cultivar IC-5527. The maximum yield reduction (> 90%) was observed in cultivars IC-4200 (94.9%) and IC-5569 (91.4%) compared to other cultivars. The results showed that Amaranthus cultivars exhibited variable response towards ozone stress where foliar ozone injury does not always correspond with grain yield reductions. Among the indices, Relative Yield Index (RYI), Stress tolerance (TOL), Abiotic Tolerance Index (ATI), Susceptibility Index (S) and Stress Susceptibility Index (SSSI) were positively correlated with relative yield loss in all the cultivars under ozone stress. With the help of cluster analysis and principal component analysis (PCA), the cultivars were categorized into ozone tolerant, moderately ozone tolerant and ozone susceptible category. The most tolerant cultivars were IC-5527 and IC-1733 which exhibited lower yield losses whereas the most susceptible cultivars were IC-3599 and IC-7924 having high foliar injury and maximum yield losses as compared to other cultivars. The most ozone tolerant cultivars of Amaranthus identified in this study may be recommended for cultivation to farmers in the areas experiencing EO3 during the Amaranthus crop growth period.

Epidemiological derivation of flux-based critical levels for visible ozone injury in European forests

The European MOTTLES project set-up a new-generation network for ozone (O3) monitoring in 17 plots in France, Italy and Romania. These monitoring stations allowed: (1) estimating the accumulated exposure AOT40 and stomatal O3 fluxes (PODY) with an hourly threshold of uptake (Y) to represent the detoxification capacity of trees (POD1, with Y = 1 nmol O3 m−2 s−1 per leaf area); and (2) collecting data of forest-response indicators, i.e. crown defoliation and visible foliar O3-like injury over the time period 2017–2019. The soil water content was the most important parameter affecting crown defoliation and was a key factor affecting the severity of visible foliar O3-like injury on the dominant tree species in a plot. The soil water content is thus an essential parameter in the PODY estimation, particularly for water-limited environments. An assessment based on stomatal flux-based standard and on real plant symptoms is more appropriated than the exposure-based method for protecting vegetation. From flux-effect relationships, we derived flux-based critical levels (CLef) for forest protection against visible foliar O3-like injury. We recommend CLef of 5 and 12 mmol m−2 POD1 for broadleaved species and conifers, respectively. Before using PODY as legislative standard in Europe, we recommend using the CLec for ≥ 25% of crown defoliation in a plot: 17,000 and 19,000 nmol mol−1 h AOT40 for conifers and broadleaved species, respectively.

Flux-Based Ozone Risk Assessment for a Plant Injury Index (PII) in Three European Cool-Temperate Deciduous Tree Species

This study investigated visible foliar ozone (O3) injury in three deciduous tree species with different growth patterns (indeterminate, Alnus glutinosa (L.) Gaertn.; intermediate, Sorbus aucuparia L.; and determinate, Vaccinium myrtillus L.) from May to August 2018. Ozone effects on the timing of injury onset and a plant injury index (PII) were investigated using two O3 indices, i.e., AOT40 (accumulative O3 exposure over 40 ppb during daylight hours) and PODY (phytotoxic O3 dose above a flux threshold of Y nmol m−2 s−1). A new parameterization for PODY estimation was developed for each species. Measurements were carried out in an O3 free-air controlled exposure (FACE) experiment with three levels of O3 treatment (ambient, AA; 1.5 × AA; and 2.0 × AA). Injury onset was found in May at 2.0 × AA in all three species and the timing of the onset was determined by the amount of stomatal O3 uptake. It required 4.0 mmol m−2 POD0 and 5.5 to 9.0 ppm·h AOT40. As a result, A. glutinosa with high stomatal conductance (gs) showed the earliest emergence of O3 visible injury among the three species. After the onset, O3 visible injury expanded to the plant level as confirmed by increased PII values. In A. glutinosa with indeterminate growth pattern, a new leaf formation alleviated the expansion of O3 visible injury at the plant level. V. myrtillus showed a dramatic increase of PII from June to July due to higher sensitivity to O3 in its flowering and fruiting stage. Ozone impacts on PII were better explained by the flux-based index, PODY, as compared with the exposure-based index, AOT40. The critical levels (CLs) corresponding to PII = 5 were 8.1 mmol m−2 POD7 in A. glutinosa, 22 mmol m−2 POD0 in S. aucuparia, and 5.8 mmol m−2 POD1 in V. myrtillus. The results highlight that the CLs for PII are species-specific. Establishing species-specific O3 flux-effect relationships should be key for a quantitative O3 risk assessment.

Ozone risk assessment of grapevine ‘Cabernet Sauvignon’ using open-top chambers

ObjectiveGround-level ozone (O3) is an important photochemical pollutant that can damage plant tissue structures, seriously affect plant physiological metabolism and biochemical reactions, inhibit plant growth and accelerate leaf senescence. Some ozone-sensitive grape varieties show ozone injury symptoms in the field. The purpose of this study was to study the effects of long-term O3 stress on the plant growth, fruit quality, carbon and nitrogen absorption and distribution of the main cultivar ‘Cabernet Sauvignon’. MethodsO3 was administered for 2 h daily for three months to three-year-old Vitis vinifera L.cv. ‘Cabernet Sauvignon’ grapes at 75 nL/L, and the effects of O3 stress on the grape plants, the fruit growth and development, the leaves of photosystem II (PSII) and Psi activity and the carbon and nitrogen absorption and distribution were analyzed. ResultsThe results suggest that ozone pollution substantially affected the growth and physiology of ‘Cabernet Sauvignon’. Plant biomass and fruit quality were also negatively influenced by ozone pollution. Chlorophyll fluorescence analysis showed that O3 stress caused noticeable decreases in the maximum fluorescence Fm and the maximum photooxidizable P700 (Pm); the actual photochemical efficiency of PSII Y(II) decreased significantly, but the quantum yield of regulated energy dissipation Y(NPQ) increased significantly; the Psi donor side limitation Y(ND) increased, but there was no significant change in the Psi acceptor side limitation Y(NA); and the actual photochemical efficiency of Psi decreased. The carbon and nitrogen labeling of plants revealed that after O3 stress, compared with the control, the amounts of 15N and 13C absorbed by the leaves were significantly reduced, the amounts of 15N and 13C absorbed by the roots were significantly increased, and the proportions of 15N and 13C transported to the fruits were significantly reduced.

Chromosome Location Contributing to Ozone Tolerance in Wheat.

Breeding wheat for higher grain yield can contribute to global food security and sustainable production on less land. Tropospheric ozone can injure wheat plants and subsequently reduce grain yield. Identification of ozone tolerance in the wheat genome can assist plant breeders in developing new sources of tolerant germplasm. Our objective was to use the ‘Chinese Spring’ monosomic lines to screen for ozone response and identify the chromosomic locations contributing to ozone tolerance based on foliar injury. Two methodologies, Continuous Stirred Tank Reactors and Outdoor Plant Environment Chambers, were used to expose wheat monosomic lines to varying concentrations and durations of ozone. Each wheat monosomic line in ‘Chinese Spring’ has a missing chromosome in each of the wheat subgenomes (A, B, and D). In both methodologies, we found significant and repeatable data to identify chromosome 7A as a major contributor to tolerance to ozone injury in ‘Chinese Spring’. In every experiment, the absence of chromosome 7A resulted in significant injury to wheat due to ozone. This was not the case when any other chromosome was missing.

Macro- and microscopic leaf injury triggered by ozone stress in beech foliage (Fagus sylvatica L.)

The diversity of structural injury underlying visible symptoms by ozone stress resulted from the succession of degenerative processes and programmed-cell death events, depending on the ozone uptake and varying on a year-to-year basis. The effects of tropospheric ozone (O3) on the vegetation will remain a lasting concern during the twenty-first century, and deeper understanding of functional and structural responses to O3 in plant foliage in a changing environment is needed. Comprehensive analysis of the O3 injury spectrum, with a view to functional understanding of cellular processes in response to varying O3 doses. Characterization of macro- and microscopic symptoms in the sun crown foliage of adult trees exposed to ambient and twice ambient O3 levels in a Free Air O3 Enrichment (FACE) experiment using light and electron microscopy. Visible injury triggered by O3 resulted from (i) degenerative processes of varying severity (photobleaching, accelerated cell senescence, ACS), (ii) programmed cell death with disruption of cell content (hypersensitive reaction–like, HR-like) and occasional leakage of cellular debris into the apoplast, (iii) overlapping degenerative and disruptive processes, primarily in the upper mesophyll and within organelles prone to oxidative stress (chloroplasts and mitochondria) and (iv) necrosis in lower mesophyll with leakage of cellular debris in the intracellular space. Especially the degenerative and disruptive traits showed contrasting structural features. In the case of stippling symptoms, the structural variability was particularly high, as a consequence of interactions between early degenerative and late disruptive processes. These findings thus confirmed the close dependency of processes—and a further spectrum of ozone injury—on rates of ozone uptake. Such relationships and development of injury, as observed in the case of beech (Fagus sylvatica L.) foliage, are expected to be basically similar in other broadleaved tree species.

Toward stomatal-flux based forest protection against ozone: The MOTTLES approach.

European standards for the protection of forests from ozone (O3) are based on atmospheric exposure (AOT40) that is not always representative of O3 effects since it is not a proxy of gas uptake through stomata (stomatal flux). MOTTLES "MOnitoring ozone injury for seTTing new critical LEvelS" is a LIFE project aimed at establishing a permanent network of forest sites based on active O3 monitoring at remote areas at high and medium risk of O3 injury, in order to define new standards based on stomatal flux, i.e. PODY (Phytotoxic Ozone Dose above a threshold Y of uptake). Based on the first year of data collected at MOTTLES sites, we describe the MOTTLES monitoring station, together with protocols and metric calculation methods. AOT40 and PODY, computed with different methods, are then compared and correlated with forest-health indicators (radial growth, crown defoliation, visible foliar O3 injury). For the year 2017, the average AOT40 calculated according to the European Directive was even 5 times (on average 1.7 times) the European legislative standard for the protection of forests. When the metrics were calculated according to the European protocols (EU Directive 2008/50/EC or Modelling and Mapping Manual LTRAP Convention), the values were well correlated to those obtained on the basis of the real duration of the growing season (i.e. MOTTLES method) and were thus representative of the actual exposure/flux. AOT40 showed opposite direction relative to PODY. Visible foliar O3 injury appeared as the best forest-health indicator for O3 under field conditions and was more frequently detected at forest edge than inside the forest. The present work may help the set-up of further long-term forest monitoring sites dedicated to O3 assessment in forests, especially because flux-based assessments are recommended as part of monitoring air pollution impacts on ecosystems in the revised EU National Emissions Ceilings Directive.

Integrated analysis of the detoxification responses of two Euramerican poplar genotypes exposed to ozone and water deficit: Focus on the ascorbate-glutathione cycle

Ozone (O3) and drought increase tree oxidative stress. To protect forest health, we need to improve risk assessment, using metric model such as the phytotoxic O3 dose above a threshold of y nmol·m−2·s−1 (PODy), while taking into account detoxification mechanisms and interacting stresses. The impact of drought events on the effect of O3 pollution deserves special attention. Water deficit may decrease O3 entrance into the leaves by reducing stomatal opening; however, water deficit also induces changes in cell redox homeostasis. Besides, the behaviour of the cell antioxidative charge in case of stress combination (water deficit and O3) still remains poorly investigated. To decipher the response of detoxification mechanisms relatively to the Halliwell-Asada-Foyer cycle (HAF), we exposed poplar saplings (Populus nigra × deltoides) composed of two genotypes (Carpaccio and Robusta), to various treatments for 17 days, i.e. i) mild water deficit, ii) 120 ppb O3, and iii) a combination of these two treatments. Ozone similarly impacted the growth of the two genotypes, with an important leaf loss. Water deficit decreased growth by almost one third as compared to the control plants. As for the combined treatment, water deficit protected the saplings from leaf ozone injury, but with an inhibitory effect on growth. The pool of total ascorbate was not modified by the different treatments, while the pool of total glutathione increased with POD0. We noticed a few differences between the two genotypes, particularly concerning the activity of monodehydroascorbate reductase and glutathione reductase relatively to POD0. The expression profiles of genes coding for the dehydroascorbate reductase and glutathione reductase isoforms differed, probably in link with the putative localisation of ROS production in response to water deficit and ozone, respectively. Our result would argue for a major role of MDHAR, GR and glutathione in the preservation of the redox status.

Physiological and biochemical responses of elevated ozone on Pterocarpus indicus under well-watered and drought conditions

Seedlings of Pterocarpus indicus were grown in both well-watered and drought stress conditions in phytotron. Seedlings grown under well-watered and drought stress conditions were exposed to either combined or without ozone of 200 ppb for one month. First, the physiological responses to elevated ozone levels indicated a decreased biomass. The seedlings grown in arid soil and exposed to ozone showed less biomass than those grown in arid soil but not exposed to ozone. Moreover, all the seedlings except the well-watered and unexposed ones showed a significantly lower photosynthetic rate (PN) over time. However, with the accumulation of ozone injuries, the antioxidant enzyme activities increased overall. In the study results, when exposed to ozone, the well-watered seedlings exhibited more antioxidative enzyme activity than did the seedlings grown in arid soil. Generally, P. indicus in arid soil suffered less damage from elevated ozone than did the well-watered plants.

Beta-2 Adrenergic and Glucocorticoid Receptor Agonists Modulate Ozone-Induced Pulmonary Protein Leakage and Inflammation in Healthy and Adrenalectomized Rats.

We have shown that acute ozone inhalation activates sympathetic-adrenal-medullary and hypothalamus-pituitary-adrenal stress axes, and adrenalectomy (AD) inhibits ozone-induced lung injury and inflammation. Therefore, we hypothesized that stress hormone receptor agonists (β2 adrenergic-β2AR and glucocorticoid-GR) will restore the ozone injury phenotype in AD, while exacerbating effects in sham-surgery (SH) rats. Male Wistar Kyoto rats that underwent SH or AD were treated with vehicles (saline + corn oil) or β2AR agonist clenbuterol (CLEN, 0.2 mg/kg, i.p.) + GR agonist dexamethasone (DEX, 2 mg/kg, s.c.) for 1 day and immediately prior to each day of exposure to filtered air or ozone (0.8 ppm, 4 h/day for 1 or 2 days). Ozone-induced increases in PenH and peak-expiratory flow were exacerbated in CLEN+DEX-treated SH and AD rats. CLEN+DEX affected breath waveform in all rats. Ozone exposure in vehicle-treated SH rats increased bronchoalveolar lavage fluid (BALF) protein, N-acetyl glucosaminidase activity (macrophage activation), neutrophils, and lung cytokine expression while reducing circulating lymphocyte subpopulations. AD reduced these ozone effects in vehicle-treated rats. At the doses used herein, CLEN+DEX treatment reversed the protection offered by AD and exacerbated most ozone-induced lung effects while diminishing circulating lymphocytes. CLEN+DEX in air-exposed SH rats also induced marked protein leakage and reduced circulating lymphocytes but did not increase BALF neutrophils. In conclusion, circulating stress hormones and their receptors mediate ozone-induced vascular leakage and inflammatory cell trafficking to the lung. Those receiving β2AR and GR agonists for chronic pulmonary diseases, or with increased circulating stress hormones due to psychosocial stresses, might have altered sensitivity to air pollution.