Abstract  Jasmonates, composed of jasmonic acid (JA) and methyl jasmonate (MeJA), are widely distributed signaling compounds in plants. Jasmonate-mediated signaling suppresses ozone-induced ethylene biosynthesis as well as cellular injury since an ozone-sensitive Arabidopsis mutant, ojil, showed increased ozone-induced ethylene production and reduced sensitivity to MeJA (KANNA & al. 2003). Although ojil plants had higher JA contents than the wild-type (Ws-2) plants during exposure to 0.2ppm ozone,. microarray analysis revealed decreased expression of genes for enzymes in JA biosynthesis in this mutant. On the other hand, salicylic acid contents and expression of salicylic-acid inducible and biosynthetic genes in ojil plants were similar to those in the wild-type plants until 12 h after the beginning of ozone exposure. In spite of foliar injury, ascorbate contents increased in Arabidopsis by ozone exposure. While ojil plants revealed lower ascorbate contents than the wild-type plants, exogenous MeJA suppressed the increase in ascorbate contents in the wild-type plants at 6 h after the beginning of ozone exposure. These results imply that jasmonate-mediated signaling is involved in the regulation of the defense system in the surviving cells under stress conditions.

Abstract  The causal relationships among ethylene emission, oxidative burst and tissue damage, and the temporal expression patterns of some ethylene biosynthetic and responsive genes, were examined in the Never ripe (Nr) tomato (Lycopersicon esculentum) mutant and its isogenic wild type (cv. Pearson), to investigate the role played by the ethylene receptor LE-ETR3 (NR) in mediating the plant response to ozone (O-3). Tomato plants were used in a time-course experiment in which they were exposed to acute O-3 fumigation with 200 nl l(-1) O-3 for 4 h. The pattern of leaf lesions indicated similar sensitivities to O-3 for cv. Pearson and Nr. In both genotypes, O-3 activated a hydrogen peroxide (H2O2)-dependent oxidative burst, which was also ethylene-driven in Nr leaves. Ozone induced some ethylene and jasmonate biosynthetic and inducible genes, although with different timings and to different extents in the two genotypes. The overall data indicate that Nr retains partial sensitivity to ethylene, suggesting only a marginal role of the NR receptor in mediating the complex response of tomato plants to O-3.

Abstract  Ozone, a major photochemical oxidant, induces leaf injury. Salicylic acid (SA) is a kind of plant hormone and an important regulator of plant resistance to pathogens. In ozone-exposed plants, SA participates in both the formation of leaf injury and the defense response. In pathogen-infected plants, SA is synthesized via two pathways involving phenylalanine or isochorismate. Biosynthesis of SA in ozone-fumigated plants had not been well defined, so we examined it in tobacco and Arabidopsis. Salicylic acid accumulated in tobacco exposed to 0.2 ppm ozone for 6 h. At the same time, phenylalanine ammonia-lyase (PAL) activity, its mRNA level, and the level of chorismate mutase (CM) transcripts increased remarkably, whereas isochorismate synthase (ICS) activity did not increase. These results may suggest that ozone-exposed tobacco synthesized SA via the phenylalanine pathway. Salicylic acid levels also increased in ozone-exposed Arabidopsis, but not in sid2 (salicylic acid induction-deficient 2) mutants, in which ICSI is defective. Furthermore, ICS activity and the mRNA level of ICSI increased dramatically in wild-type Arabidopsis after the start of ozone exposure. These results suggest that ozone-exposed Arabidopsis synthesizes SA from isochorismate. Therefore, our results imply that the main pathway of ozone-induced SA biosynthesis differs between tobacco and Arabidopsis.

Abstract  In this paper optical indices calculated from leaf reflectance measurements, acquired with a high resolution spectroradiometer, were investigated to monitor 03 stress on Fagus sylvatica L. from the strain phase to the damage phase when visible symptoms occur (e.g. chlorosis, leaf browning). The CI (Chlorophyll Index) was the most sensible index to a wide range of chlorophyll (Chl) concentrations (R-2=0.93), the simple ratio R-695/R-740 (Ctr2) was the most correlated to carotenoids/chlorophyll (Car/Chl) ratio (R-2=0.65), while Yl (Yellowness Index) was sensible to Car/Chl ratio and to low Chl values but tends to saturate at moderate to high Chl concentrations. PRI (Photochemical Reflectance Index) was correlated with the physiological parameters NPQ (Non Photochemical Quenching) and Delta F/F-m' confirming this index is a good indicator of photosynthetic efficiency. Results from this experiment showed that Cl, Ctr2 and PRI were reliable indices of 03 effects on Fagus sylvatica L. before visible symptoms occurred, while Yl was able to detect the senescence anticipation when visible symptoms already spread. These results were confirmed by physiological parameters measured in field (F-v/F-m, NPQ and Delta F/F-m').

Abstract  A new parameterisation of ozone uptake by vegetation, based on the observational determination of functional dependence of stomala ozone conductances on environmental parameters such as temperature, wind speed, top-of-canopy ozone concentrations, water vapour pressure deficit, and soil water content, is proposed. Measurements of ozone fluxes and related parameters have been made using micrometeorological methods over wheat in the Po river plain, Nor-them Italy. The results show the discrepancy between the AOT40 index, based on the ozone concentration cumulated function over the season, and the cumulated stomatal ozone flux. The new parameterisation proposes a corrected AOT index, which takes environmental and plant physiological effects into account. The corrected AOT is in agreement with the cumulated stomatal ozone uptake flux.

Abstract  This study is part of a three-year project on biogenic volatile organic compound (VOC) emissions from trees of the temperate warm Atlantic rainforest found in the metropolitan area of Sao Paulo City ( MASP). No study of VOC emission rates from plant species has been carried out in the temperate warm Atlantic rainforest of Brazil prior to this work. Eleven species were selected (Alchornea sidifolia, Cupania oblongifolia, Cecropia pachystachia, Syagrus romanzoffiana, Casearia sylvestris, Machaerium villosum, Trema micrantha, Croton floribundus, Myrcia rostrata, Solanum erianthum and Ficus insipida) and some of them were studied in urban, sub-urban and forest areas inside the MASP in order to evaluate biogenic VOC composition at sites characterized by different emission sources. Biogenic VOC emissions were determined by placing branches of plants in a dynamic enclosure system, an all-Teflon cuvette, and by sampling the compounds in the air leaving the cuvette. Pre-concentration using adsorbents to retain the VOC, followed by GC-MS after thermal desorption of the sample, was employed to determine the amount of biogenic hydrocarbons. The collection of carbonyl compounds on a 2,4-dinitrophenylhydrazine coated silica followed by HPLC-UV was used to analyze low molecular weight carbonyl compounds. Emission rates of isoprene, α-pinene, camphene and limonene ranged from 0.01 to 2.16 μ g C h(-1) g(-1) and emission rates of aldehydes (C-2-C-6), acrolein, methacrolein and 2-butanone ranged from 1.5 x 10(-2) to 2.3 μ g C h(-1) g(-1). Ambient and leaf temperatures, relative humidity, light intensity, O-3 and NOx levels in the local atmosphere were monitored during experiments. It was possible to identify different biogenic VOCs emitted from typical plants of temperate warm Atlantic rainforest. The emission rates were reported as a function of the type of site investigated and were only provided for compounds for which quanti. cation was feasible. Other biogenic compounds were only identified.

Abstract  Biogenic hydrocarbons emitted by vegetation are important contributors to secondary organic aerosol (SOA), but the aerosol formation mechanisms are incompletely understood. In this study, the formation of aerosols and gas-phase products from the ozonolysis and photooxidation of a series of biogenic hydrocarbons (isoprene, 8 monoterpenes, 4 sesquiterpenes, and 3 oxygenated terpenes) are examined. By comparing aerosol growth (measured by Differential Mobility Analyzers, DMAs) and gas-phase concentrations (monitored by a Proton Transfer Reaction Mass Spectrometer, PTR-MS), we study the general mechanisms of SOA formation. Aerosol growth data are presented in terms of a "growth curve", a plot of aerosol mass formed versus the amount of hydrocarbon reacted. From the shapes of the growth curves, it is found that all the hydrocarbons studied can be classified into two groups based entirely on the number of double bonds of the hydrocarbon, regardless of the reaction systems (ozonolysis or photooxidation) and the types of hydrocarbons studied: compounds with only one double bond and compounds with more than one double bond. For compounds with only one double bond, the first oxidation step is rate-limiting, and aerosols are formed mainly from low volatility first-generation oxidation products; whereas for compounds with more than one double bond, the second oxidation step may also be rate-limiting and second-generation products contribute substantially to SOA growth. This behavior is characterized by a vertical section in the growth curve, in which continued aerosol growth is observed even after all the parent hydrocarbon is consumed.

Abstract  Intra-genus and intra-specific variation and the influence of nitrogen enrichment on net assimilation and stomatal conductance of some annual Trifolium species of Mediterranean dehesa grasslands were assessed under experimental conditions. Also gas exchange rates were compared between some Leguminosae and Poaceae species growing in the field in a dehesa ecosystem in central Spain. The results showed that the previously reported different O-3 sensitivity of some Trifolium species growing in pots does not seem to be related to different maximum g(s) values. In addition, no clear differences on gas exchange rates could be attributed to Leguminosae and Poaceae families growing in the field, with intra-genus variation being more important than differences found between families. Further studies are needed to increase the database for developing a flux-based approach for setting O-3 critical levels for semi-natural Mediterranean species. (c) 2006 Elsevier Ltd. All rights reserved.

Abstract  Ozone-sensitive (NC-S clone) and resistant plants (NC-R clone) of Trifolium repens and Centaurea jacea were exposed to moderate ozone concentrations in ambient air. The aim of this study was the investigation of the relation between ozone-sensitivity and leaf concentrations of antioxidants (ascorbic acid, total phenolics and total antioxidant capacity). NC-R clone showed the highest concentrations of antioxidants with 50-70% more ascorbic acid than NC-S. NC-R had about 5 times more ascorbic acid in the young leaves and 9 times more in the old leaves than Centaurea. In a fumigation experiment with acute ozone stress (100 nl L-1) the antioxidant levels changed profoundly. The ozone-injured leaves of NC-S had 6-8 times more total phenolics than uninjured leaves. Generally older leaves had lower antioxidant concentrations and were more prone to ozone injury than younger leaves. Ascorbic acid concentrations were closer related to the appearance of visible ozone injury than the other antioxidative parameters. (c) 2006 Elsevier Ltd. All rights reserved.

Abstract  Modelling-based studies to assess the extent and magnitude of ozone (O-3) risk to agriculture in Asia suggest that yield losses of 5-20% for important crops may be common in areas experiencing elevated O-3 concentrations. These assessments have relied on European and North American dose-response relationships and hence assumed an equivalent Asian crop response to O-3 for local cultivars, pollutant conditions and climate. To test this assumption we collated comparable dose-response data derived from fumigation, filtration and EDU experiments conducted in Asia on wheat. rice and leguminous crop species. These data are pooled and compared with equivalent North American dose-response relationships. The Asian data show that at ambient O-3 concentrations found at the study sites (which vary between similar to 35-75 ppb 4-8 h growing season mean), yield losses for wheat, rice and legumes range between 5-48, 3-47 and 10-65%, respectively. The results indicate that Asian grown wheat and rice cultivars are more sensitive to O-3 than the North American dose-response relationships would suggest. For legumes the scatter in the data makes it difficult to reach any equivalent conclusion in relative sensitivities. As such, existing modelling-based risk assessments may have substantially underestimated the scale of the problem in Asia through use of North American derived dose-response relationships. (c) 2009 Elsevier Ltd. All rights reserved.

Abstract  Ultraviolet-B (UV-B, 280-320 nm) radiation may have severe negative effects on plants including damage to their genetic information. UV protection and DNA-repair mechanisms have evolved to either avoid or repair such damage. Since autotrophic plants are dependent on sunlight for their energy supply, an increase in the amount of UV-B reaching the earth's surface may affect the integrity of their genetic information if DNA damage is not repaired efficiently and rapidly. Here we show that overexpression of cyclobutane pyrimidine dimer (CPD) photolyase (EC 4.1.99.3) in Arabidopsis thaliana (L.), which catalyses the reversion of the major UV-B photoproduct in DNA (CPDs), strongly enhances the repair of CPDs and results in a moderate increase of biomass production under elevated UV-B.

Abstract  Incomplete stomatal closure during the night is observed in a diverse range of C3 and C4 species (Fig. 1 ; Supplemental Table S1) and can lead to substantial nighttime transpirational water loss. Although water loss is an inevitable consequence of stomatal opening for photosynthetic carbon gain, nighttime stomatal opening is unexpected because carbon gain is not occurring and the need to cool leaves is reduced or absent. Most species have the ability to close stomata more than is commonly observed at night, as demonstrated by reduced nighttime leaf conductance (gnight) in response to water stress, abscisic acid (ABA), and other treatments reviewed in this Update.

Abstract  Tropospheric ozone represents a relevant atmospheric pollutant, because of its strong oxidizing potential. The risk for animal (human) and plant health, at molecular and cellular level, arises from the oxidative damage to lipids, proteins and nucleic acids, depending on the dose. Therefore, ozone concentration and exposure time determine the chronic or acute toxicity and, consequently, the severity of injury at biochemical and physiological level. In living organisms, reactive oxygen species (ROS), directly or indirectly derived from ozone exposure, are scavenged by enzymatic and non-enzymatic antioxidant defensive mechanisms, overall deputed to preserve cell structures and biomacromolecules from the oxidative damage. These defences are essentially those also involved in detoxifying the ROS inevitably produced by the metabolism of organisms living in oxygenic atmosphere.

Abstract  Tropospheric ozone is a growing environmental menace in Italy and in the whole Mediterranean basin. The importance of active biomonitoring of this pollutant with hypersensitive Bel-W3 tobacco plants is stressed, and several examples of field studies carried out in Italy with this technique are presented. Current limitations are discussed, with special emphasis on data quality assessment and the opportunity of adopting easy-to-use kits based on tobacco germlings instead of adult plants. A standardization of methodologies (from cultivation to scoring and data elaboration), also at an international level, is strongly felt to be needed, in order to get official acknowledgement of biomonitoring procedures. Potential educational implications, with the active involvement of students and environmentalists, are shown. Other biological indicators are used. namely sensitive and resistant white clover (Trifolium repens) clones (as descriptors of biomass reduction in crops species) and Centaurea jacea (brown knapweed) as a model species to evaluate the relationship between ozone exposure and effects on the performance and injury symptoms of native plants which are largely used in the framework of European programmes.

Abstract  This article reviews major impacts of climate change on agriculture and forestry.

Abstract  Experiments were conducted with two commonly grown mungbean varieties viz., M-28 and 6601, in open top chambers and ambient field conditions with the aim of ascertaining the effects of air pollution on yield. The 8-h daily mean ozone concentrations were 41-73 nl litre(-1). A considerable reduction of 47.06% and 51.12% in seed yield for M-28 and 6601, respectively were found which are substantially more than might be predicted elsewhere. These reductions in economic yield were due to decrease in both numbers of seed per pod and individual seed weight.

Abstract  Photosynthetic stimulation and stomatal conductance (Gs) depression in Quercus ilex leaves at a CO2 spring suggested no down-regulation. The insensitivity of Gs to a CO2 increase (from ambient 1500 to 2000 mu mol mol(-1)) suggested stomatal acclimation. Both responses are likely adaptations to the special environment Of CO2 Springs. At the CO2-enriched site, not at the control site, photosynthesis decreased 9% in leaves exposed to 2x ambient O-3 concentrations in branch enclosures, compared to controls in charcoal-filtered air. The stomatal density reduction at high CO2 was one-third lower than the concomitant Gs reduction, so that the O-3 uptake per single stoma was lower than at ambient CO2. No significant variation in monoterpene emission was measured. Higher trichome and mesophyll density were recorded at the CO2-enriched site, accounting for lower O-3 sensitivity. A long-term exposure to H2S, reflected by higher foliar S-content, and CO2 might depress the antioxidant capacity of leaves close to the vent and increase their O-3 sensitivity. (c) 2006 Elsevier Ltd. All rights reserved.

Abstract  The study examined air pollution tolerance indices ( APTI) of ten plant species around the Erhoike-Kokori oil exploration station of Delta state. Four physiological and biochemical parameters; leaf relative water content (RWC) ascorbic acid content ( AA), total leaf chlorophyll (TCh) and leaf extract pH were used to compute the APTI values. The result showed that combining variety of these parameters gave a more reliable result than those of individual parameter. The order of tolerance is as follows: Psidium guajava < Elaesis guineensis < Musa paradisiaca < Bambosa bambosa < Anacadium occidentale < Terminalia catappa < Manihot exculenta < Impereta cylindrical < Chromolaena odorata < Manifera indica.

Abstract  Maintaining healthy forests is the major objective for the Forest Service scientists and managers working for the U.S. Department of Agriculture. Air pollution, specifically ozone (O-3) and nitrogenous (N) air pollutants, may severely affect the health of forest ecosystems in the western U.S. Thus, the monitoring of air pollution concentration and deposition levels, as well as studies focused on understanding effects mechanisms, are essential for evaluation of risks associated with their presence. Such information is essential for development of proper management strategies for maintaining clean air, clean water, and healthy ecosystems on land managed by the Forest Service. We report on two years of research in the central Sierra Nevada of California, a semi-arid forest at elevations of 1100-2700 m. Information on O-3 and N air pollutants is obtained from a network of 18 passive samplers. We relate the atmospheric N concentration to N concentrations in streams, shallow soil water, and bulk deposition collectors within the Kings River Experimental Watershed. This watershed also contains an intensive site that is part of a recent Forest Service effort to calculate critical loads for N, sulfur, and acidity to forest ecosystems. The passive sampler design allows for extensive spatial measurements while the watershed experiment provides intensive spatial data for future analysis of ecosystem processes.

Abstract  Cutleaf coneflower (Rudbeckia laciniata L) seedlings were placed into open-top chambers in May, 2004 and fumigated for 12 wks. Nine chambers were fumigated with either carbon-filtered air (CF), nonfiltered air (NF) or twice-ambient (2x) ozone (O-3). Ethylenediurea (EDU) was applied as a foliar spray weekly at 0 (control), 200, 400 or 600 ppm. Foliar injury occurred at ambient (30%) and elevated O-3 (100%). Elevated O-3 resulted in significant decreases in biomass and nutritive quality. Ethylenediurea reduced percent of leaves injured, but decreased root and total biomass. Foliar concentrations of cell-wall constituents were not affected by EDU alone; however, EDU x O-3 interactions were observed for total cell-wall constituents and lignocellulose fraction. Our results demonstrated that O-3 altered the physiology and productivity of cutleaf coneflower, and although reducing visible injury EDU may be phytotoxic at higher concentrations. (C) 2008 Elsevier Ltd. All rights reserved.

Abstract  Critical levels to determine plant response to ozone (O-3) have been used in Europe since the 1980s, utilizing the concentration-based AOT40 to relate plant response to ambient O-3 exposure. More recently, there has been progress in Europe toward utilizing flux-based critical levels, because plant response is more closely related to O-3 uptake than to the amount of O-3 in ambient air. Flux-based critical levels are plant species specific; data for parameterization of flux-based critical levels models are lacking for most plant species. Although flux-based critical levels are now being used for a limited number of agricultural crops and tree species where data are available, the use of flux-based critical levels is limited by the lack of adequate consideration and incorporation of plant internal detoxification mechanisms in flux modeling. Critical levels have not been used in North America; however, recent interest in the U.S. and Canada for using critical loads for nitrogen and sulfur has generated interest in using critical levels for O-3. A major obstacle for utilization of critical levels in North America is that ambient air quality standards for O-3 in the U.S. and Canada are concentration based. It appears that cumulative exposure-based metrics, particularly when implemented with a quantification of peak concentrations and environmental variables, such as a drought index, are currently the most useful to relate O-3 to vegetation response. Because data are unavailable to quantify detoxification potential of vegetation, effective flux models are not available to determine plant response to O-3.

Abstract  Surface ozone concentration and surface air temperature was measured hourly at three coastal sites, four low elevation inland sites and two high elevation inland sites in southwestern Sweden. Diurnal ozone concentration range (DOR) and diurnal temperature range (DTR) were strongly correlated, both spatially and temporally, most likely because both depended on atmospheric stability. Accumulated ozone exposure above a threshold concentration of x nmol mol(-1) (AOTx) was estimated from time-integrated ozone concentration (as from diffusive sampling) and measures of ozone concentration variability. Two methods both estimated 24-h AOTx with high accuracy (modelling efficiencies >90% for x <= 40 nmol mol(-1)). Daytime (08:00-20:00) AOTx could not be equally well estimated. Estimates were better for lower AOT thresholds. Diffusive ozone concentration sampling, combined with hourly temperature monitoring, could be a valuable complement to ozone concentration monitoring with continuous instruments. (C) 2009 Elsevier Ltd. All rights reserved.

Abstract  Surface ozone pollution may cause reductions in rice (Oryza sativa L.) yield. Ozone sensitivity in rice cultivars is often evaluated based on visible leaf injury at an early growth stage. However, it is not clear whether reduction in grain yield is related to visible injury. Therefore, visible damage and grain yield reduction were examined in Japanese and Asian rice cultivars exposed to ozone. In experiment 1, 3-week-old rice seedlings were exposed to ozone (min.: 20 nl center dot l-1, max.:120 nl center dot l-1) for 12 h in open-top chambers (OTCs). Visible leaf injury was quantified according to a leaf bronzing score. In experiment 2, rice plants were exposed to ozone in OTCs throughout the cropping season until grain harvest. Daily mean ozone concentrations were maintained at 2, 23, 28, 42, and 57 nl center dot l-1 with a regular diurnal pattern of exposure. After harvest, grain yield was determined. Based on visible injury to the uppermost fully expanded leaf, the indica cultivar 'Kasalath' was most tolerant, and the japonica cultivar 'Kirara 397' was most sensitive to ozone. However, grain yields for both 'Kasalath' and 'Kirara 397' were significantly decreased after ozone exposure. The indica cultivar 'Jothi' suffered severe injury after ozone exposure but had no reduction in grain yield. Therefore, ozone sensitivity of rice cultivars evaluated by visible injury did not coincide with that evaluated by the reductions in grain yield. These results suggest that mechanisms that induce acute leaf injury do not relate to chronic ozone toxicity that reduces yield.

Abstract  Global climatic change scenarios predict a significant increase in future tropospheric ozone (O-3) concentrations. The present investigation was done to assess the effects of elevated O-3 (70 and 100 ppb) on electron transport, carbon fixation, stomatal conductance and pigment concentrations in two tropical soybean (Glycine max L.) varieties, PK 472 and Bragg. Plants were exposed to O-3 for 4 h center dot day-1 from 10:00 to 14:00 from germination to maturity. Photosynthesis of both varieties were adversely affected, but the reduction was higher in PK 472 than Bragg. A comparison of chlorophyll a fluorescence kinetics with carbon fixation suggested greater sensitivity of dark reactions than light reactions of photosynthesis to O-3 stress. The O-3-induced uncoupling between photosynthesis and stomatal conductance in PK 472 suggests the reduction in photosynthesis may be attributed to a factor other than reduced stomatal conductance. An increase in internal CO2 concentration in both O-3-treated soybean varieties compared suggests that the reduction in photosynthesis was due to damage to the photosynthetic apparatus, leading to accumulation of internal CO2 and stomatal closure. The adverse impact of O-3 stress increased at higher O-3 concentrations in both soybean varieties leading to large reductions in photosynthesis. This study suggests that O-3-induced reductions in photosynthesis in tropical and temperate varieties are similar.