Bel W3 Research Articles

CB&I announces joint development agreement with Saudi Aramco

The ozone (O3) hypersensitive species Nicotiana tabacum Bel W3 was used to assess the impact on O3 contamination profile by a natural gas-powered thermoelectric plant (TP) that provides power to an oil refinery at Cubatão (SE-Brazil). An increase in O3 levels would represent an even more harmful effect to the Atlantic Rainforest present in the region. The biomonitoring study was performed along TP pre-operation, transition and TP post-operation phases. Tobacco plants were biweekly exposed at urban, industrial and forest areas at different altitudes. O3-induced leaf injuries were evaluated at the end of each exposure. N. tabacum plants at forest sites at mountain slope were usually more affected by O3, especially at higher layers. As TP started operating, nitrogen dioxide (O3 precursor) mean concentrations increased considerably (6 ppb to 16 ppb). The contamination of the Atlantic Rainforest by high levels of N created a favourable scenario for an increase in O3 concentrations. In fact, F200, F300 and F350 sites (forest sites at 200, 300 and 350 m.a.s.l.) had plants showing a significant increase in O3-induced leaf injuries. Phytotoxic levels were similar to those found at F700 site (forest site at 700 m.a.s.l.), which were high for the whole study period. The new O3 contamination profile persisted for F200 and F300 sites during TP post-operation phase. Although slightly lower levels than those seen on transition phase, the intensity of O3-injuries remained higher compared to the original conditions. The use of Nicotiana tabacum Bel W3 allowed to see the negative impact on the air quality after TP started operating, contributing to an increase in O3 concentrations and phytotoxic levels at forest sites at mountain slope. Plant community were then exposed to an even higher harmful effect compared to the first phase. The stability and fitness of the Atlantic Rainforest influenced by the pollution coming from Cubatão are still under potential risk. However, how the vegetation will behave at this new scenario is unknown and requires time.

Will the shift from crude oil to natural gas burning for power generation at an oil refinery increase ozone concentrations in the region of Cubatão (SE-Brazil)?

The ozone (O3) hypersensitive species Nicotiana tabacum Bel W3 was used to assess the impact on O3 contamination profile by a natural gas-powered thermoelectric plant (TP) that provides power to an oil refinery at Cubatão (SE-Brazil). An increase in O3 levels would represent an even more harmful effect to the Atlantic Rainforest present in the region. The biomonitoring study was performed along TP pre-operation, transition and TP post-operation phases. Tobacco plants were biweekly exposed at urban, industrial and forest areas at different altitudes. O3-induced leaf injuries were evaluated at the end of each exposure. N. tabacum plants at forest sites at mountain slope were usually more affected by O3, especially at higher layers. As TP started operating, nitrogen dioxide (O3 precursor) mean concentrations increased considerably (6ppb to 16ppb). The contamination of the Atlantic Rainforest by high levels of N created a favourable scenario for an increase in O3 concentrations. In fact, F200, F300 and F350 sites (forest sites at 200, 300 and 350m.a.s.l.) had plants showing a significant increase in O3-induced leaf injuries. Phytotoxic levels were similar to those found at F700 site (forest site at 700m.a.s.l.), which were high for the whole study period. The new O3 contamination profile persisted for F200 and F300 sites during TP post-operation phase. Although slightly lower levels than those seen on transition phase, the intensity of O3-injuries remained higher compared to the original conditions. The use of Nicotiana tabacum Bel W3 allowed to see the negative impact on the air quality after TP started operating, contributing to an increase in O3 concentrations and phytotoxic levels at forest sites at mountain slope. Plant community were then exposed to an even higher harmful effect compared to the first phase. The stability and fitness of the Atlantic Rainforest influenced by the pollution coming from Cubatão are still under potential risk. However, how the vegetation will behave at this new scenario is unknown and requires time.

Effect of tropospheric ozone on morphological characteristics ofNicotiana tabacumL.,Phaseolus vulgarisL. andPetunia×HybridaL. in ambient air conditions

The cumulative ozone effect on morphological parameters (visible leaf injury, plant height and leaf growth, number of bean pods, petunia flowers and stalks) was examined in this study. Well-known ozonesensitive (Bel W3) and ozone-resistant (Bel B) tobacco cultivars as well as bean cv. Nerina and petunia cv. White cascade, both recognized as ozone sensitive, were used in the experiment. Investigations were carried out at two exposure sites varying in tropospheric ozone levels. Ozone negatively affected the leaf growth of both tobacco cultivars and bean. A negative relation was also found for ozone concentration and tobacco plant height. Number of petunia flowers and stalks and bean pods was positively correlated with ozone concentration. This could have been connected with earlier plant maturation due to faster generative development of plants in ozone-stress conditions.

Differences in morpho-anatomical structure of ozone-sensitive and ozone-resistant tobacco cultivars

Tropospheric ozone causes visible injuries in selected plants. Some plant species have been recognized as resistant and sensitive to ozone. Differences in the response to ozone of two kinds of plants are interesting because of practical implications. Resistant cultivars (without visible symptoms) will be more valuable for agriculture, forestry and horticulture. It is, however, necessary to find out the reason of the occurrence of the visible symptoms. The presented studies focused on selected morphological and anatomical differences between well-known ozone-sensitive (Bel W3) and -resistant (Bel B) cultivars of tobacco plants. Daily growth of the sensitive cultivar was higher than that of the resistant one. This tendency was also valid for the leaf growth which might have been the response of the sensitive cultivar to decreased photosynthetic leaf area (necrosis) caused by ozone. Morphological investigations revealed thinner upper epidermal cells in the sensitive cultivar. Moreover, a decrease of spongy mesophyll cell layers was observed. The obtained results suggest that it is the anatomical structure that may be partly responsible for ozone resistance - wider epidermal cells, more spongy mesophyll cell layers.

Design and assembly of an experimental laboratory for the study of atmosphere–plant interactions in the system of fumigation chambers

An experimental laboratory was designed and assembled at the Botanical Institute of São Paulo, Brazil, in order to research atmosphere-plant interactions through the use of a system of fumigation chambers. A system of three "closed" fumigation chambers was designed to be used inside or outside the laboratory. The system was built to be used with a single pollutant or a mix of them. The innovation in this system is to allow chemical reactions inside the chambers that simulate atmospheric chemistry, especially photochemical processes involving high levels of ozone. Assessment of the performance and applicability of the system was based on the response of Nicotiana tabacum Bel W3 exposed to ozone produced alternatively by a generator and inside the chamber by reactions of its precursors. The results showed that the system can be well applied to the study of atmospheric chemistry interactions and the effects on plants.

Integrating monitoring networks to obtain estimates of ground-level ozone concentrations — A proof of concept in Tuscany (central Italy)

Prior to 2000 a network of conventional ozone (O 3) analysers existed in the Province of Firenze (Tuscany, central Italy). Between 2000 and 2004 the network was extended to incorporate a newly designed bioindicator network of tobacco plants ( Nicotiana tabacum Bel W3). The objective was to set-up an integrated monitoring system to obtain estimates of ground-level O 3 concentrations over the whole study area (3513 km 2) in order to fill data gaps and cover reporting requirements. The existing conventional monitors were purposefully located mainly in urban areas. A total of 45 biomonitoring sites were selected using a systematic design to cover the target area. Two to five additional biomonitoring sites were co-located with conventional O 3 analysers for calibration purposes, and five more sites for independent validation of modelled O 3 concentrations. Visible Leaf Injury Index (LII) on the tobacco plants was significantly correlated ( P: 0.018 ÷ 0.0014) with a series of O 3 exposure variables (mean of weekly 1-hour maxima, M1; mean of 7-hour means, M7; 24-hour mean, M24; and weekly AOT40). LII was found to be a significant predictor of weekly means of the O 3 exposure variables with a standard error of estimates between 13.6 and 24.3 μg m − 3 (absolute values). LII was mapped with an ad-hoc spatial model over the study area at a 2 ⁎ 2 km grid resolution, and mapped values were used to predict O 3 concentrations by means of a first order linear model. Results showed that high estimates of O 3 (up to 188 μg m − 3 as mean of weekly maxima, M1) occurred more frequently in hilly and mountainous areas, with a spatial pattern changing on an annual basis. Predicted O 3 concentrations were not significantly different from the measured concentrations ( P: 0.34), although marked differences were observed for individual sites and years. The study provided evidence that integration of monitoring networks using different methods can be a viable option to obtain estimates of O 3 concentrations over large areas.

Suitability of Nicotiana tabacum ‘Bel W3’ for biomonitoring ozone in São Paulo, Brazil

Nicotiana tabacum ‘Bel W3’ is a widely used sensitive bioindicator for ambient ozone, but it is rarely used in tropical countries. Our goal was to determine the suitability of this plant for biomonitoring ozone in the city of São Paulo by evaluating the relationships between leaf necroses and ozone under field conditions and measurements of chlorophyll a fluorescence and antioxidants in plants exposed to different concentrations of ozone in closed chambers. While a weak linear relationship between leaf injury and ozone concentrations ( R 2 = 0.10) was determined in the field, a strong linear relationship was observed in the chamber experiments. Maximum leaf injury was observed in plants submitted to 40 ppb, which coincided with a significant decrease in fluorescence and total ascorbic acid. The relationship between leaf damage observed in the field and ozone was improved when the concentrations were limited to 40 ppb ( R 2 = 0.28).

O- 2 Activates Leaf Injury, Ethylene and Salicylic Acid Synthesis, and the Expression of O3-Induced Genes in O3-Exposed Tobacco

O3 is the major component of photochemical oxidants and gives rise to visible injuries on plant leaves. In O3-exposed plants, O2- is produced before the formation of the injury, but the role that O2- plays in plant response to 03 exposure is still unknown. To clarify its role, we observed the behavior of plants during O3 exposure after pretreatment with tiron, which is an O2- scavenger. When tiron-pretreated tobacco cv. Bel W3 was exposed to O3, leaf damage was attenuated. In O3-exposed tobacco, tiron inhibited increases in the levels of ethylene and salicylic acid, which promote leaf injury. Tiron pretreatment also suppressed increases in the expression of O3-induced genes. These results suggest that O2- is involved in many plant responses induced by O3 exposure. Bel B, a tobacco cultivar that is genetically related to Bel W3, is reported to be more resistant to O3 than Bel W3, but the reason for this difference is unclear. We investigated the differences between the responses of Bel B and tiron-pretreated Bel W3 to O3 exposure, and we discuss the reasons for the resistance to O3 by comparing the phenotype of Bel B with that of tiron-pretreated Bel W3.

Interaction Between Ozone Exposure and Iron Nutrition in Two Tobacco Cultivars

ABSTRACT The initial objective was to confirm evidence, obtained from field grown plants, for iron (Fe) accumulation in leaves under ozone exposure. Tobacco plants were grown in pots under either open air or growth chamber conditions. The ozone-sensitive cultivar Bel W3 showed symptoms of ozone injury only when grown outside, while the cultivar Virginia never developed symptoms. In both cultivars, basal leaves of plants grown outside had higher concentration of Fe, but not of manganese (Mn) or zinc (Zn), than those from the growth chamber. Results suggest an interference of the oxidative stress with the mechanisms regulating Fe homeostasis. A second objective was to test whether differences in tolerance to ozone correspond with differences in tolerance to Fe toxicity. Iron toxicity was induced by supplying an excess of Fe-EDTA to plants, grown hydroponically in a growth chamber, upon partial root cutting. Symptoms in leaves were more severe in Bel W3 than in Virginia, which suggested that mechanisms of tolerance to ozone were also effective against Fe toxicity. In both cultivars, a good correlation was determined between Fe accumulation and ethylene production in the leaves.

Uptake of gaseous nitrous acid (HONO) by several plant species

Uptake of gaseous nitrous acid (HONO) by sunflower ( Heliantus annuus L. var. gigantheus), tobacco ( Nicotiana tabacum L. var. Bel W3), castor ( Rhicinus communis L. var. Carmencita), and birch ( Betula pendula L.) was studied under controlled conditions in a continuously stirred tank reactor. Exposing plants to HONO at concentrations between 60 ppt and 10 ppb led to significant uptake by the plants. The uptake was proportional to HONO concentrations and linearly related to stomatal conductivity. HONO losses at the cuticle were of minor importance. Our data imply a quick metabolism of HONO and it is concluded that the uptake of HONO by plants is only limited by diffusion of HONO through the plants stomata. Comparing results from measurements with and without plants in the chamber it is furthermore concluded that a compensation point for HONO uptake is below 20 ppt if it exists at all. Heterogeneous formation of HONO by reactions of NO 2 on the plant surfaces was either not effective or compensated by the stomatal uptake of HONO. The data of the present study imply that plant surfaces represent a sink for HONO. Therefore, it was concluded that processes on plant surfaces cannot explain HONO formation on ground surfaces as observed in field studies.

Simulated solar irradiation with enhanced UV-B adjust plastid- and thylakoid-associated polyamine changes for UV-B protection

Polyamines have been described to protect against numerous oxidative stresses in plants. Increasing UV-B radiation (280–315 nm) in the biosphere may also induce an increase in radical formation in tissues. This study employed the tobacco cultivars Bel B and Bel W3 to describe possible protective functions of polyamines against UV-B radiation in sun light simulators (GSF/Munich) with natural diurnal fluctuations of simulated UV-B. Polyamine measurements on a whole leaf basis in isolated chloroplasts and thylakoids were paralleled to photosynthetic and respiration rates, photosynthetic efficiency, leaf thickness and photosynthetic pigment compositions. The study revealed that an increase of polyamines, and especially of putrescine level in thylakoid membranes upon elevated UV-B exposure comprises one of the primary protective mechanisms in the photosynthetic apparatus of the tobacco variety Bel B against UV-B radiation. The tobacco cultivar Bel W3, sensitive to ozone, was also proved to be sensitive to UV-B. This sensitivity is attributed to its incapability to enhance putrescine level in thylakoid membranes. After prolongation of UV-B exposure, when endogenous plant balances are being gradually restored, due to secondary responses, (e.g., biosynthesis of carotenoids and of additional flavonoids) and the plant is adapting to the altered environmental conditions, then the polyamine level is being reduced. Thus, we can discriminate the UV-B induced stress period from a UV-B acclimation period.

Lichens and tobacco plants as complementary biomonitors of air pollution in the Grenoble area (Isère, southeast France)

Abstract This biomonitoring study was aimed at providing an overall assessment of nitrogen oxides (NOX) and tropospheric ozone (O3) in the Grenoble area (Isere, France). Two bioindicators, lichens and tobacco plants, were used to estimate, respectively, the spatial distribution of NOX and O3. The following methodological approaches were adopted: bioaccumulation of nitrogen in the lichen Physcia adscendens, bioindication of ozone as shown by visible injury to tobacco plants (cv. Bel W3), and biomonitoring at the lichen community level (IAP). Complementary biomonitoring maps, the first based on nitrogen concentrations of lichens and the second based on tobacco leaf injuries, were highly comparable with results obtained from physico-chemical analyses. Multivariate analyses (Canonical Correspondance Analysis) were used to determine the relationships between levels of atmospheric NO2 and O3 and the lichen communities (IAP). A lichen sensitivity scale to NO2 and O3 was attempted for 43 epiphytic species, from which it was possible to define five clusters according to their indifference, sensitivity or resistance to NO2 and O3.

Ozone has dramatic effects on the regulation of the prechorismate pathway in tobacco (Nicotiana tabacum L. cv. Bel W3)

The accumulation of aromatic secondary metabolites is a well-known element of the plant response to ozone. Most of these metabolites are synthesized via the three aromatic amino acids phenylalanine, tyrosine and tryptophan. Before branching, the biosynthetic pathway to the three amino acids shares seven enzymatic steps, called the prechorismate pathway, catalysed by 3-deoxy-D: -arabino-heptulosonate-7-phosphate (DAHP) synthase [EC 2.5.1.54], 3-dehydroquinate synthase [EC 4.2.3.4], 3-dehydroquinate dehydratase [EC 4.2.1.10]-shikimate 5-dehydrogenase [EC 1.1.1.25], shikimate kinase [EC 2.7.1.71], 5-enolpyruvylshikimate 3-phosphate synthase [EC 2.5.1.19] and chorismate synthase [EC 4.2.3.5]). We have studied the transcript level of these enzymes and the aromatic metabolite profile in the ozone sensitive tobacco cultivar BelW3 (Nicotiana tabacum L. cv Bel W3), when exposed to an acute ozone pulse (160 nl l(-1), 5 h). Specific cDNA-fragments of the corresponding six genes were isolated from tobacco Bel W3 and used as probes for determining the expression of the prechorismate pathway genes. The fully expanded leaves of ozone treated plants, which developed symptoms like necrotic leaf spots and accumulation of aromatic metabolites, showed a clear induction of the shikimate pathway genes; indicating, that this induction is linked to the development of the symptoms. Distinct kinetics and magnitudes were observed in tobacco leaves for the ozone dependent enhanced mRNA accumulation of the aforementioned genes in BelW3. The strongest and earliest induction due to ozone treatment could be observed for DAHP synthase. An isoform-specific analysis of the transcripts showed a strong induction on transcript level only for one of three isoforms, which was followed by the induction of the DAHP synthase also on protein level. The different induction kinetics of the prechorismate pathway genes indicate that their regulation in response to ozone might be regulated by different signals, for example, ethylene, reactive oxygen species or salicylic acid, which also occur with different kinetics and thus may play different roles in the plant response to ozone.

Ozone induced emissions of biogenic VOC from tobacco: relationships between ozone uptake and emission of LOX products

ABSTRACTVolatile organic compound (VOC) emissions from tobacco (Nicotiana tabacum L. var. Bel W3) plants exposed to ozone (O3) were investigated using proton‐transfer‐reaction mass‐spectrometry (PTR‐MS) and gas chromatography mass‐spectrometry (GC‐MS) to find a quantitative reference for plants’ responses to O3 stress. O3 exposures to illuminated plants induced post‐exposure VOC emission bursts. The lag time for the onset of volatile C6 emissions produced within the octadecanoid pathway was found to be inversely proportional to O3 uptake, or more precisely, to the O3 flux density into the plants. In cases of short O3 pulses of identical duration the total amount of these emitted C6 VOC was related to the O3 flux density into the plants, and not to ozone concentrations or dose–response relationships such as AOT 40 values. Approximately one C6 product was emitted per five O3 molecules taken up by the plant. A threshold flux density of O3 inducing emissions of C6 products was found to be (1.6 ± 0.7) × 10−8 mol m−2 s−1.

Ozone-induced cell death in tobacco cultivar Bel W3 plants. The role of programmed cell death in lesion formation.

Treatment of the ozone-sensitive tobacco (Nicotiana tabacum L. cv Bel W3) with an ozone pulse (150 nL L(-1) for 5 h) induced visible injury, which manifested 48 to 72 h from onset of ozone fumigation. The "classical" ozone symptoms in tobacco cv Bel W3 plants occur as sharply defined, dot-like lesions on the adaxial side of the leaf and result from the death of groups of palisade cells. We investigated whether this reaction had the features of a hypersensitive response like that which results from the incompatible plant-pathogen interaction. We detected an oxidative burst, the result of H2O2 accumulation at 12 h from the starting of fumigation. Ozone treatment induced deposition of autofluorescent compounds and callose 24 h from the start of treatment. Total phenolic content was also strongly stimulated at the 10th and 72nd h from starting fumigation, concomitant with an enhancement in phenylalanine ammonia-lyase a and phenylalanine ammonia-lyase b expression, as evaluated by reverse transcriptase-polymerase chain reaction. There was also a marked, but transient, increase in the mRNA level of pathogenesis-related-1a, a typical hypersensitive response marker. Overall, these results are evidence that ozone triggers a hypersensitive response in tobacco cv Bel W3 plants. We adopted four criteria for detecting programmed cell death in ozonated tobacco cv Bel W3 leaves: (a) early release of cytochrome c from mitochondria; (b) activation of protease; (c) DNA fragmentation by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling of DNA 3'-OH groups; and (d) ultrastructural changes characteristic of programmed cell death, including chromatin condensation and blebbing of plasma membrane. We, therefore, provide evidence that ozone-induced oxidative stress triggers a cell death program in tobacco cv Bel W3.

Different responses of two tobacco cultivars and their cell suspension cultures to quercinin, a novel elicitin from Phytophthora quercina

In this study we describe the response of two tobacco cultivars ( Nicotiana tabacum L. cv. Bel B and Bel W3) and their cell suspension cultures to quercinin, a novel elicitin produced by the oak pathogen Phytophthora quercina. N-terminal sequencing of the purified protein proved that it belongs to the basic β-elicitins with threonine on position 13. Both tobacco leaves and cells of the cultivar Bel W3 showed hypersensitive cell death after quercinin treatment. Leaves of Bel B also developed quercinin-induced necrosis but higher concentrations of quercinin were necessary as compared to Bel W3. Also Bel B cells showed cell death induction only at the highest quercinin concentration (20 nM). In cell suspension experiments we also measured the quercinin-induced oxidative burst, which occurred in both cultivars. H 2O 2 production in Bel B increased with increasing quercinin concentration and was inhibited only at the highest elicitin concentration (20 nM) whereas the oxidative burst in Bel W3 was completely abolished by 5 nM quercinin. Furthermore we demonstrated that neither H 2O 2 nor superoxide were responsible for cell death induction since neither the inhibitor diphenyleneiodonium (DPI) nor the enzymes catalase (CAT) and superoxide dismutase (SOD) influenced the hypersensitive reaction (HR) in Bel W3 cells. Due to the different response of Bel W3 and Bel B towards the P. quercina elicitin, our system represents an interesting tool to elucidate signaling pathways in tobacco leading to hypersensitive cell death.

Ozone impact on the photosynthetic apparatus and the protective role of polyamines

One of the primary plant mechanisms protecting leaf cells against enhanced atmospheric ozone is the accumulation of polyamines, generally observed as an increase in putrescine level, and in particular its bound form to thylakoid membranes. Ozone-sensitive plants of tobacco (cultivar Bel W3) in contrast to ozone-tolerant Bel B, are not able to increase their endogenous thylakoid membrane-bound putrescine when they are exposed to an atmosphere with enhanced ozone concentration, resulting in reduction of their photosynthetic rates and consequently reduction in plant biomass formation. In comparison to the tolerant cultivar Bel B, a prolongation of ozone exposure thus can lead to typical visible symptoms (necrotic spots) in leaves of the sensitive plant. Exogenously manipulated increase of the cellular putrescine levels of the ozone-sensitive Bel W3 is sufficient to revert these effects, whereas a reduction in endogenous putrescine levels of the tolerant cultivar Bel B renders them sensitive to ozone treatment. The results of this work reveal a regulator role for polyamines in adaptation of the photosynthetic apparatus and consequently to its protection in an environment polluted by ozone.

Oxidative burst and cell death induced by b-quercinin and zoospores of Phytophthora quercina in tobacco cell cultures

Mode of action of β-quercinin, a novel elicitin on tobacco cell suspension cultures (cvs. Bel B and Bel W3) was investigated by measuring the oxidative burst and cell death in these cell cultures. β-quercinin induced an oxidative burst comparable to that excited by zoospores from P. quercina. Adding superoxidedismutase, catalase and diphenyleneiodonium to elicited cell cultures, it could be demonstrated, that the induction of cell death in tobacco cell cultures is not correlated to the oxidative burst.

Ozone-response mechanisms in tobacco: implications of polyamine metabolism.

• Polyamines have been suggested to counteract oxidative damage in plants. Here, we present a detailed analysis of polyamine accumulation and its relationship to photosynthetic parameters in two tobacco (Nicotiana tabacum) cultivars (ozone-sensitive Bel W3 and ozone-tolerant Bel B) after a single ozone pulse and after a 1-month exposure in the open air. • Free putrescine accumulated in undamaged tissue of both cultivars, whereas putrescine conjugated to soluble and cell-wall bound components accumulated predominantly in tissue undergoing cell death in Bel W3 plants. Accumulation was caused by a redirection of the conjugation pathway, as well as by a transient increase in arginine decarboxylase and ornithine decarboxylase specific activity. This increase seemed to be regulated at post-transcriptional level. • Measurements of chlorophyll content and fluorescence showed that, in addition to visible necrotic lesions, Bel W3 plants suffered considerable photosynthetic damage in other parts of the leaf. • Accumulation of conjugated putrescine is part of the ozone-induced programmed cell death response in Bel W3 plants. Ozone-induced synthesis of free putrescine is not correlated with ozone-resistance in Bel B plants, which are apparently impaired in signal transduction pathways that are necessary to control the cellular redox state. However, Bel B plants are able to perceive ozone stress and to induce a series of defense mechanisms without activating hypersensitive cell death.

Ozone uptake and its effect on photosynthetic parameters of two tobacco cultivars with contrasting ozone sensitivity

Leaf discs of the ozone tolerant tobacco ( Nicotiana tabacum L.) cv. Bel B and of the ozone sensitive cv. Bel W3, were exposed to an acute ozone fumigation (300 ppb) for 3 h. We measured ozone uptake by leaves and physiological characteristics before, during and after the treatment, in order to determine if the different O 3 sensitivity was correlated to the leaf uptake. In the tolerant cv. Bel B, O 3 uptake was high during the first 2 h of ozone exposure and then decreased. In the sensitive cv. Bel W3, the rate of O 3 uptake decreased constantly during ozone fumigation. The estimated cumulative uptake over the treatment time was higher (200 ± 30 μmol m –2) in Bel B than in Bel W3 (130 ± 12 μmol m –2). Thus, the ozone sensitivity was not correlated with ozone uptake. Stomatal conductance and photosynthesis were significantly inhibited during the fumigation in both cultivars. However, these reductions were strong and irreversible in the cv. Bel W3, while in the cv. Bel B both parameters recovered in the post-fumigation period. Thus, ozone tolerance may be related to a sustained capacity of recovery. There was no linear correlation between ozone uptake and photosynthesis reduction, but a threshold of ozone uptake was found after which photosynthesis was substantially impaired. This threshold may or may not be reached under the same external ozone level, indicating that the AOT40 may not be a sufficiently accurate index for the detection of ozone damage in plants.