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EuroBionet, the 'European Network for the Assessment of Air Quality by the Use of Bioindicator Plants', is an EU-funded cooperative project currently consisting of public authorities and scientific institutes from 12 cities in 8 countries. In 2000, the bioindicator plants tobacco (Nicotiana tabacum Bel W3), poplar (Populus nigra 'Brandaris'), spiderwort (Tradescantia sp. clone 4430), Italian rye grass (Lolium multiflorum italicum) and curly kale (Brassica oleracea acephala) were exposed to ambient air at 90 monitoring sites according to standardised methods. Visible injuries and growth parameters were assessed and the accumulation of toxic substances in leaves determined. The exposure of tobacco resulted in a gradient with low levels of ozone-induced foliar injury in N and NW Europe, and medium to high values in the southern and central regions. The results of heavy metal and sulphur analyses in rye grass samples generally showed low to very low sulphur and low to medium heavy metal concentrations in leaves. In some cities, however, local hot spots of heavy metal contamination were detected. Analyses of the PAH contents in curly kale leaves gave low to medium values, with locally elevated levels at traffic-exposed sites.

Ozone (O 3 )-induced cell death in two suspension-cultured cell lines of tobacco (Nicotiana tabacum L.) derived from Bel-W3 (hyper-sensitive to O 3 ) and Bel-B (highly tolerant to O 3 ) varieties were studied. By exposing the newly prepared cell lines to the pulse of ozonized air, we could reproduce the conditions demonstrating the difference in O 3 sensitivity as observed in their original plants, depending on the exposure time. Since O 3 -induced acute cell death was observed in the dark, the requirement for photochemical reactions could be eliminated. Addition of several ROS scavengers and chelators inhibited the cell death induced by O 3 , indicating that singlet oxygen ( 1 O 2 ), hydrogen peroxide (H 2 O 2 ), hydroxyl radical and redox-active metals such as Fe 2+ play central roles in O 3 -induced acute damages to the cells. As expected, we observed the generation of 1 O 2 and H 2 O 2 in the O 3 -treated cells using chemiluminescent probes. On the other hand, an NADPH oxidase inhibitor, superoxide dismutase (SOD), and some SOD mimics showed no inhibitory effect. Thiols added as antioxidants unexpectedly behaved as prooxidants drastically enhancing the O 3 -induced cell death. It is noteworthy that some ROS scavengers effectively rescued the cells from dying even treated after the pulse of O 3 exposure, confirming the post-ozone progress of ROS-dependent cell death mechanism. Since one of the key differences between Bel-B and Bel-W3 was suggested to be the capacity for ROS detoxification by catalase, the endogenous catalase activities were compared in vivo in two cell lines. As expected, catalase activity in Bel-B cells was ca. 7-fold greater than that in Bel-W3 cells. Interestingly, Ca 2+ chelators added prior to (not after) the pulse of O 3 effectively inhibited the induction of cell death. In addition, increases in cytosolic Ca 2+ concentration sensitive to Ca 2+ chelators, ion channel blockers, and ROS scavengers were observed in the transgenic Bel-W3 cells expressing aequorin, suggesting the action of Ca 2+ as a secondary messenger initiating the oxidative cell death. The O 3 -induced calcium response in Bel-W3 cells was much greater than Bel-B cells. Based on the results, possible pathways for O 3 -dependent generation of the lethal level of ROS and corresponding signaling mechanism for induction of cell death were discussed.

-Stomatal function and photosynthesis were investigated in beech seedlings submitted to excess Al, or/and to a deficiency in Ca and Mg. Excess Al in the nutrient solution promoted a decrease of Ca and Mg leaf contents, while K was increased. Stomatal responses to darkness, ABA and ambient CO 2 remained normal. In contrast, steady-state stomatal conductance in light was significantly smaller and correlated to a lower accumulation of K in the guard cells. Similar stomatal responses were observed for Ca-Mg deficient plants. In response to combined Al stress and low Ca and Mg nutrition, stomata remained almost insensitive to the different stimuli. The constancy in K guard cell concentration revealed a disturbance in K fluxes. Lower CO 2 assimilation rates and chlorophyll contents, on a leaf area basis, were recorded in response to all treatments. In conclusion, excess Al associated to low Ca and Mg nutrition lead to a strong stomatal dysfonction and reduced photosynthesis of beech seedlings.

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