Two cultivars of tobacco and bean and two clones of poplar differing in their phenomenological response to ozone were exposed to a single ozone pulse. The first visible foliar injury appeared after 24-48 h in the sensitive material only. The constitutive levels of PAL activity of ozone resistant and sensitive cultivars/ciones were similar. In sensitive material, ozone induced a marked, but transient, increase in PAL activity, which in tobacco cv. Be!-W3 and Pinto bean was associated with necrosis development. In the resistant material ozone stimulated PAL activity, but the levels remained lower than those observed in the sensitive material. Quantitative and quahtative determinations of phenolic compounds were carried out in the poplar clones. In the sensitive clone only the behaviour of caffeic acid was different, an increase being observed a week after the treatment. The resistant clone exhibited marked increase of al! compounds assayed. The results are discussed in relation to the possible role of PAL and secondary metabolites to ozone toxicity mechanisms.
An innovative miniaturized kit based on the use of 2-week-old ozone-supersensitive tobacco germlings (Nicotiana tabacum L. cv. Bel-W3) raised in tissue culture plates was utilized, in conjunction with four calibrated automatic analyzers, to monitor the distribution of phytotoxic ground level ozone in Tuscany during the summer of 1993 at 27 sites differing in nature. Germlings of ozone-resistant Bel-B tobacco were also included in the protocol. The intensity of visible injury on the cotyledons of Bel-W3 was linearly correlated with several ozone statistical descriptors. The occurrence of phytotoxic levels of photochemical ozone was detected in all the monitoring sites, which included rural and remote areas, whose local sources of pollution were negligible. The suitability of the new methodology for low-cost, space-saving, user-friendly monitoring of ozone on a large geographical scale is discussed.
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