PAL Activity and Differential Ozone Sensitivity in Tobacco, Bean and Poplar

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.