PAL ACTIVITY AND DIFFERENTIAL OZONE SENSITIVITY IN TOBACCO, BEAN AND POPLAR

Two cultivars of tobacco and bean and two clones of poplar differing i n their phenomenological response to ozone were exposed to a single oz one pulse. The first visible foliar injury appeared after 24-48 h in t he sensitive material only. The constitutive levels of PAL activity of ozone resistant and sensitive cultivars/clones were similar. In sensi tive material, ozone induced a marked, but transient, increase in PAL activity, which in tobacco cv. Bel-W3 and Pinto bean was associated wi th necrosis development. In the resistant material ozone stimulated PA L activity, but the levels remained lower than those observed in the s ensitive material. Quantitative and qualitative determinations of phen olic compounds were carried out in the poplar clones. In the sensitive clone only the behaviour of caffeic acid was different, an increase b eing observed a week after the treatment. The resistant clone exhibite d marked increase of all compounds assayed. The results are discussed in relation to the;possible role of PAL and secondary metabolites to o zone toxicity mechanisms.