[en] Centaurea jacea has been suggested as a potential bioindicator for ozone, but little is known about its intraspecific variation in sensitivity, especially at molecular level. The effects of ozone (200 ppb, 5 h) on sensitive and resistant lines of Centaurea have been investigated at the end of fumigation. Sensitive plants showed characteristic symptoms of injury in the form of diffuse discoloration stipples on leaves. A PCR-based approach was used to identify and isolate a partial-length cDNA coding for PAL and CHS genes. The northern analysis of PAL showed accumulation of transcript in both lines correlated with a typical increase of PAL activity (+41 and +91% in resistant and sensitive material, respectively, compared to controls). On the contrary, the transcripts of CHS, in resistant and sensitive plants, did not change after treatment. Total phenols were not affected by ozone, while anthocyanins were quickly utilised by resistant clone as antioxidant compounds. - Characterization and isolation of PAL and CHS genes in Centaurea jacea exposed to O₃

[en] Ozone (O₃) exposure at Italian background sites exceeds UN/ECE concentration-based critical levels (CLe_c), if expressed in terms of AOT40. Yet the occurrence of adverse effects of O₃ on forests and crops is controversial. Possible reasons include (i) ability of response indicators to provide an unbiased estimate of O₃ effects, (ii) setting of current CLe_c in terms of cut-off value and accumulation level, (iii) response functions adopted to infer a critical level, (iv) environmental limitation to O₃ uptake and (v) inherent characteristics of Mediterranean vegetation. In particular, the two latter points suggest that critical levels based on accumulated stomatal flux (CLe_f) can be a better predictor of O₃ risk than CLe_c. While this concept is largely acknowledged, a number of factors may limit its applicability for routine monitoring. This paper reviews levels, uptake and vegetation response to O₃ in Italy over recent years to discuss value, uncertainty and feasibility of different approaches to risk assessment. - While the flux-based approach is scientifically sounder, a more practical concentration-based approach is still necessary for routine monitoring