Ozone induces a differential accumulation of phenyalanine ammonia-lyase, chalcone synthase and chalcone isomerase RNA transcripts in sensitive and resistant bean cultivars

On exposure to a realistic ozone dose, an enhanced mRNA accumulation for ph enyalanine ammonia-lyase (EC 4.3.1.5), naringenin-chalcone synthase [malony l-CoA:4-coumaroyl-CoA malonyltransferase (cyclising); EC 2.3.1.74] and chal cone isomerase [flavanone lyase (decyclising); EC 5.5.1.6] genes, whose pro ducts are involved in the biosynthesis of phenylpropanoid molecules, flavon oid pigments and isoflavonoid phytoalexins, was observed in primary leaves of the bean (Phaseolus vulgaris L.) cv. Pinto. This cultivar was previously known to be ozone-sensitive on the basis of the appearance of macroscopic foliar injury, but not in coeval leaves of the bean cv. Groffy, known to be ozone-resistant on the basis of the aforementioned criterion. Distinct tim e patterns were observed in Pinto leaves for the ozone-dependent enhanced m RNA accumulation for the aforementioned genes, which in all cases largely p receded the appearance of visible injury symptoms. These results lend suppo rt to the view of ozone as an abiotic elicitor of plant defence responses. By analogy with other case studies, it is also suggested that proneness to develop visible ozone symptoms might rest on a sequence of molecular events similar to that leading to the hypersensitive response during plant-pathog en incompatible interactions.