Reactions of cloned poplars to air pollution : Ozone-induced increase of stress ethylene and possible antisenescence strategies.

Ozone-induced changes in ethylene production, ACC oxidase activity and the contents of ACC, MACC and free PAs were studied inPopulus nigra L. cv. Loenen with high ozone sensitivity as judged by the degree of chlorophyll degradation and premature leaf abscission.Ethylene production, ACC oxidase activity, ACC content and MACC levels were induced by the one-, two-, and three-week ozone exposure (36±9 ppb O3 for 11 hours a day). In addition, increases in PA levels, especially in spermidine, were measured in ozone treated plants.The role of free PAs and MACC synthesis as possible antisenescence reactions is discussed.