Ozono: percezione del pericolo e reazioni precoci di difesa. Il caso del pioppo

Ozone: perception of the threat and early defense reactions. The poplar case. Air pollution is believed to be one of the main factors contributing to forest decline. There is growing evidence that ozone, the concentration of which is continuously increasing and in many European region exceeds the threshold of toxicity for sensitive species, is involved in the genesis of this phenomenon. Recently, the similarities between O3-induced responses and the hypersensitive reactions induced by a pathogen attack, led to the suggestion that O3 phytotoxicity could be the consequence of a cascade of events regulated by signaling molecules, interacting with each others in a rather complex manner and ultimately leading to the induction of defense responses or cell death. The present work was addressed at investigating the mechanisms of O3 perception and some early responses carried out by the plant cell in an attempt to counteract its effects. Two poplar clones showing different sensitivity towards the pollutant as far as visible symptoms are concerned (I-214 O3-resistant and Eridano O3-sensitive) were used as a model system. The obtained data let us to hypothesize that the major sensitivity shown by Eridano could derive from a marked H2O2 accumulation and increase in salicylic acid content and ethylene evolution which were more pronounced than in I-214. Thus, the O3- induced damage could be the consequence of an abnormal uncontrolled induction of metabolic pathways usually involved in the defensive response, the exaggerated and prolonged stimulation of which could lead to cell death.