PLANT DEFENSE SYSTEMS INDUCED BY OZONE

Recent advances in the understanding of the molecular basis of plant r esponse to ozone attack are reviewed. Plants grown in elevated atmosph eric ozone are known to undergo several biochemical changes before any actual damage can be detected. These reactions include increases in t he activities of enzymes associated with general plant defence mechani sms. Ozone exposure often causes a surge in the production of the plan t hormone ethylene, as well as changes in polyamine metabolism and inc reases in the activities of several phenylpropanoid and flavonoid path way enzymes. The activities of superoxide dismutase and peroxidases th at protect cells from the oxidative damage caused by hydroxyl radicals , H2O2 and superoxides also increase, However, ozone-induced changes i n plant cells at the gene level are almost unknown. The limited data a vailable suggest close similarities between ozone-induced and pathogen -induced defence responses in plants. Several general defence genes th at have been cloned in other studies will soon be applied to studies o f gene expression in ozone-exposed plants. The use of molecular biolog ical tools in ozone research should enable the development of highly s pecific and sensitive molecular markers for biomonitoring ozone-induce d injuries in plants.