OZONE-INDUCED OXIDATIVE STRESS - MECHANISMS OF ACTION AND REACTION

In this review we explore several models which might explain ozone (O- 3)-induced injury to plant foliage. Ozone enters the cell through the wall and plasma membrane where active oxygen species are generated. If the concentration of O-3 is very high, unregulated cell death will oc cur. Alternatively, the active oxygen species, or succeeding reaction products, may serve as elicitors of regulated plant responses. These r egulated responses include the induction of ethylene which could serve as a primary signal for - or a facilitator of - subsequent responses. The role of regulated suppression of photosynthetic genes and inducti on of chitinases and beta-1,3-glucanase in programmed cell death is ex plored. Induction of antioxidants, enzymes of lignification and glutat hione-S-transferase are discussed in the context of O-3-induced cell r epair or cell protection. A second model is postulated to explain indu ction of accelerated foliar senescence by low levels of O-3. The notio n that O-3-induced elicitation of responses in the nucleus might lead to increased oxidative stress in the chloroplast is considered as a me chanism for accelerating the rate of degradation of ribulose-1, 15-bis phosphate carboxylase/oxygenase (Rubisco). The mechanisms by which O-3 induces loss of Rubisco, and the relationship to accelerated foliar s enescence are discussed.