Ozone-induced oxidative stress: Mechanisms of action and reaction

In this review we explore several models which might explain ozone (O₃)-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 O₃ is very high, unregulated cell death will occur. Alternatively, the active oxygen species, or succeeding reaction products, may serve as elicitors of regulated plant responses. These regulated 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 induction of chitinases and β-1,3-glucanase in programmed cell death is explored. Induction of antioxidants, enzymes of lignification and glutathione-S-transferase are discussed in the context of O₃-induced cell repair or cell protection. A second model is postulated to explain induction of accelerated foliar senescence by low levels of O₃. The notion that O₃-induced elicitation of responses in the nucleus might lead to increased oxidative stress in the chloroplast is considered as a mechanism for accelerating the rate of degradation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). The mechanisms by which O₃ induces loss of Rubisco, and the relationship to accelerated foliar senescence are discussed.