Ozone: a tool for probing programmed cell death in plants

Rapid increases in industrialization and other human activities during the twentieth century have contributed significant amounts of toxic gaseous pollutants to the tropospheric environment that pose a significant threat for the survival and productivity of native and cultivated ecosystems (Krupa and Kickert, 1989). Among various pollutants studied to date, the gaseous air pollutant ozone (O3) has caused more damage to both natural and cultivated crop plants in industrialized nations than any other pollutant (Heagle, 1989; Krupa and Kickert, 1989). O3 is produced both in the troposphere and in the stratosphere. Stratospheric O3 is generated through photolysis of molecular oxygen by ultraviolet solar radiation (Chameides et al, 1994). In the troposphere, O3 is produced by oxygen/ozone equilibrium reactions involving NO2/NO and light (Figure 1, reaction 1). In addition, reactions involving the photo-oxidation of carbon monoxide (Figure 1, reaction 2), unburned hydrocarbons such as methane (Figure 1, reaction 3), formaldehyde and other non-methane organic compounds (Figure 1, reaction 4; Fishman et al, 1985) also contribute to tropospheric O3.