The physiology of ozone induced cell death

Ozone (O-3) is a toxic air pollutant that is, somewhat paradoxically, both beneficial and harmful to life on earth. While stratospheric O-3 shields biologically harmful UV radiation from reaching the earth's surface, tropospheric O-3 is toxic to biological organisms. The discovery of the phytotoxicity of O-3 during the mid 1950s (Richards et al. 1958) prompted widespread studies on the effects of O-3 on plant growth and development. The effect of O-3 on biological organisms is attributed to its ability to spontaneously dismutate or react with cellular constituents to generate excess active oxygen species (AOS; Rao et al. 2000a). Several excellent reviews that discuss the source and the chemical reactions of O-3 formation, and the physiological effects of O-3 on flora are available, and will not be discussed here (Darrall 1989; Heath and Taylor 1997; Pell et al. 1997). Instead, recent advances on the complex signal transduction pathways of O-3-induced cell death will be reviewed.