OVEREXPRESSION OF COPPER ZINC SUPEROXIDE-DISMUTASE IN THE CYTOSOL OF TRANSGENIC TOBACCO CONFERS PARTIAL RESISTANCE TO OZONE-INDUCED FOLIAR NECROSIS/

Ozone damage to plants has been attributed to the action of oxygen fre e-radicals and other ozone degradation products against which cellular antioxidant systems have been considered to be a front-line defense. The activity of superoxide dismutase (SOD), one such antioxidant, has been shown to increase in ozonated plants. Past work with pea (Pisum s ativum L.) in our laboratory showed that the cytosolic Cu/Zn-SOD isofo rm and its transcript were most responsive to ozone, compared to chlor oplastic Cu/Zn-SOD. in the current work we tested the hypothesis that plants that constitutively overexpress cytosolic SOD are more tolerant of ozone. Pea cytosolic Cu/Zn-SOD was overproduced in the cytosol of two cultivars of transformed tobacco (Nicotiana tabacum), Eel W3 and W isconsin 38. Young and recently expanded leaves of transgenic plants o f both cultivars showed less foliar necrosis than nontransformed contr ols when exposed to acute doses of ozone. We suggest that this may dem onstrate the importance of Cu/Zn-SOD in the cytosol as a protector of the integrity of the plasma membrane and possibly other cellular const ituents.