plants are highly susceptible to ozone. Soil grown four weeks old wild-type Col-0, max2 point mutation (max2-1), Salk (max2-4) and rcd1-4 (as an ozone sensitive control) lines were exposed to 350 ppb ozone (O3) for 6 h in a controlled O3 chamber. The plants were photographed before and 1 day after O3 exposure in order to show cell death on the leaves. A) Non-treated Col-0, max2-1, max2-4 and rcd1-4 lines grown in clean air. B) O3 phenotype of Col-0, max2-1, max2-4 and rcd1-4 lines 1 day after 6 h O3 exposure. C) Ion leakage in Col-0, max2-1, max2-4 and rcd1-4 lines measured at different time points after O3 exposure indicating the amount of cell death. The result is presented as ratio of ion leakage of total ion concentration. Data represent the means ± SE of 3 independent experiments with 5 plants/line in every time point in each experiment. **P < 0.01; two-tailed t test.