Figure 5

O3-exposed leaves protected new leaves against the effects of subsequent O3 exposure. Control seedlings were cultured in indoor ambient air (NF, n = 20) for 3 weeks then transferred to a charcoal-filtered chamber. For the treatment, 21-day-old seedlings were grown in NF air, defoliated, and then transferred to CF air for 7 days to allow new foliage to grow (n = 38). There was a significant difference in the leaf injury index percentages (LII%) of seedlings with and without old leaves after exposure to 150 ppb O3 for 8 hours (p < 0.001).