Figure 1.

SAG13 promoter-driven GUS activity was induced by O₃ treatment. Fifteen-day-old Arabidopsis ecotype Landsberg erecta plants transformed with the SAG13 promoter-GUS fusion were exposed to 0.15 μL L⁻¹ O₃ for 6 h d⁻¹ for 14 d. The fifth and sixth leaves were harvested from a single plant and GUS activity was measured by fluorometric quantification of 4-methyl umbelliferone (MU). Black bars, O₃-Treated leaves; white bars, nontreated leaves. Each bar represents the mean of four samples ± se, except control bars on d 2 and 10, where the mean of three samples was taken. No GUS activity was detected in nontransformed plants (data not shown).