FIGURE 3.

Time course of reactive oxygen species (ROS) in Quercus ilex plants well-watered (open circle) or water stressed (20% of the effective evapotranspiration daily for 15 days, closed circle) and exposed to acute ozone (200 nL L^-1 for 5 h). Data are shown as mean ± standard deviation. The measurements were carried out at 0, 1, 2, 5, 8, and 24 h from the beginning of exposure. According to the two-way ANOVA with treatment and time as variability factors, different letters indicate significant differences (P = 0.05). DW, dry weight; H₂O₂, hydrogen peroxide (A); ${\mathrm{O}}_{\mathrm{2}}^{\mathrm{–}}$, superoxide anion (B). The thick bottom line indicates the time (5 h) of ozone exposure.