Figure 4.

The apx1 mutants show increased effector-triggered accumulation of ROS, as detected by 3,3′-DAB. A, Images of representative leaves after DAB staining. The seventh to ninth leaves of 4-week-old Col-0, delt4, apx1-2, and rbohD plants were infiltrated with Pseudomonas syringae pv. tomato (Pst) DC3000 (avrRpt2) at an OD₆₀₀ of 0.003, with MgCl₂ as the control. Bacterial suspensions were infiltrated into the left side of the leaf and the mock control (MgCl₂) was into the right side. The leaves were collected 10 h after infiltration and stained with DAB solution. ROS production was visualized as dark-brown precipitates in the detached leaves. Scale bars, 100 μm. B, The subcellular distribution of effector-triggered ROS accumulation. Images were taken from the left half of DAB-stained leaves in (A) under microscopy. Scale bars, 10 μm. C, The intensity of brownness from DAB-stained leaves in (A). DAB staining per unit area of leaves was quantified using the ImageJ software. Data are shown as the mean ± SE (n = 10). Different letters above the bars indicate significant differences (P ≤ 0.05, one-way ANOVA). The experiment was repeated 3 times with similar results. D, apx1 mutants showed enhanced resistance against Pst (avrRpt2). Leaves derived from 5-week-old plants with the indicated genotypes were inoculated with Pst (avrRpt2) at an OD₆₀₀ of 0.0001. The bacterial population in the leaf was determined 3 dpi (day postinoculation). Data are presented as the mean ± SE (n = 9). Different letters above the bars indicate significant differences between different genotypes (P ≤ 0.05, one-way ANOVA).