Lipid A is responsible for the second burst of ROS. A, The ROS burst triggered by lipid A and LPS extracted from P. aeruginosa PAO1. B, The ROS burst triggered by lipid A and LPS extracted from P. syringae pv. tomato DC3000. C, The ROS burst triggered by lipid A extracted from commercial LPS of P. aeruginosa serotype 10. LPS (25 μg/mL) and lipid A (25 μg/mL) were used in these assays. ROS was monitored for 24 h with luminol as a substrate. The data are shown as means ± se (n = 8).