Reactive oxygen species (ROS) play diverse roles in plant cell responses to various stimuli, but their action mechanisms remain largely unclear. Biswas and Mano (on pp. 1432-1442) found that reactive carbonyl species (RCS) such as acrolein and HNE, which are degradation products of lipid peroxides, trigger PCD through the activation of caspase-3-like protease (C3LP). This study not only demonstrates the critical importance of RCS in ROS signaling, but also provides a specific biochemical mechanism of oxidative injury in plant cells. This paper features as part of the special focus issue on “How do photosynthetic organisms manage light stress?”