Reactive Oxygen Species are Not All Bad for Plants Either
The cytochrome b6f complex of oxygenic photosynthesis contains a newly described site of production of reactive oxygen species (ROS), whose production has been found to be more than 10 times efficient than in the analogous mitochondrial respiratory complex. Superoxide generation, whose site of generation is marked in red in the accompanying figure, can inflict oxidative damage. However, superoxide, and ROS generated from it, also contribute to metabolic signaling from the chloroplast to the cytosol and nucleus for the regulation of plant responses to pathogen defense response and environmental stress.
Mechanism of Enhanced Superoxide Production in the Cytochrome b6f Complex of Oxygenic Photosynthesis. Baniulis D, Hasan SS, Stofleth JT, Cramer WA. Biochemistry 52: 8975-83, 2013; doi: 10.1021/bi4013534