Mehler reaction
The Mehler reaction reduces oxygen O2 to superoxide anion O2 by donation of an electron in Photosystem I. Superoxide anion can then be converted to hydrogen peroxide (H2O2) by superoxide dismutase, and H2O2 can be converted to water by ascorbate peroxidase. As the electrons originally come from water, this set of reactions is known as the photosynthetic water-water cycle. It is not related to photorespiration, as it comprises different reactions and results in no net oxygen consumption.