Mehler reaction

The Mehler reaction reduces oxygen O₂ to superoxide anion O−
2 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.