[1] Mehler observed that the H2O2 formed in this way does not present an active intermediate in photosynthesis; rather, as a reactive oxygen species, it can be toxic to surrounding biological processes as an oxidizing agent.
In scientific literature, the Mehler reaction often is used interchangeably with the Water-Water Cycle[2] to refer to the formation of H2O2 by photosynthesis.
Beginning in the 1970s, Professor Kozi Asada elucidated that oxygen can be reduced by electrons emerging from ferredoxin of photosystem I, to form superoxide, which is then reduced by superoxide dismutase to form H2O2.
Asada argued that oxygen presents an important sink for excess excitation energy acquired during plant exposure to bright light.
[4][5][6] In algae and other uni-cellular photosynthetic organisms, however, this amount can account for 20 to 30% of total electron transport.