Many regulatory mechanisms of photosynthetic light use are subjected to a redox control. Redox regulations take place at different levels. Redox changes finetune photosynthetic electron transfer at the photosynthetic reaction centers, the reduction state of the electron transport chain has a signalling function and thiol-modifications mediated by the redoxin network do not only activate the Calvin-Benson Cycle but also modulate alternative electron transport routes. These redox regulations affect the generation of reactive oxygen species like singlet oxygen and superoxide.
The midpoint potential of the primary quinone acceptor QA in PSII changes upon replacement of bicarbonate ligand at the non-heme iron by small carboxylic acids. According to our data, photorespiratory metabolites like glycolate shift this midpoint potential towards a more positive value and reduce thereby the amount of singlet oxygen. This observation may be relevant under drought conditions. (...)