Respiratory terminal oxidases alleviate photo-oxidative damage in photosystem I during repetitive short-pulse illumination in Synechocystis sp. PCC 6803.

Oxygenic phototrophs are vulnerable to damage by reactive oxygen species (ROS) that are produced in photosystem I (PSI) by excess photon energy over the demand of photosynthetic CO2 assimilation. In plant leaves, repetitive short-pulse (rSP) illumination produces ROS to inactivate PSI. The production of ROS is alleviated by oxidation of the reaction center chlorophyll in PSI, P700, during the illumination with the short-pulse light, which is supported by flavodiiron protein (FLV). In this study, we found that in the cyanobacterium Synechocystis sp. PCC 6803 P700 was oxidized and PSI was not inactivated during rSP illumination even in the absence of FLV. Conversely, the mutant deficient in respiratory terminal oxidases was impaired in P700 oxidation during the illumination with the short-pulse light to suffer from photo-oxidative damage in PSI. Interestingly, the other cyanobacterium Synechococcus sp. PCC 7002 could not oxidize P700 without FLV during rSP illumination. These data indicate that respiratory terminal oxidases are critical to protect PSI from ROS damage during rSP illumination in Synechocystis sp. PCC 6803 but not Synechococcus sp. PCC 7002.