Ambiguous Role of Oxygen in the Photoinactivation of PSII Particles

The PSII photoinactivation in vitro can be accelerated by anaerobic conditions (1–5). The protecting role of oxygen is probably due to its capacity to accept electrons delivered by PSII. On the other hand, the active species created by the oxygen reduction are probably responsible for the second, antagonistic role of oxygen in PSII photoinactivation that is expressed when the aerobic photoinactivation is slowed down by lowering the partial pressure of oxygen or by adding scavengers of oxygen radicals (3,6).