Photoinhibition of Photosystem II and photodamage of the oxygen evolving manganese cluster

Light drives photosynthesis, but at the same time, light also damages the photosynthesis machinery. The damaging reaction is termed photoinhibition, and its target is Photosystem II. The photodamaged Photosystem II reaction centre is repaired by degradation and resynthesis of the D1 protein. Both visible and ultraviolet light inhibit Photosystem II but ultraviolet light is much more efficient. This review describes the different hypotheses about the molecular mechanisms of photoinhibition. A special focus is put on the effect of light on the oxygen-evolving complex and on the recent hypothesis suggesting that light absorption of the manganese cluster of the oxygen-evolving complex plays a crucial role in photoinhibition. The manganese hypothesis is extended to show how the production of singlet oxygen by photoinhibited Photosystem II centres may occur.