Fast oxygen-independent degradation of the D1 reaction center protein in photosystem II.

The D1 reaction center protein in photosystem II is rapidly degraded during illumination of chloride-depleted or Tris-washed thylakoids. The degradation is independent of oxygen and occurs under anaerobic conditions provided that electrons can flow through the acceptor-side of photosystem II. This shows that oxygen-derived reactive species are not necessarily involved in the light-dependent damage of the D1 protein. Instead the illumination of chloride-depleted or Tris-washed thylakoids induces long-lived, strongly oxidizing radicals on the donor-side of photosystem II which are suggested to be the damaging species for the D1 protein.