Recovery of photosystem II activity in photoinhibited Synechocystis cells:Light-dependent translation activity is required besides light-independentsynthesis of the D1 protein

Irreversible photoinactivation of photosystem II (PSII) results in the degr adation of the reaction center II D1 protein. In Synechocystis PCC 6714 cel ls, recovery of PSII activity requires illumination. The rates of photoinac tivation and recovery of PSII activity in the light are similar in cells gr own in minimal (MM) or glucose-containing medium (GM). Reassembly of PSII w ith newly synthesized proteins requires degradation of the D1 protein of th e photoinactivated PSII. This process may occur in darkness in both types o f cells. The degraded D1 protein is, however, only partially replaced by ne wly synthesized protein in MM cells in darkness while a high level of D1 pr otein synthesis occurs in darkness in the GM cells. The newly synthesized D 1 protein in darkness appears to be assembled with other PSII proteins. How ever, PSII activity is not recovered in such cells. Illumination of the cel ls in absence but not in the presence of protein synthesis inhibitors allow s recovery of PSII activity.