Abstract
Extrinsic proteins PsbO, P, and Q are bound to PhotosystemII(PSII)at the lumenal surface of thylakoid of higher plants, and maintain oxygen evolution activity. The PsbO protein is known as the manganese stabilizing protein, which is released from PSII by light or heat stresses. Moderate heat stress(40 degrees for 30 min)induces damage to the reaction center-binding D1 protein of PSII, and our recent data suggest that reactive oxygen species are involved in this event. As it is possible that reactive oxygen species generated around PSII induce damage to the extrinsic proteins, we investigated heat-induced release of PsbO from PSII under aerobic and anaerobic conditions using PSII-enriched membranes from spinach. We found that the release of the PsbO protein was suppressed under anaerobic conditions. The addition of Na-ascorbate suppressed the release of PsbO under aerobic conditions. These results suggest that reactive oxygen species are involved in the release of extrinsic proteins.
