Abstract
Photosynthetic organisms regulate their components and/or reaction mechanisms according to the changes in the environmental temperature so as to keep them in a good condition. We examined changes in the thermosensitivity of photosystem II (PSII) in Synechocystis sp. PCC 6803 grown under different temperatures. Thylakoid membranes and purified PSII complexes were isolated from those cells. Temperature dependencies of the oxygen-evolving activity in thylakoids were different between cells grown under different temperatures, while, those in the purified PSII complexes were the same between those cells. Temperature dependencies of the reaction center activity were the same both in the thylakoids and purified PSII complexes irrespective of the growth temperature. No remarkable difference was observed in protein compositions in thylakoids and purified PSII complexes. These results suggest that one of the major factor for the changes in the thermosensitivity of PSII complexes is the change in the lipid composition of thylakoid membranes.
