Temperature-induced decoupling of phycobilisomes from reaction centers

Temperature-induced decoupling of phycobilisomes (PBSs) from the reaction centers in the PBS-thylakoid membrane complexes was observed at 0 degrees C. The fluorescence yields of photosystem (PS) I and PSII decreased and that of PBSs increased with selective excitation of PBSs at 0 degrees C, while the yield of PBSs decreased and those of the two photosystems increased with selective excitation of chlorophyll a at room temperature (RT). It indicated that the decoupling of PBSs from the two photosystems led to changes of energy transfer efficiencies, which can be explained by partial detachment of PBSs from thylakoid membrane. The temperature-dependent processes were reversible, i.e. with temperature going up to RT, the complexes could restore to the functionally coupled state with a time constant about 30 s. Based on these results, it could be deduced that PBSs should be in parallel connection with the two photosystems.