State transitions in a phycobilisome-less mutant of the cyanobacterium Synechococcus sp. PCC 7002

State transitions were investigated in the cyanobacterium Synechococcus sp. PCC 7002 in both wild-type cells and mutant cells lacking phycobilisomes. Preillumination in the presence of DCMU induced State1 and dark-adaptation induced State 2 in both wild-type and mutant cellsas determined by 77 K fluorescence emission spectroscopy. Light-induced transitions were observed in the wild-type after preferential excitation of phycocyanin (State 2) or preferential excitation of Chi a (State 1). Light-induced transitions were also observed in the phycobilisome-less mutant after preferential excitation of short-wavelength Chi a (State 2) or carotenoids and long-wavelength Chi a (State 1). We conclude that the mechanism of the light-state transition in cyanobacteria does not require the presence of the phycobilisome. Our results contradict proposed models for the state transition, which require phosphorylation of, and an active role for, the phycobilisome.