Picosecond time-resolved fluorescence emission spectra indicate decreased energy transfer from the phycobilisome to Photosystem II in light-state 2 in the cyanobacterium Synechococcus 6301

Abstract

Picosecond time-resolved fluorescence emission spectra were recorded for cells of the cyanobacterium Synechococcus 6301. Fluorescence decay was measured by single-photon timing and kinetic components were resolved by global data analysis. Time-resolved fluoresence decay components were assigned to PS I, PS II and the phycobilisome terminal emitter by comparing spectra for cells with open PS II centres (fluorescence at F o) with those for cells with closed PS II centres (fluorescence at F m) for excitation wavelengths of 620 nm and 670 nm. Time-resolved spectra were recorded under these conditions for cells adapted to state 1 or to state 2. The state 2 transition reduced the amplitude of the PS II fluorescence emission by about 60%, with a complementary increase in the apparent amplitude of the emission from the phycobilisome terminal emitter. Similar changes in amplitude were observed for cells at F o and at F m. State transitions had no significant effect on the lifetime of PS II fluorescence decay. These results indicate that state transitions alter the extent of energy transfer from the phycobilisome to PS II.