Excitation energy transfer between photosystem II and photosystem I in red algae: Larger amounts of phycobilisome enhance spillover

We examined energy transfer dynamics from the photosystem II reaction center (PSII-RC) in intact red algae cells of Porphyridium cruentum, Bangia fuscopurpurea, Porphyra yezoensis, Chondrus giganteus, and Prionitis crispata. Time resolved fluorescence measurements were conducted in the range of 0–80 ns at − 196 °C. The delayed fluorescence spectra were then determined, where the delayed fluorescence was derived from the charge recombination between P680+ and pheophytin a in PSII-RC. Therefore, the delayed fluorescence spectrum reflected the energy migration processes including PSII-RC. All samples examined showed prominent distribution of delayed fluorescence in PSII and PSI, which suggests that a certain amount of PSII attaches to PSI to share excitation energy in red algae. The energy transfer from PSII to PSI was found to be dominant when the amount of phycoerythrobilin was increased.

Research highlights
► Energy transfer from PSII to PSI (spillover) was monitored using spectroscopy.
► Time-resolved fluorescence spectra of intact cells of red algae were analyzed.
► Delayed fluorescence derived from charge recombination in PSII distributed to PSI.
► Spillover occurred frequently in red algae containing large amount of phycobilisome.