Abstract
A balanced distribution of absorbed light energy between photosystem I (PSI) and II (PSII) is required for maximum efficiency in photosynthesis. One of the balancing mechanisms is state transition. The mobile light-harvesting antenna could attach to PSI or PSII. The other proposed mechanism is spillover, where PSII transfer its energy to PSI. Red algae have a large light-harvesting antenna, phycobilisome, which attaches to PSII. Here, partial energy harvested by phycobilisome is transferred to PSI. However, the detail energy transfer pathway is still unknown. Since both PSI and PSII have similar chromophores, excitation photon is absorbed by both photosystems. To examine the balancing mechanism, it is required to observe excitation energy flow after selective excitation of PSI or PSII. PSII reaction center specifically emit delayed fluorescence in the range of 15-60 ns, whereas PSI reaction center and phycobilisome show little fluorescence in this time range. Therefore, the delayed fluorescence spectrum reflects energy migration pattern from PSII. We will discuss the energy balancing mechanisms by means of delayed fluorescence spectra of various red algae.
