Adaptation of light-harvesting systems of Arthrospira platensis to light conditions, probed by time-resolved fluorescence spectroscopy.

Cyanobacteria change the quantity and/or quality of their pigment-protein complexes in response to light conditions. In the present study, we analyzed excitation relaxation dynamics in the cyanobacterium, Arthrospira (Spirulina) platensis, grown under lights exhibiting different spectral profiles, by means of steady-state absorption and picosecond time-resolved fluorescence spectroscopies. It was found that F760, which is the PSI red-chlorophyll characteristic of A. platensis, contributes to slower energy-transfer phase in the PSI of A. platensis. Excitation energy transfers in phycobilisome and those from PSII to PSI were modified depending on the light quality. Existence of quencher was suggested in PSI of the blue-light grown cells. Phycobilisomes in the green-light grown cells and the far-red-light grown cells transferred excitation energy from phycobilisome to chlorophyll without loss of energy. In these cells, excitation energy was shared between two photosystems. Fast energy transfer was established in phycobilisome under the yellow-light condition where only the phycobilisome can absorb the cultivation light. Differences in light-harvesting and energy-transfer processes under different cultivation-light conditions are discussed. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.