Adaptation of light-harvesting functions of unicellular green algae to different light qualities
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Oxygenic photosynthetic organisms perform photosynthesis efficiently by distributing captured light energy to photosystems (PSs) at an appropriate balance. Maintaining photosynthetic efficiency under changing light conditions requires modification of light-harvesting and energy-transfer processes. In the current study, we examined how green algae regulate their light-harvesting functions in response to different light qualities. We measured low-temperature time-resolved fluorescence spectra of unicellular green algae Chlamydomonas reinhardtii and Chlorella variabilis cells grown under different light qualities. By observing the delayed fluorescence spectra, we demonstrated that both types of green algae primarily modified the associations between light-harvesting chlorophyll protein complexes (LHCs) and PSs (PSII and PSI). Under blue light, Chlamydomonas transferred more energy from LHC to chlorophyll (Chl) located far from the PSII reaction center, while energy was transferred from LHC to PSI via different energy-transfer pathways in Chlorella. Under green light, both green algae exhibited enhanced energy transfer from LHCs to both PSs. Red light induced fluorescence quenching within PSs in Chlamydomonas and LHCs in Chlorella. In Chlorella, energy transfer from PSII to PSI appears to play an important role in balancing excitation between PSII and PSI.
KeywordsLight harvesting Energy transfer Light adaptation Green algae Photosystem
Fluorescence decay-associated spectrum (spectra)
Light-harvesting chlorophyll protein complex
Light-harvesting complex stress-related
Time-resolved fluorescence spectrum (spectra)
This work was supported in part by Special Coordination Funds for promoting Science and Technology, Creation of Innovation Centers for Advanced Interdisciplinary Research Areas (Innovative Bioproduction, Kobe), Japan, and by JSPS KAKENHI (Grant No. 16H06553 to S.A.). We thank Benjamin Knight, MSc., from Edanz Group (http://www.edanzediting.com/ac) for editing a draft of this manuscript.
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