High-light modification of excitation-energy-relaxation processes in the green flagellate Euglena gracilis

Ryo Nagao, Makio Yokono, Ka Ho Kato, Yoshifumi Ueno, Jian Ren Shen, Seiji Akimoto

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)


Photosynthetic organisms finely tune their photosynthetic machinery including pigment compositions and antenna systems to adapt to various light environments. However, it is poorly understood how the photosynthetic machinery in the green flagellate Euglena gracilis is modified under high-light conditions. In this study, we examined high-light modification of excitation-energy-relaxation processes in Euglena cells. Oxygen-evolving activity in the cells incubated at 300 µmol photons m−2 s−1 (HL cells) cannot be detected, reflecting severe photodamage to photosystem II (PSII) in vivo. Pigment compositions in the HL cells showed relative increases in 9′-cis-neoxanthin, diadinoxanthin, and chlorophyll b compared with the cells incubated at 30 µmol photons m−2 s−1 (LL cells). Absolute fluorescence spectra at 77 K exhibit smaller intensities of the PSII and photosystem I (PSI) fluorescence in the HL cells than in the LL cells. Absolute fluorescence decay-associated spectra at 77 K of the HL cells indicate suppression of excitation-energy transfer from light-harvesting complexes (LHCs) to both PSI and PSII with the time constant of 40 ps. Rapid energy quenching in LHCs and PSII in the HL cells is distinctly observed by averaged Chl-fluorescence lifetimes. These findings suggest that Euglena modifies excitation-energy-relaxation processes in addition to pigment compositions to deal with excess energy. These results provide insights into the photoprotection strategies of this alga under high-light conditions.

Original languageEnglish
Pages (from-to)303-311
Number of pages9
JournalPhotosynthesis research
Issue number3
Early online dateMay 26 2021
Publication statusE-pub ahead of print - May 26 2021


  • Euglena gracilis
  • Photoprotection
  • Photosynthesis
  • Time-resolved fluorescence

ASJC Scopus subject areas

  • Biochemistry
  • Plant Science
  • Cell Biology


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