Exploring photoprotective function of carotenoid under strictly anaerobic conditions

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K06220
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 44030:Plant molecular biology and physiology-related
• Research Institution: Chuo University (2023); Ritsumeikan University (2021-2022)
• Principal Investigator: Azai Chihiro 中央大学, 理工学部, 准教授 (70706564)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 緑色硫黄細菌 / カロテノイド / 配糖体 / cruC / 嫌気 / 光阻害 / 非光化学的消光 / 三重項励起状態

Outline of Final Research Achievements

We have discovered a novel photosynthetic phenomenon, “anaerobic photoinhibition”, which is the photoinhibition but does not involve the production of reactive oxygen species. This phenomenon occurs in the strictly anaerobic culture of the photosynthetic green sulfur bacterium Chlorobaculum tepidum. The harmful effect of the anaerobic photoinhibition was more pronounced in the ΔcruC mutant strain lacking carotenoid glycosides than in the wild-type strain, indicating that the carotenoid glycoside mediates non-photochemical quenching driven in the photosynthetic reaction center complex and suppresses the occurrence of photoinhibition. Ultrafast transient absorption spectroscopy also revealed the existence of an excitation energy transfer process that depends on the presence of the carotenoid glycoside.

Free Research Field

光合成

Academic Significance and Societal Importance of the Research Achievements

本研究課題で発見に至った「嫌気的な光阻害」は，光合成に関する既存の知識では想定すらされていなかった，全く新しい光合成現象である。活性酸素種の生成が関与しないため，無酸素状態であっても，強光下では光合成によって細胞毒性を示す物質が生成されることがわかった。緑色硫黄細菌ではカロテノイド配糖体がこの嫌気的な光阻害の発生を抑制していたことから，本研究の成果を契機に，補助色素でありながら光合成生物に普遍的に存在するカロテノイドの存在意義の解明が進むと期待される。