Superoxide and Singlet Oxygen Produced within the Thylakoid Membranes Both Cause Photosystem I Photoinhibition

• Published in: Plant physiology (Bethesda) Vol. 171; no. 3; pp. 1626 - 1634
• Main Authors: Takagi, Daisuke, Takumi, Shigeo, Hashiguchi, Masaki, Sejima, Takehiro, Miyake, Chikahiro
• Format: Journal Article
• Language: English
• Published: United States American Society of Plant Biologists 01-07-2016
• Subjects: Ascorbate Peroxidases - metabolism; Chlorophyll - metabolism; Chloroplasts - drug effects; Chloroplasts - metabolism; Ionophores - pharmacology; Nigericin - pharmacology; Oxygen - pharmacology; Paraquat - pharmacology; Photosystem I Protein Complex - metabolism; Photosystem I Protein Complex - physiology; Plant Proteins - metabolism; Reactive Oxygen Species - metabolism; Singlet Oxygen - metabolism; Spinacia oleracea - drug effects; Spinacia oleracea - physiology; Superoxide Dismutase - metabolism; Superoxides - metabolism; Thylakoids - metabolism
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.16.00246

Photosystem I (PSI) photoinhibition suppresses plant photosynthesis and growth. However, the mechanism underlying PSI photoinhibition has not been fully clarified. In this study, in order to investigate the mechanism of PSI photoinhibition in higher plants, we applied repetitive short-pulse (rSP) illumination, which causes PSI-specific photoinhibition in chloroplasts isolated from spinach leaves. We found that rSP treatment caused PSI photoinhibition, but not PSII photoinhibition in isolated chloroplasts in the presence of O₂. However, chloroplastic superoxide dismutase and ascorbate peroxidase activities failed to protect PSI from its photoinhibition. Importantly, PSI photoinhibition was largely alleviated in the presence of methyl viologen, which stimulates the production of reactive oxygen species (ROS) at the stromal region by accepting electrons from PSI, even under the conditions where CuZn-superoxide dismutase and ascorbate peroxidase activities were inactivated by KCN. These results suggest that the ROS production site, but not the ROS production rate, is critical for PSI photoinhibition. Furthermore, we found that not only superoxide (O₂⁻) but also singlet oxygen (¹O₂) is involved in PSI photoinhibition induced by rSP treatment. From these results, we suggest that PSI photoinhibition is caused by both O₂⁻ and ¹O2 produced within the thylakoid membranes when electron carriers in PSI become highly reduced. Here, we show, to our knowledge, new insight into the PSI photoinhibition in higher plants.