1932

Abstract

Photoreduction of dioxygen in photosystem I (PSI) of chloroplasts generates superoxide radicals as the primary product. In intact chloroplasts, the superoxide and the hydrogen peroxide produced via the disproportionation of superoxide are so rapidly scavenged at the site of their generation that the active oxygens do not inactivate the PSI complex, the stromal enzymes, or the scavenging system itself. The overall reaction for scavenging of active oxygens is the photoreduction of dioxygen to water via superoxide and hydrogen peroxide in PSI by the electrons derived from water in PSII, and the water-water cycle is proposed for these sequences. An overview is given of the molecular mechanism of the water-water cycle and microcompartmentalization of the enzymes participating in it. Whenever the water-water cycle operates properly for scavenging of active oxygens in chloroplasts, it also effectively dissipates excess excitation energy under environmental stress. The dual functions of the water-water cycle for protection from photoinihibition are discussed.

Loading

Article metrics loading...

/content/journals/10.1146/annurev.arplant.50.1.601
1999-06-01
2024-03-29
Loading full text...

Full text loading...

/content/journals/10.1146/annurev.arplant.50.1.601
Loading
/content/journals/10.1146/annurev.arplant.50.1.601
Loading

Data & Media loading...

  • Article Type: Review Article
This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error