Singlet oxygen affects the activity of the thylakoid ATP synthase and has a strong impact on its gamma subunit.

Singlet oxygen is reported to have the most potent damaging effect upon the photosynthetic machinery. Usually this reactive oxygen molecule acts in concert with other ROS types under stressful conditions. To understand the specific role of singlet oxygen we took advantage of the conditional flu mutant of Arabidopsis thaliana. In flu, the negative feedback loop is abolished, which blocks chlorophyll biosynthesis in the dark. Therefore high amounts of free protochlorophyllide accumulate during darkness. If flu gets subsequently illuminated, free protochlorophyllide acts as a photosensitiser leading almost exclusively to high amounts of (1)O2. Analysing the thylakoid protein pattern by using 2D PAGE and subsequent MALDI-TOF analysis, we could show, in addition to previous described effects on photosystem II, that singlet oxygen has a massive impact on the thylakoid ATP synthase, especially on its gamma subunit. Additionally, it could be shown that the activity of the ATP synthase is reduced upon singlet oxygen exposure and that the rate of non-photochemical quenching is affected in flu mutants exposed to (1)O2.