9,10-anthraquinone reduces the photosynthetic efficiency of Oscillatoria perornata and modifies cellular inclusions

The natural compound 9,10-anthraquinone was found to inhibit the growth of the musty odor-producing cyanobacterium Oscillatoria perornata at a low concentration (1 mu M) in previous laboratory studies. In this study, the mode of action of 9,10-anthraquinone was investigated by observing ultrastructural changes in O. perornata and by monitoring chlorophyll fluorescence as an indicator of photosynthetic efficiency. Results indicate that 9,10-anthraquinone inhibits photosynthetic electron transport, probably at PSII, and thereby affects growth. Moreover, 9,10-anthraquinone treatment caused thylakoid disorganization and reduced the number of ribosomes in O. perornata. The thylakoid disorganization is identical to reported modification in a cyanobacterium treated with simazine, a PSII inhibitor.