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 con centration (1 mu M) in previous laboratory studies. In this study, the mode of action of 9,10-anthraquinone was investigated by observing ultrastructu ral changes in O. perornata and by monitoring chlorophyll fluorescence as a n indicator of photosynthetic efficiency. Results indicate that 9,10-anthra quinone inhibits photosynthetic electron transport, probably at PSII, and t hereby affects growth. Moreover, 9,10-anthraquinone treatment caused thylak oid disorganization and reduced the number of ribosomes in O. perornata. Th e thylakoid disorganization is identical to reported modification in a cyan obacterium treated with simazine, a PSII inhibitor.