Dichlorophenylurea-resistant oxygen evolution in Chlorella after cerulenin treatment.

Fluorescence spectra at 77 K, oxygen evolution at 30 degrees C and delayed fluorescence at 25 degrees C were measured in Chlorella pyrenoidosa cultures with and without cerulenin and subsequent 3-(3,4-dichlorophenyl)-1,1-dimethyl-urea (DCMU) treatment, respectively. In pure algal cultures the oxygen evolution was inhibited by DCMU and the long-time component of fluorescence was highly influenced by DCMU, as expected. In contrast, both oxygen evolution and delayed fluorescence became DCMU-resistant in cerulenin-treated cultures. The DCMU-resistance is correlated with a change in the fatty acid distribution of the thylakoid membrane, which also leads to changes in the prompt fluorescence. Cerulenin appears to be a promising new tool of diagnostics for the hitherto unsatisfactorily understood processes of oxygen evolution in photosynthesizing organisms.