Analysis and characterization of DCMU-resistant Euglena gracilis : III. Thylakoid modifications and dark "recovery" of photosynthesis.

Dark-grown, DCMU-adapted Euglena gracilis Z (ZR) are able to undergo light-induced chloroplast development in the presence or absence of DCMU. The differentiated chloroplasts are photosynthetically active and are resistant not only to DCMU, but also to an analog, o-phenanthrolene. When DCMU overdoses are added to ZR cells or to chloroplasts isolated from these cells, photosynthesis is partially inhibited. A brief period of darkness removes this inhibition. This recovery phenomenon is related to DCMU resistance, since it is not exhibited by non-resistant control cells. The chloroplast protein synthesis apparatus is not involved in DCMU resistance. Rather, this phenomenon is apparently related to new characteristics of thylakoids. It is shown that photosynthetic recovery by ZR cells depends on the accessibility and fluid properties of membranes. The analysis of fluorescence induction kinetics shows that changes in the environmental conformation of photosystem II units occur during recovery.