Impaired photosystem II in a mutant of Chlamydomonas reinhardtii defective in sulfoquinovosyl diacylglycerol.

The photosynthetic apparatus was characterized in a mutant of Chlamydomonas reinhardtii, hf-2, defective in the synthesis of a chloroplast-specific lipid, sulfoquinovosyl diacylglycerol (SQui-acyl2Gro). hf-2 showed reduced photosystem II (PSII) activity with little effect on photosystem I (PSI) activity, as compared with the parent. PAGE in the presence of dodecyl beta-D-maltoside (DodGlc2) of C. reinhardtii thylakoid membranes was used to isolate chlorophyll-protein complexes without chlorophyll (Chl) release in order to examine lipid species bound to these complexes. The four complexes obtained were shown to be the PSI complex, the PSII core complex and the two groups of the light-harvesting complex of PSII by analyses of 77-K emission spectra of Chl fluorescence and of subunit compositions. Lipid analysis of Chl-protein complexes in the parent revealed the localization of SQui-acyl2Gro in the PSII core complex and the two groups of the light-harvesting complex of PSII, but not in the PSI complex. These results suggest that SQui-acyl2Gro is responsible for PSII activity by associating with the core and light-harvesting complexes of PSII.