FREEZE-FRACTURE STUDIES ON BARLEY PLASTID MEMBRANES .3. LOCATION OF THE LIGHT-HARVESTING CHLOROPHYLL-PROTEIN

The thylakoids of chloroplasts from wild-type barley and the nuclear gene mutant chlorina-f2 were examined by freeze-fracturing and rotary shadowing. The advantages of rotary shadowing were: the shape of freeze-fracture particles was revealed, particles on membrane surfaces were seen in greater detail, estimation of particle density was more reliable, and measurements could be made of membrane thickness. When wild-type and chlorina-f2 thylakoid ultrastructure were compared, the most significant difference was the large reduction in the number of particles on the PFs face of the mutant. In addition, EFs particles were about 12% smaller in the mutant, whereas the appearance of the EFu, PFu and PSu was substantially the same as for wild-type thylakoids. These ultrastructural differences are correlated with the complete absence of the light-harvesting chlorophyll a/b-protein from chlorina-f2 thylakoids. Freeze-fracturing of purified light-harvesting complex in vesicles revealed particles similar in size and shape to those missing from the PFs face of chlorina-f2 but present on the PFs face of wild-type. It is concluded that in wild-type granal thylakoids, the light-harvesting chlorophyll a/b-protein is located in particles which are closely associated with EFs particles, but which cleave with the PFs face during freeze-fracturing. © 1979 Carlsberg Laboratory.