Freeze-fracture studies on barley plastid membranes V. viridis-n34, a photosystem I mutant

Abstract

Thylakoids of chloroplasts isolated from the nuclear gene barley mutant, viridis-n34, were examined by electron microscopy of rotary shadowed freeze-fracture replicas. This mutant was known to be partially deficient in the P700 chlorophyll a-protein 1, which is the reaction centre of photosystem I. The ultrastructure of the four fracture faces was characterised in terms of particle density and size distribution. When compared with wild-type thylakoids, the major difference was a reduction in the average size of the PFu particles, due to the specific loss of many of the large, heavily shadowed particles from this face. This was accompanied by a similar reduction in the number of pits in the complementary EFu face. It is concluded that the P700 chlorophyll a-protein 1 is localised in the large particle population of the PFu face, and that these particles form the pits on the EFu face during freeze-fracturing. Loss of this chlorophyll protein causes a reduction in particle size, without significant change in particle density. This is in marked contrast to earlier results (13,15) with the light-harvesting chlorophyll a/b-protein 2 complex and the reaction centre of photosystem II containing chlorophyll a-protein 3, the loss of which causes a loss of particles on the PFs and EFs faces respectively. © 1982, Carlsberg Laboratory. All rights reserved.