The membrane geometry of the prolamellar body

Summary When etioplasts are exposed to light, the branched tubular lattice of the prolamellar body becomes the large flat discs of the primary lamellae. We show that in spite of the very different apparent morphology of these two membranous structures, their membranes have similar average curvature and inside-outside surface areas. This implies that the packing or molecular organization of the lipids and proteins can be similar in the two structures, and that consequently the transformation does not require much high energyflip-flop of membrane components from one side to the other. We also discuss the relative physiological stability of the two structures.