Insights into the consequences of grana stacking of thylakoid membranes in vascular plants: A personal perspective

The striking structural architecture of thylakoid membranes of higher plant and some green algal chloroplasts that house the light harvesting and energy transducing functions of chloroplasts have evoked many hypotheses concerning the significance of grana. The differentiation of the thylakoids into grana and stroma membrane regions is a morphological reflection of the non-random distribution of the photosystems II and I between appressed and non-appressed membrane domains, which became known as lateral heterogeneity. In this overview, the first section deals with changing concepts regarding the distribution of the photosystems between stacked and unstacked thylakoid domains from a personal historical perspective. The remaining section describes some functional implications of the lateral separation of most PSII complexes in appressed membrane regions of grana stacks from PSI complexes, ATP synthase and auxiliary proteins located in non-appressed membrane domains.