Function and evolution of grana.
Chloroplasts are descended from cyanobacteria, and they retain many features of the cyanobacterial photosynthetic apparatus. However, land-plant chloroplasts have a strikingly different thylakoid membrane organization to that of cyanobacteria. Usually the two photosystems are laterally segregated; Photosystem II is concentrated in complex stacked-membrane structures known as grana. The function of grana has long been debated. Recent studies on membrane organization in chloroplasts, cyanobacteria and purple bacteria now offer a new perspective. I argue that grana allow the presence of a large light-harvesting antenna for Photosystem II, without excessively restricting electron transport. Other organisms solve this problem in different ways. Land plants evolved from macroalgae that were adapted to high light conditions; they evolved grana as a new solution to the problem of efficient photosynthesis in shade.
Mullineaux
Conrad W
CW
School of Biological and Chemical Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS, UK. c.mullineaux@qmul.ac.uk
D005075:Biological Evolution; D002736:Chloroplasts / Q000502:physiology*; D000458:Cyanobacteria / Q000502:physiology / Q000648:ultrastructure; D010788:Photosynthesis; D020524:Thylakoids / Q000502:physiology / Q000648:ultrastructure*