<P> Cyanobacteria are photosynthetic prokaryotes with highly differentiated membrane systems . Cyanobacteria have an internal system of thylakoid membranes where the fully functional electron transfer chains of photosynthesis and respiration reside . The presence of different membrane systems lends these cells a unique complexity among bacteria . Cyanobacteria must be able to reorganize the membranes, synthesize new membrane lipids, and properly target proteins to the correct membrane system . The outer membrane, plasma membrane, and thylakoid membranes each have specialized roles in the cyanobacterial cell . Understanding the organization, functionality, protein composition and dynamics of the membrane systems remains a great challenge in cyanobacterial cell biology . </P> <P> The thylakoid membranes of the cyanobacteria are not differentiated into granum and stroma regions as observed in plants . They form stacks of parallel sheets close to the cytoplasmic membrane with a low packing density . The relatively large distance between the thylakoids provides space for the external light harvesting antennae, the phycobilisomes . This macrostructure, as in the case of higher plants, shows some flexibility during changes in the physicochemical environment . </P>

Groups of photosynthetic pigment molecules situated in the thylakoid membrane are called