The organization of Arabidopsis thaliana photosystem II (PSII) and its associated light-harvesting antenna (LHCII) was studied in isolated PSII–LHCII supercomplexes and native membrane-bound crystals by transmission electron microscopy and image analysis. Over 4000 single-particle projections of PSII– LHCII supercomplexes were analyzed. In comparison to spinach supercomplexes [Boekema, ., van Roon, H., van Breemen, . & Dekker, . (1999) Eur. J. Biochem. 266, 444–452] some striking differences were revealed: a much larger number of supercomplexes from Arabidopsis contain copies of M-type LHCII trimers. M-type trimers can also bind in the absence of the more common S-type trimers
