Supermolecular organization of photosystem II and its associated light-harvesting antenna in the wild-type and npq4 mutant of Arabidopsis thaliana

Abstract

The organization of photosystem II (PSII) and its associated light-harvesting antenna (LHCII) in Arabidopsis thaliana was studied by transmission electron microscopy and image analysis on isolated PSII-LHCII supercomplexes and native grana-membrane crystals. In comparison to spinach supercomplexes [1], the analysis of supercomplexes from wild-type Arabidopsis revealed a much larger number of supercomplexes with M-type LHCII trimers and, in contrast to spinach, M-type trimers could even bind in the absence of the more common S-type trimers. Analysis of native crystals from wild-type Arabidopsis revealed a novel type of crystal with a unit cell of 25.6 x 21.4 nm (angle 77 degrees), which is larger than any of the PSII lattices observed before. The data show that the unit cell is built up from C2S2M2 supercomplexes, rather than from C2S2M supercomplexes observed before in native membrane crystals from spinach [2]. We have also been able to prepare super- and megacomplexes and native membrane crystals from the npq4 mutant of Arabidopsis. This mutant lacks the PsbS protein and can not dissipate excess light energy by non-photochemical quenching [3]. An EM analysis of these complexes will be presented at the meeting. [1] E.J. Boekema et al. (1999) Eur. J. Biochem. 266, 444-452. [2] E.J. Boekema et al. (2000) J. Mol. Biol. 301, 1123-1133. [3] X.-P. Li et al. (2000) Nature 403, 391-395.