1994; Dobrikova et al. 2003); these bands are also associated with long tails outside the principal absorbance bands, which originate

from differential scattering of the left and right circularly Crenigacestat concentration polarized light (Garab 1996). Ψ-type bands correlate with the macro-organization of the main Chl a/b light selleck inhibitor harvesting complexes, e.g., in LHCII-only domains, as indicated by correlations between the intensity of these bands and the LHCII-content of the sample (e.g., Garab et al. 1991; Garab and Mustárdy 1999). The arrays of PSII-supercomplexes might also contribute to the Ψ-type CD signal. For example, in a mutant lacking one of the minor light-harvesting complexes, namely, CP24, the macro-organization of the PSII-supercomplexes is modified

as compared to WT. This results in the loss Selleck Nutlin3a of the main Ψ-type band in the red at around (+)690 nm (Kovács et al. 2006). The intensities of the Ψ-type CD bands between 660 and 700 (Fig. 1a) differ for WT and dgd1 thylakoids. These CD signals are shown to be determined by the long-range organization of the pigment–protein complexes, in particular LHCII (e.g., Garab et al. 1991; Garab and Mustárdy 1999) and PSII-supercomplexes (Kovács et al. 2006). Thus, the reduced intensity of the main Ψ-type CD bands (CD(685–703) and CD(685–671)) in the mutant (Fig. 1a) might either be due to a smaller size of the chiral macrodomains or to a different organization of the complexes affecting the learn more pigment–pigment

interactions. It should be noted that DGDG has been found to be required for the formation of ordered 3D crystals of LHCII (Nuβberger et al. 1993). Hence, our CD data strongly suggest that also in vivo in the thylakoid membranes DGDG modulates the macroorganization of the main light-harvesting complexes of PSII. As shown by Chl fluorescence lifetime measurements, alterations in the macroorganization in dgd1 affected only marginally the energy migration and trapping (Figs. 3, 4). The mutant exhibited a somewhat longer average Chl a fluorescence lifetime (Figs. 3f, 4). The assignment of the fluorescence lifetimes to particular protein complexes or macroassemblies is a rather complicated task for intact chloroplasts and isolated thylakoids, where a large variety of complexes and supercomplexes co-exist. For example, most studies on whole chloroplasts and intact thylakoid membranes suggested average values for the trapping time in PSII between ~300 and ~500 ps (e.g., Roelofs et al. 1992; Gilmore et al. 1996; Vasile’v et al. 1998). A very detailed study of the fluorescence kinetics of thylakoid membranes with varying composition was recently performed, using different combinations of excitation and detection wavelengths to assign the various lifetimes to PSI and PSII but this is not a trivial task (van Oort et al. 2010).