2006, 2008), whereas three major decay times are found for PSI: 5–20, 20–60, 80–130 ps (Turconi et al. 1994; Croce et al. 2000; Ihalainen et al. 2002, 2005; van Oort et al. 2008; Slavov et al. 2008). Because of the various complications, only FDA-approved Drug Library in vivo the average lifetimes (τave) measured for WT and dgd1 thylakoid membranes and intact leaves are compared in this article. The longer lifetime in dgd1 can most easily be explained by taking into account the lower PSI content of the membranes (Ivanov et al. 2006)—this photosystem exhibits short lifetimes

(e.g., van Oort et al. 2010). Further, excess amounts of LHCI might also contribute to the longer lifetimes—according to Ivanov et al. (2006) the amount AZD1208 of LHCI was unchanged; hence, a fraction of these antenna complexes might not be connected to the reaction center. As reported by the lipophilic fluorescence probe MC540, alterations in the lipid composition in dgd1 bring about changes in the lipid packing. The spectroscopic properties of MC540 are determined by the dielectric

constant of its local environment (Lelkes and Miller 1980). Thus, it exhibits different fluorescent lifetimes when present in different environments (interacting with lipids or solubilized in the aqueous phase). Earlier it has been shown that the shortest lifetime (200 ps) component originates from dyes in aqueous environment and the 1- and 2-ns components from MC540 in hydrophobic environments, i.e., in the lipid phase (Krumova et al. 2008a). These lifetimes might be assigned either to two discrete populations of the molecules, reflecting two different microenvironments

or to a broad distribution of lifetimes due to incorporation of MC540 in a variety of environments with small differences in their physical properties. Our data reveal significant differences in the lipid packing between dgd1 and WT membranes. Most prominently, the increased amplitude of the 200 ps component suggest that in dgd1 the MC540 molecules Teicoplanin are more exposed to the aqueous phase than in WT (Fig. 5). The lower extent of incorporation of MC540 in the thylakoid membranes isolated from dgd1 in comparison with WT membranes might be due to two factors: (i) tighter lipid packing in dgd1, which could be the consequence of modified lipid–protein interactions and changes in the macroorganization, and/or (ii) modified surface charge of the membrane, i.e., due to conformational changes in the protein complexes or to differences in lipid–protein interactions. Despite the altered lipid composition (increased non-bilayer:bilayer lipid ratio) and alterations in the lipid packing, the ΔA515 measurements indicate that the dgd1 thylakoid membranes are perfectly adjusted to generate and maintain the transmembrane electrochemical potential difference at 25°C (Fig. 6a). ΔA515 is a voltmeter of thylakoid membranes.