2007). The application of new water-based AFM techniques (Liu et al. 2011) could probe the native rearrangements that take place in the thylakoid. Such imaging techniques should be extremely valuable for assessing the changes in chlorophyll connectivity in the membrane. In addition, thermodynamic models will be useful for understanding the strength and directionality of energetic interactions between proteins required for causing changes in membrane organization (Drepper et al. 1993; Kirchhoff et al. 2004; Schneider and Geissler 2013). It will be important to use images and models of membrane rearrangements to interpret fluorescence lifetimes, #buy Trichostatin A randurls[1|1|,|CHEM1|]# a technique that is discussed in the

next section. Fluorescence lifetimes The chlorophyll fluorescence lifetime measures the relaxation of the chlorophyll excited state Alvocidib concentration and contains information about the energy transfer network of the grana membrane.

The benefits of lifetime measurements can be seen in scenarios that give rise to the same fluorescence yield, but different fluorescence lifetimes. Figure 7a illustrates the difference between quenching (A1), in which the lifetime of the excited state is shortened, and bleaching (A2), in which the number of fluorophores decreases. Because the fluorescence yield, which is measured in the PAM experiment, is equal to the area under the fluorescence lifetime curve, PAM measurements cannot differentiate between bleaching and quenching. Figure 7b illustrates how two different energy transfer networks can be resolved by measuring fluorescence lifetimes, but not by

measuring fluorescence yields. Fig. 7 Scenarios that give rise to indistinguishable fluorescence yield measurements, but that can be distinguished by fluorescence lifetime measurements. a Illustration of fluorescence lifetimes of quenching (case A1, solid line), which reduces the fluorescence lifetime, and bleaching (case A2, dashed line), which reduces the overall fluorescence amplitude. These two situations could give the same fluorescence yields even thought they display different fluorescence lifetimes. selleck compound b Illustration of fluorescence lifetimes of moderate quenching of all fluorophores (case B1, solid line) and strong quenching of a small fraction of fluorophores (case B2, dashed line) which cannot be differentiated using fluorescence yield measurements The two decays in Fig. 7b correspond to two different energy transfer networks. For instance, the fast component of B2 could be due to chlorophylls that are very close to sites with high quenching rates and the slow component due to chlorophylls far from quenching sites. The excited state lifetime is affected by any properties that affect the energy transfer network, including the location of the quenchers with respect to the light harvesters, the connectivity between chlorophylls, and the rate of quenching at qE sites.