Thylakoid membranes morphology

In an effort to generate images of the morphology of thylakoid membranes inside plant chloroplasts, isolated chloroplasts resuspended in a buffer solution containing a herbicide, 3-(3,4-dichlorophenyl)-l,l-dimethylurea (DCMU), have often been used [10, 11]. The DCMU inhibits photosynthesis by blocking electron transport at the electron acceptor side of PSII and enhances chlorophyll fluorescence from PSII. 

In the case of Anabaena, we found that the morphology and sensitivity of the thylakoid membrane, which are dependent on growth conditions, can be readily studied. Although the fluorescence spectra at room temperature are not so easily, or so well, resolved, they certainly show shoulders and dips, which reflect constituent pigment-protein complexes. It should be noted that the ratio of concentrations of the pigment-protein complexes and/or energy transfer efficiencies between them are position dependent in some cases. 

Figure 1. Diagram of the thylakoid membrane showing the four different fracture faces (EFu, PFu, EFs, PFs) and four different membrane surfaces (ESu, PSu, ESs, PSs). Each of these can be distinguished on the basis of the size and density of the particles which are found on them, as well as by their morphology.

The problem of the adequate determination of internal pH is complicated in the heterogeneous populations of vesicles. Chloroplasts are a typical example of such systems. According to electron microscopy data, there are at least two morphologically different membrane systems stroma- and grana-exposed thylakoids (see the sketch in Fig. 3.7). The numerous data in the last two decades brought evidence of the lateral heterogeneity of the chloroplasts lamellar system (see references [60-69]). Stroma- and grana-exposed thylakoids differ with respect to the content of the electron transport and the ATP-synthase complexes. 

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