Thylakoid stacking

It is thought that membrane appression results from the localized decrease in the net negative surface charge of the many LHC II proteins surrounding each core PS II complex, thereby decreasing the overall electrostatic repulsive forces between adjacent membrane surfaces, and also increasing the van der Waals attrac- 

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Figure 3. Example of intracellular membrane organisation a transmission electron microscopy (TEM) image of a section through the thylakoid stack from a chloroplast. (Source http //www.ru.ac.za/administrative/emu/grl0p6.htm, Reproduced with permission from Dr. R. Cross)...

Thylakoids Stack of membranes located in the chloroplasts of plant cells. They contain the chlorophyll molecules that capture light during photosynthesis. 

Miller, K.R. and Cushman R.A. 1979. A chloroplast membrane lacking photosystem II. Thylakoid stacking in the absence of the photosystem II particle. Biochim. Biophys. Acta 546.481 197. 

As you hopefully recall, the parts of a chloroplast include the outer and inner membranes, intermembrane space, stroma, and thylakoids stacked in grana. The chlorophyll is built into the membranes of the thylakoids. 

The photosynthetic performance of the mutant does not change significantly under non-stress light conditions. However, the major LHCII isolated from this mutant appears less stable, as it dissociates more easily from the trimeric to the monomeric state and also into protein and unbound pigments (Tardy and Havaux, 1996). It may be this reduced amount and/or the reduced stability of trimeric LHCII in the aba mutant that is responsible for its reduced thylakoid stacking (Rock et al., 1992). 

Rhee KH, Morris EP, Zheleva D, Hankamer B, Kiihlbrandt W and Barber J (1997) Two dimensional structure of plant Photosystem II at 8 A resolution. Nature 389 522-526 Rock CD and Zeevaart JAD (1991) The aba mutant of Arabidopsis thaliana is impaired in epoxy-carotenoid biosynthesis. Proc Natl Acad Sci USA 88 7496-7499 Rock CD, Bowlby NR, Hoffmann-Benning S and Zeevaart JAD (1992) The aba mutant of Arabidopsis thaliana (L) Heynh. has reduced chlorophyll fluorescence yields and reduced thylakoid stacking. Plant Physiol 100 1796-1801 Romer S, Humbeck K and Senger H (1990) Relationship between biosynthesis of carotenoids and increasing complexity of Photosystem I in mutant C-6D of Scenedesmus obliquus. Planta 182 216-222... 

The specific surface o is defined as the area of one surface of the thylakoid membrane per total chlorophyll contained therein. By means of this quantity the specific volume of the membrane from its thickness or the average distance between the plane thylakoid membranes from specific volumes can be estimated. Such distances are required for the computation of the electrical potential profile across thylakoid stacks (If 2). The specific surface has not yet been measured but only inferred from indirect evidence. The value most frequently used is 1.5 m /yumol as estimated by Barber (3). 

Table 1. Thylakoid stacking, lipid/protein ratios, surface charge densities (a) and fluidity of thylakoid membranes isolated from leaves of wheat grown with or without treatment with SAN-9789 during seed imbibition. The fluidity is expressed as steady-state DPH fluorescence polarization (p). a, = 0.70 (9,10).

It is thought that the amino-terminal surface-exposed regions of the complex are sites of membrane adhesion that cause thylakoid stacking (5). This is consistent with the three-dimensional structure proposed by Kuhlbrandt on the basis of electron microscopy of two-dimensional crystals (6). This structure has three-fold rotational symmetry and a platform at one surface that could provide for interaction with a neighbouring platform through van der Waals forces. 

Barber, J. (1980). An explanation for the relationship between salt-induced thylakoid stacking and the chlorophyll fluorescence changes associated with changes in spillover of energy from photosystem II to photosystem I. FEBS Lett., 118 1-10. 

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