Stromata lamellae

PS I occurs in the unstacked stroma lamellae in contact with the stroma, where it has access to NADP1. 

Chloroplasts fill most of the cytoplasm around the junction of three cells of Arabidopsis thaliana seen in this micrograph. Both grana stacks and stroma lamellae (pictured in more detail in Fig. 23-19) can be seen. Also present are several small mitochondria. Portions of the large vacuoles, characteristic of plant cells, are seen at top, right, and bottom. Micrograph courtesy of Kenneth Moore. 

FIGURE 1. Thin section of part of an isolated chloroplast showing the internal thylakoid membrane system which consists of appressed grana lamellae (g) and non-appressed stroma lamellae (s) embedded in the stroma protein matrix and surrounded by a double membrane envelope (e). 

The exclusive localisation of photosystem I in stroma lamellae was demonstrated directly by immunogold labelling of isolated thylakoids (Vallon et al. 1985, 1986, 1987b). Monoclonal antibodies raised against the barley photosystem I reaction centre (P700 Chla-Pl or CPI) are incubated with thin sections of wild type... 

Vallon, O., Hoyer-Hansen G. and Simpson D.J. 1987a. Photosystem II and cytochrome b-559 in the stroma lamellae of barley chloroplasts. Carlsberg Res. Commun. 52, in press. 

PV Sane and RB Park (1970) Purification of photosystem I reaction centers from spinach stroma lamellae. Biochem Biophy Res Commun 41 206-219... 

Chloroplasts have inner and outer membranes. A third membrane forms within the aqueous, enzyme-rich stroma into flattened sacs called thylakoids. A stack of thylakoids is called a granum. Unstacked, connecting thylakoid membrane is referred to as stroma lamellae, (a) An electron micrograph of a chloroplast, (b) a diagrammatic view of a chloroplast,... 

The internal structure of chloroplasts (Figure 17.4c) resembles that of the mitochondrion (see here). Note the presence of an outer, relatively permeable membrane and an inner membrane that is selectively permeable. The stroma of the chloroplast is analogous to the mitochondrial matrix. Immersed in the stroma are many flat, saclike membrane structures called thylakois which are stacked like coins. The stacks are called grana. Grana are irregularly interconnected by thylakoid extensions called stroma lamellae. The thylakoid membrane encloses the lumen (or interior) of the thylakoid. 

The interior membrane layers of the grana are rich in photosystem II by contrast, the stroma lamellae (structures that connect grana) are rich in photosystem I (Figure 17.16). 

Photosystems I and II, the cytochrome b6f complex, and ATP synthase (CFO-CFl) are all individual entities in the thylakoid membrane, but are not necessarily contiguous. Components that link the photosystems (plastoquinone in the lipid phase of the membrane and plastocyanin in the thylakoid lumen) are mobile. Figure 17.16 shows the arrangement of components of the two photosystems on the thylakoid membrane. Note that the interior membrane layers of the grana are rich in PSII, whereas the stroma lamellae are rich in PSI. 

The mild SDS-PAGE analysis of chlorophyll-protein complexes were performed as in(8). The grana and stroma lamellae were isolated as in(7). The analysis of polypeptide composition of grana and stroma lamellae and re-electrophoresis were performed according to (9). 

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