Golgi bodies

Lipids are transported between membranes. As indicated above, lipids are often biosynthesized in one intracellular membrane and must be transported to other intracellular compartments for membrane biogenesis. Because lipids are insoluble in water, special mechanisms must exist for the inter- and intracellular transport of membrane lipids. Vesicular trafficking, cytoplasmic transfer-exchange proteins and direct transfer across membrane contacts can transport lipids from one membrane to another. The best understood of such mechanisms is vesicular transport, wherein the lipid molecules are sorted into membrane vesicles that bud out from the donor membrane and travel to and then fuse with the recipient membrane. The well characterized transport of plasma cholesterol into cells via receptor-mediated endocytosis is a useful model of this type of lipid transport. [9, 20]. A brain specific transporter for cholesterol has been identified (see Chapter 5). It is believed that transport of cholesterol from the endoplasmic reticulum to other membranes and of glycolipids from the Golgi bodies to the plasma membrane is mediated by similar mechanisms. The transport of phosphoglycerides is less clearly understood. Recent evidence suggests that net phospholipid movement between subcellular membranes may occur via specialized zones of apposition, as characterized for transfer of PtdSer between mitochondria and the endoplasmic reticulum [21]. 

Fig. 1 and 2. TEM ofpositively stained isolated Golgi bodies. TEM ofnegatively stained isolated Golgi bodies. From Morre and Buckhout (16) with permission. 

The process of infection of lupine nodule cells by Rhizobia was examined by the thin-section electron microscopic technique, as well as the freeze-fracture technique. Different membranes such as infection thread membranes, peribacterioid membranes, plasma membranes, membranes of cytoplasmic vesicles, and membranes of the Golgi bodies and ER were stained with uranium-lead, silver, phosphotungstic acid, and ZIO (31). ZIO stained the membranes of the proximal face of the Golgi bodies and endoplasmic reticulum. ZIO staining has given good contrast in thick sections such as a cotyledon cell, a root cell, and an aleurone layer for ER, dictyosomes cisternae, mitochondria, and nuclear envelopes (17,32-37). 

The ER, Golgi bodies, and nuclear envelopes in cotyledon cells and cells of Chara corallina showed a marked increase in density by ZIO staining (38,39). We investigated the continuity of the Golgi apparatus into the ER of cultured tobacco protoplasts by ZIO staining (40). 

Robertson JG, Lyttleton P, Bullivant S, Grayston GF. Membranes in lupine root nodules. I. The role of Golgi bodies in the biogenesis of infection threads and peri-bacteroid membranes. J Cell Sci 1978 30 129-149. 

The cell organellae in woody plants are the nucleus, mitochondrion, rough-endoplasmic reticulum (r-ER), smooth endoplasmic reticulum (s-ER), Golgi-body, plastid, vacuole, microbody, etc. Their functions are very complicated, and some have definite roles in the biosynthesis of cell-wall components. Hence, changes in size of cell organellae are likely to occur, since cell-wall composition depends upon the stage of wall development. 

Figure 8. Changes in the structure of cell organellae during cell wall formation. Upper, middle, and lower photographs are Golgi-body, r-ER, and plastid, respectively. Abbreviations are as follows P, primary wall stage S2B, early part of S2 stage S2L, later part of S2 stage.

Figure 11. A tracheid in the early part of S2 stage. Radioactivities are observed on the Golgi-bodies and compound middle lamella.

Our electron microscopy observations have revealed some of the roles of cell organellae involved in biosynthesis of cell wall components (i) the plasma membrane is the site of cellulose synthesis. This supports the proposal that terminal and rosette complexes at the plasma membrane are responsible for cellulose synthesis, (ii) The Golgi-bodies and small circular vesicles derived from the r-ER s are involved in the biosynthesis and/or transport of the hemicelluloses. Our investigations, however, could not distinguish between what type of cell organellae contained what kind of hemicelluloses, and how these polymers were processed in the organellae. 

This general theory is sometimes made more precise by considering that the Golgi body is involved in producing the matrix material while the endoplasmic reticulum transfers calcium to the developing vesicle. The endoplasmic reticulum has been studied most intensively in muscle where its ability to transport calcium into vesicles of the sarcoplasmic reticulum is well known. There is, however, some doubt as to how this ability is developed in non-contractile cells627. ... 

On the basis of present evidence, it seems probable that pectic polymers and hemicelluloses are synthesized by the Golgi bodies before transport to the cell wall by Golgi vesicles and insertion intact into the wall after fusion of these vesicles with the plasma membrane.247-249... 

On the basis of this limited evidence, the most feasible conclusion is that hydroxy-L-proline-rich protein, synthesized on ribosomes, is glycosylated in the Golgi bodies, transported to the cell surface in Golgi vesi-... 

Figure 1-7 Electron micrograph of a thin section of a young epidermal cell of a sunflower. The tissue was fixed and stained with uranyl acetate and lead citrate. Clearly visible are the nucleus (N), mitochondria (M), chloroplasts (C), a Golgi body dictyosome (G), endoplasmic reticulum, vacuole (V), cell wall, plasmodesmata, and cuticle (upper right, thin dark layer). Micrograph courtesy of H. T. Horner.

Eukarotic cells contain complex membraneous organelles known as the Golgi apparatus or Golgi body which occupy a central position in the transport system of the cell. There is a wealth of information indicating that the Golgi is a key element in biomineralization. It is, for this reason, that we will look more closely into its functionality. 

Golgi bodies, which occur in some types of cells. These are flattened bodies of material that serve to hold and release substances produced by the cells. 

Structural Organization of the Plasma Membrane. Although our purpose here is not to describe in detail the structure of cell membranes, a brief look at the structure of the plasma membrane will help us to understand the major problems and the role of specific proteolysis related to membrane assembly. All cells—those of bacteria (prokaryotes), higher plants, and animals (eukaryotes)—have plasma membranes, but other distinct internal membranes (88) are found in eukaryotic cells (nuclei, golgi bodies, mitochondria, endoplasmic reticula, and lysosomes). 

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