Figure 1. Microscopy of the plant Golgi apparatus. (a) The Golgi apparatus in living tobacco leaf epidermal cells. By expressing a chimaeric protein comprised of green fluorescent protein and a protein that recycles between the ER and Golgi (the HDEL receptor ERD2; see Boevink et al., 1998 ) the endomembrane system can be observed by confocal fluorescence microscopy. Golgi bodies (bright fluorescent dots arrowed) can be seen to be associated with the reticulate network of cortical ER tubules. Bar, 10 mm. (b) The Golgi apparatus can be located by immunofluorescence staining of glycan epitopes. In this onion prophase root tip cell observed by confocal microscopy, the Golgi bodies (small green fluorescent dots) are widely distributed throughout the cytoplasm. The antibody also stains the plasma membrane. Condensing chromatin (red) is stained with propidium iodide. Bar, 10 mm. (c) Transmission electron micrograph of two Golgi stacks in a maize root cap hypersecretory cell. Note the massive, slime-producing vesicles associated with the medial- and trans-Golgi. Bar, 300 nm. (d) Different views of Golgi in a pea root meristematic cell. The Golgi (G) and endoplasmic reticulum (ER) have been stained selectively by an osmium impregnation technique. In cross-section, the stacks are more heavily stained at the cis-face (small arrows). Fine tubules and vesicles are associated with the fenestrated margins of cisternae. This can be seen most clearly in stacks that have been sectioned in face view (large arrowheads). Bar, 500 nm.

Figure 2. Pathway of N-linked glycosylation events leading to the production of a complex bi-antennary glycan. In the ER, the oligosaccharide precursor undergoes a glucosidase-mediated trimming of the three terminal glucose residues (1). In the trans-Golgi further trimming occurs when -mannosidase removes up to four mannose residues (2). Then a series of transferases sequentially add two terminal N-acetyl glucosamine residues along with the removal of further mannose residues (3–4). Fucosyl and xylosyltransferases add fucose and xylose to N-acetyl glucosamine and mannose residues on the core glycan, respectively (5). Finally, terminal fucose and/or galactose residues can be added to give the final complex glycan structure (6). Shown in the diagram is the formation of a complex glycan with terminal Lewis a antigens. Further processing of glycans can occur such as trimming by exoglycosidases en route to the vacuole (7).

Figure 3. The maturation model for transport across the Golgi stack. Product and membrane are produced from domains in the ER and transported to the cis-Golgi (via vesicles or tubules) where they coalesce to form a new cis-cisterna. Within each cisterna secretory products (glycosylation of proteins and biosynthesis of wall material) are sequentially built through the action of transferases. At the medial- and trans-side of the Golgi stack membrane is lost through conversion into secretory vesicles and clathrin-coated vesicles. This membrane loss may also be partly balanced by an endocytic flow and retrograde shuttle of vesicles across the Golgi, where they help with the construction of new cis-cisternae. (Claude Saint-Jore is acknowledged for her help in constructing this diagram.)