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Fig. 3. The older and younger basal bodies. (A-D) Consecutive longitudinal sections through a basal apparatus. The cartwheel of the right bb consists of four tiers (A) and so this bb is assumed to be the developmentally older (A, 1), whereas the cartwheel of the left bb consists of seven tiers (C) and so this bb is assumed to be developmentally younger (A, 2). Membrane fragments (B,C, double arrowheads) associated with the doublet outer projections (B,C, small arrows) make contact with the distal end of the transitional fibers (B,C, large arrows). Above the center of the distal connecting fiber, a triangular structure is visible (A-D, asterisks) that is connected by a fine filament to the distal end of at least the transitional fiber attached to triplet 9 (B, open triangle). Lying below the dcf, the SMAFs (A-D, small arrowheads) seem to form a continuous fiber in the center region of the basal apparatus (B,C, small arrowheads) and are connected to the outer bands of the dcf by fine filaments (visible in C). The median proximal connecting fiber (A-D, large arrowheads) and the proximal connecting fiber of bb 2 (D, pcf) are visible. (E) Longitudinal section through a basal apparatus (the bbs are numbered). The cartwheel of bb 1 consist of three tiers, whereas the cartwheel of bb 2 exhibits four tiers. The complex system of filaments present in the lumen of the bbs is clearly visible in bb 1 and seems to be more dense in bb 1 than in bb 2. This is also the case for the bbs shown in A-D. (F) Transverse section through the proximal end of a bb showing the hub and spoke complex of the cartwheel (triplet numbers are indicated). Parts of the pcf and sf2 are visible. Notice that the C-tubules are filled with electron-dense material. Scale bar, 250 nm.
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