Fig. 7. The basal apparatus of Chlamydomonas reinhardtii (transverse sections, from distal to proximal, doublets/triplets are numbered). (A-F) The transitional region and distal part of a bb. Centrin-containing filaments are depicted in blue and triplets to which the dcf is attached are filled with blue stripes. (A-C) The transitional region. The doublet outer projections attached to the A/B-tubule junction at the outside of the doublets are shown in light gray. (B) The region containing the transitional plate (tp). (D-F) Transition between transitional region and bb, and distal part of the bb with the attached transitional fibers (tf, dark green). (D) Filaments are attached in an asymmetrical way at the inner surface of the microtubular cylinder exactly at the transition between transitional region and bb. A filament outlining the shape of an acorn (red) is attached to doublets (rarely triplets) 7, 8, 9, 1 and 2. The lumenal side of the acorn is crossed by a V-shaped filament system; two filaments extend from triplets 4 and 5 to fuse in the center of the bb lumen and continue to the other side of the bb, making contact with triplet 9. The acorn and V-shaped filament system are already present at the distal end of the pbbs (G, pbb). (G-I) The bb root complex. (G) Median part of the bb root complex at a level where the microtubular roots and striated microtubule associated fibers (SMAFs) are present. The distal connecting fiber has been omitted for clarity but its position is outlined by dotted blue lines and the triplets to which the dcf is attached are filled with blue stripes. At this level, the acorn is actually not present in the bb but it is given in this schematic diagram for a better understanding of its positional relationship with the other elements of the basal apparatus. The cruciate microtubular roots are labeled 1d, 1s, 2d and 2s. Each microtubular root is associated with a SMAF, which are shown in green. The microtubular roots and SMAFs are also shown in cross sectional view, with individual root microtubules numbered. The first set of s-fibers (1sf¹, 2sf¹) connecting the bbs to their corresponding four-stranded microtubular roots (s-roots, 1s, 2s) are shown in red. The d-fibers (1df, 2df) that interconnect the bbs with their corresponding two-stranded microtubular roots (d-roots, 1d, 2d) are given in purple. The nucleus-bb connectors (NBBC, blue) are seen attached to the bbs in this region. At the distal ends of the pbbs (pbb, shades of gray) the acorn (red) and the V-shaped filament system are present (compare with D). (H) Proximal part of the bb root complex at a level below the microtubular roots and SMAFs (for a better orientation outlined in gray and green, respectively). The second set of s-fibers (1sf², 2sf²) connecting the bbs to their corresponding four-stranded microtubular roots (s-roots, 1s, 2s) is shown in red. The proximal connecting fibers (pcf, yellow) interconnect the bbs and also make contact with the adjacent pbb (with pbb triplets 8 and 9). The pbbs (their microtubular triplets are numbered) are attached by the lateral striated fiber (arrows) to their corresponding d-root and the sf² of the neighboring bb. In this region, the median proximal connecting fiber is attached to triplets 5 and 6 (mpcf, yellow). (I) Structures lying below the proximal ends of the bbs (faintly outlined) are the median proximal connecting fiber (mpcf, yellow) and the proximal parts of the sf² (red). Of the pbbs, only the hub and spoke complex of the cartwheels are visible at this level.