Tomographic sections of flagella from fla14 mutant C. reinhardtii. (a and b) Approximately 13-nm-thick tomographic sections along the central planes of the axonemes. The central pair complex (cp), with its lateral projections, and the MT doublets (md) are visible. In the upper part of the pictures, two long IFT trains are visible in the space between the flagellar membrane (m) and the MT doublets (md). Notice the bulges of IFT trains accumulated in the space between the flagellar membrane and the MT doublets in the bottom part of panels a and b (white ovals), below the axonemes. White arrowheads indicate the links of IFT trains to the MT doublet. Black arrowheads indicate the links between the IFT particles and the flagellar membrane. The white circle in panel a shows one of the zones that has been selected from the tomogram for particle averaging so that each volume contains a tract of the MT doublet, three contiguous IFT particles, and a portion of the flagellar membrane. The inset shows a close up view of the structures in the white circle. Notice the association of IFT particles with the flagellar membrane. g, glycocalyx. (c–f) Montage of 0.66-nm-thick individual planes of tomograms reconstructed from flagella of fla14 cells. Planes were cut with the same orientation used in panels a and b, and colors were assigned to different flagellar structures using semiautomatic segmentation. Yellow, axonemal MTs; red, IFT trains; white, flagellar membrane; green, glycocalyx. (c and d) These sectioning levels show the links of IFT trains with the flagellar membrane and reveal a structural pattern very similar to that shown in Fig. 6, panel 1. (e and f) In fla14 flagella, IFT trains are frequently visible on top of each other, giving rise to multiple layers of IFT trains (arrows). All the images are oriented so that the tip of flagellum points to the left of the plate. Video 1 shows a tomographic reconstruction related to panel a.