Figure 1

Ultrastructure of short regenerating flagella. Electron micrographs of cells fixed at various times after deflagellation (a-q). r, s: non-deflagellated control cells. a-d: very short regenerating flagella fixed at 7 minutes after deflagellation lack a bona fide CP. Arrows in a and d: granular material. Closed arrowheads in b: elongated microtubules. Open arrowheads in b: linear structures in the axonemal lumen which could represent a nascent CP. Arrowheads in c and d: singlet microtubules indicative of outer doublet formation. e-k: regenerating flagella at 14 minutes after amputation. Arrow in e: CP with projections. Arrowheads in e and h: fibrous material underlying the flagellar membrane. Arrowheads in f: staggered ends of the two CP microtubules. g, h: distal end of flagellum showing a ring of doublets without CP (g) and with a single CP microtubule (h). i: outer dynein arms are missing from the doublet microtubules but projections (open arrowheads) are visible on the CP. Small arrow in h and i: residual granular material in the axonemal lumen. j: projections are present on both CP microtubules (open arrowheads) but some outer dynein arms are missing (arrows). k: section revealing a full complement of dynein arms and CP projections. l-s: distal portions of regenerating flagella at 22 minutes after deflagellation (l–q) and of steady-state (r, s) flagella. Open arrowheads in l, n, o, r, and s: electron opaque tip sheet between the two CP microtubules. Arrows in l, m, n, p and o: fibrous material between the doublets and the membrane. Solid arrowhead in r: A-tubule cap forming a connection to the CP. V (in a, b, e, and m): vesicle at the flagellar tip. Bars = 200 nm (a, b, e, f, l, m, r) or 100 nm.