Fig. 2. (A) Serial 2.2 nm tomographic slice images (every third slice is shown) through the plus ends of a horned microtubule in which the protofilaments (arrowheads) are curling, characteristic of a disassembling microtubule. (B-M) Tomographic images and 3D models of reconstructed microtubule plus ends collected from all stages of phragmoplast development. (B-D') Tomographic slices and corresponding models of blunt-ended microtubules. The blunt end architecture is somewhat variable, with one side often being slightly longer. (E-G') Tomographic slices and corresponding models of microtubules with extended ends. (H-I') Tomographic slices and corresponding models of horned microtubules. (J,J') Tomographic slice and corresponding model of a microtubule with a hybrid (horned/extended) end. (K-M') Tomographic slices and corresponding models of microtubules with flared ends. Because the thickness of a tomographic slice is 2.2 nm and the thickness of a protofilament 4 nm, we were unable to model each protofilament individually. Therefore, the architecture is `relatively mapped' and not all of the microtubules modeled exhibit 13 protofilaments. Color coding of the different microtubule plus-end types: blunt-ended, yellow; extended, green; horned, red; flared, blue; hybrid extended/horned, orange. Scale bars, 0.05 µm.