Fig. 6.

Severing in higher plants. In higher plants, microtubule severing is used to create and enhance microtubule density, and to align the cortical microtubule array. γ-Tubulin ring complexes (green cap) bind to the sides of microtubules to nucleate new microtubules. These branched microtubules are cut by katanin (blue scissors) and the new free microtubules treadmill within the cortical array. Darkened areas represent photobleached ‘fiduciary’ markers to demonstrate that microtubules are treadmilling by adding dimers (red circles) to growing ends and dissociating dimers from the depolymerizing ends, and to show that microtubules are not gliding.