Figure 3 Microtubules have many roles during the cell division cycle. The following stages can be seen in cells from a wheat root tip stained with fluorescent-labelled antibody to the protein tubulin (from left to right): (i) pre-(or post-) division, when microtubules lie transverse to the long axis of a cortical cell, just under the plasma membrane. Microtubules govern congruent deposition of cellulose in the growing cell wall; (ii) the cell has become committed to divide and is establishing the future site and plane of division by laying down a dense band of microtubules (the ‘pre-prophase band’) that passes right around the cell; (iii) the metaphase stage of mitosis, with chromosomes lined up on the equator of the division figure, connected to poles of the mitotic spindle by bundles of microtubules that ultimately separate daughter chromosomes; (iv-v) early and later stages of development of the ‘phragmoplast’, an apparatus of microtubules and actin in which a new cell wall is initiated between the daughter nuclei; (vi) division almost complete, with just a few remnants of the phragmoplast visible and two daughter cells almost separated, although their cortical microtubules are not yet recognised; (vii) daughter cells have formed new arrays of cortical microtubules, similar to those of stage (i). (Based on Gunning and Steer 1996)