Plant Cytokinesis – Insights Gained from Electron Tomography Studies 257
Fig. 3 Large volume tomographic reconstructions of different stages of mitosis and cy-
tokinesis in Arabidopsis meristem cells. Based on Austin et al. (2005).ALate-anaphase
(volume = 5.9×5.9×0.8mm^3 ), which shows two opposing sets of spindle microtubules
(mt),redandgreen, above and between the migrating sister chomatids (ch), and vesi-
cles (v).BPhragmoplast initials stage (vol = 5.9×5.9×0.8mm^3 ), in which MT arrays
arrange parallel to the spindle axis, between the decondensing chromatin masses. Indi-
vidual phragmoplast initials arise in the cell equator surrounded by clouds of cell plate
forming vesicles.CSolid phragmoplast stage (vol = 4.3×4.3×1.2mm^3 ), which displays
two dense sets of opposing MTs (mt) between the re-forming daughter nuclei (n). The
growing cell plate (cp) is surrounded by numerous vesicles and is sandwiched between
the two sets of MTs.DTransitional phragmoplast stage (vol = 2.8×2.8×0.8mm^3 ), which
lacks a CPAM and displays many short MTs on both sides of the maturing cell plate.
ERing phragmoplast stage (vol = 5.9×2.8×0.9mm^3 ). Two dense sets of opposing MTs
flank the growing edge of the cell plate. The more mature central cell plate region has
fewer interacting MTs. Thescale barsrepresents 1 μm
solid phragmoplasts inArabidopsismeristem cells are comprised of 800 to
1,000 MTs (Austin and Seguí-Simarro, unpublished results).
A controversy has arisen recently over the question as to whether the
phragmoplast MTs overlap in the equatorial plane or not. The unambiguous
answer to this question, based on the analysis of cells preserved by HPS-FS