Induction, polarity and spatial control of cytokinesis in some abnormal subsidiary cell mother cells ofZea mays

Abstract

Cytokinesis in the subsidiary cell mother cells (SMCs) ofZea mays leaves grown in the presence of 5 mM of caffeine solution is usually partially inhibited. A continuous wall strip, resembling a portion of the subsidiary cell (SC) wall, is laid down in the preprophase microtubule band (PMB) cortical zone. Sometimes, the incomplete SC (“SC”) wall grows centripetally in the absence of a phragmoplast and the gap becomes smaller or closes. The “SC” nucleus escapes through the “SC” wall gap into the larger SMC compartment and may fuse with the other nucleus. The aberrant SMCs (a-SMCs) pass through another division cycle, reattempting to produce a SC. A typical PMB is found in the “SC” space, in the site of the previous PMB. Moreover, in some preprophase SMCs, the cytoplasm adjacent to the “SC” wall is traversed by a small number of microtubules. The preprophase nuclei are partly or totally separated from the PMB by the perforated “SC” wall and may lie far from the latter. Usually, one mitotic spindle is assembled. The cycling paired polarized nuclei appear to synchronize and their chromosomes line up together on a single metaphase plate. Although the mitotic spindle axis is diversely oriented, one of its poles tends to be stabilized in the proximity of the “SC” wall gap. These divisions separate abnormal cells. Most or all the cell plate edges fuse with wall regions far from the PMB cortical zone. However, when some of them approach the “SC” wall strips, they are “attracted” and intersect their rims. In rare occasions the cell plate, invading the “SC” space is guided by the PMB cortical zone to create a SC-like curved wall portion, in absence of a daughter nucleus. Observations show that the cell plate arrangement in redividing aberrant SMCs is not subjected to a strict spatial control. The disorder of polarization sequence generated by the “SC” wall ring and especially the perturbation of the spatial (and functional?) relationship between PMB-PMB cortical zone and the nucleus—mitotic spindle is a causal factor of the variable cell plate arrangements.