Preprophase microtubule bands in some abnormal mitotic cells of wheat.

Caffeine treatment of growing wheat tissues was used to form binucleate or polyploid cells; preprophase microtubules in subsequent division cycles in these and some other abnormal cells were then examined. In root tips, binucleate cells or those with greatly enlarged nuclei usually contained one transverse preprophase band of microtubules; sometimes this was slightly asymmetrical or skew, and less commonly two bands were seen. In coleoptile vascular bundles, there were generally two or more bands in the greatly elongated cells, these sometimes appearing in different planes. During formation of the stomatal complexes, preprophase microtubules were almost invariably found where expected, preceding abnormal development both in untreated and also in caffeine-treated material, regardless of the number, disposition or size of nuclei. This occurred even when wall stumps, formed during a previous abortive division, indicated that that previous division was also asymmetrical. It is concluded that the position(s) of preprophase band(s) of microtubules is not particularly influenced by the nucleus or nuclei, being more susceptible to external morphogenetic influences which can persist for some considerable time. Particularly in the case of stomatal complexes, a cell wall seems necessary to seal off or otherwise fulfil the tendency towards asymmetrical division.