Effect of Digitonin on Cellular Division Part VI

Inducement of oversized tubular elements in treated Allium cells

Abstract

Exposure of Allium sativum root tip cells to digitonin prevents the formation of conventional microtubules and thus the assembly of a functional mitotic spindle. With the appearance of arrested meta-anaphase stages, however, a new tubular element (480 to 520Å in diameter) appears among the scattered chromosomes. These large “macrotubules” are randomly distributed within the sections in groups of several closely associated tubules. Cross linkages similar to intermicrotubule bridges are regulary found. Tubules intermediate in size between the macrotubules and the occasionally encountered conventional microtubules are not observed. These macrotubules, like microtubules, possess a wall thickness of approximately 60 to 70Å. Attempts to demonstrate filamentous subunits or microcylinders within the wall of these tubular elements were unsuccessful. In cross-section, a centrally located electron-opaque material is often discernible within the lumen of many of these macrotubules. Since such macrotubules were not observed in dividing untreated cells, it seems probable that they are the digitonin-induced polymerization products of tubulin. The presence of these oversized tubular elements further sup-ports the hypothesis that functionally separable microbutular systems may be different chemically and architecturally.