Experimental Modification of Cell Division Patterns in the Root Meristem of Zea mays

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Abstract
In the meristem of the young primary root of maize seedlings the first transverse division in the cortex 250 μm from the root apex results in two daughter cells of distinctly unequal size. This division could be rendered equal by raising the seedlings in up to 7.5% methanol. The pattern of the subsequent two or three transverse divisions in the cortex, as revealed by the arrangement of the newly divided cells in the resultant cellular packets, was acropetal in the methanol-treated roots but basipetal in the control roots. The sequence of division within a cellular packet tended to follow the distribution of cell sizes - larger cells divided earlier than smaller cells. A temporary arrest of cell division by exposing roots to cold (5 °C) conditions had no effect on the sequence of divisions that followed when the roots were allowed to recover at 20 °C. The results suggest that the normally asymmetric position of the cell wall formed at cytokinesis is subject to active regulation and that methanol interferes with this process. The cytoplasm of certain cells in the root meristem was also found to be unequally distributed, as judged by Azure B staining, between the two ends of the cell. Cytoplasmic asymmetry was not directly correlated with inequality of division, although it too was affected by methanol.