The Proportion of Cells that Divide in Root Meristems of Zea mays L.

Abstract

The proportion of cells that divide in four regions of the root meristem of Zea mays has been determined by an analysis of its cells pulse-labelled with tritiated thymidine. In the quiescent centre less than half of the cells divide and the fastest of these (less than half of them) have a mitotic cycle duration of about 40 h at 23 °C compared with a cell-doubling time of 230 h for the region. In the cap initials 80–90 per cent of the cells divide and about 80 per cent of these divide once in 10 h. In the stele about 80 per cent of cells divide near the quiescent centre and all divide at 200 μm from the quesecent centre. The fast cells divide every 14 h in both regions, but the cell-doubling time increases from 18 to 25 h near the quiescent centre. The root cap is completely replaced by its initials every day and 10 000 cells are sloughed off. The rest of the meristem adds about 170 000 cells to the root every day. These figures are discussed in relation to the role of the quiescent centre and the control of cell division.