THE DNA CONTENT OF THE CELLS OF THE QUIESCENT CENTRE AND ROOT CAP OF ZEA MAYS

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Abstract
Summary: The light absorption of Feulgen‐stained nuclei in regions of the root apical meristems of Zea has been measured in sections by an integrating microdensitometer. Most of the cells of the quiescent centre are at the 2C level of DNA and most of the cap initials are at or near the 4C level as predicted from pulse labelling data. But, in the quiescent centre, there are more cells between 2C and 4C and fewer cells at 4C than are predicted from pulse labelling. Possible reasons discussed for these discrepancies include stopping the mitotic cycle in S, nuclei entering mitosis before the 4C level is attained and stimulation of the quiescent centre by radiation damage to the meristem from labelling methods.The cap initials include some cells with more than the 4C amount of DNA, but, when the cap cells stop dividing, they remain at 2C for some time. Some of them then attain higher DNA contents, but there is no evidence to support the common view that the root cap is highly polyploid.