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THE DURATION OF THE G 1 PHASE OF THE MITOTIC CYCLE AND ITS RELATION TO RADIOSENSITIVITY
Author(s) -
CLOWES F. A. L.
Publication year - 1965
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/j.1469-8137.1965.tb07544.x
Subject(s) - mitosis , radiosensitivity , biology , meristem , stele , cell cycle , microbiology and biotechnology , genetics , botany , biophysics , irradiation , physics , cell , gene , nuclear physics
SUMMARY The duration of each phase of the mitotic cycle in four regions of the root meristem of Zea mays has been determined by pulse labelling with 3 H thymidine. S, G 2 and mitosis are similar in length in all the regions, but G 1 differs considerably and is largely responsible for the diversity in rates of mitosis. G 1 is non‐existent in the cap initials, 151 hours in the quiescent centre, and 2–4 hours in the stele. These data, together with information on sensitivity to ionizing radiation, suggest that it is the ratio of the lengths of G 1 to the rest of the mitotic cycle that decides how resistant a tissue will be to radiation and they lead to a general explanation of the law that rapidly dividing cells are more susceptible than slowly dividing cells. The extreme sensitivity of the cap initials and the high resistance of the quiescent centre are correlated with the brevity of G 1 , in the former and the prolongation of G 1 in the latter. The fraction of the mitotic cycle spent in G 1 (when each nucleus has only the 2 C amount of DNA) therefore probably determines both radio‐sensitivity and rates of division.