Mitotic Delay induced by Gamma Radiation in Broad Bean Root Meristems

Abstract

IN attempting to interpret quantitative data on the yield of structural changes induced in chromosomes by radiation, the difficulty arises with material containing cells in random stages of development, as in root tips, that a given dose of radiation delays the arrival of cells at metaphase to an unknown extent. There is thus an uncertainty as to the developmental stage at the time of irradiation of those cells observed in metaphase at a particular fixation time. If sensitivity to induction of structural changes varies with the stage of cell development¹, then this uncertainty may make a precise interpretation of the dose-yield relationship impossible, for the amount of mitotic delay is itself dependent upon dose². In such asynchronous cell populations, an approximate picture of mitotic delay has usually been obtained by comparing mitotic index values of control and irradiated tissues. This method, however, falls short of giving an accurate determination of the delay, as of necessity mitotic index depends partly upon the length of time taken by a cell to pass through mitosis and this has also been shown to be affected by irradiation².