The Effect of Ionizing Radiations on the Broad Bean Root

Abstract

In a number of papers dating from 1913, J. C. Mottram has described some of the effects of γ rays, β rays, and X rays on the growing tip of the broad bean root. Some deal with changes in nuclear structure, and the others with changes in the rate of growth and the lethal action made evident by cessation of growth.1,2,3,4 The latter class may be summarised as follows:—A section of a root tip is shown in Fig. 1. Region “a” is a mass of cells from the division of which are derived all the cells of the mature root. This division gives rise distally to the root cap, and proximally to columns of cells, which by further (limited) division and differentiation form the several structures of the full-grown root. Growth of the root is the result of two processes: (1) division of the cells forming the apical cell mass, (2) subsequent elongation of the proximal daughter cells in the second and third mm. from the tip. During the night the apical cells “a” are found to be undergoing mitosis; during the day when elongation is occurring, very few, if any, mitotic figures are to be found. Roots which have experienced the normal alternation of daylight and darkness are more sensitive to radiation given at night than to radiation given in the daytime. This was an early demonstration (1913) that cells at or near division are much more sensitive to radiation than are resting cells.1, 2