Changes in the Chromosome Complements of Cells ofVicia fabaRoots following Irradiation

Abstract

1. Primary roots of Vicia faba were irradiate after one day's germination. The X-ray dose was 620 r 2. Cells with changed chromosome complements appeared in lateral roots. It is inferred that these cells are descended from cells damaged by irradiation; chromosome breakage was seen in the first mitoses in the irradiated roots but was not scored. 3. Six types of chromosomal rearrangements were found. One type had been reported previously in primary roots of V. faba after X-raying. 4. The new complements appear to be stable because they occur several cells of a lateral. Affected laterals could contain up to five new complements. The primordium of such a lateral must have consisted of five changed and at least one normal cell. It had previously been suggested that a root of Vicia had three or four initial cells. 5. The survival of the cells with changed complements is not due solely to successful competition with, not to support by, normal cells, otherwise other types of changes should also have been found. 6. It is suggest that the changes found were perpetuated because they were induced in initial cells of the primary root, and that cells in which they were present beca,e part of the primordial and continued as initial cells in apical meristems of lateral roots. 7. Apical cells appear to have a lower sensitivity than other meristematic cells, so providing, after treatment, a reservoir of normal cells from which regeneration can occur.