Radiation-induced Chromosomal Aberration in Relation to DNA Synthesis

Abstract

Using autoradiographic technique with 3H-TdR as a marker for DNA synthesis, the average duration of the each phase of mitotic cycle in barley roots was estimated and was found to be as follows: G1 (preDNA synthesis stage) 4.5 hrs., S (DNA synthesis stage) 4.5 hrs., G2 (post-DNA synthesis stage) 4 hrs., and M (mitosis) 2 hrs. Autoradiographic studies also showed that an asynchronous replication of DNA was occurring in a barley chromosome, terminal portions of the chromosome arms being first replicated. The examination of radiation-induced terminal deletions in anaphase cells revealed that chromosome sensitivity changed according to the stage of the cell cycle at which the cells were irradiated. The chromosome was more sensitive in late S and G2 than in G1 and the most sensitive in early S and/or late G1. It was discussed that DNA is a primary target for cell killing caused by irradiation.

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