CHROMOSOME BREAKAGE PRODUCED BY TRITIUM-LABELED THYMIDINE IN TRADESCANTIA PALUDOSA

Abstract

Root tips of Tradescantia paludosa were grown in aerated nutrient solution containing 1 [mu]c/ml H3-thymidine for 8-56 hrs before fixation, or in media containing 1 or 2 [mu]c/ml for 4, 6 or 8 hrs and washed, transferred to isotope-free nutrient and fixed after 0-20 hrs of further growth. As many as 31 fragments per 100 cells occurred in roots grown by the latter method. The highest fragment frequency could be correlated with the period during which the maximum amount of labeled thymidine was incorporated. After continuous exposure of root tips to 1 [mu]c/ml H3-thymidine, up to 72 fragments per 100 cells at anaphase were measured. There was a drop in the mitotic index (cells in mitosis/ total cells X 100) in roots immersed in solutions for over 8 hrs. Autoradiographs of cells absorbing large quantities of H3 -thymidine indicate that these cells are damaged and the onset of mitosis is delayed or prevented. The average grain count over dividing nuclei showed a roughly linear increase with degree of fragmentation appearing at anaphase in roots exposed to 1 uc/ml H3-thymidine for 25-56 hrs.