Total Uptake and Incorporation into DNA of3H-Thymidine,3H-Deoxyuridine, and3H-Thymine in the Primary Root ofVicia fabaL.

Abstract

Total uptake of ³H-thymidine, ³H-thymine, and ³H-deoxyuridine and incorporation of these substances into DNA have been investigated in excised roots in Vicia faba. Total uptake was found to be higher in excised roots than in intact ones. This was a consequence of exogenous ³H-DNA precursors entering the excised roots through the cut surface. Where the cut surface was not immersed in the ³H-thymidine solution ³H uptake was also higher than in intact roots. In this case ³H uptake scemed to be correlated with water-loss from the cut surface. Incorporation of ³H-thymidine, ³H-thymine, and ³H-deoxyuridine into DNA was found to be higher in excised roots than in intact ones, probably as a result of a decrease in the size of the relevant endogenous precursor pools. It is suggested that this decrease resulted from the cessation of the supply of DNA precursors to these roots from the cotyledons.