Effect of 2'-deoxyadenosine on thymidine utilization by tradescantia pollen grains

The uptake of ³H-thymidine into pollen grains of Tradescantia paludosa was studied in the presence of 2′-deoxyadenosine. 1) Millimolar deoxyadenosine caused an immediate inhibition of incorporation of ³H-thymidine into DNA extracted with hot trichloroacetic acid. 2) The radioactivity in acid-soluble derivatives of ³H-thymidine was examined by paper chromatography and, following incubation of pollen grains in the presence of millimolar deoxyadenosine, was found to be increased several-fold in ³H-deoxythymidine triphosphate. 3) The time-course of inhibition showed that the acid-soluble derivatives of ³H-thymidine accumulated initially at a rate unaffected by deoxyadenosine, despite the nearly complete inhibition of incorporation of ³H-thymidine into DNA. This is discussed in relation to possible mechanisms of inhibition by deoxyadenosine.