Metabolically labile DNA in aseptically grown seedlings of Pisum sativum L.

Pea seedlings (Pisum sativum L.) were grown aseptically in a sterile flexible film animal isolator. Radioactivity from [Me-(3)H]thymidine, supplied to the roots of the seedlings, was specifically incorporated into pea DNA. There was no incorporation into RNA or into bacterial DNA; neither was there any non-specific binding of label to carbohydrate. Much of the radioactivity incorporated into the DNA was lost during a cold chase. The loss could not be accounted for by net DNA synthesis and cell division, and is therefore taken as strong evidence for DNA turnover. The significance of these results is discussed.