It has been shown that when Arabidopsis seeds are incubated with different heteropycnic labelled DNA during the first 4 days of germinating, large fragments of exogenous DNA are taken up by the seedling plant tissues (cotyledons and rootlet) and remain polymerized and double-stranded during the entire growth period. Only a small percentage of the population of exogenous DNA molecules appears to be destroyed and reutilized for DNA synthesis de novo. Most of the exogenous DNA remains free or becomes integrated with the Arabidopsis DNA as double-stranded molecules, not separable by alkali denaturation, but easily separable by ultrasonication.
Analysis of different tissues and organs of growing plants reveals that a large amount of foreign DNA remains in the cotyledons during the vegetative growth phase, but is redistributed at the flowering stage (when cotyledons etiolate). At this time, the foreign DNA leaves the cotyledons and migrates towards the flowering buds where it accumulates as a highly molecular and double-stranded material. In the F1 progeny, radioactive molecules are found which do not correspond to the endogenous material and which have a density depending on that of the foreign DNA used.