Transposable elements can be used to study cell lineages in transgenic plants.

The beta-glucuronidase reporter gene has been used to develop a sensitive assay for the excision of transposable elements introduced into transgenic plants. The reporter gene, inactivated by the insertion of the maize transposable element Activator (Ac) into the 5'-untranslated leader, was introduced into the genome of tobacco by Agrobacterium-mediated transformation. Reactivation of the beta-glucuronidase gene was detected in transgenic plants using a fluorometric or histochemical assay. Reactivation of the reporter gene was dependent on the presence of the transposase of Ac, and resulted from the excision of the Ac element. This assay, together with the improved methods for visualization, will provide a valuable and rapid method for studying the basic mechanism of transposition in plants and for developing modified transposable element systems suitable for gene tagging in transgenic plants.