In higher plants, root and shoot apical meristems are established during embryogenesis. The structures of several shoot apical meristems have been deduced by combining histological studies with clonal analysis. However, the application of this approach to root apical meristems has been limited by a lack of visible genetic markers. The aim of the proposed research is to circumvent this problem by performing clonal analysis on roots from transgenic plants containing the maize transposable element Ac in a B- glucuronidase (GUS) reporter gene. The gene is normally inactive. Transposition of Ac activates the gene, however, leading to sectors of cells expressing GUS. The distribution of these sectors can be used to establish whether the root apical meristems generates rot tissue continuously or in units (phytomers) and whether the meristem is organized in single or multiple layers. In the one year period of the present grant, methods will be developed for positive identification of GUS-expressing cells, and statistical data will be obtained relating to the occurrence of different classes of sectors in transgenic roots of tomato, tobacco and Arabidopsis.
