Molecular genetic approaches to plant development.

Higher plant morphogenesis has received renewed interest over the past few years. The improvement of molecular genetic approaches to generate tagged developmental mutants, for instance by T-DNA insertion, facilitated the isolation and characterization of the altered genes. Here we present recent progress on flower and root morphogenesis in the small crucifer Arabidopsis thaliana. The current model of Arabidopsis flower development is presented. We report on FLOWER1 (Fl1), which is a T-DNA-tagged ap2 allele. Our observations indicate that this Fl1 mutant has, besides the homeotic Ap2 phenotype, an aberrant seed coat, suggesting that this gene has also a function late in flower development. Furthermore, we present a brief summary about root development and focus on the super root (Sur) mutant, which is an ethyl methanesulfonate-induced mutant that produces excess lateral roots. Root explants of the Sur mutant, that do not develop further than the 4-leaf stage, can be induced to produce normal-looking shoots and flowers by addition of only cytokinin to the medium. The phenotype of Sur and its relation to the action of phytohormones is discussed.