Cell fate in the inflorescence meristem and floral buttress of Arabidopsis thaliana

The flowers and leaves of Arabidopsis are arranged in a spiral with successive organs positioned at intervals of approximately 140°. This simple phyllotaxy determines the organization of the flowers of the inflorescence. Here we describe the analysis of X‐ray‐induced albino sectors in the L2 layer of the Arabidopsis inflorescence. No evidence was found of lineage restrictions within the inflorescence meristem. Comparison of the spatial relationships between albino and green tissue in the sepals of 43 chimeric inflorescences allowed the generation of a three‐dimensional fate map. The map relates the initiation of flowers in the plant apex to their final arrangement. The map was found to be a shallow dome with phyllotaxy superimposed on its surface. A similar map was prepared of the floral buttress and this was found to be a ridge with sepal primordia at its edges. Unlike other fate maps of plants these maps relate the relative positions and sizes of organ primordia in terms of the frequency with which they are of the same somatic phenotype, and not the number of cells giving rise to them.