Flower development in the organ number mutant clavata1‐1 of Arabidopsis thaliana (Brassicaceae)

Abstract

Flowers of the organ number (meristic) mutant clavata1‐1 of Arabidopsis thaliana (Brassicaceae) were studied to examine timing and patterns of floral organogenesis as compared to the wild type. All clavata1‐1 flowers examined had four‐ instead of two‐loculed gynoecia; half showed increased numbers of stamens; and 10% formed increased numbers of sepals. An inflorescence plastochron index was used to establish the timing of developmental events during flower organogenesis. clavata1‐1 flowers initiate faster but grow more slowly than in the wild type. The stages of sepal and stamen initiation were prolonged compared to those of the wild type. Although gynoecial initiation was not prolonged, the preceding stage was and it was characterized by a proliferation of meristematic cells above the initiating stamens. The clavata1‐1 flower apex did not become wider than that of the wild type until after the establishment of the gynoecium. We propose that clavata1‐1 is a heterochronic mutant, where flower organ number increases are due partly to prolongation of organ initiation stages.