Floral and Vegetative Morphogenesis in California Poppy (Eschscholzia californicaCham.)

Abstract

For studies of the evolution of development in angiosperms, early‐diverging eudicot taxa are of particular interest for comparisons with established core eudicot model plants, such as Arabidopsis. Here we provide a detailed description of shoot and floral development of the basal eudicot California poppy (Eschscholzia californica). Rosette formation in the vegetative phase is accompanied by increased leaf complexity and shoot apex size. The flowering phase is characterized by internode elongation, formation of dissected cauline leaves, terminal flowers, and basipetal inflorescence branching. For developing flowers and fruits, we have defined 14 stages according to important landmark events, from inflorescence primordium initiation through seed dispersal. Floral organ initiation, morphogenesis, increase in floral meristem size, and the surface structure of mature floral organs are recorded in detail. The duration of the later floral stages, as well as the path of pollen tube growth in the gynoecium, is documented. Comparison of California poppy floral development with that of Arabidopsis indicates considerable differences in terms of organ fusion, whorl proliferation, and variability of size and organ number between the two species. Transitions in meristem identity from germination to floral organogenesis were monitored using expression of the developmental control gene EcFLO, the Eschscholzia ortholog of FLORICAULA/LEAFY. We found that the pattern of expression of EcFLO in the flanks of the shoot apex is maintained from late embryogenesis to flower initiation, indicating a continuous role for this gene in meristem function. As flower organs develop, EcFLO expression becomes more restricted to petal and stamen primordia. Development of the gynoecium occurs without EcFLO expression, indicating that EcFLO may not be necessary for the activation of C‐class genes.