GENETIC ABLATION OF PETAL AND STAMEN PRIMORDIA TO ELUCIDATE CELL-INTERACTIONS DURING FLORAL DEVELOPMENT

Two models have been proposed to explain the coordinated development o f the four whorls of floral organs. The spatial model predicts that po sitional information defines the four whorls simultaneously, and that individual organs develop independently of surrounding tissues, The se quential model suggests that inductive events between the outer and in ner whorl primordia are required for appropriate organogenesis. To tes t these models we have genetically ablated second and third whorl flor al organ primordia to determine if organ identity, number or position are perturbed in the first or fourth whorls. We used diphtheria toxin to specifically ablate floral cells early in development in Nicotiana tabacum and in Arabidopsis thaliana. Second and third whorl expression of the diphtheria toxin A chain coding sequence (DTA) was conferred b y the Arabidopsis APETALA3 (AP3) promoter. Both Nicotiana and Arabidop sis flowers that express the AP3-DTA construct lack petals and stamens ; it appears that the second and third whorl cells expressing this con struct arrest early in floral development, These results show that fir st and fourth whorl development is normal and can proceed without info rmation from adjacent second and third whorl primordia, We propose tha t positional information specifies the establishment of all four whorl s of organs prior to the expression of AP3 in the floral meristem.