Day C D, Galgoci B F, Irish V F
Department of Biology, Osborn Memorial Laboratories, Yale University, New Haven, CT 06520-8104, USA.
Development. 1995 Sep;121(9):2887-95. doi: 10.1242/dev.121.9.2887.
Two models have been proposed to explain the coordinated development of the four whorls of floral organs. The spatial model predicts that positional information defines the four whorls simultaneously, and that individual organs develop independently of surrounding tissues. The sequential model suggests that inductive events between the outer and inner whorl primordia are required for appropriate organogenesis. To test these models we have genetically ablated second and third whorl floral 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 by the Arabidopsis APETALA3 (AP3) promoter. Both Nicotiana and Arabidopsis flowers that express the AP3-DTA construct lack petals and stamens; it appears that the second and third whorl cells expressing this construct arrest early in floral development. These results show that first and fourth whorl development is normal and can proceed without information from adjacent second and third whorl primordia. We propose that positional information specifies the establishment of all four whorls of organs prior to the expression of AP3 in the floral meristem.
已经提出了两种模型来解释花器官四轮结构的协调发育。空间模型预测，位置信息同时定义四轮结构，且单个器官独立于周围组织发育。顺序模型表明，外轮和内轮原基之间的诱导事件是适当器官发生所必需的。为了验证这些模型，我们通过基因手段去除了第二轮和第三轮花器官原基，以确定第一轮或第四轮中的器官特性、数量或位置是否受到干扰。我们使用白喉毒素在烟草和拟南芥发育早期特异性地去除花细胞。白喉毒素A链编码序列（DTA）在第二轮和第三轮中的表达由拟南芥APETALA3（AP3）启动子介导。表达AP3-DTA构建体的烟草和拟南芥花均缺少花瓣和雄蕊；似乎表达该构建体的第二轮和第三轮细胞在花发育早期就停止了发育。这些结果表明，第一轮和第四轮的发育是正常的，并且可以在没有来自相邻第二轮和第三轮原基信息的情况下进行。我们提出，位置信息在花分生组织中AP3表达之前就指定了所有四轮器官的建立。
