The Origin of Phyllotactic Pattern

苏塞克斯9604072在营养生长期间，给定植物物种的顶端分生组织以可预测的模式启动叶片。这种叶在茎周围的排列被称为叶序。尽管叶序分类是发育生物学家、生理学家和数学家大量研究的主题，但我们对这种模式形成过程的理解仍然处于初级阶段。这个项目研究了商业种植的亚麻植物亚麻新形成的不定分生组织上的叶序模式的出现。这种方法与以前的研究不同，以前的研究主要集中在老枝条上维持已建立的叶序模式。这项研究的长期目标是更好地理解建立系统发育模式所涉及的过程。亚麻不定分生组织是研究叶系格局发生的一个很好的模式系统。当亚麻幼苗在子叶正下方被斩首时，许多新的茎分生组织在残留的下胚轴的残端上形成。由于这些不定芽分生组织是由少量的表皮细胞形成的，所以分生组织和叶原基的形成很容易观察和实验操作。由这些不定分生组织形成的第一片叶子总是在可预测的位置出现。此外，第一片叶通常表现为“复叶”型，表明两片叶原基已经融合在一起。叶位的可预测性和多叶的形成都提供了检验文献中所阐述的叶系统学的许多理论解释的机会。这项提案将涉及三个具体目标。首先，将使用各种外科和生理操作来研究由亚麻不定分生组织形成的第一片叶的可预测位置所涉及的影响。这些实验将直接检验分生组织的物理和化学性质在叶系模式形成中的重要性。第二，亚麻不定分生组织上多叶的形成将用分生组织系列复制物的扫描电子显微镜来表征。在其他植物中，多叶的存在经常被报道在正在经历叶系模式转变的新梢上，但这些叶的个体发育还没有被仔细地研究。这个项目将集中于多叶形成的过程，强调这些叶的发展与叶系学理论之间的联系。最后，只在分生组织中表达绿色荧光蛋白的转基因植物将被开发出来；共聚焦显微镜将被用来观察活组织中不定分生组织发育的早期阶段，并可能区分分生组织和初生的叶原基。在活的植物中可视化非常年轻的分生组织和叶原基的能力将提供对叶系模式事件的洞察，这是以前所没有的。

Sussex 9604072 During vegetative growth, the shoot apical meristems of a given plant species initiate leaves in a predictable pattern. This arrangement of leaves about the stem is called phyllotaxy. Although phyllotaxy has been the subject of a great deal of research by developmental biologists, physiologists and mathematicians, our understanding of this patterning process remains rudimentary. This project examines the emergence of phyllotactic pattern on newly formed, adventitious meristems of the commercially cultivated flax plant, Linum usitatissimum. This approach differs from previous studies which focused primarily on the maintenance of the established phyllotactic pattern on older shoots. The long term objective of this research is to better understand the processes involved in the establishment of phyllotactic pattern. Flax adventitious meristems are an excellent model system in which to study the emergence of phyllotactic pattern. When flax seedlings are decapitated just below the cotyledons, many new shoot meristems form on the stump of the hypocotyl which remains. Because these adventitious shoot meristems are derived from a small number of epidermal cells, meristem and leaf primordium formation are easily observed and experimentally manipulated. The first leaf formed by these adventitious meristems consistently emerges in a predictable position. In addition, the first leaf often displays a "multiple" leaf phenotype suggesting that two leaf primordia have fused together. Both the predictability of leaf position and the formation of multiple leaves provide opportunities to test many of the theoretical explanations of phyllotaxy which have been set forth in the literature. Three specific aims will be addressed in this proposal. First, a variety of surgical and physiological manipulations will be used to investigate the influences involved in the predictable positioning of the first leaf formed by a flax adventitious meristem. These experiments will directly test the importance of p hysical and chemical properties of the meristem in phyllotactic patterning. Second, the formation of multiple leaves on flax adventitious meristems will be characterized using scanning electron microscopy of serial replicas of meristems. In other plant species, the presence of multiple leaves has often been reported on shoots which are undergoing a shift in phyllotactic pattern, but the ontogeny of these leaves has not been carefully studied. This project will focus on the process by which multiple leaves form, emphasizing the connections between the development of these leaves and theories of phyllotaxy. Finally, transgenic plants which express green fluorescent protein exclusively in meristematic tissue will be developed; confocal microscopy will be used to observe the earliest stages of adventitious meristem development in living tissue and, perhaps, to distinguish between meristematic tissue and incipient leaf primordia. The ability to visualize very young meristems and leaf primordia in living plants will provide insight into phyllotactic patterning events which has not been available previously.