The Origin of Phyllotactic Pattern

苏塞克斯9604072 在营养生长期间，给定植物物种的茎顶端分生组织以可预测的模式启动叶片。这种围绕着茎的叶的排列叫做叶序。虽然叶序是发育生物学家、生理学家和数学家进行大量研究的主题，但我们对这种模式化过程的理解仍然是初步的。本项目研究了商业化种植的亚麻植物亚麻（Linum usitatissimum）新形成的不定分生组织上叶序图案的出现。这种方法不同于以往的研究，主要集中在老枝上的既定叶序格局的维护。本研究的长期目标是更好地了解叶序格局建立的过程。亚麻不定分生组织是研究叶序格局形成的理想模式系统。当亚麻幼苗在子叶下方被切断时，许多新的芽分生组织在残留的下胚轴残端上形成。由于这些不定芽分生组织来源于少量的表皮细胞，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始终出现在可预测的位置。此外，第一片叶经常显示出“多”叶表型，表明两个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机会来检验文献中提出的许多叶序理论解释。 本提案将涉及三个具体目标。首先，各种手术和生理操作将被用来调查的影响，在可预测的定位亚麻不定分生组织形成的第一叶。这些实验将直接检验分生组织的物理和化学性质在叶序格局形成中的重要性。第二，亚麻不定分生组织上多叶的形成将使用扫描电子显微镜的分生组织的系列副本的特点。在其他植物物种中，经常报道在叶序模式发生转变的枝条上存在多片叶子，但这些叶子的个体发育尚未被仔细研究。这个项目将集中在多个叶子形成的过程中，强调这些叶子的发展和叶序理论之间的联系。最后，将开发专门在分生组织中表达绿色荧光蛋白的转基因植物;将使用共聚焦显微镜观察活组织中不定分生组织发育的最早阶段，并可能区分分生组织和初期叶原基。能够可视化非常年轻的分生组织和叶原基在活的植物将提供深入了解叶序图案的事件，这是以前没有。

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.