The Origin of Phyllotactic Pattern

在营养生长过程中，植物的茎尖分生组织以一种可预测的方式产生叶片。这种围绕茎的叶子排列被称为叶分制。尽管发育生物学家、生理学家和数学家对树叶分类学进行了大量研究，但我们对这一模式形成过程的理解仍处于初级阶段。本项目研究了商业种植亚麻植物Linum usitatissimum新形成的不定分生组织中层序模式的出现。这种方法不同于以往的研究，这些研究主要集中在维持老枝上已建立的层状格局。本研究的长期目标是更好地了解层序模式建立的过程。亚麻不定分生组织是研究层序模式发生的一个很好的模式系统。当亚麻幼苗在子叶下方被斩首时，许多新的芽分生组织形成在剩余的下胚轴残端。由于这些不定芽分生组织来源于少量表皮细胞，因此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一个可预测的位置出现。此外，第一片叶子经常显示“多叶”表型，这表明两片叶子的原基已经融合在一起。叶片位置的可预测性和多叶的形成都为检验文献中提出的叶分学的许多理论解释提供了机会。这一建议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子的可预测定位所涉及的影响。这些实验将直接测试分生组织的理化性质在层序图案中的重要性。其次，利用分生组织序列复制品的扫描电镜对亚麻不定分生组织上多叶的形成进行表征。在其他植物物种中，经常有报道称在茎层状格局发生转变的芽上存在多叶，但这些叶片的个体发育尚未得到仔细研究。本项目将重点关注多个叶片形成的过程，强调这些叶片的发育与叶分学理论之间的联系。最后，开发在分生组织中只表达绿色荧光蛋白的转基因植物；共聚焦显微镜将用于观察活组织中不定分生组织发育的最早阶段，并可能用于区分分生组织和早期叶原基。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以前无法获得的层序模式事件的洞察力。

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.