International Research Fellowship Program: Characterization and Modeling of Higher Order Phyllotaxis in Helianthus

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。国际研究奖学金项目使美国科学家和工程师能够在国外进行9至24个月的研究。该计划的奖励为联合研究提供了机会，并利用独特或互补的设施、专业知识和国外的实验条件。该奖项将支持Siobhan a . Braybrook博士与瑞士伯尔尼大学的Christopher Kuhlemeir博士进行为期24个月的研究。叶序性描述了植物器官在发育过程中形成的排列。空中器官的形成主要发生在茎尖分生组织，这是一种特殊的种群。干细胞?位于主茎顶端的。在向日葵头状花序（Helianthus annuus）中观察到的高阶分叶性显示出明显的螺旋状图案，这是分生组织精确图案的结果。在一个给定的头状体中，这些螺旋的数量是斐波那契数列的成员，这可能是由于头状体中黄金角的重复而产生的一种新兴现象。年代的发展。近年来，植物激素生长素在叶状排列螺旋模式的建立和黄金角的重复中发挥了重要作用；然而，所有这些工作都是在番茄和拟南芥的低阶叶状组织中完成的，并且涉及小的圆柱形分生组织，而不像向日葵的大而扁平的头状花序。历史上有大量的数学和生物力学工作试图描述向日葵头状花序的高阶模式。这些作品假设分生系统内的机械力也可能是重要的模式生成器或执行者。研究人员正在研究化学建立的模式（通过生长素）和机械强制模式之间的相互作用，研究人员使用跨学科的方法，结合生物学、物理学、数学和计算模型，在向日葵头状花序发育中进行了研究。利用免疫组织学观察生长素运输蛋白PIN1的动态，生长素运输蛋白PIN1建立了生长素的定向流动。向日葵PIN1基因（HaPIN1）的克隆和表达在茎尖。此外，还在开发工具，将生长素浓度的分子标记引入向日葵植物中。随后，在控制生长素水平和头盖机械特性后，研究了生长素动力学的变化。各种方法被用来破坏小头骨中的机械力，如显微解剖、激光消融和通过压缩施加外来力。利用微机电系统（MEMS）力传感器收集了小头骨不同组织刚度的生物力学测量数据。在上述的生长素水平和机械性能的操作之后也进行了测量。所得到的数据描述了生长素动力学和组织生物力学之间的关系，研究人员正在使用这些数据来完善和扩展现有的叶状性计算模型，以包括在向日葵头状花序中看到的高阶模式。这种多学科和综合的方法来研究一个古老的现象，在自然界建立斐波那契模式，将增加对生物力学和植物生物学领域的理解。它还将有助于增加生物学家和非生物学家之间的科学论述和合作，这本身就是科学领域内紧急适应的一个可能的例子。

0853105BraybrookThis award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad.This award will support a twenty-four-month research fellowship by Dr. Siobhan A. Braybrook to work with Dr. Christopher Kuhlemeir at the University of Bern in Switzerland.Phyllotaxis describes the arrangement of plant organs as they are formed during development. The formation of aerial organs occurs mainly from the shoot apical meristem, a specialized population of ?stem cells? situated at the apex of the main stem. The high order phyllotaxis observed in Helianthus annuus floral heads (sunflower capitulum) displays striking spiral patterns which develop as a result of precise patterning at the meristem. The numbers of these spirals in a given capitulum are members of the Fibonacci series, which is likely an emergent phenomenon resulting from the repetition of the Golden Angle during the capitulum?s development. Recent work in phyllotaxis research has highlighted the important role of the plant hormone auxin in establishing spiral phyllotactic patterns and the repetition of the Golden Angle; however, all of this work has been done with lower order phyllotaxis in tomato and Arabidopsis and involves small cylindrical meristems unlike the large flat sunflower capitulum. Historically there has been a large body of mathematical and biomechanical work attempting to describe the high order patterns seen in sunflower capitula. These works postulate that mechanical forces within the meristem may also be important pattern generators or enforcers. The investigators are examining the interplay between chemically established patterning (via auxin) and mechanically enforced patterning is investigated in the developing sunflower capitulum using an interdisciplinary approach by combining biology, physics, mathematics, and computational modeling. The dynamics of auxin transport are being examined using immunohistollogy to visualize the auxin transport protein PIN1 which establishes directional auxin flow. The gene encoding sunflower PIN1 (HaPIN1) has been cloned and its expression is found in the shoot apex. In addition, tools are being developed to introduce molecular markers for auxin concentration into sunflower plants. Subsequently, changes in auxin dynamics are being examined after manipulation of both auxin levels and mechanical properties of the capitpulum. Various methods are being employed to disrupt mechanical forces in the capitulum such as microdissection, laser abalation, and the imposition of extraneous forces via compression. Biomechanical measurements of differential tissue stiffness across the capitulum are being gathered using a MicroElectroMechanical Systems (MEMS) force sensor. Measurements are also being made after the aforementioned manipulations of auxin levels and mechanical properties. The resulting data describing the relationship between auxin dynamics and tissue biomechanics is being used by the investigators to refine and expand existing computational models of phyllotaxis to include the high order patterns seen in sunflower capitula. This multidisciplinary and integrative approach to an age old phenomenon, the establishment of Fibonacci based patterns in nature, will add understanding to the fields of biomechanics and plant biology. It will also serve to increase scientific discourse and collaboration between biologists and non-biologists, itself a likely example of emergent adaptation within the field of science.