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

0853105 Braybrook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。国际研究奖学金计划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。 该计划的奖项提供了联合研究的机会，以及使用独特或互补的设施，专业知识和国外的实验条件。叶序性描述了植物器官在发育过程中形成时的排列方式。 地上器官的形成主要发生在茎尖分生组织，一个特化的群体？干细胞？位于主茎的顶端。 在向日葵花头（向日葵头状花序）中观察到的高级叶序显示出惊人的螺旋图案，这些图案是分生组织精确图案化的结果。 在一个给定的头状花序中，这些螺旋的数量是斐波那契数列的成员，这可能是一种由于在头状花序期间黄金角重复而产生的紧急现象。的发展。 最近在叶序研究中的工作突出了植物激素生长素在建立螺旋叶序模式和重复的黄金角中的重要作用;然而，所有这些工作都是在番茄和拟南芥的低阶叶序中完成的，并且涉及小的圆柱形分生组织，不像大的扁平向日葵头状花序。 从历史上看，有大量的数学和生物力学工作试图描述向日葵头状花序中的高阶模式。这些工作假定，分生组织内的机械力也可能是重要的模式发生器或执行者。 研究人员正在研究化学建立的图案（通过生长素）和机械强制图案之间的相互作用，通过结合生物学，物理学，数学和计算建模，使用跨学科的方法在发育中的向日葵头状花序中进行研究。 生长素运输的动力学正在使用免疫组织学检查，以可视化生长素运输蛋白PIN 1，它建立了定向生长素流。编码向日葵PIN 1（HaPIN 1）的基因已被克隆，并且在茎尖中发现其表达。 此外，正在开发将生长素浓度的分子标记引入向日葵植物的工具。随后，生长素动态的变化正在检查后操纵的生长素水平和机械性能的capitpulum。 各种方法被用来破坏头状突中的机械力，如显微切割、激光消融和通过压缩施加外力。 正在使用微机电系统（MEMS）力传感器收集头状突上不同组织刚度的生物力学测量结果。 在对生长素水平和机械性能进行上述操作后，也进行了测量。 研究人员正在使用描述生长素动力学和组织生物力学之间关系的所得数据来改进和扩展现有的叶序计算模型，以包括在向日葵头状花序中看到的高阶模式。 这种对古老现象的多学科和综合方法，建立自然界中基于斐波那契的模式，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话语和合作，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.