This 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.
