Presentation Information
[MS12-07]Phyllotaxis without symmetry: Lessons learned from flower heads.
*Adam Runions1,2, Przemyslaw Prusinkiewicz1, Teng Zhang3, Andrew Owens1, Niloufar Ashayeri1, Mikolaj Cieslak1, Paula Elomaa3 (1. University of Calgary (Canada), 2. Max Planck Institute for Plant Breeding Research (Germany), 3. University of Helsinki (Finland))
Keywords:
Phyllotaxis,Fasciation,Flower head,Asteraceae
Phyllotaxis – the arrangement of plant organs on a common supporting structure – has been a topic of enduring fascination within the natural sciences and mathematics. This interest has been driven by the conspicuous spiral patterns these organs form and their intriguing mathematical properties. For instance, the numbers of such spirals (parastichies) turning in the clockwise and counterclockwise directions are often successive Fibonacci numbers. The developmental origin of this and related features has been the subject of intense, yet not entirely conclusive, studies for centuries.
Consistent with observations of model plants such as Arabidopsis and tomato, it is typically assumed that organs arise sequentially on a radially symmetric support. However, in flower heads, florets emerge in concurrent bursts rather than in a strictly sequential order. Moreover, spiral patterns with Fibonacci parastichy numbers are occasionally observed in non-circular (fasciated) heads. These observations challenge the framework typically used to characterize and understand phyllotaxis.
In my talk, I will examine how the conceptual framework commonly used to describe phyllotactic patterns can be revised to account for non-circular supporting structures. To characterize these patterns, I will revisit the notions commonly used to describe phyllotaxis. I will show that some, in particular parastichies and parastichy numbers, maintain their significance in the non-circular and non-sequential case, whereas others, in particular the divergence angle (the angular distance between consecutively inserted organs), need to be revised or lose their significance entirely. I will illustrate these observations with a model of phyllotaxis that can operate on non-circular heads, including possible topological changes in the domain where new organs are placed.
Consistent with observations of model plants such as Arabidopsis and tomato, it is typically assumed that organs arise sequentially on a radially symmetric support. However, in flower heads, florets emerge in concurrent bursts rather than in a strictly sequential order. Moreover, spiral patterns with Fibonacci parastichy numbers are occasionally observed in non-circular (fasciated) heads. These observations challenge the framework typically used to characterize and understand phyllotaxis.
In my talk, I will examine how the conceptual framework commonly used to describe phyllotactic patterns can be revised to account for non-circular supporting structures. To characterize these patterns, I will revisit the notions commonly used to describe phyllotaxis. I will show that some, in particular parastichies and parastichy numbers, maintain their significance in the non-circular and non-sequential case, whereas others, in particular the divergence angle (the angular distance between consecutively inserted organs), need to be revised or lose their significance entirely. I will illustrate these observations with a model of phyllotaxis that can operate on non-circular heads, including possible topological changes in the domain where new organs are placed.