Thursday, June 20th, 14h00, Room 454 A, Condorcet Building.

PhD defense of Camille Le Scao

A propagation front model for leaf growth.

supervised by Stéphane Douady and Julien Derr


Leaves are photosynthetic organs with primarily determinate growth and come in an immense variation of shapes, sizes, and vascular networks. The vascular system, distributing water and collecting nutrients, also presents a variance of architecture with parallel, ramified, or looped vein networks but often shows a primary vein with regular left-right oscillations. During morphogenesis, two modes of growth are distinguished: diffuse and marginal. As many different molecular pathways are involved in leaf development, we require simplification to understand how leaf shape emerges from local rules.
This thesis explores the coupling between leaf growth and venation pattern formation. We consider a growth focused on the leaf margin and describe a minimal leaf growth model based on propagating interfaces and regular vein spacing. We first investigated an imposed leaf shape with unidirectional growth and found an unstable primary vein. Its dynamics are described by an iterated function whose geometry explains the instability. In a second case, when the growth of the vascular system and the growth of the leaf are interdependent, the vascular network dynamics and the leaf shape are stabilized by local growth. To verify our hypothesis, we present a proof of concept for leaf growth tracking of an Osmunda regalis fern leaf.