Wendy K. Silk, University of California at Davis, One Shields Ave., Davis, CA 95616 and Bruno Moulia, UMR PIAF, Centre INRA de Clermont-Fd-Theix, Site de Crouelle, 234, avenue du Brézet, CLERMONT-FERRAND Cedex 02, 63100, France.
Any understanding of the physiology of leaf growth, including the underlying molecular biology, must begin with knowledge of the spatial distribution of growth and space-time relationships. These can be clarified using concepts and methods from fluid dynamics. Growth trajectories provide a space-time map useful for inferring a developmental time course from spatial patterns in the leaf. Many environmental stresses affect growth, as quantified with marking experiments in which proper attention is paid to the spatial and temporal scales for the analysis, visualized by a field of growth rate tensors. Leaf nutrition can be understood in terms of nutrient deposition rate, calculated using a continuity equation with data on nutrient densities and growth rates. Longitudinal and transverse curvatures are coupled in leaves and play important roles in regulating light capture and water loss. The convex curved form at the base of the growing gramineous leaf is a steady structure composed of changing cells and produced by a growth gradients from the ad- to the abaxial surfaces. In contrast the concave form of the older part of the leaf is a material property hypothesized to originate by contraction of fibers that are more abundant on the abaxial leaf surface. Recent work invokes elasticity theory to show that ruffles at the leaf edge are produced by a transverse growth gradient coupled to mechanical properties of the thin blade.
