The possible role of reaction-diffusion in leaf shape.

We consider mechanisms that may determine certain simple leaf shapes. Compared with other aspects of plant morphogenesis, such as phyllotaxis or spiral leaf arrangement, rather little is known about leaf-shape-determining mechanisms. We develop mathematical models for the gross pattern of leaf shape based on reaction diffusion systems. These models are consistent with what is known about factors that might determine leaf shape. They show that diverse leaf shapes may be obtained from a single reaction diffusion system. This has implications in terms of both convergent and divergent evolution. The models make predictions that can be tested experimentally. We predict the form of pre-patterns of growth promoters in leaf primordia of different sizes when the morphogens either diffuse into the primordia or are produced locally. We also predict the effects on leaf shape of removing parts of primordia at different times. The models can also predict the effects on leaf shape of the topical application of activators and inhibitors to leaf primordia.