Simulation models of phyllotaxis and morphogenesis in plants

The research presented here is focused on the construction of simulation models intended to improve our understanding of phyllotaxis and related patterning mechanisms in plants. Most mechanistic models of phyllotaxis proposed in the literature are based on the idea that existing primordia inhibit the formation of new primordia nearby. This idea is explored at two different levels of abstraction. At a more abstract level, a simulation is presented in which the inhibiting effect is modeled as a simple mathematical function of distance and primordium age. The resulting model can generate a wide variety of the phyllotactic patterns observed in nature, and is more robust than previous models in which primordium age did not influence the inhibition directly. A second simulation model is presented that offers a explanation for phyllotaxis in molecular terms. A theory inspired by recent experimental work is explored, that suggests that self-enhancing transport of the morphogen auxin could be responsible for phyllotaxis patterning. This is fundamentally different from traditional reaction-diffusion models often proposed for patterning in animals.;Although visually there is little similarity between phyllotaxis and leaf venation, the transport-based mechanism proposed over 25 years ago for leaf venation is believed to involve the same molecular components. The same morphogen, and the same transport machinery is hypothesized to be the basis for both patterning models. Simulation results presented here and in previous work show that the dramatic difference in the patterns created by the two mechanisms could be the result of changing the way the transport machinery obtains its polarity. However, almost nothing is known about how this polarity is achieved. Furthermore, some experimental evidence suggest that both mechanisms may actually be operating within the same cells, perhaps even at the same time. Exploring this possibility, several models of early leaf venation are investigated, using a similar cellular surface and the same molecular components as the phyllotaxis model. These models provide some initial inroads into the still open problem of integrating the two patterning mechanisms.