Simulation modeling of plant tissue with an emphasis on the moss physcomitrella patens leaf development
Creators: name: Chelladurai, Jeyaprakash
Publisher: name: University of Calgary
Year: 2012

description: Bibliography: p. 142-151
description: A few pages are in colour.
description: The presented research aims to elucidate the mechanisms of leaf development in the moss, Physcomitrella patens, through the construction of simulation models. Leading to this objective, models of several other multicellular structures have also been devised, and the modeling methodology was refined to increase the biological faithfulness of the models. Leaf growth in P. patens is initiated by a single leaf apical cell. This cell divides in alternating fashion, each time giving rise to a new primary segment. The final form of a leaf is determined by the growth and division of cells within segments. This scheme of P. patens leaf development is similar to that of fern gametophytic development in Microsorium linguaeforme and Dryopteris thelypteris. Consequently, previously de­scribed simulation models of these gametophytes development were re-implemented and re-examined as a stepping stone for P. patens leaf modeling. The gametophyte models operated under the assumption that genetically controlled division patterns, arising from cell lineages, determine the final form. They reproduced cell shapes and sizes inadequately due to the limitations of the pressure-tension model for assigning cell geometries. In this thesis, the pressure-tension model was refined to allow for continuous growth and asynchronous cell divisions. Additionally, a positional-based mechanism was incorporated into the model, where differential growth determines how cells divide. The improved models capture the development of fern gameto­phytes more precisely than the original models with respect to cell sizes, shapes, and the overall gametophyte form. Based on the experience from modeling fern gametophytic development, the P. patens leaf model was devised. General descriptions of cell division patterns during the early stages of P. patens leaf development suggested these patterns could arise stereotypically from cell lineages. However, visual examination of confocal images reveals variation within the general cell division schemes. Consequently, in this thesis an alternative hypothesis is examined, relating the observed pattern of apical and segment cell divisions to the size and shape of the cell. Modeling suggests that the overall leaf shape in P. patens results from an interplay between the distribution of growth across the leaf tissue, which influences when and how cells divide, and basipetal cessation of cell divisions. A heteroblastic series of P. patens leaves can be generated by exploring the parameter space. The simulated leaves reproduce the cell numbers along the median longitudinal axis of the leaf and the transverse axis at the widest point of the leaf in accordance with real L1 and L3 leaves. The construction of simulation models of fern gametophyte and leaf development points to the paramount role of self-organization in biological development, where complex patterns and shapes emerge from simple local processes.