Transformations of Cellular Pattern: Progress in the Analysis of Stomatal Cellular Complexes Using L-Systems

Abstract

AbstractStomatogenesis involves a progressive transformation of selected protodermal cells on primary plant tissue surfaces, especially those of leaves, and culminates in the formation of a functional stomatal apparatus. The transformations are accompanied by species-specific stereotypical productions of cells, commencing with an asymmetric cell division which produces a meristemoid having a prescribed number of future divisions and concludes with a symmetric division that produces a pair of guard-cells. Where all cells of the stomatal cellular complex descend from a meristemoid, and where subsidiary epidermal cells are produced from intervening steps, the pathway is said to be mesogenous. It is often found in dicot plants. In contrast, the perigenous pathway often consists of fewer divisions of the meristemoid and incorporates into the ontogeny of the stomatal complex one or more of the protodermal cells which neighbour the meristemoid; it is their asymmetric divisions which produce subsidiary cells. This pattern is often found in monocots. The auto-reproductive meristemoidal state may, in certain cases of the mesogenous pathway, be perpetuated by means of a stomatogenic branching process in one of the subsidiary cells, as shown by the formation of “satellite” stomatal cellular complexes on leaves of Arabidopsis thaliana. L-system algorithms are developed that prescribe not only the cell divisions and transformations but also the stomatogenic cellular patterning that occurs throughout the angiosperms. Mutations of the patterning process, and natural variations, such as stomatal clustering, are also discussed. All the division patterns (normal, mutant, and unusual) necessary for the structuring of leaf stomatal complexes, including examples of the so-called “one-cell rule” of stomatal spacing, can be modelled by an appropriate deterministic L-division system. Because the division systems can be analogised to states of the wall and peripheral cytoplasm that attract the attachment of new division walls, this cytological aspect of meristemoids would appear to deserve more attention. Gene regulation is an additional component of stomatal construction. Such processes help to initiate the cytological analogues that are reproduced by L-systems within a framework composed of hitherto uncommitted protodermal cells. Gene regulation also terminates the auto-reproductive property of the division system and leads to the differentiation of the cells which construct the stomatal complexes.KeywordsLeaf SurfaceSubsidiary CellDivision SystemCellular PatternStomatal ComplexThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.