Exploring the diversity of epidermal pavement cell shapes
Pavement cells in the leaf epidermis can exhibit a wide variety of shapes. Undulations in the anticlinal cell wall are a particularly interesting feature present in many model species: for example, Arabidopsis thaliana, tobacco and maize; but absent in others, like Brachypodium distachyon. Epidermal cell patterning is qualitatively similar between individuals of the same species but different species can have wildly different shapes and there is no comprehensive data set available for epidermal cell shapes. Moreover, the cell shape changes during development – this has only been quantitatively studied in Arabidopsis.
This work presents and analyses three sets of cell shape data. The first part examines the morphogenesis of the curiously shaped pavement cells of maize leaves – these cells are highly elongated and form deep undulations in the anticlinal wall as they mature. The second part analyses the cell shapes of more than 200 species and concludes that strong undulations like those observed in Arabidopsis and maize are quite extreme: 95% of the species examined develop more shallow undulations or none at all. This part also investigates the extent to which cell shape features correlate with leaf shape features and the phylogenetic distance. The third part studies more subtle variances in the patterning of the cotyledons of different Arabidopsis thaliana ecotypes.
Analysing cell shapes also poses an interesting mathematical challenge: quantifying two- dimensional shapes is a nontrivial mathematical problem as it requires representing the information defined by the coordinates of the outline by only a few quantities. Throughout this project, different metrics have been used alongside principal component analysis to reduce the number of variables. These metrics include traditional morphometric variables, elliptic Fourier descriptors and various other state-of-the-art methods for shape characterisation.