Abstract
Summary Epidermal cells of leaves are diverse: tabular pavement cells, trichomes, and stomatal complexes. Pavement cells from the monocot Zea mays (maize) and the eudicot Arabidopsis thaliana (Arabidopsis) have highly undulate anticlinal walls. The molecular basis for generating these undulating margins has been extensively investigated in these species. This has led to two assumptions: first, that particular plant lineages are characterized by particular pavement cell shapes; and second, that undulatory cell shapes are common enough to be model shapes.To test these assumptions, we quantified pavement cell shape in epidermides from the leaves of 278 vascular plant taxa.We found that monocot pavement cells tended to have weakly undulating margins, fern cells had strongly undulating margins, and eudicot cells showed no particular undulation degree. Cells with highly undulating margins, like those of Arabidopsis and maize, were in the minority. We also found a trend towards more undulating cell margins on abaxial leaf surfaces; and that highly elongated leaves in ferns, monocots and gymnosperms tended to have highly elongated cells.Our results reveal the diversity of pavement cell shapes, and lays the quantitative groundwork for testing hypotheses about pavement cell form and function within a phylogenetic context.
Highlights
The first cell was described by Robert Hooke in 1665; the empty cells of sectioned cork, seen under a microscope, were likened to the cells of a honeycomb (Hooke, 1665)
We used the traditional shape descriptors of area, circularity, AR, and solidity (S) (Fig. 2; see the Materials and Methods section for definitions). We utilized these traditional metrics because we found that elliptical Fourier analysis did not perform well with our extremely diverse dataset (Fig. S2); elliptical Fourier analysis did a reasonable job of capturing aspect ratio variance but not margin undulations (Fig. S2)
In a Principal component analysis (PCA) with the traditional metrics, the sum of the principal component (PC)1 and PC2 together accounted for 69.7% of shape variance (Fig. 2a, monocots and eudicots as an example; Fig. S2, all clades)
Summary
The first cell was described by Robert Hooke in 1665; the empty cells of sectioned cork, seen under a microscope, were likened to the cells of a honeycomb (Hooke, 1665). Molecular studies of pavement cell shape generation have focussed almost exclusively on model genetic species such as Arabidopsis, maize, and Oryza sativa (rice) (Smith, 2003; Zhou et al, 2016; Belteton et al, 2018). All of these epidermides present dramatically undulating cell margins, while maize and rice (both grasses) exhibit extreme cell elongation. Intensely studied at a molecular level, and despite an early qualitative survey of leaf pavement cell shape (Linsbauer, 1930), it remains unclear how common margin undulation is across vascular plants
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