Fig. 1.

SLGCs are the ideal system to study cell-shape acquisition. (A) Image of pavement cells from the third leaf of Arabidopsis (cell walls are stained with propidium iodide). (B) Outlines of the cells in the image from A with marked spiral patterning originating from asymmetric divisions of meristemoid cells. Numbers mark the cell stage in the spiral from the youngest (1) to the oldest (3) and arrows mark the clockwise or counterclockwise direction of the spiral. M, meristemoid; S, stoma. (C) Asymmetric division of the meristemoid cell produces a new meristemoid cell and an SLGC (1). During growth and development, the SLGC (2) always produces its first lobe (marked with an arrow) into an older neighboring cell. Example of an older SLGC (3) forming three lobes (marked with arrows) into older neighboring cells. (D) Position of first-lobe outgrowth in SLGCs. In these cells the vast majority of lobe outgrowth occurs opposite the stoma. Each bar represents the proportion of analyzed lobes for which outgrowth occurred in the indicated 15° angle range. Angles were measured from the lobe outgrowth to the center of the neighboring stoma. n = 47 lobes. (Scale bars, 20 μm.)