Bringmann Abstract
The Arabidopsis leaf epidermis is constituted by two kinds of cells: Jigsaw puzzle- shaped pavement cells and kidney- shaped guard cells forming stomatal pores. Both of these cell types are derived from the stomatal lineage, which accounts for up to 82% of cells in the leaf epidermis (Geisler et al. 2000). This cell lineage therefore is well suited to explore how different cell types self- organize to attain a functional and complex tissue.
Stomatal lineage cells arise from asymmetric cell divisions of the stomatal lineage. In order to divide asymmetrically, these cells polarize by distribution of membrane- associated proteins in local subdomains. BREAKING OF ASYMMETRY IN THE STOMATAL LINEAGE (BASL) and BASL INTERACTING PROTEIN (BIP) were characterized (Dong et al., 2009; Rowe, unpublished) which segregate between daughter cells, similar to polarized protein complexes in animals. Without the activity of these proteins, many divisions become symmetric.
Polarization, asymmetric division and morphogenesis are fairly intuitive concepts, listing them however reveals a large gap in our understanding about how these steps are physically accomplished. Recently, mechanical forces have gained a lot of attention in the plant developmental community. It could be shown that artificially induced changes in mechanical forces in the shoot apical meristem lead to re- orientation of microtubules and polarized PIN proteins (Hamant et al. 2008). PINs are not polarized in the leaf epidermis. Using cell ablation and a stretching method, I found that polarized proteins like BIP react to changes in tissue mechanics, too. How this ties in with cytoskeleton dynamics, cell wall properties and chemical signaling in the leaf epidermis is part of my ongoing investigation.