Differentiation in plant epidermal cells.

The plant epidermis is a multifunctional tissue playing important roles in water relations, defence and pollinator attraction. This range of function is performed by a number of different types of specialized cells, which differentiate from the early undifferentiated epidermis in adaptively significant patterns and frequencies. These various cells show different degrees of morphological specialization, but there is evidence to suggest that even the less specialized cell types may require certain signals to ensure their correct differentiation and patterning. Epidermal cells may potentially adopt certain fates through a cell lineage based mechanism or a cell interaction mechanism. Work on stomatal development has focused on the cell lineage mechanism and work on trichome differentiation has focused on the cell interaction model. Recent work on the Arabidopsis trichome suggests that interactions between neighbouring cells reinforce initial differences, possibly in levels of gene expression or cell cycle stage, to commit cells to different developmental programmes. In this review these mechanisms are explored in a number of specialized cell types and the further interactions between different developmental programmes are analysed. It is in these interactions between differentiating cells adopting different cell fates that the key to the patterning of a multifunctional tissue must lie.