Signalling in cell type specification

Positional information is an important determinant in the establishment of cellular identity in plants. It is established during pattern formation and is maintained in growing organs. Cells maintain the ability to respond to changes in positional information during development indicating that the me chanism for perceiving such information must remain intact until relatively late in development. Once positional cues are perceived they set in motion a number of cascades resulting in the differentiation of particular cell t ypes in defined locations. The circuitry underpinning these later events is being teased out using genetics. Evidence is emerging for the existence of an array of both positive and negative genetic regulators from studies in a number of diverse plant model systems.