WHAT CHIMERAS CAN TELL US ABOUT PLANT DEVELOPMENT

The generation and analysis of plant chimeras and other genetic mosaic s have been used to deduce patterns of cell division and cell fate dur ing plant development and to demonstrate the existence of clonally dis tinct cell lineages in the shoot meristems of higher plants. Cells der ived from these lineages do not have fixed developmental fates but rel y on positional information to determine their patterns of division an d differentiation. Chimeras with cells that differ genetically for spe cific developmental processes have been experimentally generated by a variety of methods. This review focuses on studies of intercellular in teractions during plant development as well as of the coordination of cells during meristem function and organogenesis. Recent experiments c ombining mosaic analysis with molecular analysis of developmental muta nts have begun to shed light on the nature of the signals involved in these processes and the mechanisms by which they are transmitted and r eceived among cells.