CELL FATE IN THE ARABIDOPSIS ROOT-MERISTEM DETERMINED BY DIRECTIONAL SIGNALING

POSTEMBRYONIC development in plants is achieved by apical meristems. S urgical studies and clonal analysis have revealed indirectly that cell s in shoot meristems have no predictable destiny(1-3) and that positio n is likely to play a role in the acquisition of cell identity(4-7). I n contrast to animal systems(8-10) there has been no direct evidence f or inductive signalling in plants until now. Here we present evidence for such signalling using laser ablation of cells in the root meristem of Arabidopsis thaliana. Although these cells show rigid clonal relat ionships, we now demonstrate that it is positional control that is mos t important in the determination of cell fate. Positional signals can be perpetuated from more mature to initial cells to guide the pattern of meristem cell differentiation. This offers an alternative to the ge neral opinion that meristems are the source of patterning information( 12).