Root development: new meanings for root canals?

During Arabidopsis root development, a radial pattern of tissues is extended by the meristem. These tissues form continuous layers and recent data suggest that tissue continuity is instrumental for constraining the direction of signaling in a process termed channeling. In the ground tissue, fate-determining signals originate from contiguous cells of the same layer, possibly due to specific symplastic connections. Mutant analysis supports the hypothesis that vascular tissue continuity may facilitate and depend on the directional transport of a vascular fate-determining signal, possibly the phytohormone auxin.