Vein patterning in growing leaves: axes and polarities.

Network and branching structures play essential roles in transport and/or mechanical support in multicellular organisms. In plant leaves, vasculature contributes to both processes. Recent descriptions of network leaf vein patterning in the model plant Arabidopsis thaliana indicate that veins initially extend from local maxima of the plant hormone auxin in the leaf margin, and network patterns then form within the blade. Auxin influences patterning through a feedback between auxin-mediated gene activation and auxin transport. Patterning of the adaxial-abaxial domains of the leaf and patterning of the leaf margin are proposed to affect vein patterning through interactions with this feedback mechanism, which may in the future provide a united view of leaf development.