The complex vasculature seen in the vascular plants provides a scaffolding of structural support and is responsible for the movement of water, minerals, photosynthate and some hormones. The auxin canalization model proposes that a positive feedback mechanism causes auxin-transporting cells to become vascular cells. We have isolated a leaf-patterning mutant, unhinged (unh), which shows a simplified leaf vascular pattern with more freely ending veins and fewer secondary veins. Expression of the ATHB8::GUS reporter construct indicates that the UNH gene acts prior to procambial patterning of the first presumptive secondary veins. Expression of the auxin responsive reporter gene DR5::GUS is reduced in unh leaves and roots, indicating that UNH may be involved in auxin signaling. Increasing the level of auxin in unh leaves through the addition of auxin transport inhibitors, low concentrations of 2,4-dichlorophenoxyacetic acid, and through introducing unh into mutants in which auxin transport is defective partially rescues the unh phenotype, supporting this hypothesis. The unh mutation maps to a 60kb region near the top of chromosome IV. No other leaf vascular mutant or auxinassociated mutant have been reported in this area, thus UNH represents a novel component of leaf vascularization and auxin signaling. / xi, 65 leaves : ill. (some col.) ; 29 cm.