Auxin metabolism in the root apical meristem

Within the root meristem of flowering plants is a group of mitotically inac tive cells designated the quiescent center (QC). Recent work links the quie scent state to high levels of the growth regulator auxin that accumulates i n the QC via polar transport. This in turn results in elevated levels of th e enzyme ascorbic acid oxidase (AAO), resulting in a reduction of ascorbic acid (AA) within the QC and mitotic quiescence. We present evidence for add itional interactions between auxin, AAO, and AA, and report that, in vitro, AAO oxidatively decarboxylates auxin, suggesting a mechanism for regulatin g auxin levels within the QC. We also report that oxidative decarboxylation occurs at the root tip and that an intact root cap must be present for thi s metabolic event to occur. Finally, we consider how interaction between au xin and AAO may influence root development by regulating the formation of t he QC.