Root apices have been studied through the analysis of cell lineage based on histological sections. Theories of apical organization derived from such analyses led to the view that there existed "ultimate initials" at the focus of the cell lineage, just proximal to the root cap. As a result of continuous mitotic activity, it was believed, the ultimate initials produced derivative cells that formed the root. The discovery in 1956 that these cells rarely divided in a growing root initiated a reassessment of root development. Collectively, these inactive "ultimate initials" comprise a region called the quiescent center (QC). Since its discovery, plant biologists have tried to understand what the QC cells do, why they are quiescent, and how and when quiescence arises. The work outlined in this proposal addresses these questions. The objectives of this proposal are to use molecular, genetic, and physiological approaches to link the known biochemistry of the root to the biophysics which determines the cellular architecture of the root. Specific attention will be directed to measuring the levels, distributions and interactions between auxin, ascorbic acid and ascorbic acid oxidase with the objective of relating changes in these substances to properties of the quiescent center. Using various experimental approaches, levels of these substances will be manipulated and the status of the quiescent center and apical anatomy investigated. The significance of this effort lies in the advancement of a new hypothesis to account for and understand the establishment and developmental role of the quiescent center and ultimately patterning in roots.
