Organs are composed of cells with distinct identities designed to interpret stimuli in specialized ways and coordinately fulfill complex functions. In order to understand how cells perform these specialized functions I plan to study the mechanisms by which cell identity alters the quality and quantity of a stimulus response. I propose to use Fluorescent Activated Cell Sorting (FACS) in combination with cell-type specific fluorescent marker lines to isolate individual cell types of the root after treatment with a stimulus. Using microarrays, I will then analyze the transcriptional changes that occur in each cell type of the root and identify genes that demonstrate cell-type specific transcriptional responses. These data will not only lead to a better understanding of the relationship between cell identity and stimulus perception and response but will also lead to the development of markers to monitor this regulation and marker-based mutant screens to identify the genetic mechanisms that control it. In addition, I propose to collaborate in the development of a high-throughput platform for visualizing root development and physiology termed the """"""""root array"""""""" that will facilitate the work proposed here and contribute to the design of future experiments.