9723895 Verbeke The process of cellular differentiation is of fundamental significance to our understanding of plant growth and development, yet experimental studies in this area have been rare. During development, each cell must somehow determine its position relative to others, and must differentiate accordingly. However, almost nothing is known about the mechanisms by which cells establish their positions and subsequently give rise to appropriate cell types. Although cell and tissue differentiation must certainly be the result of selective expression of the genome, a critical problem has been our inability to make the connection between phenotype and genotype. At a time when knowledge of gene structure and even function seems to be increasing exponentially, there is still little known about how these genes actually cause cells to differentiate and form tissues, organs, and organisms. Determination is a reflection of the state of differentiation of individual cells. For this reason, it may be quite useful to study cells which display a high degree of determination, as indicated by a resistance to redifferentiate. Plant epidermal cells are such entities. In the absence of wounding (and usually in spite of wounding), plant epidermal cells are developmentally incompetent to redifferentiate or change their fate. However, fusing floral organs are naturally occurring exceptions to this rule. The overall goal of the work described here is to learn more about the controls of plant cell differentiation. These experiments represent an ongoing characterization of the cell-to-cell communication events and signals which convey positional information. The specific question to be addressed will focus on characterization of the chemical identity of the redifferentiation factors. The periwinkle system described here is one of only a few plant systems in which dire ct experimental evidence documenting cell-cell interaction in the form of diffusible factors has been shown. This is also the first clear documentation in a plant system that two apparently identical organs in the same flower may be inherently and critically different from one another.
