Abscission is an almost universal phenomenon by which plants shed organs. In terms of ecology and adaptation, it allows flexibility in dealing with stresses, injuries, and failure of pollination. It accommodates fruit and seed dispersal and seasonal dormancy. Economically it becomes important in terms of leaf removal, flower/young fruit removal, and mature fruit harvest. There are agricultural situations where it would be desirable to either promote or reduce leaf, flower/young fruit or mature fruit abscission. Abscission can be divided into three stages. First, the development of a region where abscission will occur --- the abscission zone (AZ); second, the actual separation of the organ from the plant; and third, the formation of a protective layer of cells on the proximal end of the zone. Although the process of cell separation between cells of fully developed AZs has been well investigated, the process by which certain cells differentiate as an abscission zone is not well understood. Experiments described in this proposal will examine the molecular and cellular mechanisms involved in the process by which an AZ forms on tomato pedicels. The long term goals of this program are to establish a model system that can be utilized to study the gene regulation and cell biology of abscission zone development. Tomato is an ideal system with which to set up such a model system. The PI hopes to determine the role of the jointless gene in the abscission process and relate the pattern of expression of this gene with the development of abscission zones in chimeric plants.
