Determination is a developmental event which programs the future fate of a cell or a group of cells. It is often a stable state but not necessarily an irreversible condition. In general terms, a cell or group of cells is determined when it exhibits the same developmental fate whether grown in situ, in isolation, or at a new place in or on the organism. Determination has been extensively documented and studied, primarily in animals. In plant development, determination is often an obscure component because many plant cells are totipotent. Nevertheless, Dr. McDaniel has identified a situation in plant development, flowering in both day neutral and photoperiodic plants, in which determination is stable enough to permit investigation. The proposed study will continue his characterization of floral determination in the genus Nicotiana and extend his approach to the single cycle, long day plant, Lolium temulentum. Four topics will be addressed: 1) Employing clonal analysis, establish the developmental fate of cells in the meristem of florally determined terminal and axillary buds of day neutral tobacco, 2) Via tissue culture, establish the stability of the capacity of pedicle tissues to produce floral shoots, 3) Using reciprocal grafts, establish if the number of nodes produced by a N. tabacum cv. Wisconsin 38 shoot (scion) can be influenced by the roots (stock) of other cultivars of N. tabacum, 4) Using meristem/apex culture, establish the time for floral evocation, the time of floral determination, and characterize the influence of various gibberellic acids on the flowering process in Lolium temulentum. %%% Understanding determination is critical for any in depth, comprehensive understanding of development in multicellular organisms. This has proved a very difficult problem to attack in plant systems. The determination of a plant to flower has been developed into an approachable system for this study.
