| This thesis focuses on various aspects of the action of plant hormones called jasmonates. They play an essential role in the defense response against microbial and herbivorous plant parasites and as such have a potential value for pesticide-free crop design. They also exert an inhibitory effect on plant growth, when applied exogenously. This trait greatly aided in identification of genes involved in jasmonate biosynthesis and signaling. Unfortunately, despite major efforts, still no sufficient information is available to construct a model of jasmonate action in plants analogous to their animal counterpart, prostaglandins.; The work, presented in this thesis, focused on the mechanisms responsible for the growth inhibition caused by external jasmonate application. The effect of jasmonic acid on the plant cell cycle progression was examined and compared to another plant growth inhibitor, abscisic acid. To perform the experiments a tobacco BY-2 cell line was selected because of its ability to achieve a high level of synchrony. With the use of thymidine incorporation and flow cytometry it was possible to determine that jasmonic acid could block cell cycle progression. It prevented G1/S and G2/M transitions while abscisic acid could only interfere with G1/S transition.; Literature data suggested that not only jasmonic acid but also its amino acid conjugates had biological activity. Arabidopsis thaliana plants, deficient in enzyme which adenylates jasmonic acid lose capacity to properly respond to jasmonic acid. In order to examine whether the cell cycle arrests were caused directly by jasmonic acid or by its derivatives formed upon application, the metabolism of jasmonic acid in tobacco BY-2 cells was studied. Several compounds, which were formed during the first hours of feeding, were identified, including jasmonyl-1-D-glucose, jasmonyl-1-gentiobiose, 11-hydroxy jasmonic acid, 12-hydroxyjasmonic acid, 11-hydroxy jasmonyl-1-D-glucose and 12-hydroxy-jasmonyl-1-D-glucose. A similar metabolic pathway was also observed in Arabidopsis thaliana. However none of those compounds, could arrest BY-2 cells in G2 phase of the cell cycle like jasmonic acid, yet they all could induce starch accumulation in tobacco BY-2 cells and inhibit root growth in Arabidopsis thaliana seedlings. In contrast, a synthetic analog of jasmonic acid, dihydrojasmonic acid could inhibit root growth and arrest synchronized cells, but it failed to induce starch accumulation in tobacco BY-2 cells. (Abstract shortened by UMI.)... |
