ABSTRACT
The development of antagonists, as well as agonists, is of potential value in studies of the mechanism of action of biologically active compounds. In general, searches for cytokinin antagonists were conducted among purine analogs. A search among analogs of substituted ureas, some of which have cytokinin properties, was made by N. P. Kefford et al. Cytokinin antagonists may be found among analogs, since they might satisfy requirements as antagonists; i.e., similarity in structure to cytokinins, which allows for competition for the same receptor, but renders them ineffective as cytokinins. In the early 1970s, biochemical studies of cytokinins showed that a variety of plants convert cytokinins to their 7-glucosides. In the early 1970s, scientists in Australia discovered that exogenous cytokinins were converted to stable 7-glucosyl derivatives in tissues of various plants. Calcium intensified several cytokinin-regulated responses, such as the retardation of senescence and ethylene production.
