ABSTRACT
The quest for cytokinin receptors began a little over 20 years ago with the discovery that plant ribosomes possessed cytokinin-binding abilities. Searching for cytokinin-binding proteins (CBPs) on ribosomes was an obvious choice, since the stimulatory effects of cytokinins on protein synthesis had been well established by then. This chapter reviews the data on CBPs and putative cytokinin receptors, that have accumulated since the mid-1970s. In addition, there will be commentary on the nature of cytokinin binding at the molecular level and some concluding thoughts about the biological and semantic differences between receptors and binding proteins. The chemical nature of the purine ring in cytokinins is both a blessing and a bane to the study o cytokinin binding. Seed lectins, proteins with carbohydrate binding sites, have also been shown to bind cytokinins. Cytokinins are known to stimulate the activity of a protein kinase in barley leaf chromatin.
