ABSTRACT
This chapter discusses the distribution, biosynthesis, and function of cytokinin-active nucleosides in tRNA. Special emphasis is given to the distribution of cytokinins among organisms, organelles, and tRNA species. Cytokinins have been found in tRNA preparations from virtually all organisms. However, the distribution of cytokinin-active modified bases among organisms seems to show inter-kingdom differences. The greatest diversity of cytokinins occurs in plant tRNA preparations, from which as many as six different compounds have been isolated. The variety of cytokinins in plant tRNA has led to studies concerning the possible subcellular localization of cytokinin-containing tRNA. The fact that few algal tRNA preparations have been examined for cytokinin content does little to clarify the proposed relationships between algal chloroplasts and cyanobacteria. The subcellular localization of cytokinin-containing tRNA in mitochondria has been little studied. Growth conditions affect the cytokinin content of prokaryotic tRNA, with stress often causing undermodification.
