ABSTRACT
This chapter is concerned with the naturally occurring adenine cytokinins. In addition to their widespread occurrence in plant tissues, numerous cytokinins have also been isolated from tRNAs of plant and animal origin and from fungi, bacteria, algae, and marine organisms such as blue coral. Cytokinins are generally extracted from plant tissues with aqueous methanol or ethanol or with ethyl acetate in the presence of aqueous potassium phosphate. The original investigations of Zea mays extracts indicated that only a small proportion of the cytokinin activity is due to zeatin; moreover, bioassays of chromatogram zones generally reveal the presence of at least three active materials. The ready availability of 6-N-benzylamino-purine, and its cytokinin activity, has long made it a prime candidate for metabolic studies. Large numbers of 6-N-substituted aminopurine derivatives have been prepared, and their cytokinin activities have been compared, although assay results tend to vary substantially according to the specific method used.
