A study of the hypothetical role of cytokinins in completion of tRNA.

It has been suggested that the effect of cytokinins in retarding leaf senescence comes about through their incorporation into tRNA. To test this hypothesis, kinetin-8-(14)C, 6-benzylaminopurine-benzyl-7-(14)C and adenine-8-(3)H were applied to detached tobacco leaves, and the nucleic acids were thereafter extracted and chromatographed on MAK columns. Kinetin-8-(14)C and adenine-8-(3)H were readily incorporated into RNA in a similar pattern. 6-Benzylaminopurine-benzyl-7-(14)C was effective in delaying chlorophyll loss but was not incorporated into any nucleic-acid fraction. It is concluded that the possibility of cytokinins retarding leaf senescence by completion of tRNA is not supported.