N-(Delta-Isopentenyl)adenosine: Its Occurrence as a Free Nucleoside in an Autonomous Strain of Tobacco Tissue.

Cytokinins from both the free nucleoside pool and the transfer RNA have been isolated and identified in a habituated strain of tobacco pith callus (Nicotiana tabacum [L] var. Wisconsin 38). The transfer RNA of this strain contains both N(6)-(Delta(2)-isopentenyl) adenosine and N(6)-(4-hydroxy-3-methylbut-2-cis-enyl) adenosine. The trans-hydroxylated derivative is absent from the transfer RNA of this dark-grown tissue. N(6)-(Delta(2)-Isopentenyl)-adenosine was identified as a component of the free nucleoside pool in concentrations of about 10 micrograms per kilogram of tissue.The cytokinin-requiring tissue grown in the presence of N(6)-furfurylaminopurine contains less than 85 nanograms per kilogram of N(6)-(Delta(2)-isopentenyl) adenosine. This is the detectable limit under the conditions of the experiment.