Effects of cytokinins on the auxin requirement and auxin content of tobacco calluses1

High concentrations (0.1–1 mg/liter) of kinetin permitted continuous growth of auxin-requiring and cytokinin-nonrequiring tobacco calluses on a medium without auxin. This effect of kinetin did not seem to be due to perpetuating change in the tissue character, because tissue was auxin-requiring when returned to a kinetin free medium. Cytokinins, i.e. benzylaminopurine and geranylaminopurine, showed the same effect as kinetin in making auxin-requiring calluses grow without a supply of auxin. In auxin-requiring and cytokinin-nonrequiring calluses subcultured for 3 years on a medium containing 1 mg/liter kinetin without auxin, at least 3 auxins were detected by bioassay; 2 in the acidic and 1 in the neutral fraction. One was identified as IAA by paper chromatography (bioassay), thin-layer chromatography and gas chromatography. Reduced or no auxin activity was found in calluses transferred to a medium without kinetin. Kinetin was apparently required to maintain the endogenous auxin level in callus tissues. Kinetin may act on the auxin requirement of callus via its effects on auxin metabolism.