Identity of cytokinins in Begonia leaves and their variation in relation to photoperiod and temperature

The identity of cytokinins extracted from leaves of Begonia × cheimantha Everett cv. Nova has been studied by purification and fractionation on Dowex 50 H’ and Sephade× L.H 20 columns followed by reverse‐phase HPLC separation and determination by enzyme immunoassay. The following four cytokinins were identified: trans‐zeatin, trans ‐zeatin riboside, isopentenyladenin and isopentenyladenosin. At least three other compounds, possibly glucosides, were detected by activity in the tobacco callus bioassay but not yet identified. The quantity of the identified cytokinins was several times higher at 15 than at 24°C, the former temperature being optimal for regeneration of adventitious buds. At 15°C there was no clear effect of photoperiod whereas short days at 24°C increased the activity several‐fold compared with long day conditions.