An Improved Bioassay for Cytokinins Using Cucumber Cotyledons

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Abstract
The cucumber cotyledon greening bioassay is frequently used for detecting cytokinins. Beneficial modifications of the original technique included using 5-day-old cucumber (C. sativus L., cv. National Pickling) cotyledons treated with combinations of 40 mm KCl and various concentrations of cytokinins. A dark incubation period of 20 h was followed by an exposure to light for 3.5 h. Under these conditions, extremely low (0.0001 mg/l) concentrations of N6-benzyladenine, zeatin, kinetin or zeatin riboside can be detected. Of the 4 cytokinins tested, kinetin appeared to be the least active. With these improvements, the assay is 10 times more sensitive than is the previously described cucumber cotyledon greening bioassay for cytokinins.