Endogenous cytokinin levels in embryogenic and non-embryogenic calli of Medicago arborea L.

Abstract Levels of endogenous cytokinins in petiole explants of Medicago arborea and in embryogenic and non-embryogenic calli induced from petiole explants on different culture media were analysed. The inter-relationships between externally applied growth regulators at different concentrations, the endogenous hormonal content and observed embryogenic response were studied. When cytokinins (2 mg l −1 of either kinetin or 6-benzylaminopurine (BAP)) are applied exogenously, total levels of endogenous cytokinin increase after the first month of culture. This increase is about sixfold higher when BAP is added. Total levels of endogenous cytokinins from 3 month callus cultures were higher in the non-embryogenic calli than in embryogenic calli. Levels of isopentenyl derivatives, and iP-type/zeatin-type cytokinins and iP-type/total cytokinins ratios were also different for embryogenic and non-embryogenic calli after the third month of culture, regardless of the induction medium used during the first and second months. Hence, these levels and ratios of endogenous cytokinins could be considered as reliable markers for the embryogenic response in M. arborea .