Embryogenic Response in Different Medicago arborea L. Explants Depending on Cytokinin/Auxin Balances

This paper analyses the effect of various combinations of 2,4-dichlorophenoxyacetic acid and a number of cytokinins on the induction of somatic embryogenesis in hypocotyl, cotyledon, petiole and leaf explants of Medicago arborea. 2,4-dichlorophenoxyacetic acid was used at concentrations of 1 and 2 mg L−1 . The cytokinins tested in combination with 2,4-dichlorophenoxyacetic acid were kinetin (0.25, 0.5 and 2 mg L−1), 6-benzylaminopurine (2 mg L−1) or thidiazuron (2 mg L−1). Significant differences have been found in embryogenic response, both among different media and among different explants. The medium with the highest concentration of 2,4-dichlorophenoxyacetic acid (2 mg L−1) and kinetin (2 mg L−1) was optimal for embryogenic calli induction, whereas in the media containing kinetin or 2,4-dichlorophenoxyacetic acid alone, the mentioned response was absent. Among the explants analysed, hypocotyl and petiole show a significantly greater capacity to evoke an embryogenic response. In general, an increase in the kinetinl2,4-dichlorophenoxyacetic acid balance has a positive effect on the embryogenic response in all of the different explants analysed. The results obtained seem to suggest the possible existence of an endogenous hormonal gradient from the first trifoliate leaf to the hypocotyl, which can affect embryogenic capacity.