Embryogenic response in different Medicago arborea L. explants depending on cytokinin/auxin balances

This paper analyses the effect of various combinations of 2,4;dichloropheno xyacetic acid and a number of cytokinins on the induction of somatic embryo genesis in hypocotyl, cotyledon, petiole and leaf explants of Medicago arbo rea. 2,4-dichlorophenoxyacetic acid was used at concentrations of I and 2 m g L-1 The cytokinins tested in combination with 2,4-dichlorophenoxyacetic a cid were kinetin (0.25, 0.5 and 2 mgL(-1)), 6-benzylaminopurine (2 mg L-1) or thidiazuron (2 mg L-1). Significant differences have been found in embry ogenic response, both among different media and among different explants. T he medium with the highest concentration of 2, 4-dichlorophenoxyacetic acid (2 mgL(-1)) and kinetin (2 mgL(-1)) was optimal for embryogenic calli indu ction, 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 e mbryogenic response. In general, an increase in the kinetin/2,4-dichlorophe noxyacetic acid balance has a positive effect on the embryogenic response i n all of the different explants analysed. The results obtained seem to sugg est the possible existence of an endogenous hormonal gradient from the firs t trifoliate leaf to the hypocotyl, which can affect embryogenic capacity.