INFLUENCE OF SUCROSE CONCENTRATION ON IN-VITRO MORPHOGENESIS IN CULTURED CUCUMBER COTYLEDON EXPLANTS

When cucumber cotyledon explants were cultured on an initiation medium (a modified MS medium containing different concentrations of 2,4-D) c ontaining 131 mM sucrose, somatic embryogenic competence was very resp onsive to 2,4-D concentration: 2,4-D at 8 mu M resulted in the greates t frequency of somatic embryogenesis. By contrast, sucrose at a higher concentration (263 mM) weakened this response of cultured tissues to 2,4-D; concentrations ranging from 1 to 16 mu M all induced high frequ encies of somatic embryogenesis (82 to 95%). Highest multiplication ra tes of normal embryos were achieved with 2,4-D at 4 and 8 mu M. Subseq uent results demonstrated that elevated sucrose concentrations could a lso change the morphogenic regeneration patterns inducible by IAA. In the presence of IAA at a given concentration (57.1 mu M) and with sucr ose at 131 mM, only adventitious shoot formation occurred, whereas 263 mM sucrose induced both shoot organogenesis and somatic embryogenesis . Raising sucrose to 394 mM resulted in somatic embryogenesis only, an d increased somatic embryo formation to about 70%. It appeared that IA A combined with high sucrose concentration can also be used for the in duction of somatic embryogenesis in cucumber.