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) containing 131 mM sucrose, somatic embryogenic competence was very responsive to 2,4-D concentration: 2,4-D at 8 mu M resulted in the greatest 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 frequencies of somatic embryogenesis (82 to 95%). Highest multiplication rates of normal embryos were achieved with 2,4-D at 4 and 8 mu M. Subsequent results demonstrated that elevated sucrose concentrations could also change the morphogenic regeneration patterns inducible by IAA. In the presence of IAA at a given concentration (57.1 mu M) and with sucrose 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, and increased somatic embryo formation to about 70%. It appeared that IAA combined with high sucrose concentration can also be used for the induction of somatic embryogenesis in cucumber.