Morphology of carrot somatic embryos formed in medium with abscisic acid

Somatic embryogenesis was induced from embryogenie cells derived from cotyledon expiants cultured on MS medium supplemented with 1 mg/L 2,4-D. In order to clarify the effect of abscisic acid (ABA) on the morphology of somatic embryos, embryogénie cell clumps or developing somatic embryos were treated continuously, or briefly, with ABA during culture. When embryogenie cells in MS medium without 2,4-D were treated with 0.04 mg/L ABA for the first week, normal embryos with two cotyledons increased slightly and embryos with anomalous cotyledons decreased. However when cell clumps in 2,4-D-free medium were treated with ABA in the second week normal embryos with two cotyledons decreased prominently and this decrease of normal embryos also occurred in the continuous ABA treatment during culture. Thus the morphological abnormalities in somatic embryogenesis occurred by exogenous ABA treatment beyond globular stage or by continuous treatment. The length of somatic embryos with anomalous cotyledons was larger than that of normal embryos with two cotyledons in control but both the normal and anomalous somatic embryos treated with ABA were almost similar in length. Somatic embryos formed in medium with ABA were larger in size than those in control due mainly to enlarged cotyledons. The enlarged cotyledons were composed of a greater number of cells than those of control. Therefore the enlargement of cotyledon by exogenous ABA seems to be not due to the enlargement of cells in cotyledons.