MATERIALS AND METHODS The maturation of soybean (Glycine max L. Merr.) somatic embryos was characterized. Maturation was assayed by evaluating the ability of somatic embryos to make the transition to a plantlet through a germination-like process. Somatic embryos were organized from cotyledons of immature soybean embryos. Maturation of somatic embryos occurred on a Murashige-Skoog basal medium supplemented with activated charcoal and 0.28 molar sucrose. After 8 weeks on this medium, somatfc embryos exhibited vigorous, high frequency development to plantdets. The "germination" frequency (conversion) of somatic embryos, and plantlet recovery frequency varied concurrently with maturation period. Conversion and plant recovery required no exogenous growth regulators. Desiccation of immature somatic embryos under controlled humidity regimes resulted in increased frequency of conversion of immature somatic embryos. Morphological abnormalities appeared in the somatic embryos, but few were detrimental to conversion velocity. There was little effect of genotype on conversion velocity or frequency.There have been several contemporary reports concerning the production of somatic embryos from cotyledons of immature soybean embryos (5,6,15,23,24). Although considerable effort has been expended in the characterization of somatic embryo induction, there is sparse quantitative information on the subsequent performance of the somatic embryos, especially with regard to their morphology, anatomy, development, physiology, and biochemistry. Although somatic embryogeny recapitulates zygotic embryology in many ways (7,22,28), this correlation has yet to be developed in soybean. Plant cell and tissue culture provides an excellent opportunity to study developmental processes in a controlled environment. However, cell and tissue cultures typically are not well-synchronized in development or differentiation. Therefore, the goals of this study are to understand the processes of soybean somatic embryo development, and to control expression of this process in a reproducible and controlled fashion. Our long-term goal is to determine if the requirements for somatic embryo maturation and development are comparable to that demanded by zygotic embryos. In this way, somatic embryos may function as a model for zygotic embryogenesis. '
Induction and Maturation of Somatic EmbryosSomatic embryos were generated on cotyledons of immature soybean (Glycine max L. Merr.) embryos as described by Ranch et al. (23,24). The genotypes used in these studies were cv 'Gem,' 'Star,' 'Shawnee,' 'A3127,' 'Williams 82,' and 'Union.' Immature seed were harvested from greenhouse or field-grown plants. At the appropriate stage for explant, the immature embryo possessed cotyledons 3 to 5 mm long and were 15 to 21 DAF in field-grown plants. Cotyledons were cultured abaxial surface down on solidified induction medium composed of Murashige and Skoog (17)
Growth and Different during the Maturation RegimeAt the time of initial transfer to MM, and at intervals for 70 ...