Maturation of somatic embryos as a model for soybean seed development

摘要

Soybean somatic embryos have attracted attention both as a model of zygotic embryos and as explants for the generation of stable transgenic plants. We have now characterized the maturation of soybean somatic embryos in detail by examining both the accumulation of the major seed storage proteins beta-conglycinin and glycinin as well as changes in cellular organization. Protein storage vacuoles and oil bodies, which are the main depositories of seed storage reserves, formed within cells during the maturation of somatic embryos. The seed storage proteins were gradually synthesized and accumulated in the protein storage vacuoles in a manner similar to that apparent in seeds. The alpha and alpha' subunits of beta-conglycinin were detected earlier than the beta subunit of this protein and glycinin. In addition, The alpha and alpha' subunits of beta-conglycinin accumulated in both the cotyledons and the hypocotyl of somatic embryos, whereas the beta subunit of beta-conglycinin and glycinin accumulated only in the cotyledons. These temporal and spatial characteristics of storage protein production in maturating somatic embryos are similar to those in developing seeds, although the maturation of somatic embryos ceases prematurely without attainment of the final stages of development. Our findings suggest that somatic embryos are suitable for verification of seed-specific traits such as the biosynthesis of seed components.