Somatic embryogenesis in conifers - With special emphasis on Picea abies

Plant regeneration via somatic embryogenesis has practical application in vegetative propagation of conifers. In addition the process offers unique opportunities to study embryology. Surprisingly, the appearance and the development of the somatic embryos seem to be rather similar in most coniferous species. Therefore, one coniferous species can be used as a model system for learning more about the regulation of embryo development in conifers. We have chosen to work with Picea abies. Differentiated cells in the primary explant (zygotic embryos or seedlings) are stimulated to go through repeated divisions so that dense nodules are formed from which somatic embryos differentiate. The first formed somatic embryos proliferate and give rise to embryogenic cell lines. Somatic embryos can be stimulated to go through a maturation process when treated with ABA. Mature somatic embryos are first desiccated and then stimulated to convert into plantlets. The plantlets can be transferred to the field where they develop normally and start to flower at the same time as seedplants of the same origin. The morphology of somatic embryos is similar within each cell line but differs among cell lines. We have concluded that: (1) embryogenic cell lines of Picea abies contain embryos which have reached various developmental stages; (2) the morphology of the embryos is reflected by the pattern of extracellular proteins and AGPs; (3) the embryos are stable blocked at a certain stage of development but can be rescued by addition of proteins; (4) a characteristic of the blocked embryos is that the cells in the embryonic region separate and enlarge at such an early stage that normal embryo development is inhibited; (S) proteins identified as having a putative regulatory effect on embryo development include chitinases, peroxidases, zeamatin-like proteins and AGPs. We are studying extracellular proteins and their regulatory effect on embryo development.