Developmental and Molecular Studies of Spruce Embryogenesis in Vitro

Since first described in the mid-eighties somatic embryogenesis of spruce has been extensively utilized both as a tool for mass propagation and as a model system for the investigation of structural, physiological and molecular events occurring during embryo development in conifers. Despite the increased efforts to optimize media composition and culture environment, production of somatic embryos still poses problems, especially for recalcitrant genotypes. Low yield and/or poor quality embryos which are not able to regenerate viable plants are often observed in culture. Improvements to the system have been made possible through the combined applications of developmental, physiological and molecular studies. Cell tracking techniques have defined the different phases of embryo development with great precision and have allowed for comparative structural studies between somatic and zygotic embryos. Physiological work has revealed ways to improve embryo development in culture. Manipulating the embryonic environment during the early phases of development through changes in osmoticum and redox state, or during germination through applications of ascorbic acid, has improved embryo regeneration. Furthermore, recent molecular work has identified several genes involved in embryo development. Advances in spruce transformation have revealed the functional relevance of such genes in regulating the developmental fate of somatic embryos. The focus of this review is to provide an up-date on the current status of spruce embryogenesis and to emphasize developmental and molecular events characterizing the process. _____________________________________________________________________________________________________________