Epsilon Open Archive

Abstract

Somatic embryogenesis is an attractive method to propagate conifers vegetatively. However, many species belonging to Pinus are recalcitrant to somatic embryo development. The overall aim of this thesis has been to gain a better understanding of the developmental pathway leading to cotyledonary somatic embryos of Scots pine (Pinus sylvestris).

By comparing the developmental pathway of somatic embryos in a normal and in an abnormal cell line, differences between the cell lines were identified. An important difference was the high ratio of early and late embryos carrying supernumerary suspensor cells in the abnormal cell line compared to embryos in the normal cell line. This unbalanced ratio between the embryonal mass and the suspensor is at least partly caused by a disturbed polar auxin transport. Furthermore, a high proportion of early and late embryos degenerated in both cell lines. The degenerating embryos in the normal cell line were eliminated in a similar way as subordinate embryos in the seed. Contrastingly, the degenerating embryos in the abnormal cell line were not eliminated; instead the degenerated embryos started to differentiate new embryos creating a loop of embryo degeneration and embryo differentiation. During initiation of embryogenic tissue, the protruding early zygotic embryo(s) started to degenerate before a proliferating embryogenic culture was established, indicating that the initiation of embryogenic cultures is not a direct continuation of cleavage polyembryony. The results further suggest that there is a high risk that cell lines initiated from early zygotic embryos at the stage of cleavage develop abnormally.

To be able to use more differentiated tissues as explants for initiation of embryogenic cultures, more knowledge is needed about totipotence and embryogenic potential. Treatment with the histone deacetylase inhibitor trichostatin A (TSA) during maturation of somatic embryos of Norway spruce inhibited the maturation progression of the embryos. Furthermore, although TSA-treatment maintained the embryogenic potential in germinating somatic embryos, it did not enable the embryos to regain embryogenic potential after it was lost.

By analysing global changes in gene expression during early zygotic embryo development in Scots pine, we identified genes and processes that might be important for regulating the cleavage process and for the development of a dominant embryo.

Together these results contribute to the knowledge that in turn can lead to improved protocols for large scale propagation of Pinus species via somatic embryos.