Externí autoři: Marie-Anne Lelu-Walter

Somatic embryogenesis is a useful method for propagating selected plant material. However, before using this technique for forest tree deployment, it is important to ensure high-quality somatic embryos (SEs). This quality depends on how closely SEs resemble zygotic embryos (ZEs). At the end of their maturation, SEs usually resemble ZEs from fresh seeds due to their high water content and biochemical composition.

It is assumed that the production of somatic embryos (SEs), which closely resemble fully mature zygotic embryos (ZEs), increases the chance of producing somatic plants equivalent to seedlings. Desiccation is crucial to reduce the water content of SEs and to initiate biochemical changes that support germination and conversion into plants. We investigated the biological, histological, biochemical and molecular changes in the SEs of hybrid larch Larix eurolepis exposed to desiccation at high relative humidity (RH; 98 %), reduced RH (59 %), or a combination of both.

Somatic embryogenesis of conifers yields somatic embryos (SEs) that closely resemble non-mature cotyledonary zygotic embryos (ZEs). The most common method to improve the biochemical composition of SEs and reduce their water content to bring SEs closer to fully mature ZEs is cold treatment or desiccation at different relative humidity (RH). Both treatments can not only lead to successful SE germination but can also induce a stress response.

Exposure of Norway spruce (Picea abies) somatic embryos and those of many other conifers to post-maturation desiccation treatment significantly improves their germination. An integration analysis was conducted to understand the underlying processes induced during the desiccation phase at the molecular level. Carbohydrate, protein and phytohormone assays associated with histological and proteomic studies were performed for the evaluation of markers and actors in this phase.

Somatic embryogenesis techniques have been developed for most coniferous species, but only using very juvenile material. To extend the techniques’ scope, better integrated understanding of the key biological, physiological and molecular characteristics of embryogenic state is required. Therefore, embryonal masses (EMs) and non-embryogenic calli (NECs) have been compared during proliferation at multiple levels.

This first report of cellular and molecular changes after repetitive somatic embryogenesis in conifers shows that each cycle enhanced the structure and singularization of EMs through modulation of growth regulator pathways, thereby improving the line´s embryogenic status.