Pine somatic embryogenesis: analyses of seed tissue and medium to improve protocol development

Abstract

The shift from vegetative to embryogenic growth requires tissue to enter a radically different program of development and can be studied in vitro through the development of somatic embryos. From an applied perspective somatic embryogenesis (SE) is expected to play an important role in increasing productivity, sustainability, and uniformity of future forests. For commercial use, SE technology must work with a variety of genetically diverse trees. Since the first reports of SE in Picea abies and Larix decidua in 1985, many different coniferous species have shown the ability to produce embryogenic tissue. However, initiation frequency is often low, many desired seed sources are recalcitrant, and culture survival is often poor, raising costs of somatic seedlings produced from successful genotypes. A number of tools are now available to improve embryogenic tissue initiation and somatic embryo development in vitro that have resulted from analytical studies of seed tissues, the seed environment and gene expression in megagametophyte, zygotic embryos and somatic embryos. Benefits have occurred from medium supplementation with hormones, plant growth regulators, hormone inhibitors and polyamines. Somatic embryo growth has been enhanced with medium supplementation of nutritional components including specific sugar types, vitamins, organic acids, and redox potential modifiers. Control of environmental factors including, water potential, pH, adsorption of medium components by activated carbon and liquid versus gelled medium have also led to SE protocol improvements. The use of analytical studies to duplicate the seed environment in vitro is improving protocol development resulting in increased initiation, improved yields and higher-quality somatic embryos.