Conifer Somatic Embryogenesis, Embryo Development, Maturation Drying, and Plant Formation

Abstract

Somatic embryogenesis in conifers was first reported in 1985, and since then remarkable progress has been made in understanding factors controlling induction and development of conifer somatic embryos (reviewed by Attree and Fowke 1993; Gupta et al. 1993). For conifers, induction of somatic embryogenesis usually requires the culture of zygotic embryos on medium containing auxin and cytokinin. A proportion of the cultured zygotic embryos give rise to immature somatic embryos, which undergo continued proliferation in the presence of auxin and cytokinin and which proliferate rapidly in liquid shake culture. Thus, the potential exists for obtaining unlimited numbers of immature somatic embryos from a single zygotic embryo. When the auxin and cytokinin are removed and abscisic acid (ABA) and high osmoticum are applied, somatic embryos undergo synchronous development to mature forms which closely resemble zygotic embryos with respect to storage reserves, moisture contents, and development into normal plantlets. The embryos gradually lose moisture during development and acquire the ability to tolerate further drying to moisture contents similar to, or below, those of zygotic embryos from mature seeds. For large-scale applications, the potential now exists for producing quiescent somatic embryos throughout the year and storing them for germination in the spring. Adapting the technology could simplify production and possibly reduce costs as well as provide uniform plants. Embryo drying also promotes normal germination of the somatic embryos, and thus provides plants with greater vigor.