Somatic Embryogenesis and Plant Regeneration in the Culture of Arabidopsis thaliana (L.) Heynh. Immature Zygotic Embryos

Immature zygotic embryos (IZEs) of Arabidopsis thaliana (L.) Heynh., a model species for plant ­genomics, provide efficient explants for a simple, rapid, and effective system for inducing somatic embryogenesis (SE) under in vitro culture. The process of SE can be induced directly from explant tissue, or indirectly through a callus stage, and the mode of morphogenesis depends on the developmental stage of the IZEs that are used. Auxin treatment, preferably with 2,4-D, results in the formation of embryogenic callus tissue in cultures derived from IZEs less advanced in development, i.e., at globular and torpedo stages, while IZE at the late cotyledonary stage rapidly produces somatic embryos, mostly via a direct pathway. In the best SE-responsive genotypes, including the commonly used Col-0 ecotype, up to 90% of the late cotyledonary-stage zygotic embryos undergo rapid and efficient SE. The subculture of somatic embryos onto auxin-free medium results in their conversion into plantlets with an average frequency of 80%. Such a high frequency of somatic embryos developing rapidly from explant tissue, followed by efficient regeneration of fertile plants with a low level of somaclonal variation, is the recommended system for wide application in studies on mechanisms governing plant totipotency; and especially for identifying genetic factors controlling embryogenic transition of somatic plant cells. In this chapter, the induction, development, and maturation of somatic embryos leading to subsequent regeneration of Arabidopsis plantlets in culture of IZEs are presented.