Development and Characterization of in Vitro Embryogenic Systems in Conifers

Abstract

Our progress is reviewed on development of somatic embryogenesis in conifers for mass propagation. A distinct embryogenic callus (EC) pheno-type, white, mucilaginous, and rapidly growing, has been initiated on modified MS media with 2,4-D or NAA (2–5 mg/L) and BA(0–1 mg/L) from immature embryos of Norway spruce (Picea abies), white spruce (Picea glauca), loblolly pine (Pinus taeda), pond pine (Pinus serotina), and white pine (Pinus strobus). EC has also been initiated from mature embryos of Norway spruce and maintained as rapidly growing (48 hour doubling) liquid suspensions. Initiation of EC in Picea and Pinus differ markedly in several ways. Precotyledonary embryos were optimal in Pinus and EC originated from the suspensor region. In Picea EC originated from the hypocotyl and cotyledon region of predominantly post-cotyledonary embryos. Biochemically, EC of Picea and Pinus were similar and distinctly different from nonembryoge-nic callus (NEC) in terms of ethylene evolution rates (EC low and NEC high), level of total reductants, including glutathione (EC low and NEC high), and protein synthesis rates (EC high and NEC low). Conifer somatic embryos contained proplastids closely resembling those found in early zygotic embryos. On proliferation medium in the light, EC was white and maintained the proplastid morphology, whereas, NEC was green and contained mature chloroplasts with grana. These biochemical and ultrastructural differences served to both verify and predict embryogenic potential.