Theor Appl Genet (1988) 76:501-506 9 Springer-Verlag 1988 Enhancement of somatic embryogenesis in Norway spruce (Picea abies L.) S. Mohan Jain, R.J. Newton and E.J. Soltes Department of Forest Science, Texas Agricultural Experiment Station, The Texas A & M University System, College Station, TX 77843, USA Received June 30, 1988; Accepted July 7, 1988 Communicated by Hu Han Summary. Embryogenic callus developed in 55% of the mature embryo explants of Norway spruce (Picea abies L.) growing on a LP medium minus the amino acids and sugars (except sucrose). This is the highest reported yield of embryogenic callus from mature embryos of P. abies that has ever been reported. Callus induction from either the middle or the end of the hypocotyl of the embryos began after 2-3 weeks. Three types of calli were recov- ered: (a) globular, (b) light green-compact, (c) white mucilaginous. Only the white mucilaginous calli were embryogenic. The globular and light green-compact calli never become embryogenic, even after several subcul- tures. The development of somatic embryos was accom- plished on half-strength macro-elements of NSIII medi- um containing 1 gM e-naphthaleneacetic acid, 1 gM ab- scisic acid, and 3% sucrose. The addition of 10-7M buthionine sulfoximine to the medium increased the de- velopment of somatic embryos by three fold. These re- sults suggest that there is a great potential for increasing the frequency and development of somatic embryos in P. abies. Careful selection of the genotype and modifi- cation of the culture medium is required. Key words: Norway spruce - Picea abies - Modified LP medium - Somatic embryogenesis - DL-Buthionine sulf- oximine Introduction The regeneration and clonal propagation of conifer trees by tissue culture has been extensively reported (Jain et al. 1988 a; von Arnold and Tillberg 1987; Abdullah et al. 1985; Kim et al. 1985; Ahuja 1983, 1984; Biondi and Offprint requests to S. Mohan Jain Thorpe 1981; Bonga 1981; Palta-Mehra et al. 1978). The prospects for their use in tree improvement has become more feasible due to recent reported successes of plant regeneration via somatic embryogenesis in Picea abies (Hakman and von Arnold 1985; von Arnold 1987; von Arnold and Hakman 1986; Hakman et al. 1985), P. taeda (Gupta and Durzan 1987), P. glauea (Lu and Thorpe 1987), and Larix decidua (Nagmani and Bonga 1985). However, plant regeneration from somatic embryos of forest trees is still a complex task. Cultured immature embryos have given rise to em- bryogenic callus in gymnosperms (Becwar et al. 1987 a; Hakman and von Arnold 1985; Lu and Thorpe 1987; Gupta and Durzan 1987; Norstog and Rhamstine 1967) and in angiosperms (Rangaswamy 1986; Vasil 1987). Furthermore, somatic embryogenesis has also been ini- tiated from mature zygotic embryos in P. abies (von Arnold 1987) and P. Iambertiana (Gupta and Durzan 1986). However, in conifers, the efficiency of somatic embryoggenesis from mature embryos has not been as high as that derived from immature embryos. Recently, von Arnold (1987) reported the induction of embryo- genic callus in 50% of the P. abies mature embryo ex- plants: 15% of these calli produced plantlets. Recent research indicated that the develoment of embryogenic callus may be enhanced by varying culture methods and media (Rangaswamy 1986; Lazzeri et al. 1987 a, b). The objective of this study was to enhance the fre- quency of somatic embryogenesis from cultured mature embryos of Norway spruce (P. abies L.). Materials and methods Plant material Seeds of Norway spruce (Picea abies L.) were stored in plastic bags at 4~ for I year. They (60-70) were then soaked in a small