| Sorbus pohuashanesis Hedl. is an important ornamental and economic species. The effects of explants and media on somatic embryogenesis and biological substance changes during somatic embryogenesis of it were conducted by taking mature and immature zygotic embryos as explants, for the purpose of providing effective in vitro culture system for its micropropagation, physiological and biochemical studies. The results are as follows:(1)Intact zygotic embryo was the best explants for somatic embryogenesis of Sorbus pohuashanesis. The sample site sequence from better to worse of somatic embryogenesis status was JD, HS, YW and HW for mature zygotic embryo explants and JJ, HS and HY for immature zygote embryo explants. The best sampling period for immature zygotic embryo explant is the middle of July.(2)MS+NAA 2.0 mg·L-1+BA 1.5 mg·L-1 was the best induction medium for mature zygote embryo explant, the callus induction rate was up to 91.67%, the somatic embryo initiation rate was up to 30.67%. MS+2, 4-D 0.2 mg·L-1 +BA 1.0 mg·L-1 was the best induction medium for immature zygote embryo explant and somatic embryo initiation rate was up to 39.20%. MS+BA 1.5 mg·L-1+2, 4-D 0.5 mg·L-1 was the optimum medium for subculture. When subculture generations exceeded 4, nearly the entire somatic embryo changed to callus, then became brown and dead finally. Dark culture fit for somatic embryo induction of Sorbus pohuashanesis.(3)The content of starch and soluble protein and the activity of superoxide dismitase (SOD), peroxides (POD) and catalase (CAT) in embryogenic callus were higher than that in other types of calli. The soluble sugar content in embryogenic callus formed under light was higher than those other types of calli. Dry mass of slowly multiplicated embryogenic callus was obviously higher than that of fast multiplicated non-embryogenic callus.(4)Soluble sugar content was highest in Torpedo embryo stage and starch content was highest in embryogenic callus stage, they two were lowest in globular embryo stage. The activity of SOD and POD decreased from embryonic tissues to globular embryos and from globular embryos to heart-shaped embryos, and then increased from heart-shaped embryos to torpedo embryos and from torpedo embryos to cotyledon embryos. The activity of CAT showed a decrease-increase-decrease pattern during the first 3 stages from embryogenic tissues to torpedo embryos and increased slightly in the last stage from torpedo embryos to cotyledon embryos.
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