Abstract: [Objective] The study is to explore the effect of different plant growth regulators on embryonic callus induction and the effect of nitrogen source and mineral concentration in MS medium on somatic embryogenesis and plant regeneration of Sophora davidii, and to establish a technical system of somatic embryogenesis,development and regulation, which would provide a basis for the establishment of rapid propagation system and genetic transformation of S. davidii.[Method] Leaves from S. davidii were used as explant to study the effects of growth regulators 2,4-D (1.0,2.0,3.0,4.0 mg·L^-1), NAA (0,0.5,0.8,1.0 mg·L^-1), 6-BA (0.2,0.5,1.0,2.0 mg·L^-1) and TDZ (0,0.2,0.5,1.0 mg·L^-1) on embryonic callus induction, and NAA (0,0.2,0.5 mg·L^-1), 6-BA (0,0.5,1.0 mg·L^-1)and TDZ (0,0.2,0.5 mg·L^-1)on somatic embryogenesis, which aimed to screen optimum medium. Ratio of KNO₃ and NH₄NO₃, mineral concentration (1/5MS, 1/4MS, 1/3MS, 1/2MS)in MS medium were tested to obtain a good culture condition for somatic embryogenesis and germination.[Result] The optimum medium for embryonic callus induction was MS + 2,4-D 3.0 mg·L^-1+ NAA 0.5 mg·L^-1 + 6-BA 0.2 mg·L^-1 + TDZ 1.0 mg·L^-1 + 40 g·L^-1 sucrose + 7.0 g·L^-1 agar,and the rate of embryonic callus induction reached to 42.0%. MS medium supplied with 0.5 mg·L^-1 NAA, 1.0 mg·L^-1 6-BA, 0.5 mg·L^-1 TDZ, 40 g·L^-1 sucrose, 100 mg·L^-1 glutamine and 7.0 g·L^-1 agar was suitable for somatic embryo formation, somatic embryogenesis rate was 78.46%, the number of somatic embryos was 3.6-fold compared with control. Improved MS supplied with 2-fold KNO₃ and half NH₄NO₃ was beneficial to somatic embryogenesis, somatic embryogenesis rate was 91.33%, and the total number of embryos was 1.4-fold compared with the optimal basic medium. 1/3MS was beneficial to somatic embryo germination, and somatic embryo germination rate was 82.75%. Regenerated plantlets were developed well in 1/3MS medium, and mean fresh weight was 76 mg. Plantlets were successfully acclimatized with a survival rate of 90% and grew vigorously.[Conclusion] Different growth regulators,such as 2,4-D, NAA, 6-BA and TDZ combinations were helpful for inducting callus or embryonic callus, 2,4-D had a great influence on morphology and texture of callus. TDZ was helpful for the formation of somatic embryos. Proper auxin combination with cytokinin and proportion of nitrate and ammonium nitrogen can regulate the formation and development of somatic embryos. The rate of somatic embryo germination can be increased by reducing MS inorganic salt concentration. The survival rate of transplanted plantlets reached 90% in this experimental system.

Key words: Sophora davidii, embryonic callus, somatic embryogenesis, growth regulator, culture medium