Abstract: In this study,effects of the different medium,and the kinds and concentrations of plant growth regulator on callus induction,growth and triterpenoid production in birch (Betula platyphylla) stem extant culture were investigated. The results showed that calli were all obtained on IS medium supplemented with 6-BA and NAA,KT and 2,4-D,or 6-BA and TDZ,but the shape and growth state of callus were different. The combination of 0.8 mg·L^-1 6-BA+0.6 mg·L^-1 NAA was the best in inducing callus from the extant,with the frequency of callus induction 100%,and the callus grew well after multiple subculture. Furthermore,the effect of 5 types of media (MS,NT,IS,WPM,B5) and different combinations of plant growth regulators on callus growth and triterpenoid accumulation were compared. It was found that WPM medium was most suitable for callus growth,the fresh weight on harvest was 6.6 g. IS medium was most suitable for triterpenoid accumulation,the content of triterpenoid on harvest was 2.37 mg·g^-1 . The most beneficial combination of plant growth regulators for fresh weight was 0.4 mg·L^-1 6-BA+0.1 mg·L^-1 TDZ,the fresh weight on harvest was 14.08 g,while the most suitable combination of plant growth regulators for triterpenoid accumulation was 0.8 mg·L^-1 6-BA+0.6 mg·L^-1 NAA,the content of triterpenoid on harvest was 3.53 mg·g^-1. It was concluded from above results that the best culture condition for callus growth and triterpenoid accumulation was IS+0.8 mg·L^-1 6-BA+0.6 mg·L^-1 NAA.

Key words: Birch(Betula platyphylla), triterpenoid, callus, medium, plant growth regulator