Abstract:Effect of exogenous Spermine on concentration of endogenous free polyamines in flower-bud differentiation of Dendrobium officinate Kimura et Migo in vitro was researched, in which derooted seedlings were collected as experimental materials. It was found that the rate of flower-bud differentiation in derooted seedlings cultured on MS mixed with 14.5mg/L Spm accounted for 15.0%, while the control group was 0. During the floral-bud differentiation, the endogenous concentration of free Spm, Spd and the ratio of Spm to Put, Spd to Put in derooted seedlings cultured on MS mixed with 14.5mg/L Spm exceeded those in the control, which indicated that high levels of endogenous free Spm, Spd, Spm to Put rate and Spd to Put rate could promote the flower-bud differentiation. The concentration of free Put was lower than that in the control during the flower-bud differentiation process, indicating that exogenous Spermine promoted the conversion of Put to Spm and Spd. It was found that exogenous Spermine could promote the flower-bud differentiation by means of the changes of endogenous free polyamines concentration and its ratio in Dendrobium officinate Kimura et Migo.