Abstract:The changes in contents of endogenous IAA,CTK, ABA and RNA in the in vitro cultural cutting stem excised from mature and juvenile plant of tube plantlet of Paulownia fortunei(Seem.)Hemsl. were analysed during the development of adventitious root.The endogenous hormones were measured by HPLC. The results showed that the contents of endogenous IAA and CTK in the stem cutting from plantlet(juvenile state)reached their peaks on the second day of culture, whereas the peaks of endogenous IAA and CTK in stem cutting from mature plant (mature state) appeared on the fourth day. From the stem paraffin sections, it was observed that the emergence time of root primordia was the same as that of endogenous IAA and CTK peaks in two states of cultural materials. However, the variation in endogenous ABA content was different between juvenile and mature states. During the rooting period,the level of RNA in both juvenile and mature states of stem cutting slightly decreased on the second day of culture, and then increased markedly.The origin of root primordia come from some peripheral cells of vascular cylinder,and some cells between vascular bundles as well as some pith cells recovering cell division. But the emergence of root primordia in mature stem cutting was 2 days later than that in juvenile cutting of plantlets,and the number of adventitious root in the former was less than that in the latter.