Abstract: The apoplast and plant cells are inextricably linked, yet the response to drought stress within apoplast has rarely been reported. In this paper, the drought stress responses of apoplastic endogenous hormones in tender stems of three poplar species were studied by using MD-HPLC coupled technique. Four kinds of endogenous hormones in the apoplast of tender stems of living poplar which were dialyzed by microdialysis probe, i.e. benzylaminopurine (6-BA), gibberellic acid (GA₃), indole aceticacid (3-IAA), and abscisic acid (ABA), were then simultaneously determined by HPLC. The results show that drought stress has a significant effect on the content of endogenous hormones within the apoplast (P<0.05). As the drought stress was intensified and lasting, the contents of GA-3, 6-BA and 3-IAA obviously decreased while the content of ABA increased significantly (P<0.01), meanwhile the contents of GA₃, 6-BA, 3-IAA and ABA has changed differently among poplar species. This paper has provided a new basis for study on physiological response mechanism to drought stress and it also provides a new method for the dynamically quantitative analysis of the apoplastic endogenous hormone in vivo.

Key words: MD-HPLC, apoplast, endogenous hormones, drought stress