Taking potted 'Populus wutunensis' and Populus ×euramericana cv.'N3930' as experimental materials,the changes of endogenous hormone in apoplast of poplar immature stem were determined by microdialysis technique and high performance liquid chromatography,under NaCl(0,200,300 mmol/L) stress.The results showed that under the NaCl stress,ABA content in two poplar apoplastic increased,while other hormones decreased.ABA accumulation under high concentration salt stress was greater than that under middle concentration salt stress.When under the same salt stress,Populus ×euramericana cv.'N3930' accumulated more ABA than 'Populus wutunensis' to resist the coercive environment;salt balance coefficient of 'Populus wutunensis' was less than that of Populus ×euramericana cv.'N3930'.CTK and IAA,CTK and GA,IAA and GA of the two poplar were significantly correlated.The results indicated that salt tolerance of 'Populus wutunensis' was stronger than that of Populus ×euramericana cv.'N3930'.

The apoplast dialysates from poplar trees were obtained using the microdialysis technique. To compare the salt tolerance of Populus×wutunensis and Populus×euramericana, the dynamics of their endogenous hormones were determined by high performance liquid chromatography and the difference in chlorophyll photosynthetic fluorescence parameters was analyzed under salt stress. The results showed that ABA level in P. ×wutunensis under the high-concentration salt stress for fifteenth days was 1.3 times higher than that under the normal condition, while it was 1.8 times higher in P. ×euramericana under salt stress. The Fv/Fm and ETR values in P.×euramericana were significantly lower than those in P. ×wutunensis, indicating that the photosynthetic system of P. ×euramericana was more severely affected. Furthermore, the salt balance coefficient of P. ×euramericana is obviously bigger than that of P. ×wutunensis, suggesting that under highconcentration salt stress the coordinative capacity of hormones in P. ×euramericana was decreased and its growth was more severely inhibited by stress than that in P. ×wutunensis. Together, our results suggest that P. ×wutunensis has higher salt tolerance than P. ×euramericana. Our approaches used in this study may be useful for studying the physiological mechanisms of salt tolerance in poplar apoplast and for selection and breeding salt tolerant varieties of Populus.

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(GA 3),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(P0.05).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(P0.01),meanwhile the contents of GA 3,6-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.

Microdialysis is a sampling technique that can be employed to monitor biological events both in vivo and in vitro,it can be coupled with a variety of analytical instruments,can provide monitoring information for biological active substances changed with time and concentration in other aqueous environment or outside the cells dynamically in realtime.It is advantageous in fast,selective and sensitive analysis while preserving temporal information without affecting the growth of organisms.At the same time,the changes of analyte can be detected immediately in external environment.Furthermore,microdialysis samples without pretreatment,which are coupled with high-precise analytical systems,will realize truly real-time,online and cheap tracking detection.Although microdialysis sampling focusing on intercellular matrix has been applied in animals and human,it has not been extensively employed to detect various material changes in plant apoplast.So microdialysis sampling technique can overcome the bottleneck of previous research on plants.An overview of microdialysis system about principle,probe,membrane and parameters,furthermore sampling for plants and analytical methods employed for online analysis,including gas chromatography(GC),high performance liquid chromatography(HPLC),capillary electrophoresis(CE),and so on,were reviewed.