Sequence Analysis Of Internal Transcribed Spacers (ITS) Of Populus Wutunensis And Physiological Responses To Salt Stress

Poplar is one of tree species which not only has the world's fastest growth rate, the most widely distribution area and the largest artificial planting area, but also has the potential to meet the needs of human life, improve the human environment in the 21st century.In this paper, we compare and analysis the 17 poplar species′internal transcribed spacer (ITS) sequences which are cultivated in Northwest region of Liaoning. Moreover, we also understand their genetic characteristics and phylogenetic relationships by anglicizing the G+C content, genetic distance and the phylogenetic tree. Then we selected the fast-growing Populus wutunensis and studied the physiological and biochemical responses at a high concentration of NaCl stress by analysising four kinds of endogenous hormones, Chlorophyll parameters, photosynthetic pigments and other indicators. The main conclusions of this study are as follows:(1) In the paper,the entire internal transcribed region(ITS) of nuclear ribosomal DNA of 17 spices of populus were compared and analyzed, and further their phylogenetic tree was constructed. The result showed that the sequences of ITS ranged from 594 to596bp in size and G+C content varied from 64.1% to 66.4%, the sequences of ITS1 ranged from 218 to 220bp in size, G+C content varied from 67.7% to 70.2%, the sequences of ITS2 ranged from 210 to 213bp in size, G+C content varied from 69.0% to 71.7%. Moreover, the length of the ITS region of the Populus wutunensis is 594bp and G+C content is 65.3% with 68 variable sites and 28 information sites compared to other varieties, informative sites in ITS2 is higher than in ITS1. The base diversity tapy of poplar is mainly based on transition. Meanwhile, phylogenetic analysis of ITS sequence indicat that Populus wutunensis is affiliated to Tacamahaca and'Populus pseudo-cathayana×P.deltodides cv. ShanHaiGuan'and'Populus×xiao hei T.S.Hwang et Liang'14''are its close relationship species. The phylogentic tree constructed on the basis of the ITS sequences showed that populus was discriminated among different species, and provided new molecular foundation for identify and evaluate populus species.(2) In this paper, the impact on endogenous hormones in poplar under the different NaCl concentrations (0 (CK), 100, 200, 300mmol/L) is studied by microdialysis sampling technique. The results showed: with the increasing concentration of NaCl, abscisic acid (ABA) content of endogenous hormone increased gradually and reached the maximum after the first day of the NaCl stress, then dropped between two weeks and reached a relatively stable state. Other endogenous hormones gibberellin(GA3), auxin(IAA), cytokinin(CTK) and IAA/ABA, GA3/ABA ratio showed a decreasing trend with increasing stress concentration and time. It suggested that the contents of IAA, GA3, CTK are positively closely correlated and content of ABA is negatively correlated with others contents of 3 hormones.(3) Surveying chlorophyll fluorescence parameters and photosynthetic pigment of poplar leaves under salt stress can learn the effect of salt stress on physiology and biochemistry of poplar. The results showed that: variable fluorescence (Fv), variable fluorescence and maximum fluorescence ratio (Fv/Fm), variable fluorescence to initial fluorescence ratio (Fv / Fo), PSⅡelectron transport rate (ETR) decreased with the increase of salt concentration and treatment time, while the initial fluorescence (Fo) increased, indicating that NaCl hurted the PSⅡa nd lowered the potential activity of PSⅡand the original energy conversion efficiency. Chla and total Chl content increased with salt concentration, Chlb did not change significantly, and Car took the tendency of low-high-low as the increase of salt concentration.(4) Under the NaCl salt stress, we detected the content of chlorophyll fluorescence parameters and photosynthetic pigment of of three poplar species, and the result showed the salt resistance of three poplar varieties is that:'Populus wutunensis'>'Populus simonii×P. euphratica'>'Populus simonii×(Populus pyramidalis+Salix matsudana)'.