Preliminary Studies On Molecular Mechanism Of Salt Tolerance Of P. Euphratica

Populus euphratica oliv, a member of Populus, Salicaceae, is famous for its ability to endure high salinity. There are many researches about its physicological changes under salt stress, but little is known on its moleculer mechanism of salt tolerance. Here, we studied the expression of PeSOS1(Populus euphratica oliv Salt Overly Sensitive 1), a putative P. euphratica Na~+/H~+ antiporter, and analysed the elements ratio of different organs of P. euphratica after salt treatment.To address the function of PeSOS1, complementation studies on the salt-sensitive Escherichia coli EP432 mutant strain, lacking activity of the two Na~+/H~+ antiporters EcNhaA and EcNhaB were carried out. Expression of PeSOS1 suppresses some of the salt sensitive phenotypes of the EP432. The results of Na~+ tolerance conferred by PeSOS1 correlated with lower Na~+ content and higher K~+ content.To examine the expression of PeSOS1 gene under stress, RT-PCR and Western blotting analysis were performed. The transcript level of PeSOS1 corresponding to the time course was measured after 200 mM NaCl treatments. Relative amounts of the mRNA in salt-resistant P. euphratica leaves were initially increased under salt stress. Western blotting analysis showed that PeSOS1 was detected without stress treatment but was up-regulated significantly by salt stress in leaves and roots of P. euphratica, after NaCl treatment for 12 h, 24 h and 48 h. The expression level was not much increase in the stems of P. euphratica.To examine the localization of PeSOS1 protein in plant cells, we isolated the plasma membrane fractions and the toloplast fractions from the leaves after 200 mM NaCl treatments, and carried out Western-blotting analysis. Our results showed that PeSOS1 was detected in plasma membrane fractions but not in toloplast fractions. The results suggest that PeSOS1 protein is located on PM, which is accordance with our h-omology analysis.To analyse the elements ratio of different organs of P. euphratica after salt treatment, the leaves, roots and stems were collected from Populus euphratica that had been were exposed to 200 mM NaCl for different times, and used for determination of ratio of elements with x-ray microanalysis. The results of elements ratio analyse and Western-blotting results indicated that there are more PeSOS1 expressed in plant root and leaves where stable K~+/ Na~+ ratio is needed. Thus, PeSOS1, an important Na~+ effluxe peotein, may play an essential role in salt tolerance in P. euphratica.