Studies On Transforming Poplar By SsNHX1 Gene

Suaeda salsa show high salinity tolerance. It's an ideal plant for studying Na+ sequestration of vacuole. SsNHX1 from Suaeda salsa, encodes a vacuolar Na+/H+ antiporter and may play important roles in ion homeostasis. Maintaining a low Na+, high K+ state is a bacis strategy for plants to tolerate high soil salinity . The most direct way to maintain low cytoplasmic Na+ is to sequester it in vacuoles within each plant cell. The importance of vacuolar sequestration to plant salinity tolerance has been underlined by experiments in which constitutive overexpression of vacuolar transporters has greatly increased salinity tolerance of a range of species.The SsNHX1 gene was introduced into poplar by Agrobaterium tumefaciens-mediated transformation under the control of CaMV 35S promoter. Transformants were selected for their ability to grow on medium containing kanamycin (100mg/L), some lines that were tolerant to kanamycin were selected and used for further molecular and physiological determination. Whether the gene was transformed into poplar was confirmed by PCR and Northern blotting. The result indicated that the SsNHX1 had been intergrated into poplar genome, but the expressions in those lines were different.The overexpressing of SsNHX1 in poplar were evaluated for salt tolerance. All the transformants lines and widetype poplar were treated with different concentrations NaCl (0-200mmol/L), The results were shown as follows:1. The leaves of transgenic plants showed a tendency to accumulate less Na+ and more K+ and to keep higher cytosolic K+/Na+ ratio under saline conditions than wild type plants .No difference was observed in growth between transgenic plants and wild type plants in the low NaCl stress, but the transformants grew more vigorously in high salinity.2. The fresh weight the dry weight and relative water content of the transgenic lines were higher than that of wildtype plants under 200mmol/L concentrations of NaCl. The content of the proline was higher than that of wild type plants under different concentrations of NaCl. In this work, the transgenic plants showed a tendency to accumulate less MDA under saline condition than wild type plants.3. The results of the effect of NaCl concentrations on photosynthetic rate (Pn), stomatal conductance (Gs) and substomatal CO2 concentration (Ci) showed that the Pn, Gs and Ci of the transgenic lines were higher than that of wild type.Summarily, results from different tests indicated that after the different salt treatments, the transgenic plants reduced Na+ content and maintained higher K+content and K+/Na+ ratio compared with the wild type plants, keeping more osmoprotectants and less MDA than widetype poplar, so this Na+ sequestration strategy works to increase salt tolerance in vivo in the transgenic poplar plants.