Studies On Transforming Tomato By SsNHX1 Gene

Among the most common effects of soil salinity is growth inhibition by Na+. Tolerance to salinity involves processes in many different parts of the plant, the mechanisms can occur at a wide range of organizational levels, from the cellular (e.g. compartmentation of Na+ within cells) to the whole plant. 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. SsNHXl from Suaeda salsa, encodes a vacuolar Na+/H+ antiporter and may play important roles in ion homeostasis. S. salsa show high salinity tolerance. It's an ideal plant for studying Na+ sequestration of vacuole.The SsNHXl gene was introduced into tomato (Lycopersicon esculentum) by Agrobaterium tumefaciens-mediated transformation under the control of CaMV 35S promoter. Transformants were selected for their ability to grow on medium containing kanamycin (30mg/L), 16 lines that were tolerant to kanamycin were selected and used for further molecular and physiological determination. Whether the gene was transformed into tomato was confirmed by PCR and Northern blotting. The result indicated that the SsNHXl had been intergrated into tomato genome, but the expressions in those lines were different.The overexpressing of SsNHXl in tomato were evaluated for salt tolerance. All the transformants lines and widetype tomato were treated with different concentrations NaCl (0-300mmol/L), The results were shown as follows:1. 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 and the dry weight of the transgenic lines were much higher than that ofwildtype plants under different concentrations of NaCl.3. The shoots 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 . But there was less Na+ and K+ in the roots of transgenic lines.4. The results of the effect of NaCl concentrations on photosynthetic rate (Pn), stomatalconductance (Gs) and substomatal CO2 concentration (Ci) showed that the Pn, Gs and Ci of the transgenic lines were dramatically higher than that of wild type. The content of the chlorophyll a, b, a+b in the transgenic lines were much higher than that of wild type plants under different concentrations of NaCl.5. The content of the proline and soluble sugar contents were much higher than that of wild type plants under different concentrations of NaCl.6. In this work, the transgenic plants showed a tendency to accumulate less MDA under saline condition than wild type plants.7. The osmotic potential of leaves of the transgenic lines was little lower 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 tomato, so this Na+ sequestration strategy works to increase salt tolerance in vivo in the transgenic tomato plants.