Abstract:Saline-alkali stress is one of the important environmental factors that affect plant growth and development. Due to the development of irrigated agriculture and fertilizer misuse, soil salinization and secondary salinization have become main constraints for sustainable development of agricultural production. Methallothionein genes, which can be induced by environmental stresses such as saline-alkali, are resilience-related genes. Methallothionein genes are the most abundantly expressed in Tamarix sp. under the NaHCO3 stress. We studied the relationship of a metallothionein gene (MT1) over-expression in tobacco (Nicotiana tobacum) and plant tolerance to NaCl stress. The cDNA fragment encoding metallothionein was directionally cloned into the Xba-SacⅠGUS cassette in the pBI121 binary vector. The Cauliflower mosaic virus (CaMV) 35S promoter/-nopalin synthase terminator system and kanamycin resistant gene NPTⅡ (neomycin phosphotransfers II) were used for these constitutive expression systems. The plasmid was then introduced into Agrobacterium tumefaciens (strain EHA105) by electroporation. Tobacco primary transformants were produced by leaf disc transformation. We then performed molecular detection and physiological analysis of the transgenic tobacco plants. Results have shown that the transgenic plants with ampicillin resistance have a positive band in RT-PCR Southern hybridization analysis, indicating that MT1 gene is integrated into the tobacco genome, and this gene expresses under the control of the 35S promoter. Compared to the non-transgenic tobacco plants of the same stage (control) challenged with 150 mmol/L and 300 mmol/L of NaCl in MS media, the transgenic plants showed significant increases in plant height and fresh weight over 50%. In addition, transgenic tobacco plants had higher SOD and POD activity, but lower MDA accumulation than the control. These results demonstrate that exogenous methallothionein expression increases the capability of active oxygen cleaning up, Therefore, transgenic tobacco plants can increase tobacco tolerance to NaCl stress.