Abstract:

A metallothionein gene (MT₁, GenBank accession No. AB298390) from Tamarix sp. was directionally cloned and transformed into the pBI121 binary vector, in place of the XbaⅠ–SacⅠGUS cassette. 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 (Nicotiana tobacum) primary transformants were produced by leaf disc transformation. Southern and Northern hybridization indicated that exogenous gene was integrated into the transgenic tobacco plants, and correctly expressed under the control of 35S promoter. The Physiologic Characters of transgenic tobacco for Cd²⁺ tolerance was studied. The results showed that the activity of SOD and concentration of chlorophyll were increased, whereas the activity of POD and accumulation of MDA were decreased in transgenic tobacco than in non- transformant. Enhanced growth of transgenic tobacco was observed at the early development stages, resulting in plant height and fresh weights significantly greater than those of non-transformant. These results demonstrate that the exogenous metallothionein expression increase the ability of cleaning up reactive oxygen than that of non-transformant, showing a stronger tolerance to Cd²⁺ stress.

Key words: Tobacco, Tamarix sp., Metallothionein, Cadmium ion, Genetic transformation