Studies On Salt Tolerance Of The Suaeda Salsa SsNHX1 Gene Transformed Into Maize

For a variety of plants, high salt content in soil causes imbalance of ions, damage from oxidation, water deficit, nutrients deficiencies as well as biological macromolecular damage, slow growth and even death, thus resulting in yield reduction, In the context, it is important to develop salt-tolerant varieties in addition to biological control on and integrated utilization of saline-alkali soils. As one of the most important food crops, corn plays an important role in facilitating agricultural development of China. But most maize varieties cannot adapt to soils with high salt content due to their poor tolerance to salt. In order to achieve agricultural sustainability, environmental restoration as well as improvement of saline-alkali and waste fields, a feasible and important way is to develop new salt-resistant lines by using the genetic engineering method. The study uses the maize inbred line 18-599 as materials. Suaeda salsa’s SsNHX1 gene cloned with homology cloning techniques was introduced into the line 18-599 by using the gene gun-and Agrobacterium-mediated method. The transgenic maize over expressing SsNHX1 gene was obtained. The paper compares salt resistances between the wild variety and transgenic. The following are achievements in the study:1 We constructed overexpression vector pCPB-SsNHX1. SsNHX1 gene was transferred into immature maize embryo through embryo infection and introduced to maize callus by the means of gene gun-mediated method. PCR detection showed the gene has been integrated in corns. RT-PCR found differences in the expression of SsNHXl gene between different events.2 We optimized the genetic transformation method by which Agrobacterium was used to infect immature maize embryos of inbred lines 18-599. When the embryos are 0.8-1.2 mm in size, the rate of callus induction is highest to 96%. And after incubation for about ten weeks, we detected positive TO plants. This significantly shortened the time of the Agrobacterium-mediated genetic transformation process.3 Analysis on the salt resistance of the SsNHX1 transgenic maize plants indicated that over expression of SsNHX1 could enhance salt resistance of maize plants. When maize seeds are treated with the 1.0% NaCl solution, the wild variety’s germination rate was only 5% while the transgenic s’germination rate was up to 79%. When saline was applied subsequently, the wild variety suffered from withering of young leaves and even death while the transgenic maize plants thrived.4 Under salt stress, transgenic over expressing SsNHX1 gene accumulated more Na+ and K+ ions in leaves and roots than the wild types. As osmotic potential of transgenic maize leaves would be significantly lower than the wild-type plants with the accumulation of cations, the former could maintain higher moisture in leaves under salt stress. In addition, under salt stress, alondialdehyde concentration and relative conductivity of the transgenic maize leaves were significantly lower than those of the wild type while chlorophyll content was significantly higher than that of the wild type. These results indicated over expression of SsNHX1 gene allowed accumulation of Na+ ions in the vacuole of cells of transgenic maize plants, by which the salt resistance was improved.5 Drought stress treatment of transgenic maize plants over expressing SsNHX1 gene and reference material maize plants found that growth of the former was faster and drought resistance was higher. Under the prolonged drought conditions, the reference plants’leaves wilted and growth was so slow that they died finally, while transgenic plants remained thrived.