Research On The Expression Of SsNHXI And PDH45 Genes And The Salt Tolerance In Alfalfa

Alfalfa is one of the most important forage. As more and more saline-sodic soil grately reduced the yeild of Alfalfa, it is much more important to culture new varieties of Alfalfa with higher salt tolerance, while the transgenetic technique provides a quick and effective method to culture the new variety of Alfalfa.SsNHXI, a gene from suaeda salsa, encodes a Na+/H+ antiporter in vacuole membrane,it can pump Na+ into the vacuole to improve the salt tolerance of plants. Recent studies have shown that helicase also has key effects on stress tolerance. PDH45 is a DNA helicase from pea, which has been proved to be able to largely enhance the salt tolerance of transgenic tobacoo.In this study, the pBISsNHXI and pBIDH45 had been recombined to construct a bivalence expression vector with SsNHXI and PDH45 two genes.We transfered the two genes, SsNHXI and PDH45, into Alfalfa by Agrobacterium tumefaciems induced method to obtain a new variety of Alfalfa with higher salt tolerance. 80 kanymycin-resistant transgenic plants were obtained and PCR results proved that the interested gene had been integrated into the genome of Afalfa and then 20 transgenetic plants were selected to do further physiology test. After treated with 250mmol NaCl for 5 weeks, the growth of both nontransgenic and transgenic plants were suppressed, but the latter grew much better than nontransgenic wild type plants. Meanwhile, the experiment of measuring the percentage of the proline and chlorophyll and cell membrane permeability was carried out between the transgenic and nontransgenic wild type plants, and the results showed that the proline content of the transgenic alfalfa was 20 fold of the wild-type plants, the chlorophyll content was 40% higher than the wild plants and the degree of membrane permeability of transgenic Afalfa was 90% lower than the wild plants. Taken togather, these results indicated that over expression of SsNHXI and PDH45 indeed greatly improve the salt tolerance of Alfalfa。This study provided some basis for culturing new salt-resistant varieties of Alfalfa by transgenetic techinique.