Initiate Study On Improving The Salt-tolerance Of Rice By Genetic Engineering

Salina spread widely in China. With human activity pricking up, such problem will become more and more serious. Breeding salt-tolerance variety is a key technology to settle the foodstuff problem of Salina area. However, most of the crops we planted can not tolerate the salted soil, and it is almost impossible to get the genuine salt-tolerance variety by traditional breeding methods (Ashraf M et al). The research progress of plant adversity resistance mechanism and the cloning of correlative gene provide us an effective approach to breed new variety with high production, adversity resistance and good quality by use of genetic engineering.One of the major damages caused by salt is osmotic stress. Advanced plants, especially those which have perfect tolerance, can resist the harm caused by osmotic stress through accumulating some low molecule weight Osmoprotectants, among which, glycine betaine is one of the most important substance. Glycine Betaine can be accumulated in many kinds of organism, but not in some important crops such as rice, potato, tomato and tobacco (Weretilnyk E A et al, 1999). We can transform the whole bataine synthesis mechanism into these important crops providing them the ability of synthesizing bataine to increase their salt-tolerance by genetic engineering. The research using two glycine betaine synthesis related genes namely Choline dehydrogenase (CMO) and Betain-aldehyde dehydrogenase (BADH) from Atriplex hortensis as donor, the japonica rice and some indica hybrid rice restorer or maintainer lines as receptor, gotsome transgenic plants by using micro-particle bombardment or agri-bacterium, and proved that the target gene have been integrated into the rice genome after molecule testing. And these gene modified rice express better salt tolerance. From the experiment, such results below were got1. Effective gene transferring system was set up with young panicles, immature embryos and mature embryos of different rice varieties. Cold pretreatment of immature embryos, desiccation culture and predifferentiation of resistence calli could increase the callus inducing ratio, resistance calli and plant regeneration ratio, respectively.2. Some hygromicine and G418 resistant'plants containing CMO and BADH were obtained in mis study, and PCR testing indicated that most of the resistant plants contained the selective gene and the foreign target gene, but some plants just integrated selective gene and lost the targetgene. Southern Blot with positive plants of PCR showed that CMO and BADH have been integrated into the rice genome.3. The salt tolerance was tested indoors with all the hygromicine and G418 resistant plants and confirmed in salt pool in greenhouse, some salt tolerance plants were screened. A few of the positive plants could not express salt tolerance and died, while some negative plants survived in salty condition.4. Both in field testing and indoors testing, all the transgenic plants show better tolerance to salt than the control, but the expression degree are different in different plants.5. Genetic analysis of the transgenic plant offspring shows that the separating ratio is in accordance with Mendel's single gene inheritance law, and the target gene can entail to the offspring and express stably.