The Effects Of Overexpression Of OsSsr1 On Stress Tolerance In Tobacco

Overexpression of Harpin-encoding genes, hph, enhances plant resistance to diseases and tolerance to drought stress in transgenic rice NJH12. Our study showed that OsSsrl was an up-regulated gene on the base of microarray. In this study, full-length OsSsrl was cloned by PCR from cDNA of rice R109, which is an unknown function gene. In this experiment, an integrated vector pVOsSsrl of the OsSsr1 gene and hph gene (hygromycin B resistant gene) with a maize ubiquitin promoter (Ubi)was constructed and introduced into tobacco mediated by Agrobacterium tumefaciens LBA4404. The result of PCR indicated that the OsSsr1 gene has been integrated into the genome of the tobacco, RT-PCR and PCR-Southen analysis of transgenic plants confirmed that OsSsr1 gene had been expressed in transgenic tobacco plants at transcription level. The physiological responses of T1 generation transgenic plants to salt, heat and cold stress were studied as follows:1) Salt resistance of the transgenic tobaccos:14-day-old seedlings transferred to plates containing 0.2 M NaCl for 3 days; 20-day-old seedlings transferred to plates containing 0.3 M NaCl for 3 days. The photograph was taken 14 days after the plants were returned to 1/2 MS medium plates.5-week-old plants were irrigated with Hogland containing 0.15M NaCl for 12 days. The content of MDA, proline and activity of SOD, POD in plant leaves were measured. The results showed that transgenic tobacco seedlings under salt stress were tolerance to salinity, while the wild type tobacco seedlings were death. In the 5-week-old tobacco plants, the contents of proline, MDA, SOD and POD activity increased with the salt treating time,but the MDA content in transgenic tobacco was lower than wild type tobacco and the accumulation of proline, SOD and POD activity were higher than wild type tobacco. Therefore, we speculate that the salt tolerance of transgenic tobacco lines is due to improving proline content, and increasing the metabolism of reactive oxygen species.2) Thermotolerance of the transgenic plants:10-day-old seedlings were exposed to high temperature of 48℃for 40min, and then transferred to normal conditions for recovery for 10 days.5-week-old plants were exposed to high temperature of 48℃for 3h, and then transferred to normal conditions for recovery. The results showed that transgenic tobacco seedlings under high temperature showed thermotolerance, while the wild-type seedlings were death. But this result hasn't been repeated. The activity of SOD, POD and the content of chlorophyll in transformed tobacco was higher than that wild type tobacco, but the difference between them was not notable. These results lead to a conclusion that overexpression of OsSsrl couldn't enhance the thermotolerance of the tobacco.3) Cold resistance of the transgenic tobaccos:After having been placed under the low-temperature of -10℃for 2.5h, the difference of growth potential between the transgenic seedlings and untransformed had not been observed.The measurement of SOD, POD activity and chlorophyll content had the same result between the 5--week-old transgenic lines and untransformed, which was placed under the low temperature of 8℃for 12d. We can conclude that overexpression of OsSsrl couldn't improve the cold resistance of the transgenic tobaccos.