Abstract：Senescence, regarded as the last stage of tobacco leaf development, seriously affects the accumulation of the photosynthetic products along with degradation of chlorophyll and lipid, resulting in the decrease of the yield and the quality of the crop. Transgenic technology is an important technical means to cultivate new varieties with high yield and resistance, which is helpful to increase the yield of the unit area of the tobacco (Nicotiana tabacum). During the growth of tobacco, the delay of senescence can increase the amount of photosynthetic products, which could increase the yield of crop. After harvesting, senescence delay of the leaves can keep the freshness of tobacco, so as to solve the problem of storage and transportation. Therefore, research on leaf senescence regulation has a very important significance in agricultural production. In this work, the Agrobacterium-mediated transformation method were adopted to introduce BAS1 (phyB activation-tagged suppressor 1) gene driven by the SAG12 promoter into tobacco and 45 SAG12-BAS1 trangenic plants were obtained according to the result of resistance screening and PCR identification. Among these transgenic plants, eight transgenic tobacco plants showed that their leaves senility were delayed. Leaf chlorophyll content, protective enzyme activity and plant growth phase were observed and measured on the wild type and transgenic SAG12-BAS1 tobacco leaves during leaf senescence. The results showed that the chlorophyll content of transgenic SAG12-BAS1 tobacco plants was higher than that of the wild type from the top to the base. The results of content analysis of super-oxide dismutase (SOD) and malondialdehyde (MDA) investigated between the wild type and transgenic SAG12-BAS1 tobacco demonstrated that SOD activity in transgenic SAG12-BAS1 tobacco plants was 31.98 % higher than that of wild type and the content of MDA was 48.28% lower than that of the wild type. The conclusion that the senescence of transgenic tobacco delayed for 10~15 d than that of the wild type was drawn through the observation of tobacco growth development process. Besides, the result of cytokinin content detected between the wild type and transgenic tobacco at the beginning of leaf senescence showed that the cytokinin content of the wild type was 40.2% lower than that of transgenic plants. The above results indicated that transgenic SAG12-BAS1 tobacco have delayed the senescence process and that may relate with the increase of cytokinin content and protective enzyme activity and the initiation of senescence promoter. This study provides a theoretical basis for the further study of the function of SAG12-BAS1 gene, and it also provides the basis for the development of genetically modified anti-aging materials.
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