| Water is one of the main factors to guarantee tobacco healthy growth and development and good quality formation. If drought happened in resettling stage, tobacco plants result in premature flowering. If which happened in vigorous growing stage, the development of leaves is bad, and the inclusion is not rich. If which happened in maturity stage, the leaves are thick and rough, sugar/nicotine ratio is imbalance, the phenomenon of drought cook and premature happen too. DREB (dehydration responsive element-binding protein) transcription factor is mainly involved in signaling pathway of obiotic stresses by plant perception. Which improves the comprehensive tolerance of low-temperature, drought, high-salt and other stresses of plants by regulated the expression of a series of downstream stress response genes. The reports on DREB-like transcription factor structure, function and studies of regulating effect gene are a lot, but there are few reports on biological properties and the physiology process of osmotic stress tolerance of plants over-expressed by DREB-like transcription factor. The tissue structure, photosynthetic characteristics and stress resistance of BnDREB1-5 transcription factor over-expression on oriental tobacco (Izmir) were preliminarily studied. The main results were as follows:1.The leaves of Izmir with BnDREB1-5 presented a better holding water capacity,the water-loss was 0.16 mg H2O / cm2 .h-1 , and was 15.9% of that of wild-types. The upper epidermis stomata density in transgenic tobacco leaves was 46.4% as large as in wild-type leaves, the width of stomata apparatus and stoma opening were slightly bigger than that of wild-type. And the lower epidermis stomata density was 56.1% as large as in wild-type leaves, the length of stomata apparatus was bigger than that of wild-type, the width was slightly smaller than that of wild-type, the stoma opening was obviously bigger than that of wild-type.2.The agricultural characters of transgenic tobacco were obviously better than that of wild-type after drought stress tenth day (T/W unit cm: plant height 51.67/39.67, leaf number 17.67/13.67, leaf length 17.67/13.67, leaf width 9.93/10.61, pitch 2.97/2.98), and the leaves of wild-type plant obviously wilted. The tissue structure analysis showed that the leaf thickness of transgenic tobacco leaves increased, the ratio between palisade and spongy tissue obviously increased, tissue structure was integrate.3. After drought stress, the amylase activity, the invertase activity, the soluble sugar content, the nitrate reductase activity, the soluble protein content of transgenic tobacco leaves were respectively 1.20 times, 1.71 times, 1.86 times, 8.47 times and 2.97 times as large as those of wild-type.4. After drought stress, the chorophyll content descreased degrees of transgenic tobacco leaves were significantly lower than that of wild-type. The carotenoid content and chla/b were obviously bigger than that of wild-type. The fluorescence parameters Fo and NPQ were significantly lower than that of wild-type, the parameters of other fluorescence and photosynthesis were bigger than those of wild-type. The PEP carboxylase activity was obviously bigger than that of wild-type.5. The BADH activity of transgenic tobacco leaves was detectable and increased after drought stress, but which of wild-type was not detectable. After drought stress, the proline content of transgenic tobacco leaves was 1.08 times as large as that of wild-type. The SOD activity was obviously bigger than that of wild-type. The MDA content was 15.9% of that of wild-types.These results showed that by DREB-like transcription factor over-expressed on tobacco, the PEP carboxylase activity increased, the BADH activity was detectable, the holding water capacity, agricultural characters, photosynthetic characteristic and defense enzyme activity and so on were obviously better than those of wild-type. The DREB-like transcription factor overexpression improved tobacco physiological function of drought resistance.
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