| AFPs have a great potential in improving cold tolerance of cold-sensitive plants. Previously,we showed that transformation with the afp gene allows tobacco plants to synthesize the 36 kD carrot antifreeze protein and enhance their ability to tolerante chilling and freezing tolerance. In this study ,we examined the change in physiological and biochemical process of the wild and transgenic tobacco plants and the relation to cold tolerance.The genetic characteristics of the transgene and the cold tolerance of the T1 plants were also assessed.The main results are as follows:Results of Fm/Fv measured after -1℃ stress showed that the photosynthetic machinery of transformed plants was more tolerant to freezing strss than that of wild-type plants after 4℃ acclimation. After cold acclimation (4℃), activities of peroxidase and superoxide dismutase, as well as the protein, proline and soluble carbohydrates contents were higher in tobacco plants transformed with Prd29A-AFP than that transformed with CaMV35S-AFP .It is implied that the differences are probably related with physiology and biochemistry mechanism of different resistance of the two transgenic plants.Kanamycin-resistance,PCR and freezing resistance tests of T1 gengeration plants indicated that the foreign afp gene delivered to the progeny according to Mendelian Law of single gene segregation.We show here that expression of the afp gene in transgenic plants resulted in improved tolerance to cold stress. However, use of the strong constitutive 35S cauliflower mosaic virus (CaMV) promoter to drive expression of afp also resulted in growth retardation under normal growing conditions. In contrast, expression of afp driven by the stress inducible Prd29A promoter from Arabidopsis gave rise to minimal effects on plant growth while providing an increased tolerance to cold stress condition. The results demonstrated the prospect of using Prd29A- AFP transgenic plants in cold- stressed conditions which will in turn benefit agriculture.
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