Effects Of Expressing Tomato GDP-D-mannose Pyrophosphorylase Gene (GMPase) In Tomato And Potato Plants

L-ascorbic acid (AsA, vitamin C) exists in different tissues of higher plants as an antioxidant protecting the plants against oxidative damage. It has multiple functions in organisms. AsA can prevent diseases, improve cell immune functions and delay senescence. But humans lack the ability to synthesize AsA, therefore, AsA must be required regularly from dietary source, primarily from plants rich in AsA. AsA protects plants against oxidative damage by scavenging free radicals and reactive oxygen species. By regulating the experssion of genes involved in plant AsA biosynthesis and metabolism, it is possible to increase the AsA contents and futher imporve the nutritive values and the stress tolerance of plants.GDP-D-mannose pyrophosphorylase (GMPase) plays a key role in ascorbic acid synthesis, for it catalyses the synthesis of GDP-D-mannose. In the present study, the transgenic tomato and potato plants which overexpress sense GMPase gene were used. And these materials had been obtained by previous works. We developed transgenic tomato plants which express antisense GMPase gene. Both the relationship between GMPase genes expression and AsA content and the relationship between the change of GMPase genes expression and the tolerance to environmental stresses in tomato and potato plants were investigated. The main results are as follows:1. The antisense GMPase cDNA was introduced into tomato by using Agrobacterium tumefaciens. Five transgenic strains were detemined by PCR and Real time RT-PCR.2. Real time RT-PCR analysis indicates that, in immature leaves, functional leaves, immature fruits and mature fruits, the relative expression of GMPase in the sense transgenic plants are significantly higher than the wild type, while the relative expression of GMPase in the antisense transgenic plants are significantly lower than the wild type.3. Compared with wild-type tomato plants, GMPase activity, AsA, DHA and AsA+DHA contents in immature leaves, functional leaves, immature fruits and mature fruits are increased by the overexpression of GMPase gene while these index are decreased by the suppression of GMPase gene .4. Compared with wild-type tomato plants, the activities of MDHAR, DHAR, APX and AAO in functional leaves and mature fruits are improved by the overexpression of GMPase, and the activities of MDHAR, DHAR, APX and AAO are decreased by the suppression of GMPase gene.5. Chlorophyll content, photosynthetic rate, potential growth and ratio of sugar to acid in mature fruits are increased in the sense transgenic tomato plants. The antisense transgenic plants increase the 1~2 node position of anthotaxy, and derease ratio of sugar to acid in mature fruits.6. In the temperature stress, compared with wild-type tomato and potato plants, the overexpression of GMPase improves GMPase activity, AsA and DHA contents in functional leaves of sense transgenic plants. The sense transgenic plants shows higher activities of DHAR, MDHAR, APX, and lower contents of MDA, H2O2 and electric leakage. Overexpressing GMPase could increase the tolerance to temperature stress of tomato and potato plants.