Functional Analysis Of L-galactono-1,4-lactone Dehydrogenase Gene Of Potato In Tomato

Vitamin C (L-ascorbic acid, AsA), a hexxose lactone, is indispensable for humans. It can be synthesized in plant and most animals, while humans lack the pathway of AsA synthesize, and must obtaine AsA from food regularly. Therefore, it has become one of the important nutritional quality factors in many horticultural crops. AsA is importance in many physiological processes such as ROS detoxification, photosynthesis and photoprotection,cell division and growth, ethylene synthesis .L-galactono-1,4-lactone dehydrogenase(GalLDH) is the key enzyme in the last step of AsA biosynthesis. In this study, the relationship between AsA metabolism and the tolerance to temperature stress in tomato were investigated, and GalLDH overexpressed transgenic tomato plants were used to further analyse effects of GalLDH on AsA metabolism and tolerance to temperature stress.The main results are as follows:1.Under high (40℃,24h)and low(4℃,24h) temperature stress, the contents of AsA, DHA and AsA+DHA and the activities of GalLDH, DHAR, MDHAR, APX and GR were all significantly higher than that in the control (25℃). However, the content of H2O2 is significantly higher than the control and the AsA/DHA is significantly lower than the control .It was proposed that AsA antioxidant system in tomato could be increased in short of time under high or low temperature stress.However, with the lasting (36h) temperature stress the AsA antioxidant system decreased, which might be responsible for the high accumulation of H2O2.2. Compared with the non-transgenic plants, the relative expression of GalLDH mRNA decreased by 29.08%,78.49% and 64.08% in antisense transgenic tomato plants of T0-1,T0-2 and T0-3 have decreased 29.08%,78.49% and 64.08%, respectively, and incresed by 88.37%,32.17%,278.7% and175.31% in sense transgenic tomato plants of T0-1,T0-2,T0-3 and T0-4 , respectively.3. Compared with the non-transgenic plants, the antisense transgenic T1 tomato showed lower relative mRNA expression and enzymatic activity of GalLDH in leaves and fruits.4. Compared with the non-transgenic plants, the contents of AsA,DHA and AsA+DHA, the ratio of AsA/DHA and activities of enzymes (APX, AAO, DHAR, MDHAR, GR) related with AsA synthesis and metabolism also decreased in antisense transgenic T1 tomato leaves and fruits.5. Compared with the non-transgenic plants,, the antisense transgene tomato plants showed lower photosynthetic rate and higher acid contents which resulted in lower ratio of sugar/acid.