Physiological And Biochemical Responses Of Transgenic Sweet Potato Expressing Both Cu/Zn-SOD And APX Genes To Drought And Rewatering Conditions

Transgenic plants have been developed to improve plant stress tolerance.Under the water tress simulated by adding PEG6000 into 1/2 Hoagland solution and rewatering conditions, two strains, Cu/Zn SOD and APX gene transferred sweet potato (TS) and non-transgenic sweet potato(Ipomoea batatas L.)(NT), were used as experimental materials to study the effects of water stress and rewatering on photosynthetic characteristics of sweet potatoes and the changes of the antioxidative system. The main results are as follows:1. The activities of SOD of both TS and NT firstly increased and then decreased under water stress, but the activity of SOD of TS was always higher than that of NT. Under 24 h water stress, the activity of SOD of TS was 20.5% higher than that of NT. The activities of SOD of TS and NT both decreased after rewatering. Under water stress, the activity of APX of TS firstly increased and then decreased; in NT it firstly decreased and then increased. After rewatering, the activity of APX of both TS and NT firstly increased and then decreased, after 12 h rewatering, the activity of APX of TS was 50.2% higher than it of NT (Table 1). When PEG treatments were imposed for 24 h and 36 h in TS, the AsA content increased by 12.3% and 53.6%, however, the AsA content was in NT increased firstly and then decreased. After PEG treatments for 0 h, 12 h and 24 h, AsA content in TS was higher by 3.3%, 18.1 % and 37.0 %, than that in NT (p<0.05), respectively. Recovery by no PEG solution, AsA content decreased in both TS and NT. Recover for 12 h, 24 h; AsA content in TS was 45.3% and 37.2% higher than that in NT (p<0.05). Under the no stress and PEG treatments for 12 h and 24 h, CAR content in NT was higher by 15.6 %, 21.1% and 13.8 %, than that in TS (p<0.05), respectively. After PEG treatments for 36 h, CAR content in TS and NT was almost the same. Recovery in on PEG solution, CAR contents decreased in TS and NT. Recovered for 12 h, CAR content in NT was 11.2% higher than in TS.2. Under water stress, the membrane structural stability of TS was better than it of NT, after 24 h water stress and 12 h rewatering, the MDA content of NT were 20.3% more than it in TS. This result showed that transferring antioxidant genes into plant could improve plant stress tolerance. 3. At the beginning of the water stress, Pn decreased in both TS and NT, when stress time became longer, Pn in TS increased, in NT Pn almost kept the same level, after 36 h stress, Pn in TS was 50.1% higher than it in NT after rewatering, Pn in both TS and NT began to increased, after 12 h rewatering, Pn in TS was 1 times higher than it in NT. Under water stress, Ci increased in both TS and NT. After 36 h water stress, Ci in NT was 40.3% higher than it in TS, after rewatering, Ci in both TS and NT decreased. The result showed that transferred both Cu/Zn SOD and APX genes,the antioxidative system of the transgenic sweet potato had a higher ability to protect and recover the photosynthetic system of the plant.4. Under the treatments,the chl content in TS and NT were almost the same, but the leaf water content in TS is always significant higher than that in NT(p<0.05). This result showed that TS had a higher ability to conserve the water.5. After 0 h,12 h,36 h water stress, and rewatering 12 h,24 h the content of Pro in TS is respectively higher than that in NT. Under water stress, the membrane structural stability of TS was better than it of NT, after 24 h water stress and 12 h rewatering, the MDA content in NT were 20.5% more than it in TS. The result showed that transferred both Cu/Zn SOD and APX genes,the antioxidative system of the transgenic sweet potato had a higher ability to protect and recover the plant, and the characters of the antioxidative system can affect the content of proline.