The Effects Of PtAPX Overexpression On Temperature Stress Tolerance In Tobacco

Tobacco (Nicotiana tabacum L.) is an annual or perennial limitedherbaceous plant of Solanaceae. It has a wide temperature range for growth (from8to38℃), but the optimum temperature is22to28℃. However, in the actual process oftobacco’s growth and development, it is not always in the most appropriateenvironmental temperature, sometimes encounter high or low temperature stressaffecting the normal growth and development of tobacco. When the environmenttemperature exceeds the tolerance range of the plant, a lot of reactive oxygen specieswhich cause oxidative damage to plant will be produced and accumulated in the plantbody. Nowadays，the global warming is becoming more and more serious, and theclimate changes drastically, the possibility that plants suffer from the temperaturestress is greatly increased, so breeding resistant varieties or cultivating strongresistance transgenic plant is especially important.Tobacco is one of the most important model plants in plant biology research field.Based on the early stage of the laboratory work, we choosed the representative APX-Ⅸgene(cytoplasmic), APX-Ⅶgene(cytoplasmic) and the APX-Ⅵ gene (chloroplastic)as the key research objects, selected T1generation seeds from five to seven transgenicstrains of tobaccos to proceed germination and ramet,when the test-tube plantlet growto the right size,selected the plants that growed broadly and measured theirphysiological and biochemical indicators, analyzed the resistance strength oftransgenic tobacco when it was faced to high and low temperature stress, main resultswere as follows:(1) After high temperature stress, both the wild type and transgenic tobaccos’leaves appeared wilting and curly, recovery after14d, the phenomenon of leaf curledand green lacked of the wild type tobacco was more obvious than that of the transgenic tobacco.(2) After low temperature stress, both the wild type and transgenic tobaccos’leaves appeared water logging, in the process of recovery, when the wild type tobaccoappeared leaf wilting, obviously lack of green, transgenic tobacco could still maintaina relatively good condition,(3) The activity of the APX enzyme both in wild type and transgenic tobaccorised when they were faced to high temperature stress, this could accelerate the rate toscavenge active oxygen in the body; plants that overexpression of APX couldaccelerate AsA reduction reaction, AsA consumption increased,its content reduced;membrane lipid peroxidation, contents of MDA and H2O2in leaves increased; thestability of cell membrane system was damaged, chloroplast disintegrated andreleased chlorophyll, made the chlorophyll content declined; cell membranepermeability increased, made a large number of ion exosmosis, relative electricalconductivity increased. During the period of recovery, activity of the APX enzymefailed to drop to the level of stress before,this illustrated45℃caused damage ontobacco, made it been in the overexpression state, AsA, H2O2, MDA and chlorophyllcontents and relative electrical conductivity were all restored to the level of stressbefore,not only just at the end of the stress, but also recovery after14d, physicalsigns of transgenic tobacco were all superior to the wild type.(4) Under the low temperature stress, the change trend of the content of varioussubstances in both wild type and transgenic tobacco was consistent with the tobaccothat under high temperature stress. Tobacco overexpression of PtAPX has strongerresistance to low temperature than the wild type.All the results above indicated that the transgenic tobaccos overexpressed PtAPXgenes have higher resistance to temperature stress than that of the wild type tobacco.