Overexpression Of APX Gene From Populus Tomentosa Enhance Plant Tolerance To Abiotic Stress

Salt stress and drought stress are viewed as two important types of abiotic stress,restrict the development of world agriculture and cause the reduction in crop yieldsand quality. When the external environment changes, such as temperature, soilmoisture, soil salinity exceed the tolerance range of the plants, they are easy toaccumulate excessive reactive oxygen, which may cause oxidative stress damage.Facing the increasingly grim situation of soil salinization and desertification, it’sutmost importan to select resistant varieties or breed new varieties with stong stresstolerance using genetic engineering methods.With the tools of bioinformatics software, the primary structure, secondarystructure, hydrophobic / hydrophilic, gene mapping and tertiary structure informationof 741 Populus tomentosa APX gene family members were analyzed deeply. Theresults showed that the nine members studied in this paper belong to four mainevolutionary branches: sub-class A (APX -Ⅰ,ⅡandⅢ), sub-class B (APX-ⅣandⅤ) , sub-class C (APX-Ⅶ,ⅧandⅨ) and APX -Ⅵ(alone in a branch). APX -Ⅵand sub class B share the same properties in many aspects. Especially, because APX-Ⅵand the two members of sub-class B had the similar tertiary structure, wespeculated that they were the only three chloroplast APX isoenzymes. The membersof sub-class A and sub-class C were located in cytoplasm. All the nine members,having ascorbate-peroxidase conserved domains but no signal peptides, werehydrophilic proteins, in which random coils were the dominant secondary structureelements. In evolution, APX genes of Populus tomentosa were consistent with theconserved fact highly, they also showed specificity between the differentsub-categories in many aspects. The results of bioinformatics research laid thefoundation for the study on biological function and regulatory mechanisms of the various isozymes.Tobacco is a model plant for molecular biological research, their genomesequence information had been mastered completely. We chosed wild-type tobacco asexperimental materials, got eight APX-overexpressed tobacco successfully bytransgenic methods. Combining with results of bioinformatics, we determined thecAPX-Ⅰand chlAPX-Ⅵgenes as the key subjects, and studied the effects ofAPX-overexpressing to tobacco resilience, key findings were as follows :1) From the phenotypic, the APX-overexpressed tobacco rooted faster than thewild-type tobacco under tissue culture, and the number of root hairs was also more.Under the salt stress, drought stress or oxidative stress, compared with wild-typetobacco, APX-overexpressed tobacco growed significantly better, higher and thicker,their stress injury phenotype appearred relatively later , the extent of injury was lesser,too.2) From physiological indicators, APX activity was higher in transgenic tobaccounder stress conditions, at the same time SOD activity was also enhanced. Both ofthem can effectively improve the ability of scavenging ROS by enzymatic system.Compared with the wild-type tobacco, AsA content of APX-overexpressed tobaccowas higher, while H2O2content was lower. APX-overexpressed tobacco got lessoxidative damages. In different stress condition, MDA content of APX-overexpressedtobacco was relatively lower, but their total chlorophyll content was higher. That wasto say, APX-overexpression enhanced the stability of tobacco’s cell membranes andchlorophyll.In a short, compared with wild-type tobacco, APX-overexpressed tobaccoshowed higher stress resilience in a certain range of stress conditions.