Effects Of Co-infection With TYLCCNV And Bemisia Tabaci On The Defensive Physiology Of Tobacco Plants

There are complex interactions among geminiviruses,vector insects and host plants.The host plants will produce different defense responses including changes in nutrients and defense substances,the generation and accumulation of ROS when they fed by insects or infected by pathogens.In this study,the changes of soluble sugar and soluble protein contents,polyphenol contents,main oxidase activities,the generation and accumulation of H₂O₂ and the changes of protein composition profiles in tobacco plants after feeding by Bemisia tabaci and co-infection with TYLCCNV were compared.The differences in defense responses of host plants induced by whitefly feeding and co-infection with TYLCCNV were investigated.The main results are as follows:（1）Induced changes of solubility sugar contents,soluble protein contents and polyphenol contents in tobacco plants after feeding by B.tabaci and the co-infection with TYLCCNV.The results showed that the solubility sugar and protein contents in tobacco plants decreased significantly,polyphenol content increased significantly after feeding by whitefly and the co-infection with TYLCCNV when compared with the control.When compared with that in the B.tabaci feeding plants,the solubility sugar content decreased significantly by 21.05%on the 1^st day after the co-infection of B.tabaci and TYLCCNV.The solubility protein content decreased significantly by 27.40%,26.84%and 20.90%,respectively,on the 3^rd,7^th and 9^th days after treatment.The polyphenol content decreased significantly by 34.60%,14.30%,3.07%and 15.19%respectively,on the 1^st,3^rd,5^th and 9^th days after treatment.（2）Induced changes of oxidase activities in tobacco plants after feeding by B.tabaci and the co-infection with TYLCCNV.The results showed that the activity of catalase increased significantly,and the activities of superoxide dismutase and peroxidase increased firstly and then decreased when compared with the control.Compared with that in the B.tabaci feeding plants,the activity of CAT increased 3.04,1.42,1.68 and 1.96 times on the 1^st,3^rd,5^th and 7^th days after treatment,respectively.The activity of SOD increased significantly on the 9^th days after treatment and the activity of POD decreased significantly on the 7^th days after treatment.（3）Induced changes of H₂O₂in tobacco plants after feeding by B.tabaci and the co-infection with TYLCCNV.Compared with that in the B.tabaci feeding plants,there was no significant difference in the content of H₂O₂ in the plants co-infected by TYLCCNV and whitefly on the first and third days.On the 5^th,7^th,and 9^th days after co-infection,the content of H₂O₂ in the tobacco plants was 1.39,1.69 and 1.66 times as that in whitefly feeding plants.No aggregation of H₂O₂ was detected in the plants fed by whitefly or co-infestion with TYLCCNV and whitefly.（4）Induced changes of protein composition profiles of tobacco plants after feeding by B.tabaci and the co-infection with TYLCCNV.Both B.tabaci feeding and the co-infection with TYLCCNV could induce different degrees of changes in the protein component profiles of tobacco plants,accompanied by the increase or disappearance of certain polypeptide bands.The intensity of the darkest and largest polypeptide bands between 45 and 66 k Da varied significantly among different treatments.