The Analysis For Isozymes And Pathogenesis-related Proteins In Citrus Plants Infected By Citrus Tristeza Virus

Citrus tristeza virus(CTV) is widely distributed in citrus planting area in worldwide and can cause citrus trees severe decline.Although no obvious symptom was observed in the citrus trees developed from the rootstocks resistant or tolerant to CTV,bad influence was still happened for their growth and fruit quality.Previous studies showed that CTV had an obvious strain differentiation,and it was classified as mild strains, decline-inducing strains and stem pitting strains according to the symptoms on their test plants.In this study,the changes of the defense enzyme activity and isoenzyme pattern of the citrus trees showing different resistances to CTV were analyzed after they were inoculated by the mild and severe strains of the virus,so did the soluble protein and pathogenesis-related protein.The results obtained are listed as followings:1.CTV was detected by TAS-ELISA in sweet orange and Poncirus trifoliate trees inoculated with its mild or severe strains,results indicated that a positive reaction was obtained from the sweet orange trees,which are susceptive to the virus,while a negative reaction from the Poncirus trifoliate trees,which are resistant to the virus.The Poncirus trifoliate trees were further analyzed using RT-PCR,results showed that a target product about 672 bp in length were obtained from all samples,which suggested that Poncirus trifoliate trees were also infected by CTV successfully,but the virus concentration was obvious different in the susceptible plants than the resistant ones.2.The enzyme activity of peroxidase(POD) and polyphenoloxidase(PPO) were analyzed in Mexican lime,sweet orange and Poncirus trifoliate trees inoculated with CTV mild and severe strains,results indicated that POD and PPO showed different activities as a result of different CTV stains or different hosts.In Mexican lime trees,the POD activity reduced evidently in the samples inoculated with the mild or severe strains, and it gave a largest reduction in the samples inoculated with a mild strain of N4 than in the control sample without CTV inoculation,but PPO activity showed no obvious difference both in the samples inoculated with N4 or another mild strain of N21 and the control,but PPO activity in the samples inoculated with N25 increased evidently.In sweet orange trees,POD activity showed no difference both in the samples inoculated by N4 and not,but it increased evidently after the samples were inoculated by the severe strain of N21 or N25,and PPO activity showed no difference between the samples inoculated with the mild strain and the samples with the severe.In Poncirus trifoliate trees,the activities of POD and PPO had no obvious difference between in the samples inoculated with the mild strain and in the samples with the severe. 3.The isozyme pattern changes of POD,PPO and EST were analyzed in Mexican lime,sweet orange and Poncirus trifoliate trees inoculated with the mild and severe strains of CTV or not.The results indicated that the isozymes pattern of POD and PPO changed nothing in the tested samples,while the EST isozyme pattern changed due to the virus inoculations,and four different bands more were found in the sweet orange trees than the ones inoculated with the mild strain of N4 than with the severe strain of N25, and it showed two different bands in Poncirus trifoliate inoculated with the mild strain of N25 than without.4.The concentration changes of soluble proteins(SPR) were analyzed in the host trees infected by CTV,results showed that SPR content increased in Mexican lime leaves after they were inoculated by CTV severe strains,especially in their young leaves.The electrophoresis results of soluble proteins indicated that the band number of the soluble proteins gave a tiny change in sweet orange,Mexican lime and sour orange trees after they were inoculated with CTV mild or severe strains,and soluble protein bands had no change in Poncirus trifoliate trees after they were inoculated with the CTV mild or severe strains.5.The sour pathogenesis-related proteins were investigated from leaves in different positions in the sweet orange trees inoculated with the CTV mild strains,and results indicated that the content and number of the sour pathogeneses-related protein bands were higher in basal old leaves than in top young.Basal old leaves were subjected to analyzing changes of the sour pathogenesis-related proteins of sweet orange and Poncirus trifoliate trees inoculated with CTV mild and severe strains,results showed that 6 and 2 bands of the sour pathogenesis-related proteins were found only in sweet orange trees inoculated with the severe strain of N25 and the mild strain of N4,respectively.