The Effects Of Granulovirus On Haemolymph Protein, Immune System, The Microfilament Cytoskeleton And Protective Enzymes In Plutella Xylostella L.

The diamondback moth,Plutella xylostella(L.) is one of the most harmful pests of Brassicaceae in the world,greatly affecting the quality of cruciferous vegetable products and production.The pest is difficult to control since it is resistant to many insecticides. PlxyGV is pathogenic to the insect with high specificity,and is considered a useful biocontrol agent.However,the larvaes of diamondback moths infected by PlxyGV take long time to die.During the period,the larvaes still feed on vegetables and make dameges.Currently,datas about interaction between PlxyGV and diamondback moth are limited.In this study,experiments were performed to analyze changes in haemolymph proteins,haemocytes,activities of phenoloxidase and protective enzymes,the microfilament cytoskeleton,in the bodies of the larvae of diamondback moth,resulting from infection by PlxyGV.The results are below:1.Changes in hemolymph proteins.Insect hemolymph is not only a main metabolism place,but also a main place to store and exchange materials in metabolic processes.Hemolymph contains a variety of proteins.These proteins closely relate to the material-metabolism in tissue formation, hormone regulation in body growth,insecticide-resistance and immune mechanism.In the experiments,hemolymph protein concentration in the control group generally increased with the development of larvae;Protein concentration in infection group was slightly more than control in the 1^st day post infection,and obviously reduced in the 2^nd-7^th days post infection.PAGE analysis revealed changes in protein bands in haemolymph of the larvae infected by PlxyGV.Protein bands in infection group were slightly more than control in the 1^st day post infection.No obvious change was observed between infected and control groups from 2 to 4 days post infection.However,both bands and contents of hemolymph protein significantly reduced from the 5 to 7 days post infection,compared to the control.2.Changs in hemocytes and activity of Phenoloxidase.Insects have a unique immune system.It divides into cellular immunity and humoral immunity,mainly endured by haemolymph.Hemocytes undertake for cellular immunity. Phenoloxidase,lectin,antimicrobial peptide in plasma react as humoral immunity. Prophenoloxidase activation system and haemocytes play a crucial role in the defense process of exogenous foreign bodies.In the experiments,the spreading function of plasmatocytes was inhibited with the days of infection,hemocytes and nuclei bacame larger.Some cells vacuolized,or contained dense particles(maybe occluded viruses). Some hemocytes lysed to release large particles.The number of total hemocytes in infection group was higher than control in the first three days,the percent of plasmatocytes significantly increased,but granulocytes almost unchanged.PO activity in control group kept dropping down up to the end.PO activity in infection group was always much higher than that in the control,except the 5^th day.PO activity in infection group was up and down.3.Changes in cell microfilament cytoskeleton.Datas indicate that many viruses destroy the cytoskeleton system.In this experiment, microfilament cytoskeleton of hemocytes was visualized by FITC-phalloidin staining. Microfilament cytoskeleton of hemocytes almost did not change with development of the larvae in control group,but it was abnomal in the infection group.Plasmatocyte microfilament cytoskeletons appeared only small short filopodia in the 1^st day.Some appeared small black vacuoles in the 2^nd day.There were filopodia and dendritic pseudopodium in the 3^rd day.Some appeared brush-like pseudopodiums on one end,and some appeared larger vacuoles and filopodia surrounding in the 4^th day.They aggregated in the 5^th day.They appeared yellow granules in the 6^th day.They appeared more vacuoles and became fragmentary in the 7^th day.4.Changes in protective enzymes.There are protective enzymes,namely peroxidase(POD),catalase(CAT) and superoxide dismutase(SOD) in insects.They can clear free radicals,prevent free radical toxicity,and maintain normal physiological activities of insects.In the experiments,the effects of PlxyGV to the three protective enzymes were variable.CAT activity kept rising from 1 to 7 days in both groups of infection and control.CAT in infection group was significantly higher than that in control group.In contrast,SOD and POD were less affected by PlxyGV infection.