The Preliminary Study On The Mechanism Of Enhancement Of Optical Brightener For Baculovirus Infection

It has been demonstrated that optical brightener (or fluorecent brightener) can enhance viral activity, provide UV protection for nucleopolyhedrovirus (NPV) and increase host susceptibility. The mechanism of enhancement of the optical brightener is not known. Shapiro et al. postulated that selected brightener including M2R inhibit or alter the chitinous peritrophic membrane (PM), creating gaps in the membrane or gut lining and perhaps allowing more virions to pass from the gut lumen into the hemocoel. Our study further support the viewpoint that the mode of action for the optical brightener is at the PM level.The PM is formed of protein, carbohydrate and chitin. PM proteins are strongly bound to the PM. However, in vitro incubation of PMs with 1%M2R released a significant amount of proteins from the PM structure. These proteins were not extractable by 50mM GlcNAc , 6M urea , 20mM acetic acid , 6M guanidine-HCl. hi addition, another chitin binding agent Congo Red , also solubilized proteins from the PM structure. PM proteins were obtained by extraction with 1%M2R solution followed by removal of M2R by chromatographic desalting. The binding of PM proteins to regenerated chitin demonstrated then" chitin binding properties. The high binding affinity of these isolated PM proteins to the regenerated chitin was similar to the binding of these proteins to the native PM structure.Employing environmental scanning electron microscopy, we found that the normal PM surface was smooth and wrinkled without pores or slits. The PM treated with 1%M2R for 2h was found pores and slits. With the tune going, the PM structure was badly destructed. After 4h, the PM completely disppeared.Feeding the larvae with a single 51 dose of 1%M2R complete inhibition of PM formation. Mocroscopical observation of dissected midguts showed that at 2.5h post fed with M2R no PMs were present in the treated larvae, in contrast to the presenceof a fully formed PM of control larvae. Feeding larvae with 5 10.05%M2R did not result in complete inhibition of PM. In the fifth instar larvae fed on diet containing 1%M2R for 4h PM formation was inhibited.Continuous feeding of larvae on diet incorporated with 1%M2R significantly retarded larvae development. All of the control larvae pupated synchronously in 9-13 days without mortality. In contrast, the larvae reared on the 1%M2R containing diet pupated asynchronously over a 17-38 day period with 54.5% mortality. The pupae and the adult moths were smaller as compared to the untreated group.A single dose feeding of early third instar larvae with 1%M2R significantly increased larval susceptibility to SfaMNPV infection. Feeding of early third instar larvae with 106PIBs/ml SfaMNPV plus 1%M2R resulted virus mortality of 93%, significantly higher than the 73% mortality in the corresponding control larvae.