Abstract
Chapter 4 Results 4.1 Resistanceto B.thuringiensis endotoxin 55 4.1.1A soluble B.thuringiezsls -binding protein in the gut lumen 55 4.1.2Coagulation of GalNAc specific protein (p85)in resistance strain 5l 4.2.Function of lectins in coagulation and adhesion 6l 4.3 Induction of macropinocytosis in the presence of lectins 67 4.3.1 Glycodeterminats in insects 68 4.3.2Lectin-mediatedspreading and endocytosis 69 4.3.3Induction of cellular functions by oligomeric lectins 70 4.3.4Lipophorin-mediatedendocytosis 70 4.4 B. thuringiensrs-toxins are tetrameric complexes 7I 4.5 B. thuringienszs binding protein is a lepidopteran low density lipophorin complex 72 4.6 Glycosilation status of glycoproteins in the gut lumen 73 4.6.1Location of the immune-related proteins in the gut 74 of caterpillar 4.7 Immune reactions in the B. thuringiensls resistant insects 17 4.7.1 Immune elicitors in the gut 7l 4.T.2Melanisation reactions 78 4.7 .3The B. thuringiersls -resistant strain may be resistance to other pathogens 79 Chapter 5 General discussion 5.1 Coagulation versus Endocytosis in insect hemolymph 5 .2Lectin-mediated macropinocytosis 5.3 Alternative model of B. thuringiensis toxin-insertion into the membrane 5.4 Are oligomeric lectin of Bt-toxin involved in endocytosis ?5.5 Resistance against Bt-toxin References 9I 1 SummaryInsecticidal crystal proteins (ICPs) from Bctcillus thuringiensis (Br) in sprays and transgenic crops are extremely useful for environmentally sound pest management.However, some important agricultural insect pests show increasing resistance to Bttoxin.This resistance problem has prompted intensive investigations on the mechanisms of resistanceto B. thuringiensis, including genetic and molecular aspects of the mode of toxin action.Although a great deal of information exists on the mode of action of Bt- toxin, the mechanisms of toxin insertion into the membrane during the process of pore formation is still not known.The major aim of this study was to investigate the possible molecular mechanism of resistance against Bt-toxin based on observations that Bt-toxin binds to a soluble immune-defence component.Since the binding protein may also be involved in cellular adhesion and endocytosis processes, the proposed resistance mechanism may be discussed in the context of a speculative mechanisms of toxin insertion into the membrane during the process of cellular uptake of the toxin.The finding of an immune- related resistance mechanism can be useful to combat evolution of resistance in insect pests as it may provide novel B.thuringiersis resistant management strategies in the field.The specific aim of this study was to examine whether Bt-toxins act like a lectin and whether lectin functions can be used as a paradigm for Br-toxicity.Observations that oligomeric lectins are involved in cell spreading, macropinocytosis and coagulation reactions, suggest a basic functional involvement of oligomeric adhesion molecules in a range of cellular functions.Otto Schmidt who continuously gave me his ideas and criticisms, without his support, things wouldn't be working the way they are.His compassion, energy, enthusiasm, have been invaluable.I have enjoyed his academic philosophy throughout the course of study.Also to Dr.