The Peritrophic Envelope as a Barrier to Absorption of Ingested Allelochemicals in Insect Herbivores

点击翻译按钮获取中文摘要

9407128 Martin The goal of this project is to clarify the role of the peritrophic envelope (PE) in protecting insects from ingested toxins. The PE is thin membranous sheath that lines the midguts of insects, which is the section of the digestive track where digestion of food and absorption of nutrients occurs. Several functions have been proposed for the PE: (1) protection of the gut lining from damage by abrasive food items; (2) prevention of access to the gut wall by bacteria and viruses; and (3) compartmentation of the midgut resulting in improved efficiency of digestion and assimilation. In this study the PI will test the hypothesis that the PE also serves as a barrier to the absorption of many toxins. The PI has already demonstrated that the PEs of two caterpillar species are impermeable to tannic acid, which is a toxic phenol that occurs in plants. In order to determine whether the failure of common plant toxins to penetrate the PE is a general phenomenon, or one limited to tannins, we will determine the permeability of the PEs from a selection of species of both caterpillars (Lepidoptera) and grasshoppers (Orthoptera) to a wide range of toxin classes that include compounds with a variety of chemical and physical properties. Possible mechanisms that might result in the containment of chemicals within the PE include: (1) absorption on the inner surface; (2) the presence of pores in the PE that are too small for the toxin molecules, either free or complexed within other molecules, to pass through; (3) association of the toxin with lipid aggregates that are too large to pass through the pores of the PE; and (4) repulsion between negatively charged groups on the toxin molecule and negative charges present in the matrix of the PE. Results obtained to date rule out absorption as the mechanism in Lepidoptera, and measurements of PE pore size suggest that the pores are too large to restrict the passage of uncomplexed toxin molecules. Additional expe riments will be conducted to test the other possible mechanisms. This study will advance our understanding of the basic physiological and biochemical adaptations of insects to natural and synthetic toxins. Our findings might have practical significance in the area of pesticide development and in efforts to produce pest-resistant crops by plant- breeding programs or by genetic engineering. ***