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

小行星9407128 本项目的目标是阐明围食膜（PE）在保护昆虫免受摄入毒素的作用。PE是排列在昆虫中肠上的薄膜鞘，中肠是消化道的一部分，食物的消化和营养物质的吸收发生在这里。已经提出了PE的几种功能：（1）保护肠道内层免受研磨性食物的损害;（2）防止细菌和病毒进入肠道壁;以及（3）中肠的区室化，从而提高消化和同化的效率。在本研究中，PI将检验PE也可作为许多毒素吸收屏障的假设。PI已经证明，两种毛虫的PE对单宁酸是不可渗透的，单宁酸是一种存在于植物中的有毒酚。为了确定常见植物毒素穿透PE的失败是否是一种普遍现象，或者仅限于单宁，我们将确定从毛毛虫（鳞翅目）和蚱蜢（直翅目）的选择物种到广泛的毒素类别（包括具有各种化学和物理性质的化合物）的PE的渗透性。 可能导致PE内包含化学品的可能机制包括：（1）内表面上的吸收;（2）PE中存在的孔太小，毒素分子（游离或与其他分子复合）无法通过;（3）毒素与脂质聚集体缔合，脂质聚集体太大，无法通过PE的孔;以及（4）毒素分子上的带负电荷的基团与PE基质中存在的负电荷之间的排斥。迄今为止获得的结果排除了吸收的机制，在鳞翅目，和PE孔径的测量表明，孔太大，以限制未复合的毒素分子的通过。将进行额外的实验以测试其他可能的机制。 这项研究将促进我们对昆虫对天然和合成毒素的基本生理和生化适应的理解。我们的研究结果可能在农药开发领域以及通过植物育种计划或基因工程生产抗虫害作物的努力中具有实际意义。 ***

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. ***