The peritrophic membrane of Spodoptera frugiperda secretion of peritrofinas and role in the immobilization and recycling of digestive enzymes

Author(s)

Renata Bolognesi

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ)
• Defense date: 2001-03-08

Examining board members

Clelia Ferreira Terra; Antonio Gildo de Bianchi; Sirlei Daffre

• Advisor: Clelia Ferreira Terra

Abstract

Insects have a film-like anatomical structure (peritrophic membrane, PM) which lines the midgut. It is composed of chitin and proteins (peritrophins). Besides the functions of protection against food abrasion and microrganisms, PM has specific functions that depend on the fact that this structure compartimentalizes the midgut lumen into an endoperitrophic and an ectoperitrophic space. Knowledge on these specific functions are based only in indirect evidence and include: prevention of non-specific food binding onto cell surface; prevention of enzyme excretion by allowing enzyme recycling and restriction of oligomer hydrolases to ectoperitrophic space. A peritrophin from Spodoptera frugiperda PM, as well as microvillar proteins from S. frugiperda anterior midgut, were isolated and used to raise antibodies in a rabbit. These antibodies, a Tenebrio molitor anti-amylase antibody that cross-reacts with S. frugiperda amylases, and wheat-germ aglutinin were used in immunolocalization experiments performed with the aid of confocal fluorescence and immunogold techniques. The results showed that the peritrophin is secreted by anterior midgut columnar cells in vesicles that pinched-off the microvilli (microapocrine secretion). The resulting double membrane vesicles become single membrane vesicles by membrane fusion, releasing peritrophin and part of the amylase and trypsin. The remaining vesicle membranes (still containing microvillar proteins and membrane-bound amylase and trypsin) are incorpored into a jelly-like material associated with PM. Calcofluor-treated larvae lacking a PM were shown to lose the trypsin and chymotrypsin decreasing gradient observed along the midgut of control larvae. This gradient is thought to be formed by a countercurrent flux of fluid (in the space between PM and midgut cells) that powers enzyme recycling. (AU)