The peritrophic membrane of Spodoptera frugiperda: Secretion of peritrophins and role in immobilization and recycling digestive enzymes

A peritrophin from the Spodoptera a frugiperda peritrophic membrane (PM) an d microvillar proteins from S. frugiperda anterior midgut cells were isolat ed and used to raise antibodies in a rabbit. These antibodies, as well. as a Tenebrio molitor amylase antibody that cross-reacts with S. frugiperda am ylases, and wheat-germ aglutinin were used in immunolocalization experiment s performed with the aid of confocal fluorescence and immunogold techniques . The results showed that the peritrophin was secreted by anterior midgut c olumnar cells in vesicles pinched-off the microvilli (microapocrine secreti on). The resulting double membrane vesicles become single membrane vesicles by membrane fusion, releasing peritrophin and part of the amylase and tryp sin. The remaining membranes still containing microvillar proteins and memb rane-bound amylase and trypsin are incorporated into a jelly-like material associated with PM. Calcofluor-treated larvae lacking a PM were shown to lo se the decreasing gradient of trypsin and chymotrypsin observed along the m idgut of control larvae. This gradient is thought to be formed by a counter current flux of fluid (in the space between PM and midgut cells) that power s enzyme recycling. (C) 2001 WileyLiss, Inc.