Abstract
The morphology of the midgut epithelium cells of Anticarsia gemmatalis (Hübner) larvae is described by light and transmission electron microscopy. The midgut of A. gemmatalis is the largest portion of the digestive tract, with three distinct regions: proximal, media and distal. Its wall is formed by pseudostratified columnar epithelial tissue having four cell types: columnar, goblet, regenerative, and endocrine cells. The columnar cells are numerous and long, with the apical portion showing many lengthy microvilli and the basal portion invaginations forming a basal labyrinth. The goblet cells have a large goblet-shaped central cavity delimited by cytoplasmic projections filled with mitochondria. The regenerative cells present electron-dense cytoplasm and few organelles. The endocrine cells are characterized by electron-dense secretory granules, usually concentrated in the cytoplasm basal region.
Highlights
The digestive tract of insects is considered an effective physical and chemical barrier against potentially invasive pathogens that are ingested with food
The midgut wall of the A. gemmatalis consist of an acellular peritrophic membrane that delimits the midgut lumen in ectoperitrophic and endoperitrophic spaces, a pseudostratified columnar epithelial tissue with a brush border, a basement membrane, and muscular layers composed of bundles of inner circular and outer longitudinal muscles (Figs. 1-3)
Three distinct portions were recognized in this cell type, from apex to base: the apical portion, rich in long microvilli and large quantities of mitochondria (Figs. 5-6); the middle portion, characterized by large amounts of rough endoplasmic reticulum, developed Golgi complex, and some mitochondria (Fig. 7); and the basal portion, with mitochondria frequently associated with basal plasma membrane infolds forming the basal labyrinth (Fig. 8)
Summary
The digestive tract of insects is considered an effective physical and chemical barrier against potentially invasive pathogens that are ingested with food. The infection starts when the caterpillar present in treated soybean tillage ingests the polyhedra that are dissolved and whose derived virions are released in the midgut lumen. These virions supposedly pass through the peritrophic membrane and fuse with the microvillar membrane of the midgut epithelial cells, initiating the replication cycle (Flipsen et al, 1995; Volkman, 1997). This work provides a description by light and transmission electron microscopy of the epithelial cell types observed in the midgut of the A. gemmatalis noninfected larvae, aiming to improve the understanding of the morphophysiological mechanisms involved in the defense of this insect, when in contact with the AgMNPV
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