Effects of phytohemagglutinin (PHA) on the structure of midgut epithelial cells and localization of its binding sites in western tarnished plant bug, Lygus hesperus Knight

Two histological techniques, bright-field microscopy and immunofluoresecent staining were used to elucidate the lethal effect, target tissues and binding sites of phytohemagglutinin (PHA), a lectin from Phaseolus vulgaris L., on the western tarnished plant bug. Bright-field microscopy showed that the nuclei of the foregut epithelial cells were slightly disrupted and elongated but the lumen of the gut was open. The midgut epithelial cells also showed severe disruption. However, the cells of the first and the third ventriculus were much more sensitive to PHA than those in the second ventriculus. The epithelial cells in these two regions were severely disrupted and swollen toward the lumen, resulting in complete closure of the gut. Most of the cells in these regions contained two nuclei. Also, interestingly, the epithelial cells of the hindgut were drastically disrupted leading to complete closure of the lumen. Immunofluoresecent images from the midgut showed that strong binding occurred on brush-border microvilli of the epithelial cells only within the first and third ventriculi, and some signals within their cytoplasm. Thus, immunofluoresecent studies showed that PHA binds preferentially to the midgut region which demonstrates the most severe effects, and that these cells may endocytose the bound PHA.