IMMUNOHISTOCHEMICAL AND DEVELOPMENTAL STUDIES TO ELUCIDATE THE MECHANISM OF ACTION OF THE SNOWDROP LECTIN ON THE RICE BROWN PLANTHOPPER, NILAPARVATA-LUGENS (STAL)

Rice brown planthoppers (Nilaparvata lugens) were fed on artificial di et containing snowdrop lectin (Galanthus nivalis agglutinin; GNA), whi ch has been shown to be toxic towards this insect pest. In addition to decreasing survival, the lectin affected development, reducing the gr owth rate of nymphs by approximately 50% when present at a concentrati on of 5.3 mu M. Immunolocalisation studies showed that lectin binding was concentrated on the luminal surface of the midgut epithelial cells within the planthopper, suggesting that GNA binds to cell surface car bohydrate moieties in the gut. Immunolabelling at a lower level was al so observed in the fat bodies, the ovarioles, and throughout the haemo lymph. These observations suggest that GNA is able to cross the midgut epithelial barrier, and pass into the insect's circulatory system, re sulting in a systemic toxic effect. Electron microscope studies showed morphological changes in the midgut region of planthoppers fed on a t oxic dose of GNA, with disruption of the microvilli brush border regio n. No significant proteolytic degradation of GNA was observed either i n the gut or honeydew of planthoppers fed on lectin-containing diet. T he presence of glycoproteins which bind GNA in the gut of the brown pl anthopper was confirmed using digoxigen-labeled lectins to probe blots of extracted gut polypeptides. (C) 1998 Elsevier Science Ltd. All rig hts reserved.