The effect of arcelin-1 on the structure of the midgut of bruchid larvae and immunolocalization of the arcelin protein

Some wild accessions of the common bean (Phaseolus vulgaris) contain a fami ly of proteins called arcelins, that are toxic to the larvae of certain bru chid species. Among the six allelic variants of arcelin tested so far, arce lin-5 and arcelin-1 confer the highest level of resistance against the Mexi can bean weevil, Zabrotes subfasciatus. The same proteins are not toxic to the bean weevil. Acanthoscelides obtectus, which is also a serious pest of cultivated beans. Arcelins belong to the bean lectin family that includes p hytohemaggutinins and alpha-amylase inhibitors. Although homologous to lect ins, arcelins are themselves only very weak lectins, and their binding prop erties have not been clearly established. The toxic properties of arcelins may be related to their recognition of and interaction with the glycoprotei ns and other constituents of the membranes along the digestive tract of ins ects. Since arcelin-1 was shown to have growth inhibitory effects for the l arvae of Z. subfasciatus but not of A. obtectus, we examined the effect of an arcelin-1 containing diet on the structure of the cells that line the in testinal tract of the larvae of these two bruchid species, and used antibod ies against arcelin to examine the distribution of arcelin within the cells and tissues. Hen we show that dietary arcelin-1 caused an alteration of th e gut structure and the penetration of arcelin into the haemolymph in Z. su bfasciatus but not in A. obtectus. These results lead us to suggest that ar celins exert their toxic effect by severely damaging the epithelial cells. (C) 2000 Elsevier Science Ltd. All rights reserved.