Insect chitin is a potential target for resistance plant proteins, but plant-derived chitin-degrading enzymes active against insects are virtually unknown. Commercial beta-N-acetylhexosaminidase (NAHA), a chitin-degrading enzyme from jack bean Canavalia ensiformis, caused significant mortality of fall armyworm Spodoptera frugiperda larvae at 75 microg/gm, but no significant mortality was noted with Aspergillus niger NAHA. Maize Zea mays callus transformed to express an Arabidopsis thaliana clone that putatively codes for NAHA caused significantly higher mortality of cigarette beetle Lasioderma serricorne larvae and significantly reduced growth rates (as reflected by survivor weights) of S. frugiperda as compared to callus that expressed control cDNAs. Tassels from model line Hi-II maize (Z. mays) plants transformed with the NAHA gene fed to S. frugiperda caused significantly higher mortality than tassels transformed to express glucuronidase; mortality was significantly correlated with NAHA expression levels detected histochemically. Leaf disks from inbred Oh43 maize plants transformed with the NAHA gene on average had significantly less feeding by caterpillars than null transformants. Leaf disks of Oh43 transformants caused significant mortality of both S. frugiperda and corn earworm Helicoverpa zea larvae, which was associated with higher expression levels of NAHA detected by isoelectric focusing, histochemically, or with antibody. Overall, these results suggest that plant NAHA has a role in insect resistance. Introduction of NAHA genes or enhancement of activity through breeding or genetic engineering has the potential to significantly reduce insect damage and thereby indirectly reduce mycotoxins that are harmful to animals and people.

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Tobacco (Nicotiana tabacum) plants grown from seed obtained by crossing a tobacco line that expressed an activated maize ribosome-inactivating protein (RIP) with a line that overexpressed tobacco anionic peroxidase were tested for their effects on corn earworm Helicoverpa zea and cigarette beetle Lasioderma serricorne larvae as compared to the wild-type plant cross. Significant feeding reductions were noted for transgenic plants expressing both resistance proteins as compared to wild-type plants for both H. zea and L. serricorne. Significant increases in mortality were also noted for those insects fed on the transgenic cross as compared to wild-type plants in some cases. Levels of both peroxidase and maize RIP were significantly higher in transgenic as compared to wild-type plants (which did not produce maize RIP). The degree of feeding was significantly negatively correlated with the level of RIP or peroxidase individually.