Submitted to: International Symposium For Plant Peroxidases
Publication Type: Proceedings
Publication Acceptance Date: 7/21/1999
Publication Date: 4/1/2000
Citation: DOWD, P.F., HERMS, D.A., BERHOW, M.A., LAGRIMINI, L. MECHANISMS OF INSECT RESISTANCE IN TRANSGENIC PLANTS (OVER)EXPRESSING A TOBACCO ANIONIC PEROXIDASE. PLANT PEROXIDASES NEWSLETTER. 2000. (14). p. 93-101. Interpretive Summary:
Technical Abstract: Enhanced resistance in plants transformed to (over)express tobacco anionic peroxidase has been noted with two different strains of Nicotiana tabacum (leaf tobacco), N. sylvestris (ornamental tobacco), Lycopersicon esculentum (tomato), Liquidamber styraciflua (sweetgum), and Zea mays (maize). Present evidence derived from experiments with tobacco and sweetgum suggests insect resistance of transgenic plants is primarily due to peroxidase generation of new, more toxic metabolites, some of which are probably quinones. Based on comparisons with the degree of enhanced overall peroxidase activity in leaves of tobacco (ca. 10 x) vs. tomato (ca. 400 x) and corresponding relative resistance to insect feeding (ca. 2 x for both), it appears that the potential level of resistance conferred with enhanced peroxidase activity can be limited by the levels of available phenolic substrates in the leaves. Studies with sweetgum indicate antibiosis (toxicity) rather than antixenosis (deterrence) is the primary basis for resistance, although studies with sweetgum and tomato suggest elevated peroxidase activity can also indirectly decrease nutritional quality of leaves. Insects are apparently unable to sense the presence of the toxic compounds, based on preference studies with tomato leaves. Chemical analysis shows that additional secondary metabolites are produced in transgenic sweetgum and tobacco compared to wild type plants, and at least some of these new compounds are toxic to caterpillars at naturally relevant concentrations.