Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/17/1997
Publication Date: N/A
Interpretive Summary: Insects can cause devastating economic damage to plants. Finding and understanding the mechanism plants use to resist insects may ultimately result in the development of more resistant plants. Genetically engineered tobacco lines that produced different levels of an enzyme were studied to understand how differing levels of the enzyme might affect the degree of resistance. Leaves from plants producing higher than normal levels of the enzyme were generally more resistant to the corn earworm, while those producing lower than normal levels were sometimes more susceptible. The degree of resistance was also dependent on the age of the leaf, and whether the plant the leaf had come from had been previously fed on by caterpillars. This information indicates this enzyme has potential value in increasing insect resistance.
Technical Abstract: First instar larvae of the false tobacco budworm (corn earworm) (Helicoverpa zea) that fed on either intact plants, leaf disks from undamaged plants, or leaf disks from insect-damaged plants of Nicotiana sylvestris and N. tabacum "Coker" plants overproducing a tobacco anionic peroxidase generally caused significantly less damage than those caged with corresponding material from wild type plants. In some cases mortality was significantly higher and weights significantly less for caterpillars feeding on leaf material from overproducing vs. wild type plants. First instar H. zea fed on the same type of leaf material from N. tabacum "xanthi" underproducing tobacco anionic peroxidase generally caused significantly more damage than those fed leaf material from wild type plants. However, first instar H. zea fed on underexpressing leaf material from N. sylvestris did not cause significantly greater damage compared to wild type material. In cases where peroxidase enzyme activity was determined, significantly higher mean peroxidase activity was seen in leaves of plant types that also had significantly less mean feeding ratings. This information suggests that peroxidase activity can contribute to leaf resistance to chewing insects. However, the context of the peroxidase can mediate the degree of influence seen by changes in individual peroxidase isozyme levels.