Date of Graduation

5-2012

Document Type

Thesis

Degree Name

Master of Science in Entomology (MS)

Degree Level

Graduate

Department

Entomology

Advisor/Mentor

Fiona Goggin

Committee Member

Tim Kring

Second Committee Member

Donn Johnson

Third Committee Member

Argelia Lorence

Keywords

Biological sciences, Absorbic acid, Herbivores, Insects

Abstract

Ascorbic acid (AsA), vitamin C, is an important molecule that is vital for both human and plant health, because it aids in the detoxification of reactive oxygen species (ROS) caused by various abiotic and biotic stresses including UV, salinity, ozone, and attack from pathogens In order to understand the role of AsA in the plant-herbivore interaction, we looked at the effects of the wound-responsive hormones, jasmonate, wounding, and herbivory on AsA content. Our study is the first to directly compare the effects of wounding and jasmonates on AsA levels in plants. We looked at the effects of wounding and methyl jasmonate (MeJA) on JA-deficient and JA-insensitive genotypes of tomato to further determine if JA mediates the effects of wounding on AsA in plants, because JA is involved in many other wound responses. Wounding in two cultivars of tomato lowered AsA content as did exogenous MeJA application, suggesting a link between these two. Wounding of mutant lines impaired in JA signaling showed a decrease in AsA content similar to wild type, indicating AsA response to wounding does not require JAs. These results show a complicated relationship between AsA, JA, and wounding, in which both JA and wounding appear to but may act independently. Few studies explore ascorbate's role in actual plant systems with associated herbivores. We evaluated the effects of multiple types of herbivores on AsA of both tomato and Arabidopsis, providing the first comparison of different types of herbivore damage on AsA content among plant types. Tomato and Arabidopsis responded differently to herbivory. Ascorbate decreased significantly in response to caterpillar feeding in tomato foliar tissue with no significant difference in systemic or root tissue. Whereas, Arabidopsis saw no significant difference in treated tissue but saw significant decrease in AsA of systemic tissue of aphid and caterpillar treated plants. We were, also, able to determine high AsA content of a MIOX4 overexpression line and use it in determining the effects of AsA on caterpillars in conjunction with WT, moderate AsA, and vtc1 mutant, low AsA. The MIOX4 overexpressing line supported caterpillars of a greater weight than either WT or vtc1.

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