Effects of UVB Radiation & Herbivory on Induced Resistance Traits in Datura Wrightii

Plants can produce phenolics as a form of protection against ultraviolet B radiation, which act as sunscreens to reduce UVB penetration through the epidermis. Phenolic compounds have also been shown to have deleterious effects against herbivores. This raises questions as to how UVB exposure and herbivory may overlap in the expression of induced plant traits. In this field study I attempt to discern how UVB exposure and herbivory interact in the expression of plant phenolics (rutin and chlorogenic acid), polyphenol oxidase activity, and protease inhibitors in Datura wrightii. In the field, cages wrapped in plastic films that differed in UVB transmittance were used to control for UVB exposure. After two or four weeks in the field, treatment plants were exposed to two feeding adult Lema daturaphila individuals. Herbivores were removed after 24 hours, and both locally damaged and undamaged systemic tissue adjacent to damaged tissue were subsequently harvested and analyzed. An herbivore performance bioassay was then used to test for the effects of phenolics on Lema daturaphila growth rate. UVB exposure had a significant effect in priming chlorogenic acid, inducing higher concentrations of chlorogenic acid in local and systemic tissue following herbivory. Conversely, herbivory alone induced rutin in locally damaged tissue, but UVB had no effect on rutin induction. Herbivory induced polyphenol oxidase activity and protease inhibitors in locally damaged leaves as well, but UVB did not affect induction of these traits. High concentrations of rutin also had a deleterious effect on the biomass gain of herbviores, while chlorogenic acid had no significant effect. Although UVB had no effect on protease inhibitors on polyphenol oxidase activity, the discrepancies in induction responses found between chlorogenic acid and rutin indicate a clear role for UVB mediated induction in this system