Induction of hypericins and hyperforins in Hypericum perforatum in response to damage by herbivores

Plants respond to herbivore and pathogen attack by a variety of direct and indirect mechanisms that include the induction of secondary metabolites. The phytomedicinal plant Hypericum perforatum L. produces two different classes of secondary metabolites: hyperforins, a family of antimicrobial acylphloroglucinols; and hypericins, a family of phototoxic anthraquinones exhibiting antimicrobial, antiviral, and antiherbivore properties in vitro. To determine whether these compounds are part of the herbivore-specific inducible plant defense system, we used an in vitro detached assay to assess the effects of specialist and generalist herbivore damage on the levels of hypericins and hyperforin. Greenhouse-grown H. perforatum plant sections were challenged with the specialist, Chrysolina quadrigemina, or with one of the following generalist feeders: Spilosoma virginica, Spilosoma congrua, or Spodoptera exigua. Feeding by the specialist beetle or mechanical wounding caused little change in phytochemical levels in plant tissue, whereas the small amount of feeding by the generalists caused 30-100% increases in hypericins and hyperforin as compared to control levels. Although the leaf damage index of the specialist feeding was 2.7 times greater, C. quadrigemina had little effect on H. perforatum chemical defenses in response to feeding damage in comparison to generalist feeding.