HERBIVORY AND CATERPILLAR REGURGITANTS AMPLIFY THE WOUND-INDUCED INCREASES IN JASMONIC ACID BUT NOT NICOTINE IN NICOTIANA-SYLVESTRIS

Both herbivory and mechanical damage result in increases in the concen tration of the wound-signal molecule, jasmonic acid (JA), and the defe nse metabolite, nicotine, in native tobacco plants, Nicotiana sylvestr is Speg. et Comes (Solanaceae). We found that higher concentrations of JA resulted from herbivory by Manduca sexta (L.) larvae than from the mechanical damage designed to mimic the herbivory. While both herbivo ry and mechanical damage increased JA concentrations in roots of wound ed plants, herbivory did not induce either higher root JA or nicotine responses than mechanical damage. In a separate experiment in which me chanical damage was not designed to mimic herbivory, JA responses to h erbivory were higher than those to mechanical damage, but the whole-pl ant (WP) nicotine responses were smaller. Furthermore, when regurgitan ts from M. sexta larvae were applied to standardized mechanical leaf w ounds, leaf JA responses were dramatically amplified. However, neither the root JA response nor the WP nicotine response was comparably ampl ified by application of regurgitants. Our findings demonstrate that th e response of N. sylvestris to herbivory is different from its respons e to mechanical damage; moreover, oral secretions from larvae may be p artly responsible for the difference. During feeding, M. sexta larvae appear to modify the plant's normal defensive response to leaf woundin g by reducing the systemic increase in root JA after leaf damage and t he subsequent WP nicotine response.