EXOGENOUS JASMONATES SIMULATE INSECT WOUNDING IN TOMATO PLANTS (LYCOPERSICON-ESCULENTUM) IN THE LABORATORY AND FIELD

Wounding increases the levels and activities of several defense-relate d proteins in the foliage of the tomato plant, Lycopersicon esculentum Mill. Evidence indicates that two of these responses, the systemic in creases in polyphenol oxidase and proteinase inhibitors, are regulated by an octadecanoid-based signalling pathway which includes the wound hormone, jasmonic acid. It is not known whether other responses to wou nding are also regulated by this same signalling pathway. In this pape r, we show that application of jasmonates (jasmonic acid or its volati le derivative, methyl jasmonate) in low concentrations to foliage of y oung tomato plants induced, in a dose-dependent manner, the same prote in responses-polyphenol oxidase, proteinase inhibitors, lipoxygenase, and peroxidase-as does Helicoverpa tea Boddie feeding. Application of jasmonic acid to a single leaflet of four-leaf tomato plants induced t hese four proteins in a spatial pattern nearly identical to that produ ced by localized feeding of H. tea. Exogenous jasmonic acid also decre ased suitability of foliage for the beet armyworm, Spodoptera exigua H ubner in the laboratory. Based on these results, we conducted an exper iment to measure the effects of jasmonic acid spray under field condit ions. We provide the first evidence that jasmonic acid spray on field plants induces production of chemical defenses above the levels found in unsprayed controls. Exogenous jasmonic acid sprayed on plants in ag ricultural plots increased levels of polyphenol oxidase and proteinase inhibitors. Because application of jasmonic acid induces these defens ive compounds at low concentrations in a manner similar to natural wou nding, it may prove to be a useful tool for stimulating plant resistan ce to insects in the field.