Tobacco mosaic virus inoculation inhibits wound-induced jasmonic acid-mediated responses within but not between plants
Jasmonic acid (JA) and salicylic acid (SA) have both been implicated as important signal molecules mediating induced defenses of Nicotiana tabacum L. against herbivores and pathogens. Since the application of SA to a wound site can inhibit both wound-induced JA and a defense response that it elicits, namely nicotine production, we determined if tobacco mosaic virus (TMV) inoculation, with its associated endogenous systemic increase in SA, reduces a plant's ability to increase JA and nicotine levels in response to mechanical damage, and evaluated the consequences of these interactions for the amount of tissue removed by a nicotine-tolerant herbivore, Manduca sexta. Additionally, we determined whether the release of volatile methyl salicylic acid (MeSA) from inoculated plants can reduce wound-induced JA and nicotine responses in uninoculated plants sharing the same chamber. The TMV-inoculated plants, though capable of inducing nicotine normally in response to methyl jasmonate applications, had attenuated wound-induced JA and nicotine responses. Moreover, larvae consumed 1.7- to 2.7-times more leaf tissue from TMV-inoculated plants than from mock-inoculated plants. Uninoculated plants growing in chambers downwind of either TMV-inoculated plants or vials releasing MeSA at 83- to 643-times the amount TMV-inoculated plants release, exhibited normal wound-induced responses. We conclude that tobacco plants, when inoculated with TMV, are unable to elicit normal wound responses, due likely to the inhibition of JA production by the systemic increase in SA induced by virus-inoculation. The release of volatile MeSA from inoculated plants is not sufficient to influence the wound-induced responses of neighboring plants.
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