Does salicylic acid act as a signal in cotton for induced resistance to Helicoverpa zea?

Our previous study indicated that insect herbivory on cotton induced resistance to the cotton bollworm (Helicoverpa zea). Here we examine the role of salicylic acid as a signal in cotton for the induced resistance. Abundant evidence has accumulated showing that salicylic acid plays a key role in coordinating the expression of systemic acquired resistance against phytopathogens. We report that herbivory results in significant increases in foliar salicylic acid and H2O2, a response frequently observed following pathogenesis. In other well-studied systems (e.g., tobacco), salicylic acid inhibits the enzymatic decomposition of H2O2 by catalase and ascorbate peroxidase, but in cotton, salicylic acid has no effect on these enzymes in vitro. Furthermore, while herbivory enhances foliar catalase and ascorbate peroxidase activities, the application of salicylic acid or methyl salicylate to cotton plants does not affect foliar resistance to H. zea. The possible role of salicylic acid as a signal for induced resistance is discussed in light of these findings.