Figure 1.

A conceptual model of defense priming in plant-herbivore interactions. The classic model of induced resistance is highlighted at the top of the flow chart, where a relaxed leaf is induced by herbivore feeding. Induced defenses include a suite of chemical changes that are plant and situation specific and may include direct defenses by synthesizing chemicals that are toxic or unpalatable to the herbivore. Induced defenses may also include indirect defenses such as the production of volatile compounds or EFN, both of which can attract natural enemies of the herbivores. Some of the chemical changes to the wounded leaf may act as wound signals to undamaged regions within the plant or to adjacent plants. The wound signals include internal signals such as JA or external signals such as volatiles. The recognition of these signals may initiate priming, which evidently comprises changes at the molecular level and leads to a so-called primed state in undamaged leaves. Leaves in a primed state are then able, by mechanisms that are poorly understood, to respond more quickly or vigorously to herbivore attack should such an attack occur. But, primed leaves theoretically pay fewer costs relative to a fully induced defense in the event that they do not actually experience herbivory. TFs, Transcription factors. See text for citations.