Fig. 7.

Proposed model demonstrating the mode of action of 4-FPA in inducing the observed resistance of plants to piercing and sucking herbivores. Four-FPA can be absorbed by plants and is then immediately converted into 4-FP. Four-FPA alone or together with 4-FP induce the production of H₂O₂, peroxidases (PODs), and flavonoids. Four-FP and flavonoids are then catalyzed by PODs to form polymers using H₂O₂ as electron acceptors. Phenolic polymers in the parenchyma cells may inhibit the stylets of piercing and sucking from reaching the phloem sap in the plant sieve elements and/or may block the esophagus in the stylets, and hence inhibit feeding thus decreasing performance and survival of piercing and sucking herbivores.