A model describing the different modes of jasmonic acid (JA) accumulation in maize seedlings in response to insect elicitor treatment, mechanical wounding, and exposure to green leaf volatiles. Insect elicitors (IE) and green leaf volatiles (GLV) induce JA accumulation without the concomitant induction of free 12-oxo- phytodienoic acid (OPDA) . In contrast, mechanical wounding (MW) also induces the accumulation of free OPDA . But while IE- and MW-induced JA is synthesized de novo (grey arrows) through the complete octadecanoid pathway, GLV-induced JA appears to be derived from a pool of protein- associated OPDA in the leaves (black arrows). Restoring this pool of protein-bound OPDA requires the activation of the first part of the octadecanoid pathway through a yet unknown mechanism (dashed line).