Insect herbivore-induced plant volatile emission and the subsequent attraction of natural enemies is facilitated by
fatty acid-
amino acid conjugate (FAC) elicitors, such as
volicitin [N-(17-hydroxylinolenoyl)-
L-glutamine], present in caterpillar oral secretions. Insect-induced
jasmonic acid (JA) and
ethylene (E) are believed to mediate the magnitude of this variable response. In maize (Zea mays) seedlings, we examined the interaction of
volicitin, JA, and E on the induction of volatile emission at different levels of
nitrogen (N) availability that are known to influence E sensitivity. N availability and
volicitin-induced
sesquiterpene emission are inversely related as maximal responses were elicited in N-deficient plants. Plants with low N availability demonstrated similar volatile responses to
volicitin (1 nmol plant(-1)) and JA (100 nmol plant(-1)). In contrast, plants with medium N availability released much lower amounts of
volicitin-induced
sesquiterpenes compared with JA, suggesting an alteration in
volicitin-induced JA levels. As predicted, low N plants exhibited greater sustained increases in
wound- and
volicitin-induced JA levels compared with medium N plants. N availability also altered
volicitin-E interactions. In low N plants, E synergized
volicitin-induced
sesquiterpene and
indole emission 4- to 12-fold, with significant interactions first detected
at 10 nL L(-1) E. Medium N plants demonstrated greatly reduced
volicitin-E interactions.
Volicitin-induced
sesquiterpene emission was increased by E and was decreased by pretreatment the E perception inhibitor
1-methylcyclopropene without alteration in
volicitin-induced JA levels. N availability influences plant responses to insect-derived elicitors through changes in E sensitivity and E-independent JA kinetics.