Plant seeds are primed by herbivore-induced plant volatiles

Mature plants can detect and respond to herbivore-induced plant volatiles (HIPVs) by priming or directly activating defenses against future herbivores. Whether other plant life stages can respond to HIPVs in similar manners is poorly understood. For example, seeds are known to respond to a variety of environment cues that are essential for proper germination timing and survival. Seeds may also be exposed to HIPVs prior to germination, and such exposure may affect the growth, development, and defense profiles when the seeds grow into mature plants. Here, we investigated the effect of seed exposure to common HIPVs on growth, reproduction and defense characteristics in the model plants Arabidopsis thaliana and Medicago truncatula . Of all the HIPVs tested, indole specifically reduced both beet armyworm growth on A. thaliana and pea 33 aphid fecundity on M. truncatula . Induction of defense genes was not affected by seed exposure to indole in either plant species, suggesting that seed priming operates independently of induced resistance. Moreover, neither species showed any negative effect of seed exposure to HIPVs on vegetative and reproductive growth. Rather, M. truncatula plants derived from seeds exposed to z -3-hexanol and z -3-hexenyl acetate grew faster and produced larger leaves compared to controls. Our results indicate that seeds are sensitive to specific HIPVs, which represents a novel ecological mechanism of plant-to-plant communication.