Herbivore-induced volatiles as rapid signals in systemic plant responses: how to quickly move the information?

Plants respond to local herbivory or pathogen infection with phenotypic changes, which reduce the danger of future attack. This so-called induced resistance is usually not restricted to the attacked plant organ but is also expressed in distant, so far undamaged parts of the plant. Signaling compounds such as jasmonic acid and salicylic acid have been discovered that move within the plant via the xylem or the phloem and elicit the resistance, thus acting as plant hormones. We now found that volatiles released in response to herbivore damage are required to elicit extrafloral nectar secretion in other parts of the same plant. Extrafloral nectar attracts ants and other carnivorous arthropods and serves as an effective indirect defense against herbivores. So called green leaf volatiles are released within minutes in response to tissue damage and were among the compounds that induced nectar secretion in yet undamaged parts of the damaged plant, but also in neighboring plants. Being gaseous and transported via the air, green leaf volatiles can serve a rapid within-plant communication, which moves much faster from one plant organ to the other than any plant-internal compound.