Volatile organic compounds (VOCs) are constantly emitted by plants, and play a major role in information transfer between plants and other organisms. One of the consequences of VOC-mediated information transfer is that plants ‘warn’ neighbouring plants when they are attacked, enabling these neighbours to prime defence responses in anticipation of future attack. Priming refers to a memory effect in which previous exposure to a stimulus (i.e. VOCs) enables plants to respond faster and more strongly when presented with a future stimulus (i.e. herbivory, pathogen infection). In recent years, our knowledge of how VOCs are perceived by plants, and the broad-scale phenotypic changes they induce, has grown dramatically. Multiple plant species seem to prime defence responses following exposure to herbivore-induced VOCs. However, the mechanisms underlying priming remain speculative. In the present article we highlight recent advancements in our understanding of stress perception by plants and discuss hypotheses of what might be happening on a molecular level in primed plants. Furthermore, we discuss ecological consequences of priming responses such as consequences for plant competitive interactions, and interactions with mutualistic and antagonistic animals.

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