On the cover: In response to feeding by arthropod herbivores, plants defend themselves directly by producing toxins, repellents and digestibility reducers. Induced indirect defenses of plants against herbivores have also been documented in which plants respond to herbivory by emitting specific blends of volatiles [herbivore-induced plant volatiles (HIPVs)] that attract carnivorous natural enemies of the herbivores. Since the blends of HIPVs may vary with the attacking herbivore, various components and their biosynthetic regulation are thought to be responsible for the characteristic volatile blend, mainly consisting of terpenoids and green leaf volatiles. Volatile terpenoids and green leaf volatiles have distinct natures, especially regarding their de novo synthesis and biochemical features, whereas they play similar roles in ecosystems. Arimura et al. (pp. 911-923) overview recent progress on the ecological significance of HIPVs by integrating the molecular mechanisms involved in the production of HIPVs and their ecological functions to explain sizable arrays of interactions between plants and arthropods shown in the cover photographs. For example, there is a tritrophic interaction in which Brassica plants, when damaged by diamondback moth larvae, start emitting HIPVs that attract female parasitic wasps, which then lay their eggs inside the host larvae. In nature, a suite of other HIPV-mediated communications between plants and microorganisms, undamaged neighboring plants or undamaged sites within the plant are also observed.
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