Abstract
Apocarotenoids, such as β-cyclocitral, α-ionone, β-ionone, and loliolide, are derived from carotenes via chemical or enzymatic processes. Recent studies revealed that β-cyclocitral and loliolide play an important role in various aspects of plant physiology, such as stress responses, plant growth, and herbivore resistance. However, information on the physiological role of α-ionone is limited. We herein investigated the effects of α-ionone on plant protection against herbivore attacks. The pretreatment of whole tomato (Solanum lycopersicum) plants with α-ionone vapor decreased the survival rate of western flower thrips (Frankliniella occidentalis) without exhibiting insecticidal activity. Exogenous α-ionone enhanced the expression of defense-related genes, such as basic β-1,3-glucanase and basic chitinase genes, in tomato leaves, but not that of jasmonic acid (JA)- or loliolide-responsive genes. The pretreatment with α-ionone markedly decreased egg deposition by western flower thrips in the JA-insensitive Arabidopsis (Arabidopsis thaliana) mutant coi1-1. We also found that common cutworm (Spodoptera litura) larvae fed on α-ionone-treated tomato plants exhibited a reduction in weight. These results suggest that α-ionone induces plant resistance to western flower thrips through a different mode of action from that of JA and loliolide.
Highlights
Attacks by herbivore pests cause severe losses in crop yield and quality
We recently demonstrated that loliolide induced resistance to multiple herbivore pests, such as the two-spotted spider mite (Tetranychus urticae), western flower thrips (Frankliniella occidentalis), and common cutworm (Spodoptera litura), through the activation of jasmonic acid (JA)-independent defense responses [5]
Leaves, α-ionone female western western flower flower thrips and egg deposition by the same pest without exhibiting its insecticidal activity. This thrips and egg deposition by the same pest without exhibiting its insecticidal activity. This result result suggests that and egg deposition were due to suggests that reductions reductionsin inthe thesurvival survivalofoffemale femalewestern westernflower flowerthrips thrips and egg deposition were due defense responses induced in the plant after the treatment with α-ionone
Summary
Attacks by herbivore pests cause severe losses in crop yield and quality. Insecticides have been widely used for pest control because of their highly effective and rapid action on targets. A well-known example is the phytohormone jasmonic acid (JA), which plays an important role in herbivore resistance [4]. We recently demonstrated that loliolide induced resistance to multiple herbivore pests, such as the two-spotted spider mite (Tetranychus urticae), western flower thrips (Frankliniella occidentalis), and common cutworm (Spodoptera litura), through the activation of JA-independent defense responses [5]. The exogenous application of β-cyclocitral inhibited infestation by the two-spotted spider mite (T. urticae Koch) application of β-cyclocitral inhibited infestation by the two-spotted spider mite (T. urticae Koch) in in African spider plants and reduced disease symptoms caused by the plant pathogenic oomycete. Β-ionone is a major scent compound emitted from plants and and has been widely used as a fragrant material in the cosmetic and food industries [18]. Α-ionone is a scent compound, its physiological activities for plants and its physiological roles in plants remains unclear.
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