Intake and transformation to a glycoside of (Z)-3-hexenol from infested neighbors reveals a mode of plant odor reception and defense

Abstract

Plants receive volatile compounds emitted by neighboring plants that are infested by herbivores, and consequently the receiver plants begin to defend against forthcoming herbivory. However, to date, how plants receive volatiles and, consequently, how they fortify their defenses, is largely unknown. In this study, we found that undamaged tomato plants exposed to volatiles emitted by conspecifics infested with common cutworms (exposed plants) became more defensive against the larvae than those exposed to volatiles from uninfested conspecifics (control plants) in a constant airflow system under laboratory conditions. Comprehensive metabolite analyses showed that only the amount of (Z)-3-hexenylvicianoside (HexVic) was higher in exposed than control plants. This compound negatively affected the performance of common cutworms when added to an artificial diet. The aglycon of HexVic, (Z)-3-hexenol, was obtained from neighboring infested plants via the air. The amount of jasmonates (JAs) was not higher in exposed plants, and HexVic biosynthesis was independent of JA signaling. The use of (Z)-3-hexenol from neighboring damaged conspecifics for HexVic biosynthesis in exposed plants was also observed in an experimental field, indicating that (Z)-3-hexenol intake occurred even under fluctuating environmental conditions. Specific use of airborne (Z)-3-hexenol to form HexVic in undamaged tomato plants reveals a previously unidentified mechanism of plant defense.

Keywords: defense induction; glycosylation; green leaf volatiles; herbivore-infested plant volatiles; plant–plant signaling.

Fig. 1.

Performance of CCWs on exposed leaves. (A) Survival rates of CCWs. The survival rates on a leaf of an exposed plant (black bar) were significantly lower than those on a leaf of a control plant (white bar) (P = 0.048, n = 21, t test after angular transformation). (B) Weight gains of CCWs. The weight gains on detached exposed leaves (black bars) were significantly smaller than those on control leaves (white bars) (P = 0.0078, n = 8, Wilcoxon paired signed-rank test).

Fig. 2.

Chemical structure of (Z)-3-hexenylvicianoside, which specifically accumulated in volatile-exposed tomato plants. Represented chromatograms are shown from control (dotted lines) and exposed (solid lines) leaf extracts at m/z = 412.2. The asterisk indicates a significantly accumulated compound, and its structure as determined by NMR spectroscopy is shown in the Inset. The analysis was performed more than 11 times with four independent experiments.

Fig. 3.

Performance of CCWs on HexVic-embedded artificial diet. (A) Survival rates of CCWs. The survival rates on the embedded diets (black bar) were significantly lower than those on control diets (white bar) (P = 0.039, n = 10, t test after angular transformation). (B) Weight gains of CCWs. The weight gains on the embedded diets (black bars) were significantly smaller than those on control diets (white bars) (P = 0.037, n = 10, Wilcoxon paired signed-rank test).

Fig. 4.

Conversion of airborne (Z)-3-hexenol into glycoside. Accumulation of (Z)-3-hexenylvicianoside (HexVic) (A) and d₂-HexVic (B) was analyzed by LC–MS in undamaged plants exposed to chemically synthesized (Z)-3-hexenol and d₂-(Z)-3-hexenol for 6 h. HexVic exclusively accumulated in (Z)-3-hexenol–exposed plants and d₂-HexVic in d₂-(Z)-3-hexenol exposed plants. P < 0.05, Tukey’s multiple comparisons. Data are mean ± SE of more than three independent experiments.

Fig. 5.

Accumulation of (Z)-3-hexenylvicianoside (HexVic) in jasmonate-treated tomato plants. (A) After treating plants with jasmonate for 2 h, the plants were placed in a container without jasmonate, and their leaves were harvested 2, 6, and 26 h after the onset of jasmonate treatment. Accumulation of HexVic was hardly observed in untreated (white bars) and MeJA-treated (black bars) tomato plants (two-way ANOVA: n = 3). (B) After treating plants with jasmonate for 2 h, the plants were placed in a container with (Z)-3-hexenol, and their leaves were harvested 0, 0.5, 1, 2, 3, and 6 h after the onset of (Z)-3-hexenol treatment. Identical rates of HexVic accumulation occurred in untreated (solid squares) and MeJA-treated (open circles) tomato plants (two-way ANOVA). Data are mean ± SE of three independent experiments.