Ion channel-forming alamethicin is a potent elicitor of volatile biosynthesis and tendril coiling. Cross talk between jasmonate and salicylate signaling in lima bean

Abstract

Alamethicin (ALA), a voltage-gated, ion channel-forming peptide mixture from Trichoderma viride, is a potent elicitor of the biosynthesis of volatile compounds in lima bean (Phaseolus lunatus). Unlike elicitation with jasmonic acid or herbivore damage, the blend of substances emitted comprises only the two homoterpenes, 4,11-dimethylnona-1,3,7-triene and 4,8,12-trimethyltrideca-1,3,7,11-tetraene, and methyl salicylate. Inhibition of octadecanoid signaling by aristolochic acid and phenidone as well as mass spectrometric analysis of endogenous jasmonate demonstrate that ALA induces the biosynthesis of volatile compounds principally via the octadecanoid-signaling pathway (20-fold increase of jasmonic acid). ALA also up-regulates salicylate biosynthesis, and the time course of the production of endogenous salicylate correlates well with the appearance of the methyl ester in the gas phase. The massive up-regulation of the SA-pathway (90-fold) interferes with steps in the biosynthetic pathway downstream of 12-oxophytodienoic acid and thereby reduces the pattern of emitted volatiles to compounds previously shown to be induced by early octadecanoids. ALA also induces tendril coiling in various species like Pisum, Lathyrus, and Bryonia, but the response appears to be independent from octadecanoid biosynthesis, because inhibitors of lipoxygenase and phospholipase A(2) do not prevent the coiling reaction.

Figure 1

Gas chromatographic profile of volatile compounds after treatment of lima bean leaves with a solution of ALA (10 μg mL⁻¹). The chromatogram is normalized to the main constituent (100%). Composition of the blend: DMNT, MeSA, TMTT, and small amounts of linalool.

Figure 2

Typical spectrum of volatile compounds after treatment of lima bean leaves with cellulysin (50 μg mL⁻¹). Identification of compounds: a, (3Z)-hexenyl acetate; b, β-ocimene; c, linalool; d, DMNT; e, C₁₀H₁₄; f, C₁₀H₁₆O; g, indole; h, (3Z)-hexenyl methylbutanoate; IS, internal standard (1-bromodecane); and i, cis-jasmone.

Figure 3

Quantification and time course of the endogenous JA and SA levels after treatment of lima bean leaves with aqueous solutions of ALA at 10 μg mL⁻¹. ▪, Salicylate (SA); ▴, JA; ●, control of SA. Data represent results of at least four individual replicates (mean ± sd).

Figure 4

Quantification of endogenous OPDA and JA in AcSA (0.5 mm)-pretreated lima bean leaves. Samples were taken at maximum concentration of endogenous JA (40 min). Induction: ALA at 10 μg mL⁻¹. Data represent results of at least four individual replicates (mean ± sd).