2-hexenal--z-isomer and 2-hexanol

(E)-2-alkenals are aldehydes containing an unsaturated bond between the alpha and beta carbons. 2-alkenals are produced by many organisms for defense against predators and secretions containing (E)-2-alkenals cause predators to stop attacking and allow the prey to escape. Chemical ecologists have described many alkenal compounds with 3-20 carbons common, having varied positions of double bonds and substitutions. How do these defensive alkenals act to deter predators? We have tested the effects of (E)-2-alkenals with 6-12 carbons on transient receptor potential channels (TRP) commonly found in sensory neurons. We find that (E)-2-alkenals activate transient receptor potential ankyrin subtype 1 (TRPA1) at low concentrations-EC50s 10-100 µM (in 0 added Ca(2+) external solutions). Other TRP channels were either weakly activated (TRPV1, TRPV3) or insensitive (TRPV2, TRPV4, TRPM8). (E)-2-alkenals may activate TRPA1 by modifying cysteine side chains. However, target cysteines include others beyond the 3 in the amino-terminus implicated in activation, as a channel with cysteines at 621, 641, 665 mutated to serine responded robustly. Related chemicals, including the aldehydes hexanal and decanal, and (E)-2-hexen-1-ol also activated TRPA1, but with weaker potency. Rat trigeminal nerve recordings and behavioral experiments showed (E)-2-hexenal was aversive. Our results suggest that TRPA1 is likely a major target of these commonly used defensive chemicals.

Topics: Action Potentials; Aldehydes; Animals; Calcium; Calcium Channels; Cysteine; Habituation, Psychophysiologic; HEK293 Cells; Hexanols; Humans; Male; Microscopy, Fluorescence; Nerve Tissue Proteins; Patch-Clamp Techniques; Rats; Rats, Sprague-Dawley; Transient Receptor Potential Channels; Trigeminal Nerve; TRPA1 Cation Channel

An expression profile of genes induced by non-pathogenic Alternaria alternata on rough lemon leaves was obtained by sequencing 500 subtractive PCR clones generated from mRNA of leaves inoculated with the fungus after subtraction with that of non-inoculated leaves. About 6% of the cDNA sequences had homology to known putative defense-related genes including epoxide hydrolase. A full-length cDNA (951 bp) from rough lemon that encoded epoxy hydrolase was isolated by random amplification of cDNA ends (RACEs), based on sequence information from subtractive PCR, and designated as RlemEH. The product of this gene expressed with an in vitro translation system with Escherichia coli also had activity of a soluble type of epoxide hydrolase. The transcript of rough lemon RlemEH was not detected in flowers, fruits, stems or leaves, but was induced after inoculation of leaves with conidia of Alternaria alternata, wounding, or treatment with C6 volatiles, including trans-2-hexenol and cis-3-hexenol, and methyl jasmonate. The response of the epoxide hydrolase gene correlated well with the activation of defense mechanisms induced in plant-fungus interactions.

Topics: Aldehydes; Alternaria; Amino Acid Sequence; Base Sequence; Blotting, Northern; Citrus; Cloning, Molecular; DNA, Complementary; Epoxide Hydrolases; Gene Expression Profiling; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Plant; Hexanols; Molecular Sequence Data; RNA, Messenger; Sequence Analysis, DNA; Stress, Mechanical; Transcription, Genetic; Volatilization