C6-volatiles derived from the lipoxygenase pathway induce a subset of defense-related genes

Authors

  • Nicholas J. Bate,

    Search for more papers by this author
    • Present address: Molecular Genetics Section, Agriculture and Agri-Food Canada Research Station, 107 Science Place, Saskatoon, Saskatchewan, Canada, S7N 0X2.

    • Present address: Pioneer Hibred International, Trait and Technology Development, 7300 Northwest 62nd Avenue, P.O. Box 1004, Johnston, IA 50131, USA.

  • Steven J. Rothstein

    Search for more papers by this author
    • Present address: Pioneer Hibred International, Trait and Technology Development, 7300 Northwest 62nd Avenue, P.O. Box 1004, Johnston, IA 50131, USA.


*For correspondence (fax +306 956 7247; e-mail baten@em.agr.c).

Summary

Six-Carbon (C6-) volatiles, including the aldehydes trans-2-hexenal, hexanal and cis-3-hexenal, as well as their corresponding alcohols, are produced from damaged or wounded plant tissue as a product of the enzymatic activity of hydroperoxide lyase (HPL), a component of the lipoxygenase (LOX) pathway. Aerial treatment of Arabidopsis seedlings with 10 μM concentrations of trans-2-hexenal induces several genes known to be involved in the plant’s defense response, including phenylpropanoid-related genes as well as genes of the LOX pathway. Genes encoding the pathogenesis-related proteins PR-1 or PR-2, however, were not induced. Trans-2-hexenal induction thus closely mimics the group of genes induced by methyl jasmonate (MeJA), also a LOX-derived volatile. However, unlike MeJA, trans-2-hexenal did not induce hydroxymethylglutaryl-coenzyme A reductase (HMGR) or thionin2–1. The inductive effect seemed to be limited to C6-related volatiles, as C8-, C9- and other related volatiles did not induce LOX mRNA levels. As has been demonstrated for MeJA, trans-2-hexenal quantitatively reduced wild-type seed germination. Trans-2-hexenal also reduced the germination frequency of the MeJA resistant Arabidopsis mutant, jar1–1, supporting the notion that trans-2-hexenal and MeJA are recognized via different mechanisms. In addition, trans-2-hexenal had a moderate inhibitory effect on root length relative to similar concentrations of MeJA and was approximately 10-fold less effective than MeJA at inducing anthocyanin accumulation in Arabidopsis seedlings. These results suggest that C6-volatiles of the LOX pathway act as a wound signal in plants, but result in a moderate plant response relative to MeJA at both the physiological and molecular level.

Ancillary