Formation of lipoxygenase-pathway-derived aldehydes in barley leaves upon methyl jasmonate treatment.
In barley leaves, the application of jasmonates leads to dramatic alterations of gene expression. Among the up-regulated gene products lipoxygenases occur abundantly. Here, at least four of them were identified as 13-lipoxygenases exhibiting acidic pH optima between pH 5.0 and 6.5. (13S,9Z,11E,15Z)-13-hydroxy-9,11,15-octadecatrienoic acid was found to be the main endogenous lipoxygenase-derived polyenoic fatty acid derivative indicating 13-lipoxygenase activity in vivo. Moreover, upon methyl jasmonate treatment > 78% of the fatty acid hydroperoxides are metabolized by hydroperoxide lyase activity resulting in the endogenous occurrence of volatile aldehydes. (2E)-4-Hydroxy-2-hexenal, hexanal and (3Z)- plus (2E)-hexenal were identified as 2,4-dinitro-phenylhydrazones using HPLC and identification was confirmed by GC/MS analysis. This is the first proof that (2E)-4-hydroxy-2-hexenal is formed in plants under physiological conditions. Quantification of (2E)-4-hydroxy-2-hexenal, hexanal and hexenals upon methyl jasmonate treatment of barley leaf segments revealed that hexenals were the major aldehydes peaking at 24 h after methyl jasmonate treatment. Their endogenous content increased from 1.6 nmol.g-1 fresh weight to 45 nmol.g-1 fresh weight in methyl-jasmonate-treated leaf segments, whereas (2E)-4-hydroxy-2-hexenal, peaking at 48 h of methyl jasmonate treatment increased from 9 to 15 nmol.g-1 fresh weight. Similar to the hexenals, hexanal reached its maximal amount 24 h after methyl jasmonate treatment, but increased from 0.6 to 3.0 nmol.g-1 fresh weight. In addition to the classical leaf aldehydes, (2E)-4-hydroxy-2-hexenal was detected, thereby raising the question of whether it functions in the degradation of chloroplast membrane constituents, which takes place after methyl jasmonate treatment.
Kohlmann
M
M
Institut für Pflanzenbiochemie, POB 110432, D-06018 Halle, Germany. ifeussne@ipb.uni-halle.de
Bachmann
A
A
Weichert
H
H
Kolbe
A
A
Balkenhohl
T
T
Wasternack
C
C
Feussner
I
I
D000085:Acetates / Q000494:pharmacology*; D000446:Aldehyde-Lyases / Q000378:metabolism*; D000447:Aldehydes / Q000032:analysis / Q000378:metabolism*; D003517:Cyclopentanes / Q000494:pharmacology*; D003577:Cytochrome P-450 Enzyme System; D008401:Gas Chromatography-Mass Spectrometry; D001467:Hordeum / Q000187:drug effects* / Q000378:metabolism; D008084:Lipoxygenase / Q000302:isolation & purification / Q000378:metabolism*; D054883:Oxylipins; D010937:Plant Growth Regulators / Q000494:pharmacology*; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism
D000085:Acetates; D000447:Aldehydes; D003517:Cyclopentanes; D054883:Oxylipins; D010937:Plant Growth Regulators; C072239:methyl jasmonate; D003577:Cytochrome P-450 Enzyme System; D008084:Lipoxygenase; D000446:Aldehyde-Lyases; C054540:hydroperoxide lyase