Formation of lipoxygenase‐pathway‐derived aldehydes in barley leaves upon methyl jasmonate treatment

Abstract

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-dinitrophenylhydrazones 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 21 fresh weight to 45 nmol´g 21 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 21 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 21 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.

Oxygenation of (3Z)-Alkenals to 4-Hydroxy-(2E)-Alkenals in Plant Extracts: A Nonenzymatic Process

“…To determine if HHE and HNE were formed in an enzymatic reaction, (3Z)-hexenal or (3Z)-nonenal were incubated with recombinant LOX-100, which should be the enzyme responsible for HHE formation in case of barley leaves (6). Furthermore, (3Z)-hexenal or (3Z)-nonenal were incubated with oxidizing chemicals such as 13-HPOD, 13-HPOT or H 2 O 2 , or with a combination of 13-HPOD/T or H 2 O 2 and LOX-100.…”

“…The analysis of HHE and HNE was performed as described before using some modifications (6). In order to form the 2,4-dinitrophenylhydrazone (DNPH) derivatives of aldehydes, the incubation mixtures were stirred in the presence of 1 ml of DNPHreagent (0.1% 2,4-dinitrophenylhydrazine in 1 M HCl) at room temperature for 1 h. The reaction mixture was extracted three times with 5 ml hexane each, and the collected organic phases were dried under a stream of N 2 .…”

Oxylipin Profiling Reveals the Preferential Stimulation of the 9-Lipoxygenase Pathway in Elicitor-treated Potato Cells

“…The identity of colneleic and colnelenic acid was proven by adding 750 l of methanol and 250 l of 20% HCl to 10 g of colneleic acid and incubating it for 30 min at room temperature. After addition of 200 l of DNPH, the derivatized aldehyde was analyzed as described (31).…”

Lipid metabolism in arbuscular mycorrhizal roots of Medicago truncatula

“…Heptanal was added as an internal standard. The hydrazones were extracted twice with hexane, evaporated under a stream of nitrogen and subjected to HPLC analysis (Kohlmann et al, 1999). ESI/MS analyses were done by direct injection of derivatized aldehydes into ESI interface of an LCQ ion trap mass spectrometer (Thermo Elektron, Germany).…”