Wounding Stimulates the Accumulation of Glycerolipids Containing Oxophytodienoic Acid and Dinor-Oxophytodienoic Acid in Arabidopsis Leaves

Abstract

Although oxylipins can be synthesized from free fatty acids, recent evidence suggests that oxylipins are components of plastidlocalized polar complex lipids in Arabidopsis (Arabidopsis thaliana). Using a combination of electrospray ionization (ESI) collisionally induced dissociation time-of-flight mass spectrometry (MS) to identify acyl chains, ESI triple-quadrupole (Q) MS in the precursor mode to identify the nominal masses of complex polar lipids containing each acyl chain, and ESI Q-time-offlight MS to confirm the identifications of the complex polar lipid species, 17 species of oxylipin-containing phosphatidylglycerols, monogalactosyldiacylglycerols (MGDG), and digalactosyldiacylglycerols (DGDG) were identified. The oxylipins of these polar complex lipid species include oxophytodienoic acid (OPDA), dinor-OPDA (dnOPDA), 18-carbon ketol acids, and 16-carbon ketol acids. Using ESI triple-Q MS in the precursor mode, the accumulation of five OPDA-and/or dnOPDAcontaining MGDG and two OPDA-containing DGDG species were monitored as a function of time in mechanically wounded leaves. In unwounded leaves, the levels of these oxylipin-containing complex lipid species were low, between 0.001 and 0.023 nmol/mg dry weight. However, within the first 15 min after wounding, the levels of OPDA-dnOPDA MGDG, OPDA-OPDA MGDG, and OPDA-OPDA DGDG, each containing two oxylipin chains, increased 200-to 1,000-fold. In contrast, levels of OPDA-hexadecatrienoic acid MGDG, linolenic acid (18:3)-dnOPDA MGDG, OPDA-18:3 MGDG, and OPDA-18:3 DGDG, each containing a single oxylipin chain, rose 2-to 9-fold. The rapid accumulation of high levels of galactolipid species containing OPDA-OPDA and OPDA-dnOPDA in wounded leaves is consistent with these lipids being the primary products of plastidic oxylipin biosynthesis.

Traumatin- and Dinortraumatin-containing Galactolipids in Arabidopsis

“…Neither MGDGs containing C12/C10 oxoacids without hydroxylation nor those with only one hydroxylation were detected under these experimental conditions. Arabidopsides A and B were present in very low quantities in intact leaves, but their quantities increased markedly after disruption of the leaves as reported previously (13) (Fig. 4).…”

“…The detection limit for MGDG 7-OH-dinortraumatin/9-OH-traumatin and MGDG bis-9-OH-traumatin was 0.2 nmol g FW Ϫ1 with a signal/noise ratio on the multiple reaction monitoring chromatogram of more than 10. Arabidopsides A and B were identified from their MS and MS/MS spectra according to parameters reported by Buseman et al (13). Because standard arabidopsides were unavailable, the ratios of their areas to that of the IS were calculated.…”

“…Detection of MGDGs Containing Traumatin DerivativesEsterified oxylipins have been found predominantly in galactolipids (12,13). The most abundant C6 compounds produced after wounding of Arabidopsis leaves are formed from octadecatrienoic acid (18:3) and hexadecatrienoic acid (16:3).…”

“…Mono-and digalactosyldiacylglycerols (MGDGs and DGDGs) that contain 12-oxophytodienoic acid and/or 12-oxodinorphytodienoic acid (collectively known as arabidopsides) have been identified in Arabidopsis (Col-0) (12,13). The oxidative modification of MGDG to yield arabidopsides occurs on esterified fatty acids (14).…”

Biosynthesis of plant‐derived flavor compounds

“…In plants, fatty acids are stored as triacylglycerides and therefore enzymatic oxidative degradation of lipids is preceded by the action of acyl hydrolase, liberating the free fatty acids from acylglycerols. However, identification of a number of oxylipin-containing phosphatidylglycerols, monogalactosyldiacylglycerols and digalactosyldiacylglycerols demonstrated that direct oxidation of the fatty acid side chain in acylglycerides is possible (Buseman et al, 2006).…”