Lipoxygenase-mediated metabolism of storage lipids in germinating sunflower cotyledons and ?-oxidation of (9Z,11E,13S)-13-hydroxy-octadeca-9,11-dienoic acid by the cotyledonary glyoxysomes

Abstract

During the early stages of germination, a lipid-body lipoxygenase is expressed in the cotyledons of sunflowers (Helianthus annuus L.). In order to obtain evidence for the in vivo activity of this enzyme during germination, we analyzed the lipoxygenase-dependent metabolism of polyunsaturated fatty acids esterified in the storage lipids. For this purpose, lipid bodies were isolated from etiolated sunflower cotyledons at different stages of germination, and the storage triacylglycerols were analyzed for oxygenated derivatives. During the time course of germination the amount of oxygenated storage lipids was strongly augmented, and we detected triacylglycerols containing one, two or three residues of (9Z,11E,13S)-13-hydro(pero)xy-octadeca-9,11-dienoic acid. Glyoxysomes from etiolated sunflower cotyledons converted (9Z,11E,13S)-13-hydroxy-octadeca-9,11-dienoic acid to (9Z,11E)-13-oxo-octadeca-9,11-dienoic acid via an NADH-dependent dehydrogenase reaction. Both oxygenated fatty acid derivatives were activated to the corresponding CoA esters and subsequently metabolized to compounds of shorter chain length. Cofactor requirement and formation of acetyl-CoA indicate degradation via beta-oxidation. However, beta-oxidation only proceeded for two consecutive cycles, leading to accumulation of a medium-chain metabolite carrying an oxo group at C-9, equivalent to C-13 of the parent (9Z,11E,13S)-13-hydroxy-octadeca-9,11-dienoic acid. Short-chain beta-oxidation intermediates were not detected during incubation. Similar results were obtained when 13-hydroxy octadecanoic acid was used as beta-oxidation substrate. On the other hand, the degradation of (9Z,11E)-octadeca-9,11-dienoic acid was accompanied by the appearance of short-chain beta-oxidation intermediates in the reaction mixture. The results suggest that the hydroxyl/oxo group at C-13 of lipoxygenase-derived fatty acids forms a barrier to continuous beta-oxidation by glyoxysomes.

Biogenesis and functions of lipid droplets in plants

“…These types of lipid transformations are frequently associated with oxylipin metabolism in plants, which involves the production of various lipophilic hormone-like molecules associated with plant stress response and innate immunity ( 65 ). Alternatively, caleosins have been implicated in the degradation of polyunsaturated fatty acids, as the products of peroxidized linoleic acid can accumulate to high levels in germinated seeds, and these products can subsequently be broken down by ␤ -oxidation in glyoxysomes ( 66,67 ). Additional support for a role of caleosins in oil breakdown comes from the analysis of gene knockout mutants in Arabidopsis , where disruption of the major seed-expressed caleosin resulted in a decreased rate of fatty acid degradation ( 68 ).…”

Green tea catechins and broccoli reduce fat-induced mortality in Drosophila melanogaster

“…Free fatty acids were prepared according to Gerhardt et al [20] with some modification. In brief, 35 g potassium hydroxide was ground into power and dissolved into 2 L methanol solution containing 130 g of lard.…”

Purification and properties of lipoxygenase from opium poppy seedlings(Papaver somniferum L.)

“…LOX activity has been reported during germination in cytoplasm and on the phospholipid monolayer of oil bodies. LOX-catalyzed oxygenation of polyenoic fatty acids preceded the degradation of storage lipids during seed germination in certain oilseeds (Feussner et al, 2001;Gerhardt et al, 2005;Yadav and Bhatla, 2011).…”