LIPOXYGENASE-CATALYZED OXYGENATION OF STORAGE LIPIDS IS IMPLICATED INLIPID MOBILIZATION DURING GERMINATION

The etiolated germination process of oilseed plants is characterized b y the mobilization of storage lipids, which serve as a major carbon so urce for the seedling. We found that during early stages of germinatio n in cucumber, a lipoxygenase (linoleate:oxygen oxidoreductase, EC 1.1 3.11.12) form is induced that is capable of oxygenating the esterified fatty acids located in the lipid-storage organelles, the so-called li pid bodies. Large amounts of esterified (13S)-hydroxy-(9Z,11E)-octadec adienoic acid were detected in the lipid bodies, whereas only traces o f other oxygenated fatty acid isomers were found. This specific produc t pattern confirms the in vivo action of this lipoxygenase form during germination. Lipid fractionation studies of lipid bodies indicated th e presence of lipoxygenase products both in the storage triacylglycero ls and, to a higher extent, in the phospholipids surrounding the lipid stores as a monolayer. The degree of oxygenation of the storage lipid s increased drastically during the time course of germination. We show that oxygenated fatty acids are preferentially cleaved from the lipid bodies and are subsequently released into the cytoplasm. We suggest t hat they may serve as substrate for beta-oxidation. These data suggest that during the etiolated germination, a lipoxygenase initiates the m obilization of storage lipids. The possible-mechanisms of this implica tion are discussed.