Lipoxygenase activity and lipid composition of cotyledons and oil bodies of two sunflower hybrids

Lipoxygenase (linoleate: oxygen oxidoreductase, EC 1.13.11.12) and lipid fatty acid composition of cotyledons and oil bodies of two near-isogenic high and low oleic acid sunflower hybrids (Helianthus annuus L.) were investigated during seedling growth. Triacylglycerol fatty acid content decreased strongly in cotyledons of both hybrids between days 1 and 7 of seedling growth. Oil bodies contained mostly neutral lipids and small amounts of phospholipids and proteins. Between days 1 and 7 of germination the degradation rate of oil body neutral lipids was lower for the high oleic acid hybrid compared to the low oleic acid hybrid. From days 0 to 9 of germination, neutral lipids and phospholipids of cotyledons and oil bodies from the high oleic acid hybrid contained more oleic acid and less linoleic acid than those of the low oleic acid hybrid. The presence of an oil body lipoxygenase was shown enzymatically and by immunodetection. In both hybrids, lipoxygenase activity of oil bodies and whole cotyledons was lower in 7 than in 1 day-old seedlings. Moreover, the high oleic acid hybrid showed a lower oil body lipoxygenase activity than the low oleic acid hybrid, both at 1 and 7 days of germination. Immunoblot analysis indicated that differences in enzyme activity between the two hybrids were not due to changes in the amount of antigenic protein. Oleic acid was found to be a competitive inhibitor of oil body lipoxygenase. Based on these results it is concluded that oleic acid could act as a natural inhibitor of sunflower oil body lipoxygenase.