LIPOXYGENASE ACTIVITY AND LIPID-COMPOSITION OF COTYLEDONS AND OIL BODIES OF 2 SUNFLOWER HYBRIDS

Lipoxygenase (linoleate: oxygen oxidoreductase, EC 1.13.11.12) and lip id fatty acid composition of cotyledons and oil bodies of two near-iso genic 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 lo wer for the high oleic acid hybrid compared to the low oleic acid hybr id. 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 ac id hybrid. The presence of an oil body lipoxygenase was shown enzymati cally and by immunodetection. In both hybrids, lipoxygenase activity o f oil bodies and whole cotyledons was lower in 7 than in 1 day-old see dlings. Moreover, the high oleic acid hybrid showed a lower oil body l ipoxygenase activity than the low oleic acid hybrid, both at I and 7 d ays 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 conc luded that oleic acid could act as a natural inhibitor of sunflower oi l body lipoxygenase. (C) Elsevier, Paris.