High Oleic Sunflower: Studies on Composition and Desaturation of Acyl Groups in Different Lipids and Organs

A selection o f lipids from achenes, cotyledons after germination, roots and leaves o f normal and high oleic varieties o f sunflower were analyzed with regard to their fatty acid profiles. The lipids included triacylglycerol and phosphatidylcholine as ER-made components and monoand digalactosyl diacylglycerol as plastid-localized glycolipids. A comparison o f fatty acid pat­ terns showed that the block in oleate desaturation o f the high oleic variety is confined to the ER o f fat accumulating embryos, but that upon germination the oleate desaturation in the cotyledonary ER is rapidly derepressed. These data are supported by enzymatic experiments. In microsomes from maturing fruits o f the high oleic variety oleoyl-phosphatidylcholine desaturase could not be detected, whereas oleoyl-C oA : lyso-phosphatidylcholine acyltransferase and components o f the microsomal electron transport chains were not affected. A correlation in the expression o f desaturation blocks in seed and root fatty acids as observed in mutants o f other species was not observed which, therefore, cannot be generalized. Our data are discussed in terms o f the existence o f two ER-specific oleate desaturase activities.