Genetic Control of Fatty Acid

Isolation of rapeseed plants containing no erucie acid in their seed oil gave simultaneous selection for low eieosenoic acid. Genetic analysis of populations segregating for erueie acid content indicated that the synthesis of these fa t ty acids was controlled, in the developing embryo, by two genes which displayed no dominance and acted in an additive manner. As the genetic capacity for crucie acid synthesis decreased, there was an increase in percentage of oleic acid with no corresponding decrease in total oil content. The percentage of eicosenoic acid remained relatively constant with decreasing erucie acid except in the zero erucie acid genotype where only 1% eieosenoie was detected instead of approx 12%. These observations were interpreted to mean that eicosenoic and erueie acids were formed by a genetically controlled carbon chain lengthening system operating by the addition of acetate moleeules to the carboxyl end of oleic acid. This hypothesis was supported by data obtained from the injection of radioactive sodium acetate into immature rapeseed pods. In the monoene fraction of the oil, eieosenoate had three times the speeifie activity of oleate and erucate had twice the activity of eieosenoate. On oxidation, the monoearboxylie fragments of these three acids had low and similar specific activities while in the diearboxylic acids, where chain elongation has presumably taken place, activity increased in the ratio of 1:5:19.