The synthesis of linoleate and phosphatidic acid and its relationship to oil production in the microsomes of developing seeds of safflower ( Carthamus tinctorius, L. var. Gila)

Abstract

Microsomes from the developing cotyledons of safflower seeds (var. Gila) were incubated, under desaturating conditions, with [1- 14C]oleoyl-CoA in the presence of glycerol 3-phosphate. The mass and specific radioactivity of oleate and linoleate in acyl-CoA, phosphatidylcholine and phosphatidic acid showed that (i) the oleate in oleoyl-CoA was selectively transferred to position 2 of phosphatidylcholine by acyl exchange where it underwent desaturation to linoleate; (ii) the newly formed linoleate was returned by further acyl exchange, to the acyl-CoA pool from which it was selectively utilised in the acylation of glycerol 3-phosphate to yield phosphatidic acid, a precursor of triacylglycerol. The results confirm that acyl exchange between acyl-CoA and phosphatidylcholine plays a major role in regulating the quality of C18 unsaturated fatty acids in the acyl-CoA pool for oil synthesis.