Involvement of Phospholipids in Polyunsaturated Fatty Acid Synthesis in Developing Soybean Cotyledons

Abstract

Developing soybean (cv. Dare) cotyledons harvested at 30 days after flowering were pulse-labeled with II-'4Cloleoyl-CoA. The metabolic interrelation of radiolabeled unsaturated fatty acids between the major glycerolipid classes was determined at various time intervals. At chase time zero, 1I4CIoleic acid accounted for 99.2% of the total glycerolipid radioactivity, and phospholipids contained 92% of the total incorporated radioactivity. With time, phospholipids were metabolized in triacylglycerol biosynthesis and radioactivity was detected in polyunsaturated fatty acids. The hypothesis that phospholipids were metabolc intermediates in polyunsaturated fatty acid biosynthesis was tested by comparing the theoretical and the actual amount of radiolabeled oleic acid that was associated with triacylglycerol as a function of time. The radioactive oleic acid found in triacylglycerol at various intervals was derived from phospholipids via a diacylglycerol intermediate. Assuming no phospholipid desaturation, the potential or theoretical amounts of 1j4Cjoleic acid that could be transferred to triacylglycerol from phospholipids was defined by a system of differential equations. The results demonstrated that the decline in 114CIoleic acid from phospholipid after long chase intervals was equal to the total amount of radioactive unsaturated fatty acids found in neutral lipids. The difference between the theoretical and actual amounts of It4CIoleic acid present in triacylglycerol after long time intervals was equal to the amount of radioactivity present in polyunsaturated fatty acids. Based upon those findings in soybeans, the desaturation of oleic acid associated with phospholipids was highly probable.For the past decade, the mechanism of polyunsaturated fatty acid biosynthesis in plant tissues has been a subject for debate. An important issue of that debate has been the nature of the substrate for the 18:12 desaturase system. In one opinion, the thio-ester theory, the reaction, was described as a consecutive desaturation of 18:l-CoA to form 18:2-CoA and 18:3-CoA, which occurred before any of the unsaturated fatty acids were incorporated into

Fatty Acid Distribution in Polar and Nonpolar Lipid Classes of Hazelnut Oil (Corylus avellana L.)

“…SFA and PUFA follow the opposite trend to MUFA. Although there is no evident explanation for this, some authors have suggested that polar lipids such as glucolipids and phospholipids are substrates for fatty acid desaturases in oilseeds, which are responsible for MUFA and PUFA biosynthesis in oilseeds (Andrews and Heinz, 1987;Heinz, 1990, 1993;Slack et al, 1979;Stymme and Appleqvist, 1978;Wilson et al, 1980). On this basis we could expect the negative correlation coefficient found between mono-and polyunsaturated fatty acid contents.…”

Metabolic mechanisms associated with alleles governing the 16:0 concentration of soybean oil

“…TPL also has been shown to be the most metabolically active glycerolipid fraction in developing soybean cotyledons (27), therefore, genotypic differences in endogenous 16:0 incorporation in TPL at 35 DAF should provide metabolic indicators of fap allele function. In vivo saturation kinetics of exogenous acetate metabolism in developing seed at 35 DAF were used to test this hypothesis.…”

Correlation between seed size, protein and oil contents, and fatty acid composition in soybean genotypes

“…Current biochemical evidence indicates that in soybeans and in several other plant species the polyunsaturated fatty acids (18:2 and 18:3) are produced by the consecutive desaturation of 18:1 (Wilson et al, 1980). Liu et al (1995) have suggested that genes encoding enzymes responsible for desaturation of oleoyl-phosphatidylcholine (PC) to linoleoyl-PC and further to linolenoyl-PC are related not only to each other but also to genes controlling seed size.…”