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Seiler, G.L. 2002. Potential source of reduced palmitic and stearic fatty acids in sunflower oil from a population of wild Helianthus annuus. p. 150152. In: J. Janick and A. Whipkey (eds.), Trends in new crops and new uses. ASHS Press, Alexandria, VA.
In recent years consumers have become more concerned about the consumption of saturated fats in their diet. High levels of saturated fat consumption may contribute to increased blood serum cholesterol, and high blood serum cholesterol increases the risk of coronary heart disease (Mensink et al. 1994; Willett 1994). Prompted by nutritional recommendations to consume fats lower in saturates and food manufacturers interest in reducing the use of hydrogenated oil, food processors are interested in sunflower oil with specific fatty acid profiles (Fitch-Haumann 1994). Vegetable oils are the principal source of fats in many diets. Compared to other edible vegetable oils, the saturated fatty acid concentration in sunflower (Helianthus annuus L., Asteraceae) oil of 120 g kg-1 is considered moderate, with the principal saturated fatty acids being palmitic (65 g kg-1) and stearic (45 g kg-1) acids. Rapeseed (Brassica napus L.) oil has only 40 g kg-1 of palmitic and 20 g kg-1 stearic acids which is considered low in saturated fats. A reduction of saturated fatty acids in sunflower oil to the 60 to 80 g kg-1 level would increase the acceptability of sunflower oil as a healthier edible oil.
The genus Helianthus contains 50 species, 36 perennial and 14 annual (Schilling and Heiser 1981). Wild species of the genus have been utilized to improve economic and agronomic characteristics of cultivated sunflower (Seiler 1992; Seiler and Rieseberg 1997). Considerable emphasis has been placed on oil concentration and fatty acid composition of the oil. Interest has centered on the enhancement of linoleic or oleic fatty acids, and the reduction of saturated palmitic and stearic fatty acids. Wild sunflower species serve as a resource for improving fatty acid composition in cultivated sunflower (Dorrell and Whelan 1978; Thompson et al. 1981; Seiler 1985, 1994). Accessions of wild sunflower species with lower saturated palmitic and stearic acids have been identified (Seiler 1998), but their stability and transfer into cultivated sunflower have not been documented.
This study evaluated populations of wild annual H. annuus, the closest relative of cultivated sunflower, for lower palmitic and stearic acids, to determine their stability and to explore the possibility of introgressing the lower saturated fatty acid genes into cultivated sunflower.
Achenes of 86 populations of H. annuus were collected from the central Great Plains of the US (Seiler 1994). Achenes were stored at 5°C and low humidity (<40%) until analyzed. Each sample represented an isolated open-pollinated population, usually having achenes collected from at least 25 plants.
Fatty acid composition of achene oil of the wild populations was determined on a composite of 20 achenes. For F1, F2 and BC1F1 interspecific hybrids, 10-achene samples were used for analysis. A small portion of pulverized sample (10 to 20 mg) was transferred to a disposable filter column and eluted with 3.5 ml of diethyl ether. The oil in the diethyl ether solution was converted to methyl esters using an organic base-catalyzed transesterification of the triacylglycerol by the addition of 200 ml of tetramethylammonium hydroxide (10% in methanol), followed by vortexing (Metcalfe and Wang 1981). After 30 minutes, water was gently added to the reaction mixture, and the upper diethyl ether layer was transferred to a glass vial and capped. The sample was injected into a Hewlett-Packard 58901 gas chromatograph containing a DB-23 capillary column (25 m × 0.25 mm, J&W Scientific1). The detection was a flame ionization detector (FID). The fatty acid standard (15a, NU-CHEK-PREP, INC.1) contained the following acids: palmitic (C16:0), stearic (18:0), oleic (C18:1), linoleic (C18:2), linolenic (C18:3), and arachidic (C20:0). Fatty acid peaks were identified by comparing the fatty acid methyl ester peaks and retention times of standards with sample peaks. Fatty acid concentrations were determined in two samples per population.
The stability of the lower saturated fatty acids for a selected population of wild H. annuus (ANN-2229, PI 586886) was evaluated by growing the plants of the original population in a common environment (greenhouse) to see if the low levels of saturated fatty acids observed in the population from its native habitat were expressed in the progeny.
Interspecific F1 hybrids were produced in the field using a nuclear male-sterile analogue of NMS HA89 as the female parent and the wild H. annuus population (ANN-2229) as the male parent. Pollen from the F1 plants was used to backcross to NMS HA89 to produce BC1F1 progeny. The nuclear male-fertile analogue of NMS HA89 was used as the check for normal levels of fatty acids for all generations.
The average palmitic and stearic fatty acid concentration of populations of H. annuus varied by state (Table 1). The lowest average stearic acid concentration was observed in populations from North Dakota with 23 g kg-1, while the highest was observed in populations from Illinois with 37 g kg-1. The lowest average palmitic acid concentration was observed in North Dakota with 41 g kg-1, while the highest was observed in Illinois with 65 g kg-1.
Table 1. Average palmitic and stearic fatty acids from several populations of wild H. annuus from natural habitats in the US.
|Content (g kg-1)||Total palmitic and
|Stearic acid||Palmitic acid|
Of the individual populations analyzed, a population of wild H. annuus (ANN-2229, PI 586886 from Holmquist, South Dakota, Day County, Long. 97.38°W and Lat. 45.21°N) had the lowest palmitic acid concentration with 39 g kg-1 and the lowest stearic acid concentration with 19 g kg-1, totaling 58 g kg-1 for both. This level is 50% lower than the level generally observed in oil of cultivated sunflower. This population was chosen to check the stability of the lower saturated fatty acids to see if the genes controlling these acids were dominant and if they could be transferred into cultivated sunflower.
Progeny of ANN-2229 were grown in the greenhouse at 22° to 25°C and 16 hr of daylight. The plants were sib-pollinated. The saturated fatty acids in achene oil of the population were very similar to the levels observed in the original population (Table 2).
Table 2. Comparison of palmitic and stearic fatty acids from ANN-2229 plants from the original habitat and those grown in a common environment in the greenhouse.
|Content (g kg-1)||Total palmitic and
|Palmitic acid||Stearic acid|
A standard cultivated line, HA 89, which was also grown in the greenhouse as a check had a palmitic acid concentration of 65 g kg-1 and a stearic acid concentration of 44 g kg-1, for a total of 109 g kg-1. The low levels of saturated fatty acids observed in the original population appear to be stable, indicating the lower levels of palmitic and stearic acids have a genetic base and the potential to be introgressed into cultivated sunflower.
The F1 achenes produced in the field had an average palmitic acid concentration of 39 g kg-1 and a stearic acid concentration of 21 g kg-1 in the oil. These values were the average of 20 F1 plants. The cultivated inbred line NMS HA 89 used to produce F1 hybrids averaged 61 g kg-1 palmitic and 51 g kg-1 stearic fatty acids. F1 plants were self-pollinated to produce F2 seed, which was planted in the field. Achene oil of F2 plants averaged 41 g kg-1 palmitic acid and 18 g kg-1 stearic acid totaling 59 g kg-1 of saturated fatty acids. The averages are based on 19 individual plants.
In addition, F1 plants were backcrossed in the field with cultivated NMS HA89 as the female to produce BC1F1 plants. Achene oil of the BC1F1 plants averaged 38 g kg-1 palmitic acid and 19 g kg-1 stearic acid. These values were based on 40 observations from four different backcross families. In comparison, the cultivated NMS HA 89 line averaged 65 g kg-1 of palmitic acid and 42 g kg-1 of stearic acid.
Preliminary results indicate that palmitic and stearic acid levels in sunflower oil can be lowered by introgressing genes from a population of the closest wild relative of the cultivated crop. The genes appear to be relatively stable after transfer. Further research will be needed to study the inheritance of the genes controlling palmitic and stearic fatty acids and their relationship to other important traits. Acceptable agronomic traits will also have to be bred into the lines and monitored during the introduction of the genes into cultivated sunflower.