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CROP BREEDING, GENETICS & CYTOLOGY

A fap5 Allele for Elevated Palmitate in Soybean

Dep. of Food Science and Human Nutrition, Iowa State Univ., Ames, IA 50011 USA

wfehr{at}iastate.edu

	ABSTRACT

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results and discussion REFERENCES

 
Soybean [Glycine max (L.) Merr.] oil with elevated palmitate content may be useful for producing plastic fats without hydrogenation. The mutant line A27, with 160 g kg^-1 palmitate, was developed by treatment of seeds of `Kenwood' with ethyl methanesulfonate. The objective of this study was to determine the genetic control of elevated palmitate content in A27. A27 was crossed to Kenwood and to lines possessing the fap1, fap2-b, fap3, fap4, or fap6 alleles for altered palmitate. Analysis of the F₁, F₂, and F₃ generations indicated that A27 had an allele for elevated palmitate at a single locus, designated fap5, that exhibited additive gene action with Fap5 and mutant alleles for altered palmitate content. The fap5 locus was independent of the fap1, fap3, fap4, and fap6 loci, but closely linked to the fap2-b locus.

	INTRODUCTION

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results and discussion REFERENCES

 
THE PALMITATE CONTENT of soybean oil can influence its physical properties and usefulness for food and industrial applications. Soybean oil with 250 g kg^-1 palmitate has an increased melting point and higher oxidative stability than conventional oil with 110 g kg^-1 palmitate (Shen et al., 1997). Food manufacturers utilize hydrogenation to produce plastic fats from conventional soybean oil. Hydrogenation produces trans-fatty esters that may have harmful effects on human health (Hu et al., 1997). Soybean oil with elevated levels of palmitate may be useful for plastic fat production without hydrogenation (Kok et al., 1999).

Palmitate content of soybean oil has been altered by major alleles developed by chemical mutagenesis. The fap1 and fap3 alleles reduce palmitate (70 g kg^-1) and the fap2, fap2-b, fap4, and fap6 alleles elevate palmitate (170–200 g kg^-1) (Erickson et al., 1988; Fehr et al., 1991a,b; Schnebly et al., 1994; Narvel et al., 2000). A mutant line A27 with 160 g kg^-1 palmitate was developed as an M₄ plant selection from treatment of seeds of Kenwood with ethyl methanesulfonate. The objective of this study was to determine the inheritance of elevated palmitate in A27.

	Materials and methods

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results and discussion REFERENCES

 
A27 was crossed to lines containing mutant alleles for altered palmitate content. C1726 has the fap1 allele and A22 the fap3 allele for reduced palmitate. A21 has the fap2-b allele, A24 the fap4 allele, and A25 the fap6 allele for elevated palmitate. Crosses were made at the Agricultural Engineering and Agronomy Research Center near Ames, IA, during 1996. Reciprocal crosses were made between A27 and its parent Kenwood to test for maternal effects and dominance. The identity of the F₁ and selfed seed from each plant used as female was maintained at harvest. Individual plants used as male were harvested separately.

The F₁ and parent seeds were analyzed for palmitate content in a randomized complete-block design with each block consisting of a hybrid seed and a selfed seed from each parent (Table 1) . Each seed was cut into two portions with a razor blade. The one-third portion of the seed that lacked the embryonic axis was used for fatty ester analysis. Fatty ester content was measured by gas chromatography as described by Hammond (1991).

The evaluation of segregation in each cross was based on the mean palmitate content ± two standard deviations (2SD) of the seed from the parents grown in the same environment. Seed with a palmitate content ± 2SD of a parent were considered equal to that parent. Seed outside ± 2SD of the parents were placed in phenotypic classes appropriate to the cross. The F₂ split seeds for the A27 x Kenwood cross were categorized as: =Kenwood; >Kenwood to <A27; and = A27. If there was only one allele for elevated palmitate with no dominance, a 1:2:1 ratio would be expected for the three classes. The F₂ seeds for the reduced palmitate x A27 crosses were categorized as = P1; >P1 to <A27; and = A27. If the alleles for altered palmitate were at two independent loci with no dominance, a 1:14:1 ratio would be expected for the three phenotypic classes. The genotypes for the three phenotypic classes are provided in Tables 3 and 4 . The F₂ seeds for the elevated palmitate x A27 crosses were categorized as < Parents (P); =P; and >P. If the alleles for elevated palmitate were at two independent loci and had no dominance, a 5:6:5 ratio would be expected. The F₂ seeds <P would have at least three alleles for normal palmitate, seeds =P would have two alleles for normal palmitate, and seeds >P would have one or no alleles for normal palmitate (Tables 5 to 7) .

	Results and discussion

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results and discussion REFERENCES

 
The F₁ seeds from the reciprocal cross between A27 and Kenwood did not have the palmitate contents that would be expected if maternal effects were expressed (Table 1). The mean palmitate content of F₁ seeds obtained on Kenwood plants was higher than that of F₁ seeds obtained on A27, even though selfed seeds of Kenwood had lower palmitate than A27. If maternal effects were expressed, the F₁ seeds obtained on Kenwood should have had lower palmitate than those obtained on A27. It was concluded that the difference between the reciprocal crosses was due to experimental error and that no maternal effects were present. The mutant allele in A27 exhibited primarily additive gene action for palmitate content in all of the crosses (Table 1). For those crosses in which differences between the F₁ and midparent were statistically significant, the deviation from the additive model did not exceed 7 g kg^-1. The absence of maternal effects and of dominance would facilitate selection for palmitate content among individual seeds of a segregating population in a cultivar development program.

The F₂ seeds from the reciprocal crosses between A27 and Kenwood were combined for data analysis because of the absence of maternal effects for palmitate content. The segregation among the F₂ seeds satisfactorily fit a 1:2:1 ratio (Table 2). In the progeny test of F₃ seed from 50 random F₂ plants, 13 plants were homozygous for the palmitate of A27, 10 were homozygous for the palmitate of Kenwood, and 27 were heterozygous. The progeny test data satisfactorily fit the 1:2:1 ratio (² = 0.68, P > 0.50) that would be expected for two alleles at a locus with additive gene action. The allele in A27 was given the designation fap5 on the basis of the analysis of the other crosses in the study.

The F₂ seeds from the cross of C1726 (fap1) with A27 satisfactorily fit the 1:14:1 ratio for additive alleles at two independent loci (Table 2). Although the F₂ plants failed to fit the 1:4:2:4:4:1 model, there was little deviation between the observed and expected frequencies for the parental types (Table 3). On the basis of the satisfactory fit of the F₂ seeds to the 1:14:1 ratio and the close fit between observed and expected frequencies for the parental types, the fap1 and fap5 alleles were considered to be at independent loci.

For the cross of A22 (fap3) with A27, the F₂ seeds did not satisfactorily fit the 1:14:1 ratio that would be expected for additive alleles at independent loci, and the F₂ plants that were progeny tested failed to satisfactorily fit the 1:4:2:4:4:1 model (Tables 2 and 4). Nevertheless, the transgressive segregation observed for the F₂ seeds and plants indicated that the alleles for elevated palmitate in the two parents were not at the same locus. If the loci were linked, the number of F₂ plants that were homozygous for the palmitate of A22 or A27 should have exceeded the expected values for the two genotypes. None of the 50 F₂ plants were homozygous for the palmitate of A22 and two were homozygous for the palmitate of A27, which indicated that the fap3 and fap5 alleles were at independent loci. The lower than expected frequency of homozygous F₂ plants for the A22 and A27 phenotypes was attributed to the difficulty in obtaining 11 random seeds from a plant that all were within ± 2SD of one of the parents because of environmental effects on the traits.

In the F₂ seed analysis of the A21 (fap2-b) cross with A27, only four transgressive segregates were observed, compared with the 112 expected for the additive alleles for elevated palmitate at independent loci (Table 2). Only one of the 50 random F₂ plants was homozygous for palmitate content less than either parent and none were homozygous for palmitate greater than either parent based on F₃ seed analysis (Table 5). To further evaluate the cross, 1005 additional F₂ seeds were split and analyzed for palmitate content. There were 15 seeds less than either parent and 31 greater than either parent. In the progeny test of the 46 transgressive segregates, only three were homozygous for palmitate less than either parent and one was homozygous for palmitate greater than either parent. These data indicated that the fap5 allele in A27 was closely linked to the fap2-b locus in A21.

The segregation of F₂ seed from the cross of A24 (fap4) and A27 satisfactorily fit the 5:6:5 ratio that would be expected for additive alleles for elevated palmitate at independent loci (Table 2). The progeny test of the 50 random F₂ plants satisfactorily fit the 1:4:2:4:4:1 ratio (Table 6). The fap5 allele in A27 was considered to be independent of the fap4 locus in A24.

For the cross of A25 (fap6) with A27, the segregation of the F₂ seeds satisfactorily fit the 5:6:5 ratio and the 50 random F₂ plants satisfactorily fit the 1:4:2:4:4:1 ratio (Tables 2 and 7). These results indicated that the fap5 allele in A27 was independent of the fap6 locus in A25.

The fap5 allele in A27 will be a useful resource for manipulating the palmitate content of soybean oil. By combining the fap2-b, fap4, and fap5 alleles, palmitate contents > 300 g kg^-1 have been achieved. Further increases may be possible by combining additional alleles that control palmitate content.

	NOTES

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results and discussion REFERENCES

 
Journal Paper No. J-18381 of the Iowa Agric. and Home Econ. Exp. Stn., Ames; Projects No. 2799 and 3107.

Received for publication May 18, 1999.

	REFERENCES

TOP NOTES ABSTRACT INTRODUCTION Materials and methods Results and discussion REFERENCES

 

• Erickson E.A., Wilcox J.R., Cavins J.F. Inheritance of altered palmitic acid percentages in two soybean mutants. J. Hered. 1988;79:465-468.[Abstract/Free Full Text]
• Fehr W.R., Welke G.A., Hammond E.G., Duvick D.N., Cianzio S.R. Inheritance of reduced palmitic acid content in seed oil of soybean. Crop Sci. 1991;31:88-89 a.
• Fehr W.R., Welke G.A., Hammond E.G., Duvick D.N., Cianzio S.R. Inheritance of elevated palmitic acid content in soybean seed oil. Crop Sci. 1991;31:1522-1524 b.[Abstract/Free Full Text]
• Hammond E.G. Organization of rapid analysis of lipids in many individual plants. In: Linskens H.F., Jackson J.F., eds. Modern methods of plant analysis. Vol. 12. Berlin: Springer-Verlag, 1991:321-330.
• Hu F.B., Stampfer M.J., Manson J.E., Rimm E., Colditz G.A., Rosner B.A., Hennekens C.H., Willett W.C. Dietary fat intake and the risk of coronary heart disease in women. N. Eng. J. Med. 1997;337:1491-1499.[Abstract/Free Full Text]
• Kok L.L., Fehr W.R., Hammond E.G., White P.J. Trans-free margarine from highly saturated soybean oil. J. Am. Oil Chem. Soc. 1999;76:1175-1181.[ISI]
• Narvel J.M., Fehr W.R., Ininda J., Welke G.A., Hammond E.G., Duvick D.N., Cianzio S.R. Inheritance of elevated palmitate in soybean seed oil. Crop Sci. 2000;40:635-639 (this issue).[Abstract/Free Full Text]
• Schnebly S.R., Fehr W.R., Welke G.A., Hammond E.G., Duvick D.N. Inheritance of reduced and elevated palmitate in mutant lines of soybean. Crop Sci. 1994;34:829-833.[Abstract/Free Full Text]
• Shen N., Fehr W., Johnson L., White P. Oxidative stabilities of soybean oils with elevated palmitate and reduced linolenate contents. J. Am. Oil Chem. Soc. 1997;74:299-302.[ISI]

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