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a USDA-ARS, Crop Production and Pest Control Research and Dep. of Agronomy, Purdue Univ., W. Lafayette, IN 47907-1150
b Prof. Emeritus, Dep. of Agronomy, Iowa State Univ., Ames, IA 50011-1010
Corresponding author (jwilcox{at}purdue.edu)
| ABSTRACT |
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, total carbohydrates
, and sucrose
. Sulfur increased with increasing protein
, but S/N ratios were constant across protein concentrations. Decreases in carbohydrates with increases in protein would contribute to increased nutritional value of the meal from these breeding lines. The consistent S/N ratio across the range of seed protein concentrations indicates that S-containing amino acids were not sacrificed with increases in seed protein.
Abbreviations: *, ** Significant at the 0.05 and 0.01 probability levels, respectively
| INTRODUCTION |
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Krober and Cartter (1962) evaluated seed compositional traits of soybean strains either very high or very low in seed protein concentration. Nonprotein constituents of seed of high protein samples, averaging 483 g kg-1 seed protein, on a dry seed basis, decreased by one-third for sugars, one-third for oil, and one-third for holocelluloses and pentosans, compared with samples averaging 391 g kg-1 seed protein. Among low protein samples, averaging 318 g kg-1 protein, oil increased from one-half to one-third, and holocellulose and pentosans increased about one-third compared with samples averaging 391 g kg-1 protein.
Hymowitz et al. (1972) evaluated oligosaccharides in 60 plant introductions that varied widely in seed protein and oil. They reported ranges of 2.5 to 8.2 g for sucrose, 0.1 to 0.9 g for raffinose, and 1.4 to 4.1 g for stachyose per 100 g seed. They observed a positive relationship between stachyose and seed protein
that they felt would pose difficulties for the soybean breeder who wanted to reduce stachyose content of the seed while maintaining high seed protein.
Hartwig et al. (1997) measured quantities of raffinose, stachyose, and sucrose among 20 soybean lines high in oil and among 20 breeding lines high in protein. Correlation coefficients between stachyose + raffinose and protein of
, and oil
, were not significant. In contrast, there was a strong inverse relationship between sucrose and protein
and a positive relationship between sucrose and oil
among all lines combined across the two groups. These relationships demonstrated the feasibility of developing soybean germplasm with high seed protein and low stachyose + raffinose in the meal.
The nutritional value of soybean meal could be improved by increasing amounts of the S-containing amino acids, methionine and cysteine. Soy protein is deficient in these amino acids and must be supplemented with other protein sources, or with synthetic methionine, when soy meal is used as the primary source of protein for humans and for monogastric animals. Glycinin (11S) and ß-conglycinin (7S) are the two main classes of multisubunit seed storage proteins and account for
70% of total soybean seed protein (Meinke et al., 1981). Glycinin is a well-balanced protein with 3.0 to 4.5% of its amino acid residues consisting of cysteine and methionine (Nielsen et al., 1989; Fukushima, 1991), but ß-conglycinin is very deficient in S-amino acids. Only 1% of its amino acid residues contain S (Harada et al., 1989; Sebastiani et al., 1990), with one of its three subunits, the ß-subunit, having no S-amino acids at all (Coates et al., 1985). In hydroponic nutrition studies in which `Harper' soybean was grown on various compositions of N during seed filling, Paek et al. (1997) learned that total protein concentration of seed could be increased 4.5 to 5.0%, from 369 to 420 g kg-1 in one experimental run and from 410 to 455 g kg-1 in the second, by substitution of NH3N for NO3 in the growth medium. Storage proteins were increased by
4% in both runs, but the increase in storage protein was entirely because of an increase in ß-conglycinin, in particular of the S-devoid, ß-subunit of ß-conglycinin. Thus, protein quality declined with increases in protein concentration. Paek et al. (1997) concluded that breeding efforts to improve soybean seed protein should not focus entirely on concentration. Potentially, soy protein quality could decline as lines with greater protein concentration are developed.
Information reported to date compares quantities of oligosaccharides among groups of soybean lines that differ widely in seed protein and oil concentration. The objective of this study was to determine the interrelationships among seed protein, oil, oligosaccharides, and S among random progenies from a cross between parents that differed in seed protein and oil.
| MATERIALS AND METHODS |
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A 25 g sample of seed from each replication at each environment was analyzed for seed protein, oil, total carbohydrate, and stachyose + raffinose by near-infrared reflectance at the National Center for Agricultural Utilization Research at Peoria, IL. Sucrose was determined as total carbohydrate minus raffinose + stachyose. Near-infrared reflectance spectroscopy is a demonstrated effective method of determining concentrations of sugar in plant materials (Giangiacomo et al., 1981; W. Rayford, USDA-ARS, 1999, personal communication). Sulfur was determined by inductively-coupled plasma emission spectrometry as described in Sexton et al. (1998).
Analyses of variance were computed on the data in which lines were considered random and environments fixed. Regression analyses were computed to evaluate relationships among specific traits.
| RESULTS AND DISCUSSION |
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No relationships were found between concentrations of any of the carbohydrates and seed yield in this population (Table 3). These data indicate that concentrations of either total or component carbohydrates could be altered without affecting seed yield. Carbohydrates in the seed decreased as protein increased, with the greatest decrease in sucrose (Fig. 1
, Table 3). Increases in protein among these lines occurred at the expense of both oil and carbohydrates. Conversely, total carbohydrates
and sucrose
increased with increases in seed oil (Table 3). This is consistent with the strong inverse relationship between protein and oil among these lines.
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associated with the decrease in protein with increasing oil content. Radford et al. (1977) reported close relationships between percentage S and mg of methionine
, mg cysteine
, and mg of methionine plus cysteine
for 13 lines of G. max and G. soja (Sieb. and Zucc.).
The ratio of S/N was regressed on seed protein to determine if the amount of S in the protein increased with increasing seed protein concentration. This would be indicative of higher amounts of S-containing amino acids, relative to other amino acids, as protein increased. No relationship was observed between the S/N ratio and seed protein
. This indicated that the amount of S-containing amino acids was relatively constant regardless of the amount of protein in the seed of these breeding lines. Burton et al. (1982) reported no significant changes in methionine among cycles of recurrent selection for high protein where protein increased from 438 in Cycle 0 to 474 g kg-1 in Cycle 6 in one population and from 450 in Cycle 0 to 472 g kg-1 in Cycle 4 in a second population. In contrast, Krober and Cartter (1966) reported a positive association between percentage methionine in the protein and percentage protein in the seed
among 12 soybean strains that varied from 390 to 480 g kg-1 seed protein.
Paek et al. (1997) found the proportion of S-poor protein to increase as protein concentration increased in a nutrition study with Harper soybean, so that protein quality declined as protein concentration increased. This suggested that it may be difficult to maintain protein quality when breeding for increased seed protein concentration. In the population of breeding lines reported in this study, soybean S assimilation was adequate to maintain S-amino acid level across a wide range of protein concentrations, as indicated by a constant S/N ratio with protein concentration. We caution, however, that seed yields were not high in this population, ranging from 2000 to 2600 kg ha-1. Thus, there still remains a question whether S-amino acid concentration can be maintained while breeding for high protein concentration and simultaneously maintaining yields of
4000 kg ha-1.
The data demonstrated that increases in seed protein in this population were at the expense of both oil and carbohydrates, particularly sucrose. The decreases in seed carbohydrates with increasing seed protein would contribute to increased nutritional value of the meal. A consistent ratio of S/N across the range of seed protein among these breeding lines indicated that S-containing amino acids were not sacrificed with increases in seed protein.
| ACKNOWLEDGMENTS |
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| NOTES |
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Received for publication December 3, 1999.
| REFERENCES |
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subunit of soybean ß-conglycinin. Plant Mol. Biol. 15:197201.[Medline]This article has been cited by other articles:
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