Amino Acid Composition of Selected Strains of Diploid Wheat,

Cereal Chem. 72(2):213-216 Diploid wheat (Triticum monococcum L., einkorn) is of interest both species of wheat and among diploid wheat strains were minimal, especially as a crop and as a source of genes unavailable in the more widely grown after amino acid values were adjusted to a common protein level. One wheat species, T. aestivum L. (common wheat) and T. durum Desf. (durum of the einkorn accessions examined, however, presented a deviant amino wheat). The biochemical constituents of its seeds, however, have been acid profile. This strain may be of use for investigating the biosynthetic investigated very little. In this study, 15 strains of T. monococcum and pathway of wheat proteins. Among einkorns, correlations between grain two modern cultivars of common wheat and durum wheat were compared protein content and amino acid values were positive for glutamine and with regard to grain protein content and amino acid composition of seed proline and negative for threonine, 1/2 cystine, valine, isoleucine, leucine, proteins. Differences in amino acid composition between these three asparagine, serine, glycine, and alanine. Diploid wheat (Triticum monococcum L., einkorn) was one of mankind's earliest plant domesticates and probably also the donor of the A genome to common wheat (T. aestivum L., genome AABBDD) and durum wheat (T. durum Desf., genome AABB) (Feldman 1976, Kerby and Kuspira 1988). At present, this ancient wheat is cultivated only in marginal farmlands of Yugoslavia, Turkey, and Italy (Vallega 1992, Ohta and Furuta 1993). However, recent reports suggest that it may still play a significant role in modern agriculture, both as a source of useful genes (Multani et al 1989) and as a crop in its own right (Vallega 1979, 1992; Waines 1983; Multani et al 1992; D'Egidio et al 1993). T. monococcum appears especially valuable for detecting recessive endosperm mutants (for high lysine, high amylose, etc.) already identified in diploid cereals such as maize and barley but as yet unavailable in the polyploid wheat taxa (Vallega 1977, 1978). Detection of such genes is expected to widen the scope of utilization of all the cultivable Triticum species and to enhance their nutritional value (Vallega 1978, Waines 1983, D'Egidio et al 1993). Einkorn has been surveyed for a number of agrobiological and technological characteristics (The 1975; Vallega 1978, 1979, 1992; Sharma et al 1981; Multani et al 1989; D'Egidio et al 1993; D'Egidio and Vallega 1994) as well as with respect to variation in grain protein and grain lysine content (Johnson and Mattern 1975; Vallega 1977, 1978; Sharma et al 1981; Blanco et al 1990), flour /3-carotene content (D'Egidio et al 1993), and electrophoretical patterns of seed proteins (Waines and Payne 1987, Galili et al 1988). Data on the amino acid composition of einkorn's seed proteins have not been published. The grain proteins of common wheat and durum wheat are notoriously rich in glutamine and proline, but low in amino acids considered essential for the human diet: especially lysine and threonine, possibly also tryptophan, methionine, and isoleucine (Wrigley and Bietz 1987). In these wheat species, as in other cereals, variation in amino acid composition is limited and very closely correlated with variation in grain protein percentage (Johnson and Mattern 1975; Mosse et al 1985, 1988; Martin del Molino et al 1989). Increases in grain protein percentage are normally accompanied by lower levels of lysine and other essential amino acids (EAA) per unit protein (Johnson and Mattern 1975, Mosse et al 1985). Major genes capable of substantially altering the nutritional adequacy of wheat proteins have been sought without 'Istituto Nazionale della Nutrizione, Via Ardeatina 546-00179 Rome, Italy. 2 Istituto Sperimentale per la Cerealicoltura, Via Cassia 176-00191 Rome, Italy. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. American Association of Cereal Chemists, Inc., 1995. success in various Triticum species, including monococcum (Johnson and Mattern 1975; Vallega 1977, 1978; Sharma et al 1981). The main goals of the present work were to determine the amino acid composition of T. monococcum's grain proteins, examine its relationship with grain protein percentage, and seek diploid wheats with a more balanced amino acid composition. MATERIALS AND METHODS The wheats examined comprised a free-threshing diploid wheat strain (T. monococcum ssp. sinskajae Filat. et Kurk., accession WIR 48993), 14 tenacious-glumed einkorns (T. monococcum ssp. monococcum), and two modern cultivars of bread wheat (cv. Centauro) and durum wheat (cv. Latino). Diploid wheat accessions were chosen on the basis of some favorable agronomical characteristic (Vallega 1992) and included strains with reportedly disparate grain protein contents (Johnson and Mattern 1975, Sharma et al 1981). Diploid and polyploid wheat entries were grown together in a field trial near Rome during 1988-89 in 10-IM plots distributed according to a completely randomized block design with three replicates. Data on their agronomical performance (Vallega 1991, 1992) and on their rheological and technological properties (D'Egidio et al 1993, D'Egidio and Vallega 1994) were presented elsewhere. All entries were threshed mechanically, and residual invested einkorn seeds were dehulled by hand. Samples for amino acid determinations were obtained by mixing 3 g of clean seed from each of three replicates. Grains were ground with a 0.129-mm sieve Cyclotec mill (Tecator, Hoganas, Sweden). Protein content of meals was determined by the Kjeldahl method (% N X 5.7 dm). Hydrolyzates were prepared according to the procedure described by Satterlee et al (1982), using 250-mg meal subsamples. Meals were dispersed in 25 ml of 6N HCl for 24 or 72 hr at 110°C under vacuum, and then derivatized with ninhydrin. Performic acid oxidation, followed by acid hydrolysis, was used for cystine-cysteine and methionine determinations. Amino acid analyses were made by ion-exchange chromatography on a Liquimat III Automatic Analyser (Kontron-Labotron, Munich, Germany) using a single column (30 cm X 4 mm i.d.) and an ion exchange Dionex DC-6A resin. Tryptophan was not determined. Results, expressed as grams of amino acid per 100 g of protein corrected to 100% recovery, are the average of three replicates. To permit direct comparisons between wheats with disparate grain protein contents, linear regression, as described by Steel and Torrie (1980), was utilized to adjust the amino acid composition of all entries to a common (16.7%) protein level. Only data collected on monococcums were used to compute regression equations. Outlying amino acid values were sought by the robust Vol. 72, No. 2,1995 213 statistical procedure described by Miller (1993), using computer software supplied by M. Mecozzi. RESULTS AND DISCUSSION Amino acid values and protein contents for the 17 wheats examined are given in Tables I and II. Grain protein content of einkorns (mean: 16.7% din) was extremely variable (from 14.1 to 25.2%). On average, about 3-4 percentage points higher than that recorded on cvs. Centauro and Latino. Despite this conspicuous protein content difference, the average amino acid composition of monococcum proteins was analogous to that of the two polyploid wheat controls and to that generally reported for common wheats and durums (Baroccio and Alessandroni 1978, TABLE I Amino Acid Composition' of Grain Proteins of Fifteen Diploid Wheats and Two Polyploid Wheats, Part 1 Thr Cys/2 Val Met lie Leu Tyr Phe Lys Diploid wheats Cl 13962 b 2.28 2.49 2.90 1.64 2.71 5.15 2.22 4.74 2.14 CI 13961 2.48 2.92 4.18 1.88 4.16 6.80 2.46 4.90 2.64 CI 13963 2.56 2.89 4.15 1.67 3.90 6.19 3.19 5.08 2.12 PI 167526 2.52 2.92 4.15 1.70 3.87 6.25 2.54 5.60 2.78 PI 290508 2.77 3.02 4.24 1.89 3.72 5.92 2.62 4.36 2.65 VV 319 2.71 2.73 4.29 1.71 3.75 6.12 2.93 5.06 2.73 WIR 8365 2.73 2.65 4.55 1.64 3.94 6.98 3.74 5.84 2.27 PI 277133 2.42 2.83 4.38 1.78 4.13 8.10 4.09 4.21 2.77 VV 281 2.70 2.99 4.02 2.00 3.65 5.95 2.65 4.14 2.63 WIR 48993 2.69 2.77 3.98 1.73 3.80 6.43 3.50 4.44 2.69 CI 2433 2.69 2.92 3.94 1.58 3.81 6.73 3.97 5.55 2.45 PI 277123 2.62 2.93 4.41 1.78 4.05 6.51 2.84 4.76 2.77 PI 277130 2.72 2.97 3.83 1.66 3.57 6.17 4.54 5.00 2.74 PI 221413 2.62 2.89 4.48 1.83 3.90 6.39 2.73 6.03 2.86 PI 306545 2.40 2.94 4.40 1.77 3.96 6.64 2.95 4.52 2.69 Mean (n = 15) 2.59 2.86 4.13 1.75 3.79 6.42 3.13 4.95 2.60 SEM .038 .037 .103 .029 .088 .166 .177 .152 .061 CVC 5.61 5.00 9.67 6.47 9.03 9.98 21.86 11.90 9.14 rd _0.573* -0.597* -0.732** -0.171 -0.662** -0.484 -0.506 -0.083 -0.642** Polyploid wheats Latino 2.91 2.99 4.45 1.89 3.65 6.70 3.02 4.75 2.85 Centauro 2.81 2.75 4.11 1.74 3.52 6.60 2.98 4.32 2.56 aGrams of amino acid per 100 g of protein corrected to 100% recovery, protein basis. bPrefixes WIR, CI or PI, and VV refer, respectively, to accessions from the N.I. Vavillov All-Union Institute of Plant Industries (Russia), the USDA Small Grains Collection, and the Cereal Research Institute (Italy). Coefficient of variation. dSimple correlation coefficients between amino acid values and protein content; * and ** are significant at the 0.05 and 0.01 probability level, respectively. TABLE II Amino Acid Composition'of Grain Proteins of Fifteen Diploid Wheats and Two Polyploid Wheats, Part 2 Protein EAAsb Asp Ser Glu Pro Gly Ala His Arg NH 3 % N Rec' % d.m. Diploid wheats Cl 13962d 26.27 3.88 3.57 35.40 15.94 2.74 2.66 2.91 4.18 2.48 116.40 25.17 CI 13961 32.42 4.66 4.07 34.42 9.04 3.08 3.02 2.16 3.96 3.17 106.33 18.86 CI 13963 31.75 4.40 4.07 34.49 10.86 2.90 2.92 2.17 3.65 2.79 109.46 18.72 PI 167526 32.33 5.40 3.95 32.30 9.01 3.43 3.26 2.21 4.98 3.13 106.21 18.12 PI 290508 31.19 5.38 4.13 33.35 9.81 3.38 3.34 2.26 4.28 2.88 106.03 17.03 VV 319 32.03 5.35 4.10 32.33 9.59 3.41 3.37 2.43 4.33 3.06 105.79 16.23 WIR 8365 34.34 4.60 3.96 27.79 10.31 3.26 3.58 2.83 6.73 2.60 107.51 16.12 PI 277133 34.71 5.32 3.78 28.97 10.47 3.37 3.36 2.38 4.57 3.07 110.14 16.02 VV 281 30.73 5.42 4.07 32.08 11.63 3.43 3.41 1.98 4.37 2.88 110.19 15.99 WIR 48993 32.03 5.54 4.44 32.03 9.62 3.26 3.32 2.17 4.21 3.38 106.89 15.36 CI 2433 33.64 5.31 4.02 31.28 9.96 3.22 3.20 2.18 3.99 3.20 110.78 15.23 PI 277123 32.67 5.48 4.36 31.58 9.15 3.41 3.32 2.42 4.38 3.23 102.43 14.48 PI 277130 33.20 5.23 4.00 28.36 9.77 3.28 3.21 2.33 5.73 4.89 111.09 14.16 PI 221413 33.73 5.85 3.93 30.27 9.01 3.74 3.46 2.23 4.77 3.01 103.91 14.12 PI 306545 32.27 5.53 4.01 30.62 10.66 3.42 3.28 2.39 4.38 3.44 102.22 14.05 Mean (n = 15) 32.22 5.16 4.03 31.68 10.32 3.29 3.25 2.34 4.57 3.15 107.69 16.66 SEM .513 .136 .053 .577 .447 .062 .059 .064 .199 .142 .964 .734 CVe 6.16 10.24 5.11 7.05 16.76 7.30 7.07 10.63 16.87 17.48 3.47 17.08 rf -0.788** -0.832** -0.554* 0.712** 0.743** -0.782** -0.794** 0.429 -0.267 -0.514* 0.627* Polyploid wheats Latino 33.21 4.92 4.41 28.70 11.50 3.61 3.53 2.30 4.70 3.10 100.34 13.42 Centauro 31.39 4.77 4.40 30.45 11.99 3.85 3.38 2.03 4.44 3.30 109.01 12.47 airam r1 amn cde0 g of prti corctdt 100% reoerprti basis 'Grams of amino acid per 100 g of protein corrected to lOO0o recovery, protein basis. bTotal essential amino acids. 'Percentage of nitrogen recovered by amino acid analysis. dPrefixes WIR, CI or PI, and VV refer, respectively, to accessions from the N.I. Vavillov All-Union Institute of Plant Industries (Russia), the USDA Small Grains Collection, and the Cereal Research Institute (Italy). 'Coefficient of variation. fSimple correlation coefficients between amino acid values and protein content; * and ** are significant at the 0.05 and 0.01 probability level, respectively. 214 CEREAL CHEMISTRY Wrigley and Bietz 1987, Martin del Molino et al 1989). Total EAA content was also nearly identical for diploid wheats (mean 32.2%) and for the two controls (mean 32.3%). Variation in amino acid values among monococcums was relatively low, except for tyrosine (CV 21.9%), arginine (CV 16.9%), and proline (CV 16.8%). Among these wheats, simple correlation coefficients between grain protein percentage and amino acid values (Table I) were mostly significant (P = 0.05); positive for glutamine and proline, and negative for threonine, 1/2 cystine, valine, isoleucine, lysine, asparagine, serine, glycine, alanine, amide, and total EAA content. Analogous correlations were reported for common wheat (Mosse et al 1985, Martin del Molino et al 1989). As might be expected, accession CI 13962, a low-yielding diploid wheat (Vallega 1992) with a grain protein as high as 25%, had a relatively low total EAA content (26.3%) and either the highest or lowest values for 13 of the 17 amino acids considered. Accessions PI 277133 and WIR 8365, on the contrary, exhibited relatively high values for both grain protein content (16.016.1 %) and total EAA content (34.1-34.4%). Fifteen of the amino acid values recorded on monococcums were classed as outliers; eight of these deviant TABLE III Amino Acid Composition' of Grain Proteins of Fifteen Diploid Wheats and Two Polyploid Wheats Adjusted to a Common Protein Level (16.7%), Part 1 Thr Cys/2 Val Met Ile Leu Tyr Phe Lys Diploid wheats CI 13962b 2.53 2.75 3.76 1.70 3.39 6.08 3.26 4.89 2.60 CI 13961 2.54 2.99 4.41 1.89 4.33 7.04 2.73 4.94 2.76 CI 13963 2.62 2.95 4.37 1.68 4.06 6.41 3.44 5.12 2.24 PI 167526 2.56 2.97 4.30 1.71 3.98 6.41 2.72 5.63 2.87 PI 290508 2.78 3.03 4.28 1.89 3.75 5.96 2.67 4.37 2.68 VV 319 2.69 2.72 4.25 1.71 3.71 6.07 2.88 5.05 2.71 WIR 8365 2.71 2.64 4.50 1.64 3.89 6.92 3.67 5.83 2.25 PI 277133 2.40 2.81 4.32 1.78 4.08 8.03 4.01 4.20 2.74 VV 281 2.68 2.97 3.96 1.99 3.59 5.88 2.57 4.13 2.60 WIR 48993 2.65 2.73 3.85 1.72 3.69 6.29 3.34 4.42 2.63 CI 2433 2.64 2.88 3.80 1.57 3.69 6.57 3.80 5.53 2.38 PI 277123 2.55 2.87 4.19 1.76 3.87 6.27 2.58 4.72 2.66 PI 277130 2.64 2.90 3.58 1.64 3.37 5.90 4.24 4.96 2.61 PI 221413 2.54 2.82 4.22 1.81 3.69 6.11 2.42 5.99 2.73 PI 306545 2.32 2.86 4.14 1.75 3.75 6.36 2.63 4.48 2.56 Mean (n = 15) 2.59 2.86 4.13 1.75 3.79 6.42 3.13 4.95 2.60 SEM .031 .029 .070 .028 .066 .145 .152 .152 .047 CVC 4.59 3.98 6.61 6.28 6.74 8.73 18.85 11.86 6.99