Structural and genetical studies on the high-molecular-weight subunits of wheat glutenin

Summary The genes controlling the synthesis of the high-molecular-weight subunits of glutenin on the long arms of chromosomes 1A and IB were mapped to the -gliadin genes on the short arms by analysing the progeny of three test crosses by sodium dodecyl sulphate, polyacrylamide-gel electrophoresis. Only very weak linkages were detected: the percentage recombination ranged from 39% to 47% and as the values did not significantly differ from each other, the data was pooled. A mean recombination of 43% was obtained and the map distance between glutenin and gliadin genes was calculated to be 66 cM. The analysis of three crosses involving telocentric lines revealed that the glutenin subunit genes on chromosomes 1A, IB and ID are tightly linked to the centromere, the mean map distance being 9.0 cM.     

Structural and genetical studies on the high-molecular-weight subunits of wheat glutenin

Summary The high-molecular-weight (HMW) subunits of glutenin from about 185 varieties were fractionated by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). About 20 different, major subunits were distinguished by this technique although each variety contained, with only a few exceptions, between 3 and 5 subunits. Further inter-varietal substitution lines to those already described (Payne et al. 1980) were analysed and the results indicate that all the HMW subunits are controlled by the homoeologous group 1 chromosomes. All hexaploid varieties studied except ‘NapHal’ contained two major subunits controlled by chromosome 1D. Their genes were shown to be tightly linked genetically for only four different types of banding patterns were observed. The nominal molecular weights determined after fractionation in 10% polyacrylamide gels were between 110,000 and 115,000 for the larger of the two subunits and between 82,000 and 84,000 for the smaller. One quarter of the varieties contained only one major HMW subunit controlled by chromosome 1B whereas the rest had two. The chromosome 1B subunits were the most varied and nine different banding patterns were detected. All the subunits had mobilities which were intermediate between those of the two chromosome 1D-controlled subunits. Only two types of HMW subunit controlled by chromosome 1A were detected in all the varieties examined; a single variety never contained both of these subunits and 40% of varieties contained neither. The chromosome 1A-controlled subunits had slightly slower mobilities in 10% gels than the largest HMW subunit controlled by chromosome 1D. About 100 single grains were analysed from each of five different crosses of the type (F₁ of variety A × variety B) × variety C. The results indicate that the genes on chromosome 1B which control the synthesis of subunits 6, 7, 13, 14 and 17 are allelic, as are the genes of the chromosome 1A-controlled subunits, 1 and 2.     

Control by homoeologous group 1 chromosomes of the high-molecular-weight subunits of glutenin,a major protein of wheat endosperm

Summary The electrophoretic mobilities of the high-molecular-weight (HMW) subunits of glutenin from 7 varieties were compared by polyacrylamide-gel electrophoresis in the presence of sodium dodecyl sulphate (SDS). In total, 12 subunits were clearly resolved and they had nominal molecular weights of between 95,000 and 140,000. The chromosomes which control their synthesis were determined using monosomic lines and inter-varietal substitution lines. All subunits were shown to be controlled by the homoeologous group 1 chromosomes. Each variety contains between 3 and 5 HMW subunits; two are under the control of the 1D chromosome, 1 or 2 are controlled by chromosome 1B and 0 or 1 by chromosome 1A. The segregation of two 1D-controlled subunits of similar electrophoretic mobilities were analysed in the F₂ progeny of crosses between Chinese Spring and Holdfast. The results suggest that the genes which code for the two proteins are allelic.     

Glutenin subunits of genetically related European hexaploid wheat cultivars: Their relation to bread-making quality

Summary The subunit composition of glutenin from 47 European wheat cultivars was studied using SDS-polyacrylamide gel electrophoresis. These cultivars are genetically related since they originate from the same stock. Moreover, the diversity of sample, containing cultivars with very different French bread-making qualities, makes it possible to investigate the relationship between glutenin subunit composition and bread-making quality. 16 electrophoretic types of glutenin subunits could be distinguished: these were grouped into four classes. Depending on the cultivar, six to eight glutenin subunits with MW more than or equal to 62,000 were detected. Subunits 3 and 5, with an approximate MW of 122,000 and 108,000 respectively, seem to play a prominent role on bread-making quality; they were found in cultivars of good quality and were absent in those unsuitable for making French bread. Two other subunits (9 and 10; MW: 71,000 and 66,000, respectively) have a less defined influence but may be needed in some types of glutenin structure. Aneuploid analysis shows that in Chinese Spring, subunit 5 is coded by a gene on the long arm of chromosome 1B. The location of genes coding for subunits 3, 9 and 10 could not be determined.     

Electrophoretic analysis of the high-molecular-weight glutenin subunits of Triticum monococcum,T. urartu,and the A genome of bread wheat (T. aestivum)

Summary The high molecular weight (HMW) subunit composition of glutenin was analysed by sodium dodecyl sulphate, polyacrylamide gel electrophoresis (SDS-PAGE) in the A genome of 497 diploid wheats and in 851 landraces of bread wheat. The material comprised 209 accessions of wild Triticum monococcum ssp. boeoticum from Greece, Turkey, Lebanon, Armenia, Iraq, and Iran; 132 accessions of the primitive domesticate T. monococcum ssp. monococcum from many different germplasm collections; one accession of free-threshing T. monococcum ssp. sinskajae; 155 accessions of wild T. urartu from Lebanon, Turkey, Armenia, Iraq, and Iran; and landraces of T. aestivum, mainly from the Mediterranean area and countries bordering on the Himalayan Mountains. Four novel HMW glutenin sub-units were discovered in the landraces of bread wheat, and the alleles that control them were designated Glu-Ald through Glu-Alg, respectively. The HMW subunits of T. monococcum ssp. boeoticum have a major, x subunit of slow mobility and several, less prominent, y subunits of greater mobility, all of which fall within the mobility range of HMW subunits reported for bread wheat. In T. monococcum ssp. monococcum the range of the banding patterns for HMW subunits was similar to that of ssp. boeoticum. However, two accessions, while containing y subunits were null for x subunits. The single accession of Triticum monococcum ssp. sinskajae had a banding pattern similar to that of most ssp. boeoticum and ssp. monococcum accessions. The HMW subunit banding patterns of T. urartu accessions were distinct from those of T. monococcum. All of them contained one major x and most contained one major y subunit. In the other accessions a y subunit was not expressed. The active genes for y subunits, if transferred to bread wheat, may be useful in improving bread-making quality.     

Identification and molecular characterization of a large insertion within the repetitive domain of a high-molecular-weight glutenin subunit gene from hexaploid wheat

High-molecular-weight (HMW) glutenin subunits are a particular class of wheat endosperm proteins containing a large repetitive domain flanked by two short N- and C-terminal non-repetitive regions. Deletions and insertions within the central repetitive domain has been suggested to be mainly responsible for the length variations observed for this class of proteins. Nucleotide sequence comparison of a number of HMW glutenin genes allowed the identification of small insertions or deletions within the repetitive domain. However, only indirect evidence has been produced which suggests the occurrence of substantial insertions or deletions within this region when a large variation in molecular size is present between different HMW glutenin subunits. This paper represents the first report on the molecular characterization of an unusually large insertion within the repetitive domain of a functional HMW glutenin gene. This gene is located at the Glu-D1 locus of a hexaploid wheat genotype and contains an insertion of 561 base pairs that codes for 187 amino acids corresponding to the repetitive domain of a HMW glutenin subunit encoded at the same locus. The precise location of the insertion has been identified and the molecular processes underlying such mutational events are discussed.     

The characterization and comparative analysis of high-molecular-weight glutenin genes from genomes A and B of a hexaploid bread wheat

Summary Two high-molecular-weight subunit (HMWS) glutenin genes from the A and B genomes of the hexaploid bread wheat Triticum aestivum L. cv Cheyenne have been isolated and sequenced. Both of these genes are of the high M_r class (x-type) of HMW glutenins, and have not been previously reported. The entire set of six HMW genes from cultivar Cheyenne have now been isolated and characterized. An analysis of the Ax and Bx sequences shows that the Ax sequence is similar to the homoeologous gene from the D genome, while the Bx repeat structure is significantly different. The repetitive region of these proteins can be modelled as a series of interspersed copies of repeat modifs of 6, 9, and 15 amino acid residues. The evolution of these genes includes single-base substitutions over the entire coding region, plus insertion/deletions of single or blocks of repeats in the central repetitive domain.     

Dosage effects of chromosomes of homoeologous groups 1 and 6 upon bread-making quality in hexaploid wheat

Summary The endosperm storage proteins, glutenin and gliadin, are major determinants of bread-making quality in hexaploid wheat. Genes encoding them are located on chromosomes of homoeologous groups 1 and 6. Aneuploid lines of these groups in spring wheat cultivar Chinese Spring have been used to investigate the effect of varying the dosage of chromosomes and chromosome arms upon bread-making quality, where quality has been assessed using the SDS-sedimentation test. Differences between the group 1 chromosomes for quality were greater than those between the group 6 chromosomes. The chromosomes were ranked within homoeologous groups for their effect on quality as follows (>=better quality): 1D>1B>1A and 6A>6B=6D. The relationship of chromosome dosage with quality was principally linear for four of the chromosomes, but not for 6B and 6D. Increases in the dosage of 1B, 6A and, especially, 1D, were associated with significant improvements in quality, whereas increases in the dosage of 1A were associated with reductions in quality. The effects of 1A and 1D were such that the best genotype for quality was nullisomic 1A-tetrasomic 1D. For group 1, effects of the long arm appeared in general to be more important than effects of the short arm. For group 6, effects were found associated with the long arms as well as with the short arms, a surprising result in view of the absence of genes encoding storage proteins on the long arms. Significant interactions were found between chromosomes and genetic backgrounds, and between individual chromosomes. Analysis of trials grown over two years demonstrated that, although additive environmental differences over years and genotype x years interaction were present, they were relatively small in magnitude compared with purely genetic differences.     

High molecular weight glutenin subunit variation in wild and cultivated einkorn wheats (Triticum spp.,Poaceae)

Variation in high molecular weight (HMW) glutenin subunit composition among wild and cultivated einkorn wheats (2n = 2x = 14, AA) was investigated using one- (SDS-PAGE and urea/SDS-PAGE) and two-dimensional (IEF × SDS-PAGE) electrophoretic analyses. The material comprised 150 accessions ofTriticum urartu, 160 accessions ofT. boeoticum, 24 accessions ofT. boeoticum subsp.thaoudar and 74 accessions of primitive domesticatedT. monococcum from many different germplasm collections. The biochemical characteristics of HMW-glutenin subunits ofT. boeoticum andT. monococcum were highly similar to one another but distinctly different from those ofT. urartu. All the species analysed were characterised by large intraspecific variation and only three HMW-glutenin subunit patterns were identical betweenT. boeoticum andT. monococcum. Consistent with the distinct nature ofT. urartu, all its HMW-glutenin patterns were different from those found inT. boeoticum andT. monococcum. The differences detected between these species might reflect their reproductive isolation and are consistent with recent nomenclatural and biosystematic treatments that recogniseT. urartu as separate species fromT. boeoticum andT. monococcum. The presence of three distinct glutenin components in some accessions of the species studied seems to be evidence for the existence of at least three active genes controlling the synthesis of the HMW-glutenin subunits in the A genome of wild and primitive domesticated diploid wheats. Results indicate also that HMW-glutenin subunits could represent useful markers for the evaluation of genetic variability present in different wild diploid wheat collections and subsequently for their conservation and future utilisation.     

Production of multiple wheat-rye 1RS translocation stocks and genetic analysis of LMW subunits of glutenin and gliadins in wheats using these stocks

Summary A triple (1AL.1RS/1BL.1RS/1DL.1RS) and three double (1AL.1RS/1BL.1RS, 1AL.1RS/1DL.1RS, 1BL.1RS/1DL.1RS) wheat-rye 1RS translocation stocks were isolated from a segregating population using the Gli-1, Tri-1 and Sec-1 seed proteins as genetic markers. These stocks carried 42 chromosomes and formed the expected multivalents (frequency of 14–25%) at metaphase 1. They gave floret fertility ranging from 40–60%. These stocks were subsequently used to determine the genetic control of low-molecular-weight (LMW) glutenin subunits in Chinese Spring and Gabo by means of two-step one-dimensional SDS-PAGE. All of the B subunits and most of the C subunits of glutenin were shown to be controlled by genes on the short arms of group-1 chromosomes in these wheats. The other C subunits were not controlled by group-1 chromosomes. The triple translocation line served as a suitable third parent in producing test-cross seeds for studying the inheritance of the LMW glutenin subunits and gliadins in wheat cultivars, e.g. Chinese Spring and Orca. The segregation patterns of the LMW glutenin subunits in these cultivars revealed that the subunits were inherited in clusters and that their controlling genes (Glu-3) were tightly linked with those controlling gliadins (Gli-1). The LMW glutenin patterns d, d and e in Orca segregated as alternatives to the patterns a, a and a in Chinese Spring controlled by Glu-A3, Glu-B3 and Glu-D3 loci on chromosome arms 1AS, 1BS and 1DS, respectively, thus indicating that these patterns were controlled by allelic genes at these loci.     

Role of D-genome chromosomes in photosynthesis expression in wheats

Summary The role of D-genome chromosomes in the expression of net photosynthesis in wheats was analysed with the nullitetrasomic and ditelosomic lines of the bread wheat cultivar Chinese Spring. The two arms of chromosome 3 D and the short arm of chromosome 6 D control major mechanisms of photosynthesis. The effect of chromosome 6 D can be thoroughly compensated by that of its homoeologues of genomes A or B, contrary to what can be observed for chromosome 3 D. Chromosome 7 D is responsible for the low photosynthesis of flag leaves developed under high irradiances in genotypes possessing the D-genome, as the likely result of ontogeny or of a loss in adaptability to irradiance.     

Specificity of an antibody to a subunit of high-molecular-weight storage protein from wheat seed and its reaction with other cereal storage proteins (prolamins)

An antiserum to subunit 2 from the high-molecular-weight (HMW) subunits of the glutenin fraction of Triticum aestivum cv. Highbury was shown to react with related subunits from other cultivars of wheat. The reaction was measured quantitatively by laser nephelometry in polyethylene glycol phosphate-buffered saline after dissolving the HMW fraction in 0.1 M acetic acid; urea used to dissolve the HMW prolamins inhibited the reaction, in some cases at the low concentration of 0.06 M. A study of the comparative reactions of other cereal prolamins was made. D hordein, the homologous HMW protein of barley, showed less reaction, which was more inhibited by urea than the wheat subunits. Some -gliadins from the wheat cultivars Chinese Spring and Cheyenne reacted more strongly than the injected fraction and there was less inhibition by urea. A-, - and ₃ of wheat also reacted with the antiserum while a secalin of rye of M_r 40000 gave a weak reaction.Abbreviations HMW high molecular weight - PAGE polyacrylamide-gel electrophoresis - PBS phosphate-buffered saline - PE pyridylethylated - SDS sodium dodecyl sulphate     

Evolution of erect growth forms in domesticated wheats: possible effects of grazing

Summary Wild wheats tend to have a prostrate growthform during the early part of their vegetative growth phase. However, at a later stage the leaves and spike-bearing stalks change the pattern of growth and develop in an erect position. Domesticated wheats develop differently, with an erect growth form dominating the entire growth phase.It is suggested that heavy grazing, especially during early winter months might have played a role in the eradication of spontaneously appearing erect mutants of wild wheat. Such mutants increased in frequency only under domestication.     

Use of recombinant inbred lines of wheat for study of associations of high-molecular-weight glutenin subunit alleles to quantitative traits

Summary Recombinant inbred lines (RILs) derived by single plant descent to F₈ from a hybrid of Anza, a low-quality cultivar, and Cajeme 71, a high-quality cultivar, differed in alleles at three high-molecular-weight glutenin (HMW-glu) seed storage protein loci. The 48 RILs were classified by SDS-PAGE for the Anza alleles Glu-Alc (null), Glu-B1b (subunits 7 + 8), and Glu-D1a (subunits 2 + 12) and for Cajeme 71 alleles Glu-A1a (sub-unit 1), Glu-B1I (subunits 17 + 18), and Glu-D1d (subunits 5 + 10). All RILs and parents were grown in a replicated field trial with three levels of nitrogen (N) fertilization. Additive and additive x additive gene effects for the three loci were detected by orthogonal comparisons of means for each of six wheat end-use quality traits. Each HMW-glu genotype was represented by three to ten RILs so that variability among RILs within each HMW-glu genotype could be examined. N effects were consistently small. All traits except flour yield were highly correlated with predictor traits studied earlier. Flour protein content, baking water absorption, dough mixing time, bread loaf volume, and bread loaf crumb score were all correlated, suggesting similar gene control for these traits; however, specific additive locus contributions were evident: _B for flour yield; _B and _D for flour protein; and _B for absorption, but differing in sign; all three loci for mixing time, but _B was negative; and all three loci were positively associated with loaf volume. Digenic epistatic effects were significant for flour yield (_AD), flour protein (_AB), and absorption and mixing time (_AD, _BD). Only flour yield showed a trigenic epistatic effect. Six of seven epistatic effects were negative, thus showing how progress in breeding for high quality may be impeded by interaction of genes which, by themselves, have strong positive additive effects. Considerable genetic variance among RILs within a HMW-glu genotype was detected for all traits, and the summation of effects accounted for a mean of 13% of the parental differences for the six traits examined in this study. Clearly, further resolution of the genetics of wheat quality would be desirable from a plant breeding point of view.     

Analysis of a genomic DNA segment carrying the wheat high-molecular-weight (HMW) glutenin Bx17 subunit and its use as an RFLP marker

Summary A genomic fragment containing the Bx17 high-molecular-weight (HMW) glutenin gene was isolated from a wheat genomic library. The fragment contains a coding region of 2.82kb with 1.98-kb downstream and 12.8-kb upstream flanking regions. The fragment was sequenced and compared with previously published glutenin genes from chromosomes 1A, 1B and 1D using a computer alignment package. The Bx17 gene shows marked similarity to the Bx7 gene sequence. A phenetic tree derived from the alignments is presented. Also shown are restriction fragment length polymorphisms (RFLPs) at the glutenin loci in a set of Australian and international wheat varieties using different regions of the glutenin clone as probes. The RFLPs correlated well with the protein composition in all cultivars analysed.     

Use of recombinant inbred lines of wheat for study of associations of high-molecular-weight glutenin subunit alleles to quantitative traits

Summary The high-molecular-weight glutenin subunits (HMW glutenin), encoded by alleles at homoeologous lociGlu-A1,Glu-B1, andGlu-D1 on the long arms of chromosomes1A,1B, and1D of a set of F₈ random recombinant inbred lines (RIL) derived from the bread wheat cross Anza × Cajeme 71, were classified by SDS-PAGE. Anza has poor breadmaking quality and HMW-glutenin subunits (Payne numbers) null (Glu-A1c), 7+8 (Glu-B1b), and 2+12 (Glu-D1a); Cajeme 71 has good quality and 1 (Glu-A1a), 17+18 (Glu-B1i), and 5+10 (Glu-D1d). The combinations of these alleles in the RIL were examined for associations with grain yield and four indicators of grain quality — protein content, yellowberry, pearling index, and SDS sedimentation volume. Data were obtained from a field experiment with three nitrogen fertilization treatments on 48 RIL and the parents. Orthogonal partitioning of the genetic variance associated with the three HMW glutenin subunit loci into additive and epistatic (digenic and trigenic) effects showed strong associations of these loci with grain yield and the indicators of quality; however, the associations accounted for no more than 25% of the differences between the parents. Genetic variance was detected among the RIL, which had the same HMW glutenin genotype for all traits. Epistatic effects were absent for grain yield and yellowberry, but were substantial for grain protein content, pearling index, and SDS sedimentation volume. All three loci had large single-locus additive effects for grain yield, protein, and SDS sedimentation volume. Yellowberry was largely influenced byGlu-B1 andGlu-D1, whereas pearling index was associated withGlu-A1 andGlu-B1. Even though the observed associations-of effects of HMW glutenin loci with the quantitative characters were small relative to the total genetic variability, they are of considerable importance in understanding the genetics of wheat quality, and are useful in the development of new wheat varieties with specific desired characteristics.     

NADP-dependent aromatic alcohol dehydrogenase in polyploid wheats and their diploid relatives. On the origin and phylogeny of polyploid wheats

Summary The three major isoenzymes of the NADP-dependent aromatic alcohol dehydrogenase (ADH-B), distinguished in polyploid wheats by means of polyacrylamide gel electrophoresis, are shown to be coded by homoeoalleles of the locus Adh-2 on short arms of chromosomes of the fifth homoeologous group. Essentially codominant expression of the Adh-2 homoeolleles of composite genomes was observed in young seedlings of hexaploid wheats (T. aestivum s.l.) and tetraploid wheats of the emmer group (T. turgidum s.l.), whereas only the isoenzyme characteristic of the A genome is present in the seedlings of the timopheevii-group tetraploids (T. timopheevii s.str. and T. araraticum).The slowest-moving B³ isoenzyme of polyploid wheats, coded by the homoeoallele of the B genome, is characteristic of the diploid species Aegilops speltoides S.l., including both its awned and awnless forms, but was not encountered in Ae. bicornis, Ae. sharonensis and Ae. longissima. The last two diploids, as well as Ae. tauschii, Ae. caudata, Triticum monococcum s.str., T. boeoticum s.l. (incl. T. thaoudar) and T. urartu all shared a common isoenzyme coinciding electrophoretically with the band B² controlled by the A and D genome homoeoalleles in polyploid wheats. Ae. bicomis is characterized by the slowest isoenzyme, B⁴, not found in wheats and in the other diploid Aegilops species studied.Two electrophoretic variants of ADH-B, B¹ and B², considered to be alloenzymes of the A genome homoeoallele, were observed in T. dicoccoides, T. dicoccon, T. turgidum. s.str. and T. spelta, whereas B² was characteristic of T. timopheevii s.l. and only B¹ was found in the remaining taxa of polyploid wheats. The isoenzyme B¹, not encountered among diploid species, is considered to be a mutational derivative which arose on the tetraploid level from its more ancestral form B² characteristic of diploid wheats.The implication of the ADH-B isoenzyme data to the problems of wheat phylogeny and gene evolution is discussed.     

Characterization of two HMW glutenin subunit genes from Taenitherum Nevski

The compositions of high molecular weight (HMW) glutenin subunits from three species of Taenitherum Nevski (TaTa, 2n = 2x = 14), Ta. caput-medusae, Ta. crinitum and Ta. asperum, were investigated by SDS-PAGE analysis. The electrophoresis mobility of the x-type HMW glutenin subunits were slower or equal to that of wheat HMW glutenin subunit Dx2, and the electrophoresis mobility of the y-type subunits were faster than that of wheat HMW glutenin subunit Dy12. Two HMW glutenin genes, designated as Tax and Tay, were isolated from Ta. crinitum, and their complete nucleotide coding sequences were determined. Sequencing and multiple sequences alignment suggested that the HMW glutenin subunits derived from Ta. crinitum had the similar structures to the HMW glutenin subunits from wheat and related species with a signal peptide, and N- and C-conservative domains flanking by a repetitive domain consisted of the repeated short peptide motifs. However, the encoding sequences of Tax and Tay had some novel modification compared with the HMW glutenin genes reported so far: (1) A short peptide with the consensus sequences of KGGSFYP, which was observed in the N-terminal of all known HMW glutenin genes, was absent in Tax; (2) There is a specified short peptide tandem of tripeptide, hexapeptide and nonapeptide and three tandem of tripeptide in the repetitive domain of Tax; (3) The amino acid residues number is 105 (an extra Q presented) but not 104 in the N-terminal of Tay, which was similar to most of y-type HMW glutenin genes from Elytrigia elongata and Crithopsis delileana. Phylogenetic analysis indicated that Tax subunit was mostly related to Ax1, Cx, Ux and Dx5, and Tay was more related to Ay, Cy and Ry.     

Genetic linkage between endosperm storage protein genes on each of the short arms of chromosomes 1A and 1B in wheat

Summary The storage proteins of the endosperm of wheat grain which are known to be controlled by genes on the short arms of the homoeologous group 1 chromosomes are (1) the -gliadins, (2) most of the -gliadins, (3) a few -gliadins and (4) the major lowmolecular-weight subunits of glutenin. Several crosses were made between varieties or genetic lines which had contrasting allelic variants for some of these proteins and which were coded by genes on chromosomes 1A or 1B. The progeny were analysed by one or more of several electrophoretic procedures. The results of all the analyses are consistent with the hypothesis that chromosomes 1A and 1B each contain just one, complex locus, named Gli-A 1 and Gli-B 1 respectively, which contain the genes for the -, - and -gliadins and the low-molecular-weight subunits of glutenin.     

Electrophoretic survey of seedling esterases in wheats in relation to their phylogeny

Summary Evolutionary and ontogenetic variation of six seedling esterases of independent genetic control is studied in polyploid wheats and their diploid relatives by means of polyacrylamide gel electrophoresis. Four of them are shown to be controlled by homoeoallelic genes in chromosomes of third, sixth and seventh homoeologous groups.The isoesterase electrophoretic data are considered supporting a monophyletic origin of both the primitive tetraploid and the primitive hexaploid wheat from which contemporary taxa of polyploid wheats have emerged polyphyletically and polytopically through recurrent introgressive hybridization and accumulation of mutations. Ancestral diploids belonging or closely related to Triticum boeoticum, T. urartu, Aegilops speltoides and Ae. tauschii ssp. strangulata are genetically the most suitable genome donors of polyploid wheats. Diploids of the Emarginata subsection of the section Sitopsis, Aegilops longissima s.str., Ae. sharonensis, Ae. searsii and Ae. bicornis, are unsuitable for the role of the wheat B genome donors, being all fixed for the esterase B and D electromorphs different from those of tetraploid wheats.