Based on previous work, which related individual H M Wglutenin subunitsto bread-making quality by genetical analysis, quality scores were assigned to each of the commonly occurring subunits. The grain proteins of 84 home-grown wheat varieties were fractionated by SDS-PAGE to determine their H M W glutenin subunit composition. The quality scores of each of the subunits were summed to create a Glu-1 quality score for each variety. The results indicated that 4760% of the variation in the independently established bread-making qualities of this set of varieties could be accounted for by variation in H M W subunits of glutenin. The presence or absence in the varieties of a translocated chromosome, which consisted of the long arm of 1 B and the short arm of I R from rye, was also established because of its known association with poor bread-making quality. A correction factor was applied to the Glu-1 quality score of those varieties that contained the 1BLllRS chromosome. The variations in the ryeadjusted Glu-1 quality scores were compared with those of the breadmaking qualities of the varieties, and the proportion of variation in quality accounted for was raised to 5 5 4 7 % . The Glu-1 quality score and the biscuit-making qualities of the same set of varieties were negatively related. The results are discussed in relation to future strategies recommended to wheat breeders for developing new varieties with improved bread-making quality.

The homoeologous group 1 chromosomes of wheat contain in total five major gene groupings which code for the high-molecular weight subunits of glutenin. Each gene group displays allelic variation that is detectable by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Some of the different allelic subunits have been assessed for their relationship to bread-making quality. The procedure has been to analyse numerous, unselected progeny of crosses between varieties for both bread-making quality (by the SDS-sedimentation test) and subunit composition (by SDS-PAGE). Two strong correlations with quality were detected in the progeny of several crosses : the presence of subunit 1, a polypeptide coded by genes of chromosome lA, and the presence of subunits 5 and 10, coded for by chromosome 1D.Other significant correlations were detected which need to be confirmed by further analyses. The results are discussed in relation to (i) the relative positions of the glutenin genes on the group 1 chromosomes; and (ii) future strategies for breeding wheats with improved bread-making quality.

No abstract

Gliadins, here defined as those proteins of defatted wheat endosperm which dissolve in 70% (v/v) ethanol at room temperature, were fractionated by gel filtration using Sephadex G-100. The protein which eluted with the void volume of the column, often described as high-molecular-weight (HMW) gliadin, was fractionated by the two different, two dimensional gel electrophoresis procedures of O'Farrell (1975) and O'Farrell et al. (1977). The next two fractions to elute from the gel column, ω-gliadin and α-, β-, γ-gliadin, were analysed similarly. The subunits of HMW gliadin and the classical (i.e. non-aggregated) gliadins map at distinctive positions on the electrophoregrams, the majority of the HMW gliadin subunits being more basic and having a slightly slower electrophoretic mobility than the α-, β-, γ-gliadins. These experiments demonstrate that those gliadins which aggregate to form HMW gliadin are distinct molecular entities and thus coded by different genes to those gliadins which do not aggregate. Glutenin, here prepared by a modification of the pH 6.4 precipitation procedure of Orth and Bushuk (1973), was also analysed by two-dimensional electrophoresis. The low-molecular-weight subunits were found to correspond exactly with the HMW gliadin subunits. Using the nullisomic-tetrasomic lines and the ditelocentric lines of 'Chinese Spring', the genes controlling the synthesis of all the major HMW gliadin subunits were shown to be located on the short arms of chromosomes 1A, 1B and 1D, as are the genes coding for the ω-gliadins and the majority of the γ-gliadins.

The genes that code for endosperm storage proteins occur at nine complex loci on six different chromosomes. Glu-A1 , Glu-B1 and Glu-D1 contain the genes for high molecular mass subunits of glutenin and are close to the centromere on the long arms of chromosomes 1A, 1B and 1D respectively. On the short arms of the same chromosomes, but distant from the centromere, are Gli-A1 , Gli-B1 and Gli-D1 . Each of these loci carry three major gene families coding for ω-gliadins, γ-gliadins and low molecular mass glutenin subunits. The remaining loci, Gli-A2 , Gli-B2 and Gli-D2 occur near the ends of the short arms of chromosomes 6A, 6B and 6D respectively and each code for α- and β-gliadins. Recombination of genes within a locus is very rare and has so far been detected only at Glu-B1 , at the rate of about one recombinant in 1000 progeny. Each locus displays allelic variation and this is responsible for differences among varieties in protein quality for making bread. The protein variants that are associated with good quality are being identified, firstly by analysing segregating populations and secondly from the development of near-isogenic lines. Current, incomplete, information on the relative qualities of different alleles at each locus indicates the following order of im portance: Glu-1 > Gli-1 > Gli-2 . Landraces of primitive agriculture are being screened for novel proteins. The genes for some of them are being incorporated into the genomes of commercial wheats.

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.

No abstract

No abstract