Ten hybrid wheat lines derived from the F4 BC1 population after crossing between Triticum aestivum cv. Aurora (2n=42, AABBDD) and the wild diploid species Ae. umbellulata Zhuk. (2n=14, UU) were investigated. As a bridge for the transfer of genes from Ae. umbellulata, the genome substituted line Aurolata was used in which the D genome of the cv. Aurora is substituted with the U genome of Ae. umbellulata (Zhirov 1989). Fig.1 presents the breeding scheme. The wheat lines having 42 chromosomes were established in the Institute of Genetics 'D. Kostoff, Sofia, Bulgaria. The seed samples of Ae. umbellulata (accession No. C01) was obtained from the collection of the same Institute. The electrophoretic resolution of the gliadins was conducted according to Cooper (1987). The glutenins and albumins were extracted with buffers containing sodium dodecyl sulphate (SDS) and 2-mercaptoethanol according to Smith and Payne (1984) and Gupta et al. (1991). The glutenin and albumin subunits were fractionated in 12% polyacrylamide gel electrophoresis (PAGE) (Laemmli 1970) on the electrophoresis apparatus GE-2/4 (Pharmacia, Sweden) using power supply EPS 500/ 400. The gel size was 175/140/1.5 mm. The protein analysis was made individually using more than fifteen seeds from each of the wheat lines. For studies of Ae. umbellulata, mixed samples from fifteen individual seeds were used.
Results and discussion
The wheat lines selected for this study showed considerable similarity in the overall composition of the three protein groups, i.e. gliadin, glutenin and albumin. However, some differences were observed in their gliadin patterns. Variants detected at the GliB1, GliA1 and GluB3 loci are shown in Table 1 together with their parental species. Two Aurora- specific gliadin subunits belonging to the omega- and gamma - gliadins respectively controlled by chromosomes 1BS and 1AS+1DS (Shepherd 1973) were lacking in the five selected lines Nos. 10-14, similar to Ae. umbellulata, while they were present in the lines Nos. 15-19. A low molecular weight (LMW) glutenin subunit controlled by the GluB3 locus on chromosome 1AS (Singh and Shepherd 1988) was present in the lines Nos. 10-14 similar to Ae. umbellulata and cv. Aurora but was absent in the lines Nos. 15-19. The probable reason for the absence of the mentioned LMW glutenin subunit is the repression of the locus in the chromosome 1AS, responsible for the same subunit in the lines Nos. 15-19.
Detectable variation occurred in several albumin subunits between cv. Aurora and Ae. umbellulata (Fig. 2). However, differences in the albumin patterns among the wheat lines were only quantitative. In the lines Nos. 15 and 16 (slots, 5 and 7 in Fig. 2) the two subunits near the cathode (arrowed in the figure) resembled those of cv. Aurora by their higher intensity than those in the lines Nos. 10 and 11 (slots 4 and 6). It was reported that the above two albumin subunits in cv. Chinese Spring were controlled by chromosomes 4DL and 4BL (Gupta et al. 1991).
The data suggest that the introgression from Ae. umbellulata in the lines Nos. 10-14 involves the short arms of the chromosomes 1BS (locus GliB1), 1AS+1DS (locus GliA1) and 1AS (locus GluB3). This result is in agreement with the statement that at least two chromosomes controlling gliadins in Ae. umbellulata are homoeologous with two chromosomes in bread wheat (Shepherd 1973). Law and Payne (1983) located GluU1 locus on the long arm of 1U chromosome of Ae. umbellulata and indicated the homoeology between this chromosome and the group 1 chromosomes of bread wheat. A possible explanation for the introgression of the gliadin and glutenin subunits controlled by the chromosomes 1BS and 1AS in the wheat lines Nos. 10-14 might be related to the position of their loci. The GliB1 locus is located near the end of the short arm of the satellited region of the chromosome 1B (Payne et al. 1981) and the GluB3 locus is also located on the short arm of the chromosome 1B (Payne and Lawrence 1983).
SDS-PAGE study of the protein bands controlled by 4DL and 4BL chromosomes indicated that they were albumins according to Gupta et al. (1991). The authors revealed by using immunoblotting that the bands correspond to beta-amylases of wheat grains. The participation of the same wheat chromosomes in the genetic control of beta-amylase isoenzymes is established by Ainsworth et al. (1983). Considering the fact that the amount of qualitative variation in these proteins observed by SDS-PAGE is limited (Gupta et al. 1991), the quantitative variation in the albumins can serve as a potential marker for the presence of Ae. umbellulata eh chromosomes homoeologous to 4DL and 4BL of wheat.
The present results provide evidence of homoeologous introgression of the first and fourth groups of chromosomes of Ae. umbellulata into bread wheat. This information is useful for breeding purposes because it can be used in diagnostic detection of Ae. umbellulata chromosomes or chromosome segments in the wheat background.
Acknowledgments
The author is grateful to Dr. Ganka Ganeva, the Institute of Genetics'D. Kostoff,' Bulgarian Academy of Sciences, for kindly providing the experimental materials.