Netsvetaev and Sozinov (Netsvetaev et al., 1983; Netsvetaev and Sozinov, 1984) have reported the identification and mapping of a new locus, designated Hrd G, which controls the presence of two hordein polypeptides in the cultivar Elgina. Although the polypeptides migrated in the B hordein region on starch gel electrophoresis at pH 3.1 Hrd G was more closely linked to the C hordein locus (Hor 1) than to the B hordein locus (Hor 2).
Dr. Netsvetzev kindly provided us with homozygous lines from his P12 population derived from the cross Nutans 244 × Elgina (Netsvetaev and Sozinov, 1984). Two of these, called P12/3 and P12/4, had identical hordein patterns on sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE), except that an additional band was present in the B hordein region of P12/3. This band was purified by preparative isoelectric focusing (Field et al., 1982) and its amino acid composition determined. This showed 33.6 mol % glutamate + glutamine and 20.5 mol % proline, similar to the values of 35.4 mol % and 20.6 mol % respectively reported for B hordein of cv. Julia (Shewry et al., 1980). Although cysteine could not be determined accurately it was clearly present, together with about 0.9 mol % methionine. The overall amino acid composition indicated a close relationship with B hordein, and this was confirmed by calculating the S n homology index of Cornish-Bowden (1981).
The linkage of the B hordein-like band in P12/3 with the B hordein (Hor 2) locus was studied by analysing single F2 seeds from the cross Bomi (Hor 2 Ze) × P12/3 (Hor 2 Ca). The number of seeds in the various genotypic classes are given in Table 1. The Hor 2 alleles were co-dominant, but we were not always able to distinguish with certainty the two classes of heterozygote differing in dosage of the alleles in the triploid endosperm. The additional band in P12/3 was scored as absent or present (i.e., as dominant), with no attempt to distinguish between homozygous present and the two types of heterozygote. Linkage was estimated by the method of maximum likelihood (Bailey, 1961), and the map distance calculated using the Kosambi function (Jensen and Jørgensen, 1975).
The results showed 13.5 ± 2.3% recombination between Hor 2 and the locus encoding the additional band in P12/3, with a map distance of 13.9 ± 2.5 cM. This is consistent with the estimates of Netsvetzev and Sozinov (1984): 20.69 ± 2.68% and 18.33 &plusm; 1.62% in two crosses. We are currently determining the linkage with Hor 1, reported by Netsvetaev and Sozinov (1984) as 2.56 ± 0.70, 0.70 ± 0.41 and 1.19 ± 0.29% in three crosses.
Netsvetaev and Sozinov (1984) designated the locus encoding the additional band as Hrd G, following their designation of six other hordein as Hrd A to Hrd F. Of these only two, Hrd A and Hrd B, have been confirmed by other workers, who have called them Hor 1 and Hor 2 respectively (Doll and Brown, 1979; Jensen et al., 1980; Shewry et al., 1980). In addition the Hor 3 locus encoding the quantitatively minor D hordein group of polypeptides has recently been mapped (Blake et al., 1982; Shewry et al., 1983). Since the designation Hor is now widely accepted for hordein structural loci, we suggest that the locus controlling the additional B hordein-like polypeptide(s) in cv. Elgina should be provisionally designated as Hor 4.
References:
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Blake, T. K., Ullrich, S. and Nilan, R. A. 1982. Mapping of the Hor 3 locus encoding 'D' hordeins in barley. Theor. Appl. Genet. 63:367-371.
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Doll, H. and Brown, A. D. H. 1979. Hordein variation in wild (Hordeum spontaneum) and cultivated (H. vulgare) barley. Can. J. Genet. Cytol. 21:391-404.
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