The Hor 1 and Hor 2 loci, located on the short arm of chromosome 5, encode the two major groups of storage proteins present in the mature grain. These are called B hordein or hordein-2 (Hor 2), and C hordein or hordein-1 (Hor 1). Each group is a polymorphic mixture of polypeptides, and the Hor 1 and Hor 2 loci appear to be clusters of closely-linked related genes.

There is great genotypic variation in the patterns of polypeptides specified by Hor 1 and Hor 2. Shewry et al. (1979) described 21 and 8 different patterns of B and C hordein polypeptides respectively in a collection of 183 cultivars and land races, while Nielsen and Johansen (1986) described 12 Hor 1 alleles and 15 Hor 2 alleles in a collection of 66 cultivars commonly grown in Denmark. Although alleles at Hor 1 and Hor 2 have been designated in a number of previous studies (Table 1), there has been no agreed system for designation, resulting in some duplication and confusion. Since all these allelic designations were originally proposed by workers at Risø or Rothamsted, we decided to prepare an agreed list of recommended designations for all the described alleles at Hor 1 and Hor 2. To facilitate this, hordein fractions from all the cultivars which had previously been proposed as standards for alleles were compared by sodium dodecylsulphate polyacrylamide gel electrophoresis (SDA-PAGE) using the methods described by Nielsen and Johansen (1986). It must be emphasized that these alleles are based only on SDS-PAGE separations, and that other one- dimensional and two-dimensional procedures may reveal further allelic variation. However, SDS-PAGE is the system which is most widely-used for studying the biochemistry and genetics of hordein. The recommended designations, standard cultivars and alternative designations are presented in Table 1. Where possible the recommended designation is the first to be proposed.

We also propose the following guidelines for the designation of hordein alleles.

1. All allelic designations should be two letters, usually the first two letters of the standard cultivar in which the allele was first described. Because hordein alleles are co- dominant, the first letter is upper case.

2. The same designations should not be used for alleles at the Hor 1 and Hor 2 loci. If the first two letters of the name of the standard cultivar have been used previously for' another allele (at Hor 1 or Hor 2), the first and third (or fourth, etc.) letters should be used.

We hope that adherence to these guidelines will facilitate the designation of new hordein alleles.

References:

Doll, H. 1980. A nearly non-functional mutant allele of the storage protein locus Hor 2 in barley. Hereditas 93:217-222.

Doll, H. and A.H.D. Brown. 1979. Hordein variation in wild (Hordeum spontaneum) and cultivated (H. vulgare) barley. Can. J. Genet. Cytol. 21:391-404.

Doll, H. and H.P. Jensen. 1986. Localization of powdery mildew resistance gene Ml-ra on barley chromosome 5. Hereditas (in press).

Jensen, J., J.H. Jørgensen, H.P. Jensen, H. Giese and H. Doll. 1980. Linkage of the hordein loci Hor 1 and Hor 2 with the powdery mildew resistance loci Ml-k and Ml-a on barley chromo- some 5. Theor. Appl. Genet. 58:27-31.

Kreis, M., S. Rahman, B.G. Forde, J. Plywell, P.R. Shewry and B.J. Miflin. 1983. Sub-families of hordein mRNA encoded at the Hor 2 locus of barley. Mol. Gen. Genet. 191:194-200.

Linde-Laursen, I., H. Doll and G. Nielsen. 1982. Giemsa C banding patterns and some biochemical markers in a pedigree of European barley. Z. Pflanzenzuchtg. 88:191-219.

Nielsen, G. and H.B. Johansen. 1986.. Identification of 66 European barley varieties by isoenzymes and hordein patterns. Submitted to Euphytica.

Shewry, P.R., H.M. Pratt, A.J. Faulks, S. Parmar and B.J. Miflin. 1979. The storage protein (hordein) polypeptide pattern of barley (Hordeum vulgare L.) in relation to varietal identification and disease resistance. J. Natl. Inst. Agric. Bot. 15:34-50.

Shewry, P.R., A.J. Faulks, R.A. Pickering, I.T. Jones, R.A. Finch and B.J. Miflin. 1980. The genetic analysis of barley storage proteins. Heredity 44:383-389.

Shewry, P.R., M.S. Wolfe, S.E. Slater, S. Parmar, A.J. Faulks and B.J. Miflin. 1982. Barley storage proteins in relation to varietal identification, malting quality and mildew resistance. Barley Genetics IV.

Shewry, P.R., R.A. Finch, S. Parmar, J. Franklin and B.J. Miflin. 1983. Chromosomal location of Hor 3, a new locus governing storage proteins in barley. Heredity 50 (2):179-189.