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Methods for the extraction and separation of hordein fractions from single or halfseeds of barley have been evaluated. Sodium dodecylsulphate-polyacrylamide gel electrophoresis at pH 8.9 gave rapid and reproducible separations of reduced and alkylated hordein, and this system was used to analyse hordein fractions from 88 barley varieties. On the basis of this character the varieties can be divided into 29 groups, each containing between one and 25 varieties. The largest group can be further divided into four subgroups on the basis of minor hordein polypeptide differences revealed by a second electrophoretic system, urea polyacrylamide gel electrophoresis at pH 4.6. Of the samples of the varieties studied, all except five contained seed homogeneous with respect to hordein polypeptide pattern. It is concluded that analysis of hordein polypeptide patterns from single seeds is of great potential value, both for the commercial identification of grain samples and as an aid to existing techniques for the establishment of varietal distinctness.

Methods have been developed for extracting and comparing the hordein fractions of barley seed as a means of identifying different varieties. A rapid method involving a single extraction with 55 % (v/v) propan-2-01 + 2% (v/v) 2-mercaptoethanol at 60°C removed slightly less nitrogen from milled grain than a more detailed procedure in which three sequential extractions were made with the same solvent. The hordein fractions extracted by these two procedures were alkylated and their component polypeptides separated by four one-dimensional and two two-dimensional systems. The results showed that the hordein extracted by both techniques had the same polypeptide composition and thus the rapid method was satisfactory for use in comparing varieties. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis and isoelectric focusing were used to compare the polypeptide composition of the hordein fractions from 29 varieties. Using the former system a total of 1 1 different patterns were recognised while further small differences between several varieties were revealed by isoelectric focusing or two-dimensional analysis. If the polypeptide patterns obtained by these techniques are considered in conjunction with other grain characters it should be possible to identify almost all of the 29 varieties.

SUMMARYThe' b' protein components specific to virus infected tobacco leaves (Gianinazzi, Martin & Vall~e, 197o) can be partially purified by preferential extraction at pH 2.8. Evidence is presented that they are rich in aromatic amino acids. Results of treatment of the proteins with SDS and subsequent separation by gel electrophoresis in the presence of SDS suggest that b~, b~ and b~ are composed of the same monomer of mol. wt. about 16000 whilst b4 is composed of a monomer of tool. wt. about 29ooo. By purifying and concentrating the soluble protein extracts of water inoculated leaves, further evidence is provided that the 'b' proteins are not normal constituents of healthy tobacco leaves.