Water-soluble proteins (WSPs) are a group of proteins present in mature endosperm of barley grain, and other members of the Triticeae. They can be extracted from single milled grain with water, or with a solution of dithiothreitol (DTT) in 20% sucrose (Liu et al., 1989; Thompson et al., 1990; Forster et al., 1991). Crude extracts can be loaded onto isoelectric focusing (IEF) gels and the proteins separated in various pH gradients. The proteins are then visualised by Coomassic Blue staining; such procedures show the presence of several proteins, some of which are polymorphic between cultivars. As yet no function has been ascribed to these proteins, but because of their relative abundance and specificity to the endosperm, they are thought to be storage proteins. Their solubility characteristics place them into the albumin/globulin class of seed proteins (Osboume, 1924).

Six water-soluble protein genes, Wsp1-6 have been reported. Wspl has been mapped to barley chromosome 1 (7H) (Liu et al., 1989), Wsp2 to chromosome 7 (5H) (Barua et al., 1994), Wsp3 to chromosome 4 (4H) (Forster et al., 1991), Wsp4 to chromosome 2 (2H) (Macaulay et al., 1994) and Wsp5 to chromosome 7 (5H) (Macaulay et al., 1994). Wsp6 (Macaulay et al., 1994) is as yet unmapped. Because of their polymorphisms, WSPs have been used extensively as genetic markers (Forster, 1993). However, little is known about their identities, their biological roles and their role in industrial processes such as malting and brewing. Since these proteins are abundant their biological and technological roles are likely to be significant. Further studies at SCRI aim to address these important areas.

References:

Barua, U.M., Chalmers, K.J., Thomas, W.T.B., Hackett, C.A., Forster, B.P., Waugh, R. and Powell, W. 1994. Molecular mapping of genes determining height, time to heading and growth habit in barley, Hordeum vulgare L. Genome (in press).

Forster, B.P. 1993. Water-soluble proteins (WSPs) of barley: genetics and characterisation. Asp. Appl. Biol. 36:121-124.

Forster, B.P., Thompson, D.M., Watters, J. and Powell, W. 1991. Water-soluble proteins of mature barley endosperm: genetic control, polymorphism, and linkage with beta-amylase and spring/winter habit. Them. Appl. Genet. 81:787.

Liu, C.J., Chao, S. and Gale, M.D. 1989. Wsp-1, a set of genes controlling water-soluble proteins in wheat and related species. Genet. Res. Camb. 54: 173.

Macaulay, M., Laurie, D.A. and Forster, B.P. 1994. Extraction and genetic control of two new water-soluble proteins of mature barley seed. Biochem. Genet. (in press).

Osboume, T.B. 1924. The vegetable proteins. Longmans, Green & Co., London, 154 pp.

Thompson, D.M., Powell, W. and Forster, B.P. 1990. Use of isoelectricfocusing in barley varietal identification. Ann. Appl. Biol. 117:625.