The biochemical basis and implications of grain strength in sorghum and maize

This review deals with the biochemical basis and implications of hardness a nd grain strength in sorghum and maize. Grain hardness affects various aspe cts of the growth and processing of cereal grain from resistance to fungal infection to cooking quality. It is clear that the prolamins play an import ant role with the gamma-prolamins being the most important. It would appear that these prolamins help shape the protein bodies and form disulphide bon ds within themselves or with other proteins. The gamma-prolamins form the c ement while the alpha-prolamins are the bricks. Both prolamins are present in greater proportions in hard grains and in the vitreous portion of hard g rains. Genetic and environmental effects on the amounts of the different pr olamins and on their distributions within the protein body and in different parts of the endosperm also determine grain hardness. Grains that will be hard appear to deposit prolamins and antifungal proteins earlier and in gre ater amount than do soft grains. The cell wall composition is also differen t between the two types of grains while there is a higher proportions of am ylose in the starch of hard than in that of soft grains. Most of the differ ences that exist between hard and soft grains also exist between the outer and inner portion of the grain. It is postulated that there might be a mast er gene controlling the onset of strength in grains by simultaneously alter ing the levels of various apparently unrelated biochemical events. It is al so suggested that solute availability may play an important role in the reg ulation of expression of genes for hardness-related proteins. (C) 1999 Acad emic Press.