Conventional and novel approaches to the improvement of the nutritional quality of cereal and legume seeds

About 70% of all man's food comes directly from eating the seeds of cereals and legumes. A large proportion of the remainder is derived from animals which in turn are fed on seeds. Consequently the proteins present in these seeds are a major source of protein in the diet. For animals with simple stomachs this protein must contain adequate amounts of nutritionally essential amino acids. In this article we discuss how cereal and legume seeds are deficient in either lysine, threonine and tryptophan or cysteine and methionine respectively. Actual and potential ways of improving nutritional quality are then reviewed. Mutants which depress seed storage protein synthesis and lead to higher lysine content are known, although usually they also depress seed yield. Further mutants which alter the free amino acid content have been selected and may be of use in enhancing crop quality. Finally, more novel approaches involving gene isolation, modification and reinsertion are being tried in a number of research centres throughout the world. The strategies involved in such biomolecular engineering are described and the barriers to success discussed.