Modifying the Amino Acid Composition of Grains Using Gene Technology

Abstract

Animals cannot synthesise 10 of the 20 amino acids needed for protein production and must obtain these “essential” amino acids from their diet. Although cereals and legumes are major sources of protein for humans and livestock, individually these crops do not supply the full complement of essential amino acids. Cereal grains are deficient in lysine whilst legume grains are deficient in the sulfur containing amino acids cysteine and methionine. Traditional plant breeding has attempted to improve the balance of essential amino acids in seed proteins. Good progress has been made in breeding high lysine corn, but breeding of high methionine legumes has met with only limited success. More recently, gene technology (GT) has been used to introduce new metabolic enzymes or storage proteins into cereals, legumes and other plants and has shown potential in addressing the nutritional deficiencies in these crops (Falco et al., 1995; Altenbach et al., 1992; Pickardt et al., 1995; Molvig et al., 1997).