Pioneer Hi-Bred International, Inc. (Pioneer) has licensed an imidazolinone tolerant corn line from American Cyanamid that was used to develop new corn hybrids with herbicide tolerance. The mutation is known as XI-12 and the resulting hybrids as IT hybrids. The IT hybrids are very similar to imidazolinone resistant (IR) hybrids in their mechanism of herbicide resistance. IR hybrids were reviewed by Health Canada in 1995 as a novel food and determined to be safe for food consumption in Canada.<br>Corn is grown widely throughout North America as a food and feed crop. Corn is a commodity crop largely used to feed domestic animals, either as grain or silage. The remainder of the crop is exported or processed by wet or dry milling to yield products such as high fructose corn syrup and starch, oil, grits and flour. The imidazolinone tolerant corn (IT corn) was developed through mutation breeding. No foreign DNA was introduced to achieve the herbicide tolerance trait.<br>The method used for obtaining imidazolinone-tolerant corn plants was <i>in vitro</i> selection. The mutation conferring imidazolinone tolerance is referred to as XI-12. The XI-12 mutation affects the acetohydroxyacid synthase (AHAS) enzyme of maize at a specific location. The AHAS enzyme catalyses the first step in the biosynthesis of the branched chain amino acids isoleucine, leucine, and valine in corn. The mutation in the AHAS enzyme resluts in an alteration to the binding site for the imidazolinone class of of herbicides, therefore increasing the plant’s tolerance to those herbicides.<br>A mutation to the AHAS enzyme in corn could affect the biosynthesis of the essential amino acids isoleucine, leucine, and valine. The amino acid composition of an XI-12 hybrid and Pioneer® Brand hybrid 3394 was analysed in grain from field grown plants. The results of the amino acid analyses demonstrate that corn hybrids containing the XI-12 mutation do not show altered levels of valine, leucine, and isoleucine. It can be concluded that the single amino acid substitution in the XI-12 mutation results in maize hybrids, which are unchanged in their AHAS enzyme activity.