Imidazolinone herbicides are active against the enzyme acetohydroxyacid synthase (AHAS), also known as acetolactate synthase (ALS) or acetolactate pyruvate- lyase. <br>This enzyme catalyzes the first step in the biosynthesis of the essential branched chain amino acids isoleucine, leucine and valine. Herbicide induced AHAS inhibition results in a lethal decrease in protein synthesis. Unmodified wheat is not tolerant to imidazolinones, while soybeans, peas, white beans and kidney beans are naturally tolerant to them. <br>Depending on the species, plants contain single or multiple copies of the AHAS genes. The genome of <i>T. aestivum</i> is believed to contain an AHAS multigene family. <br>Modifications of AHAS genes in various plant species can result in herbicide tolerant phenotypes and typically consist of one amino acid substitution, sufficient to alter the binding site for imidazolinones such that the herbicide no longer inhibits the AHAS enzyme. Several modified AHAS plants have been isolated. References to relevant scientific publications were provided by the proponent. <br>Cyanamid Crop Protection selected four <i>T. aestivum</i> lines FS1, FS2, FS3 and FS4, with altered AHAS enzymes not inhibited by the herbicide. SWP965001 is derived from FS2. <br>The novel imidazolinone tolerance is under the control of the native AHAS promoter and is believed to be constitutively expressed. The sequence of the modified AHAS gene was submitted for both the FS2 and FS4 lines. <br>The levels of valine, leucine and isoleucine produced in T. aestivum are regulated by feedback inhibition. Cyanamid Crop Protection has provided literature references and data to support the claim that modified AHAS does not affect feedback inhibition and hence, the regulation and the levels of theses amino acids. The original mutant line was isolated from a population derived by chemical- induced mutagenesis of seed of the winter wheat cultivar Fidel with sodium azide. Four imidazolinone-tolerant seedlings, FSI, FS2, FS3 and FS4, were selected in the presence of herbicide. SWP965001 is derived from the selection line FS2. <br>SWP965001 was derived from an initial cross of FS2 to the spring wheat cultivar Grandin, followed by two backcrosses to Grandin. As a result, 87.5% of the genetic information is from the Grandin parent and the remaining 12.5% is from Fidel.