<p style="text-align: justify;">Imidazolinone herbicides are active against the enzyme acetohydroxyacid synthase (AHAS), also known as acetolactate synthase (ALS) or acetolactate pyruvate- lyase.</p>

<p style="text-align: justify;">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.</p>

<p style="text-align: justify;">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.</p>

<p style="text-align: justify;">AP602CL was selected from a population of <i> T. aestivum </i> derived by chemical-induced mutagenesis of seed of the wheat variety Gunner. One mutant, tolerant to imidazoline was selected and designated AP602CL. Tolerance to imadazoline was demonstrated by comparison of the activity of the AHAS enzyme extracted from AP602CL to that of wild type plants.</p>

<p style="text-align: justify;">The novel tolerance to imadazoline is under control of the native AHAS promoter and is believed to be constitutively expressed. Sequence information for the modified AHAS gene in AP602CL was submitted.</p>

<p style="text-align: justify;">The levels of valine, leucine and isoleucine produced in wheat are regulated by feedback inhibition of AHAS. Modified AHAS shows similar feedback inhibition to that of unmodified AHAS. AHAS is not known to be an allergen and modified AHAS also does not exhibit characteristics associated with allergens. The protein components of AHAS are not altered in comparison with unmodified Gunner wheat.</p>
