<p style="text-align: justify;"><b>The Introduced DNA</b></p>

<p style="text-align: justify;">Since the imidazolinone-tolerance trait in X8159 hybrid sunflower is from a natural point mutation of wild sunflower, there was no introduction or incorporation of heterologous DNA into the plant genome. The tolerance to imidazolinone is due to a single point mutation in the AHAS gene, such that the herbicide cannot inhibit the enzyme&rsquo;s activity. Information on the sequence of the modified AHAS gene revealed the single point mutation.</p>

<p style="text-align: justify;"><b>Genetic Stability of the Introduced Trait</b></p>

<p style="text-align: justify;">The results of segregation analyses using the wild population from which the imidazolinone trait was isolated demonstrate the inheritance of a single semi-dominant allele. The hybrid X81359, which is several generations removed from the original mutation, is consistently tolerant to imidazolinone herbicides (CFIA, 2005b).</p>

<p style="text-align: justify;"><b>Expressed material</b></p>

<p style="text-align: justify;">The modified AHAS gene, conferring tolerance to imidazolinone herbicides, is under control of the native AHAS promoter and is believed to be constitutively expressed.</p>

<p style="text-align: justify;">In the unmodified plant, the levels of valine, leucine and isoleucine are regulated by feedback inhibition of AHAS. A mutation in the AHAS enzyme could affect the regulation of the biosynthesis of these amino acids. Data were submitted to show that the modified AHAS was feedback inhibited by valine and leucine, and thus, similar to the unmodified enzyme. Levels of valine, leucine and isoleucine in X81359 sunflower were comparable to those in the unmodified plant.</p>
