<p style="text-align: justify;">X81359 (Clearfield&trade;) sunflower hybrid was developed to allow the use of imidazolinone herbicides as a post-emergence weed control option in sunflower production. The tolerance to imidazolinone herbicides in X81359 is due to a naturally occurring mutation in the AHAS gene discovered in a wild population of <i>Helianthus annus</i>. This trait was introduced into X81359 using conventional plant breeding techniques.</p>

<p style="text-align: justify;">AHAS catalyses the first step in the biosynthesis of the branched-chain amino acids isoleucine, leucine, and valine, and is active in the glycolytic pathway of plant metabolism. When conventional sunflower plants are treated with an imidazolinone, the herbicide binds to a specific site on the AHAS enzyme, thereby inhibiting its activity. The result of this enzyme inhibition is a decrease in the synthesis of these amino acids, and an accumulation of toxic levels of alpha-ketoglutarate, all of which results in the eventual death of the plant.</p>
