<p style="text-align: justify;">Harvested carnation (<i>Dianthus caryophyllus</i> L.) flowers have a defined &#39;vase life&#39;, or time for which the flowers will stay fresh prior to beginning to shrink, dry out and die. This senescence process is triggered by production of a natural plant hormone, ethylene, by the flower. Flower death can also be triggered by exposure of flowers to external sources of ethylene, such as fruit and exhaust fumes. Typically, flower growers have controlled wilting by treating flowers with chemicals (<i>e.g.</i> silver thiosulfate) that either inhibit ethylene synthesis in the flower, or prevent the flower from responding to ethylene.</p>

<p style="text-align: justify;">The enzyme 1-aminocyclopropane-1-carboxyllic acid (ACC) synthase, normally found in carnations, is responsible for the conversion of s-adenosylmethionine to ACC, which is the immediate precursor of ethylene. The transgenic carnation line 66 was developed using recombinant DNA techniques to display suppressed ACC synthase activity, and thus reduced ethylene synthesis and therefore longer vase life, by inserting an additional truncated copy of the ACC synthase encoding gene. The presence of the truncated ACC synthase gene suppresses the normal expression of the native ACC synthase gene, and while not completely understood, the mechanism of &ldquo;downregulation&rdquo; is likely linked to the coordinate suppression of transcription of both the endogenous gene and the introduced truncated ACC synthase gene.</p>

<p style="text-align: justify;">An additional gene encoding a variant form of the enzyme acetolactate synthase (ALS) was also introduced into this transgenic carnation line in order to confer the trait of tolerance to sulfonylurea type herbicides (<i>e.g.</i>, chlorsulfuron, commonly known as Glean&trade;), which are potent inhibitors of ALS. Acetolactate synthase (also known as acetohydroxy acid synthase; AHAS) is involved in the conversion of threonine to alpha-aceto-alpha-hydroxybutyrate and pyruvate to alpha-acetolactate, which are key precursors in the biosynthesis of the essential branched chain amino acids isoleucine and valine, respectively. Alpha-acetolactate is also a precursor in the synthesis of leucine. The variant form of ALS introduced into this carnation line was isolated from a chlorsulfuron tolerant tobacco (<i>Nicotiana tabacum</i>). This trait was introduced as a means of selecting for transformed plants during tissue culture regeneration as sulfonylurea herbicides are not, and will not be, used in the carnation industry.</p>
