Sulfonylurea herbicides, such as triasulfuron and
metsulfuron-methyl, target and bind to the enzyme acetolactate
synthase (ALS) thereby inhibiting the biosynthesis of the branched
chain amino acids valine, leucine and isoleucine and resulting in
the accumulation of toxic levels of alpha-ketoglutarate.
In addition to its native ALS gene, CDC Triffid contains an als
gene from a chlorsulfuron tolerant line of Arabidopsis thaliana.
This variant als gene differs from the wild type A. thaliana gene
by one nucleotide and the resulting ALS enzyme differs by one amino
acid from the wild type ALS enzyme. The inserted als gene is linked
to its native promoter and terminator.
Enzyme extracts from CDC Triffid exhibited a slightly higher ALS
activity compared to its non-modified counterpart cv. Norlin.
Whereas the statistical significance of this higher activity could
not be verified, it may be expected due to the presence of at least
two additional copies of the als gene in CDC Triffid.