The canola line HCN92 was genetically engineered to express
tolerance to glufosinate ammonium, the active ingredient in
phosphinothricin herbicides (Basta®, Rely®, Finale®, and Liberty®).
Glufosinate chemically resembles the amino acid glutamate and acts
to inhibit an enzyme, called glutamine synthetase, which is
involved in the synthesis of glutamine. Essentially, glufosinate
acts enough like glutamate, the molecule used by glutamine
synthetase to make glutamine, that it blocks the enzyme's usual
activity. Glutamine synthetase is also involved in ammonia
detoxification. The action of glufosinate results in reduced
glutamine levels and a corresponding increase in concentrations of
ammonia in plant tissues, leading to cell membrane disruption and
cessation of photosynthesis resulting in plant withering and death.
Glufosinate tolerance in HCN92 is the result of introducing a gene
encoding the enzyme phosphinothricin-N-acetyltransferase (PAT)
isolated from the common aerobic soil actinomycete, Streptomyces
viridochromogenes, the same organism from which glufosinate was
originally isolated. The PAT enzyme catalyzes the acetylation of
phosphinothricin, detoxifying it into an inactive compound.