The canola line T45 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 T45 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. The PAT
enzyme is not known to have any toxic properties. Line HCN28 was
derived from T45.
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