The maize line DLL25 (synonym B16) 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 this maize line is the result of
introducing a gene encoding the enzyme
phosphinothricin-N-acetyltransferase (PAT) isolated from the common
aerobic soil actinomycete, Streptomyces hygroscopicus, the same
organism from which glufosinate was originally isolated. The PAT
enzyme catalyzes the acetylation of phosphinothricin, detoxifying
it into an inactive compound.