The glufosinate ammonium tolerance gene (bar gene),
derived from the common soil bacterium Streptomyces
hygroscopicus, codes for phosphinothricin acetyltransferase
(PAT) and leads to increased tolerance to herbicides containing
glufosinate ammonium, such as 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 blocks the
activity of glutamine synthetase by mimicking the enzyme's
substrate glutamate which is used to produce glutamine. 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.
Phosphinothricin N-acetyltransferase (PAT) acts by catalyzing the
acetylation of glufosinate (phosphinothricin) so that it no longer
inhibits the enzyme glutamine synthase and, thus, eliminating its
herbicidal activity.
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