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.