The cotton line LLCotton25 was developed to allow the use of glufosinate ammonium (trade name Liberty®), as a weed control option in cotton production. The herbicidal mode of action of glufosinate ammonium is related to the activity of glutamine synthetase (GS), the enzyme required for the synthesis of the amino acid glutamine. L-phosphinothricin, the active ingredient of glufosinate ammonium, is a structural analog of glutamate, and acts as a competitive inhibitor. After application of the herbicide, L-phosphinothricin competes with glutamine for its active sites on GS. The results of the inhibition of GS are an accumulation of ammonia in the plant, a reduction in the synthesis of glutamine, and an inhibition of photosynthesis. This causes the death of plant cells, and eventually, the entire plant. This modified cotton line LLCotton25 contains the bar gene, which codes for the production of the enzyme phosphinothricin acetyl-transferase (PAT). This enzyme acetylates glufosinate ammonium, rendering it inactive in the plant. The expression of the bar gene in LLCotton25 allows it to survive the otherwise lethal application of glufosinate ammonium. The bar gene was isolated from Streptomyces hygroscopius, a gram-positive soil bacterium.

LLCotton25 was developed by Agrobacterium-mediated transformation of the cotton variety ‘Coker312’ with a plasmid vector containing the bar gene. Whole plants were treated with glufosinate ammonium and successful transformants were detected by selecting plants that had not exhibited the phytotoxic effects of glufosinate ammonium