Phosphinothricin is an glutamine synthetase inhibitor that binds to the glutamate site. Glufosinate-treated plants die due to a buildup of ammonia and corresponding decrease in pH in the thylakoid lumen, leading to the uncoupling of photophosphorylation. The uncoupling of photophosphorylation causes the production of reactive oxygen species, lipid peroxidation, and membrane destruction.
Now, in this article from the University of California (Weed control, management, ecology, and minutia), it states:
Researchers in Malaysia reported a few years ago on a population of goosegrass resistant to glufosinate in vegetable and orchard systems (Lee L J & Ngim J (2000). A first report of glyphosate-resistant goosegrass (Eleusine indica (L) Gaertn) in Malaysia. Pest Management Science, 56, 336-339). For a number of years this was the only reported case of resistance to this herbicide.
What would have to happen in the weed for it to become resistant to this chemical/mode of action, and what would initiate this process?