Effect of phosphinothricin herbicide on nitrogen metabolism in Pinus radiata and Laccaria bicolor

The phosphinothricin (PPT) herbicide inhibited the glutamine synthetase act ivity (GS) extracted from Laccaria bicolor (transferase and semibiosyntheti c activities). In pine needle PPT had an inhibitory effect in the transfera se assay, while it acted as an activator for the semibiosynthetic activity. The close relationship observed between CO2 assimilation rate, Fv/Fm ratio and ammonia is a good indicator of the interrelation between nitrogen meta bolism and photosynthetic carbon assimilation. The capacity to deaminate PP T by L-amino acid oxidase seems to confer Laccaria bicolor quite tolerance to this herbicide, since the increment in GS activity allow the adaptation of the fungus to grow in presence of this herbicide.