TEMPORAL STUDY OF THE EFFECT OF PHOSPHINOTHRICIN ON THE ACTIVITY OF GLUTAMINE-SYNTHETASE, GLUTAMATE-DEHYDROGENASE AND NITRATE REDUCTASE IN MEDICAGO-SATIVA L

In a preliminary work we showed that when plants were sprayed with several doses of glufosinate, GS activity of the leaf was reduced by 50% after 48 h of application of 250 µM herbicide. Enzyme inhibition was accompained by a dramatic accumulation of ammonia. In this paper we analyze the time-course effect of phosphinothricin on nitrogen metabolism. Our results show that GS activity is the first process affected; more than 50% activity reduction is observed after 2 h of a 1,000 µM treatment, whereby ammonia values 400% higher than control were reached. NRase did not change until 24 h of assay, whereas protein content was reduced after 48 h. GDH activity was enhanced, but only 24 h after starting the treatment. These results indicate that the main target of PPT action is on GS activity, and other processes are long-term modified. GDH could, perhaps, reassimilate some of the ammonia produced but its activity is not able to completely prevent, the injury caused by phosphinothricin. © 1990, Gustav Fischer Verlag, Stuttgart. All rights reserved.