The effect of phosphinothricin on the assimilation of ammonia in Plants

Abstract

The effects of DL-phosphinothricin and L-methionine sulfoximine on the enzym es of nitrogen assimilation were studied. Furthermore we investigated the accum ulation of ammonia and the photosynthetic activity after the treatment of mustard plants with phosphinothricin. P hosphinothricin was a specific and very strong inhibitor of glutam ine synthetase. Major differences, however, were found between the phosphinothricin affinity of the leaf enzym e and that of the root of mustard plants. The leaf enzyme was 50% inhibited at a concentration of 10-4 M phosphinothricin (pI50 = 4), whereas the root enzyme already showed the sam e effect at a concentration of 2 x 10-5M (pI50 = 4.7). In addition Ki values of about 0.03 mM for the leaf enzyme and 0.002 mM for the root enzyme respectively were determ ined. Phosphinothricintreatment of plants caused an ammonia accumulation in tissues. The accum ulation was light dependent. At the beginning of the light period the major sources of am m onia accum ulation could be the nitrogen assim ilation as well as catabolic processes of nitrogen com pounds. A clear contribution of photorespiration was only found when higher concentrations of am m onia were reached. The application of phosphinothricin induced a strong reduction of CO2 assimilation. © 1984, Walter de Gruyter. All rights reserved.