The Effect of Bialaphos on Ammonium-Assimilation and Photosynthesis I. Effect on the Enzymes of Ammonium-Assimilation

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Abstract
In this investigation, the effect of bialaphos (phosphinothricyl-alanyl-alanine) on the enzymes involved in NH4 +-assimilation - glutamine synthetase, glutamine-2-oxoglutarate aminotransferase, glutamate dehydrogenase - is examined and compared to the effect of phosphinothricin (glufosinate) on the same enzymes. Bialaphos was given to whole plants (in vivo) and to leaf homogenate (in vitro). The investigation showed that bialaphos has an inhibiting effect on glutamine synthetase in vivo, but not in vitro. In contrast to this, phosphinothricin inhibits glutamine synthetase in vitro as well as in vivo. It was found that bialaphos, similar to phosphinothricin, does not inhibit glutamine-2-oxoglutarate aminotransferase and glutamate dehydrogenase in vivo or in vitro. Only at bialaphos concentrations exceeding 10 mM, there is an inhibition of glutamate dehydrogenase in vitro. Using radioactive [3H]bialaphos (phosphinothricyl-3H-alanyl-alanine) it could be demonstrated that in the plant, bialaphos is split into phosphinothricin and alanine. The phosphinothricin released is probably the active herbicide component. Consequently, the herbicidal effects of phosphinothricin and bialaphos are the same.

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