Effect of L-methionine sulphoximine on the enzymes of nitrogen metabolism in barley leaves

Abstract

L-methionine sulphoximine, a potent inhibitor of glutamine synthetase decreased nitrate reductase activity by 50% at the end of 12h of treatment while nitrite reductase was insignificantly affected. By 3 h the inhibition of glutamine synthetase activity was complete. Elevated levels of ammonia induced by L-methionine sulphoximine did not influence glutamate dehydrogenase. It is inferred that ammonia accumulation does not affect photosynthetic electron transport which supplies reducing power to nitrite reductase. The failure of glutamate dehydrogenase activity to be induced by high ammonium levels shows that it is not involved in the process of ammonia assimilation in the leaves.