ABSTRACT
Effects of methionine sulphoximine (MSX) on glutamine synthetase activity and ammonia accumulation in the leaves of barley, sorghum and Moricandia arvensis were studied. Glutamine synthetase activity of sorghum leaves was relatively resistant to MSX treatment during initial stages. All the three plant species exhibited considerable accumulation of ammonia arising from non-photorespiratory sources, in response to MSX treatment. Minimal estimates of the rate of glycine decarboxylation were made employing MSX and isonicotinyl hydrazide together in the treatment solution. Changes in the pool sizes of amino acids involved in photorespiratory nitrogen metabolism as affected by MSX have also been investigated.
Subject(s)
Ammonia/metabolism , Plants/metabolism , Amino Acids/metabolism , Glutamate-Ammonia Ligase/metabolism , Hordeum/metabolism , Methionine Sulfoximine/pharmacology , Plants/drug effectsABSTRACT
Glycine, a photorespiratory intermediate, enhanced the in vivo reduction of nitrate in barley (Hordeum vulgare L.) leaf slices, when included in the assay medium. Isonicotinyl hydrazide, an inhibitor of glycine oxidation, partially reduced NO(2) (-) production. The enhancement caused by glycine treatment was reversed by isonicotinyl hydrazide when both were present together in the medium. Similar effects were observed when the excised leaves were preincubated with the metabolite and the inhibitor. Glycine also partially relieved the inhibition of nitrate reduction caused by malonate, an inhibitor of the tricarboxylic acid cycle. The results support the hypothesis that glycine decarboxylation activity is a source of NADH for nitrate reductase activity.
