Glycine Supports in Vivo Reduction of Nitrate in Barley Leaves

Abstract

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 NO2 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.done. Wherever preincubation was involved, the excised leaves were incubated with different treatment solutions for 3 h under light (800 ,uE m-2 S-') at 30°C. RESULTS AND DISCUSSIONGlycine enhanced nitrate reduction in barley leaves when included in the in vivo assay medium (Fig. 1). The maximum enhancement was attained at 10 mm concentration. Three possible explanations could be attributed to explain this enhancement: a. possible induction ofNR by the amino acid; b. increased stability of the enzyme in the presence of ammonium (13) released during glycine oxidation; c. increased supply of reducing power to the enzyme. It has been observed by many workers that amino acids either repress the synthesis or reduce the activity of NR (10). We observed no considerable change in NR activity by using a wide range of amino acids other than glycine in the NR'(EC

Improvement of the diphenylamine-based spectrophotometric method for nitrate determination

“…24 Also, glycine seems to be another reducing agent able to act on nitrate, as that has been reported in an in vivo assay concerning barley (Hordeum vulgare L.) leaf slices. 25 Of course, the NC reduction must in principle follow the law of mass action. Consequently the difference between initial (real) and nal (theoretical, obtained aer handling the sample) NC values, i.e.…”