Control of Nitrite Reductase Activity in Excised Embryos of Agrostemma githago

Abstract

When excised embryos of Agrostemnna githago were incubated with nitrate, the activities of both nitrate reductase and nitrite reductase were enhanced. By contrast, benzyladenine induced nitrate reductase only. Our data suggest that nitrate affected nitrite reductase activity directly, without first being reduced to nitrite. When the endogenous nitrite production was increased by raising the level of nitrate reductase through simultaneous treatment with nitrate and benzyladenine, the activity of nitrite reductase was not higher than in embryos treated with nitrate alone. On the other hand, tungstate given together with nitrate drastically inhibited the development of nitrate reductase activity without reducing the enhancement of nitrite reductase activitv. Nitrite enhanced nitrite reductase activity, though less efficiently than nitrate.mogenates, obtained according to Kende and Shen (6), were used as enzyme sources. In some experiments, the fractions precipitated at 50% and 50 to 75% saturation of (NH4)2SO0were used as sources of NR and NiR, respectively. Each precipitate was redissolved in a small volume of 0.1 M potassium phosphate buffer, pH 7.5, containing 1 mm EDTA, 1 mM L-Cysteine, and 1 bLM FAD.Enzyme Assays. NADH-NR was assayed according to Wray and Filner (9), and NiR according to Kelker and Filner (4) with minor modifications as described below. The reaction mixture was prepared by mixing 20 ,wmoles of potassium phosphate buffer (pH 7.5), 0.7 ,umole of methyl viologen chloride, 0.8 ,umole of KNO2, and the enzyme preparation with distilled water to give a final volume of 0.5 ml. The reaction was started by adding 0.1 ml Na2S20 (100 mm in 0.29 M NaHCO,) and was carried out at 30 C for 45 min. The conditions were sufficiently anaerobic so that no N2 atmosphere was required.

Cytokinin enhancement of the light induction of nitrate reductase transcript levels in etiolated barley leaves

“…1-2). Cytokinins have previously been reported to induce NR in excised embryos of Agrostemma githago [3,11,15]. However, in the absence of nitrate, the induction of NR activity in barley and other plant leaves [ 17,22] is negligible.…”

“…One of these enzymes, nitrate reductase (NR), a key enzyme in the pathway of nitrogen assimilation, has been shown to be regulated by cytokinins [3,11,15,17]. However the mechanism of cytokinin regulation of NR activity is still unknown.…”

Cytokinin regulation of a soybean pollen allergen gene

“…Among the mRNAs that have been shown to accumulate in response to cytokinin are those encoding the light-harvesting chlorophyll a/b-binding protein [ 14,15,23,40], the small subunit of ribulose-l,5-bisphosphate carboxylase (Rubisco) [13,14,21,24], nitrate reductase [10,11,19,22,25], an early nodulin…”

Nitrate reduction in the wildtype and a nitrate reductase deficient mutant of Arabidopsis thaliana

“…Available genetic data are in agreement with the hypothesis that nitrate is the inducer of both nitrate and nitrite reductase (see also Mendel and Muller 1979). Physiological data are conflicting and point either to nitrate (Kelker andFilner 1971, Dilworth andKende 1974) or nitrite (Ingle et al 1966, Huckelesby et at. 1972 as the inductor for nitrate and/or nitrite reductase.…”