Nitrogen Metabolism of the Upper Three Leaf Blades of Wheat at Different Soil Nitrogen Levels. I. Nitrate Reductase Activity and Content of Various Nitrogenous Constituents

The phototrophic bacterium Rhodobacter capsulatus E1F1 possesses an assimilatory, inducible nitrate reductase that is regulated by carbon and nitrogen metabolism. Nitrate reductase activity was detected in cells cultured with amino acids and nitrate as simultaneous nitrogen source but it required an additional carbon source such as D,L-malate. A significant rise in nitrate reductase activity was observed in media with increasing nitrate concentrations up to 10 mM KNO3, although higher nitrate concentrations had an inhibitory effect. Growth yield, generation time, and nitrate reductase activity were also dependent on the concentration of D,L-malate in cells growing with 10 mM nitrate. In carbon-starved cells, nitrate reductase activity dropped even in the presence of nitrate. The intracellular concentration of keto acids such as oxaloacetate or 2-oxoglutarate fluctuated widely depending on the presence of nitrogen and carbon sources in the culture medium. The increase in the intracellular concentration of oxaloacetate or 2-oxoglutarate in R. capsulatus E1F1 correlated well with a rise in nitrate reductase activity. These results suggest that the intracellular carbon–nitrogen balance regulates nitrate uptake in R. capsulatus E1F1, thus affecting the expression of nitrate reductase.Key words: carbon–nitrogen balance, nitrate reductase, Rhodobacter capsulatus.

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The effect of various light conditions and different nitrogen forms on nitrogen metabolism in pepper fruits

Folia Horticulturae ◽

10.2478/v10245-012-0019-8 ◽

2012 ◽

Vol 24 (2) ◽

pp. 153-160 ◽

Cited By ~ 4

Author(s):

Anna Kołton ◽

Renata Wojciechowska ◽

Maria Leja

Keyword(s):

Nitrate Reductase ◽

Nitrogen Metabolism ◽

Nitrite Reductase ◽

Nitrate Reductase Activity ◽

Reductase Activity ◽

Red Pepper ◽

Ammonium Ion ◽

Light Conditions ◽

Nitrogen Forms ◽

Ammonium Ions

Abstract The ‘Spartacus’ F1 sweet pepper was grown in a plastic tunnel on rockwool during 2006-2008. A fertigation technique was used for water and fertiliser application. The tunnel was divided into two parts covered with different plastic films. The first part of the tunnel was covered with a film that transmitted less light than the film covering the second part. In both parts of the tunnel, the plants were divided into two groups. One group of plants was fertilised with just nitrate nitrogen (100% N-NO3) and the other one with three forms of nitrogen (N-NO3:N-NH4:N-NH2 in a ratio of 50:13:37). Fruits were harvested mature green and red. Concentrations of nitrate and ammonium ions as well as total nitrogen and free amino acids were analysed in the plant material. Nitrate and nitrite reductase activities were also investigated, and dry matter content and soluble sugars were also determined. Higher light intensity increased nitrate concentration in red pepper fruits but decreased ammonium ion content. These tendencies were not as obvious in green fruits. In most cases, red fruits fertilised with three nitrogen forms accumulated more nitrates than those fertilised with N-NO3. This observation was similar in the case of green fruits. In most cases, pepper fruits accumulated more ammonium ions in the case of N-NO3 fertilisation than when three forms of nitrogen were applied, but the differences were not always statistically significant. Higher nitrate reductase activity was observed in the case of better light conditions as well as mixed nitrogen fertilisation in red pepper fruits. No differences were observed in the case of nitrite reductase activity between fruits harvested from various treatments in red and also green fruits, with some exceptions. The green fruits of pepper had higher nitrate reductase activity than the red ones. It can be summarised that various light conditions influenced the nitrogen metabolism of pepper fruits as well as the different nitrogen forms applied with fertilisers.

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