Evidence for two different nitrate-reducing activities at the plasma membrane in roots ofZea mays L. |
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Authors: | Ario de Marco Chen Jia Elke Fischer-Schliebs Zeno Varanini Ulrich Lüttge |
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Institution: | (1) Dipartimento di Produzione Vegetale e Tecnologie Agrarie, Università di Udine, via delle Scienze 208, I-33100 Udine, Italy;(2) Institut für Botanik, Technische Hochschule Darmstadt, Schnittpahnstrasse 3-5, D-64287 Darmstadt, Germany;(3) College of Biological Sciences, Beijing Agricultural University, 100094 Beijing, Republic of China |
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Abstract: | Plasma-membrane (PM) vesicles isolated from 6-d-old corn roots by sucrose gradient centrifugation or two-phase partitioning showed an NADH-dependent nitrate reductase (NR) activity averaging at 40 nmol per milligram PM protein per hour. This membrane-associated NR activity could not be removed from two-phase-partitioned PM vesicles by salt washing, osmotic shock treatment, sonication, or freeze-thawing to reverse vesicle sidedness. Therefore, it could not be attributed to contamination of membrane vesicles by the soluble, cytosolic NR. Plasma-membrane vesicles reduced NO
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in the presence of the electron donors NADH or NADPH at an activity ratio of 2.2. The NADH- and NADPH-dependent NR activities of outside-out oriented PM vesicles differed in their sensitivity toward the detergent Brij 58, leading to a latency of 65% or 29% using NADH or NADPH as electron donor, respectively. The activities of NO
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reduction in the presence of saturating concentrations of NADH and NADPH were additive. Furthermore, both activities were characterized by a different pH dependence with a pH optimum of 7.5 for the NADH-dependent activity and of 6.8 for the NADPH-dependent activity. The membrane-associated NAD(P)H-dependent NR activities responded to different nitrogen nutrition of plants in a manner different from the soluble forms of the enzyme. The data confirm the existence of a corn PM NR and suggest that there may be two different NO
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-reducing enzymes located at the PM of corn roots.Abbreviations PM
Plasma membrane
- NR
nitrate reductase
This research was supported by grants from the National Research Council of Italy (bilateral project between Italy and Germany to Z.V. and U.L.), by the Ministero dell' Università e Ricera Scientifice e Tecnologica (MURST 40%) and by the Deutsche Forschungsgemeinschaft. |
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Keywords: | Nitrate reductase Plasma membrane bound Plasma membrane Redox activity Zea |
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