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© 1995 Oxford University Press

RESEARCH-ARTICLE

Possible interaction between peroxidase and NAD(P)H-dependent nitrate reductase activities of plasma membranes of corn roots

Ario de Marco1,3, Roberto Pinton1, Elke Fischer-Schliebs2 and Zeno Varanini1

1 Dipartimento di Produzione Vegetale e Tecnologie Agrarie, Universita di Udine via delle Scienze 208, 1–33100 Udine, Ital
2 Institut für Botanik, Technische Hochschule Darmstadt Schnittspahnstrasse 3-5, D-64287 Darmstadt, FRG

3 To whom correspondence should be addressed: Fax: +39 432 558603

The relationship between the plasma membrane bound NAD(P)H-nitrate reductase (NR) and a plasma membrane (PM)-bound peroxidase was investigated using highly purified PM vesicles isolated from corn roots. The PM-bound NR activity was strongly enhanced by MnCl2 and SHAM, which stimulated peroxidase activity. Since both activities, the NAD(P)H-dependent NR and the peroxidase compete for NAD(P)H as electron donor, we propose a model in which a product of peroxidation is able to offer electrons to the nitrate reductase in a more reactive form with respect toNAD(P)H. Our hypothesis was confirmed by experiments in which the effects of inhibitors of peroxidative reactions, catalase, superoxide dismutase, and ascorbate on the PM-bound NR were studied. Results indicate that the putative electron donor for nitrate reduction could be a radicalic species, possibly NAD. Furthermore, since cytochrome c decreased the activity of the plasma membrane-bound NAD(P)Hdependent NR, cytochrome b557 might be the site of the enzyme accepting electrons from NAD.

Our results indicate that the PM environment of the NR may be involved in the extent of the membrane associated nitrate reduction and that redox enzymes at the PM, the NAD(P)H-NR and a peroxidase-like NADH-oxidase, can interact.

Key words: Plasma membrane-bound nitrate reductase, peroxidase, Zea mays


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