Nitric oxide as signalling molecule in plants: nitrate reductase or alternative sources for NO?

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Based on and related to the tremendous amount of research on the role of NO in vertebrates, the potential role and production of NO in plants has gained increasing attention during the last decade (Leshem 2000). The aim of this proposal is to find out by what reactions, how much, when and where NO is produced by plants and how NO synthesis is regulated, with emphasis on plant-pathogen interactions. We intend to focus on two potential NO sources. One is nitrate reductase (NR), which produces NO by reduction of nitrite with NAD(P)H, the other one is nitric oxide synthase (NOS) which is supposed to produce NO by converting L-arginine into citrulline, using NAD(P)H, oxygen and various co-factors. Other NO-producing enzymes, like xanthine oxidases, will also be considered (Nakagawa). We wish to study NO production in leaves in response to environmental factors and in response to elicitors and pathogens by using various tobacco-, Arabidopsis- and spinach mutants and transformants over- or underexpressing nitrate- or nitrate-reductase. We will apply gas phase NO measurements by chemiluminescence detection (Kaiser) as well as fluorescent NO indicators (DAF 2 and DAF 2 DA, Nakagawa), and use conventional assays for determination of enzyme activities and gene expression. The Nakagawa group will also isolate the three functional domains of NR in order to find out which domain is involved in NO production.