title: Novel metabolism of nitrogen in plants.
abstract: Our previous study showed that approximately one-third of the nitrogen of 15N-labeled NO2 taken up into plants was converted to a previously unknown organic nitrogen (hereafter designated UN) that was not recoverable by the Kjeldahl method (Morikawa et al., 2004). In this communication, we discuss metabolic and physiological relevance of the UN based on our newest experimental results. All of the 12 plant species were found to form UN derived from NO2 (about 10-30% of the total nitrogen derived from NO2). The UN was formed also from nitrate nitrogen in various plant species. Thus, UN is a common metabolite in plants. The amount of UN derived from NO2 was greatly increased in the transgenic tobacco clone 271 (Vaucheret et al., 1992) where the activity of nitrite reductase is suppressed less than 5% of that of the wild-type plant. On the other hand, the amount of this UN was significantly decreased by the overexpression of S-nitrosoglutathione reductase (GSNOR). These findings strongly suggest that nitrite and other reactive nitrogen species are involved in the formation of the UN, and that the UN-bearing compounds are metabolizable. A metabolic scheme for the formation of UN-bearing compounds was proposed, in which nitric oxide and peroxynitrite derived from NO2 or endogenous nitrogen oxides are involved for nitrosation and/or nitration of organic compounds in the cells to form nitroso and nitro compounds, including N-nitroso and S-nitroso ones. Participation of non-symbiotic haemoglobin bearing peroxidase-like activity (Sakamoto et al., 2004) and GSNOR (Sakamoto et al., 2002) in the metabolism of the UN was discussed. The UN-bearing compounds identified to date in the extracts of the leaves of Arabidopsis thaliana fumigated with NO2 include a delta2-1,2,3-thiadiazoline derivative (Miyawaki et al., 2004) and 4-nitro-beta-carotene.
authors.affiliation: Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University, Higashi-Hiroshima, Japan. hmorikaw@sci.hiroshima-u.ac.jp
authors.forename: Hiromichi
authors.initials: H
authors.lastname: Morikawa
authors.forename: Misa
authors.initials: M
authors.lastname: Takahashi
authors.forename: Atsushi
authors.initials: A
authors.lastname: Sakamoto
authors.forename: Manami
authors.initials: M
authors.lastname: Ueda-Hashimoto
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Matsubara
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Miyawaki
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Kawamura
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Hirata
authors.forename: Hitomi
authors.initials: H
authors.lastname: Suzuki
mesh_terms: D017360:Arabidopsis / Q000378:metabolism; D001467:Hordeum / Q000378:metabolism; D008954:Models, Biological; D009584:Nitrogen / Q000378:metabolism*; D009587:Nitrogen Isotopes; D009609:Nitrous Oxide / Q000378:metabolism; D009930:Organic Chemicals / Q000378:metabolism; D010944:Plants / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000378:metabolism; D013025:Glycine max / Q000378:metabolism; D018724:Spinacia oleracea / Q000378:metabolism
chemical_list: D009587:Nitrogen Isotopes; D009930:Organic Chemicals; D009609:Nitrous Oxide; D009584:Nitrogen