title: Nitrate-independent expression of plant nitrate reductase in Lotus japonicus root nodules.
abstract: Nitrate-independent nitrate reductase (NR) activity is generally found in legume root nodules. Therefore, the effects of nitrate on plant NR activity and mRNA were investigated in the root nodules of Lotus japonicus (L. japonicus). Both NR activity and mRNA levels in roots and root nodules were up-regulated by the addition of nitrate. In the absence of nitrate, NR activity and mRNA were detected in root nodules but not in roots. Southern blotting analysis indicates that NR is encoded by a single gene in L. japonicus. No nitrate was detected in the root nodules or roots of plants grown in the absence of nitrate, while its accumulation was observed in plants supplied with exogenous nitrate. These results indicate that inducible-type NR can be expressed in root nodules in the absence of nitrate. The activation state of the nitrate-independent activity of NR was as high as that of NR activity induced by nitrate. NR mRNA expressed independently of nitrate in root nodules without nitrate was localized in the infected regions of the root nodules. Thus, the expression could be related to the specific structure and environment of root nodules.
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, 1-1 Tsutsumidori-Amamiyamachi, Aoba-ku, Sendai 981-8555, Japan.
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Kato
authors.forename: Yoshimichi
authors.initials: Y
authors.lastname: Okamura
authors.forename: Koki
authors.initials: K
authors.lastname: Kanahama
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Kanayama
mesh_terms: D000595:Amino Acid Sequence; D015152:Blotting, Northern; D015139:Blotting, Southern; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D018507:Gene Expression Regulation, Developmental; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D017403:In Situ Hybridization; D000070116:Lotus / Q000187:drug effects / Q000201:enzymology* / Q000254:growth & development; D008969:Molecular Sequence Data; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000235:genetics* / Q000378:metabolism; D009566:Nitrates / Q000378:metabolism / Q000494:pharmacology*; D009586:Nitrogen Fixation / Q000502:physiology*; D018517:Plant Roots / Q000254:growth & development* / Q000378:metabolism / Q000382:microbiology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D017422:Sequence Analysis, DNA; D013559:Symbiosis / Q000187:drug effects / Q000235:genetics / Q000528:radiation effects
chemical_list: D018076:DNA, Complementary; D009566:Nitrates; D012333:RNA, Messenger; D009565:Nitrate Reductases; D050901:Nitrate Reductase