title: A temporal and spatial contribution of asparaginase to asparagine catabolism during development of rice grains.
abstract: BACKGROUND
  Asparagine is one of the most dominant organic nitrogen compounds in phloem and xylem sap in a wide range of plant species. Asparaginase (ASNase; EC, 3.5.1.1) catabolizes asparagine into aspartate and ammonium; therefore, it is suggested to play a key role in asparagine metabolism within legume sink organs. However, the metabolic fate of asparagine in source and sink organs during rice seed production remains to be elucidated. Therefore, the main objective of this study is to investigate the asparagine metabolism in a temporal and spatial manner during rice seed production.
  
  
  RESULTS
  For this purpose, the expression of genes involved in asparagine catabolism, such as asparaginase1 (OsASNase1) and 2 (OsASNase2), were quantitatively measured, and contents of asparagine, aspartate and ammonium ions were determined in sink and source organs during spikelet ripening. Quantitative real-time PCR and in situ localization studies determined that OsASNase2 is expressed in the dorsal vascular bundles and nucellar projection of developing grains, as well as in mesophyll and phloem companion cells of senescent flag leaves. Amino acid measurements revealed that the aspartate concentration is higher than asparagine in both source and sink organs.
  
  
  CONCLUSIONS
  This work suggests that asparaginase dependent asparagine catabolism occurred not only in sink but also in source organs.
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, 468-1 Aoba, Aramaki, Sendai, 9800845, Japan.
authors.forename: Yui
authors.initials: Y
authors.lastname: Yabuki
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, 468-1 Aoba, Aramaki, Sendai, 9800845, Japan.
authors.forename: Miwa
authors.initials: M
authors.lastname: Ohashi
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, 468-1 Aoba, Aramaki, Sendai, 9800845, Japan.
authors.forename: Fumi
authors.initials: F
authors.lastname: Imagawa
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, 468-1 Aoba, Aramaki, Sendai, 9800845, Japan.
authors.forename: Keiki
authors.initials: K
authors.lastname: Ishiyama
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, 468-1 Aoba, Aramaki, Sendai, 9800845, Japan.
authors.forename: Marcel Pascal
authors.initials: MP
authors.lastname: Beier
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, 468-1 Aoba, Aramaki, Sendai, 9800845, Japan.
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Konishi
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, 468-1 Aoba, Aramaki, Sendai, 9800845, Japan.
authors.forename: Toshiko
authors.initials: T
authors.lastname: Umetsu-Ohashi
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, 468-1 Aoba, Aramaki, Sendai, 9800845, Japan.
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Hayakawa
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, 468-1 Aoba, Aramaki, Sendai, 9800845, Japan.
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Yamaya
authors.affiliation: Graduate School of Agricultural Science, Tohoku University, 468-1 Aoba, Aramaki, Sendai, 9800845, Japan. soichi.kojima.a2@tohoku.ac.jp.
authors.forename: Soichi
authors.identifier: http://orcid.org/0000-0002-4260-8394
authors.initials: S
authors.lastname: Kojima
keywords: Asparaginase; Asparagine; Nitrogen; Rice; Translocation