title: Metabolic changes and associated cytokinin signals in response to nitrate assimilation in roots and shoots of Lolium perenne.
abstract: The efficiency of inorganic nitrogen (N) assimilation is a critical component of fertilizer use by plants and of forage production in Lolium perenne, an important pasture species worldwide. We present a spatiotemporal description of nitrate use efficiency in terms of metabolic responses and carbohydrate remobilization, together with components of cytokinin signal transduction following nitrate addition to N-impoverished plants. Perennial ryegrass (L. perenne cv. Grasslands Nui) plants were grown for 10 weeks in unfertilized soil and then treated with nitrate (5 mM) hydroponically. Metabolomic analysis by gas chromatography-mass spectrometry and liquid chromatography-tandem mass spectrometry revealed a dynamic interaction between N and carbon metabolism over a week-long time course represented by the relative abundance of amino acids, tricarboxylic acid intermediates and stored water-soluble carbohydrates (WSCs). The initial response to N addition was characterized by a rapid remobilization of carbon stores from the low-molecular weight WSC, along with an increase in N content and assimilation into free amino acids. Subsequently, the shoot became the main source of carbon through remobilization of a large pool of high-molecular weight WSC. Associated quantification of cytokinin levels and expression profiling of putative cytokinin response regulator genes by quantitative reverse transcription polymerase chain reaction support a role for cytokinin in the mediation of the response to N addition in perennial ryegrass. The presence of high levels of cis-zeatin-type cytokinins is discussed in the context of hormonal homeostasis under the stress of steady-state N deficiency.
authors.affiliation: School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand.
authors.forename: Jessica
authors.initials: J
authors.lastname: Roche
authors.affiliation: School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Love
authors.affiliation: School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand.
authors.forename: Qianqian
authors.initials: Q
authors.lastname: Guo
authors.affiliation: School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand.|School of Life Sciences, Yantai University, Yantai, 264005, China.
authors.forename: Jiancheng
authors.initials: J
authors.lastname: Song
authors.affiliation: AgResearch Grasslands Research Centre, Tennent Drive, Private Bag 11008, Palmerston North, New Zealand.
authors.forename: Mingshu
authors.initials: M
authors.lastname: Cao
authors.affiliation: AgResearch Grasslands Research Centre, Tennent Drive, Private Bag 11008, Palmerston North, New Zealand.
authors.forename: Karl
authors.initials: K
authors.lastname: Fraser
authors.affiliation: AgResearch Grasslands Research Centre, Tennent Drive, Private Bag 11008, Palmerston North, New Zealand.
authors.forename: Jan
authors.initials: J
authors.lastname: Huege
authors.affiliation: AgResearch Grasslands Research Centre, Tennent Drive, Private Bag 11008, Palmerston North, New Zealand.
authors.forename: Chris
authors.initials: C
authors.lastname: Jones
authors.affiliation: Laboratory of Growth Regulators and Department of Chemical Biology and Genetics, Centre of the Region Haná for Biotechnological and Agricultural Research, Faculty of Science, Palacký University and Institute of Experimental Botany AS CR, Šlechtitelů 27, 783 71, Olomouc, Czech Republic.
authors.forename: Ondřej
authors.initials: O
authors.lastname: Novák
authors.affiliation: School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand.
authors.forename: Matthew H
authors.initials: MH
authors.lastname: Turnbull
authors.affiliation: School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand.
authors.forename: Paula E
authors.initials: PE
authors.lastname: Jameson
mesh_terms: D001692:Biological Transport; D002244:Carbon / Q000378:metabolism*; D003583:Cytokinins / Q000378:metabolism*; D005308:Fertilizers; D008401:Gas Chromatography-Mass Spectrometry; D018527:Hydroponics; D008129:Lolium / Q000187:drug effects / Q000502:physiology*; D055432:Metabolomics; D009566:Nitrates / Q000378:metabolism / Q000494:pharmacology*; D010937:Plant Growth Regulators / Q000378:metabolism*; D018517:Plant Roots / Q000187:drug effects / Q000502:physiology; D018520:Plant Shoots / Q000187:drug effects / Q000502:physiology; D015398:Signal Transduction; D012987:Soil / Q000737:chemistry; D015026:Zeatin / Q000378:metabolism
chemical_list: D003583:Cytokinins; D005308:Fertilizers; D009566:Nitrates; D010937:Plant Growth Regulators; D012987:Soil; D002244:Carbon; D015026:Zeatin